Chapter 2

Literature Survey

24

The application of semiconductor photocatalysis is an emerging area of science

and technology, which has grown significantly with industrial development for

effective removal of various pollutants in aqueous system as well as in the air. It

has received significant attention in the last couple of decades.1 Heterogeneous

photocatalysis is an advanced oxidation process which has been the subject of a

extensive area of studies related to air cleaning and water purification because of

following reasons;2

They are inexpensive.

They show low or no toxicity.

They are showing tunable properties that can be modified such as by size

reduction and their surface properties.

They show substantial stability and durability.

2.1. Zinc oxide (ZnO)

In addition to TiO2, there are many other binary metal oxides have been studied to

determine their photocatalytic oxidation properties. Among them ZnO has been

often considered as alternative to TiO2 because of its good optoelectronic, catalytic

and photochemical properties. The band gap energy of ZnO is 3.3 eV, it is lower

than most active TiO2 phase i.e. anatase. Upon the illumination of light, ZnO

generates holes that are strong enough to oxidized organic pollutants into less

harmful materials.3 So far, various ZnO nanostructures have been used to degrade

the harmful dyes into less harmful components by photocatalytic reaction under

UV and visible light illumination. Wang et al. successfully synthesized reduced

graphene coated ZnO composite via simple method and it was found that the

synthesized composite exhibited an improved RhB adsorption capacity and an

25

improved photocatalytic activity for degrading RhB in comparison to neat ZnO

NPs. The composite showed an excellent recycling performance for organic

pollutant removal up to 99% recovery over several cycles via simulated sunlight

irradiation.4 The photocatalytic activity of a material is directly influenced by its

crystal structure. Kislov et al. studied degradation of methyl orange over single

crystalline ZnO. The efficiency of dye degradation is strongly dependent upon the

orientation of different phases of ZnO photocatalyst.5 Interestingly, it has been

reported that ZnO absorb more fraction of solar spectrum than TiO2. Sakthivel et

al. studied the photocatalytic activity of commercial ZnO powder and compared

with that of Degussa P25 TiO2 over Acid Brown 14 as the model pollutant. These

catalysts were examined for surface area, particle size and crystallinity and studied

for the influence of the effect of initial dye concentration, amount of catalyst,

illumination time interval, pH of solution and adsorption of acid brown 14 on ZnO

and TiO2. The photodegradation rate was highest for ZnO which suggest that it

absorbs more fraction of solar spectrum in compared to TiO2.6 Behnajady et al. has

studied the photocatalytic reaction of C.I. Acid Yellow 23(AY23) mediated over

common semiconductor ZnO. The effects of process parameters such as, catalyst

loading, initial dye concentration, light intensity, and pH on the extent of

photodegradation have been investigated. The results show that the adsorption

constant (Kads) and rate constant (kL–H) in L–H model are dependent to the light

intensity, and increase with increasing the light intensity. With inserting the light

intensity parameter to L–H equation, this model can be used for predicting the

removal rate at different light intensities and initial concentrations of AY23.7 So, it

has been successfully reported in many papers, ZnO exhibited better photocatalytic

efficiency in compared to most widely studied photocatalyst TiO2.8

26

Mai et al. demonstrated facile degradation of Methyl green under visible light

illumination over ZnO. The effects of various factors viz. pH values, amount of

catalyst, initial dye concentration, and the presence of NaCl, Na2CO3, H2O2, and

Na2S2O8 on the degradation efficiency were studied. Thirty-two intermediates

were separated, identified, and characterized by high-performance liquid

chromatography photodiode arrayelectrospray ionization-mass spectrometry

(HPLC–ESI-DAD-MS) technology, giving insight into the pathways of the

degradation process.9 Usni H. reported the surfactant assisted chemical synthesis of

ZnO nanorods and used as-synthesized ZnO nanorods as photocatalyst for efficient

degradation of MB dye, also shown a ~90% degradation of MB in 7 hours.10 Pare

et al. have found ZnO experimentally to be a highly efficient photocatalyst for the

degradation of acridine orange dye. It observed that addition of an optimal amount

of hydrogen peroxide and potassium persulphate increase the degradation rate

while NaCl and Na2CO3 decrease degradation rate. The effect of addition of

cationic and anionic surfactants has also been investigated. Bubbling of nitrogen in

the reaction solution decreases the reaction rate.11

Dindar B. and lcli S. studied the photodegradations of phenol under concentrated

sunlight. ZnO exhibited most promising photoactivity and was as active as TiO2

under concentrated sunlight. The enhanced photocatalytic activity of ZnO under

these conditions may be related to absorption characteristics of ZnO in the 300-400

nm region. It was interesting to report that ZnO, exhibited better photocatalytic

activity in compared to either most commonly employed photocatalyst TiO2 or

Fe2O3.12 Pardeshi S. K. and Patil A. B. confirmed that phenol was degraded more

effectively under solar light in comparison to artificial visible light irradiation. It

was observed that photodegradation of phenol is favorable in weakly acidic or

neutral solutions. The demineralization of substrate was checked by Chemical

27

Oxygen Demand (COD) reduction method. It was good to observe that ZnO was

reused for five times as it underwent photocorrosion only to a negligible extent.

This work envisages great potential towards sunlight mediated photocatalysis for

removal of phenol from waste water.13 Sobana N. and Swaminathan M. have

successfully reported that enhanced photocatalytic activity of ZnO by mixing it

with different proportion of activated carbon for the solar assisted photocatalytic

degradation of Direct Blue 53.The synergistic effect observed was to an extended

adsorption of DB53 on activated carbon followed by its transfer to ZnO where it

was photocatalytically degraded. The synergistic effect is responsible for the

enhanced photocatalytic activity of AC-ZnO in comparison to bare ZnO.14 Yu J.

and Yu X. discovered a facile route to synthesize hollow spheres of ZnO with

porous crystalline by hydrothermal treatment of glucose/ZnCl2 mixtures at 180 °C

for 24 h, and then calcined at different temperatures for 4 h. The photocatalytic

activity of the as-synthesized ZnO samples was evaluated by photocatalytic

decolorization of RhB. After many recycles, it was found that ZnO catalyst

exhibited efficient photodegradation of RhB and it does not lose it photocatalytic

activity which further confirms that as-synthesized ZnO hollow spheres show

stability and photocorrodibility.15

Zewei et al. present a facile method for fabrication of hollow ZnO spheres, in

which Zinc ion was first adsorbed on sulphonated polystyrene surface then reacted

with NaOH to form ZnO. During the formation of ZnO nanoshells, the temples

spheres were dissolved in the same medium to obtain ZnO hollow spheres directly.

Neither additional dissolution nor calcination process was needed in this method to

remove the templates, and the reaction conditions were very mild:  neither high

temperature nor long time was needed. The as-synthesized ZnO hollow spheres

exhibited good photocatalytic activity.16

28

Comparelli et al. reported that the presence of passivating molecules i.e. different

organic molecules (surfactant) on the ZnO surface preserved the oxide from

photocorrosion and pH-dependent dissolution. The results demonstrate that

surfactant capped ZnO nanocrystals exhibit more facile photocatalytic degradation

than those of conventional ZnO-based because surface organic coating makes the

oxide resistant to photocorrosion and to pH changes which directly impact on the

photocatalytic activity.17 Zhang et al. reported that surface hybridization of ZnO

with graphite like carbon layers could significantly suppress the coalescence and

suppress growth of ZnO particles during high temperature treatment. The

Photocatalytic activity of ZnO was enhanced by hybridization with carbon layers

attributed to the improved adsorption ability and crystallinity.The as-prepared

samples exhibited high activity even after 720 h of photocatalysis reaction, while

pure ZnO almost deactivates its photoactivity in just 100 h due to serious

photocorrosion.18

It has been reported in many research papers that ZnO was quite active under

visible light illumination for the photodegradation of some organic compounds in

aqueous solution.19, 20 Etacheri et al. successfully synthesized Mg doped ZnO

nanoparticles through simple oxalate co-precipitation method. Textural properties

of as-synthesized Mg-doped ZnO studied at various calcined temperature were

superior in comparison to bare ZnO. In addition to this, Mg doped ZnO

nanoparticles exhibited a blue-shift in the near band edge photoluminescence (PL)

emission, decrease of PL intensities and superior sunlight-induced photocatalytic

decomposition of methylene blue in contrast to undoped ZnO.19 Lu et al.

demonstrated degradation of Basic Blue 11 under visible light illumination over

ZnO. They successfully studied the effect of various factors i.e. initial dye

concentration, catalyst dosage, and initial pH on the photocatalytic reaction.20

29

Becker et al. synthesized different crystallite and particle size of ZnO by

solvothermal process. It was found that particle size of ZnO nonmaterial could be

easily controlled by changing the nature of solvent. The photocatalytic activity of

ZnO nanoparticles was effectively demonstrated by measuring the discoloration of

RhB under visible light illumination.21 Zhang et al. prepared a hybrid material by

monomolecular-layer polyaniline dispersed on the surface of zinc oxide (ZnO).

The hybrid photocatalysts exhibited promising photocatalytic activity for the

degradation of the methylene blue (MB) because of high separation of

photogenerated electron and holes on the interface of hybrid ZnO. The

photocorrosion inhibition of ZnO could be attributed to the rapid transfer of

photogenerated holes by the polyaniline monolayer.22 El-Kemary et al.

Synthesized ZnO nanoparticles by simple heating of zinc acetate dihydrate and

triethylamine in ethanol at 50-60 °C for 60 min. The photocatalytic activity of ZnO

was executed for the degradation of ciprofloxacin under UV light irradiation. It

was good to note that the rate of discoloration was affected by change of pH,

degradation process was effective at pH 7 and 10, but it was rather slow at pH 4.23

Kansal et al. prepared ZnO nanoparticles using precipitation method by using zinc

acetate and triethylamine as template agent. Further the comparative evaluation of

the photocatalytic activity of the synthesized ZnO and commercial ZnO powder

was made. It was observed that the synthesized nanoparticles exhibited better

photocatalytic activity. Experiments were also performed to investigate the

reusability of the synthesized ZnO.24 Li B. and Wang Y. successfully synthesized

ZnO hierarchical microstructures with uniform flower-like morphology were

prepared on a large scale through a template- and surfactant-free low-temperature

(80 °C) aqueous solution route. The flower-like ZnO sample shows an enhanced

photocatalytic performance compared with the other nanostructure ZnO materials

30

like nanoparticles, nanosheets, and nanorods, which can be attributed to the special

structural feature with an open and porous nanostructured surface layer that

significantly facilitates photodegradation of RhB.25 Mohajerani et al. have

synthesized various shaped ZnO nanostructures like particle, rod, and flower by

using different schemes. He effectively demonstrated photocatalytic activity of as-

synthesized various shaped nanostructures for discoloration of CI acid red 27 under

direct sunlight irradiation. The photoactivity of the nanorods was slightly superior

to that of the nanoparticles while flower-like and microsphere 3D nanostructures

showed much lower photoactivity. 26

2.2. Strontium Titanate (SrTiO3)

Since, the discovery of water splitting on the surface of TiO2 semiconductor, the

photocatalytic properties of various metal oxide semiconductors have been

extensively studied. Among them, SrTiO3 is a typical ternary perovskite type oxide

with a wide band gap of ∼3.2eV that has been largely studied for the

photocatalytic water splitting because of its superior physical and chemical

properties, such as excellent thermal stability and photocorrosion resistance. The

perovskite characteristic of SrTiO3 enhances its physical properties like high

temperature chemical stability and photocorrodibility.

Hideki Kato and Kudo A. effectively synthesized codoped TiO2 and SrTiO3 with

antimony and chromium which successfully lower the band gap energy of these

materials by 2.2 and 2.4eV respectively. Cr and Sb codoped TiO2 exhibited

photocatalytic generation of Oxygen from an aqueous silver nitrate solution under

visible light irradiation, while SrTiO3 codoped with antimony and chromium

evolved H2 from an aqueous methanol solution. The activity of TiO2 photocatalyst

codoped with antimony and chromium was remarkably higher than that of TiO2

31

doped with only chromium. It was due to the charge balance by codoping of Sb5+

and Cr3+ ions, resulting in the suppression of formation of Cr6+ ions and oxygen

defects in the lattice which should work as effectively nonradiative recombination

centers between photogenerated electrons and holes.27 Konta et al. successfully

synthesized noble metal Mn, Ru, Rh, and Ir doped SrTiO3 with solid state reaction

method. Doped SrTiO3 possessed intense absorption bands in the visible light

region due to the excitation from the discontinuous levels formed by the dopants to

the conduction band of the SrTiO3 host. Mn and Ru doped SrTiO3 showed

photochemical evolution of O2 from aqueous silver nitrate solution, while Rh and

Ir doped SrTiO3 loaded with Pt cocatalysts produced H2 from an aqueous methanol

solution under visible light irradiation (λ > 440 nm). The Rh (1%)-doped SrTiO3

photocatalyst loaded with a Pt cocatalyst (0.1 wt %) gave 5.2% of the quantum

yield at 420 nm for the H2 evolution reaction.28 Wang et al. has synthesized La

and N codoped SrTiO3 by a mechano-chemical reaction method using SrTiO3,

urea and La2O3 as the raw materials. N-doped SrTiO3 could be prepared by

heating the mixture of SrTiO3 and La2O3 under flowing NH3 gas at 600 ºC. The

sample prepared with 0.2 mol% La2O3, 22 mol% urea and 77.8 mol% SrTiO3

which has nearly the same nitrogen and lanthanum doping atomic fractions could

be obtained by a mechano-chemical method and exhibited high photocatalytic

activities. A new absorption edge formed in the visible reason. La and N codoped

SrTiO3 exhibited enhanced photocatalytic activity for NO destruction as compared

to bare SrTiO3 under visible light.29 S, C cation-codoped strontium titanium

dioxide (SrTiO3) was synthesized by Ohno et al. by mixing of thiourea and SrTiO3

powders in appropriate amount then calcined at appropriate temperatures (400,

500, or 600 oC). After successful calcinations C and S ions were doped into

SrTiO3, which are responsible for shift in absorption edge of SrTiO3 powder. The

S and C codoped SrTiO3 showed better photocatalytic activity for oxidation of 2-

32

propanol in comparison to bare SrTiO3 under a wide range of light irradiation at

wavelengths longer than 350 nm. The formation of this new absorption edge might

be the reason for the high level of visible-light photocatalytic activity of this

substance.30

SrTiO3 is usually synthesized by solid state reaction method at high temperature

but the main drawback of this method is possibility of segregation and does not

show reproducibility, which diminishes the photocatalytic activity of synthesized

photocatalyst. Puangpetch et al. synthesized mesoporous SrTiO3 nanocrystal via

simple sol-gel method by using strontium nitrate Sr(NO3)2 and tetraisopropyl

orthotitanate (TIPT) as precursors and CTAB as structure-directing agent in

anhydrous ethanol, ethylene glycol (EtOH/EG) was selected as a solvent. The

mesoporous SrTiO3 shows excellent crystallinity, specific surface area, and pore

size of material which directly show impact on the photocatalytic activity of

SrTiO3. The photocatalytic activity for the degradation of Methyl Orange exhibited

by the sample obtained at a calcination temperature of 700 ºC was much higher

than that of a nonmesoporous commercial SrTiO3.31 Wang et al. have successfully

synthesized SrTiO3 nanocrystallines by a solvothermal method using H2TiO3 as

starting material and found more active for the photodegradation of MB than

commercial SrTiO3 nanoparticles.32 Chen et al. synthesized SrTiO3 via a simple

sol-gel process and successfully demonstrated their photocatalytic activities for NO

degradation under either UV light and sunshine.33

Zheng et al. synthesized SrTiO3 hollow microspheres built by regular nanocubes

by a general and facile hydrothermal method. The synthesized hollow

SrTiO3 microspheres exhibit excellent photocatalytic activity in photoreduction of

Cr(VI). The SrTiO3 possess higher reducing ability in compare to TiO2 because

the conduction band edge position of SrTiO3 (−1.4 V vs. SCE) is more negative

33

than that of anatase TiO2 (−1.2 V vs. SCE). So, the photocatalytic activity of

SrTiO3 is higher than TiO2.34 Jia et al. synthesized a series of highly reactive Ni

and La codoped SrTiO3 photocatalysts via simple sol-gel method by mixing

strontium chloride hexahydrate, nickel chloride and lanthanum chloride in proper

stoichiometry. Successful incorporation of Ni and La into the SrTiO3, were

supported by the presence of extended absorption shifted from 380 nm to 700 nm.

Under a 100W incandescent lamp irradiating for 14 h, a 100% of MB was

degraded, which is much higher than those of either bare SrTiO3 or commercial

Degussa P25. The optimal range of Ni and La dopants is 0.1 - 1.0 mol%. The

formation of a new absorption edge and the large surface area may be the main

reasons for the high activity.35

Jia et al. synthesized Ni and La codoped SrTiO3 via simple sol-gel method and it

was found that the calcination temperature strongly affects not only the structural

properties and the visible light photocatalytic activities but also the stability of the

synthesized photocatalysts. It was executed that rate of discoloration of malachite

green over synthesized photocatalyst decreases with increasing calcination

temperature because high temperature causes loss in specific area, pore volume

and initial adsorption rate as well as the large lattice distortion. While, the catalysts

calcined at lower temperatures were more stable and exhibited extended broad

absorption tail in visible region after co-doping of Ni and La. Although bare

SrTiO3 shows a high activity due to dye-sensitization, codoping of Ni and La did

enhance the visible light activity, especially for the catalysts calcined at high

temperature. Moreover, the optimal doping amount of Ni and La is 1.0%. The

photocatalytic activities of all synthesized photocatalysts are found to be higher

than that of the commercial P25 under visible light irradiation.36 Sulaeman et al.

reported a facile method to synthesize Strontium titanate nanoparticles by a

34

microwave-assisted solvothermal reaction of SrCl2·6H2O, Ti(OC3H7)4 in KOH

methanol–oleic acid solution. The particle size of synthesized SrTiO3 nanoparticles

were about 15-18 nm. The photocatalytic activity of SrTiO3 under visible light

irradiation could be generated by modification of the surface with the carboxyl

group (–COO-) from oleic acid which enabled the absorption of visible light.37

2.3. Copper oxide (CuO)

CuO is an important p-type transition-metal-oxide semiconductor, with a narrow

band gap (eg =1.2 eV) and exhibiting a versatile range of applications such as

fabrication of solar cell38, optical and photovoltaic devices39, gas sensing40, and

many others. These splendid properties make CuO a useful material.41, 42 Xu et al.

synthesized octahedral Cu2O crystals via effective and facile method by reducing

copper hydroxide with hydrazine without using any surfactant. The length of

octahedral crystal can be adjusted by change of concentration of OH- and Cu2+ ions

in solution. It was found that the as synthesized octahedral Cu2O crystals shows

better photodiscoloration for methyl orange as compared to cubic Cu2O particles.43

Later Zhang et al. further support Xu’s work by successfully preparing Cu2O

microcrystals by a hydrothermal process with use of stearic acid as a structure-

directing agent. They compared the photodiscoloration for methyl orange, the

photocatalytic properties of Cu2O are strongly dependent on the shape of the

crystals i.e. number of atoms located at the edges, corners or surfaces. 44

Ma et al. Synthesized flower like Cu2O architecture by simple polyol process in

the presence of acetamide. The size of petal of flower is about 5-6 nm. The novel

architecture shows a blue shift of absorption edge compared to Cu2O nanocubes

and good photocatalytic activity for the degradation of dye brilliant red X-3B

under simulated solar light.45 Vaseem et al. successfully synthesized flower-shaped

35

CuO nanostructures consisting of triangular-shaped leaves, having sharpened tips

with the wider bases, grown by simple aqueous solution process and demonstrated

its photocatalytic activity over methylene blue.46 Liu et al. reported facile synthesis

of various morphologies of CuO nanostructures by hydrothermal process, PEG200

as a structure directing reagent to tailor the morphology of CuO nanostructures.

The photocatalytic activity has been correlated with the different nanostructures of

CuO. The 1D CuO nanoribbons exhibit the best performance on the RhB

photodecomposition because of the exposed high surface energy crystal plane.47

Wang et al. successfully synthesized hollow CuO microspheres through a simple

hydrothermal method in the presence of cetyltrimethylammonium bromide

(CTAB). The effects of reaction temperature, surfactant, and the molar ratio of

Urea/Cu2+ on the morphologies of the resulting products were investigated. The

CuO hollow microspheres show good photocatalytic activity for decolorization of

RhB under UV-light illumination.48

Mukherjee et al. synthesized CuO nanowhiskers like structure via electrochemical

route by using metallic copper as precursor. The Structural characterization

showed the formation of cubic phase for both the Cu and CuO films, whereas, the

grains were found to change their shapes from cubic to nano-whiskers as an effect

of annealing (in air at 600 °C for 30 min). The photocatalytic activity of the as-

synthesized nanomaterial CuO films was determined by measuring the degradation

of Rose Bengal (RB) dye, it was found the synthesized CuO showed good

photocatalytic activity and it can be used for its potential application in waste water

treatment.49 Liu et al. prepared CuO nanowires using Cu foil as substrate via a

solution route i.e. simple, low cost, and can be completed in the absence of any

surfactant. The morphological investigation of synthesized CuO products wire-

shaped and are grown in large quantity. The as-grown CuO exhibited excellent

36

photocatalytic activity, it was successfully measured that 90% of the methyl orange

was degraded after 180 min under nature light.50

37

References

[1] Hoffman A. J., Carraway E. R., and Hoffmann M. R., (1994), ‘Photocatalytic

production of H2O2 and organic peroxides on quantum-sized semiconductor

colloids.’ Environmental Science and Technology, vol. 28, pp.776-785.

[2] Kubacka A., García M. F., and Colon G., (2012), ‘Advance Nanoarchitecture

for Solar Photocatalytic Applications,’ Chem. Rev., vol.112, pp.1555-1614.

[3] Miyauchi M., Nakajima A., Watanabe T., and Hashimoto K., (2002),

‘Photocatalysis and photoinduced hydrophilicity of various metal oxide thin

films,’ Chem. Mater., vol. 14, pp.2812-2816.

[4] Wang J., Takuya Tsuzuki T., Bin Tang B., Hou X., Lu Sun, and Wang X.,

(2012), ‘Reduced Graphene Oxide/ZnO Composite: Reusable Adsorbent for

Pollutant Management,’ Appl. Mat. and Interface, vol.4, pp.3084-3090.

[5] Kislov N., Lahiri J., Verma H., Goswami D. Y., Stefanakos E., and Batzill M.,

(2009), ‘Photocatalytic degradation of methyl orange over single crystalline

ZnO: orientation dependence of photoactivity and photostability of ZnO,’

Langmuir, vol. 25, pp.3310-3315.

[6] Sakthivel S., Neppolian B., Shankar M.V., Arabindoo B., Palanichamy M., and

Murugesan V., (2003), ‘Solar photocatalytic degradation of azo dye:

comparison of photocatalytic efficiency of ZnO and TiO2,’ Sol. Energy Mater.

Sol.Cells., vol.77, pp.65-82.

[7] Behnajady M.A., Modirshahla N., and Hamzavi R., (2006), ‘Kinetic study on

photocatalytic degradation of C.I. Acid Yellow 23 by ZnO photocatalyst,’

Journal of Hazardous Materials, vol.133, pp.226-232.

38

[8] Colón G., Hidalgo M. C., Navío J. A., E. Melián E.P., Díaz O. G., and

Rodríguez J.M. D., (2008), ‘Highly photoactive ZnO by amine capping-assisted

hydrothermal treatment,’ Appl. Catal. B., vol. 83, pp.30-38.

[9] Mai F.D., Chen C.C., Chen J.L., and Liu S.C., (2008), ‘Photodegradation of

methyl green using visible irradiation in ZnO suspensions. Determination of

the reaction pathway and identification of intermediates by a high-

performance liquid chromatography–photodiode array-electrospray

ionization-mass spectrometry method,’ J. Chromatography A, vol.1189,

pp.355-365.

[10] Usni H., (2009), ‘Surfactant conecntration dependence of structure and

photocatalytic properties of zinc oxide rods prepared using chemical synthesis

in aqueous solutions,’ J. Colloid Interface Sci.,vol., 336, pp.667-674.

[11] Pare B., Jonnalagadda S.B., Tomar H., Singh P., and Bhagwat V.W., (2008),

‘ZnO assisted photocatalytic degradation of acridine orange in aqueous

solution using visible irradiation,’ Desalination, vol.232, pp.80-90.

[12] Dindar B., and lcli S., (2001) ‘Unusual photoreactivity of zinc oxide

irradiated by concentrated sunlight,’ J. Photochem. Photobiol. A: Chem.,

vol.140, pp. 263-268.

[13] Pardeshi S. K., and Patil A.B., (2008), ‘A simple route for photocatalytic

degradation of phenol in aqueous zinc oxide suspension using solar energy,’

Sol. Energy, vol. 82, pp.700-7005.

[14] Sobana N., and Swaminathan M., (2007), ‘Combination effect of ZnO and

activated carbon for solar assisted photocatalytic degradation of Direct Blue

53,’ Sol. Energy Mater. Sol. Cells, vol.91, pp.727-734.

39

[15] Yu J., and Yu X., (2008), ‘Hydrothermal synthesis and photocatalytic

activity of Zinc oxide hollow spheres,’ Environmental Science and Technology,

vol.42, pp. 4902-4907.

[16] Ziwei. D., Min C., Guangxin G., and Limin W., (2007), ‘A Facile Method to

Fabricate ZnO Hollow Spheres and Their Photocatalytic Property,’ J.

Phys.Chem. B, vol.112, pp.16-22.

[17] Comparelli R., Fanizza E., Curri M. L., Cozzi P. D., Mascolo G., and

Agostiano G., (2005), ‘UV-induced photocatalytic degradation of azo dyes by

organic-capped ZnO nanocrystals immobilized onto substrates,’ Appl. Catal.

B: Environ., vol. 60, pp.1-11.

[18] Zhang L., Cheng H., Zong R., and Zhu R., (2009), ‘Photocorrosion

suppression of ZnO nanoparticles via hybridization with grahite-like carbon

and enhanced photocatalytic activity,’ J. Phys.Chem. C, vol.113, pp.2368-2374.

[19] Etacheri V., Roshan R., and Kumar V., (2012), ‘Mg-Doped ZnO

Nanoparticles for Efficient Sunlight-Driven Photocatalysis,’ Applied Material

and Interface, vol.4, pp. 2717-2725.

[20] Lu C., Wu Y., Mai F., Chung W., Wu C., Lin W., and Chen C., (2009),

‘Degradation efficiencies and mechanisms of the ZnO-mediated photocatalytic

degradation of Basic Blue 11 under visible light irradiation,’ J. Mol. Catal. A:

Chem., vol.310, pp.159-165.

[21] Becker J., Raghupathi K. R., Pierre J. S., Zhao D, and Koodali R.T., (2011),

‘Tuning of the Crystallite and Particle Sizes of ZnO Nanocrystalline Materials

in Solvothermal Synthesis and Their Photocatalytic Activity for Dye

Degradation,’ J. Phys. Chem. C, vol.115, pp.13844-13850.

40

[22] Zhang H., Zhong R., and Zhu Y., (2009), ‘Photocorrosion inhibition and

photoactivity enhancement for zinc oxide via hybridization with monolayer

polyaniline,’ J. Phys. Chem. C, vol.113, pp.4605-4611.

[23] El-Kemary M., El-Shamy H., and El-Mehasseb I., (2010), ‘Photocatalytic

degradation of ciprofloxacin drug in water using ZnO nanoparticles,’ J.

Luminescence, vol.130, pp.2327-2331.

[24] Kansal S. K., Ali A. H., and Kapoor S., (2010), ‘Photocatalytic

decolorization of biebrich scarlet dye in aqueous phase using different

nanophotocatalysts,’ Desalination, vol. 259, pp.147-155.

[25] Li B., and Wang Y., (2010), ‘Facile synthesis and enhanced photocatalytic

performance of flower-like ZnO hierarchical microstructures,’ J. Phys. Chem.

C, vol.114, pp. 890-896.

[26] Mohajerani M. S., Lak A., and Simchi A., (2009), ‘Effect of morphology on

the solar photocatalytic behavior of ZnO nanostructures,’ J. Alloys Compd.,

vol. 485, pp. 616-620.

[27] Hideki Kato H., and Kudo A., (2002), ‘Visible-Light-Response and

Photocatalytic Activities of TiO2 and SrTiO3 Photocatalysts Codoped with

Antimony and Chromium,’ J. Phys. Chem. B, vol.106, pp.5029-5034.

[28] Konta R., Ishii T., Kato H., and Kudo A., (2004), ‘Photocatalytic Activities

of Noble Metal Ion Doped SrTiO3 under Visible Light Irradiation,’ J. Phys.

Chem. B, vol.108, pp. 8992-8995.

[29] Wang J.,Yin S., Komatsu M., and Sato., (2005), ‘Lanthanum and nitrogen

co-doped SrTiO3 powders as visible light sensitive photocatalyst,’ J. Euro.

Cera. Soci., vol. 25, pp. 3207-3212.

41

[30] Ohno T., Tsubota T., Nakamura Y., and Sayama K., (2005), ‘Preparation of

S, C cation-codoped SrTiO3 and its photocatalytic activity under visible light,’

Applied Catalysis A: General, vol. 288, pp.74-79.

[31] Puangpetch T., Sreethawong T., Yoshikawa S., and Chavadej S., (2008),

‘Synthesis and pho-tocatalytic activity in methyl orange degradation of

mesoporous-assembled SrTiO3 nanocrystals prepared by sol–gel method with

the aid of structure-directing surfactant,’ J. Mol. Catal. A: Chem., vol.287, pp.

70-79.

[32] Wang N., Kong D., and He H., (2011), ‘Solvothermal synthesis of strontium

titanate nanocrystallines from metatitanic acid and photocatalytic activities,’

Powder Technol., vol. 207, pp.470-473.

[33] Chen L., Zhang S.,Wang L., Xue D., and Yin S., (2009), ‘Preparation and

photocatalytic properties of strontium titanate powders via sol–gel process,’ J.

Cryst. Growth, vol. 311, pp. 746-748.

[34] Zheng Z., Huang B., Qin X., Zhang X., and Dai Y., (2011), ‘Facile synthesis

of SrTiO3 hollow microspheres built as assembly of nanocubes and their

associated photocat-alytic activity,’ J. Colloid and Interface Sci., vol. 358, pp.

68-72.

[35] Jia A., Su Z., Lou L. L., and Liu S., (2010), ‘Synthesis and characterization

of highly active nickel and lanthanum co-doped SrTiO3,’ Solid State Science,

vol.12, pp.1140-1145.

[36] Jia A., Lianga X., Sua Z., Zhub T., and Liua S., (2010), ‘Synthesis and the

effect of calcination temperature on the physical chemical properties and

42

photocatalytic activities of Ni, La codoped SrTiO3,’ Journal of Hazardous

Materials, vol.178, pp. 233-242.

[37] Sulaeman U., Yin S., and Sato T., (2011), ‘Visible light photocatalytic

activity induced by the carboxyl group chemically bonded on the surface of

SrTiO3,’ Applied Catalysis B: Environmental, vol.102, pp. 286-290.

[38] Musa A. Q., Akomolafe T., and Carter M. J., (1998), ‘Production of CuO A

solar cell material by thermal oxidation and a study of its physical & electrical

properties,’ Sol. Energy Mater. Sol. Cells, vol.51, pp.305-316.

[39] Poizot P., Laruelle S., Dupont L, and Taracon J. M., (2000), ‘Nano-sized

transition-metal oxides as negative-electrode materials for lithium-ion

batteries,’ Nature, vol.407, pp.496-499.

[40] Zhang J., Liu J., Wang Q. X., and Li Y., (2006), ‘Nearly Monodisperse

Cu2O and CuO nanospheres: Preparation & applications for sensitive gas

sensors,’ Chem. Mat., vol.18, pp. 867-871.

[41] Rao C. N. R., and Cheetham A.K., (2001), ‘Science and technology of

nanomaterials: Current status and future prospects,’ Journal of Materials

Chemistry, vol.11, pp. 2887-2894.

[42] Partzke G. R., Krumeich F., and Nesper R., (2002), ‘Oxidic nanotubes and

nanorods-Anisotropic modules for a future nanotechnology,’ Angew.Chem.

Int.Ed., vol.41, pp. 2446-2461.

[43] Xu H., Wang W., and Zhu W., (2006), ‘Shape evolution and size-

controllable synthesis of Cu2O octahedral and their morphology-dependent

photocatalytic properties,’ J. Phys. Chem. B, vol.110, pp.13829-13834.

43

[44] Zhang Y., Deng B. Zhang T.,Gao D., Xu A. W., (2010), ‘Shape effects of

Cu2O polyhedral microcrystals on photocatalytic activity,’ J. Phys. Chem. C,

vol. 114, pp. 5073-5079.

[45] Ma L. L., Li J. L., Sun H. Z., Qiu M. Q., Wang J. B., Chen J. Y., and Yu Y.,

(2010), ‘Self-assembled Cu2O flowerlike architecture polyol synthesis,

photocatalytic activity and stability under simulated solar light,’ Mater. Res.

Bull., vol.45, pp.961-968.

[46] Vaseem M., Umar A., Hahn Y. B., Kim D. H., Lee J. S., Jang J. S., (2008),

‘Flower shaped CuO nanostructures: structural, photocatalytic and XANES

studies,’ Catalysis Communications, vol.10, pp.11-16.

[47] Liu J., Jin J., Deng Z., Huang S. Z., Hu Z. Y., Wang L., Wang C., Chen L. H.,

Li Y., Tendeloo G.V., and Su B. L.,(2012), ‘Tailoring CuO nanostructures for

enhanced photocatalytic property,’ J. Colloid and Interface Science, vol. 384,

pp.1-9.

[48] Wang S., Xu H., Qian L., Wang J., Liu Y., and Tang W., (2009), ‘CTAB

assisted synthesis and photocatalytic property of CuO hollow microshperes,’

J. Solid State Chem., vol. 182, pp.1088-1093.

[49] Mukherjee N., Show B., Maji S. K., Madhu U., Bhar S. K., Mitra B. C., Khan

G. G., and Mondal A., (2011), ‘CuO nano-whiskers: Electrodeposition, Raman

analysis, Photoluminescence study and Photocatalytic activity,’ Material

Letters, vol.65, pp. 3248-3250.

[50] Liu X., Li Z., Zhang Q., Li F., and Kong T., (2012) ‘CuO nanowires

prepared via a facile solution route and their photocatalytic property,’

Materials Letters, vol.72, pp. 49-52.

44