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Abstract: Although NiCoP has attracted much attention in the field of electrocatalysis, the study of its photocatalytic activity and mechanism have been somewhat limited. NiCoP/g‐C3N4, synthesized by simple one‐pot method, is a highly efficient photocatalyst for hydrogen production from water. NiCoP/g‐C3N4 exhibits a hydrogen evolution rate of 1643 μmol h−1 g−1, which is 21 times higher than that of bare g‐C3N4. The excellent performance is due to a combination of improved separation efficiency and effective charge transfer efficiency. The photogenerated charge behavior is characterized by the surface photovoltage (SPV), transient photovoltage (TPV), and photoluminescence spectroscopy. The photogenerated charge transport is investigated by electrochemical impedance spectroscopy and polarization curve. Moreover, the effective charge transfer efficiency was measured according to the mimetic apparent quantum yield. SPV and TPV measurements, whereby 10 vol % of a triethanolamine–water mixture was added into the testing system, were taken to simulate the real atmosphere for photocatalytic reaction, which can give rise to the photogenerated charge transfer process. A possible photocatalytic mechanism was also proposed. This study may provide an efficient theoretical basis to design transition metal phosphide cocatalyst‐modified photocatalysts. [ABSTRACT FROM AUTHOR]

Bimetallic materials hold promise for improving catalyst activity, yet little is known about the photocatalytic mechanism that these systems undergo during photocatalytic reaction that lead to efficient catalyst. Herein, we synthesized g-C3N4 combined with PtNi x, which shows much higher photocatalytic activity than that of pure g-C3N4 and achieves the highest H2 evolution rate of 8456 μmol h−1 g−1 for 2.5 % PtNi x/g-C3N4. The excellent photocatalytic activity resulted from the enhanced charge-separation efficiency compared to the pristine g-C3N4, which was proved by surface photovoltage, photoluminescence, and transient photovoltage spectra. Electrochemical impedance spectroscopy in the dark further confirms the ability of charge transfer of 2.5 % PtNi x/g-C3N4 is superior to that of pure g-C3N4. This effective separation efficiency gives rise to the observed excellent photocatalytic activity. This study not only provides us with an efficient catalyst for water splitting, but opens new avenues for designing and developing platinum-based photocatalysts. [ABSTRACT FROM AUTHOR]

The photocatalytic activity of cobalt phthalocyanine (CoPc) immobilized onto MCM-41 was investigated for decomposition of methyl orange in aqueous solutions. The morphology and structure of the catalyst were analyzed by diffuse reflectance ultraviolet-visible (DR UV–vis), X-ray diffraction, Fourier transform infrared, and scanning electron microscopy (SEM). Photocatalytic efficiency of the prepared catalyst for degradation of methyl orange was tested under illumination of visible light. The photodegradation process is completed within 2 h using a dose of 0.04 g/L of the catalyst in the 0.05 g/L of methyl orange solution under Xenon lamp, and the removal rate was 98.3%. The obtained results revealed that the photocatalyst was very active in degradation of methyl orange. [ABSTRACT FROM PUBLISHER]

A facile synthetic route is presented that produces a porous Ga-In bimetallic oxide nanophotocatalyst with atomically thin pore walls. The material has an unprecedented electronic structure arising from its ultrathin walls. The bottom of the conduction band and the top of the valence band of the material are distributed on two opposite surfaces separated with a small electrostatic potential difference. This not only shortens the distance by which the photogenerated charges travel from the sites where they are generated to the sites where they catalyze the reactions, but also facilitates charge separations in the material. The porous structure within the walls results in a large density of exposed surface reactive/catalytic sites. Because of these optimized electronic and surface structures, the material exhibits superior photocatalytic activity toward the hydrogen evolution reaction (HER). [ABSTRACT FROM AUTHOR]

A series of nano-spindly BiVO 4 and Ag-BiVO 4 were synthesized by a simple solvothermal method. X-ray photoelectron spectroscopy (XPS) and high resolution electron microscopy (HRTEM) analysis indicated that the chemical state of the Ag particles was metallic Ag. Their photocatalytic activities were evaluated by the decolorization of rhodamine B (RhB) under visible light irradiation ( λ > 420 nm). The research of photoinduced charge properties of samples studied by surface photovoltage spectroscopy (SPS) and electric field-induced surface photovoltage spectroscopy (FISPS) measurement system and the results indicated that the existence of Ag attained the enhancement of photoinduced charge carriers’ separation. This was thought to be responsible for the higher efficient photocatalytic activity of Ag-BiVO 4 in the degradation of RhB. [ABSTRACT FROM AUTHOR]

With the purpose of high-efficiency separation of photo-generated charges and an improved photocatalytic performance, herein we report novel heterojunctions of p-type BiOBr and n-type ZnO constructed by loading amounts of BiOBr nanoflakes onto the surface of ZnO nanoflowers via a two-step hydrothermal/solvothermal method. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and UV-vis diffuse reflectance spectroscopy (UV-vis DRS) are employed to characterize the as-synthesized nanomaterials. The results indicate that p–n heterojunctions formed between BiOBr and ZnO. When evaluated as a photocatalyst for methyl orange (MO) decolorization, BiOBr–ZnO-40 shows excellent photocatalytic activity, superior to that of pristine BiOBr and ZnO. Notably, the photochemical process for the MO decolorization is elucidated by reactive species trapping and hydroxyl radical quantification experiments, suggesting that ṖOH and O2Ṗ− are the main oxygen active species for BiOBr–ZnO heterojunctions in the MO decolorization. Moreover, the separation and transfer process of photo-generated charges at the surface or interface of the BiOBr–ZnO composites is also investigated by means of surface photovoltage (SPV). On the basis of experimental and theoretical results, the enhanced photocatalytic activity mechanism for the BiOBr–ZnO heterojunctions is proposed. The effective separation and transfer of photo-generated charges are responsible for an improved photocatalytic performance due to the existence of the interfacial electric field located between BiOBr and ZnO. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) BiVO4/Bi2WO6 composite microspheres with enhanced visible-light (λ ＞ 420 nm) photodegradation activity of methylene blue (MB) were synthesized by a simple, one-pot, template-free solvothermal method. A mixture of ethylene glycol (EG) and H2O (volume ratio of EG-H2O was 1 : 1) was used as the solvent. To investigate the relationship between structure and photocatalytic performance, the as-synthesized samples were characterized by XRD, FESEM, HRTEM, UV-vis DRS, SPS and TPV. Structural characterizations indicated that the composite nanostructure mainly consisted of two single-crystal phases, which were BiVO4 and Bi2WO6. In addition, a possible growth mechanism of this microsphere composite and the separation process of photoinduced charge carriers in the heterojunction are discussed. [ABSTRACT FROM AUTHOR]

CuS/Zn0.8Cd0.2S composites have been successfully prepared by simple hydrothermal and cation exchange method. The Cu species loaded on Zn0.8Cd0.2S, together with the intimate contact formed between CuS and Zn0.8Cd0.2S, was clearly demonstrated with X-ray photoelectron spectroscopy and transmission electron microscopy. The optimized CuS/Zn0.8Cd0.2S photocatalyst has a high H2 evolution rate of 2792 μmol g−1 h−1 at CuS content of 3 wt% and the apparent quantum efficiency of 36.7% at 420 nm. The photophysical mechanism of the photocatalytic activity was investigated with the help of surface photovoltage spectroscopy (SPS) and transient photovoltage (TPV) techniques. The results revealed that photogenerated charge separation efficiency in Zn0.8Cd0.2S was enhanced and the photogenerated electrons were trapped by the loaded CuS, which benefits photo-reduction. Those were the reasons for significant enhancement in the photocatalytic H2 evolution from water splitting. [ABSTRACT FROM AUTHOR]

Abstract: Different morphologies of monoclinic BiVO4 with smaller size were hydrothermal synthesized by simply adjusting the amount of surfactant (polyvinyl pyrrolidone PVP K30) added. The detailed field emission scanning electron microscope (FESEM) analysis revealed that the amount of PVP added could significantly affect the morphology and size of BiVO4. Their photocatalytic activities were evaluated by the decolorization of methylene blue (MB) aqueous solution under visible-light irradiation (λ >400nm), and the as-prepared sample with well-assembled flower-like morphology showed a much higher photocatalytic activity due to larger specific surface area and higher separation efficiency of photo-induced carriers. The relationship between the behavior of photo-induced carriers and photocatalytic activity was studied using the surface photovoltage spectroscopy (SPS) and corresponding phase spectra. [Copyright &y& Elsevier]

Abstract: Carbon-doped anatase TiO2 was prepared by a facile hydrothermal process without adding additional carbon source. The as-prepared sample shows highly efficient photocatalytic activity, which only requires 4min and is about 11 times higher than that of Degussa P25 TiO2 in degradation of methyl orange (MO) dye under UV light irradiation. Moreover, a highly visible-light activity is also observed. UV–vis diffuse reflectance spectra and X-ray photoelectron spectroscopy confirm that the carbon atoms are incorporated into the interstitial positions of TiO2 lattice and form a strong interaction with titanium atoms and extend photoresponding range to 700nm. Surface photovoltage spectra (SPS) and transient photovoltage (TPV) suggest that the presence of interstitial carbons induce several localized occupied states in the gap, enhance the separation extent and restrain the recombination of the photo-induced electron and hole carriers in TiO2. [Copyright &y& Elsevier]

Abstract: ZnO nanostructures materials with two-dimensional (2D) plate-like and three-dimensional (3D) flower-like morphologies have been synthesized via facile hydrothermal process. Scanning electron microscopy (SEM), high resolution transmission electron microscope (HRTEM) and X-ray diffraction (XRD) have been used to characterize the samples. We have compared the surface photoelectric properties of flower-like ZnO with that of plate-like ZnO by means of surface photovoltage (SPV), field-induced surface photovoltage (FISPV), transient photovoltage (TPV) and surface photocurrent (SPC) techniques. Based on the photovoltage responses, the influence of the morphology on transfer characteristics of photogenerated charge carriers was discussed. The synthesized flower-like ZnO exhibited more efficient separation and transfer properties of photogenerated charge carriers than that of plate-like ZnO in the UV region due to the special flower-like hierarchical nanostructures. We have also evaluated the photocatalytic activity of the ZnO samples by photodegradation efficiency of RhB. The experiments demonstrated that RhB in aqueous solution was more efficiently photodegraded using flower-like ZnO than plate-like ZnO. The results also show the consistency between the carrier dynamics of photogenerated electron–hole pairs and photocatalytic activity. [Copyright &y& Elsevier]

Abstract: TiO2(B) was prepared by a facile green solvothermal method and further characterized by the powder X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), raman spectroscopy and nitrogen sorption analysis, and it has been found that the as-synthesized sample possesses a unique crystallites/nanopores structure and has a very large surface area (484m2 g−1). Surprisingly, it exhibits the very high photocatalytic activity and good stability for the decomposition of methyl orange (MO) compared to that of P25. [ABSTRACT FROM AUTHOR]

Abstract: The ZnO nanorods with different diameters (∼300, 100, 40nm) and nanoparticles (∼6nm) were prepared, and their sensitivities to formaldehyde at room temperature were measured with and without the UV light irradiation (the intensity of light is 0.155mW/cm2). The XRD, TEM and SEM were utilized to examine the size of crystal and the morphology of material. The transient photovoltage and photoluminescence spectra were utilized to investigate the photoelectric properties of ZnO. The ZnO nanorods with diameter of ∼40nm own the highest response to formaldehyde with the UV light illumination than that of other samples. It is attributed to the large surface-to-volume ratio and high photo-generated charge efficiency, which are two key parameters to determine the gas response. The transient photovoltage results further demonstrate that the photo-generated charge efficiency of gas sensing element decreases as the surface-to-volume ratio increases (i.e. the size of crystal decreases). Therefore, the particles with highest sensitivity are of a certain size, neither the largest nor the smallest tested. Our work may supply a direction to fabricate the high performance gas sensor with UV light illumination. [Copyright &y& Elsevier]

Abstract: Zinc oxide nanorods were synthesized using a simple hydrothermal method. Formaldehyde-sensing characteristics were investigated without and with ultraviolet (UV) light irradiation. The gas response of nanorods to 110ppm formaldehyde with UV light irradiation was about 120 times higher than that without UV light irradiation. The detection limit was as low as 1.8ppm at room temperature. This high gas response under the UV light is attributed to photocatalytic oxidation. Furthermore, the significant improvements of the selectivity and recovery time were obtained after irradiating the nanorods with UV light. Our results demonstrated that applying UV light irradiation on the zinc oxide nanorods is an effective approach to achieve higher response and excellent selectivity to formaldehyde at room temperature. [Copyright &y& Elsevier]

In this paper, a series of BiOI/ZnO photocatalysts containing various BiOI contents were prepared by a facile two-step synthetic method. The structure and crystal phase, morphology, surface element analysis, optical property of as-prepared samples are measured by X-ray diffraction (XRD), Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and UV–Vis diffuse reflectance spectrometry (DRS). BiOI/ZnO photocatalytic activities of the prepared photocatalysts were evaluated by photocatalytic degradation of phenol under simulated light irradiation. The phenol degradation rate reached 99.9% within 2 h under simulated solar light irradiation. The probable photocatalytic mechanism of composites photocatalysts is discussed by active species trapping experiments, the surface photovoltage (SPV), the transient photovoltage (TPV) and photoluminescence (PL) measurements. The results manifest that the superior photocatalytic activity of BiOI/ZnO composites is derived from the strong internal electric field between BiOI and ZnO, which is beneficial for the effective separation and transfer of photogenerated charges in ZnO. Moreover, the loading of BiOI on the surface of ZnO inhibited the recombination of photogenerated charge carriers in ZnO, resulting in excellent photocatalytic activity. On the contrary, the effect of an extension of the light absorption range induced by the introduction of BiOI on the phenol degradation activity is not significant. [ABSTRACT FROM AUTHOR]

In this study, Ce-doped ZnO photocatalysts are successfully prepared by using a simple and facile one-pot water bath method. The as-prepared samples are characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), ultraviolet–visible (UV–Vis) diffuse spectroscopy and Brunauer-Emmett-Teller (BET) surface area analysis. It is found that the as-synthesized Ce-doped ZnO possessed hollow porous structure, high surface areas and large pore volumes. The photocatalytic degradation efficiency (99%) of methyl orange (MO) with an optimal molar ratio of 0.3% Ce-doped ZnO is realized. The separation behavior of photogenerated electrons-holes pairs was investigated by surface photovoltage (SPV) and transient photovoltage (TPV) technique. The results illuminate that Ce element in Ce-doped ZnO tremendously promotes the separation of charges and inhibits the recombination of photogenerated charge carriers, corresponding to the excellent photocatalytic performance. [ABSTRACT FROM AUTHOR]

To better understand the behavior of photogenerated charges in the composite photocatalyst interface is beneficial to the designing of effective photocatalyst for photocatalytic reaction. In our work, the separation and transfer process of photogenerated charges in NiO/TiO 2 nanotube arrays (NiO/TiO 2 NTAs) has been studied by surface photovoltage (SPV) spectroscopy and transient photovoltage (TPV) measurement. Through the experimental results analysis, we find that an interfacial electric field is formed at NiO/TiO 2 NTAs interface, which is attributed to the work function difference between NiO and TiO 2 NTAs. The photogenerated holes in TiO 2 can transfer to the NiO layer along the interface electric field under the ultraviolet irradiation. A large amount of photogenerated holes can be separated effectively and then prolonged the holes lifetime to participate in the photocatalytic oxidation reaction. The above results show that the favorable hole-collecting process of NiO in the surface of TiO 2 NTAs is the main factor being responsible for the increase the photocatalytic efficiency. [ABSTRACT FROM AUTHOR]

Abstract: The ZnO microrods modified by Cu2O nanocrystals were prepared in aqueous solution. ZnO microrods acted as carrier to immobilize the Cu2O nanocrystals and improved the recovery rate from solution. The ZnO/Cu2O compounds promoted the separation of photo-induced electrons and holes, which was proved by surface photovoltage spectroscopy (SPS). Therefore, the compounds showed an enhanced photocatalytic activity than pure ZnO and pure Cu2O under both UV–vis light and visible light. [Copyright &y& Elsevier]

Abstract: The ZnO nanorods (diameter of 40nm and 100nm) were modified with Ru(dcbpy)2(NCS)2 (RuN3), and their responses to formaldehyde were measured at room temperature. All the results showed that the responses to formaldehyde of modified ZnO were higher than that of bare ZnO; especially the responses of modified ZnO nanorods with diameter of 40nm–5ppm formaldehyde was about 200% higher than that of bare ZnO. The UV–vis absorption spectrum and transient photovoltage analysis showed that the high responses of modified ZnO mainly arose from the strong photocatalytic oxidizing effect induced by the increasing of the absorption and photo-generated electron–hole separation. Our results demonstrate that the modification of RuN3 is a promising approach on improving the formaldehyde responses of ZnO nanorods. [Copyright &y& Elsevier]

Abstract: A water–dichloromethane interface-assisted hydrothermal method was employed to grow rutile TiO2 nanowires (NWs) on electrospun anatase TiO2 nanofibers (NFs), using highly reactive TiCl4 as precursor. The water–dichloromethane interface inhibited the formation of rutile NWs in water phase, but promoted the selective radial growth of densely packed rutile NWs on anatase NFs to form a branched heterojunction. The density and length of rutile NWs could be readily controlled by varying reaction parameters. A formation mechanism for the branched heterojunction was proposed which involved (1) the entrapment of rutile precursor nanoparticles at water–dichloromethane interface, (2) the growth of rutile NWs on anatase NFs via Ostwald ripening through the scavengering of interface-entrapped rutile nanoparticles. The heterojunction formed at anatase NF and rutile NW enhanced the charge separation of both under ultraviolet excitation, as evidenced by photoluminescence and surface photovoltage spectra. The branched TiO2 heterostructures showed higher photocatalytic activity in degradation of rodamine B dye solution than anatase NFs, and the mixture of anatase NFs, and P25 powders, which was discussed in terms of the synergistic effect of enhanced charge separation by anatase–rutile heterojunction, high activity of rutile NWs, and increased specific area of branched heterostructures. [Copyright &y& Elsevier]

Abstract: The N-doped anatase TiO2 photocatalysts were prepared via solvothermal and ethylenediamine reflux treatment, followed by the sequential calcination in air and NH3/N2 atmosphere. The resulting photocatalysts were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and UV–vis diffuse reflectance spectra. The results revealed that the prepared N-doped anatase TiO2 had characteristics of small crystallite size, large surface area, high crystallinity and visible light response. The prepared N-doped anatase TiO2 photocatalysts showed much higher photocatalytic activity than N-doped Degussa P25 for the degradation of phenol under both ultraviolet and visible light irradiation, owing to more highly oxidizing hydroxyl radical which was the main oxidative species responsible for the degradation of phenol. [Copyright &y& Elsevier]