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Vertically aligned core–shell PbTiO3@TiO2 heterojunction nanotube arrays are fabricated on F:SnO2 (FTO) glass substrate via a unique three-step process: an electron beam vapor deposition of Ti thin film on FTO, anodic oxidation of the Ti film to TiO2 nanotubes, and finally formation of PbTiO3 perovskite layer at the inner wall of the TiO2 nanotubes. The PbTiO3@TiO2 nanotube array exhibits dramatically improved photoactivity relative to TiO2 nanotubes or PbTiO3/TiO2 composite powders in photoelectrochemical water splitting and photocatalytic isopropyl alcohol decomposition under visible light irradiation (>420 nm). In the core–shell heterojunction electrodes, PbTiO3 serves as a visible light responsive inorganic photosensitizer with its small band gap and forms a heterojunction with TiO2 for effective charge separation.

CaFe2O4 (CFO) nanoparticles with the orthorhombic phase were synthesized using solid state reaction (SSR), polymer complex (PC), microwave sintering (μW) and self-propagating combustion (SPC) methods. Hydrogen (H2) evolution by photocatalytic water splitting (WS), over these nanoparticles have been investigated and compared. Their crystallinity, surface area, and band energetics have been studied. It reveals that the CFO synthesized by SSR, PC, μW methods exhibit high crystallinity than that obtained in SPC. The μW synthesized CFO photocatalysts (PHC) exhibited better optical properties than those obtained using conventional SSR route, though they took

Electron-deficient and porous WO 3 particles were prepared by the simple thermal oxidation of commercial bulk WC. The crystal structure of as-prepared WO 3 particles was monoclinic phases and its crystallinity and morphology were controlled by varying the calcination temperature. Small and interconnected WO 3 particles were divided and formed from bulk WC particles with increasing calcination temperature. The electronic structure of thermally oxidized particles was studied by W L III -edge XANES. Interestingly, as-prepared WO 3 samples were in an electron-deficient state (W +6−δ ). The photocatalytic performance of as-prepared samples was investigated in terms of oxygen production in AgNO 3 aqueous solution and decomposition of the organic dye, Rhodamine B. The photoelectrochemical and photocatalytic activity were correlated and the results were most favorable for WO 3 particles thermally oxidized at 700 °C for oxygen production and 600 °C for photocurrent production.

Magnesium ferrite (MgFe2O4) exhibiting a spinel phase was synthesized by using the polymerized complex and the solid-state reaction methods, and its physico-chemical properties were studied to explore the water-splitting under visible light photons. The study revealed the potential for using MgFe2O4 particles for photo-catalytic application. The structural study provided information on ferrite nano-crystallites fabricated by using the polymer complex method. The morphological studies demonstrated that, in contrast to the solid-state reaction method, a homogenous, monodispersed ferrite photocatalyst could be formed by using the polymerized complex method. The optical study revealed a larger visible-light absorption capability for the nanosized MgFe2O4 photocatalysts prepared by using the polymer complex methods, and indicated a red-shift of the bandgap by 0.06 eV as compared to the bandgap of the bulk. These nanocrystallites were highly photoactive with respect to the photodegradation and photocatalytic hydrogen evolution applications. The electrochemical analysis showed that they exhibited favorable bandedge positions suitable for photocatalytic H2 evolution. Thus, nanocrystalline MgFe2O4 is an active visible-light photocatalyst, that might be useful for the decomposition of water.

Nanostructured titanium dioxide (NTiO2) is known to possess efficient photocatalytic activity and to have diverse applications in many fields due to its chemical stability, high surface area/volume ratio, high transmittance, and high refractive index in the visible and the near-ultraviolet regions. These facts prompted us to develop TiO2 nanotube (TiO2 NT) arrays through electrochemical anodic oxidation involving different electrolytes comprised of phosphoric acid — hydrofluoric acid aqueous systems by varying the voltage and the time. The annealing temperature of the nanotubes, TiO2 NTs, were varied to modify the surface morphology and were characterized by using X-ray diffraction and scanning electron microscopy. Scanning electron microscopy and X-ray diffraction results showed that the samples had uniform morphologies and good crystalline structures of the anatase phase at lower annealing temperatures and of the rutile phase at higher annealing temperatures. A secondary-ion mass-spectrometry analysis was used to investigate the surface atoms and to conduct a depth profile analysis of the TiO2 NTs. The efficiency of the photocatalytic activity of the TiO2 NT arrays in degrading methylene blue (MB) was investigated under UV-Vis light irradiation. The maximum photocatalytic activity was achieved for the samples with lower annealing temperatures due to their being in the anatase phase and having a higher surface area and a smaller crystal size, which play important roles in the degradation of organic pollutants.

MO(=CuO, Co 3 O 4 , NiO)/BiVO 4 p–n junction composites were synthesized by urea-precipitation and wet impregnation method. The physicochemical and optical properties of the as-prepared materials were investigated by X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and UV–visible diffuse reflectance spectra. The photocatalytic performance of the as-prepared materials was investigated for decomposition of azo dye, acid orange 7. The CuO/BiVO 4 and Co 3 O 4 /BiVO 4 p–n junction composite photocatalysts exhibited the higher photocatalytic degradation of acid orange 7 than those of BiVO 4 and NiO/BiVO 4 as-prepared samples under visible light irradiation. We also discussed the mechanism of enhanced photocatalytic activity of p–n junctioned composites based on their energy band structures.

The titanate nanotube (TNT) and iron intercalated titanate nanotube (Fe-TNT) were synthesized in-situ single step hydrothermal method at 150 °C for 72 h. The electronic and local coordination structures of iron species intercalated in the interlayer space of ion exchangeable titanate nanotubes were investigated by X-ray absorption near edge structure (XANES) and X-ray photoelectron spectroscopy (XPS). The iron intercalated into the nanotube was formed as hydrated iron complex of [FexII(OH)2x−1(OH2)]+ and the iron complex played a harmful role in the photocatalytic hydrogen production from methanol–water mixed solution and the photocatalytic decomposition of acid orange 7 (AO7) under UV light irradiation. A higher photocurrent generation, however, was also observed from the Fe-intercalated titanate nanotube film from 0.1 M NaOH solution under UV light irradiation.

The effect substitution of Ti4+ at the Fe4+ site in a CaFe2O4-MgFe2O4 bulk hetero-junction (BH) lattice photocatalyst was explored and the Ti ion concentration was optimized to fabricate an efficient photocatalyst. A BH consisting of an optimum dopant concentration (Ti+4) level of x = 0.03 exhibited an increased band gap and generated a 1.5 times higher photocurrent. The newly fabricated Ti ion doped photocatalyst showed an enhanced quantum yield (upto ∼13.3%) for photodecomposition of a H2O-CH3OH mixture, as compared to its undoped BH counterpart under visible light (λ ≥ 420 nm). In contrast, the material doped with a very high Ti-dopant concentration displayed deteriorated photochemical properties. An efficient charge-separation induced by Ti-ion doping seems to be responsible for the higher photocatalytic activity in a doped bulk BH.

Mesoporous cobalt-doped ZnS and ZnO nanoplates were fabricated by calcination of a Zn 0.95 Co 0.05 S(en) 0.5 complex (en = ethylenediamine), which was hydrothermally synthesized using ethylenediamine as a single solvent and chelating agent. When the as-prepared Zn 0.95 Co 0.05 S(en) 0.5 complex was calcined, mesoporous nanoplates of wurtzite Zn 0.95 Co 0.05 S were formed, which then transformed to Zn 0.95 Co 0.05 O platelets upon further oxidation. Photocatalytic performance of the as-prepared materials was investigated for decomposition of the azo dye (acid red 14) and photoelectrochemical current generation in aqueous Na 2 S/Na 2 SO 3 solution as probe reactions. The Zn 0.95 Co 0.05 S calcined at 500 °C exhibited the highest photocatalytic activity under UV irradiation and also showed the photocatalytic performance under visible light irradiation.

Heterojunction semiconductors are discussed as a strategy to develop efficient visible light photocatalysts for water splitting. The concept has been demonstrated in photovoltaic cells and optoelectronic devices, for which junction-type semiconductors show greatly enhanced efficiency compared to the devices consisting of a single semiconductor. We applied this proven concept to fabricate photocatalysts of inorganic semiconductors. Thus heterojunction structures of Shottky junctions, p–n junctions (or p–n diode), p–n junctions with Ohmic layer, and bulk heterojunctions were fabricated and their photoactivity was tested for reduction or oxidation of water under visible light. The formation of heterojunctions results in the efficient separation of electron–hole pairs to minimize the energy-wasteful electron–hole recombination, which leads to the high photocatalytic activity. As the complexity and sophistication of the photocatalyst fabrication increased, the photoactivity also increased. Modern nanomaterial synthetic techniques were employed to bring into reality the highly engineered material configurations.

solid solution photocatalysts were synthesized by iron doping during the conventional solid state reaction at for 5 h and characterized by ultraviolet-visible (UV-vis) absorption spectroscopy, X-ray diffraction, morphological analysis. We found that samples not only absorb UV but also the visible light photons. This is because the Fe substitution at Ti-site in lattice induces the band transition from Fe3d to the Fe3d + Ti3d hybrid orbital. The photocatalytic activity of Fe doped samples for hydrogen production under UV light irradiation decreased with the increase in the Fe concentration. There exists an optimized concentration of iron in , which yields a maximum photocatalytic activity under visible light () photons.

Nitrogen-doped titania with a unique two-level hierarchical structure and visible light photocatalytic activity is reported. Thus, nitrogen-doped titanium oxide microrods decorated with N-doped titanium oxide nanosheets were synthesized by a hydrothermal reaction in NH4OH and postcalcination. During the calcination, the in situ incorporation of nitrogen atoms of ammonium ion into titania lattice was accompanied by the structural evolution from titanate to anatase titania. The morphological and structural evolution was monitored by scanning electron microscopy (SEM), x-ray diffraction (XRD), thermogravimetric analysis/differential thermal analysis (TGA/DTA), Raman, Fourier transform infrared (FTIR), x-ray absorption near edge structure (XANES), x-ray photoelectron spectroscopy (XPS), and adsorption isotherms. The N-doping brought visible light absorption, and the material exhibited high photocatalytic activity in the decomposition of Orange II under visible light irradiation (λ ≥ 400 nm), especially when it was loaded with 1 wt% Pt as a cocatalyst.

Zn2 Ti 1-x Fe x O 4 (0≤ × ≤ 0.7) photocatalysts were synthesized by polymerized complex (PC) method and investigated for its physico-chemical as well as optical properties. Zn 2 Ti 1-x Fe x O 4 can absorb not only UV light but also visible light region due to doping of Fe in the Ti site of Zn 2 TiO 4 lattice because of the band transition from Fe 3d to the Fe 3d + Ti3d hybrid orbital. The photocatalytic activity of Fe doped Zn 2 TiO 4 samples for hydrogen production under UV light irradiation decreased with an increase in Fe concentration in Zn 2 TiO 4 . Consequently, there exists an optimized concentration of iron for improved photocatalytic activity under visible light (λ≥ 420 nm).

Nanocrystalline ZnFe 2 O 4 oxide-semiconductor with spinel structure was synthesized by the polymerized complex (PC) method and investigated for its photocatalytic and photoelectric properties. The observation of a highly pure phase and a lower crystallization temperature in ZnFe 2 O 4 made by PC method is in total contrast to that was observed in ZnFe 2 O 4 prepared by the conventional solid-state reaction (SSR) method. The band gap of the nanocrystalline ZnFe 2 O 4 determined by UV-DRS was 1.90 eV (653 nm). The photocatalytic activity of ZnFe 2 O 4 prepared by PC method as investigated by the photo-decomposition of isopropyl alcohol (IPA) under visible light (≥ 420 nm) was much higher than that of the ZnFe 2 0 4 prepared by SSR as well as TiO 2-x N x . High photocatalytic activity of ZnFe 2 O 4 prepared by PC method was mainly due to its surface area, crystallinity and the dispersity of platinum metal over ZnFe 2 O 4 .

Nanocrystalline CaFe2O4 oxide semiconductor with spinel structure was synthesized by polymerized complex (PC) method and investigated for its physical and optical properties. The crystallization of CaFe2O4 made by PC method was found to occur in the temperature range of 700-1100 degrees C. The observation of highly pure phase and such lower crystallization tempearture in CaFe2O4 made by PC method, is in total contrast to that observed in CaFe2O4 prepared by the conventional solid-state reaction (SSR) method. The activation energy required for the growth of nanocrystalline CaFe2O4 in PC sample was found to be 8.4 kJ/mol. The band gap of nanocrystalline CaFe2O4 determined by UV-DRS was 1.91 eV (647 nm). The photocatalytic activity of PC materials for iso-propyl alcohol photodegradation under visible light (> or =420 nm) was much higher than that of SSR materials.

ZnFe2O4 with a spinel crystal structure was synthesized by using the solid-state reaction method. A single-phase ZnFe2O4 was obtained in the temperature range of 900 { 1200 C. The as-synthesized particles were agglomerates of crystals with an average size of 51.9 nm, as estimated from X-ray di raction analysis. The band gap of the n-type semiconducting metal oxide, as determined by using UV-vis di use re ectance spectroscopy (UV-DRS) was found to be 1.90 eV (657 nm). The photocatalytic activity of ZnFe2O4 was investigated by using the photo-decomposition of isopropyl alcohol (IPA) under visible light ( 420 nm) and was found to be much higher than that of the well-known TiO2 xNx photocatalyst.

An aurivillius phase Layered perovskite Bi5FeTi3O15 system was synthesized for first time by the solid-state reaction method yielding a single phase Bi5FeTi3O15 at only 1030°C. The electronic band structure and optical properties as well as the crystallization behavior of the materials were studied by using UV-DRS and XRD. The as-prepared particles those were the agglomerates of 25 nm crystals, exhibited the band gap of 2.38 eV (525 nm). Their visible light (λ ≥ 420 nm) photocatalytic activity as studied by the photo-decomposition of isopropyl alcohol (IPA) was found to be much higher than that of well-known TiO2-xNx photocatalyst.

A CdS/TiO2 composite photocatalyst consisting of one-dimensional CdS nanowire (NW) with a high crystallinity decorated with nanosized TiO2 particles (NP) was fabricated by solvothermal method and sol–gel synthesis. The new configuration photocatalyst exhibited higher rate of hydrogen production than that of single CdS NW under visible light irradiation (λ ≥ 420 nm) from water containing sulfide and sulfite ions as hole scavengers. Physicochemical properties of CdS NW/TiO2 NP composite photocatalysts were investigated together with the effect of the mole ratio of TiO2 and CdS for photocatalytic hydrogen production from water under visible light irradiation.

Nanosized TiO2 particles were prepared by hydrothermal method of the amorphous powders, which were precipitated in an aqueous peroxotitanate solution. The physical properties of prepared nanosized TiO2 particles were investigated. We also examined the activity of TiO2 particles as a photocatalyst on the decomposition of orange II. The particle size increases from 9 to 25 nm as the initial pH of the solution changes from 2 to 12. The titania particles prepared at pH=2 show the highest activity and the titania particles calcined at 400 °C also show the highest activity on the photocatalytic decomposition of orange II.

Nanosized TiO2 particles were prepared by the hydrothermal method from the amorphous powders which were precipitated in an aqueous peroxotitanate solution. The physical properties of the nanosized TiO2 particles prepared were investigated. We also examined the activity of TiO2 particles as a photocatalyst on the decomposition of orange II. The titania sol can be successfully crystallized to the anatase phase through hydrothermal aging at temperatures higher than 160°C. The particle size increases from 18 to 26 nm as the synthesis temperature increases from 140 to 200°C. Titania particles prepared at 180°C show the highest activity, and titania particles calcined at 400°C show also the highest activity on the photocatalytic decomposition of orange II.

A process of simultaneous hydrogen production and H 2 S removal has been investigated over a highly active composite photocatalyst made of bulk CdS decorated with nanoparticles of TiO 2 , i.e. CdS(bulk)/ TiO 2 . The photocatalytic activity was evaluated for hydrogen production from aqueous electrolyte solution containing H 2 S dissolved in water or alkaline solution under visible light irradiation. The rate of hydrogen production from the H 2 S -containing alkaline solution was similar to the rate obtained from photocatalytic hydrogen production from water containing sacrificial reagents ( Na 2 S + Na 2 SO 3 ) in the similar concentration. The isotope experiment was carried out with D 2 O instead of H 2 O to investigate the source of hydrogen from photocatalytic decomposition of H 2 S dissolved in H 2 O or alkali solution under visible light. Hydrogen originated from both H 2 S and H 2 O when the reaction solution contained H 2 S absorbed in alkaline water.

The nanosized titania and TiO2/SiO2 particles were prepared by the microwave-hydrothermal method. The effect of physical properties TTIP/TEOS ratio and calcination temperature has been investigated. The major phase of the pure TiO2 particle is of the anatase structure, and a rutile peak was observed above 800°C. In TiO2/SiO2 particles, however, no significant rutile phase was observed, although the calcination temperature was 900°C. No peaks for the silica crystal phase were observed at either silica/titania ratio. The crystallite size of TiO2/SiO2 particles decreases as compared to pure TiO2 at high calcination temperatures. The TiO2/SiO2 particles show higher activity on the photocatalytic decomposition of orange II as compared to pure TiO2 particles.

Nanosized TiO2 particles were prepared by hydrothermal method of the amorphous powders which were precipitated in an aqueous peroxotitanate solution using different amine group-containing organics. The physical properties of prepared nanosized TiO2 particles were investigated. We also examined the activity of TiO2 particles as a photocatalyst for the decomposition of orange II. The TiO2 particles calcined at 400 °C were shown to have a stable anatase phase which has no organic compounds. The particles size of titania particles decreased from 15 to 10 nm as the carbon chain length increased. The titania nanoparticles were shown to have a polygonal shape prepared using NH4OH and tetramethylammonium hydroxide (TMAOH) as additives, however, the micrographs showed the spherical and narrow size distribution prepared using tetraethyl-ammonium hydroxide (TEAOH) and tetrabutylammonium hydroxide (TBAOH). The titania particles prepared using TEAOH as an amine group-containing organic showed the highest activity on the photocatalytic decomposition of orange II. In addition, the titania particles calcined at 500 °C showed the highest activity on the photocatalytic decomposition of orange II.

Amorphous precursors to nitrogen-doped TiO2 (NTP) and pure TiO2 (ATP) powders were synthesized by hydrolytic synthesis and sol–gel method (SGM), respectively. Corresponding crystalline phases were obtained by thermally induced transformation of these amorphous powders. From FT-IR and XPS data, it was concluded that a complex containing titanium and ammonia was formed in the precipitate stage while calcination drove weakly adsorbed ammonium species off the surface, decomposed ammonia bound on surface of precipitated powder and led to substitution of nitrogen atom into the lattice of TiO2 during the crystallization. The activation energies required for grain growth in amorphous TiO2−xNx and TiO2 samples were determined to be 1.6 and 1.7 kJ/mol, respectively. Those required for the phase transformation from amorphous to crystalline TiO2−xNx and TiO2 were determined to be 129 and 142 kJ/mol, respectively. A relatively low temperature was required for the phase transformation in NTP sample than in ATP sample. The fabricated N-doped TiO2 photocatalyst absorbed the visible light showing two absorption edges; one in UV range due to titanium oxide as the main edge and the other due to nitrogen doping as a small shoulder. TiO2−xNx photocatalyst demonstrated its photoactivity for photocurrent generation and decomposition of 2-propanol (IPA) under visible light irradiation ( λ ⩾ 4 2 0 nm ).

The layered perovskite materials were found to give the high photocatalytic activity in water splitting reaction under UV irradiation, where the electronic structure of perovskite slab constructing the layered structure (the total cation valency) was the most crucial factor to the high photocatalytic activity. Both the excessive cation valency and the layered structure were required for active photocatalysts, while the slab thickness of layered perovskites had an insignificant effect on water-splitting activity. In order to identify key variables that affected photocatalytic activity and to optimize the performance of (110) layered perovskite, La2Ti2O7 was modified by various methods. The optimum amount of loaded nickel had a great effect and the amount depended on the surface area of the perovskite phase. When an alkaline-earth element such as Ba, Sr, and Ca was doped on La2Ti2O7, the photocatalytic activity was enhanced markedly. Introduction of an alkaline hydroxide into the reaction system as an external additive enhanced the activity further showing extremely high quantum yields close to 50%.

Nanosized iron oxide particles were intercalated into the interlayer of layered compounds HTiNb(Ta)O5 by a successive ion-exchange reaction. The electronic and local coordination structures of iron oxide in the interlayer space of these proton-containing compounds were investigated by X-ray absorption near edge structure (XANES) and X-ray photoelectron spectroscopy (XPS). The intercalated nanosized iron oxide was Fe2O3, which exhibited a high electron deficiency. Unlike in a previous report, Fe2O3-intercalated layered compounds did not produce hydrogen from an aqueous methanol solution in a photocatalytic manner under visible light. Instead, the material produced a stoichiometric mixture of hydrogen and oxygen photocatalytically under UV irradiation and produced oxygen from an aqueous AgNO3 solution photocatalytically under visible light.

In search for efficient photocatalysts for water splitting under visible light, the effect of cation substitution on a layered perovskite, La 2 Ti 2 O 7 has been studied . Among various types of dopants, only Cr and Fe showed intense absorption in the visible light region ( λ >420 nm), over which H 2 was produced photocatalytically from water–methanol solution. XPS measurements indicated that the oxidation state of doped Cr and Fe was +3. The band gap energies of Cr and Fe-doped La 2 Ti 2 O 7 were 2.2 and 2.6 eV, respectively, and the H 2 evolution rate was a little higher for the Cr-doped catalyst than that for the Fe-doped one. The theoretical calculation of electronic band structure revealed that the contribution of these dopants on the overall band structure of La 2 Ti 2 O 7 was negligible, but that they formed a partially filled 3d band in the band gap of La 2 Ti 2 O 7 , from which photoelectrons are excited to the conduction band upon visible light absorption.

In the search for efficient photocatalysts working under visible light, we have investigated the effect of cation substitution on a layered perovskite, La2Ti2O7. Among various metal dopants, only Cr and Fe induced intense absorption of visible light (lambda400 nm), and only these catalysts produced H2 photocatalytically from water in the presence of methanol under visible light irradiation (lambda420 nm). The polymerized complex method was found to be more efficient for fabrication of the present catalysts producing a more homogeneous structure than the solid-state reaction. The characterization by XRD, UV-vis DRS, XPS, and XANES revealed that doped Cr and Fe were present in the Cr3+ and Fe3+ states substituting for Ti sites in the La2Ti2O7 lattice. The theoretical calculation indicated that the most significant feature in the electronic band structure of the metal-doped La2Ti2O7 was the formation of a partially filled 3d band in the band gap of La2Ti2O7, while the contribution of these dopants on the valence band was negligible. Excitation of electrons from this localized interband to the conduction band of La2Ti2O7 was responsible for visible light absorption and the H2 evolution from water under visible light.

Highly donor-doped (110) layered perovskite materials, La2Ti2O7, with high surface areas were synthesized by the polymerizable complex (PC) method. Relative to La2Ti2O7 prepared by the solid state reaction (SSR) method, PC catalysts showed higher surface areas, crystallization at lower temperatures, higher phase purity, more uniform morphology and better-distributed nickel on the outer surface of La2Ti2O7. All these factors led to higher photocatalytic activity for overall water splitting under UV irradiation. The quantum yield of the reaction over La2Ti2O7 prepared by the PC method was as high as 27%, which was about twofold greater than that over La2Ti2O7 prepared by the SSR method.

A highly donor-doped (110) layered perovskite, La2Ti2O7, was found to be an efficient photocatalyst comparable to TiO2 P25 and better than K2La2Ti3O10, the latter being an undoped (100) layered per...

Highly donor-doped (110) layered perovskite materials loaded with nickel are efficient photocatalysts for overall water splitting with photon yields as high as 23% under UV irradiation. These novel photocatalysts are a series of homologous structures with a generic composition of AmBmO3m+2 (m=4, 5; A=Ca, Sr, La; B=Nb, Ti). The high electron density of these donor-rich materials would create a narrower charge depletion region of the semiconductor and an increased band bending, which allow more efficient electron-hole separation and higher quantum yields than undoped materials. Effects of catalyst preparation conditions are discussed on photocatalytic activity in water splitting.

The recent fl ourishing of nanostructured materials has widened its potential applications in the much-desired effi cient energy materials. Specifi cally, materials for solar hydrogen production by water splitting should possess superior optoelectric properties in addition to suitable band energetics and durability in aqueous solutions. The tunability of the physicochemical properties of nanostructred materials by virtue of their size and shape renders a wider applicability. Since the critical limitation of popular TiO 2 photocatalyst that absorbs only UV light, [ 1 , 2 ] the fi eld of visible light water splitting photocatalyst is currently being nurtured by various kinds of conventional and new single component materials (CdS, WO 3 , Fe 2 O 3 , TaON, etc.), as well as composite materials. [ 3–20 ] However, there is still much potential for nanostructured materials in this area. There have been several reports on the binary [ 3–6 ] and ternary metal oxides, [ 7–13 ]

A bulk heterojunction photocatalyst of interfacing CaFe2O4 and MgFe2O4nanoparticles is highly active for oxidative degradation of isopropyl alcohol and hydrogen production from water under visible light, because the exciton easily reaches the interface and dissociates to minimize recombination.

Nitrogen-doped perovskite type materials, Sr2Nb2O7−xNx (0, 1.5 < x < 2.8), have been studied as visible light-active photocatalysts for hydrogen production from methanol–water mixtures. Nitrogen doping in Sr2Nb2O7 red-shifted the light absorption edge into the visible light range and induced visible light photocatalytic activity. There existed an optimum amount of nitrogen doping that showed the maximum rate of hydrogen production. Among the potential variables that might cause this activity variation, the crystal structure appeared to be the most important. Thus, as the extent of N-doping increased, the original orthorhombic structure of the layered perovskite was transformed into an unlayered cubic oxynitride structure. The most active catalytic phase was an intermediate phase still maintaining the original layered perovskite structure, but with a part of its oxygen replaced by nitrogen and oxygen vacancy to adjust the charge difference between oxygen and doped nitrogen. These experimental observations were explained by density functional theory calculations. Thus, in Sr2Nb2O7−xNx, N 2p orbital was the main contributor to the top of the valence band, causing band gap narrowing while the bottom of conduction band due to Nb 4d orbital remained almost unchanged.

A novel photocatalyst, PbBi2Nb2O9 has been discovered that shows high activities for degradation of organic pollutants, generation of photocurrent, and water decomposition into O2 or H2, all under visible right irradiation (lambda/= 420 nm). This is the first example of an undoped, single-phase oxide photocatalyst that shows such reactivity. Its quantum yields are much higher than those for most of the previously reported materials, especially in water decomposition to generate oxygen (29%). Since it is an oxide, there is much less concern for stability under light irradiation.

Nickel-loaded La2Ti2O7, one of the highly donor-doped (110) layered perovskite materials, has been found to be an efficient photocatalyst for simultaneous H2 production from water splitting and decomposition of tetramethylammonium hydroxide (TMAH) under UV irradiation.

TiO2 nanobarbed fibers (NBFs) were prepared by growing rutile TiO2 nanorods on anatase TiO2 nanofibers via electrospinning and hydrothermal reaction processes. There was a large increase in the photocatalytic activity of O2-plasma-treated (OP)-TiO2 NBFs relative to that of the TiO2 NBFs; this is due to the hydroxylation of the surface of the TiO2 NBFs by OP treatment. The repeatability of the photocatalytic activity of the OP-TiO2 NBFs was found to be high and the decolorization rate after ten cycles was 88.3% of the initial value. These results indicate that OP-TiO2 NBFs have great potential for use as a photocatalyst.

A bulk heterojunction photocatalyst of interfacing CaFe(2)O(4) and MgFe(2)O(4) nanoparticles is highly active for oxidative degradation of isopropyl alcohol and hydrogen production from water under visible light, because the exciton easily reaches the interface and dissociates to minimize recombination.

The Pb substitution effect was investigated experimentally and theoretically on the crystal structure of BaSnO3 and on the photo-oxidation activity of H2O. The chemically doped Pb in BaSnO3 induced a concentration-dependent redshift of the experimental band gap (BG). The BaPb0.8Sn0.2O3 system produced 32μmol∕h of O2 under λ⩾420nm photons, but no O2 for BaSnO3. The DFT calculations of BaPbxSn1−xO3 (x=0,0.5,1) by using generalized approximation, implying the BG alteration and the photocatalytic activity of BaPbxSn1−xO3, are due to the induced Pb 6s orbital in the BG of BaSnO3. Thus Pb modified the insulating nature of BaSnO3 to semiconducting and semimetallic.

The WO3∕W∕PbBi2Nb1.9Ti0.1O9 photocatalyst was fabricated by depositing the tungsten clusters over the p-type perovskite base material with the chemical vapor deposition method, and later partly oxidizing the surfaces of these clusters to obtain n-type WO3 overlayers and W metal layer as an Ohmic junction. This NCPC showed unprecedented high activity for the photocatalytic oxidation of water, photocurrent generation, and acetaldehyde decomposition under visible light irradiation (λ⩾420nm).