Poly(vinylalcohol)/Lamellar Germanium Phosphate Nanocomposite Membranes

International Journal of Science and Technology Volume 3 No. 2, February, 2014

IJST © 2014– IJST Publications UK. All rights reserved. 140

Poly(vinylalcohol)/Lamellar Germanium Phosphate Nanocomposite

Membranes

S. K. Shakshooki, B.Najeh- Ali, S.S. Rais , A. M.Hamassi Department of Chemistry, Faculty of Science, Tripoli University,POB.13203 Tripoli, Libya.

ABSTRACT

Novel nanosized lamellar germanium phosphate, α-Ge(HPO4)2.1.84 H2O(nGeP), with interlayer spacing (d001 ) = 7.71Ǻ, was prepared.

Preparations of poly(vinylalcohol) / lamellar germanium phosphate nanocomposite membranes were carried out by mixing slurry

aqueous solution of (nGeP) , of different weight percentages (2.5, 5, 10, and 20 wt %) , with aqueous solution of 10% (PVA) in

concentration at 45oC . The resultant composite membranes are transparent flexible thin films and were characterized by XRD, TGA,

FT-IR , scanning electron microscopy (SEM) and transmission electron microscopy(TEM). Size particles of lamellar germanium

phosphate calculated from XRD broadening method using the Scherrer,s equation , found to be 44.6 nm . TEM images of PVA/nGeP

nanocomposites show that the (nGeP) in the nanometer scale , in the range 38-53 nm , well dispersed in the PVA matrix. The composite

materials show to have mechanical and thermal stability properties superior to that of the original polymer, which a result of the

enhancement of the thermal properties of PVA/nGeP nanocomposites.

Keywords: Poly(vinylalcohol), lamellar germanium phosphate , nanocomposite membranes.

1. INTRODUCTION

Inorganic ion exchange materials of tetravalent metal

phosphates are very insoluble compounds with good thermal

stabilities, and posses high ion exchange capacities. They have

been known as amorphous for some time [1,2]. The discovery

of their layered crystalline materials [3,4], represent a

fundamental step in chemistry of these compounds . Increase

attention direct toward their intercalation [5,6], catalytic[7],

electrical conductance [8], and sensors [9]. Their layered

crystalline materials , resemblance clay minerals, exist as

twodimensional (2-D) and three-dimensional (3-D)structures

[10]. Layered twodimensional structure exist in α , γ and θ-

forms of general formula α-M(IV)(HPO4)2.H2O, γ-

M(IV).PO4.H2PO4.2H2O, θM(IV)(HPO4)2.5H2O, respectively

[11-13] ( where M = Ti, Zr, Hf, Ge, Sn , Ce ….etc).

Inorganic layered nanomaterials are receiving great attention

because of their size, structure, and possible biochemical

applications [14], that have been proven to be good carriers for

organic polar molecules. Examples of these are zirconium

phosphates[15], taking advantage of the expandable interlayer

space of the layered materials. Researchers have been capable

of encapsulating functional biomolecules into these inorganic

matrices protecting them from interacting with invironment,

avoiding denaturation and enhancing their shelf [14,16].

Nanoscaled tetravalent metal phosphates and their organic

polymer composites comprise an important class of synthetic

engineering. However , research in such area is still in its

infancy [17-20] Nanotechnologies are at the center of

numerous investigations and huge investments. However

chemistry has anticipated for long the importance decreasing

the size in the search of new properties of materials, and of

materials structured at the nanosize in a number of

applications relate to daily life. Organic-inorganic

nanocomposite membranes have gained great attention

recently [19,20] . The composite material may combine the

advantage of each material, for instance, flexibility,

processability of polymers and the selectivity and thermal

stability of the inorganic filler [19-22].

Poly(vinylalcohol), hydrophilic and biodegradable polymer , is

gaining increase attention, such as proton exchange

membranes, and polymer electrolyte fuel cells [23,24]

permeability membranes[25] ,drug delivery[26] . These

applications have stimulate interest in improving the properties

of PVA. The interaction between PVA and the

nanoadditives[27-29] mainly through hydrogen bonding ,

which allow efficient load transfer, are responsible for marked

increase in mechanical propertie. In case of PVA , dispersion

and interface interaction are mainly related to the hydroxyl

groups in the PVA and the nanoadditives. This paper describes

the preparation and characterization of novel nanosized

germanium phosphate and its Poly(vinylalcohol)

nanocomposite membranes.

2. EXPERIMENTAL

2.1 Chemicals

GeCl4 , H3PO4(85%) of BDH , PVA MWt = 25125 g/mol of

Aldrich. Other reagents used were of analytical grade.

2.2 Apparatus

X-ray powder diffractometer Siemens D-500, using Ni-filtered

CuKα (λ= 1.54056Å) , TG/DTA SII Extra 6000 Thermogram.

and TG/DTA Perkin-Elmer SII , Scanning electron microscopy

(SEM) Jeol SMJ Sm 5610 LV , Forier Transform IR

spectrometer, model IFS 25 FTIR, Bruker , pH Meter WGW

International Journal of Science and Technology (IJST) – Volume 3 No. 2, February, 2014


521 and Transmission electron microscopy (TEM) Zeiss TEM

10 CR.

2.3 Preparation of lamellar germanium phosphate

5 ml of GeCl4 in 78.5 ml distilled water were mixed with 25

ml of H3PO4 (85%). The resultant mixture was refluxed for 10

h to obtain white precipitate , filtered , washed with ethanol

and dried in air . Then subjected to three times stepwise

refluxing in 10 molar H3PO4 (1.0 g : 25 ml H3PO4) (one week

a time ) the resultant precipitate was filtered , washed with

distilled water and ethanol and dried in air.

2.4 Exchange Capacity Determination

Exchange capacity of nanosized germanium phosphate was

determined by addition of 25 ml of 0.10 M NaCl solution to

100 mg of the material, with stirring for one h, then titrated

with 0.10 M NaOH solution.

2.5 Thermal Analysis

Thermal analyses were carried out at temperature range about

C/min.oC in nitrogen atmosphere, the rate was 10 o700 -20

2.6 Preparation of PVA/ lamellar germanium

phosphate composites

Poly(vinylalcohol) in 10 % concentration was prepared by

dissolving 10g of PVA in 125 ml distilled water at 80oC with

stirring for 1h. kept at the same temperature until the total

volume is equal to 100 ml. Different PVA/ Lamellar

germanium phosphate composite membranes were prepared

where (nGeP) weight % loading were( 2.5, 5, 10 , and 20 wt

%).

Typically; 0.1g (nGeP) was dispersed in 5 ml distilled water

with vigorous stirring at 45oC for 15min. , to that 9 ml of PVA

(10% in concentration) were added. The stirring was continued

for 48 h at 45oC. The resultant mixture was poured into flat

surface container, of desired thickness, and was allowed to dry

in air. The fully dried transparent flexible thin film was pealed

from the glass container and kept for characterization, and

found to be PVA/ (nGeP) 10 wt% composite membrane. In

similar manner different wt % of 2.5, 5, and 20% (nGeP) were

used for the preparation of the rest composite membranes.

3. RESULTS AND DISCUSSION

Lamellar germanium phosphate , α-

Ge(HPO4)2.1.84H2O(nGeP), was prepared and characterized

by chemical , XRD, TGA, FT-IR , SEM and TEM.

3.1 XRD

The X-ray diffraction pattern(XRD) of α-Ge(HPO4)2.1.84H2O

is shown in Figure (1), which indicate good degree of

crystalline with interlayer spacing (d001) equal to 7.71 Ǻ. The

average diameter of (nGeP) was found to be 44.6 nm ,which

was calculated from the full width at half maximum of the peak

using Scherrer,s equation:

0.9λ

= D

maxCosθ2θB

Where D is the average crystal size in nm , λ is the

characteristic wave length of x-ray used (λ=1.54056 Å ) , Ө is

the diffraction angle , and the B2Ө is the angular width in the

radius at intensity equal to half of the maximum peak

intensity [30]. Figure (2) shows x-ray pattern of the α-

germanium phosphate , that include the value of full width at

half maximum of the peak which is 0.1770.

O (nGeP).2.1.84H2)4Ge(HPO-Figure 1: XRD pattern of α

O (nGeP)2.1.84H2)4Ge(HPO-Figure 2: XRD of α

full width at half maximum of the peak

3.2 FT-IR

FT-IR spectra , taken from thin 30 mg , lightly weighed (1%)

, found to be similar to 1-400 cm-KBr in the range 4000

O[31].2.H2 )4Ge(HPO-That reported for α

3.3 TGA

Thermogram of α-Ge(HPO4)2. 1.84H2O (GeP) , is shown in

Figure (3) , indicates three weight losses regions. Dehydration

process at termperature range 90-430oC. It seems to occur in

two steps , since two endothermic effects are observed in this

range of temperature . The weight loss is 11.19% . The

anhydrous germanium phosphate undergoes a weight loss

equal to 6.07 % , correspond to mole of water per formula

weight. This weight loss is related to the condensation process

of the anhydrous phase to germanium pyrophosphate

GeP2O7.



O2.1.84H2)4Ge(HPO-Figure 3: TG/DTA of α

3.4 Ion exchange capacity

O found 2. 1.84H2)4Ge(HPO-The ion exchange capacity of α

to be equal to 7.63 meq/g.

3.5 Composites PVA/ lamellar germanium phosphate

membranes

Flexible transparent thin films homogeneous composites of

PVA/(nGeP) were prepared and characterized by, SEM ,TEM,

XRD and TGA. Their exchange capacities found to be in

agreement with the wt % content of the layered inorganic

material , as expected.

3.6 SEM

Typical SEM morphology image of the nanocompsite is

shown in Figure (4). The photograph shows that (nGeP) is

well and regularly dispersed in the PVA matrix. The average

size of dispersed lamellar germanium phosphate is ~ 39.5 nm.

Figure 4: Typical, SEM image of PVA/ (nGeP) nanocomposite

membrane

3.7 TEM

Typical TEM image of the nanocomposite film is shown in

Figure (5). The average size of dispersed lamellar germanium

phosphate is ~ 41.5 nm.

Figure 5: Typical, TEM image of PVA/ (nGeP) nanocmposite

film

3.8 XRD of poly(vinylalcohol)

Figure(6) shows the XRD of the pure poly(vinylalcohol) with

intense peak appearing near 2θ = 19.75o.

Figure 6: XRD pattern of PVA

3.9 TGA

The TGA measurements of (PVA) and PVA/(nGeP)

nanocompsites membranes with different (nGeP) contents are

shown in ( Figures 7-11), respectively.

The thermal decomposition of (PVA) is shown in Figure (7).

Three temperature regions can be identified over which most

of the weight change occurs. The first weight loss occurs

between 75 – 115 oC corresponds to the loss of water of

hydration. The second weight loss occurs ~ 300 – 360 oC and

corresponds to the side chain decomposition of (PVA). Third

degradation between 410-600oC corresponds to

decomposition of main chain [17] leaving about 42 % residue.

The thermal decomposition of all the composite materials

found to follow the same trend. Thermal decomposition of the



composites 2.5, 5, 10, and 20 wt% (nGeP) content are shown

in Figures (8-11) , which shows four temperature range , can

be identified over which most of the weight change occurs.

Thermal decomposition of composite membrane of 2.5 wt%

(nGeP), is given in Figure (8), shows the first weight loss

occurs between 70-180oC is concern to the loss of water

molecules. The weight loss occurs between 180-350oC

corresponds to the decomposition of side chain of (PVA) , third

and fourth degradation between 350oC and 700oC corresponds

to the decomposition of (PVA) main chain and condensation

of P-OH groups of the inorganic material to pyrophosphate ,

GeP2O7.the residue results from thermal decomposition found

to be equal to 37.55%.

Figure 7: TG/DTA of PVA

Thermogram of composite membrane of 5 wt% (nGeP), given

in Figure (9), shows the first weight loss occurs between 90–

180oC is relate to the loss of water molecules. The weight

loss occurs between 180-380oC corresponds to the

decomposition of side chain of (PVA) , third and fourth

degradation between 360oC and 700oC corresponds to the

decomposition of (PVA) main chain and condensation of P-

OH groups of the inorganic material to pyrophosphate ,

GeP2O7. The residue results from thermal decomposition

found to be equalto 23.26%.

Thermogram of composite membrane of 10 wt% (nGeP),

given in Figure (10), shows the first weight loss occurs

between 70–180oC is concern to the loss of water molecules.

The weight loss occurs between 180-380oC is corresponds to

the decomposition of side chain of (PVA) , third and fourth





found to be equal to 36.25%.

For composite membrane of 20 wt% (nGeP), Its thermogram

is shown in Figure (11) the first stage decomposition occurs

between 70–170oC is concern to the loss of water molecules.

The weight loss occurs between 170-390oC is corresponds to

the decomposition of side chain of (PVA) , third and fourth





found to be equal to 25%.

An improvement in the thermal stability , to a certain extent of

the nanocomposites can be noticed .All weight losses

accompanied by endothermic peaks and leaving residues ,

which are related to carbonceous PVA plus GeP2O7 , the final

product from thermal decomposition of (nGeP).

Figure 8: TG/DTA of PVA/ (nGeP) nano composite

membrane(2.5 wt%)

Figure 9: TG/DTA of PVA/ (nGeP) nano composite membrane(5

wt%).

Figure10: TG/DTA of PVA/ (nGeP) nano composite

membrane(10 wt%).



Figure11: TG/DTA of PVA/ (nGeP) nano composite

membrane(20 wt%).

4. CONCLUSION

Novel nanosized lamellar germanium phosphate, α-

Ge(HPO4)2. 1.84H2O (GeP) was prepared . A series of

nanocomposite membranes were prepared from PVA and

(nGeP). The results from XRD, and TEM indicated that PVA

and (nGeP) posses good miscibility which lead to the

formation of homogeneous transparent flexible thin films. The

thermal stability was improved. Consequently the presence of

(nGeP) in PVA favored the increase of the thermal stability

and mechanical properties, that may combine physical

properties and characteristics of both organic and inorganic

components within the single composite. These composites are

promising for utilizations in fuel cells and as new sorbents.

Acknowledgments

To department of chemistry, faculty of science, Tripoli

university, for providing facilities for this research, to Adel

Bayomi Instiute of geologyical survey and mineral resources,

Cairo, Egypt for providing facilities for TGA , ESM and

TEM analysis..

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Poly(vinylalcohol)/Lamellar Germanium Phosphate Nanocomposite Membranes

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