•The addition of iron increased valence state of manganese.•The addition of tungsten introduced new acid site.•High temperature selectivity is significantly improved.•Modified catalysts showed excellent SCR activity, selectivity and H2O resistance.The influence of iron and tungsten in the Mn/Ti catalyst system on the activity and H2O induced deactivation was evaluated for the Selective Catalytic Reduction (SCR) of NO. The properties of the catalysts were characterized by physicochemical measurements, including BET surface area, X-ray diffraction (XRD), H2 temperature-programmed reduction (H2-TPR), NH3 temperature-programmed desorption (NH3-TPD), NO oxidation, X-ray photoelectron spectroscopy (XPS) and in situ diffuse reflectance infrared spectroscopy (DRIFT) analyses. The results indicated that the addition of iron promoted surface species dispersion and increased valence state of manganese species, which enhanced the low-temperature activity. The addition of tungsten enhanced the acid sites and improved the thermal stability of the acid sites. Thus, the Mn10Fe10/W3Ti exhibited excellent NOx conversion and N2 selectivity during high temperature compared with Mn10/Ti and Mn10Fe10/Ti catalysts. Furthermore, the addition of tungsten exhibited excellent resistance to H2O induced deactivation. Accordingly, the co-addition of iron and tungsten with proper ratios to Mn/Ti resulted in excellent NOx conversion, N2 selectivity and H2O resistance.Download high-res image (78KB)Download full-size image

•Solvothermal method was introduced to modify bulk g-C3N4.•High crystalline and dispersive (Na, O) co-doped g-C3N4 was obtained.•The absorption of both the UV and visible light for (Na, O)-g-C3N4 was enhanced obviously compared with bulk g-C3N4.•The photocatalytic activities of (Na, O)-g-C3N4 is improved with the apparent quantum yield as high as 22.3% at 420 nm.The photocatalytic activity of bulk g-C3N4 is rather low. Many strategies have been adopted to improve the photocatalytic performance of g-C3N4. Here, Na and O co-doped g-C3N4 was prepared by a feasible solvothermal method. The band structure was modulated mainly by introducing O into lattice of g-C3N4, resulting in simultaneously enhanced absorption and red shift. Moreover, the separation and migration of photogenerated carriers under visible light was enhanced by Na doping. In addition, well dispersion of (Na, O)-g-C3N4 in pure water was observed due to its high surface electronegativity. The photocatalytic H2 production activity of (Na, O)-g-C3N4 was improved tremendously, especially under visible light, and the apparent quantum yield was as high as 22.3% at 420 nm.Download high-res image (126KB)Download full-size image

•A new photocatalyst, BiVO4:YVO4 solid solution, is successfully prepared.•A novel dodecahedron, BiVO4:YVO4, with only two facets exposed, is found.•This BiVO4:YVO4 solid solution can split pure water under visible light.•The facets exposed can separate photogenerated electrons and holes efficiently.BiVO4, an excellent photocatalyst for oxygen production, has been studied extensively. Many attempts have been made to change the conduction band of BiVO4 to satisfy the H2O/H2 potential. In this paper, yttrium is introduced to adjust the energy band structure of BiVO4. A novel BiVO4:YVO4 solid solution with a new dodecahedron shape exposing two facets, {1 0 1} and {1 0 0}, is successfully prepared. On doping with Y, the crystal system of BiVO4 changes from monoclinic to tetragonal. The improved symmetry of the crystal system makes the (1 0 0) and (0 1 0) of {1 0 0} facets entirely identical, resulting in dodecahedron tetragonal BixY1−xVO4. The energy levels of the two facets show slight nonconformity. So the photogenerated electrons and holes can be separated efficiently between the adjacent exposed facets to produce H2 and O2, respectively. Through the study of photocatalytic performance, BixY1−xVO4 with Pt as co-catalyst shows highly efficient photocatalytic activity and can split pure water at the stoichiometric ratio.Download high-res image (54KB)Download full-size image

•BYV was firstly synthesized by molten salt in a relatively low temperature.•Y content has an influence of photocatalytic performance of BYV.•The porous structure on the surface occurs with the addition of molten salt.•The higher the temperature, the more the pore structure on the surface.•BYV prepared by molten salt showed better performance than solid state reaction.BixY1−xVO4 crystallite (BYV) was successfully synthesized by molten salt method in a relatively low temperature. In this paper, the influence of calcination temperature and the weight ratio of the precursor to the salt on photocatalytic activity for water splitting were investigated. The content of Y species increases with the temperature increased, resulting the better photocatalytic activity at high temperature. The morphology on the surface of BYV can be changed with the addition of molten salt. The porous structure on the surface occurs with the addition of molten salt from the SEM, which was caused by the evaporation of molten salt at higher temperature. Compared with solid state reaction method, BYV prepared by molten salt method showed better photocatalytic performance, which was due to the lower synthesis temperature and porous structure on the surface. And BYV via 550 °C calcination with 5:1 as weight ratio showed the highest photocatalytic activity, by which the amounts of hydrogen and oxygen produced were about 1630 μmol h−1 g−1 and 680 μmol h−1 g−1 respectively.

Photodeposition of H2PtCl6 in the presence of methanol promotes the formation of highly dispersed, metallic Pt nanoparticles over titania, likely via capture of photogenerated holes by the alcohol to produce an excess of surface electrons for substrate-mediated transfer to Pt complexes, resulting in a high density of surface nucleation sites for Pt reduction. Photocatalytic hydrogen production from water is proportional to the surface density of Pt metal co-catalyst, and hence photodeposition in the presence of high methanol concentrations affords a facile route to optimising photocatalyst design and highlights the importance of tuning co-catalyst properties in photocatalysis.

Diesel soot, a major contributor to PM emission, severely threatens human health and the environment. Catalytic oxidation of trapped diesel soot is a feasible solution to alleviating this problem. In this study, highly active Co–Ce catalysts were synthesized by the citric acid complex method and their catalytic behaviour was investigated by means of TG analysis. The best catalytic performance was acquired over the Co0.93Ce0.07 catalyst with T10 = 315 °C and T50 = 370 °C. These catalyst samples were also characterized by XRD, Raman spectrum, soot-TPR, H2-TPR, O2-TPD, XPS and in situ Raman spectra. Cerium cations were partially incorporated into the lattice of Co3O4 in Co–Ce mixed oxides, which led to the lattice expansion. This structure modification brought about a series of changes in the surface and the lattice of these catalysts. The capability of oxygen adsorption and desorption was slightly improved, and the redox ability of mixed oxides was intensified owing to the strong interaction between Co3O4 and CeO2. Surface lattice oxygen and bulk lattice oxygen could also be activated at a lower temperature. Moreover, active oxygen species (superoxide and peroxide) as well as carbon–oxygen intermediates (carbonyl and formate species) were discovered in soot combustion. Reactions for producing formate species were important steps for the soot–O2 reaction. The enhanced effects of both redox mechanism and oxygen spillover mechanism were probably due to the synergistic effect between the two oxides.

•The nickels/CdS is prepared from a composite by a sample photocatalytic reaction.•The composite is CdS and flowerlike Ni/Ni(OH)2.•The photocatalytic activity is even higher than CdS loaded with 1 wt% Pt.•The flowerlike superstructures were broken due to the reduction of Ni(OH)2.Nickels/CdS photocatalyst was prepared by a simple photocatalytic reaction of CdS and flowerlike Ni/Ni(OH)2 nanocomposite. The photocatalyst shows effectively photocatalytic H2 production activity, and reaches to the maximum rate of 373.5 μmol h−1 when the mass ratio of CdS and flowerlike Ni/Ni(OH)2 is 2, even higher than the one of CdS loaded with 1 wt% Pt. Characterization results (FESEM, TG, FT-IR, XPS, etc.) indicate that the effective photocatalytic H2-production activity was predominantly attributed to the porous flowerlike superstructures, in which CdS could be well fixed. Thus, CdS could contact fully with flowerlike Ni/Ni(OH)2. Ni is an excellent cocatalyst, which can transfer electrons efficiently. Furthermore, Ni2+ of Ni(OH)2 were effectively reduced to Ni. These nickels could also act as cocatalyst to promote the separation and transfer of photogenerated electrons. Therefore, the flowerlike superstructures was gradually broken during the photocatalytic progress because of Ni(OH)2 reduction, while resulted in effective photocatalytic H2 production activities.

Volatile organic compounds (VOCs), common chemical contaminants found in office and home environments, are one of the main causes of sick building syndrome. To efficiently remove the VOCs in terms of energy efficiency, product selectivity, safety and durability is the main target for current indoor VOCs control study toward the aim for future commercial application. The main challenge to achieve this goal is represented by removal specific VOCs with low concentration under room temperature. In a chemical kinetics sense, this means overcoming the activation barriers to achieve considerable reaction rate for reactants with low concentration without the aid of increasing temperature. Assistance the VOCs catalysis degradation reaction with oxidizing species or pre-degradation the reactants to easier treated substances could also help to increase the reaction rate by providing an alternative route for the reaction with lower activation energy. This technique route thus holds great promise to achieve commercial application for indoor VOCs degradation study. Therefore, we provide here an overview of the efforts that have been developed already on combing traditional photocatalysis and catalysis technology with techniques capable of producing highly active species to remove indoor VOCs. The assistance techniques include, but not limited to technologies, such as vacuum ultraviolet, ozone, plasma. Special emphasis is placed on rational catalyst designing to meet the challenge of indoor VOCs removal in the kinetic sense. Last but not least, we also identified future opportunities for indoor air quality control including: (a) combining high-voltage electrostatics in the system using post catalyst bed configuration to solve the issues of VOCs abatement and particulate matter capture in one basket. (b) To obtain a more complete understanding of the mechanism underlying the combination effects, which is crucial to get a better catalyst designing.

•Novel photocatalysts H-ABi2Ta2O9 for overall water splitting were synthesized.•Cations in interlayer could influence photocatalytic activity.•High dispersion of Pt particles contributes to the high photocatalytic activity.Novel photocatalysts, protonated layered perovskite oxides H-ABi2Ta2O9 (A = Ca, Sr, Ba, K0.5La0.5) for overall water splitting were synthesized by ion exchange with acid treating. The characterization by XRD, HRTEM indicated that all of ABi2Ta2O9 (A = Ca, Sr, Ba, K0.5La0.5) were able to form new single-phase protonated layered oxides. The measurement of photocatalytic activity showed every protonated layered oxide could overall split water into H2 and O2, although the ratios of H2 and O2 are unstoichiometric. The sequence of photocatalytic H2 production is HCBT(107.0 μmol/h) < HBBT(119.5 μmol/h) < HSBT(162.7 μmol/h) < HKLBT(189.3 μmol/h). The difference of ionic radius of cations in interlayer influenced the band gaps, and resulted in the distinction of photocatalytic activity. Pt loading enhanced apparently the photocatalytic activity. Among all of photocatalysts in this study, 0.1 wt%Pt/HSBT showed the highest photocatalytic activity for H2 evolution, reaching 491 μmol/h.

•The preparation process of photocatalyst is simple and efficient.•Dual co-catalysts MS can improve the efficiency of TiO2 photocatalytic activity.•CuS–NiS/TiO2 is low-priced and stable.TiO2 photocatalysts loaded CuS and NiS as co-catalyst were prepared by hydrothermal approach and characterized by XRD, UV–visible DRS, BET, XPS, SEM and TEM. When TiO2 was loaded MS as co-catalyst, it showed higher photocatalytic activities for splitting water into hydrogen in methanol aqueous solution under 500 W Xe lamp. Among the photocatalysts with various compositions, the maximum evolution of H2 obtained from 5 wt% CuS–5 wt% NiS–TiO2 sample was about 800 μmol h−1, which was increased up to about twenty-eight times than that of TiO2 alone. It was proven that CuS, NiS can act as effective dual co-catalysts to enhance the photocatalytic H2 production activity of TiO2.

Non-thermal plasma (NTP) was produced in a dielectric barrier discharge reactor for degradation of acetaldehyde and benzene, respectively. The effect of volatile organic compounds (VOCs) chemical structure on the reaction was investigated. In addition, acetaldehyde was removed in different background gas. The results showed that, no matter in nitrogen, air or oxygen, NTP technology always exhibited high acetaldehyde removal efficiency at ambient temperature. However, it also caused some toxicity by-product such as NOx and ozone. Meanwhile, some intermediates such as acetic acid, amine and nitromethane were formed and resulted in low carbon dioxide selectivity. To solve above problems, Co–OMS-2 catalysts were synthesized and combined with plasma. It was found that, the introduction of catalysts improved VOCs removal efficiency and inhibited by-product formation of plasma significantly. The plasma-catalysis system was operated in a recycling experiment to investigate its stability. The acetaldehyde removal efficiency can be kept at 100 % in the whole process. However, slight deactivation in ozone control was observed at the later stage of the experiment, which may be ascribed to deposition of VOCs on the catalysts surface and reduction of catalysts surface area.

•Novel 2D monolayer titania quantum dots (MTQDs) were synthesized from protonic lepidocrocite titania nanotubes in supercritical water.•The thickness of MTQDs is only ∼0.4 nm and lateral size is ∼2 nm.•PL, UV–vis, Raman properties of MTQDs were different from TNTs and anatase TiO2.•Structure and growth mechanism of MTQDs were discussed.•MTQDs were considered to be the crystal seeds for the phase transition from TNTs to anatase TiO2.Two-dimensional monolayer titania quantum dots (MTQDs) with ∼0.4 nm thickness and ∼2 nm lateral size are synthesized by supercritical water (SCW) treatment of titania nanotubes (TNTs). The morphology, chemical characteristics and the structure of MTQDs are studied. The formation mechanism of the MTQDs and the differences between SCW and low-temperature hydrothermal treatment are discussed. During the reaction, the high temperature, high pressure and high H+/OH− concentration of SCW dissolved TNTs into MTQDs, and the intercalation property of the “active” water clusters formed from the broken hydrogen bonding network facilitated the detachment of the MTQDs from the TNTs. The above two reasons lead to the capture of the dissolved tiny particles, which could hardly preserved in low-temperature hydrothermal treatment. The MTQDs may be the minimum constituent unit existing in the reality of the anatase TiO2. As a new member of the monolayer family, this new kind of 2D material may shed new light on the study of the monolayer materials.

Visible-light-driven CdS/HKLBT photocatalyst was prepared by ion exchange of Cd2+ in aqueous Cd(CH3COO)2 solutions, then by sulfurization in aqueous N2H8S solutions. The characterization by XRD, SEM, HRTEM and XRS revealed that CdS nanoparticles exist both on the surface and in the interlayer of HKLBT. The composite CdS/HKLBT showed higher photocatalytic activity for hydrogen evolution (504.2 μmol/h) than that of pure CdS (187.3 μmol/h), even than that of 0.5 wt%Pt/CdS (496.0 μmol/h) under visible light (λ > 400 nm) in the presence of lactic acid as sacrificial reagent. The enhancement of photocatalytic activity is attributed to the strong contact between CdS and HKLBT in CdS/HKLBT as well as the effective separation of photogenerated carrier in CdS through electron rapid injection into CB of HKLBT.Highlights► CdS/H1.9K0.3La0.5Bi0.1Ta2O7 photocatalyst were prepared. ► Higher photocatalytic activity for hydrogen evolution under visible light. ► CdS nanoparticles exist both on the surface and in the interlayer of HKLBT.

In recent years, the research of photocatalyst splitting of water to hydrogen by using semiconductor has been developed rapidly. CdS are attractive photocatalytic materials for the conversion of solar energy into chemical energy under visible-light irradiation. In this paper, a kind of recyclable cocatalyst that the wool supported palladium cocatalyst was synthetized and characterized by X-ray diffraction, diffuse reflectance UV–vis spectroscopy, energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopic (XPS) studies and transmission electron microscopy (TEM). The optimal weight percentage of wool–Pd was found to be 3.0 wt %, which resulted in a high visible-light photocatalytic average H2-production rate of 1555 μ mol/h. It showed that the recycled cocatalyst wool–Pd could improve the efficiency of photocatalytic hydrogen production because of introducing oxidation cocatalyst PdS and reduction cocatalyst Pd. This study indicated that the prepared recyclable cocatalyst wool–Pd not only could improve the efficiency of photocatalytic hydrogen production, but also eco-friendly and recyclable.Graphical abstractHighlights► A novel wool–Pd cocatalyst was prepared. ► Wool–Pd can improve the efficiency of CdS photocatalytic activity. ► Wool–Pd is eco-friendly and recyclable.

TiO2/reduced graphene oxide composite (T-rGO) was synthesized and its performance was evaluated with photocatalytic hydrogen evolution. It was found that the hydrogen evolution rate of T-rGO increased significantly after injecting small amount of air into the vacuum pumped and UV irradiated sealed reaction cell. The IR, XPS, Raman and ESR spectra analysis indicated that the O2•−, which generated from the reaction of photoinduced electrons and the injected O2 can moderately and controllably increase the oxygen groups on graphene planar of T-rGO at ambient condition. The amount of oxygen groups on graphene planar of T-rGO will affect the p-doping concentration of graphene, thus affect the p–n junction and the performance of T-rGO for photocatalytic hydrogen evolution.Graphical abstractHighlights► The O2•−, which generated from the reaction of photoinduced electrons and O2 can increase the oxygen groups on graphene planar in TiO2/graphene composite at ambient condition. ► This O2•− oxidation is moderate and controllable. ► Moderate oxidized graphene by O2•− can significantly promote the photocatalytic hydrogen evolution performance of the TiO2/graphene composite.

It is found that low-temperature synthesized nanoTiO2 particles and reduced graphene oxide (rGO) would make up for each other's shortcomings: on the one hand, negatively charged nanoTiO2 particles could obviously enhance the dispersion of rGO. The nanoTiO2–rGO colloid synthesized at a low temperature (95 °C) remained stable for at least 6 months; on the other hand, for the ultrathin and transparent nanoTiO2–rGO films prepared using this stable colloid, rGO loading could enhance the connection of the nanoTiO2 particles and the substrate and therefore effectively increase the photocurrent to 4.8 times more than the photocurrent generated by pure nanoTiO2. The as-prepared transparent flexible film can be shaped into triangular calandrias which could make full use of the incident UV light, and thus increase the removal efficiency from the pass through of gas-phase acetaldehyde.

Hydrogen energy has been regarded as the most promising energy resource in the near future due to that it is a clean and sustainable energy. And the heterogeneous photocatalytic hydrogen production is increasingly becoming a research hotspot around the world today. As visible light response photocatalysts for hydrogen production, cadmium sulfide (CdS) is the most representative material, the research of which is of continuing popularity. In the past several years, there has been significant progress in water splitting on CdS-based photocatalysts using solar light, especially in the development of co-catalysts. In this paper, recent researches into photocatalytic water splitting on CdS-based photocatalysts are reviewed, including controllable synthesis of CdS, modifications with different kinds of cocatalysts, solid solution, intercalated with layered nanocomposites and metal oxides, and hybrids with graphenes etc. Finally, the problems and future challenges in photocatalytic water splitting on CdS-based photocatalysts are described.

Clean Pt/TiO2 with highly dispersed controlled Pt nanocrystals was prepared by a novel approach combining an in situ polyol process with light induced photocatalysis oxidation. The interaction between TiO2 and Pt under the assistance of surfactants hinders the agglomeration. The preference to form three dimensional clusters as the cluster size increases enables the formation of controlled Pt nanocrystals.

Protonated layered perovskite oxides H1.9K0.3La0.5Bi0.1Ta2O7 (HKLBT) and H1.6K0.2La0.3Bi0.1Nb2O6.5 (HKLBN), which were prepared from K0.5La0.5Bi2M2O9(M = Ta; Nb)(KLBT(N)) by H ion-exchange in 3M HCl solution, were found as good photocatalysts for water splitting under UV light irradiation. The characterization by XRD, ICP and TG revealed that HKLBT(N) retained layered structure of their parent materials KLBT(N) after HCl treatment. An amount of exfoliation of Bi during the protonated process caused the decrease of contribution of Bi 6p in conduction band (CB) and thus resulted in more negative CB potential. HKLBT(N) showed considerable higher photocatalytic activity for H2 and/or O2 evolution than KLBT(N) in the absence of sacrificial reagents, which was attributed to the higher position of conduction band and the layered structure after acid treatment. It was concluded that the interlayer modification via ion-exchange for layered K0.5La0.5Bi2M2O9 (M = Ta; Nb) is a potential way to construct novel photocatalysts with high activity for water splitting.Highlights► H1.9K0.3La0.5Bi0.1Ta2O7 and H1.6K0.2La0.3Bi0.1Nb2O6.5 were prepared. ► Photocatalyst for H2 and/or O2 evolution in the absence of sacrificial reagents. ► Protonated layered perovskite oxides could be used as novel photocatalysts.

TiO2 (P25)–graphene (P25–GR) hybrids were prepared via solvothermal reaction of graphene oxide and P25 using ethanol as solvent. The as-prepared P25–GR nanocomposites were characterized by X-ray diffraction, Raman spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, photoluminescence emission spectroscopy and ultraviolet-visible (UV–vis) diffuse reflectance spectroscopy. The results indicated that P25–GR nanocomposites possessed enhanced light absorption ability and charge separation efficiency. As photocatalysts, P25–GR hybrids were much better than the bare P25, when they were used in the hydrogen evolution from aqueous methanol solution under Xe-lamp illumination. A significant enhancement in the rate of hydrogen production was achieved through using P25–GR as photocatalysts, comparing to bare P25. The optimum mass ratio of GR to P25 in the hybrids was 0.5 wt%. The higher mass ratio of GR in P25–GR would decrease the photocatalytic activity of P25.Highlights► P25–graphene hybrids are prepared via solvothermal reaction of GO and P25. ► The hybrids possess high light-absorption ability and charge-separation efficiency. ► The hybrids show the higher rate of hydrogen production than bare P25.

A series of metal oxide solid solutions Bi1−xDyxVO4 and Bi0.5M0.5VO4 (M = La, Sm, Nd, Gd, Eu, Y) were synthesized by solid state reaction at high temperature and characterized by XRD, UV–vis DRS, BET, SEM. Bi1−xDyxVO4 showed two crystal structures with the component content. For 0.3 ≤ x ≤1.0, the structure was tetragonal type, while that was monoclinic when x = 0. For 0.1 ≤ x < 0.3, tetragonal and monoclinic structures had been observed. Bi1−xDyxVO4 solid solutions of tetragonal type could split water into H2 and O2 simultaneously when loaded with 0.3 wt% Pt and 1 wt% Pt-Cr2O3 respectively as cocatalyst. Among these catalysts, Bi0.5Dy0.5VO4 showed the best photocatalytic activity for water splitting under UV light irradiation. Besides, Bi0.5M0.5VO4 (M = La, Sm, Nd, Gd, Eu, Y) were also prepared and discovered to be of tetragonal type as same as Bi0.5Dy0.5VO4. They performed high photocatalytic activities of splitting pure water into H2 and O2 under UV light irradiation when loaded with 1 wt% Pt-Cr2O3. The activities of Bi0.5M0.5VO4 (M = Dy, La, Sm, Nd, Gd, Eu, Y) solid solutions indicated band-gap engineering of metal oxide solid solutions was the feasible method to obtain a photocatalyst for overall water splitting.Highlights► Bi0.5M0.5VO4 solid solutions were novel highly efficient V-based photocatalysts for water splitting. ► Bi0.5M0.5VO4 solid solutions loaded with 1 wt% Pt-Cr2O3 were high efficient photocatalysts for overall water splitting. ► Incorporation of M is dispensable for H2 production.

Novel Bi0.5M0.5VO4 (BMV; M=La, Eu, Sm and Y) solid solutions were prepared and studied in this paper. All the samples were proved to produce H2 and O2 simultaneously from pure water under the irradiation of UV light. M–O bond lengths were proved to increase with M cations by refining cell parameters and atomic positions. Besides, band gaps, energy gaps and photocatalytic activities of BMV also changed with M cations. Both of M–O and V–O bond lengths were suggested to account for this phenomenon. Inactive A0.5Y0.5VO4 (A=La, Ce) for water splitting proved incorporation of Bi rather than distortion of VO4 tetrahedron was a critical factor for improving efficiency of overall water splitting by facilitating the generation of electron and hole with lighter effective masses. Replacement of Bi by M cations not only gave indirect effect on band structure but also raised position of conduction band minimum to meet requirement of H2 production.Graphical abstractNovel Bi0.5M0.5VO4 (M=La, Eu, Sm and Y) solid solutions showed the high and stable photocatalytic activities for overall water splitting with their crystal radii of M elements. Highlights► BMV solid solutions were novel highly efficient V-based photocatalysts for overall water splitting. ► Photocatalytic activity of BMV solid solution related to the effective ionic radii of M cations. ► Incorporation of Bi is one of key factors for the highly efficient activity of BMV solid solution. ► Incorporation of Y is dispensable for H2 production.

Series of photocatalysts K4R2M10O30 (R = Y, La, Ce, Nd, Sm; M = Ta, Nb) were presented as iso-structural compounds by solid-state reaction method. These photocatalysts showed water decomposition activities under λ > 300 nm irradiation with Na2SO3 and AgNO3 solution acting as hole and electron scavenges respectively. Among them, R = Ce demonstrated water decomposition activities under visible light irradiation (λ > 420 nm) and R = La showed overall water splitting activities under λ > 300 nm irradiation. The first principle calculation based on density functional theory with Plane-wave pseudo potential method and Generalized Gradient Approximation was conducted on M = Nb as representatives to investigate their electronic structure closely, so did on their precursor oxides. Combined with the electronic structures and absorption properties, the band structures of K4R2M10O30 (R = Y, La, Ce, Nd, Sm; M = Ta, Nb) were proposed and this model of band structure is in good agreement with their photocatalytical activities. Furthermore, the visible light responsive ability of R = Ce, as the only one among them, is regarded as the hybridization and overlap of partial occupied and unoccupied Ce 4f with O 2p and Nb 4d (Ta 5d), while in other cases, the band gap transition from O 2p to Nb 4d Ta (5d), which mainly consist their valence band and conduction band respectively, is dominant. Furthermore, there showed obvious inherent relationship between K4R2M10O30 (R = Y, La, Ce, Nd, Sm; M = Ta, Nb) and their precursor rare earth oxides in terms of electronic structure and photophysical properties.Graphical abstractHighlights► Photocatalysts K4R2M10O30 (R = Y, La, Ce, Nd, Sm; M = Ta, Nb) were presented. ► These photocatalysts showed water decomposition activities under λ > 300 nm. ► Only R = Ce showed photocatalytical activities under λ > 420 nm. ► Their electronic structures were studied based on the first principle calculation. ► The band structures were proposed and showed good agreement with activities.

The influence of the nature of TiO2 support and platinum salt precursors on the state and CO catalysis oxidation activity of supported platinum on TiO2 was investigated in this paper. Variations of the support TiO2 and platinum precursor significantly influenced the CO catalytic oxidation activity of platinum. X-ray diffraction, transmission electron microscopy, in situ diffuse reflectance infrared Fourier transform spectroscopy, and X-ray absorption fine structure analysis of the Pt/TiO2 catalysts were carried out to correlate the relationship between the state of platinum and CO catalysis activity. The dispersion of Pt on different TiO2 surfaces using diammine dinitritoplatinum as precursor decreased in the following order: Pt/rutile TiO2 (rutile phase TiO2 synthesized by hydrothermal method), Pt/anatase TiO2 (by sol–gel method), and Pt/rutile TiO2 (by sol–gel method). CO catalysis activity of Pt supported on different TiO2 decreased with the decrease of Pt dispersion. Chloroplatinic acid played an important role in the formation of electron-rich platinum with lower Pt–Pt and Pt–O coordination number on rutile TiO2 (hydrothermal) surface compared to that using diammine dinitritoplatinum as a metal salt precursor, which contributed to the highest CO catalysis oxidation activity.

Pt/TiO2 catalysts prepared by sol–gel and wetness impregnation methods were investigated for the selective catalytic reduction (SCR) of NO by C3H6 in the presence of excess oxygen. The characteristics of the prepared catalysts were analyzed through XRD, BET surface area, NO temperature programmed desorption (TPD), and NO/C3H6 temperature programmed oxidation (TPO). The effects of the crystalline phase of TiO2, O2/C3H6 concentration, and Pt loading amount have been studied. It was found that when bare support was impregnated with the noble metal Pt, the NO removal efficiency increased significantly. In particular, under the condition of 150 ppm NO, 150 ppm C3H6, and 18 vol % O2, balanced with Ar, 0.5 wt % Pt loaded TiO2 calcined at 500 °C could achieve a complete C3H6 conversion and 47.03% NOx reduction simultaneously at 180 °C. This enhanced activity may be associated with its outstanding activities in the TPO processes of NO to NO2 and C3H6 to CO2. The pure anatase crystal form together with its relatively high specific surface area for TiO2 sample calcined at 500 °C was suggested to be responsible for such an enhancement. The research results also suggested that higher concentration of O2 and higher concentration of C3H6 favored NO removal, and Pt loading played an important role in the SCR process.

Novel CdS nanomaterials were synthesized by a simple “one-pot” hydrothermal biomolecule-assisted method using glutathione (GSH) as the sulfur source and structure-directing reagent. Various morphologies of CdS photocatalysts, such as solid nanospheres (s-CdS), hollow nanospheres (h-CdS) and nanorods (r-CdS), were obtained by controlling only the hydrothermal temperatures. The X-ray diffraction patterns confirmed that all of the samples were typical hexagonal wurtzite CdS. It was found that the absorption edge of s-CdS was at 465 nm with a greater blue shift compared to that of h-CdS and r-CdS. The photocatalytic activity of s-CdS was superior to that of h-CdS and r-CdS under visible light. Photoluminescence measurements revealed their different photogenerated electron/hole recombination ability, which was in accordance with the order of s-CdS < h-CdS < r-CdS. The excellent photocatalytic activity of s-CdS was ascribed to the small sizes of sub-nanocrystallites, which make it easy for photoinduced electrons and holes on the solid sphere to migrate to the surface and react with water and the sacrificial agent quickly. It was crucial to control the temperature for preparing CdS photocatalysts via hydrothermal methods. The formation mechanism of different morphology might be due to complexation, S–C bond rupture, spherical aggregation and Ostwald ripening processes.

The electronic properties of spinel-type CuFe2O4 material and the adsorption behavior of NO molecule on CuFe2O4 (100) surface were studied by using density functional theory method with on-site correction for Coulomb interaction (DFT+U). Our studies suggest that the ground state of CuFe2O4 bulk has an inverse spinel structure, which is a magnetic semiconductor. On the inverse spinel-type CuFe2O4 (100) surface, NO molecule prefers to adsorb on the top site of surface Fe atom with the formed N–Fe bond. The adsorption energy, electronic properties, and structures were investigated to provide an initial understanding to the catalysis of NO molecule over CuFe2O4 surface.

The CdS/TiO2 composites were synthesized using titanate nanotubes (TiO2NTs) with different pore diameters as the precursor by simple ion change and followed by sulfurization process at a moderate temperature. Some of results obtained from XRD, TEM, BET, UV–vis and PL analysis confirmed that cadmium sulfide nanoparticles (CdSNPs) incorporated into the titanium dioxide nanotubes. The photocatalytic production of H2 was remarkably enhanced when CdS nanoparticles was incorporated into TiO2NTs. The apparent quantum yield for hydrogen production reached about 43.4% under visible light around λ = 420 nm. The high activity might be attributed to the following reasons: (1) the quantum size effect and homogeneous distribution of CdSNPs; (2) the synergetic effects between CdS particles and TiO2NTs, viz., the potential gradient at the interface between CdSNPs and TiO2NTs.

ZrW2O8 prepared by hydrothermal reaction was found to act as a photocatalyst for water splitting under UV light irradiation. It has good activity for water splitting to evolve H2 and O2 steadily in the presence of CH3OH and AgNO3 as electron donor and electron scavenger respectively. With respect to the band structure for photocatalytic water splitting, ZrW2O8 (4.0 eV) was found to be superior to ZrO2 (5.0 eV) with a wider band gap and WO3 (2.7 eV) with CB bottom more positive than the reduction potential of H+ to H2. The improvement of the band structure was attributed to the hybridization of W5d and Zr4d in conduction band (CB) as well as the change in crystal structure. Moreover, the absorption edge of ZrW2O8 was significantly extended to visible-light region by sulfur anion doping, and H2 could be evolved over Pt/S-ZrW2O8 under irradiation up to 360 nm in the presence of CH3OH while O2 could be evolved over S-ZrW2O8 under irradiation up to 510 nm in the presence of AgNO3. The visible-light sensitization was attributed to the S3p states, which increased the width of the VB itself and caused the decrease in the band gap energy.

ZrW2O8 was prepared by adjusting Zr:W mole ratio and HCl concentration in hydrothermal reaction processes. The obtained sample was crystallized in α-ZrW2O8 phase (cubic, P213), with band gap energy of 4.0 eV. The properties of photocatalytic water splitting were examined under UV light irradiation. The average rate of H2 evolution over 0.3wt% Pt/ZrW2O8 in the presence of CH3OH as electron donor (ED) was 23.4 μmol/h, while the average rate of O2 evolution over ZrW2O8 in the presence of AgNO3 as electron scavenger (ES) was 9.8 μ mol/h. Moreover, H2 was evolved over 0.3wt% Pt/ZrW2O8 from pure water splitting at a rate of 5.2 μ mol/h. The study indicated that the band structure of ZrW2O8 was suitable for reducing H+ to H2 and oxidizing H2O to O2. The band structure and photocatalytic water splitting properties of ZrW2O8, different from either ZrO2 (5.0 eV) or WO3 (2.7 eV), were attributed to the hybridization of W5d and Zr4d in conduction band (CB) as well as the change in crystal structure.

A set of anatase titanium dioxide (TiO2) films coated on foam nickel that modified by Al2O3 films as transition layer (indicated as TiO2/Al2O3 films) were synthesized via sol-gel route. The bulk and surface properties of the TiO2/Al2O3 films were characterized by thermal gravimetric and differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), field-emission scanning electron microscope (FE-SEM), and BET. The photocatalytic activities of TiO2/Al2O3 films were investigated based on the degradation of gaseous acetaldehyde under ultraviolet (UV) irradiation. The foam nickel is a promising substrate material in practical applications because of its excellent hydrodynamic properties for gas passing. The TiO2/Al2O3 composite films showed much higher photocatalytic activity and stability for degradation of gaseous acetaldehyde than the onefold TiO2 films. The significant enhancement in photocatalytic activity and stability can be ascribed to the coating of Al2O3 transition layer, which concentrates the target substances around TiO2 particles and increases the specific surface area (SSA) of the substrate (the SSAs of bare foam nickel and Al2O3 modified foam nickel are 0.12 and 113.7 m2/g, respectively) to provide more sites for TiO2 loading.

This paper presented a new hybrid process of vacuum ultraviolet (VUV) and TiO2/UV for the decomposition of gaseous formaldehyde (HCHO) at a typical indoor concentration level. The performance was assessed by a preliminary technical and economic analysis. Concentration, flow velocity, relative humidity and light intensity were investigated as process variables. The synergistic or combination effect between VUV and TiO2/UV was attained by comparing the experimental conversions with the calculated ones based on the purifier-in-series efficiency model. The results showed that the proposed hybrid process can be technically feasible and economically attractive for the decomposition of gaseous HCHO. The outstanding merit of the hybrid process is the complementation of advantages of VUV and TiO2/UV. VUV improved the conversion of HCHO markedly on the basis of TiO2/UV. Ozone produced by VUV could be decomposed by TiO2/UV and its concentration was less than the maximum recommended by the WHO at the flow velocity of 0.75 m/s or more. There was weak combination effect between VUV and TiO2/UV and the behavior was analyzed in terms of the actions of ozone. The hybrid process was more economical than the TiO2/UV process with a cost reduction of 60% for removing per kg HCHO.

A magnetically separable photocatalyst Bi12TiO20/SiO2/NiFe2O4 (BSN) with a typical ferromagnetic hysteresis was prepared by a simple process: the magnetic 200 wt% SiO2/NiFe2O4 (SN) dispersion prepared by a liquid catalytic phase transformation method and the visible-light-active photocatalyst Bi12TiO20 prepared by a simple coprecipitation processing were mixed, sonificated, dried, and calcined at 550 °C. The prepared photocatalyst showed high photocatalytic activity for the degradation of methyl orange in water under UV irradiation and visible-light irradiation (λ>400 nm), and it was easy to be separated from a slurry-type photoreactor under the application of an external magnetic field, being one of promising photocatalysts for wastewater treatment. Transmission electron microscope (TEM) and X-ray diffractometer (XRD) were used to characterize the structure of the photocatalyst, indicating that the magnetic SN particles adhered to the surface of the Bi12TiO20 congeries. SiO2 layer round the surface of NiFe2O4 nanoparticles prevented effectively the injection of charges from TiO2 particles to NiFe2O4, which gave rise to the increase in photocatalytic activity.

The photocatalytic production of H2 in one step is potentially one of the most promising ways for the conversion and storage of solar energy. The paper overviews our recent studies on the photocatalysts splitting water into hydrogen under irradiation. The attention was mainly focused on the promotion effects of nanosized modifications in the interlayer and surface of photocatalysts for hydrogen evolution with visible light. The photocatalytic activity depended significantly on modification techniques, such as loading, proton exchange, and intercalation. The formation of a “nest” on the particle surface promoted a uniform distribution and strong combination of the nanosized particles on the surface of catalysts. By the methods of intercalation and pillaring as well as by selecting both host and guest, a large variety of molecular designed host–guest systems were obtained. Cadmium sulfide (CdS)-intercalated composites showed higher activity and stability. This activity of K4Ce2M10O30 (M=Ta, Nb) evolving H2 under visible light irradiation was enhanced by the incorporation of Pt, RuO2 and NiO as co-catalysts. Especially, the nanosized NiOx (Ni–NiO double-layer structure) greatly prompted the photocatalytic H2 evolution significantly.

Metal oxide photocatalysts K4Ce2M10O30 (M=Ta, Nb) capable of responding to visible light were synthesized by conventional high temperature solid-state reaction. The photocatalysts have an appropriate band gap energy ca. 1.8–2.3 eV and excellent chemical potential level to evolve H2 from aqueous solutions containing a sacrificial electron donor (Na2SO3) under visible light irradiation (λ>420nm) without any co-catalyst. When they were loading with Pt, RuO2 and NiOx, the activities for evolving H2 were prompted markedly. By SEM and TEM investigations, it can be seen that these loading metal and metal oxides are dispersed on the surface of photocatalysts K4Ce2M10O30 (M=Ta, Nb) in diameter of about 10–30 nm particles, especially the NiOx loading even formed double layered structure with metal nickel (Ni) and metal oxide (NiO). The reasons for the increasing activities after these loading may be attributable to facilitate electron migrating from the conduction band of K4Ce2M10O30 (M=Ta, Nb) to the Pt, RuO2 and NiOx nanoparticles, which function as H2 production sites on the surface of catalysts. The same phenomenon appears on the solid solution K4Ce2Ta10−xNbxO30 (x=0–10x=0–10) with loading RuO2.

Visible-light-driven TiN thin films with (1 1 1) preferred orientation were deposited on monocrystalline (1 0 0) silicon wafer by a cathodic arc technique. Properties of the sample were identified by XRD, AFM and UV–vis absorption spectrum. The TiN film is a novel photocatalyst having not only a narrow band gap (ca. 2.0 eV) corresponding to the visible light absorption, but also a sufficient potential for H2 evolution from the reduction of H+ in water, representing one of novel photocatalyst candidates for continuous hydrogen evolution from water decomposition using solar energy. It was suggested that the semiconductivity and photocatalytic properties of the prepared TiN thin film resulted from the feature of preferred orientation.

A visible-light-active photocatalyst Bi12TiO20 with sillenite structure was prepared by a simple co-precipitation method. The spectrum of UV–vis absorption indicated that the absorption edge of the Bi12TiO20 was at 450 nm, corresponding to the band gap energy of 2.75 eV. The prepared Bi12TiO20 showed high photocatalytic activity for the degradation of phenol in water either under UV (300 nm < λ < 400 nm) or visible light (λ > 400 nm) irradiation. The photodegradation experiments of phenol indicated that the prepared photocatalyst calcined at 550 °C had the best photocatalytic activity.

Nitrogen (N)-doped TiO2 samples with high specific surface areas were directly prepared by heating the mixture of urea and TiO2, where the TiO2 was obtained with titanium tetrachloride as precursor. The absorption spectrum of the N-doped TiO2 shifted to wavelength up to 600 nm with increasing urea contents. X-ray photoelectron spectroscopic measurements showed that the N presented in TiO2 was in the state of both molecularly chemisorbed N2 and substituted N. While both of them contribute to the response to visible light, the latter gave the prepared samples with hydrogen evolution under visible light. The apparent photocatalytic activity of water splitting demonstrated as high amount of H2 evolution was partly due to the phase transformation from anatase to rutile for the N-doped TiO2.

Anatase TiO2 films were successfully prepared on foam nickel substrates by sol-gel technique using tetrabutyl titanate as precursor. The characteristics of the TiO2 films were investigated by XPS, XRD, FE-SEM, TEM and UV-Vis absorption spectra. The photocatalytic activities of TiO2 films were investigated by photocatalytic degradation reactions of gaseous acetaldehyde, an indoor pollutant, under ultraviolet light irradiation. It was found that Ni2+ doping into TiO2 films due to the foam nickel substrates resulted in the extension of absorption edges of TiO2 films from UV region to visible light region. The pre-heating for foam nickel substrates resulted in the formation of NiO layer, which prevented effectively the injection of photogenerated electrons from TiO2 films to metal nickel. The TiO2 films displayed high photocatalytic activity for the degradation of acetaldehyde, and were enhanced by calcining the substrates and coating TiO2 films repeatedly. The high activity was mainly attributed to the improvement of the characteristics of substrate surface and the increase of active sites on photocatalyst.

TiO2 photocatalysts coated on foam nickel were prepared by sol–gel method. Al2O3–SiO2 films introducing as transition interlayer between TiO2 and nickel metal foam were used to promote the photocatalytic activity of TiO2. The results show that TiO2/Al2O3–SiO2 composite films have much higher photocatalytic activity and stability for degradation of gaseous acetaldehyde than TiO2 films. The significant enhancement effect arises from the large specific surface area of Al2O3–SiO2, which provides more active sites for subsequent TiO2 loading and photocatalytic reaction. The Al2O3–SiO2 interlayer also inhibits the transfer of photo-generated electron from TiO2 to Ni metal and improves the photocatalytic activity of photocatalysts. Furthermore, Pt loading on TiO2 by photo-deposition was carried out to improve photocatalytic efficiency. The acetaldehyde degradation rate on Pt-loaded TiO2 photocatalyst is more than three times than that of TiO2 without Pt loading. The optimum Pt concentration is 0.3 wt%. XRD, UV–vis and SEM were used to characterize the structural, physical and chemical features of all the samples and to reveal the mechanism of the improvement of the photocatalytic activity. The effects of photocatalyst preparation parameters along with their photocatalytic behavior in deactivation and reactivation are also presented in the present study.

Diesel soot, a major contributor to PM emission, severely threatens human health and the environment. Catalytic oxidation of trapped diesel soot is a feasible solution to alleviating this problem. In this study, highly active Co–Ce catalysts were synthesized by the citric acid complex method and their catalytic behaviour was investigated by means of TG analysis. The best catalytic performance was acquired over the Co0.93Ce0.07 catalyst with T10 = 315 °C and T50 = 370 °C. These catalyst samples were also characterized by XRD, Raman spectrum, soot-TPR, H2-TPR, O2-TPD, XPS and in situ Raman spectra. Cerium cations were partially incorporated into the lattice of Co3O4 in Co–Ce mixed oxides, which led to the lattice expansion. This structure modification brought about a series of changes in the surface and the lattice of these catalysts. The capability of oxygen adsorption and desorption was slightly improved, and the redox ability of mixed oxides was intensified owing to the strong interaction between Co3O4 and CeO2. Surface lattice oxygen and bulk lattice oxygen could also be activated at a lower temperature. Moreover, active oxygen species (superoxide and peroxide) as well as carbon–oxygen intermediates (carbonyl and formate species) were discovered in soot combustion. Reactions for producing formate species were important steps for the soot–O2 reaction. The enhanced effects of both redox mechanism and oxygen spillover mechanism were probably due to the synergistic effect between the two oxides.

Clean Pt/TiO2 with highly dispersed controlled Pt nanocrystals was prepared by a novel approach combining an in situ polyol process with light induced photocatalysis oxidation. The interaction between TiO2 and Pt under the assistance of surfactants hinders the agglomeration. The preference to form three dimensional clusters as the cluster size increases enables the formation of controlled Pt nanocrystals.

Photodeposition of H2PtCl6 in the presence of methanol promotes the formation of highly dispersed, metallic Pt nanoparticles over titania, likely via capture of photogenerated holes by the alcohol to produce an excess of surface electrons for substrate-mediated transfer to Pt complexes, resulting in a high density of surface nucleation sites for Pt reduction. Photocatalytic hydrogen production from water is proportional to the surface density of Pt metal co-catalyst, and hence photodeposition in the presence of high methanol concentrations affords a facile route to optimising photocatalyst design and highlights the importance of tuning co-catalyst properties in photocatalysis.