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SYNTHESIS AND CHARACTERIZATION OF ORDERED

MESOPOROUS INORGANIC NANOCOMPOSITE MATERIALS

A dissertation submitted to Kent State University in partial fulfillment

of the requirements for the degree of Doctor of Philosophy

by

Pasquale Fernando Fulvio

December, 2009


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Pasquale Fernando Fulvio

B.Sc., Universidade Federal do Esprito Santo, 2003

Ph.D., Kent State University, 2009

A dissertation submitted to Kent State University in partial fulfillment

of the requirements for the degree of Doctor of Philosophy

Approved by

__________________________________, Chair, Doctoral Dissertation Committee

Dr. Mietek Jaroniec

__________________________________, Members, Doctoral Dissertation Committee

Dr. Anatoly K. Khitrin

__________________________________

Dr. Hanbin Mao

__________________________________Dr. John J. Portman

__________________________________

Dr. Lien-Chy Chien

Accepted by

___________________________________, Chair, Department of ChemistryDr. Michael J. Tubergen

___________________________________, Dean, College of Arts and Sciences

Dr. John R. D. Stalvey


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TABLE OF CONTENTS

List of figures ...............................................................................................................vList of schemes ..........................................................................................................xviList of tables ........................................................................................................... xviiiDedication ...................................................................................................................xxAcknowledgments .....................................................................................................xxiChapter 1...................................................................................................................... 1Introduction ................................................................................................................. 11.1 Ordered Mesoporous Silicas, SBA-15, SBA-16 and FDU-1.............................. 31.2 Ordered Mesoporous Silicas as Hard templates for Ordered Mesoporous

Carbons ...................................................................................................................... 101.3 Ordered Mesoporous Carbons Thin Films ....................................................... 141.4 Metal Oxides in the SBA-15 Pores..................................................................... 151.5 Ordered Mesoporous Silicas and Carbons as Hard templates for Ordered

Mesoporous Oxides ................................................................................................... 181.6 Research Objectives and Summary.................................................................... 20Chapter 2.................................................................................................................... 262.1 Gas Adsorption Analysis..................................................................................... 262.2 Powder X-ray Diffraction (XRD) and Small Angle X-ray Scattering (SAXS)34


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2.3 Scanning and Transmission Electron Microscopy (SEM and TEM) and

Energy Dispersive X-ray (EDX) ............................................................................... 352.4 Thermogravimetric Analysis (TG) and CHNS Elemental Analysis ................362.5 Al

27Magic Angle Spinning Nuclear Magnetic Resonance (Al

27MAS NMR)37

2.6 Ammonia Temperature Programmed Desorption (NH3-TPD)........................372.7 Diffuse Reflectance Fourier Transform Infrared Spectroscopy (DRIFTS) ...382.8 Sol-Gel Method.................................................................................................... 382.9 Materials and Methods ....................................................................................... 44

2.9.1 Synthesis of SBA-15 .....................................................................................442.9.2 Synthesis of SBA-16 .....................................................................................452.9.3 Synthesis of FDU-1 ......................................................................................462.9.4 Synthesis of Ordered Mesoporous Carbons .................................................472.9.5 Ordered Mesoporous Carbon Thin Films ....................................................492.9.6 Synthesis of Mixed Metal Oxides-SBA-15 .................................................502.9.7 Synthesis of Al-Ti Mixed Oxides .................................................................52

Chapter 3.................................................................................................................... 54Tailoring Properties of Ordered Mesoporous Silica ............................................... 543.1 SBA-15 Silica (p6mm) ........................................................................................ 55

3.1.1 Optimization of the First Step of Synthesis for SBA-15 .............................553.1.2 Optimization of the Hydrothermal Synthesis Time and Temperature forSBA-15 Silica Obtained by using Various Silica Sources ...................................60

3.2 SBA-16 Silica (Im3m) ......................................................................................... 683.3 FDU-1 Silica (Fm3m) ......................................................................................... 76Chapter 4.................................................................................................................... 83Carbon Nanostructures as Inverse Replicas of Ordered Mesoporous Silicas ......83


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4.1 Ordered Mesoporous Carbons ........................................................................... 834.2 Ordered Mesoporous Carbons Films................................................................. 99Chapter 5.................................................................................................................. 116Synthesis of Ordered Mesoporous Mixed Oxide Materials..................................1165.1 Functionalization of SBA-15............................................................................ 1175.2 Magnetic Ordered Mesoporous Carbons as Hard Templates for Inorganic

Mixed Oxides ........................................................................................................... 136Chapter 6.................................................................................................................. 165Surface Acidity Properties ...................................................................................... 1656.1 Fe-doped Al-Ti Mixed Oxide Materials for Applications as Oxidation

Catalysts and Supports ............................................................................................ 165Chapter 7.................................................................................................................. 171Conclusions.............................................................................................................. 171References................................................................................................................ 177


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LIST OF FIGURES

Figure 1 - TG curves in flowing nitrogen (heating rate of 5C.min-1

) for as-

synthesized SBA-15 samples subjected to hydrothermal treatment at 100C for 24

(panel A) and 48 hours (panel B) in comparison to the TG curve for SBA-15-24/48

(both panels). ..............................................................................................................56Figure 2 - Nitrogen adsorption isotherms (A) and the corresponding pore size

distributions (B) for the SBA-15 samples studied. Each isotherm curve was offset

vertically by 350cm3STP.g

-1and each PSD curve by 0.5cm

3.g

-1.nm

-1. ....................57

Figure 3 - SAXS patterns for the samples SBA-15-2/48 (A) and SBA-15-6/48 (B).

..................................................................................................................................... 60Figure 4 - Small angle X-ray scattering (SAXS) spectra for the calcined samples

synthesized from TEOS and sodium metasilicate by using two hours for the initial

self-assembly of polymer and silica species and by varying time and temperature of

the hydrothermal treatment; (A) SBA-15 samples obtained at 100C, (B) NaSBA-

15 samples prepared at 100C and (C) SBA-15 samples obtained at 120C. The

intensity values were shifted by 6000 a. u. in A, 5000 a. u. in B and 3000 a. u. in C

(scale not shown). .......................................................................................................62Figure 5 - Nitrogen adsorption isotherms measured at -196C for the calcined

samples synthesized from TEOS and sodium metasilicate by using two hours for

the initial self-assembly of polymer and silica species and by varying time and


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temperature of the hydrothermal treatment; (A) SBA-15 samples obtained at 100C,

(B) NaSBA-15 samples prepared at 100C and (C) SBA-15 samples obtained at

120C. The amount adsorbed values were shifted by 400cm3STP.g

-1in A,

300cm3STP.g

-1in B and 400cm

3STP.g

-1in C. ..........................................................64

Figure 6 - Pore size distribution (PSD) curves for the samples synthesized from

TEOS and sodium metasilicate by using two hours for the initial self-assembly of

polymer and silica species and by varying time and temperature of the

hydrothermal treatment; A) SBA-15 samples obtained at 100C, B) NaSBA-15

samples prepared at 100C and C) SBA-15 samples obtained at 120C. ................. 65Figure 7 - Comparison of adsorption parameters for the samples synthesized from

TEOS and sodium metasilicate by using two hours for the initial self-assembly of

polymer and silica species and by varying time and temperature of the

hydrothermal treatment; A - volume of primary mesopores (VP) and micropore

volume (Vmi) versus time of hydrothermal treatment (vertical axis break from 0.25-

0.75cm3.g

-1); B, C and D - mesopore width, mesopore wall thickness and specific

surface area versus time of the hydrothermal treatment. The insets in Figs 7C and

7D show the mesopore wall thickness and the specific surface area plotted against

the mesopore width. ...................................................................................................66Figure 8 - Comparison of the TG curves obtained for the silica-polymer composite,

solvent extracted and solvent extracted-calcined at 350C sample of SBA-16


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prepared under 4h for the first stage of synthesis and 24h of hydrothermal treatment

at 100C. .....................................................................................................................68Figure 9 Small angle XRD patterns for the template-free SBA-16 samples

synthesized using 4h for the first stage of the self-assembly and by varying

hydrothermal synthesis time. .....................................................................................70Figure 10 - Nitrogen adsorption isotherms at -196C for the template-free SBA-16

samples synthesized using different times for the first step of synthesis and

hydrothermally treated at 100C for 6 panel (A), 12 panel (B), 24 panel (C) and 48h

panel (D), respectively. ..............................................................................................71Figure 11 - Pore size distributions (PSDs) obtained for the template-free SBA-16

samples synthesized using different times for the first step of synthesis and

hydrothermally treated at 100C for 6 panel (A), 12 panel (B), 24 panel (C) and 48h

panel (D), respectively. Distributions were calculated by using method reported in

Langmuir1997, 13, 6267. ..........................................................................................73Figure 12 - Small angle XRD patterns for the samples with polymer/TEOS ratios

between 0.12-0.48 (A) and the inset for the materials with ratios of 0.60 and 0.72

(B). The diffraction peaks were found to belong to the Fm3m symmetry,

characteristic for FDU-1 materials. ...........................................................................77Figure 13 - Argon adsorption isotherms at -196C for various samples (A) and the

PSD curves calculated from Ar adsorption isotherms at -196C using the original

KJS method (Langmuir 1997, 13, 6267) (B). The curves for each sample were


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labelled from (a) to (i) correspond to the increasing polymer-TEOS ratios from 0.12

to 0.72. Adsorption isotherms were shifted in increments of 500cm3.g

-1and the

PSDs were shifted in increments of 1.0 for clarity. .................................................78Figure 14 - TG (A) and DTG (B) profiles for the FDU-1 materials. .......................82Figure 15 - Small angle XRD patterns for the polymer-free OMSs and the

corresponding carbon replicas prepared by thermal treatment of pyrrole-silica

composites at 800C in flowing nitrogen followed by silica template removal; A

patterns for the SBA-15 samples obtained by hydrothermal treatment at 100C and

140C and their inverse carbon replicas; B patterns for the SBA-16 samples

obtained by extraction and calcinations at 350 and 550C and their inverse carbon

replicas. .......................................................................................................................85Figure 16 - Nitrogen adsorption isotherms at -196C for A - SBA-15 and SBA-15

#

samples, C-SiO2 nanocomposites and carbon replicas C-15 and C-15#(isotherms for

samples labeled with#

were shifted by 800cm3STP.g

-1); B - SBA-16 and SBA-16*

samples, composites and carbon replicas (isotherms for samples coded with * were

shifted by 500cm3STP.g

-1); C and D Pore size distribution (PSD) curves for the

SBA-15 and SBA-16 samples, composites and carbon replicas (Langmuir2006, 22,

6757), respectively; PSD curves for samples labeled with#

were shifted by

1.5cm3.g

-1.nm

-1and those for samples with * by 0.4cm

3.g

-1.nm

-1. ...........................87

Figure 17 - SEM images of the C-15#

and C-16 carbons; (left panel) SEM image of

the C-15#

sample showing a long range ordering of this nanostructure composed of


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interconnected carbon rods; (right panel) SEM image of C-16 showing the

interconnected spherical carbon particles as expected for the inverse replica of the

SBA-16 silica. ............................................................................................................93Figure 18 - TEM images of the carbon materials C-15

#and C-16 carbons; (left

panel) TEM image of C-15#

showing the presence of iron-containing nanoparticles;

(right panel) TEM image of C-16. .............................................................................94Figure 19 - Wide angle powder XRD patterns for the carbon replicas of SBA-15

(A) and SBA-16 (B) obtained by thermal treatment of polypyrrole-silica

nanocomposites at 800C and etching the silica templates with 48% (w/w) HF.

These patterns were assigned using the XRD database for graphite (*, Cliftonite

JCPDS 41-1487), -Fe (, Ferrite JCPDS 6-0696), and Fe3C (o, Cementite JCPDS

35-0772)...................................................................................................................... 95Figure 20 - Raman spectra for the carbon replicas (prepared by thermal treatment

of polypyrrole-silica composites at 800C followed by the silica template removal)

possess the D and G bands characteristic for amorphous disordered and graphite-

like carbons, respectively. Note the presence of the D band characteristic for

disorder introduced to the grapheme sheets by edges or heteroatoms such as

nitrogen. Panel (a) shows spectra for C-15 and C-15#, whereas panel (b) for C-16

and C-16* carbons. .....................................................................................................97Figure 21 - Small angle powder XRD patterns for SBA-15 (A), carbon-SBA-15

(B), Ni-containing mesoporous carbons (C) and NiO-silica nanocomposites (D). 100


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Figure 22 -Nitrogen adsorption isotherms at -196C for SBA-15 and C-SBA-15-Ni

(a), SBA-15#

and C-SBA-15#-Ni (b), carbon-silica-nickel and silica-nickel oxide

nanocomposites: NiO-SBA-15 (c) and NiO-SBA-15#

(d), and carbon-nickel

composites: MC-Ni and MC#-Ni (e). The adsorption isotherms were presented by

plotting relative adsorption vs. relative pressure. ....................................................104Figure 23 - The PSD curves calculated according to the improved KJS method for

the SBA-15 templates and Ni-containing nanocomposites. ...................................106Figure 24 - The TG and DTG oxidation profiles for the C-SBA-15 and C-SBA-15

#

(a) and for C-SBA-15-Ni and MC-Ni (b) materials recorded in flowing air. ........108Figure 25 - Raman spectra for the C-SBA-15-Ni (a), C-SBA-15

#-Ni (b) and tubular

carbon inverse replicas MC-Ni (c) and MC#-Ni (d). ...............................................109

Figure 26 - Wide angle powder XRD patterns for the MC-Ni and MC#

-Ni, (a) and

(b), respectively, and peak assignments for the Ni phase (JCPDS file). Peaks from

the Al sample holder are present in both patterns. ..................................................110Figure 27 - Z-contrast TEM image of the C-SBA-15-Ni(left panel) and SEM of C-

SBA-15#-Ni (right panel). ........................................................................................111

Figure 28 - Z-contrast TEM images of MC-Ni at lower (left panel) and higher

magnifications (right panel) of the same particle. ...................................................113Figure 29 - SEM (left panel) and Z-contrast TEM (right panel) images of MC

#-Ni.

................................................................................................................................... 114


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Figure 30 - Small angle XRD data (A) and N2 gas adsorption isotherms at -196C

(B) with the calculated PSD (inset) curves for the template-free SBA-15 and

materials obtained at different calcination temperatures. The PSD curves were

obtained using the improved KJS method reported inLangmuir2006, 22, 6757. TG

curves for the SBA-15-P123 as-prepared nanocomposite and SBA-15SE (C). ....118Figure 31 Small angle XRD patterns for the materials obtained at 300C (A) and

600C (B). The patterns for the silica SBA-15* and SBA-15** samples are

represented by solid lines. The composites prepared after 1 and 2 impregnation

steps are represented by dotted and dashed lines, respectively. The peaks were

characteristic of the p6mm symmetry and at least three diffraction peaks were

identified and assigned as (100), (110) and (200). ..................................................124Figure 32 - Single pulse Al

27

MAS NMR spectra for the nanocomposites of TiAl-

SBA-15 A and ZrAl-SBA-15 B obtained after 1 [(a) and (b)] to 2 (c) deposition

procedures and calcination temperatures of 300C (a) and 600C [(b) and (c)]. Each

spectrum was measured using a frequency of 5-10 kHz and 18 pulse. .................125Figure 33 - Wide angle XRD powder patterns of the various silica-metal oxide

nanomaterials obtained after several impregnation procedures, (A) TiZr-SBA-15

and (B) TiAl-SBA-15, followed by calcinations at 600C (a), 700C (b) and 800C

(c) for 2h under air atmosphere. These patterns were shifted in increments of 125

(percent scale) for clarity and the corresponding JCPDS files for identified phases

are shown. .................................................................................................................127


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Figure 34 - Nitrogen adsorption isotherms at -196C (A and B) and PSD curves

calculate from these (C and D) for the various SBA-15 nanocomposite materials

calcined at 300C in comparison to SBA-15SE. In all figures, curves with solid dots

are for SBA-15SE, open dots after 1st

impregnation, solid triangles for the 2nd

, open

triangles and squares for the 3rd

and 4th

impregnations, respectively. The PSD

curves were obtained using the improved KJS method reported inLangmuir2006,

22, 6757. ...................................................................................................................130Figure 35 - Small angle XRD patterns of SBA-15 (A) and SBA-16 (B) materials

and respective carbon inverse replicas C-15 (C) and C-16 (D). ............................. 138Figure 36 - Nitrogen adsorption isotherms and the corresponding pore size

distributions for the SBA-15 and SBA-16 samples studied and their respective

carbon inverse replicas. ............................................................................................141Figure 37 - TG curves for as-prepared carbon-oxide precursors and carbon-oxides

in flowing nitrogen and air, (a) and (b), respectively. .............................................146Figure 38 - N2 adsorption isotherms at -196C for the oxide-carbon

nanocomposites, AlTi-15/100 (A) and AlTi-15/140 (B) thermally treated in flowing

nitrogen at various temperatures; and the corresponding PSD curves, (C) and (D),

respectively. ..............................................................................................................147Figure 39 - N2 adsorption isotherms at -196C for the oxide-carbon

nanocomposites, AlTi-16 (A) and AlTi-16* (B) thermally treated in flowing


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nitrogen at 350C and 600C; and the corresponding PSD curves, (C) and (D),

respectively. ..............................................................................................................148Figure 40 - N2 gas adsorption isotherms at -196C for the final oxide materials

prepared with the C-15 (A), C-15#

(B) and C-16 and C-16* (C) carbon templates

and subjected to calcinations in flowing air at 700C. ............................................149Figure 41 - PSD curves for the final oxide materials prepared using the C-15/100

(A), C-15/140 (B) and C-16/350 and C-16-450 (C) carbon templates and subjected

to calcinations in flowing air at 700C..................................................................... 150Figure 42 - Wide angle powder XRD for the C-15 (a) and C-15

#(b) carbon

templates with proposed phase assignments (JCPDS files). ...................................151Figure 43 - Powder XRD patterns with proposed assignments (JCPDS files) for the

Al-Ti oxide-carbon nanocomposites prepared after thermal treatment at 1000C for

4h in flowing N2. The AlTi-15 and AlTi-15#

are shown in (a) and (b), respectively,

and AlTi-16 and AlTi-16* are shown in (c) and (d), respectively. ........................152Figure 44 - Powder XRD patterns with proposed assignments for the Al-Ti mixed

oxides (JCPDS files) prepared after thermal treatment of nanocomposites at 1000C

for 4h in flowing N2 followed by calcination at 700C in air. The AlTiO-15 (a) and

AlTiO-15#

(b) in panel (A), and AlTiO-16 (a) and AlTiO-16* (b) shown in panel

(B), respectively. ......................................................................................................153Figure 45 - Elemental analysis maps for AlTiO-15-6/7 analyzed in three regions of

the sample containing different percentages of O (a)-(c), Al (d)-(f) and Ti (g)-(i).


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The maps in each row were made for the same region. For the first row, the atomic

ratio of Al/Ti is 0.75, for the second row this ratio is 0.59 and for the third row 0.61.

In all three areas the atomic % of O was of ~47%. ................................................. 156Figure 46 - TEM images of the C-15 (a) and (b), and C-15

#(c) and (d) carbons; (a)

and (c) showing hexagonal packing of carbon rods for C-15 and C-15#,

respectively; (b) and (d) showing the ordered carbon rods. ....................................157Figure 47 - TEM images for the C-16 (a) and (b), and for the C-16* (c) and (d).

These images show good textural quality of the carbon inverse replicas of SBA-16

and the long range ordering of these 3-dimensional structures. .............................159Figure 48 - TEM images for AlTiO-15-6/7 (a) and (b), showing two distinct

regions of the same sample and for AlTiO-15#-6/7, (c) and (d); (a) (110) plane with

the oxide pores parallel to each other as for SBA-15 materials; (b) particle with

disordered micropores and crystalline oxide domains; (c) and (d) images showing a

particle with disordered pores. .................................................................................160Figure 49 - The selected area electron diffraction (SAED) for AlTiO-16-6/7 (a) and

HRTEM image for the same compound (b); HRTEM images for the AlTiO-16*-6/7

(c) and (d), showing the long range ordering of theIm3m cage-like structure of this

material. ....................................................................................................................161Figure 50 NH3-TPD profiles for the Fe-doped Al-Ti mixed oxide materials

calcined at 700C after thermal treatment of the ceramic-carbon nanocomposites at

600C. .......................................................................................................................166


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Figure 51 Surface acidity as a function of BET surface areas for the various

materials investigated calculated using the NH3-TPD profiles and N2 adsorption at -

196C, respectively. ..................................................................................................168Figure 52 Room temperature (~30C) DRIFTS spectra of adsorbed pyridine and

after partial desorption in helium for 5min on AlTiO-15 (A) and AlTiO-16 (B)

systems with typical assignments for different acid sites present on the surfaces of

acid oxide materials, Lewis (L-Py), Brnsted (B-Py), Lewis and Brnsted (L+B-Py)

and Hydrogen bonded pyridine (*). DRIFTS spectra for partial desorption of

pyridine at various temperatures before complete coking of pyridine for AlTiO-

16*-6/7 and approximate band positions (C). .........................................................170


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templates, namely p6mm and Im3m in the cases of SBA-15 and SBA-16,

respectively. ................................................................................................................13Scheme 4 Types of gas adsorption isotherms (A) and desorption hysteresis loops

(B) according to the IUPAC classification. Some examples of materials such as the

microporous DFO zeolite (Type I isotherm), SBA-15 (Type IV isotherm) and

MCM-48 with narrow mesopores (Type IVc isotherm) are shown (Adapted from

Pure and Applied Chemistry 1985, 57, 603 and Chem. Mater. 2001, 13, 3169). ....28Scheme 5 - Sol-gel synthesis of inorganic ceramic materials (Adapted from Sol-Gel

science: the physics and chemistry of sol-gel processing1990, Academic Press). .39Scheme 6 Coating of SBA-15 surfaces with ultra-thin carbon films containing

pea-pod distribution of Ni nanoparticles. .............................................................115Scheme 7 Deposition of bi-metallic oxides thin films on the surfaces of SBA-15

according to the island-type mechanism: partial pore blockage by deposition of

oxide layers and the resulting disordered oxide particles after etching of SBA-15.

................................................................................................................................... 135Scheme 8 Nanocasting and replication of carbon nanomaterials and multi-

component oxide ceramics using ordered CMK-3 carbon templates (A and B) and

carbon inverse replicas of SBA-16 (C). ...................................................................164


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LIST OF TABLES

Table 1 - Comparison of the results obtained by nitrogen adsorption for the samples

studied. ........................................................................................................................58Table 2 - Adsorption and small angle-XRD data obtained for the template-free

SBA-16 samples synthesized using shorter times for the first step of synthesis and

hydrothermally treated under static conditions at 100C for 6, 12, 24 and 48h. ...... 74Table 3 - Adsorption and small angle-XRD data obtained for the template-free

SBA-16 samples synthesized using longer times for the first step of synthesis and

hydrothermally treated under static conditions at 100C for 6, 12, 24 and 48h,

continuation. ...............................................................................................................75Table 4 - Adsorption and structural parameters for the FDU-1 samples studied. ...79Table 5 - Parameters obtained from N2 adsorption at -196C and small angle XRD

data for the SBA-15 and SBA-16 silica samples and the corresponding inverse

carbon replicas. ...........................................................................................................89Table 6 - Elemental analysis and powder XRD diffraction parameters obtained for

the carbon inverse replicas of the various SBA-15 and SBA-16 silica templates. ..92Table 7 - Parameters obtained from small angle XRD and nitrogen adsorption data

at -196C for the SBA-15, nanocomposites and MC samples studied. ..................102


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Table 8 - Adsorption and low angle-XRD data obtained for the SBA-15 samples

and alumina-based mixed oxides composites obtained after the first two

impregnation steps and thermally treated at 300 and 600C. ..................................119Table 9 - Adsorption and low angle-XRD data obtained for titania and zirconia-

based oxides composites obtained after the first two impregnation steps and

thermally treated at 300 and 600C. .........................................................................120Table 10 - Adsorption parameters for the SBA-15 silicas, respective carbon inverse

replicas and the corresponding Al-Ti oxides obtained as inverse replicas of the

carbons after thermal treatments at 500-700C in flowing nitrogen and calcination

in flowing air at 700C. ............................................................................................142Table 11 - Adsorption parameters for the SBA-15 silicas, respective carbon inverse

replicas and the corresponding Al-Ti oxides obtained as inverse replicas of the

carbons after thermal treatments at 500-700C in flowing nitrogen and calcination

in flowing air at ........................................................................................................143Table 12 - Adsorption parameters of carbon-oxide materials obtained at various

thermal treatment temperatures in flowing nitrogen. ..............................................145Table 13 Adsorption and calculated NH3-TPD parameters for the Fe-doped Al-Ti

mixed oxides. ............................................................................................................167


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DEDICATION

I dedicate this Dissertation to the memory of my grandmother Irene do Carmo Reis

(1933-2005) and of my great grandmother Olinda Maria do Nascimento (1907-

2000).


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ACKNOWLEDGMENTS

I thank God, creator of all who is beyond our comprehension for his constant

forgiveness for my weak faith.

I would like to thank my research adviser, Dr. Mietek Jaroniec, for accepting me as

part of his research group, for the patience and the time he dedicated to my

research, and for his advice. From him I have learned not only the field of

nanomaterials science, but also dedication to science. I thank my research

collaborators, including Dr. Stanisaw Pikus (Poland) for his assistance with the

characterization of samples. I also thank past and present graduate students in Dr.

Jaroniecs research group with whom I have directly or indirectly collaborated.

I would like to thank the Chemistry Department for the many years of Teaching

Assistantship, as well as faculty members whom I had the pleasure to work for as a

Teaching Assistant. I thank many of my former undergraduate students; their

successes have been a great inspiration to me. I also thank all of the friends I have

made, as well as the great work and assistance from Debra Lyons (former Office of

International Affairs), Diana Skok (RAGS), Arla Dee Macpherson, Erica Lilly,

Larry Maurer and Dr. Mahinda Gangoda (Chem. Dept.). I thank my many friends

from the Liquid Crystal Institute (LCI), including Dr. Michelle M. Fontana and

Jake Fontana, as well as former graduate students and post-doctoral fellows from

both Chemistry Dept. and LCI.


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Special thanks go to several people from Saint-Gobain NorPro in Stow, OH, with

whom I worked and learned from during my 11 months of internship: Mr. Pramod

Koradya, Stephen Maddox, Terry Atkins and Dave Gough, all engineers and

technicians, Dr. Jadwiga Jaroniec, Drs. Thomas Szymanski, Steve Dahar, Steve

Rolando, James Ralph, Dave VanderWiel and William Gerdes and Mr. Mike Crisp,

to name a few.

I also thank Drs. Luiz C. Machado, Jair C. C. Freitas, Francisco G. Emmerich and

Emanuel B. Muri and Antonio A. L. Marins for opening the doors to my academic

life as an undergraduate at Universidade Federal do Esprito Santo (UFES, Brazil)

and for their constant support.

I finally thank my parents Pasquale Fulvio and Maria Olinda dos Reis Fulvio, my

sister Paola D. L. Fulvio, my niece Bianca and my brother Paolo M. Fulvio for their

constant support and for the many sacrifices they made for my accomplishments in

life. I would like to thank all close family members and uncles and cousins, and my

friends who have been real family members, Jorge A. S. Lacerda, Vinicius O.

Balthar, Evelyn C. Mello, Edward S. Moreira, Adriano de Souza, Suzanna M. Day,

Erin Michael, Thiago Franco, Dr. Italo Marcos Nunes de Oliveira, Amelie Roquelin

and John Fuller to name a few, and special thanks to Joanna Grka and to her

family.


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Chapter 1

Introduction

Nanomaterials are defined as materials that posses at least one dimension between 1 and

100nm. We have witnessed a great development in materials science in the past 50 years,

but only recently the term nanotechnology has been emphatically used to describe materials

such as thin films, nanoparticles and porous materials and their properties. It is expected

that nanomaterials will play a major role in the future of energy conversion and storage,

catalysis, medicine and engineering. The most important examples are silicas, carbons,

metals, inorganic oxides and their composites. Methods to fabricate nanostructures can be

divided into two main groups: the top down and the bottom up approaches. The top down

approach is based on the transformation of a bulk material into a nanomaterial, i.e. by

milling or nanolithography, whereas the bottom up approach is based on the use of small

building blocks and templates for the synthesis of materials at the nanometer level. While

the former approach has been extensively used for patterning surfaces, preparation of grids

and waveguide materials and for the preparation of nanoparticles, the latter approach

enables the choice of a large number of starting reagents and of well-established chemical

synthesis methods for the preparation of different types of nanomaterials. Thin films,

nanoparticles, nanowires and microporous-mesoporous materials have been successfully

prepared using the bottom up approach in combination with the sol-gel process,

electrochemical, chemical vapor deposition (CVD), self-assembly and hard-templating

(nanocasting) synthesis. Major advances in this area were achieved by the use of templates,

such as viruses, surfactants and porous nanomaterials, allowing for the design of


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biomimetic and porous structures. The use of surfactants resulted in the development of the

self-assembly synthesis and culminated in the discovery of ordered mesoporous materials,

silicas and silica hybrids, carbons and some metal oxides. Furthermore, some ordered

silicas have been found suitable to function as hard templates for the synthesis of other

inorganic materials (nanocasting synthesis). Carbons and some metal oxides have been

prepared as the inverse replicas of these nanostructured silicas. Furthermore, the ordered

mesoporous carbons prepared as inverse replicas of ordered silicas have also been used as

hard templates for the synthesis of oxides. In all cases, despite of the additional steps

introduced by the preparation and removal of the initial templates, the hard-templating

route overcomes the limitations imposed by the self-assembly synthesis. These are related

to selection of starting precursors and solvents which are more suitable for the preparation

of multicomponent materials. Also, hard templates make it possible to prepare intermediate

nanocomposites, such as carbons and silicas-supported metal and metal oxide

nanoparticles.

Simple inorganic oxides, especially those of transition metals, have been prepared so far by

self-assembly and nanocasting techniques. Few examples of mixed oxide materials have

been prepared, such as alumina-based oxides with a defective spinel structure, which have

closed-packed cubic structures of general formula MAl2O4, where M (II) and Al (III)

cations occupy two tetrahedral sites per each Al octahedral site. Oxide systems with

microporous structures other than spinel have been less investigated. Mixed oxides are of

great interest for the modification of surface properties of a single oxide component and for

the introduction of additional active sites for catalysis. Other synergistic effects resulting


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from homogeneously mixed phases have been reported by showing materials which change

from conductors to insulators or may possess stable and metastable polymorphic phases

that are not possible for a single oxide. The ability to tailor the properties of mesoporous

materials by modifying their surfaces or by using them as hard templates offers new

possibilities for the synthesis of mixed oxides and nanocomposites with improved catalytic

activity and electronic properties.

1.1 Ordered Mesoporous Silicas, SBA-15, SBA-16 and FDU-1

Ordered mesoporous silicas (OMSs) possessing 2-D and 3-D mesostructures constitute an

important class of extensively studied materials. Since the first report on the surfactant

templated silicas, MCM-41 and MCM-48,1

a large number of silica-based materials have

been developed and characterized. The formation of these ordered mesostructures was

explained by the liquid crystal template (LCT) mechanism,1

as shown in Scheme 1 (A).

After the template removal from the resulting surfactant-silica nanocomposite, an ordered

mesostructure with amorphous pore walls is formed.

Surfactants are bifunctional molecules that contain a hydrophilic head group and a

hydrophobic moiety (tail group) and because of this structure they are known as

amphiphiles. Surfactants may possess a positive (cationic), a negative (anionic) or

electrically neutral group (nonionic).2 Their amphiphilic nature allows for the aggregation

into micelles in solution depending on their concentration, solvent and temperature. The

concentration at which the micelles are formed is known as critical micelle concentration

(CMC). The micelle stability arises from the balance between hydrophilic-hydrophobic


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interactions or electrostatic interactions if charges are present. This micelle stability and

micelle symmetry also depend on the relationship between the volume and length of the

hydrophobic group and the size of the hydrophilic moiety.2

During the self-assembly of

ionic surfactants and silica species an ordered mesostructure is formed depending on the

gel composition, temperature and synthesis time.

Scheme 1 Self-assembly mechanism of silicon alkoxides and ionic surfactants (A) and

triblock copolymers (B). The hydrophilic moiety of the ionic surfactant is represented by

blue circles (head group) and its hydrophobic part (tail group) by solid orange curves.

Hydrophilic and hydrophobic moieties in triblock copolymers are decoded by blue and

orange curves, respectively. Hydrophilic blocks of triblock copolymers are shown to

interpenetrate the silica framework (B). Ordering of mesopores can be extended from

several hundred nanometers to micron size particles (see Ref. 5).

A major breakthrough in the synthesis of OMSs was the use of neutral block copolymers

as templates for the synthesis of materials, especially Pluronics EOxPOyEOx, where EO

stands for polyethylene oxide and PO for poly-propylene oxide. This led to the discovery


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of SBA-15, SBA-16,3

FDU-14

and related materials possessing novel structural

properties. Similar mechanism for the formation of these materials was proposed

[Scheme 1 (B)], but in this case, the self-assembly synthesis is dominated by van der

Waals forces.3, 5

The micelles formed from triblock copolymers can also be tailored by

varying temperature and co-solvents and by addition of salts.6-10

Since block copolymers

are inexpensive and environmentally friendly, in contrast to the alkyl ammonium

surfactants previously used, they are commonly employed as soft templates.

Among OMSs, SBA-15 [shown in Scheme 2 (a)] has become one of the most

attractive materials because of its large mesopores, thick pore walls, high

hydrothermal stability11-13

and great possibilities in tailoring its structure in

comparison to its analogue, MCM-41. It possesses a 2-dimensional hexagonal

arrangement of mesopores (p6mm symmetry) as MCM-41, but in addition it has

irregular micropores interconnecting the aforementioned mesopores.14

These

micropores are formed by penetration of hydrophilic moieties of the triblock

copolymer, Pluronic 123 (EO20PO70EO20), into the silica [see Scheme 1 (B)].15

The

latter feature is of great interest for various applications such as adsorption, catalysis,

separations and hard templating synthesis of other OMMs such as ordered carbons16

and many others that will be discussed in the next section.

Because of potential applications of SBA-15 there is great interest in the improvement

of its adsorption and structural properties as well as in the optimization of the

synthesis conditions. The surface properties of SBA-15 have been modified by

decorating the mesopore walls with either inorganic,17

or organic groups18

by post-


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synthesis grafting, template displacement and one-pot synthesis.5

Recently, materials

with pores as large as 20 nm have been synthesized at low temperature in the presence

of a suitable salt,19

whereas MCM-41 possesses pores typically below 6nm.

Therefore, there is great interest in the elaboration of effective and less-time-

consuming recipes for the synthesis of highly ordered SBA-15 structures using

various silica sources, especially inexpensive sodium metasilicate. Two years later

after the first publication on the synthesis of SBA-15 from tetraethylorthosilicate

(TEOS),3 Kim and Stucky,20 reported a recipe to obtain this material from

inexpensive sodium metasilicate (Na2SiO3.9H2O). Later, this recipe was further

modified to control the morphology of SBA-1521, 22

, porosity23, 24

as well as to study

the effect of salt addition on the hydrothermal synthesis of SBA-15 under microwave

conditions.13, 25, 26

A new insight into the mechanism of the SBA-15 formation was

recently provided by in situ SAXS/XRD,27

time-resolved NMR and TEM28

as well as

EPR29

studies indicating that the self-assembly of polymer and silica species occurs in

a relatively short time.

Also SBA-16 and FDU-1, Scheme 2 (b) and 2 (c), respectively, have attracted attention

because of their 3-dimensional structure with cage-like mesopores. As in case of SBA-15,

SBA-16 possesses mesopores interconnected by micropores due to the nature of the

polymers used, usually Pluronics F127 (EO106PO70EO106),3 F108 (EO132PO50EO132)30 or

even blends of P123 and F127.31

Furthermore, SBA-16 has a body-centered-cubic

structure (Im3m symmetry) of nearly spherical cages,32

in which each cage is connected

with 8 neighboring cages through small openings, which facilitates diffusion and


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transport of various species. In comparison to FDU-1, cubic face-centered structure

(Fm3m symmetry)33

of 12 interconnected cages, SBA-16 still remains an attractive

material due to the availability of the polymers used for its synthesis. Some of the major

objectives of the current research on SBA-16 include control of the synthesis conditions

in order to tailor pore size,34

pore volume, surface area31, 35

particle morphology,36, 37

and

insertion of organic groups into its surface or framework either by co-condensation38

or

post-synthesis modification methods, to achieve the desired selectivity in catalysis and

separations and possibly to improve its electronic and optical properties for future

devices. Also, the use of different polymers and swelling agents has been investigated to

obtain not only SBA-16, but also other cubic structures.39, 40

(a) (b)

(c) (d)

Scheme 2 Structure of SBA-15 (a) and periodic minimal surfaces of SBA-16 (b) and

FDU-1 (c). The minimal surface shown in (d) refers to the materials known as MCM-48

and KIT-6. Lighter shades of gray correspond to the external surfaces (pores surfaces),

whereas darker shades refer to the internal surface.


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Other factors have also been systematically studied, such as the silica precursor,

TEOS/polymer ratio, as well as time and temperature of the self-assembly process and

hydrothermal treatment.35

The former resulted in a slightly larger microporosity, while a

small decrease in the wall thicknesses was observed with increasing TEOS/polymer ratio.

Different results were obtained for the synthesis of samples with thick pore walls.41

In

this case, the pore wall thicknesses increased with increasing silica concentration, which

also led to a decrease in the mesopore volume. The effects of stirring, hydrothermal time

and temperature were also reported for the microwave synthesis of SBA-16.37 It was

shown that while temperature may affect the structure, the duration of both steps of

synthesis may influence the particle size and morphology of the final product.

In general, relatively small pores have been obtained for SBA-16. However, just recently,

large-pore SBA-16 materials have been reported.42

Low acid concentration and inorganic

salt NaCl were used in the synthesis of these samples.42

Also, it was noted that the

template-removal procedure plays an important role in maintaining the structure of SBA-

16, which shrinks considerably during calcination above 500C.43

To date, high-

temperature calcination has been used most often, which causes a considerable shrinkage

of the pores.44

An alternative way to remove the polymer template involves solvent

extraction by means of organic solvents under acidic conditions. However, this process

demands several extractions. Recently, the efficacy of a novel method of template

removal, which involves solvent extraction followed by low-temperature calcination, has

been demonstrated. This approach assures the complete removal of the polymeric

template and simultaneously reduces the structure shrinkage; consequently, the resulting


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samples have larger pore volumes and pore sizes in comparison to solely calcined

samples. Various calcination temperatures have been employed and an optimum

temperature range was found to exist.43

Other parameters such as stirring and

hydrothermal synthesis times have not been reported for large-pore SBA-16 samples to

date.

Besides SBA-16, FDU-1 has also attracted great attention. The latter has been prepared in

the form of powders and monolith45

using different gel compositions,34, 46, 47

silica

sources48 and microwave irradiation.49FDU-1 materials have been originally synthesized

by using the tri-block copolymer B50-6600 (EO39BO47EO39), which is commercially

unavailable. Further reports, also suggested that FDU-1 materials could also be prepared

from another tri-block copolymer F108 (EO141PO44EO141),45

which is commercially

available and that have brought again considerable attention to this material. The FDU-1

silica and other related functional materials50-53

feature higher pore volumes, larger cage

diameters, thicker pore walls and consequently better thermal and hydrothermal

stabilities than SBA-16.54

For FDU-1 materials, the use of additives such as NaCl and their effect on the pore size

and pore openings size have been reported too.47

Also, different ratios of the polymer

template to the silica source TEOS have been investigated.34

More recently, it was shown

that the addition of NaCl at much lower acid concentration is an efficient route to prepare

large pore volume FDU-1 materials.46

In all cases, very restricted conditions were found

for the preparation of uniform and well ordered materials with large pores.


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1.2 Ordered Mesoporous Silicas as Hard templates for Ordered Mesoporous Carbons

Ordered mesoporous carbons (OMCs) templated by ordered mesoporous silicas

(OMSs) have been extensively studied; especially CMK-155

and CMK-316

carbons

templated by MCM-481

and SBA-153

silicas, respectively. Due to the nature of this

templating synthesis, which involves introduction of carbon precursor into pores of

the template followed by carbonization and template dissolution, inverse carbon

replicas of the OMS templates are obtained. While carbon replicas of MCM-48 often

undergo a symmetry change55 and the MCM-41 replication results in disordered

carbon rods, the SBA-15 replication permits to obtain exact inverse replicas.16

The

observed differences in replication of the aforementioned OMSs are caused by

structural differences of these templates. As mentioned in the previous section, the

MCM-41 and MCM-48 [3-D cubic;Ia3dsymmetry shown in Scheme 2 (d)] OMSs are

synthesized by using cationic surfactants as soft templates, which afford purely

mesoporous materials. In the case of SBA-15 (p6mm), because of its fine

interconnecting pores that create a 3-D porous system, it affords a stable and exact

inverse replica, CMK-3, being a hexagonal structure composed of ordered carbon

rods interconnected by irregular carbon threads. An analogous structure to CMK-3,

CMK-5, which consists of ordered carbon pipes instead of carbon rods, is formed due

to an incomplete filling of the ordered mesopores of SBA-15 with a carbon

precursor.56

The mechanism of formation of CMK-3 and CMK-5 are shown in

Scheme 3 (a).


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Other OMSs obtained in the presence of triblock copolymers, which were

successfully used as hard templates for the synthesis of carbons, are SBA-1632

with

Im3m symmetry and KIT-640

with Ia3d symmetry. While the latter is a large pore

analogue of MCM-48, SBA-16 is composed of a 3D array of ordered spherical cages,

in which each cage is connected with eight neighboring cages through small

apertures. Similarly to SBA-15 both mesostructures possess additional irregular

micropores in the siliceous mesopore walls. In comparison to a 3D cubic bicontinuous

arrangement of cylindrical mesopores in KIT-6, the replication process of SBA-16 is

challenging due to its cage-like structure. In the case of SBA-16, its carbon inverse

replica (Im3m symmetry) consists of interconnected spherical carbon particles. While

several carbon precursors have been successfully used for the replication of SBA-15

and KIT-6, some difficulties were reported for the SBA-16 nanocasting.57-59

For

instance, the carbon replicas of SBA-16 prepared from sucrose could be only obtained

for pores exceeding 6 nm.58

Other carbon precursors such as furfuryl alcohol,57, 59-62

pitch,63-66

polyacrylonitrile

(PAN)67

and polyaniline68, 69

have been employed to obtain graphitic carbons, which

could retain, at least partially, original ordered mesostructures during graphitization

(~2000C). In a further attempt to improve the conductive properties of these carbons,

doping with a heteroatom such as nitrogen67-71 was used. For instance, nitrogen-doped

carbons with partial graphitic ordering were obtained from acetonitrile70, 71

after

thermal treatments at relatively low temperatures (below 1000C). Sulfur-doped

carbons obtained by polymerization and carbonization of thiophene in SBA-15 have


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been also studied;72

S-doping led to some enhancement of conductivity of these

carbons.

Graphitic carbons were also obtained by in situ oxidative polymerization of pyrrole in

the SBA-15 pores in the presence of iron chloride (FeCl3).73-76

The resulting iron

species after polymerization acted as a catalyst for the formation of graphitic

domains;73-75

the amount of nanocasted carbon and the extent of graphitization were

found to be dependent on the catalyst loading within the silica host.73

Further studies

of this system showed that some doped amounts of nitrogen remained in the graphitic

framework after thermal treatments up to 1000C.74, 75

Nevertheless, the presence of

iron species was not reported in the resulting carbons. Other studies suggested that

only a small fraction of the iron catalyst was deeply embedded in the carbon matrix

and consequently protected from leaching.76

The same work reports that carbonization

and silica template removal with a sodium hydroxide solution affords an amorphous

carbon containing super paramagnetic iron oxide (Fe3O4) nanoparticles with traces of

non-oxidized -Fe (ferrite).

In all of the aforementioned studies involving polypyrrole, the iron catalyst loadings inside

the SBA-15 template were similar, while differences appeared in the synthetic conditions

such as solvents (ethanol,74, 75

or water73, 76

) or the method of polymerization (CVD,73, 74

incipient wetness impregnation75 or stirring in an aqueous solution of the catalyst76). Some

results were surprisingly different and raised questions about the possibility of generating a

graphitic and nitrogen-doped carbon with embedded magnetic nanoparticles in its

framework. Also, to the best of our knowledge, there are no previous reports on the use of


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large pore SBA-16 materials as templates for the synthesis of pyrrole-based carbons. Thus,

in this work the polypyrrole-based carbon inverse replicas of SBA-15 and SBA-16 are

investigated. These replicas are nitrogen doped and partially graphitic ordered carbon

mesostructures with embedded magnetic nanoparticles.

(a)

(b)

Scheme 3 Hard-templating mechanism for SBA-15 (a) and SBA-16 (b) silicas. The

complete or partial filling of the SBA-15 pores with a carbon precursor results in

interconnected solid carbon nanorods, CMK-3, and interconnected carbon pipes, CMK-5,

respectively. The complete filling of the SBA-16 structure with a carbon precursor results

in interconnected carbon particles of nearly spherical shape which resembles the SBA-16

cages. The inverse replicas retain the symmetry of the initial templates, namely p6mm and

Im3m in the cases of SBA-15 and SBA-16, respectively.


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1.3 Ordered Mesoporous Carbons Thin Films

While significant progress has been made in the synthesis of the CMK-3 carbons with

graphitic domains57, 63, 70

and particle morphology,60, 77

the incorporation of metal oxide78-

83and metal nanoparticles

76, 84, 85and preparation of films,

86CMK-5 type of carbons have

been less explored. One possible reason of this situation is the difficulty of finding

suitable precursors that permit a strict control of the pore wall thickness in order to obtain

stable carbon replicas with graphitic pore walls similar to those in multiwall carbon

nanotubes (CNTs). There are reports showing the possibility of preparing CMK-5 with

controlled pore wall thickness by using different methods of polymerization of furfuryl

alcohol87-89

and ferrocene90

employed as carbon precursors. Also, there are a few reports

on the incorporation of highly dispersed nanoparticles of platinum56, 90

and cobalt89

into

CMK-5 in order to enhance its electrochemical and catalytic properties; in the case of

cobalt-containing CMK-5 magnetic properties are added too. It has been shown that the

nanocasting synthesis of CMK-5 by using furfuryl alcohol together cobalt, iron and

nickel salts89

resulted in carbon nanopipes materials only in the case of cobalt. In the case

of iron and nickel, only CMK-3 (rod-type structure) carbons have been reported.

A major step in the preparation of tubular carbons has been made by using chemical

vapor deposition (CVD) of acetylene in the MCM-48 channels.91

Using this route,

relatively stable carbon inverse replicas with ultra-thin pore walls have been obtained.

Furthermore, the use of phenolic resins as carbon precursors afforded stable carbon thin

films as inverse replicas of silica colloidal crystals.92

In the case of SBA-15 the stable

ultra-thin carbon films have been reported for carbon-silica nanocomposites only.93

An


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aromatic carbon precursor, 2, 3-di-hydroxynaphtalene (DHN), which reacts with silanols

present on the silica surface, was used to form homogeneous ultra-thin carbon films but

they were unstable after silica dissolution. These carbon films obtained by carbonization

of DHN attached to the siliceous pore walls were hydrophobic and electrically conductive

as graphitic carbons.93

Despite of lower molecular weight of DHN than those of

mesophase pitch molecules and phenolic resins, the ability of DHN to form chemical

bonds with the silica surface93-95

as well as its easy graphitization makes this precursor

attractive for further investigations.

1.4 Metal Oxides in the SBA-15 Pores

The existence of small complimentary pores interconnecting hexagonally ordered

mesopores, large surface area, large mesopore width and good hydrothermal stability

make SBA-15 a suitable catalyst support. The approaches used for the direct preparation

of catalysts with similar structure to that of SBA-15, such as transition metal oxides and

for the synthesis of inorganic species were either performed by post-synthesis grafting, or

co-condensation methods. The latter was based on the use of polymers as the templates

with excessive amounts of water,17, 96-101

or polymers in non-aqueous media via the

evaporation induced self-assembly method (EISA).24, 102-107

The main difficulties in the

self-assembly of inorganic frameworks arise from the different interactions that need to

be matched among the various chemical species involved.24, 102

Aqueous acidic solutions

have been the most successful in the preparation of surfactant templated materials, which

also limit the choice of ceramics precursors and other compounds due to the differences


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in the hydrolysis rates that lead to phase segregation. On the other hand, whenever non-

aqueous systems were used, evaporation of solvents with a concomitant slow hydrolysis

of inorganic species were necessary to reach the critical micelle concentration and

polymerization of the inorganic species, respectively; otherwise disordered or non-porous

structures were achieved.108

Unfortunately, controlling the evaporation rates of solvents

as well as the humidity required for hydrolysis, are not easy tasks, making this route

difficult to be reproduced.

To overcome drawbacks of hard-templating and of the co-condensation synthesis of

purely inorganic ordered mesoporous materials, the extra-framework post-synthesis

grafting109

appears to be an attractive option. The synthesis route also opens new

possibilities for selecting best conditions for each particular material to be grafted in the

form of film or particles within the pores of the OMS substrates and to explore phases

only attained by sol-gel chemistry. For instance, SBA-15 containing single Fe (III)

sites110

and TiO2 films111

were prepared by non-hydrolytic sol-gel methods involving

alkoxide precursors through condensation with silanols groups present on the silica

surface. Using similar sol-gel procedures, thin layers and small nanoparticles of TiO2,

ZrO2, MoO3, WO3 and NiO were also incorporated into SBA-15.112

Oxides mixtures such

as NiMo-SBA-15113

and Cu-loaded over a previously prepared CeO2114

were also

reported. Small particles of Ti and Zr oxides were prepared by chemical solution

decomposition of precursors, or hydrolysis of these in the presence of SBA-15.115

Other

nanoparticles such as LaCoO3 were also generated in situ using microwave conditions.116

Nevertheless, only a limited number of compositions has been examined for the synthesis


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of these inorganic oxides-SBA-15 nanocomposites prepared by sol-gel routes known to

yield mixed, or hetero bi-metallic oxides117-124

in a single impregnation step. Another

important parameter, the thermal stability of mixed oxides coatings on OMSs has not

been investigated yet. Furthermore, there is a lack of methods to qualitatively access the

presence of oxide thin films on the internal surfaces of OMSs.

Homogeneously mixed oxide materials prepared by sol-gel in many cases exhibit higher

acidity and consequently better catalytic activity with respect to single oxide systems.125-

129 In general, the mixing of distinct oxide phases, especially those containing metal

cations at different oxidation states result in generation of surface and lattice defects and

consequently, catalytically active sites.125-129

These sites can show acidic and or basic

properties. While the latter are associated with O2-

vacancies,130, 131

the former is typically

associated to exposed metal cations (Lewis sites), to surface metal cation bridged-

hydroxyls and to electron deficient hydroxyl groups bound to transition metals (Brnsted

sites).127, 128, 131

Also, the double and mixed oxide materials of Al3+

, Ti4+

, Zr4+

and Ni2+

which are largely abundant, have promising applications in catalysis,132, 133

as sensors,124

optical134, 135

, electronic136-139

and new structural materials.140-142

The latter properties are

affected not only by chemical composition but also by their nano architecture, such as

thin films and nanoparticles.143

Thus, the development of simple and environmentally

friendly synthesis routes for oxides, as well as, efficient methods for characterization of

these materials is extremely important.


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1.5 Ordered Mesoporous Silicas and Carbons as Hard templates for Ordered

Mesoporous Oxides

As previously mentioned, the interconnecting pores of SBA-15 also made it a perfect hard

template for the fabrication of ordered mesoporous carbons (OMCs). Other inorganic

species have also been prepared by following the same hard-templating method. After

filling the pores of silica with an inorganic precursor and etching the silica template, a

stable 2-D inverse replica of SBA-15 is obtained. In this way, also noble metals,144

carbons

with confined nanoparticles of Fe2O3,80 Pt and Pt-Ru,85 NiO,145 MnO2,79 Mn3O4146 and

many others81

have been successfully prepared. Transition metal oxides such as Cr2O3147

,

CeO2,148

WO3,149

-MnO2,150

NiO,151

-Fe2O3,152

and Cr, Mn, Fe, Co, Ni and In oxides

obtained by microwave digestion of the silica template153

were also reported. Some double

metal oxides were also synthesized, such as the spinel of ZnFe2O4,154

the phosphors

Zn2SiO4:Mn,155

Gd2O3:Eu+3

,156

Co3O4157

and of non-oxides semiconductors as BN,158

GaN159

and CdS.160

Similarly to SBA-15, the KIT-6 and SBA-16 silicas have also been successfully used as

hard templates for fabricating various inorganic materials because of their 3D

mesoporous structure.40, 57-59, 152, 153, 161-172

In comparison to KIT-6, the replication process

of SBA-16 is more challenging due to its cage-like structure. While several carbon

precursors have been successfully used for the replication of SBA-15 and KIT-6, some

difficulties were reported in the SBA-16 nanocasting.57-59

For instance, the carbon

replicas of SBA-16 prepared from sucrose could be only obtained for pores exceeding 6

nm,58

whereas, disordered particles and nanowires of-Fe2O3165

and carbon nanotubes-


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Fe164

have been prepared using SBA-16 films as templates.

Another major achievement in the hard-templating synthesis was possible because of

usage of the carbon inverse replicas of SBA-15 and KIT-6 as hard templates for

fabricating other inorganic materials. After filling the pores of these carbons with suitable

inorganic precursors and removing carbon templates by oxidation at high temperatures,

inorganic materials with the same structure as the OMSs used for the preparation of

carbon templates have been obtained. Some of the advantages of using OMCs as hard

templates are the possibility of carbon removal by oxidation in air if the desired material

is a metal oxide, or by chemical methods in the case of non-oxide ceramics. However, an

incomplete filling of small interconnections in the silica template may lead to the partial

collapse of the structure.

So far, the materials prepared by using OMC templates have been mostly single metal

oxides such as SiO2,173-175

MgO,176, 177

CuO,178

CeO2,179

ZnO,177, 180

-Al2O3181

and non-

oxide ceramics SiOC and SiCN182

and SixNy.183

As regards more complex oxides, only

(MgO)x(ZnO)1-xO184

has been prepared, whereas its ordering was good only for a few of

the compositions used. Also, several other disordered oxide phases such as Al2O3, TiO2,

ZrO2, V2O5, MoO3, WO3, Fe2O3 and MnO2185

have been reported. It has been suggested

that the synthesis conditions such as the presence of groups on the surface of carbons and

the use of less polar solvents may be beneficial for the quality of the resulting

materials.186

In general, the ordered mesoporous structures prepared by this route

exhibited interesting physical properties, which are much different than the

corresponding nonporous materials.176, 180, 184, 187, 188

Note that other systems of interesting


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properties such as the Ti-Al mixed oxides, which have been known for their optical,189-191

dielectric192-194

and photo- catalytic properties,195, 196

have not been prepared yet. Also, to

the best of our knowledge, there are no reports on the use of carbons with the Im3m

symmetry as hard templates for the synthesis of inorganic materials.

1.6 Research Objectives and Summary

Since the discovery of OMSs in 1992, the self-assembly synthesis of ordered mesoporous

materials (OMMs) consisting of inorganic and/or organic building blocks have been

extensively studied. A major breakthrough in this area was the use of block copolymers as

the structure directing agents, which led to the discovery of a new class of mesostructured

silicas possessing large pores, high surface areas, good hydrothermal and thermal

stabilities, as well as interconnecting micropores. The presence of complementary

micropores, which interconnect ordered mesopores in the polymer-templated OMSs,

permitted the use of these mesostructures as hard templates for the preparation of other

inorganic species, such as carbons and inorganic oxides that after template removal

represent a stable inverse replica of the original silica mesostructures. So far, numerous

publications were devoted to the modification of organic and simple inorganic species to

the pores of OMSs either by post-synthesis grafting or by co-condensation in the presence

of surfactants as soft templates; if the latter is carried in the presence of excessive amounts

of solvents, their evaporation can be used to induce self-assembly (EISA). Because the self-

assembly process requires matching interactions between various chemical species and


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requires optimization of experimental conditions to achieve the desired rates of hydrolysis

and condensation, the synthesis of multi-component OMMs is not an easy task.

The main purpose of this dissertation research is the use of ordered mesoporous silicas and

carbons as supports and hard templates for obtaining mixed metal oxides and

nanocomposites with ordered mesopores as an alternative to self-assembly. These hard

templates permit the use of non-aqueous media in the preparation of inorganic OMMs by

using the well-known sol-gel synthesis route, which involves the condensation of

homogeneous mixtures or single-source precursors.

The structure of this dissertation includes an introductory chapter (Chapter 1) dealing

with ordered mesoporous inorganic materials, silicas, carbons, mixed metal oxides and

related nanocomposites. In addition, Chapter 2 provides a brief overview of the sol-gel

method109, 197-200

and chemistry of alkoxides,117, 118, 197

synthesis procedures and the

analytical techniques used.

Chapter 3 is devoted to the optimization of the synthesis conditions for the channel-like

(SBA-15)201-203

and cage-like (SBA-16 and FDU-1)204

mesostructures. It focuses on the

tailoring of adsorption and structural properties of these materials, such as surface area,

micropore volume, mesopore volume, mesopore size and mesopore wall thickness, by

varying the time and temperature of hydrothermal synthesis. It is shown that in the case

of SBA-15 (channel-like silica) high quality samples with large and uniform pores can be

obtained during relatively short time, whereas a slightly longer time is recommended for

the synthesis of cage-like OMSs. The outcome of this study is a wider spectrum of silica

materials to be used as hard templates for the synthesis of inorganic materials.


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The following chapter (Chapter 4) describes the synthesis of mesostructured carbons by

inverse replication of the OMSs templates. Initially, carbon-silica composites were

prepared by polymerization of suitable monomers within pores of the silica templates

containing a polymerization catalyst. Pyrrole, which in the presence of Fe3+

generates

polypyrrole, was used as carbon precursor. Another advantage of using this carbon

precursor is its relatively easy graphitization. Another important feature is that iron acts

as a catalyst for pyrrole polymerization and also for graphitization during thermal

treatments. The Fe cation is reduced during the process and Fe3C/-Fe nanoparticles are

formed. After etching the silica templates with HF solution an inverse carbon replica of

the OMS structures containing magnetic Fe3C/-Fe nanoparticles were obtained.205

In addition, the preparation of ordered mesoporous carbon thin films using the OMSs as

hard templates is presented in Chapter 4. These carbons with ultra-thin walls were

prepared by the surface modification of silica templates, which after carbonization

resulted in uniform carbon coatings. By changing the adsorption properties of the silica

templates, the pore walls thickness and mesopores widths in the carbon materials were

modified. Furthermore, it was demonstrated that the use of graphitization catalysts such

as Ni2+

resulted in the formation of the aforementioned carbons with mono-dispersed

metallic and magnetic Ni nanoparticles.206

After etching the silica templates with HF, part

of the carbon nanostructures remained as stable 3-D inverse replicas with introduced Ni

nanoparticles.206

The next chapter of this dissertation (Chapter 5) covers the mixed-oxide materials

prepared by using partially-hydrolytic sol-gel method and the concept of single-source


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molecular precursors containing (M-O-M) hetero linkages or homogeneous mixtures of

these. These precursors were prepared using isopropanol as the reaction medium for the

reaction of two transition metal alkoxides, or by reaction of a metal alkoxide and an

alcoholic complex of Ni+2

followed by addition of a hard template. Hydrolysis conditions

were controlled using hydrochloric acid as catalyst to conduct a homogeneous

condensation of these molecular precursors with concomitant evaporation of the solvent.

This strategy was expected to preserve the majority of the (M-O-M) hetero linkages that

permitted for low temperature formation of mixed-oxides (below 800C). The evidence

for the presence of these oxides as thin films within the pores of the silica templates was

provided for the first time on the basis of small angle XRD studies of the resulting

composites and the templates used.

Also in Chapter 5, analogous synthesis procedures were described for various OMC

templates. The mixed oxides of Al and Ti were prepared by controlled hydrolysis of

alkoxides in the presence of carbon inverse replicas of SBA-15 and SBA-16 materials.

Ceramic-graphitic carbon nanocomposites having titanium ions in 2 oxidation states (Ti3+

and Ti4+

) intimately mixed with Al2O3 may be of future interest for catalytic applications.

The importance of the carbon template used was demonstrated to be directly linked to the

successful replication synthesis. Also, these templates containing Fe nanoparticles were

capable of transporting iron oxide to the final ceramic oxides during calcinations. Finally,

the surface properties, such as catalytically active acid sites were investigated by both

quantitative and qualitative methods which are described in Chapter 6.

This dissertation is based on the following publications:


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1) Fulvio, P. F., Liang, C, Dai, S., Jaroniec, M.; Mesoporous Carbon with Ultra-Thin

Pore Walls and Highly Dispersed Nickel Nanoparticles. European Journal of Inorganic

Chemistry, 2009 (5), 605-612, 2009.

2) Fulvio, P. F., Jaroniec, M., Liang, C., Dai, S.; Polypyrrole-based nitrogen-doped

carbon replicas of SBA-15 and SBA-16 containing magnetic nanoparticles.J. Phys. Chem.

C, 112 (34), 13126-13133, 2008.

3) Fulvio, P. F., Grabicka, B. E., Grudzien, R. M., Jaroniec, M.. Adsorptive and

structural properties of SBA-16 under various hydrothermal syntheses times and a two-step

template removal method. Adsorption Science & Technology Journal25 (6), 439-449,

2007.

4) Fulvio P. F., Pikus S, Jaroniec M. Tailoring properties of SBA-15 materials by

controlling conditions of hydrothermal synthesis.Journal of Materials Chemistry 15 (47):

5049-5053, 2005.

5) Fulvio P. F., Jaroniec M. Optimization of synthesis time for SBA-15 materials.

Studies in Surface Science and Catalysis 156, 75-82, 2005.

6) Fulvio P. F., Pikus S, Jaroniec M. Short-time synthesis of SBA-15 using various

silica sources.Journal of Colloid and Interface Science 287 (2), 717-720, 2005.

7) Fulvio,P. F., Pikus, S., Jaroniec, M.; SBA-15-Supported Mixed-Metal Oxides:

Partial Hydrolytic Sol-Gel Synthesis, Adsorption, and Structural Properties, Applied

Materials and Interfaces, DOI: 10.1021/am900625c.


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8) Fulvio,

P. F., Vinu, A., Jaroniec, M.; Nanocasting Synthesis of Iron-Doped

Ordered Mesoporous Al-Ti Mixed Oxides Using Ordered Mesoporous Carbons Templates,

J. P. Chem. C, 113, 13565-13573, 2009.

9) Fulvio, P. F., Grabicka, B. E., Grudzien, R. M., Jaroniec, M.. Argon adsorption

studies of large pore FDU-1 silica. Journal ofMicroporous and Mesoporous Materials, in

preparation.


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Chapter 2

Experimental

2.1 Gas Adsorption Analysis

2.1.1 Interpretation of Gas Adsorption Isotherms

Nitrogen and argon adsorption isotherms will be measured at -196C using ASAP 2010 and

2020 volumetric adsorption analyzers manufactured by Micromeritics (Norcross, GA).

Before adsorption measurements the calcined SBA-15 samples were degassed under

vacuum for at least two hours at 200C.

These adsorption isotherms were used for determination of the specific surface area, pore

volume, pore size distributions and other surface properties.207, 208

It is based on the

physical adsorption (physisorption) governed by van der Waals forces between an adsorbed

molecule (adsorbate) and a solid surface (adsorbent).207

Another important process is

chemisorption that results in the formation of surface complexes between active sites on the

adsorbent and adsorbate. While physisorption is a reversible process, chemisorption is

irreversible. Furthermore, in physisorption, adsorbate molecules form a uniform monolayer

of adsorbed gas on the adsorbent surface which is followed by multi-layer formation

according to a layer-by-layer mechanism, whereas chemisorption is a monolayer

process.207

Typical adsorption isotherms are shown in Scheme 4. Their shapes depend on the surface

properties and porosity.207

According to the IUPAC classification, pores of diameter below

2 nm, between 2 and 50 nm, and above 50 nm, are classified as micropores, mesopores and

macropores, respectively.207, 208

Uniform and ordered mesopores are referred to as primary


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mesopores; whereas pores originated from void spaces between particles are often referred

to as secondary mesopores.208

Microporous materials with uniform widths exhibit a large gas uptake at relatively low

pressures. Once the pores are completely filled with gas, the isotherm levels off [Type I

isotherm, see Scheme 4 (A)].207, 208

Types II and III of adsorption isotherms are typical of macroporous or non-porous solids.

While Type II isotherm exhibits an inflexion point corresponding to the formation of a

complete monolayer and the beginning of multilayer, the rare Type III isotherms do not

have this point due to weak interactions of adsorbent on the surface of the adsorbate. Type

V of adsorption isotherms is more rarely seen and is related to mesoporous solids weakly

interacting with adsorbate.207, 208

Mesoporous materials often exhibit Type IV isotherm (SBA-15, SBA-16 and FDU-1 with

relatively large mesopores) and Type IVc (MCM-41 and MCM-48 with smaller

mesopores) of adsorption isotherms.208

The initial part of the Type IV isotherms reflects

formation of a monolayer of adsorbate because of the stronger interactions between

adsorbate and adsorbent, followed by multilayer formation.207, 208

This process is followed

by capillary condensation and a plateau when all mesopores are filled. The relative pressure

at which capillary condensation occurs is related to the mesopore diameter via Kelvin-type

equation;207-210 this equation is used to calculate the pore size distributions. Furthermore,

the steepness of the capillary condensation step is dependent on the uniformity of

mesopores. More uniform mesopores and the steeper condensation steps are observed.208


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A stepwise adsorption isotherm is (Type VI, not shown) is observed for non-porous solids

with homogeneous surfaces such as graphitic carbon blacks. The height of each step

corresponds to the monolayer capacity of each adsorbed layer and it remains nearly

constant for the second and third adsorbed layers.207

(A) (B)

Scheme 4 Types of gas adsorption isotherms (A) and desorption hysteresis loops (B)

according to the IUPAC classification. Some examples of materials such as the

microporous DFO zeolite (Type I isotherm), SBA-15 (Type IV isotherm) and MCM-48

with narrow mesopores (Type IVc isotherm) are shown (Adapted from Pure and Applied

Chemistry 1985, 57, 603 and Chem. Mater. 2001, 13, 3169).

The reverse process of adsorption, desorption may follow a different path from that of

adsorption, which results in the so-called called adsorption hysteresis, see Scheme 4 (B).207,

208For materials possessing cylindrical mesopores, type H-1 of hysteresis is observed. In

case of pores having smaller openings than their width, a delay is desorption is observed. If


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the desorption closes at the relative pressure corresponding to the lower limit of

hysteresis207

(~0.40-0.50 for N2 and ~0.26-0.38 for Ar at -196C) the diameters of pore

apertures are below 5 and 4nm, respectively.208, 211

Type H-1 of hysteresis loops have desorption branches nearly parallel to the adsorption

step.207

Type H-1 is observed for mesoporous materials, such as SBA-15, whereas SBA-16

and FDU-1 show H-2 hysteresis because of the small apertures interconnecting cages.207, 211

For the latter materials, the relative pressure at which desorption ends can be used to

calculate the size of pore openings if it is above the lower limit of hysteresis closure for a

given adsorbate.211

Types H-2 and H-3 are intermediate scenarios between H-1 and H-4.

Several factors contribute to Type H-2 hysteresis, such as pore network, pore

interconnections and pore constrictions.211

Type H-3 loop does not exhibit any adsorption

limit at high relative pressures; this type is associated to aggregates of plate-like particles

forming slit-shaped pores. Similarly, Type H-4 of hysteresis loop is often found for

materials with slit-like pores with additional micropores.207, 208

2.1.2 Specific Surface Area

The specific surface area of the samples was calculated using the Brunauer-Emmett-Teller

method (BET)207

within the relative pressure range of 0.04 to 0.2.208

Initially, the amount

adsorbed on the surface of the adsorbent corresponds to one statistical monolayer known as

monolayer capacity (nm).207

This quantity, given in moles of adsorbate per gram of

adsorbent, is obtained from the slope or the intercept of the linear form of the BET

equation:207


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Cnpp

Cn

C

ppn

pp

mm

1)(

)1(

)1(0

0

0

In this equation, n is the amount adsorbed and C is the BET constant. For nm to be

expressed in (mol.g-1

), a unit conversion is required; namely the amount adsorbed

(originally expressed in cm3STP.g

-1) needs

Thesis Character

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