•Coral-like BiVO4/g-C3N4 with high specific surface area was synthesized.•Direct Z-scheme mechanism was proposed and confirmed by ESR and TA-PL experiments.•The mineralization rate of the optimum one is 4.5 times as high as that of g-C3N4.A coral-like direct Z-scheme BiVO4/g-C3N4 photocatalyst was synthesized by a calcination method for the photocatalytic oxidation of toluene. The structures and optical properties of the photocatalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), the Brunauer–Emmett–Teller (BET) method and UV–Vis diffuse reflectance spectroscopy (DRS). BiVO4/g-C3N4 composites exhibited coral-like structures, with well-defined boundaries and high specific surface area (33.97 m2 g−1) compared to a g-C3N4 sample (5.627 m2 g−1). The introduction of BiVO4 to g-C3N4 greatly enhanced the photocatalytic efficiency. For the optimum BiVO4/g-C3N4 photocatalyst, the degradation rate constant and mineralization rate of toluene were 3.2 and 4.5 times greater, respectively, than those of pure g-C3N4 under visible light (λ > 400 nm). A direct Z-scheme mechanism is proposed for the enhanced photocatalytic activity and was further confirmed by electron spin-resonance spectroscopy (ESR) and terephthalic acid photoluminescence (TA-PL) experiments. This study demonstrated a coral-like BiVO4/g-C3N4 photocatalyst for the efficient photocatalytic oxidation of toluene and provided some understanding for designing direct Z-scheme photocatalysts.

•The all-solid-state Z-scheme g-C3N4/Au/P25 was fabricated via two-step process.•The Z-scheme system supports vectorial electron transfer of P25→Au→g-C3N4.•The g-C3N4/Au/P25 is favorable for electron–hole pairs separation.•The induced Au can enhance visible light absorption due to the SPR effect.•The g-C3N4/Au/P25 exhibits super photocatalytic performance for H2 evolution.We constructed an all-solid-state g-C3N4/Au/P25 Z-scheme system combining graphitic carbon nitride (g-C3N4) and P25 with Au nanoparticles, as an electron mediator, for hydrogen production under visible-light irradiation (λ > 400 nm). The g-C3N4/Au/P25 system was characterized by X-ray diffraction (XRD), transmission electronic microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV–Vis diffuse reflection spectroscopy (UV–Vis DRS), photoluminescence (PL), time-resolved photoluminescence (TRPL), and electrochemical measurements. TEM and high-resolution transmission electron microscopy (HRTEM) clearly reveal the morphology and structure of g-C3N4/Au/P25, implying the existence of the all-solid-state Z-scheme system. The results of electrochemical impedance spectroscopy (EIS) and TRPL indicate that the Z-scheme system can effectively promote the electron transfer rate and the separation of photogenerated electron–hole pairs for the vectorial electron transfer of P25→Au→g-C3N4. The Z-scheme system can also extend the visible light absorption wavelength from 460 to 700 nm due to the surface plasmon resonance (SPR) effect of Au nanoparticles, which is confirmed by UV–Vis DRS and incident photo-to-current efficiency (IPCE) measurements. The synergistic effect of the all-solid-state g-C3N4/Au/P25 Z-scheme system and the Au-induced SPR results in a highly efficient photocatalytic performance with a turnover frequency (TOF) of 259 μmol h−1 g−1, which is 30 times higher than that of pristine g-C3N4.

•An all-solid-state Z-scheme photocatalyst BiVO4/RGO/Bi2O3 was synthesized.•The obtained BiVO4/RGO/Bi2O3 displayed the strongest visible light harvest.•RGO interlayer plays an important role in charge carriers separation.•Photocatalytic mineralization of indoor toluene was carried out upon visible light.•The photocatalytic mineralization rate of BiVO4/RGO/Bi2O3 arrived to 95.6%.To improve the photocatalytic mineralization efficiency of indoor toluene under visible light irradiation, an all-solid-state Z-scheme based on the photocatalyst of BiVO4/reduced graphene oxide/Bi2O3 was developed. High-resolution transmission electron microscopy (HRTEM) clearly revealed that reduced graphene oxide (RGO) was anchored between BiVO4 and Bi2O3 particles. The red-shift in the UV–vis diffuse reflectance spectra (DRS) implied the adequate amount of visible light harvesting of the particles. Photocurrent density vs. time and Tafel curves indicated the high electron mobility of the particles. Electronchemical impedance spectroscopy (EIS) measurement implied the increased charge separation efficiency of the particles. The larger specific surface area indicated that full contact occurred between the photocatalyst and the pollutant. As a result, the BiVO4/RGO/Bi2O3 Z-scheme photocatalyst exhibited improved photocatalytic activity, with a mineralization rate that reached up to 95.6%. Electron spin resonance (ESR) proved that the photoinduced radical species (OH and O2−·) were involved for photocatalytic mineralization of toluene. This work represents a new method to design an all-solid-state Z-scheme photocatalyst with enhanced visible-light driven photoactivity toward indoor air pollutants purification.Download high-res image (156KB)Download full-size image

NH3 is a potential hydrogen energy carrier. Here we use alcohols as hole scavengers to investigate the nitrogen photofixation mechanisms including direct and indirect electron transfer processes. The t-butanol system exhibited the highest quantum yield of 36.1%, ascribing to the in situ-formed indirect electronic transmitter ˙CO2−.

•The band gap position of (AgNbO3)1−x(SrTiO3)x can be tuned continuously.•S0.75 presents the highest photocatalytic hydrogen evolution.•The metallic silver exhibits an evident effect on photocatalytic activity.(AgNbO3)1−x(SrTiO3)x samples were successfully employed as photocatalysts for photocatalytic hydrogen evolution under visible light. The samples were characterized by a series of techniques, including X-ray diffractometry, scanning electron microscopy, UV–Vis spectrophotometry, and electrochemistry technology. The band gaps of (AgNbO3)1−x(SrTiO3)x solid solutions can be tuned continuously from 3.21 to 2.65 eV and the flat-band potentials (Vfb) can be shifted positively from −0.79 to −0.31 V vs. SHE when x decreased from 1 to 0. Band positions of (AgNbO3)1−x(SrTiO3)x samples were further testified by density functional theory, suggesting that the band gap narrowing of the solid solutions derived from the hybridization of (Ti 3d and Nb 4d) and (O 2p and Ag 4d) orbital. The photocatalytic activities of samples for H2 evolution with Pt cocatalyst were evaluated in aqueous methanol solution under visible light irradiation. The highest photocatalytic activity was obtained at (AgNbO3)0.25(SrTiO3)0.75. Photocatalytic activity in hydrogen evolution of these solid solutions proved to be closely dependent on band structures.

In the 1910s, TiO2 began to be used in building materials as pigments and opacifier due to its excellent optical property. Since the photocatalytic property of TiO2 was observed in 1972, its application field was expanded to air cleaning and sterilization. Thereafter, people added TiO2 into building materials to develop novel and facile building materials. These materials were widely used for air cleaning, sterilization, self-cleaning, anti-fogging, decoration, and building cooling. The combination of building and other functions can serve simultaneously. Although TiO2-based building materials have bright prospects, some aspects such as improving the stability and enhancing photoactive performance of the materials are of importance for future research.

Nanosized TiO2 particles were prepared by solvothermal method using tetrabutyl titanate as precursor, ethanol and water as solvents, and a facile immobilization method of nanosized TiO2 particles on woven glass fabric was developed. The samples obtained under various preparation conditions were characterized by means of thermo gravimetric analysis (TG) and differential scanning calorimetry (DSC), X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution-transmission electron microscopy (HR-TEM), and Brunauer-Emmett-Teller (BET). The results show that the cube-shape of TiO2 prepared by solvothermal method has good crystallinity of (101) surface, higher thermal stability and large specific surface area. Scanning electron microscopy (SEM) images confirmed that the immobilized TiO2 film was uniformly distributed and clung to the substrate firmly. The photocatalytic activity of the catalysts was tested using photocatalytic oxidation of gaseous benzene. The results show that the TiO2 calcined after solvothermal treatment suffers from lower specific surface area, and hence decreases its photocatalytic activity. The photocatalytic activities of the TiO2 by solvothermal treatment with or without calcination in degradation 400 mg/m3 benzene are 3.7 and 4.1 times as high as catalyst without solvothermal treatment, respectively.

The direct UV photodegradation of Diacryl Red X-GRL was studied in an immersion photochemical reactor equipped with monochromatic UV source of 253.7 nm. Different process parameters that may influence the UV photodegradation were studied. These parameters included temperature, pH, radiation flow rate of UV lamp, carrier gas flow rate, initial concentration of dye, concentration of t-BuOH, and the concentration of dissolved oxygen. Four possible photodegradation pathways of dye in the presence of dissolved oxygen were assumed to be as follows: homolysis of excited dye to radicals; electron transfer of excited dye to form radical dye cation; decomposition by superoxide radical anion; and decomposition by singlet oxygen. Based on photodegradation pathways the photodegradation rate equation was derived, and the overall quantum yield of photodegradation was determined using Line Source Spherical Emission Model (LSSE Model), which describes the radiation flow rate absorbed by the solution in the photodegradation process. The overall quantum yield is enhanced enormously from 0.46 × 10−3 in the absence of dissolved oxygen to 7.35 × 10−3 in the presence of 1.21 × 10−3 M dissolved oxygen. However, the temperature had negative effect on the overall quantum yield, which varied from 8.54 × 10−3 at 288 K to 5.53 × 10−3 at 308 K. Finally, by using non-linear regression analysis, the overall quantum yield was correlated to be a function of temperature and dissolved oxygen in a modified Arrhenius equation with activation energy of 11.3 kJ mol−1.

To improve the separation rate of photogenerated electrons and holes, a SnO2/rutile TiO2 (R-TiO2)/anatase TiO2 (A-TiO2) photocatalyst modified by Pt nanoparticles with three pairs of heterojunctions was fabricated by a facile hydrothermal method. Transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) clearly illustrated the structure of the three pairs of heterojunctions connected to each other. Heteronanostructure photocatalysts with increased specific surface area could offer more active sites when contacting pollutants, resulting in improved photocatalytic activity. The red shift in UV–vis diffuse reflectance spectra (DRS) indicated the utilization of visible-light. Photoluminescence (PL) and photoelectrochemical (PEC) measurements suggested the enhancement of electron and hole separation, in accordance with the results obtained for the photocatalytic oxidation of decomposing toluene over 4 h. A catalyst containing 1 wt % Pt/10 at. % SnO2/R-TiO2/A-TiO2 exhibited the best photocatalytic mineralization rates of toluene: 40.9% and 72.3% under visible-light and UV-light irradiation, respectively. A proposed mechanism was elaborated to reveal the effective photocatalytic progress of charge transfer along multiple pathways along the three pairs of heterojunctions doped with Pt.

NH3 is a potential hydrogen energy carrier. Here we use alcohols as hole scavengers to investigate the nitrogen photofixation mechanisms including direct and indirect electron transfer processes. The t-butanol system exhibited the highest quantum yield of 36.1%, ascribing to the in situ-formed indirect electronic transmitter ˙CO2−.