Metal Oxide Nanostructures; Synthesis, Characterizations and Applications * 1 S.C. Singh, 2 D.P. Singh, 3 J. Singh, 3 P.K. Dubey, 3 R.S. Tiwari and 3 O.N. Srivastava 1 National Centre for Plasma Science and Technology (NCPST), School of Physical Sciences, Dublin City University, Dublin-9, Ireland 2 Thin Film Nanotechnology Laboratory, Department of Physics, Southern Illinois University, Carbondale, USA 3 Condensed Matter Physics & Hydrogen Lab., Department of Physics, Banaras Hindu University, Varanasi - 221005, INDIA *[email protected]; Phone Number: +353-1700-7787
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Metal Oxide Nanostructures; Synthesis, Characterizations and Applications
*1S.C. Singh,
2D.P. Singh,
3J. Singh,
3P.K. Dubey,
3R.S. Tiwari and
3O.N. Srivastava
1National Centre for Plasma Science and Technology (NCPST), School of Physical Sciences,
Dublin City University, Dublin-9, Ireland 2 Thin Film Nanotechnology Laboratory, Department of Physics,
Southern Illinois University, Carbondale, USA
3Condensed Matter Physics & Hydrogen Lab., Department of Physics, Banaras Hindu
acetates, carbonates, acetylacetonates, etc.), which requires an additional removal of the
inorganic anion, while the alkoxide route (the most employed) uses metal alkoxides as starting
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material [459-462]. In alkoxide route a sol or gel of TiO2 is obtained by hydrolysis and
condensation of Titanium alkoxides. As titanium sources, titanium-tetra-ethoxide, titanium-tetra-
isopropaxide, and titanium-tetra-butoxide are most commonly used alkoxides.
In our studies on TiO2 nanostructures, we have prepared nanostructured TiO2 [Figure 60]
film electrodes for the hydrogen production through controlled hydrolysis of Titanium-tetra-
isopropoxide Ti[OCH(CH3)2]4 [462]. For preparing sol–gel TiO2, Ti[OCH(CH3)2]4 solution was
added slowly to propanol drop by drop. Deionized water was slowly added under vigorous
stirring conditions for duration of 10 min. During the addition, a white precipitate was formed;
then 1 ml of 70% HNO3 was added to the mixture. The mixture was then further stirred for 15
min at 80°C. The propanol, together with some water, was allowed to evaporate during this time.
In this way, stable TiO2 colloidal solution was obtained. This TiO2 solution was then
concentrated by evaporation of water in vacuum at 25C, until a viscous liquid was obtained.
Carbowax M-20000 (40% by weight of TiO2) was added and a viscous dispersion was obtained.
The chemical process can be represented as
Ti[OCH(CH3)2]4 TiO2 (sol-gel) (1)
The spin on technique using Photoresist Spinner was used for thin film deposition on titanium
substrate. The film so obtained were dried in an air oven for 15 min at 80°C and then fired at
450°C for 30 min. This process was repeated four to five times to increase film thickness.
Finally, samples were annealed in argon atmosphere at 550°C for 4 h to improve the
crystallanity.
Metal ions such as Ca2+, Sr2+, Ba2+ etc. have been introduced into nanostructured TiO2
and films by this method to improve its photocatalytic activity. Sol–gel and templating synthetic
methods were applied to prepare very large surface area titania phases [463], which exhibit a
mesoporous structure. Ionic and neutral surfactants have been successfully employed as
templates to prepare mesoporous TiO2 [464]. Block copolymers can also be used as templates to
direct formation of mesoporous TiO2 [465]. In addition, many non-surfactant organic compounds
have been used as pore formers such as diolates [463] and glycerine [466]. Sol–gel methods
coupled with hydrothermal routes for mesoporous structures [466] lead to large surface area even
after heating at temperatures up to 500 0C.
Hydrolysis 80°C
60
4.3.1.5 Microemulsion method
Water in oil microemulsion has been successfully utilized for the synthesis of
nanoparticles. Microemulsions may be defined as thermodynamically stable, optically isotopic
solutions of two immiscible liquids consisting of microdomains of one or both stabilized by an
interfacial film of surfactant. The surfactant molecule generally has a polar (hydrophilic) head
and a long-chained aliphatic (hydrophobic) tail. Such molecules optimize their interactions by
residing at the two-liquid interface, thereby considerably reducing the interfacial tension. Despite
promising early studies, there have been only limited reports of controlled titania synthesis from
these microemulsions [467]. In particular, hydrolysis of titanium alkoxides in microemulsions
based on sol–gel methods has yielded uncontrolled aggregation and flocculation [468] except at
very low concentrations [469]. Recently, an improved method using carbon dioxide instead of oil
has been applied in preparing nanosized TiO2 [470].
4.3.1.6 Combustion synthesis
Combustion synthesis (hyperbolic reaction) leads to highly crystalline fine/large area
particles [471]. The synthetic process involves a rapid heating of a solution/compound
containing redox mixtures/redox groups. During combustion, the temperature reaches about 650 0C for a short period of time (1–2 min) making the material crystalline. Since the time is so short,
particle growth of TiO2 and phase transition to rutile is hindered.
4.3.1.7 Electrochemical synthesis
Electrochemical synthesis may be used to prepare advanced thin films such as epitaxial,
superlattice, quantum dot and nanoporous ones. Also, varying electrolysis parameters like
potential, current density, temperature and pH can easily control the characteristic states of the
films. Although electrodeposition of TiO2 films by various Ti compounds such as TiCl3 [472],
TiO(SO4) [473], and (NH4)2TiO(C2O4)2 [474] is reported, use of titanium inorganic salts in
aqueous solutions is always accompanied by difficulties, due to the high tendency of the salts to
hydrolyze. In addition to that nanoporous TiO2 thin films have been synthesized anodization of
titanium sheet [475-477] in aqueous solution of fluorine containing compound.
Recently our group at Nanoscience and Technology Unit at B.H.U. has synthesized
highly ordered, densely packed and nearly oriented TiO2 nanotube arrays having different
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lengths [Figure. 61] grown through controlled specific anodization of Ti sheets [478]. The
electrolytes used correspond to H3PO4 and NaF.
Pore size (diameter) of TiO2 nanotubes has been found to increase from ~40–60 nm to
~100–125 nm with increasing anodization potential from ~10 V to ~20 V used for the synthesis
of TiO2 nanotubes. The length of TiO2 nanotubes increases from ~350–450 to ~450–550 nm with
increase in anodization time from ~1 to ~2 hrs. However it was found to decrease with increasing
concentration of the electrolyte at constant anodization voltage (~20 V).The tube length
decreases from ~450–550 to ~200–250 nm with the change of electrolyte (H3PO4 concentration
from 0.5 to 1.0 M). A tentative mechanism of the growth of TiO2 nanotubes in terms of
controlled interaction of Ti4+ ions with O2− ions in the electrolyte and the rate of oxide growth at
the metal/oxide interface and the rate of oxide dissolution at the pore bottom electrolyte interface
has been proposed also. The UV-Vis absorption spectra of the TiO2 nanotubes have shown that
the band gap energy of TiO2 nanotubes synthesized at ~10 V is 3.03 eV and at ~20 V is 2.87 eV.
In contrast, few groups have reported the formation of TiO2 nanostructures in non
fluorine containing solutions [479].
4.3.2 Gas phase methods
For the preparation of thin films gas phase method is preferred. These methods can involve
chemical or physical reaction. Powders can also be synthesized by this method. The main gas
phase synthesis techniques are as follows
4.3.2.1 Chemical vapor deposition (CVD)
Chemical Vapor Deposition is a widely used versatile technique to coat large surface
areas in a short span of time. The family of CVD is extensive and split out according to
differences in activation method, pressure, and precursors. Compounds, ranging from metals to
composite oxides, are formed from a chemical reaction or decomposition of a precursor in the
gas phase [480, 481].
4.3.2.2 Physical Vapor deposition (PVD)
Physical Vapor Deposition is another class of thin-film gas phase deposition techniques
in which precursor and product do not go under chemical changes because of the stability of gas
phase. The most commonly employed PVD technique is thermal evaporation, in which a
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material is evaporated from a crucible and deposited onto a substrate. PVD is a so-called line-of-
sight technique, i.e., the gaseous stream of material follows a straight line from source to
substrate. This leads to shadow effects, which are not present in CVD. In electron beam (E-
beam) evaporation, a focused beam of electrons heats the selected material. These electrons in
turn are thermally generated from a tungsten wire that is heated by current. TiO2 films, deposited
with E-beam evaporation, have superior characteristics over CVD grown films where
smoothness, conductivity, presence of contaminations, and crystallinity are concerned, but on the
other hand, production is slower and more laborious. The use of reduced TiO2 powder (heated at
900 0C in a hydrogen atmosphere) is necessary to make it conductive enough to focus the
electron beam in the crucible [482].
4.3.2.3 Spray pyrolysis deposition (SPD)
SPD is a type of CVD in which aerosol deposition technique is used for the synthesis of
nanostructured TiO2 thin films and powders [483]. There are several small derivatives of this
technique, mainly differing in the formation step of the aerosol and the character of the reaction
at the substrate (gas-to-particle synthesis and droplet-to-particle synthesis). Confusingly, a broad
spectrum of names for this class of techniques has evolved. It has been used for preparation of
(mixed) oxide powders/films and uses mostly metal-organic compounds or metal salts as
precursors. The size of the particles formed and the morphology of the resulting film are strongly
dependent on deposition parameters like substrate temperature, composition and concentration of
the precursor, gas flow, and substrate–nozzle distance. Some of these parameters are mutually
dependent on each other.
4.3.2.4 Other methods
There are several other methods based on vapour phase deposition for the synthesis of
thin films. Sputtering (either using direct current (DC) [484] or radio frequency (RF) [485]
currents) is used quite frequently to produce TiO2 films. Molecular beam epitaxy [486] is a
technique that uses a (pulsed) laser to ablate parts of a TiO2 ceramic target. The material is
deposited on the substrate in an argon/oxygen atmosphere or plasma. Ion implantation is seldom
used to synthesize TiO2 and is based on the transformation of precursor plasma to TiO2, which
only becomes crystalline after an annealing step. It is, however, frequently used to implant ions
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in TiO2 films (doping) to improve the photocatalytic activity [487]. Another unusual technique is
dynamic ion beam mixing [488], which uses high-energy O2+ and/or O+ beams and Ti vapour to
deposit TiO2 films with high speed and control over the composition. Sonochemical is another
method in which ultrasound waves are used for the formation of nanostructured TiO2 [489, 490].
Microwave method is also used for the synthesis of TiO2 nanomaterials [491].
4.4 Applications of titanium Dioxide
4.4.1 Photoelectrochemical generation of hydrogen (solar hydrogen)
There is a constant search of clean and renewable energy, which can effectively substitute
petroleum. Decades of R&D efforts have shown that hydrogen is the best substitute. The
production of hydrogen can reduce our dependence on imported oil and natural gas. Hydrogen
can be produced through various routes particularly, most attractive routes are
photoelectrochemical and photocatalytic decomposition of water. In 1972, Fujishima and Honda
[395] have demonstrated photoelectrolysis of water on n-type TiO2 single crystal electrode for
solar energy conversion and storage in the form of hydrogen. Unfortunately because of its large
band gap (3 -3.2 eV) TiO2 absorbs only the ultraviolet part of the solar emission, consequently
has low conversion efficiencies. Numerous attempts have been made to shift the spectral
response of the TiO2 into the visible range to increase the efficiencies of the
Photoelectrochemical solar cells either by dye sensitization or doping with species that
essentially reduce the band gap of the TiO2. Schematic view of the hydrogen production using
titanium dioxide electrode is illustrated in Figure 62.
In 1991 M. Gratzel et al have reported a new type of solar cells known as Dye Sensitized
Solar Cells, in which the mesoporous nanocrystalline TiO2 film coated with monolayer of a
charge transfer dye have been used to sensitized the film for light harvesting, have higher
efficiencies [492]. Schematics of the Dye Sensitized Solar Cells are illustrated in Figure 63.
There are a lot of reports available on the Hydrogen production using nanostructured TiO2
electrode [462, 493-495]. Recently several groups have used thin films consisting of TiO2
nanotube as photoanode for the hydrogen production. As the length of the tube and doping of
species (which can lower the band gap) play major role in band gap modification of TiO2
nanotube, several groups have reported improved rate of hydrogen production using TiO2
nanotube photoelectrode in comparison to TiO2 nanoparticulate system [475-477, 479].
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4.4.2 Water Purification
TiO2 is the most commonly used photocatalyst for environmental applications. However, the
wide technological usage of TiO2 is hampered by its wide band-gap (rutile: 3.02 eV, anastase:
3.2 eV), which thus requires ultraviolet (UV) light irradiation for photocatalytic activation. Since
UV light accounts for only a small fraction (less than 5%) of solar irradiation compared to visible
light (45%), any shift in the optical response of TiO2 from the UV (λ ≤385 nm) to the visible
spectral range (λ ≥420 nm) should have a beneficial effect on the photocatalytic efficiency of the
material. Several approaches have therefore been used to lower the band-gap energy of TiO2
photocatalysts. Commercially available TiO2 Degussa P-25, consisting of 80% of anatase and
20% of rutile with an average particle size of 30 nm, is widely used in the treatment of
contaminated wastewater. However, nanocrystalline TiO2 (particle sizes of ca. 6–8 nm), has
emerged as promising photocatalysts for water remediation and purification.
The decrease in semiconductor particle size has not only increases the surface area but also
fine tunes the band gap of the semiconductor. TiO2 nanoparticle systems on irradiation with UV
light degrade many water pollutants [496]. Visible light activated TiO2 nanoparticles modified
by complex sensitizers and platinum (Pt) deposits drastically enhanced the rate of reductive
dehalogenation of trichloroacetate and carbontetrachloride in aqueous solutions under visible
light [497]. A suspension containing TiO2 nanocrystals showed complete conversion of As(III)
to As(V) in the presence of sunlight and dissolved oxygen, through photocatalytic oxidation
within 25 min [498].
In our investigation at Nanoscience and Technology Unit at B.H.U we have synthesized
nanostructured TiO2 photocatalysts, which have been used in the photocatalytic degradation of
phenol (one of the most common water pollutants) [499]. These catalysts have been prepared
through sol–gel technique using titanium tetra-isopropoxide as a raw material for synthesis. The
average particle sizes of the TiO2 nanopowders used in this study are ~ 5–10 nm and correspond
to anatase phase. The optical characterization of this nanopowder shows its bandgap ~3.02eV.
The photocatalytic measurements were carried out in a reactor consisting of a quartz tube having
its diameter, ~ 3 cm, with an inlet tube for oxygen purging during photocatalysis and another
outlet for the collection of samples from the reactor at different time intervals. Initially ~ 2.5 g of
as synthesized nanostructured and the same amount of commercial TiO2 (P-25, Degussa)
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photocatalyst in ~ 400 cc of ~ 100 ppm phenol solution were taken. Phenol solution (~ 400 ml by
volume) was prepared by dissolving phenol crystals in double distilled water. During
illumination, oxygen gas was purged into the solution with the help of porous fused silica tube
by an external cylinder. Oxygen was bubbled through this solution at a rate of ~ 200 cc/min.
During the reaction, solution was maintained at 25°C and ~ 3 cc of the samples was collected at
given time intervals e.g. 10 min. After being sampled, the suspension was centrifuged and the
centrifugates were subjected to further analysis. The schematic diagram of the fabricated
photocatalytic reactor along with the other related accessories are given in Figure 64. UV-light
was made to fall on the reactor through the tube walls. To determine the concentration of phenol
in the solution, samples were collected at 10 min of interval upon UV-induced degradation of
phenol. The concentration of phenol was determined by UV-visible absorption spectroscopic
technique, where the absorbance was measured at a fixed wavelength (e.g. ~ 269 nm) for all the
samples. Possible mechanism for photocatalytic degradation of phenol using nanostructured
TiO2 films as photocatalyst has been described as
TiO2(ns) + hν →→→→ e- + h+,
2H2O + h+ →→→→ H2O+ + H2O →→→→ ˙OH + H3O
+,
H2O + e- →→→→ H˙ +OH˙,
OH˙ + ˙OH →→→→ H2O2,
H2O →→→→ H2O* →→→→ H2O2 + H2,
Phenol + H2O2 →→→→ Products.
Variation of phenol concentration using TiO2 photocatalysts after irradiation as a function of
time have been shown in Figure 65. It can be seen that the concentration of the phenol decreases
from 100% (initial concentration of phenol, ~ 100 ppm) to ~ 68% (final concentration of phenol,
~ 68 ppm) after ~ 1 h illumination. The total decrease in the phenol concentration using
nanostructured TiO2 synthesized in this investigation is ~ 32%, which is nearly the safe limit of
the phenol concentration in the solution. On the other hand, the decrease in phenol concentration
employing commercial TiO2 nanopowder (P-25, Degussa), is only ~ 25%. Thus the TiO2
nanopowder prepared in the investigation is more effective than the degradation of phenol
through the commercial TiO2 nanopowder. Also analysis of water after photocatalytic
degradation showed that no other compounds including any toxic components get formed. Thus
the only effect of photocatalytic reaction is the dissociation of phenol.
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Several groups have reported the improved degrading capability of the doped TiO2
nanoparticle systems for water purification [500-503]. Tubular arrays of meso and microporous
molecular sieves composed of TiO2 nanoparticles, supported by mesoporous silica have been
used for water remediation of aromatic pollutants in the presence of UV light [504]. A
schamatics of the tubular photocatalytic reactor for water purification is shown in Figure 66.
Photocatalysts composed of nanostructured TiO2, uniformly deposited onto Fe2O3, have also
been incorporated into ultrafiltration membranes and were shown to reduce the fouling burden
and improve the permeate flux successfully [505]. Highly ordered TiO2 nanotubes have also been
used by several groups for the water remediation [506, 507].
4.4.3 Self-cleaning Surfaces
The properties which TiO2 possesses are hydrophilicity and hydrophobicity.These properties
are of great interest for a number of applications such as for example rear-view mirrors, anti
fogging glasses, self cleaning windows and buildings etc. Figure 67 shows the Misericordia
Church in Rome, Italy whose walls have been coated with TiO2. The fogging of the surfaces of
mirrors and glasses occurs when steam cools down or humid air condenses, with the formation of
many small water droplets, on these surfaces which scatter light due to which glasses and mirror
becomes partially opaque. Beading of rainwater on automobile side-view mirrors can be a
serious safety problem. The formation of the droplet depends on the contact angle between the
surface and water. TiO2 coated surfaces turns into hydrophilic surface under ultraviolet
irradiation [508]. On a highly hydrophilic surface, no water drops are formed. Instead, a uniform
thin film of water is formed on the surface because of the lower contact angle between the
surface and water [509]. This uniform water film prevents the fogging. That’s why TiO2 coated
glasses and mirrors remain transparent under rainwater or mist. Figure 68 shows the images of
ordinary and TiO2 coated anti fogging mirrors respectively.
TiO2 films are used to render surfaces self-cleaning. This property is due in part to the fact
that irradiated TiO2 films are not just hydrophilic but ampiphilic: the surface contains both
hydrophilic and hydrophobic microdomains, which attract drops of polar or nonpolar liquids,
respectively. This allows a water rinse to flush away an oily coating [510].
67
4.4.4 Sensors
TiO2 nanocrystalline films have widely been studied as sensors for various gases. Grimes et
al. found that TiO2 nanotubes were excellent room-temperature hydrogen sensors not only with a
high sensitivity but also with ability to self clean photoactively after environmental
contamination [511]. Many types of TiO2 nanomaterial-based room-temperature hydrogen
sensors based on Schottky barrier modulation of devices like Pd/TiO2 or Pt/TiO2 [512-515],
SnO2-TiO2 [516] and undoped TiO2 nanotubes based sensor which exhibited 8.7 orders of
magnitude variation in electrical resistance at room temperature when exposed to hydrogen
[517]. Oxygen sensors based on TiO2 nanomaterials include TiO2-x [518], CeO2-TiO2 [519] and
doped TiO2 nanomaterial showed improved gas sensitivity, low operation temperature (350-800
°C), and short response time (<0.1 s) [520]. TiO2 nanomaterials are also promising candidates for
CO sensing and for methanol and ethanol sensing [521-527]. TiO2 nanomaterials are also used
for humidity sensing [528].
4.4.5 Cancer treatment
Cancer treatment is one of the most important topics that are associated with Titanium
dioxide photocatalysis. While surgical, radiological, immunological, thermotherapeutic, and
chemotherapeutic treatments have been developed and are contributing to patient treatment yet
the cancer has remained the cause of death in world. In mid-1980s Fujishima and coworkers used
the strong oxidizing power of illuminated TiO2 to kill tumor cells [529]. In their experiment they
used polarized illuminated TiO2 film electrodes and TiO2 colloidal suspensions for effective in
killing HeLe cells. They examined a series of experimental conditions [530-532], including the
effect of superoxide dismutase, which enhances the effect, due to the production of peroxide. In
addition, it was found possible to selectively kill a single cancer cell using a polarized,
illuminated TiO2 microelectrode [533]. In their joint research with urologists they conducted
animal experiments implanting cancer cells under the skin of mice to cause tumors to form.
When the size of the tumors grew to about 0.5 cm, they injected a solution containing fine
particles of titanium dioxide and after 2 or 3 days irradiated tumor and repeated it again after 13
days, and observed a marked antineoplastic effect [534].Photoexcited TiO2 particles also
significantly suppressed the growth of HeLa cells implanted in nude mice, compared with those
receiving TiO2 alone or UV irradiation alone.. However, this technique was not effective in
68
stopping a cancer that had grown beyond a certain size. The results of animal experiments have
shown that near-UV rays, with wavelengths of 300–400 nm, which are used in photocatalytic
reactions, are safe and do not cause mutation to the cell. Figure 69 shows the photograph of
nude mouse just after initial and 4 weeks after treatment.
4.4.6 Generation of PV electricity
Photovoltaics based on TiO2 nanocrystalline electrodes have been widely studied for the
generation of PV electricity. The mesoporosity and nanocrystallinity of the semiconductor are
important not only because of the large amount of dye that can be adsorbed due to large surface
area but also they allow the semiconductor small particles to become almost totally depleted
upon immersion in the electrolyte and the proximity of the electrolyte to all particles makes
screening of injected electrons, and thus their transport become possible. In 1991 Grätzel et. al.
reported the sensitized electrochemical photovoltaic device with a conversion efficiency of 7.1%
under solar illumination with polypyridyl ruthenium and osmium sensitizers [492] after that
[Schematic view figure 63] several groups have reported the improvement into dye sensitized
solar cells using different dyes and modifying the morphology of the nanostructured TiO2. Using
hybrid TiO2 nanocrystalline electrode such as anatase-rutile TiO2 nanocrystalline electrode [535,
536], nanocrytalline TiO2 electrode with a buffer layer [537], core-shell structured nanocystalline
TiO2 electrodes [538-543] and TiO2 nanocrystalline electrode coupled with photonic crystals
[544, 545] also enhances the efficiency of the cell.
4.4.7 Air Purification
Substances emitted into the atmosphere by human activities, in urban and industrial areas, cause
many environmental problems including air quality degradation, global warming, climate
change, and stratospheric ozone depletion. Volatile organic compounds (VOCs) are major air
pollutants, originating largely from industrial processes. Although, initially TiO2 photocatalysts
were applied for water treatment, in recent years, it has been shown that the photocatalytic
detoxification of volatile organic compounds is generally more efficient in the gas phase
compared to the liquid phase. Thus, attention for the application of this technology for air
treatments increases, including the utilization of pollutant air stripping from the liquid phase. It
69
has been reported that the use of illuminated TiO2 can result in the overall degradation of VOCs
together with nitrogen oxides and sulfur oxides in air [546].
Photocatalytic oxidation (PCO) is shown to be more cost-effective than incineration, carbon
adsorption, or bio-filtration for flow rates up to 20,000 cfm (ft3/min) for treating a 500 ppm
VOC-laden stream gas phase reactions allow the direct application of analytical tools to monitor
the composition, structure, and electronic state of the substrate and adsorbates and hence the
reaction mechanisms can be directly elucidated [547].
Other Applications
Apart from above mentioned applications TiO2 nanomaterials are used in various other
applications.TiO2 nanomaterials are used in the fabrication of electrochromic devices such as
electrochromic windows and displays and photoelectrochromic devices such as
photoelectrochromic smart windows [548-550]. TiO2 nanomaterials are also used for the
hydrogen storage [551, 552]. Recently films consisting of highly oriented TiO2 nanotubes have
been used for the size dependent selective filtration by varing the diameter of the nanotubes
[553]. Nanocrytalline Titanium Dioxide is also used in the memristor a new electronic circuit
element which is used as the solid state memory device in various electronic devices [554].
4.5 : Summary
Due to extensive studies on the nanostructured TiO2 in recent past has resulted in new
synthesis techniques which can control sizes and shapes of TiO2 nanomaterials. These new
synthesis and modification techniques of TiO2 nanomaterials have brought new properties and
new applications with improved performance. Apart from quantum-confinement effect, these
nanostructured TiO2 demonstrate size-dependent as well as shape and structure dependent
optical, electronic and thermal properties. TiO2 nanomaterials have been used in solar cells,
photocatalysis, gas sensing, hydrogen storage, Cancer treatment, electro-chromic and photo-
electrochromic devices, memory devices, water and air purification and in many new
applications due to their some new and improved properties. TiO2 nanomaterials will play an
important role in the search for new renewable and clean energy technologies and environmental
protection.
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5. Overall Conclusion
Detailed investigation on the oxides of zinc, copper and titanium reveals that these oxide
semiconductors have potential applications in the fabrication of electronic, photonic, sensing,
energy storage and harvesting devices as well as in the biological and medical diagnosis. Zinc
oxide is most efficient for the photonic application; titanium oxide has maximum IPCE for dye
sensitized solar cells and copper oxide is well known for biological and electronic applications.
Metal oxide nanostructures can be easily synthesized in various size, shape, morphologies, and
architectures, simply get self assembled for the fabrication of devices, and can be functionalized
or surface modified for various biological and chemical sensing applications without any
complex and difficult processes, as compared to the mono-atomic and their sulphide, nitride and
selenide counterparts. Bulk as well as nanomaterials of metal oxides is highly demandable by
fabric, rubber, paint, cosmetic, pharmaceutical etc. industries.
6. Future Prospects
Based on their performance, cheap and easy ways of synthesis and continuing research by highly
interested and motivated scientist and technologist, and ever increasing interest of semiconductor
industries, metal oxide nanostructures may be efficient future materials for the fabrication of
most of the semiconductor devices and electronic chips. Semiconductor and microchip industries
are continuously seeking alternative materials due to the high cost of the silicon wafers, and
requirement of highly standard quality of clean rooms for their processing. Metal oxide
nanostructures may comply with their need and create a new roadmap of the future
semiconductor industry. Due to their continuously increasing biological, medical, and cheap
device fabrication applications, it is expected that metal oxide nanostructures will be a reliable
partner of mankind and society in the near future.
Acknowledgement
Dr. S.C. Singh is thankful to Irish Research Centre for Science Engineering and Technology
(IRCSET), Ireland for providing EMPOWER Postdoctoral Fellowship Grant to carryout research
in the field of photonics.
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5 Electrical properties (a) Exciton band energy (RT) (b) Band gap energy (c) Effective masses (d) Hall mobility (RT)
60 meV 3.44 eV mh =0.59 m0, me =0.24 m0
µp= 5-50, µn=200 cm2s-
1V-1
100
Table 2:
Tab
le
3:
S. No. Physical Properties Value
1. Common Name IUPAC name: Copper(I) oxide Other names: Cuprous oxide, Dicopper oxide, Cuprite, Red copper oxide
2. Molecular formula
Cu2O
3. Appearance Brownish-red solid (The compound may appear either yellow or red, depending on the size of the particles)
4. Crystal structure Cubic, a=4.2696 Å 5. Space group , 6. Molar mass 143.09 g/mol
7. Density 6.0 g/cm3
8. Melting point 1235 °C, 1508 K, 2255 °F
9. Boiling point
1800 °C, 2073 K, 3272 °F
10. Solubility in water Insoluble
11. Solubility in acid Soluble Concentrated ammonia solution, Hydrochloric acid, Dilute sulfuric acid and Nitric acid
12. Band gap 2.137 eV
S. No. Polymorph →→→→
Property↓
Rutile Anatase Brookite
1. Molecular Formula TiO2 TiO2 TiO2
2. Crystal System Tetragonal Tetragonal Orthorhombic
3. Point Group 4/mmm 4/mmm mmm
4. Space Group P42/mnm I41/amd Pcab
5. Lattice parameters a = 4.594 Å
c = 2.959 Å
a = 3.784 Å
c = 9.515 Å
a = 9.184 Å
b = 5.447 Å
c = 5.145 Å
6. Molecules per unit cell 2 4 8
101
Figure Captions
Figure 1: Crystal structure of zinc oxide (a) Wurtzite (b) zinc blende (c) rock salt
Figure.2: SEM images of zinc oxide nanostructures synthesized by precipitation method at (a) 60° (b) 70° and (c) 80° C temperatures [Reprinted with permission from Ref. 208 Guzman et al., Matter. Chem. Phys. 115, 172, 2009; Copyright @ Elsevier (2009)]
Figure 3: SEM micrographs of mesoporous crystalline zinc oxide nanowires (a) in the PPA template and (b) released from PPA template.[Reprinted with permission from Ref. 209 Xiao
et al. Nanotech. 16, 671, 2005; Copyright @ Institute of Physics (2009)]
Figure 4: SEM images of zinc oxide nanostructures produced with precipitation method with (a) the control sample having large prisms and small needles (b) sample precipitated with 120 mg/L of EO68-b-MAA8-C12, and (d) the schematic view for dumbbell shape. [Reprinted with
permission from Ref. 212 Taubert et al., J. Phys. Chem. B, 107, 2660, 2003 Copyright @
American Chemical Society (2003)]
Figure 5: SEM images of hydrothermally synthesized zinc oxide nanomaterials (A) Nanowires [B] Nanorods [Reprinted with permission from Ref. 215 Li et al. Inorganic Chem. 42, 8105,
2003. Copyright @ American Chemical Society]
7. Cell Volume 62.07 136.25 257.38
8. Molar Volume 18.693 20.156 19.377
9. Density 4.25 3.89 4.12
10. Band gap 3.02 eV 3.2 eV 3.1 eV
11. Refraction index ⊥ to c axis 2.60
// to c axis 2.89
⊥ to c axis 2.55
// to c axis 2.48
⊥ to c axis 2.57
// to c axis 2.69
12. Dielectric constant ⊥ to c axis 89
// to c axis 173
⊥ to c axis 31
// to c axis 48 78
13. Cationic radius r (Ti4+)=0.605 Å r (Ti4+)=0.605 Å r (Ti4+)=0.605 Å
14. Anionic radius r(O2-)=1.36 Å r(O2
-)-=1.36 Å r(O2-)-=1.36 Å
102
Figure 6: SEM images of hydrothermally synthesized zinc oxide powders using 1M aqueous solution of (a) NH4OH (b) mono (c) di- and (d) tri-ethanolamine (e) 0.2M NH4OH + 1M diethanolamine (DEA) (f) 0.4M NH4OH + 1M DEA (g) 0.6M NH4OH + 1M DEA (h) 0.2M NH4OH + 1M DEA [Reprinted with permission from Ref. 219 Lu et al., J. Alloy and
Compounds, 477, 523, 2009. Copyright @ Elsevier ]
Figure 7: SEM images of hydrothermally prepared zinc oxide nanopowders at 200°C for 2h using (a) 0.25 (b) 0.5 (c) 1.0 (d) 2.0 M solution of KOH and (e) 0.025 (f) 0.05 (g) 0.20 M solution of NH3.H2O as solvent. [Reprinted with permission from Ref. 219 Xu et al., Ceramic
Figure 8: SEM images of solvothermally produced zinc oxide nanostructures with different water/EN volume (ml) (a) 60/0 (b) 30/30 (c) 20/40 (d) 50/10 (e) cross sectional view of 50/10 and (e) 0/60 [Reprinted with permission from Ref. 225 Dev et al., Nanotech., 17, 1533, 2006.
Copyright @ Institute of Physics ]
Figure 9: FESEM images of hierarchical zinc oxide micro/nanoarchitectures produced solvo thermally at 160° temperature for 12 hours with 1:7 v/v ratio of distilled water and EDA [Reprinted with permission from Ref. 226 Lu et al., Adv. Func Mater. 18, 1047, 2008
Copyright @ Willey-VCH Verlag GmbH 2008 ]
Figure 10: FESEM images of hierarchical zinc oxide micro/nanoarchitectures produced solvo thermally at 160° temperature and 1:7 v/v ratio of distilled water and EDA for different reaction times (A) 1h (B) 2h (C) 4h (D&E) 8h and (F) 16h [Reprinted with permission from Ref. 226
Lu et al., Adv. Func Mater. 18, 1047, 2008 Copyright @ Willey-VCH Verlag GmbH 2008 ]
Figure 11: SEM images of 3D zinc oxide hollow micro-sphere synthesized by the solvothermal method in the EG solution at 200 °C temperature, general view in the left, at high magnification at right Fig. 2.10 A: FESEM images of hierarchical zinc oxide micro/nanoarchitectures produced solvo thermally at 160° temperature for 12 hours with 1:7 v/v ratio of distilled water and EDA [Reprinted with permission from Ref. 227 Zhang et al., Nanotech. 18, 455604,
2007 Copyright @ Institute of Physics 2007 ]
Figure 12: SEM images of Sol-gel derived zinc oxide nanostructures on the silicon substrates (a-c) from neutral solutions (a) as-synthesized, and thermal treatment at 500°C for (b) 4h and (c) 6h and (d) as obtained from acidic solution . [Reprinted with permission from Ref. 230 Li et al.,
Figure 13: SEM images of one dimensional micro-emulsion derived zinc oxide nanostructures obtained after different reaction times (a) 10 min, (b) 30 min, (c) 1h (d) 2h (e) 4h and (f) 8 h. [Reprinted with permission from Ref. 232 Zhang et al., Cryst. Growth Design 4, 309,2004.
Copyright @ American Chemical Society 2004 ]
103
Figure 14: SEM images of zinc oxide nanostructures obtained by combustion synthesis method using (a) calcination of 0.2g Zn(NO3).6H2O for 2h at 800°C (b) By combustion and (c) by solution combustion (d) solution combustion with 1.0 ml of additional water. [Reprinted with
permission from Ref. 238 Alvarado-Ibarra et al., Colloid Surf. A: Physiochem. Eng.
Figure 15: SEM image of melting combustion synthesized zinc oxide nanostructure. [Reprinted
with permission from Ref. 239 Chen et al., Matter Lett. 61, 4603, 2007 Copyright @
Elsevier 2008]
Figure 16: SEM images of the Eelctrochemically obtained zinc oxide films prepared at the cathode potential ranging from -0.7 to -1.4V vs Ag/AgCl [Reprinted with permission from
Ref. 243 Izaki and Omi, Appl. Phys. Lett., 68, 2439, 1996. Copyright @ American Institute
of Physics 1996]
Figure 17: SEM images of electrochemically synthesized ZnO nanostructures in the electrolytic solution of (a) 0.5M ZnCl2+0.02 M citric acid (b) 0.5M ZnCl2+0.01 M citric acid (c) 0.5M ZnCl2+0.05 M citric acid (d) 0.5M ZnCl2+0.0001 M citric acid (e) 0.25 M +0.01M citric acid (f) 0.25M ZnCl2+0.01 M citric acid+0.1MKCl [Reprinted with permission from Ref. 260 Li et
al., J. Phys. Chem. C, 111, 6678, 2007. Copyright @ American Chemical Society 2007]
Figure 18: SEM images of (a) primary ZnO nanosheets and (b-d) hierarchical ZnO nanorods on hexagonal nanosheets on ITO substrates. [Reprinted with permission from Ref. 261 Xu et al.,
J. Phys. Chem. C, 111, 11560, 2007. Copyright @ American Chemical Society 2007]
Figure 19: SEM images of hierarchical ZnO nanostructures electrodeposited at a potential of -1.10 V in 0.05M [Zn(NH3)4
-2 solution for different deposition times (a) 10min, (b) 20min, (c) 40min, (d) 1.5h, (e) 2.5h, (f)3.5h [Reprinted with permission from Ref. 261 Xu et al., J. Phys.
Chem. C, 111, 11560, 2007. Copyright @ American Chemical Society 2007]
Figure 20: SEM images of sonochemically synthesized zinc oxide (a) nanorods (b) nanoups (c) nanosheets (d) nanoflowers and (e) nanospheres [Reprinted with permission from Ref. 262
Jung et al., Cryst. Growth Design, 8, 265, 2008 Copyright @ American Chemical society
2008]
Figure 21: SEM images of the ZnO samples prepared by sonochemical method using the mixture of Zn(NO3)2 and NaOH as precursor at different pH value:(a) pH 9.5 (b) pH 10.5(c) pH 11.5 and (d) pH 12.5. .[Reprinted with permission from Ref. 266 Xiao et al., J. Alloy and
Comp. 459, L18, 2008 Copyright @ Elsevier 2008]
Figure 22: SEM images of as-made ZnO powders prepared by sonochemical method using the mixture of different zincs salt and NaOH as precursor at pH 12.5 (a)Zn(NO3)2 (b)ZnCl2
104
(c)ZnSO4 and (d) Zn(C2H4O2)2 .[Reprinted with permission from Ref. 266 Xiao et al., J.
Alloy and Comp. 459, L18, 2008 Copyright @ Elsevier 2008]
Figure 23(A): FESEM images of cyclic feeding chemical vapor deposited zinc oxide flower shaped zinc oxide nanostructures on Si (a,b) 100 and (c,d) 111 substrates. [Reprinted with
permission from Ref. 273 Umar et al., Nanotech. 16, 2462, 2005 Copyright @ Institute of
Physics 2005]
Figure 23(B): FESEM images of multipod star shaped zinc oxide nanostructures grown by cyclic feeding chemical vapor deposited on Au coated Si (100) substrate [Reprinted with
permission from Ref. 274 Umar et al., J. Cryst. Growth 277, 479, 2005 Copyright @
Elsevier 2005]
Figure 24: FESEM images of zinc oxide nano columns grown by electron beam evaporation at 400°C on the Si(100) substrate for (a) 30min. and (b) 50 min. [Reprinted with permission from
Ref. 289 Qiu et al., Solid State Comm. 134, 735, 2005 Copyright @ Elsevier 2005]
Figure 25: SEM images of magnetron sputtering derived [A] as synthesized zinc oxide thin film and [B] zinc oxide nanotetrapods grown on the surface of film after annealing . [Reprinted with
permission from Ref. 291 Saw et al., J. Phys. D: Appl. Phys. 41, 055506, 2008 Copyright @
Institute of Physics 2008]
Figure 26: SEM images of zinc oxide nanostructures grown by RF sputtering for (a) 15 min. and (b) 50 min. [Reprinted with permission from Ref. 294 Youn et al., Jap. J. Appl. Phys.
45, 8957, 2006 Copyright @ Japanese J. Appl. Phys., 2006]
Figure 27 : X-ray diffraction patterns of vacuum arc deposited zinc oxide thin films at (a) low (b) high magnetic fields [Reprinted with permission from Ref. 296 Takikawa et al., Thin
Solid Films 377, 74 , 2000 Copyright @ Elsevier 2006]
Figure 28: SEM images of Spray Pyrolysis deposited zinc oxide nanostructures on ITO/glass substrate using 0.1mol/lit. solution of zinc chloride at different (a) 400°C (b) 450°C (c) 490°C (d) 540°C and (e) 560°C substrate temperatures [Reprinted with permission from Ref. 314
Krunks et al., Thin Solid Films 515, 1157 , 2006 Copyright @ Elsevier 2006]
Figure 29: (a) Emission spectra from N doped zinc oxide nanoneedle under different pumping powers (b) Output power vs pump energy curve [Reprinted with permission from Ref. 319,
Figure 30: (a) SEM image of zinc oxide vertical nanowire cavities grown on sapphire substrate (b) SEM iamge of a single verical NW with Fabry-Perot lasing modes as wavelengths λA, λB and
105
λc (c) lasing spectra of a single ZnO nanowire cavity (Left inset: Power dependence graph showing lasing threshold almost at 400 µJ/cm2. Right inset: Dark field scattering images of ZnO vertical Nanowire cavity from white light excitation (top) and lasing induced by 266 nm pulsed excitation (d) PL imaging of a single zinc oxide vertical NW cavity (inset SEM image of ZnO) (e) Diagram of ZnO vertical nanowire cavity with corresponding PL images [Reprinted with
permission from Ref. 322, Gargas et al., J. Am. Chem. Soc., 131, 2125, 2009 Copyright @
American Chemical Society 2009]
Figure 31: (Top) Schematic view of zinc oxide based hetrojunction p-n LED (Bottom) Optical microscope plan view of a zinc oxide based hetrojunction LED. [Reprinted with permission
from Ref. 53, Wang et al., Appl. Phys. Lett., 92, 112101, 2008 Copyright @ American
Institute of Physics 2008]
Figure 32: Optical photographs of the n-zinc oxide nanorods/p-SiC: (a) before measurements, (b) packaged LED (c) emission of white light and (d) EL spectra at 27 and 37V. [Reprinted
with permission from Ref. 56, Willander et al., Nanotech. 20, 332001, 2009 Copyright @
Institute of Physics 2009]
Figure 33: Cross sectional SEM image of a ZnO/polymer multi layer LED fabricated on glass substrate. [Reprinted with permission from Ref. 56, Willander et al., Nanotech. 20, 332001,
2009 Copyright @ Institute of Physics 2009]
Figure 34: (Top) Current density-voltage characteristic of (a) NPD-PFO structure and (b) PVK-TFB structure (inset shows a schematic diagram of the corresponding energy band energy band diagram) and (Bottom) Coressponding EL spectra at 14V and 0.10mA [Reprinted with
permission from Ref. 56, Willander et al., Nanotech. 20, 332001, 2009 Copyright @
Institute of Physics 2009]
Figure 35: (a) Cu2O deposited at pH 9 (0.05 mA/cm2; 0.1 C/cm2; 55°C). (b) Cu2O deposited at pH 9 (0.05 mA/cm2; 0.1 /cm2; 10°C). (c) Cu2O deposited at pH 11 (0.2 mA/cm2; 0.13 C/cm2; 55°C). [Reprinted with permission from Ref. 333 P. E. Jongh et al., Chem. Mater. 11, 3512,
1999; Copyright @ American Chemical Society (1999)] Figure 36: (a) Scanning electron micrograph of electrodeposited Cu2O nanowires. Bath temperature = 70 0C, pH =9.1, E =-1:69V/SSE. (b) Enlarged of (a). [Reprinted with permission
from Ref. 337 A. L. Daltin et al., Journal of Crystal Growth 282, 414, 2005; Copyright @
Elsevier (2005)]
Figure 37: Typical FE-SEM images of octahedral Cu2O located at the ITO substrate at different magnifications (the deposition time is 15 min; the concentration of Cu(OH)4
2- is 25 mM). [Reprinted with permission from Ref. 341 S. Guo et al., Inorganic Chemistry 46, 9537,
2007; Copyright @ American Chemical Society (2007)]
Figure 38: (a) Typical transmission electron micrographs of Cu2O nanothreads embodying beads, as collected at the bottom of the cell after electrolysis at 2 V for 1 h. (b) Figure showing coalesced beads forming nanothreads. (c) Representative TEM micrographs of the dense Cu2O
106
network of nanowires, obtained after electrolysis at 6 and 10 V respectively for 1 h; (c) The magnified TEM micrograph of the nanowires. [Reprinted with permission from Ref. 342 D. P. Singh et al., J. Phys. Chem. C 111, 1638, 2007; Copyright @ American Chemical Society
(2007)] Figure 39: (a-d) SEM micrographs of the copper electrode after electrolysis at different voltage (2, 4, 8, and 10 V, respectively). [Reprinted with permission from Ref. 342 D. P. Singh et al., J. Phys. Chem. C 111, 1638, 2007; Copyright @ American Chemical Society (2007)] Figure 40: SEM (a) and TEM (b) images of thick-shell Cu2O hollow spheres. The inset in (a) shows a broken hollow sphere. The inset in (b) shows the ED pattern corresponding to a single hollow sphere. SEM (c) and TEM (d) images of thin-shell hollow spheres of Cu2O. [Reprinted
with permission from Ref. [343] J. Gao et al., Chem. Mater. 20, 6263, 2008; Copyright @
American Chemical Society (2008)]
Figure 41: TEM images of Cu2O nanoparticles prepared with different concentrations of CTAB. From a-f, CCTAB equals 0.01, 0.02, 0.04, 0.06, 0.08, and 0.10 M, respectively. Scale bars are 500 nm (a, b, c, e) or 2 microns (d, f). [Reprinted with permission from Ref. 347 L. Gou et al., Nano Lett., 3, 1903, 2003; Copyright @ American Chemical Society (2003)]
Figure 42: TEM images of cuprous oxide nanoparticles synthesized by using ascorbic acid as the reductant. Scale bar is (a) 500 nm, (b) 100 nm. [Reprinted with permission from Ref. 347
L. Gou et al., Nano Lett. 3, 1903, 2003; Copyright @ American Chemical Society (2003)]
Figure 43: a: TEM micrograph (scale bar~100 nm) and histogram of the size distribution from sample B2; b: TEM micrograph (scale bar~100 nm) and histogram of the size distribution from sample B3; c: TEM micrograph (scale bar ~ 100 nm) and histogram of the size distribution from sample B4. [Reprinted with permission from Ref. 349 L. Gou et al., J. Mater. Chem. 14,
735, 2004; Copyright @ RSC publishing (2004)]
Figure 44: Type (ii) multipod frameworks and crystal assemblies: (a-d) prepared with 30 mL of 0.015MCu2+ solution (water at 5 vol %) and 4.5 mL of formic acid at 180°C (2 h); and (e and f) prepared with 30 mL of 0.010 M Cu2+ solution (water at 15 vol %) and 1.5 mL of formic acid at 180°C (2 h). Insets indicate the cuboctahedral cages in type (ii) structures. (g-i) Type (iii) crystal assemblies prepared at 150°C (5 h) with 30 mL of 0.015 M Cu2+ solution (water at 21 vol %) and 1.5 mL of formic acid. SEM images were taken with increasing magnifications. Type (iv) multipod frameworks and crystal assemblies: (j and k) prepared with 30 mL of 0.010 M Cu2+ solution (water at 22.5 vol %) and 1.5 mL of formic acid at 185°C (2 h); and (l and m) prepared with 30 mL of 0.010 M Cu2+ solution (water at 22.5 vol %) and 4.5 mL of formic acid at 180°C (1.5 h). (n-q) Higher-ordered multipod frameworks and crystal assemblies: prepared with 30 mL of 0.050 M Cu2+ solution and (n, type (i)) (water at 5 vol %) and 4.5 mL of formic acid at 180°C (1.5 h); (o, type (ii)) (water at 5 vol %) and 4.5 mL of formic acid at 180°C (1.5 h); (p, type (iii)) (water at 22 vol %) and 1.5 mL of formic acid at 180°C (2 h); (q, type (iv)) (water at 30 vol %) and 4.5 mL of formic acid at 180°C (2 h). [Reprinted with permission from Ref. 352 Y. Chang et al., Crystal Growth & Design, 4, 273, 2004; Copyright @ American Chemical
Society (2004)]
107
Figure 45: The core hollowing process in Cu2O nanospheres: TEM images of the samples prepared after different reactions times at 150°C (A and B, 35 h; C, 50 h; D is the SAED pattern of the sphere shown in C); starting solution, [Cu2+] ) 0.010 M, 30 mL. [Reprinted with
permission from Ref. 353 Y. Chang et al., Langmuir 21, 1074, 2005; Copyright @
American Chemical Society (2005)]
Figure 46: SEM and TEM images of sample 1 (molar ratio of Cu2+, NH3 to OH- is 1:7:2): (a, b) SEM image of the Cu2O octahedra and (c) TEM image of a single octahedron. [Reprinted with
permission from Ref. 359 X. Haolan et al., Journal of Physical Chemistry B 110, 13829,
2006; Copyright @ American Chemical Society (2006)]
Figure 47: SEM images of octahedral Cu2O prepared when R2 ) 8: (a) the octahedra with longer edge length and (b) an octahedron with arched <111> surfaces and (c) its corresponding TEM image. [Reprinted with permission from Ref. 359 X. Haolan et al., Journal of Physical
Chemistry B 110, 13829, 2006; Copyright @ American Chemical Society (2006)]
Figure 48: TEM images of the sample after various times of oxidation: 0, 30, 90, 150, and 210 min and after an aging period of 3 days. (a) Cu nanoparticles, (b) faceted Cu2O nanocrystals, (c) hexagonal nanoplates, (d) truncated nanoprisms, (e) triangular nanoplates, and (f) octahedral nanocrystals. [Reprinted with permission from Ref. 360 C. H. Bernard Ng et al., J. Phys.
Chem. B 110, 20801, 2006; Copyright @ American Chemical Society (2006)]
Figure 49: Typical FE-SEM images of the products prepared with 0.02 molâL-1 CuSO4, 0.02 molâL-1 EDTA, 0.333 molâL-1 NaOH, and 0.028 molâL-1 C6H12O6 at 60 °C for 12 h (w ) 34). (a) Low magnification image and (b) high magnification. [Reprinted with permission from
Ref. 362 H. Zhang et al., Crystal Growth & Design 7, 820, 2007; Copyright @ American
Chemical Society (2007)]
Figure 50: FE-SEM images of samples prepared with 0.02 molâL-1 CuSO4, 0.02 molâL-1 EDTA, 0.333 molâL-1 NaOH, and 0.028 molâL-1 C6H12O6 for 12 h at different reaction temperatures (w ) 34). (a) Room temperature. (b) 80 °C. [Reprinted with permission from Ref.
362 H. Zhang et al., Crystal Growth & Design 7, 820, 2007; Copyright @ American
Chemical Society (2007)]
Figure 51: FE-SEM images of samples prepared with 0.02 molâL-1 CuSO4, 0.02 molâL-1 EDTA, 0.028 molâL-1 C6H12O6, and NaOH with various concentrations at 60 °C for 12 h (w ) 34). (a) 0.225 molâL-1 and (b) 0.635 molâL-1. [Reprinted with permission from Ref. 362 H. Zhang et al., Crystal Growth & Design 7, 820, 2007; Copyright @ American Chemical Society
(2007)]
Figure 52: SEM micrographs of Cu2O nanowires organized as (a) spherical structures, or (b) cone-shaped bundles, (c) insert of the organization of nanowires, (d) conical structures of disassembled nanowires. [Reprinted with permission from Ref. 363 Z. C. Orel et al. Crystal
Growth & Design 7, 453, 2007; Copyright @ American Chemical Society (2007)]
108
Figure 53: FESEM and TEM images of Cu2O particles with different shape. (A) and (B) cubic-like Cu2O particles; (C) and (D) octahedral Cu2O particles; (E) and (F) sphere-like Cu2O particles. Inset images of (B), (D) and (F) are SAED patterns recorded from a single particle of a different shape, respectively. [Reprinted with permission from Ref. 366 Cao Hongliang et al., Chem Commun. 4548, 2006; Copyright @ RSC Publishing (2006)]
Figure 54: (a) TEM image of filled Cu2O nanocubes. (b) HR-TEM image of a representative filled Cu2O nanocube. (c) High-magnification HR-TEM image of a Cu2O nanocube exhibited in (b). The inset in (c) is the FFT pattern of a Cu2O nanocube. [Reprinted with permission from
Ref. 367 Z Yang et al., Nanotechnology 19, 025604, 2008; Copyright @ Institute of Physics
(2008)] Figure 55: TEM images of hollow Cu2O nanocubes prepared at reactions times of (a) 1, (b) 15, (c) 30, and (d) 45 min, respectively. [Reprinted with permission from Ref. 367 Z Yang et al., Nanotechnology 19, 025604, 2008; Copyright @ Institute of Physics (2008)]
Figure 56: TEM images of Cu2O particles obtained with different PVP amount: (a) 0.10 g; (b) 0.24 g; (c) 0.30 g. [Reprinted with permission from Ref. 368 H. Zhu, et al. Crystal Growth
& Design 9, 633, 2009; Copyright @ American Chemical Society (2009)]
Figure 57: (a) SEM image of Cu2O particles when the pH value of NaOH solution is 11 and (b) SEM and (c) TEM images and SAED of Cu2O particles when the pH value of NaOH solution is 12. [Reprinted with permission from Ref. 368 H. Zhu, et al. Crystal Growth & Design 9,
633, 2009; Copyright @ American Chemical Society (2009)]
Figure 58: SEM images of Cu2O products prepared with different concentrations of copper nitrate: (a) 0.05 M, (b) 0.025 M, (c) size distributions of the Cu2O microcrystal versus copper nitrate concentration; the level bar on each column indicates the weighted average size of each sample. [Reprinted with permission from Ref. 375 H. Y. Zhao et al., Crystal Growth &
Design 8, 10, 2008; Copyright @ American Chemical Society (2008)]
Figure 59. Crystal structures of rutile (a), anatase (b), and brookite (c). Figure 60 Transmission Electron Microscope image of ns-TiO2 [Reprinted with permission
from Ref 173 P. R. Mishra et al., Int. J. Hyd. Eng, 28, 1089 (2003), Copyright @ Elsevier
(2003)]
Figure 61 (a) Scanning Electron Microscope Image of the TiO2 Nanotubes top view (b) Lateral View (c) Transmission Electron Microscope Image of the single TiO2 Nanotube and (d) top view of TiO2 Nanotubes. [Reprinted with permission from Ref.189 P. K. Dubey et al. Journal of
Nanoscience and Nanotechnology, 9, 5507 (2009) Copyright @ American Scientific
Publisher (2009)]
109
Figure 62 : Hydrogen generation through water photolysis using solar energy and Titanium Dioxide Photoelectrode. [Reprinted with permission from A. Fujishima et al., Functionality
of Molecular Systems, 2, 196 (1999),Copyright @ Springer 1999] Figure 63 : Schematics of Dye Sensitized Solar Cell Reprinted with permission from Michael
Grätzel, NATURE, 414,338 (2001), [Copyright @ Nature Publishing Group (2001)]
Figure 64 Schematic diagram of the fabricated photocatalytic reactor. [Reprinted with
permission from Ref.210 P. R. Mishra et al., Bull. Mater. Sci., 31, 545 (2008), Copyright @
Indian Academy of Sciences (2008)]
Figure 65 Variation of concentration of phenol with irradiation time using as synthesized nanostructured TiO2 and commercial TiO2 (P-25, Degussa) photocatalyst. (The excitation wavelength is ~ 269 nm). [Reprinted with permission from Ref.210 P. R. Mishra et al., Bull.
Mater. Sci., 31, 545 (2008), Copyright @ Indian Academy of Sciences (2008)]
Figure 66 : Tubular photocatalytic reactor for water purification [Reprinted with permission
from Ref 208 L. Zhang et al., Separation and Purification Technology, 31, 105
(2003).Copyright @ ELSEVIER (2003)]
Figure 67: Dives in Misericordia Church, Rome, Italy. (The active photocatalytic principle) Figure 68: (a) Ordinary mirror (b)TiO2 nanoparticle coated anti-fogging mirror Reprinted with
permission from K. Hashimoto et al., Japanese Journal of Applied Physics, 44, 8269
Figure 69: Animal test of photocatalytic cancer therapy; photograph of nude mouse just after initial treatment (A) and 4 weeks after treatment (B) [Reprinted with permission from A.
Fujishima, BKC, Tokyo, 1999, Copyright @ BKC (1999)]
110
Figu
re 1:
Crystal structure of zinc oxide (a) Wurtzite (b) zinc blende (c) rock salt
(a)
(b)
(c)
111
Figure.2: SEM images of zinc oxide nanostructures synthesized by precipitation method at (a) 60° (b) 70° and (c) 80° C temperatures [Reprinted with permission from Ref. 208 Guzman et al., Matter. Chem. Phys. 115, 172, 2009; Copyright @ Elsevier (2009)]
112
Figure 3: SEM micrographs of mesoporous crystalline zinc oxide nanowires (a) in the PPA template and (b) released from PPA template.[Reprinted with permission from Ref. 209 Xiao
et al. Nanotech. 16, 671, 2005; Copyright @ Institute of Physics (2009)]
113
Figure 4: SEM images of zinc oxide nanostructures produced with precipitation method with (a) the control sample having large prisms and small needles (b) sample precipitated with 120 mg/L of EO68-b-MAA8-C12, and (d) the schematic view for dumbbell shape. [Reprinted with
permission from Ref. 212 Taubert et al., J. Phys. Chem. B, 107, 2660, 2003 Copyright @
American Chemical Society (2003)]
114
Figure 5: SEM images of hydrothermally synthesized zinc oxide nanomaterials (A) Nanowires [B] Nanorods [Reprinted with permission from Ref. 215 Li et al. Inorganic Chem. 42, 8105,
2003. Copyright @ American Chemical Society]
(a) (b)
(c) (d)
(e) (f)
(g) (h)
115
Figure 6: SEM images of hydrothermally synthesized zinc oxide powders using 1M aqueous solution of (a) NH4OH (b) mono (c) di- and (d) tri-ethanolamine (e) 0.2M NH4OH + 1M diethanolamine (DEA) (f) 0.4M NH4OH + 1M DEA (g) 0.6M NH4OH + 1M DEA (h) 0.2M NH4OH + 1M DEA [Reprinted with permission from Ref. 219 Lu et al., J. Alloy and
Compounds, 477, 523, 2009. Copyright @ Elsevier ]
(a) (b)
(c) (d)
(e) (f)
(g)
116
Figure 7: SEM images of hydrothermally prepared zinc oxide nanopowders at 200°C for 2h using (a) 0.25 (b) 0.5 (c) 1.0 (d) 2.0 M solution of KOH and (e) 0.025 (f) 0.05 (g) 0.20 M solution of NH3.H2O as solvent. [Reprinted with permission from Ref. 219 Xu et al., Ceramic
Figure 8: SEM images of solvothermally produced zinc oxide nanostructures with different water/EN volume (ml) (a) 60/0 (b) 30/30 (c) 20/40 (d) 50/10 (e) cross sectional view of 50/10 and (e) 0/60 [Reprinted with permission from Ref. 225 Dev et al., Nanotech., 17, 1533, 2006.
Copyright @ Institute of Physics ]
118
Figure 9: FESEM images of hierarchical zinc oxide micro/nanoarchitectures produced solvo thermally at 160° temperature for 12 hours with 1:7 v/v ratio of distilled water and EDA [Reprinted with permission from Ref. 226 Lu et al., Adv. Func Mater. 18, 1047, 2008
Copyright @ Willey-VCH Verlag GmbH 2008 ]
119
Figure 10 : FESEM images of hierarchical zinc oxide micro/nanoarchitectures produced solvo thermally at 160° temperature and 1:7 v/v ratio of distilled water and EDA for different reaction times (A) 1h (B) 2h (C) 4h (D&E) 8h and (F) 16h [Reprinted with permission from Ref. 226
Lu et al., Adv. Func Mater. 18, 1047, 2008 Copyright @ Willey-VCH Verlag GmbH 2008 ]
120
Figure 11: SEM images of 3D zinc oxide hollow micro-sphere synthesized by the solvothermal method in the EG solution at 200 °C temperature, general view in the left, at high magnification at right Fig. 2.10 A: FESEM images of hierarchical zinc oxide micro/nanoarchitectures produced solvo thermally at 160° temperature for 12 hours with 1:7 v/v ratio of distilled water and EDA [Reprinted with permission from Ref. 227 Zhang et al., Nanotech. 18, 455604,
2007 Copyright @ Institute of Physics 2007 ]
(a) (b) (c) (d)
121
Figure 12: SEM images of Sol-gel derived zinc oxide nanostructures on the silicon substrates (a-c) from neutral solutions (a) as-synthesized, and thermal treatment at 500°C for (b) 4h and (c) 6h and (d) as obtained from acidic solution . [Reprinted with permission from Ref. 230 Li et al.,
Figure 13: SEM images of one dimensional micro-emulsion derived zinc oxide nanostructures obtained after different reaction times (a) 10 min, (b) 30 min, (c) 1h (d) 2h (e) 4h and (f) 8 h. [Reprinted with permission from Ref. 232 Zhang et al., Cryst. Growth Design 4, 309,2004.
Copyright @ American Chemical Society 2004 ]
123
Figure 14: SEM images of zinc oxide nanostructures obtained by combustion synthesis method using (a) calcination of 0.2g Zn(NO3).6H2O for 2h at 800°C (b) By combustion and (c) by solution combustion (d) solution combustion with 1.0 ml of additional water. [Reprinted with
permission from Ref. 238 Alvarado-Ibarra et al., Colloid Surf. A: Physiochem. Eng.
Figure 15: SEM image of melting combustion synthesized zinc oxide nanostructure. [Reprinted
with permission from Ref. 239 Chen et al., Matter Lett. 61, 4603, 2007 Copyright @
Elsevier 2008]
125
Figure 16: SEM images of the Eelctrochemically obtained zinc oxide films prepared at the cathode potential ranging from -0.7 to -1.4V vs Ag/AgCl [Reprinted with permission from
Ref. 243 Izaki and Omi, Appl. Phys. Lett., 68, 2439, 1996. Copyright @ American Institute
of Physics 1996]
Figu
re
17: SEM images of electrochemically synt
hesized
ZnO nanostruc
(a) (b) (c)
(d) (e) (f)
126
tures in the electrolytic solution of (a) 0.5M ZnCl2+0.02 M citric acid (b) 0.5M ZnCl2+0.01 M citric acid (c) 0.5M ZnCl2+0.05 M citric acid (d) 0.5M ZnCl2+0.0001 M citric acid (e) 0.25 M +0.01M citric acid (f) 0.25M ZnCl2+0.01 M citric acid+0.1MKCl [Reprinted with permission
from Ref. 260 Li et al., J. Phys. Chem. C, 111, 6678, 2007. Copyright @ American
Chemical Society 2007]
127
Figure 18: SEM images of (a) primary ZnO nanosheets and (b-d) hierarchical ZnO nanorods on hexagonal nanosheets on ITO substrates. [Reprinted with permission from Ref. 261 Xu et al.,
J. Phys. Chem. C, 111, 11560, 2007. Copyright @ American Chemical Society 2007]
Figure 19: SEM
images of
hierarchical ZnO nanostructures electrodeposited at a potential of -1.10 V in 0.05M [Zn(NH3)4-2
solution for different deposition times (a) 10min, (b) 20min, (c) 40min, (d) 1.5h, (e) 2.5h, (f)3.5h [Reprinted with permission from Ref. 261 Xu et al., J. Phys. Chem. C, 111, 11560, 2007.
Copyright @ American Chemical Society 2007]
128
Figure 20: SEM images of sonochemically synthesized zinc oxide (a) nanorods (b) nanoups (c) nanosheets (d) nanoflowers and (e) nanospheres [Reprinted with permission from Ref. 262
Jung et al., Cryst. Growth Design, 8, 265, 2008 Copyright @ American Chemical society
2008]
(a) (b) (c)
(d) (e)
129
Fig. 21: SEM images of the ZnO samples prepared by sonochemical method using the mixture of Zn(NO3)2 and NaOH as precursor at different pH value:(a) pH 9.5 (b) pH 10.5(c) pH 11.5 and (d) pH 12.5. [Reprinted with permission from Ref. 266 Xiao et al., J. Alloy and Comp. 459,
L18, 2008 Copyright @ Elsevier 2008]
130
Figure 22: SEM images of as-made ZnO powders prepared by sonochemical method using the mixture of different zincs salt and NaOH as precursor at pH 12.5 (a)Zn(NO3)2 (b)ZnCl2 (c)ZnSO4 and (d) Zn(C2H4O2)2 .[Reprinted with permission from Ref. 266 Xiao et al., J.
Alloy and Comp. 459, L18, 2008 Copyright @ Elsevier 2008]
131
Figure 23[A]: FESEM images of cyclic feeding chemical vapor deposited zinc oxide flower shaped zinc oxide nanostructures on Si (a,b) 100 and (c,d) 111 substrates. [Reprinted with
permission from Ref. 273 Umar et al., Nanotech. 16, 2462, 2005 Copyright @ Institute of
Physics 2005]
(a) (b)
(c) (d)
132
Figure 23[B]: FESEM images of multipod star shaped zinc oxide nanostructures grown by cyclic feeding chemical vapor deposited on Au coated Si (100) substrate [Reprinted with
permission from Ref. 274 Umar et al., J. Cryst. Growth 277, 479, 2005 Copyright @
Elsevier 2005]
133
Figure 24: FESEM images of zinc oxide nano columns grown by electron beam evaporation at 400°C on the Si(100) substrate for (a) 30min. and (b) 50 min. [Reprinted with permission from
Ref. 289 Qiu et al., Solid State Comm. 134, 735, 2005 Copyright @ Elsevier 2005]
134
Figure 25: SEM images of magnetron sputtering derived [A] as synthesized zinc oxide thin film and [B] zinc oxide nanotetrapods grown on the surface of film after annealing . [Reprinted with
permission from Ref. 291 Saw et al., J. Phys. D: Appl. Phys. 41, 055506, 2008 Copyright @
Institute of Physics 2008]
135
Figure 26: SEM images of zinc oxide nanostructures grown by RF sputtering for (a) 15 min. and (b) 50 min. [Reprinted with permission from Ref. 294 Youn et al., Jap. J. Appl. Phys.
45, 8957, 2006 Copyright @ Japanese J. Appl. Phys., 2006]
136
Figure 27 : X-ray diffraction patterns of vacuum arc deposited zinc oxide thin films at (a) low (b) high magnetic fields [Reprinted with permission from Ref. 296 Takikawa et al., Thin
Solid Films 377, 74 , 2000 Copyright @ Elsevier 2006]
137
Figure 28: SEM images of Spray Pyrolysis deposited zinc oxide nanostructures on ITO/glass substrate using 0.1mol/lit. solution of zinc chloride at different (a) 400°C (b) 450°C (c) 490°C (d) 540°C and (e) 560°C substrate temperatures [Reprinted with permission from Ref. 314
Krunks et al., Thin Solid Films 515, 1157 , 2006 Copyright @ Elsevier 2006]
138
Figure 29: (a) Emission spectra from N doped zinc oxide nanoneedle under different pumping powers (b) Output power vs pump energy curve [Reprinted with permission from Ref. 319,
Figure 30: (a) SEM image of zinc oxide vertical nanowire cavities grown on sapphire substrate (b) SEM iamge of a single verical NW with Fabry-Perot lasing modes as wavelengths λA, λB and λc (c) lasing spectra of a single ZnO nanowire cavity (Left inset: Power dependence graph showing lasing threshold almost at 400 µJ/cm2. Right inset: Dark field scattering images of ZnO vertical Nanowire cavity from white light excitation (top) and lasing induced by 266 nm pulsed excitation (d) PL imaging of a single zinc oxide vertical NW cavity (inset SEM image of ZnO) (E) Diagram of ZnO vertical nanowire cavity with corresponding PL images [Reprinted with
permission from Ref. 322, Gargas et al., J. Am. Chem. Soc., 131, 2125, 2009 Copyright @
American Chemical Society 2009]
140
Figure 31: (Top) Schematic view of zinc oxide based hetrojunction p-n LED (Bottom) Optical microscope plan view of a zinc oxide based hetrojunction LED. [Reprinted with permission
from Ref. 53, Wang et al., Appl. Phys. Lett., 92, 112101, 2008 Copyright @ American
Institute of Physics 2008]
.
(a)
(d) (c)
(b)
141
Figure 32: Optical photographs of the n-zinc oxide nanorods/p-SiC: (a) before measurements, (b) packaged LED (c) emission of white light and (d) EL spectra at 27 and 37V. [Reprinted
with permission from Ref. 56, Willander et al., Nanotech. 20, 332001, 2009 Copyright @
Institute of Physics 2009]
142
Figure 33: Cross sectional SEM image of a ZnO/polymer multi layer LED fabricated on glass substrate. [Reprinted with permission from Ref. 56, Willander et al., Nanotech. 20, 332001,
2009 Copyright @ Institute of Physics 2009]
(a) (b)
143
Figure 34: (Top) Current density-voltage characteristic of (a) NPD-PFO structure and (b) PVK-TFB structure (inset shows a schematic diagram of the corresponding energy band energy band diagram) and (Bottom) Coressponding EL spectra at 14V and 0.10mA [Reprinted with
permission from Ref. 56, Willander et al., Nanotech. 20, 332001, 2009 Copyright @
Institute of Physics 2009]
Figure 35: (a) Cu2O deposited at pH 9 (0.05 mA/cm2; 0.1 C/cm2; 55°C). (b) Cu2O deposited at pH 9 (0.05 mA/cm2; 0.1 /cm2; 10°C). (c) Cu2O deposited at pH 11 (0.2 mA/cm2; 0.13 C/cm2; 55°C). [Reprinted with permission from Ref. 333 P. E. d. Jongh et al., Chem.
Mater. 11, 3512, 1999; Copyright @ American Chemical Society (1999)]
144
Figure 36: (a) Scanning electron micrograph of electrodeposited Cu2O nanowires. Bath temperature = 70 0C, pH =9.1, E =-1:69V/SSE. (b) Enlarged of (a). [Reprinted with
permission from Ref. 337 A. L. Daltin et al., Journal of Crystal Growth 282, 414,
2005; Copyright @ Elsevier (2005)]
(a) (b)
Figure 37: Typical FE-SEM images of octahedral Cu2O located at the ITO substrate at different magnifications (the deposition time is 15 min; the concentration of Cu(OH)4
2- is 25 mM). [Reprinted
with permission from Ref. 341 S. Guo et al., Inorganic Chemistry
46, 9537, 2007; Copyright @
American Chemical Society
(2007)]
145
Figure 39: (a-d) SEM micrographs of the copper electrode after electrolysis at different voltage (2, 4, 8, and 10 V, respectively). [Reprinted with permission from Ref. 342 D. P. Singh et al., J.
Phys. Chem. C 111, 1638, 2007; Copyright @ American Chemical Society (2007)]
a b
(c) (d)
146
Figure 41: TEM images of Cu2O nanoparticles prepared with different concentrations of CTAB. From a-f, CCTAB equals 0.01, 0.02, 0.04, 0.06, 0.08, and 0.10 M, respectively. Scale bars are 500 nm (a, b, c, e) or 2 microns (d, f). [Reprinted with permission from Ref. 347 L. Gou et al., Nano Lett., 3, 1903, 2003; Copyright @ American Chemical Society (2003)]
147
(g)
(h)
(i)
(j)
(k)
(l)
(m)
(n)
(o)
(p)
(q)
Figure 43: a: TEM micrograph (scale bar~100 nm) and histogramof the size distribution fromsample B2; b: TEMmicrograph (scale bar~100 nm) and histogram of the size distribution from sample B3; c: TEM micrograph (scale bar ~ 100 nm) and histogram of the size distribution from sample B4. [Reprinted with permission from Ref. 349 L. Gou et al., J.
Figure 45: The core hollowing process in Cu2O nanospheres: TEM images of the samples prepared after different reactions times at 150°C (A and B, 35 h; C, 50 h; D is the SAED pattern of the sphere shown in C); starting solution, [Cu2+] ) 0.010 M, 30 mL. [Reprinted
with permission from Ref. 353 Y. Chang et al., Langmuir 21, 1074, 2005; Copyright
@ American Chemical Society (2005)]
149
Figure 46: SEM and TEM images of sample 1 (molar ratio of Cu2+, NH3 to OH- is 1:7:2): (a, b) SEM image of the Cu2O octahedra and (c) TEM image of a single octahedron. [Reprinted with
permission from Ref. 359 X. Haolan et al., Journal of Physical Chemistry B 110, 13829,
2006; Copyright @ American Chemical Society (2006)]
150
Figure 48: TEM images of the sample after various times of oxidation: 0, 30, 90, 150, and 210 min and after an aging period of 3 days. (a) Cu nanoparticles, (b) faceted Cu2O nanocrystals, (c) hexagonal nanoplates, (d) truncated nanoprisms, (e) triangular nanoplates, and (f) octahedral nanocrystals. [Reprinted with
permission from Ref. 360 C. H. Bernard Ng et al., J. Phys.
Chem. B 110, 20801, 2006;
Copyright @ American
Chemical Society (2006)]
151
Figure 50: FE-SEM images of samples prepared with 0.02 molâL-1 CuSO4, 0.02 molâL-1 EDTA, 0.333 molâL-1 NaOH, and 0.028 molâL-1 C6H12O6 for 12 h at different reaction temperatures (w ) 34). (a) Room temperature. (b) 80 °C. [Reprinted with
permission from Ref. 362 H. Zhang et al., Crystal Growth & Design 7, 820, 2007;
Copyright @ American Chemical Society (2007)]
Figure 49: Typical FE-SEM images of the products prepared with 0.02 molâL-1 CuSO4, 0.02 molâL-1 EDTA, 0.333 molâL-1 NaOH, and 0.028 molâL-1 C6H12O6 at 60 °C for 12 h (w ) 34). (a) Low magnification image and (b) high magnification. [Reprinted with
permission from Ref. 362 H. Zhang et al., Crystal Growth & Design 7, 820, 2007;
Copyright @ American Chemical Society (2007)]
152
Figure 52: SEM micrographs of Cu2O nanowires organized as (a) spherical structures, or (b) cone-shaped bundles, (c) insert of the organization of nanowires, (d) conical structures of disassembled nanowires. [Reprinted with permission from Ref. 363 Z. C. Orel et al. Crystal
Growth & Design 7, 453, 2007; Copyright @ American Chemical Society (2007)]
153
Figure 53: FESEM and TEM images of Cu2O particles with different shape. (A) and (B) cubic-like Cu2O particles; (C) and (D) octahedral Cu2O particles; (E) and (F) sphere-like Cu2O particles. Inset images of (B), (D) and (F) are SAED patterns recorded from a single particle of a different shape, respectively. [Reprinted with
permission from Ref. 366 Cao Hongliang et al., Chem Commun. 4548, 2006;
Copyright @ RSC Publishing (2006)]
154
Figure 54: (a) TEM image of filled Cu2O nanocubes. (b) HR-TEM image of a representative filled Cu2O nanocube. (c) High-magnification HR-TEM image of a Cu2O nanocube exhibited in (b). The inset in (c) is the FFT pattern of a Cu2O nanocube. [Reprinted with permission from Ref. 367 Z Yang et al., Nanotechnology 19, 025604,
2008; Copyright @ Institute of Physics (2008)]
155
Figure 56: TEM images of Cu2O particles obtained with different PVP amount: (a) 0.10 g; (b) 0.24 g; (c) 0.30 g. [Reprinted with permission from Ref. 368 H. Zhu, et al. Crystal Growth
& Design 9, 633, 2009; Copyright @ American Chemical Society (2009)]
Figure 57: (a) SEM image of Cu2O particles when the pH value of NaOH solution is 11 and (b) SEM and (c) TEM images and SAED of Cu2O particles when the pH value of NaOH solution is 12. [Reprinted with permission from Ref. 368 H. Zhu, et al. Crystal
Growth & Design 9, 633, 2009; Copyright @ American Chemical Society (2009)]
156
Figure 58: SEM images of Cu2O products prepared with different concentrations of copper nitrate: (a) 0.05 M, (b) 0.025 M, (c) size distributions of the Cu2O microcrystal versus copper nitrate concentration; the level bar on each column indicates the weighted average size of each sample. [Reprinted with permission from Ref. 375 H. Y. Zhao et al., Crystal Growth & Design 8, 10,
2008; Copyright @ American Chemical Society (2008)]
157
Figure 59. Crystal structures of rutile (a), anatase (b), and brookite (c).
(a) (b) (c)
158
Figure 60 Transmission Electron Microscope image of ns-TiO2 [Reprinted with permission
from Ref 173 P. R. Mishra et al., Int. J. Hyd. Eng, 28, 1089 (2003), Copyright @ Elsevier
(2003)]
159
Figu
re 61 (a)
Scanning
Electron
Microsco
pe Image of
the TiO2
Nanotub
es top view (b) Lateral View (c) Transmission Electron Microscope Image of the single TiO2 Nanotube and (d) top view of TiO2 Nanotubes. [Reprinted with permission from Ref.189 P. K.
Dubey et al. Journal of Nanoscience and Nanotechnology, 9, 5507 (2009) Copyright @
American Scientific Publisher (2009)]
(a) (b)
(c) (d)
160
Figure 62 : Hydrogen generation through water photolysis using solar energy and Titanium Dioxide Photoelectrode. [Reprinted with permission from A. Fujishima et al., Functionality
of Molecular Systems, 2, 196 (1999),Copyright @ Springer 1999]
161
Figure 63 : Schematics of Dye Sensitized Solar Cell Reprinted with permission from Michael
Grätzel, NATURE, 414,338 (2001), [Copyright @ Nature Publishing Group (2001)]
162
Figure 64 Schematic diagram of the fabricated photocatalytic reactor. [Reprinted with
permission from Ref.210 P. R. Mishra et al., Bull. Mater. Sci., 31, 545 (2008), Copyright @
Indian Academy of Sciences (2008)]
163
Figure 65 Variation of concentration of phenol with irradiation time using as synthesized nanostructured TiO2 and commercial TiO2 (P-25, Degussa) photocatalyst. (The excitation wavelength is ~ 269 nm). [Reprinted with permission from Ref.210 P. R. Mishra et al., Bull.
Mater. Sci., 31, 545 (2008), Copyright @ Indian Academy of Sciences (2008)]
164
Figure 66 : Tubular photocatalytic reactor for water purification [Reprinted with permission
from Ref 208 L. Zhang et al., Separation and Purification Technology, 31, 105
(2003).Copyright @ ELSEVIER (2003)]
165
Figure 67: Dives in Misericordia Church, Rome, Italy. (The active photocatalytic principle)
Figure 69: Animal test of photocatalytic cancer therapy; photograph of nude mouse just after initial treatment (A) and 4 weeks after treatment (B) [Reprinted with permission from A.
Fujishima, BKC, Tokyo, 1999, Copyright @ BKC (1999)]