•High-efficient Bi3O4Cl/g-C3N4 composite was prepared via a simple method.•The Bi3O4Cl/g-C3N4 can degrade RhB 3.8 times faster than g-C3N4.•The influence factors on the photoactivity of Bi3O4Cl/g-C3N4 were investigated.This paper presents a novel composite photocatalyst Bi3O4Cl/g-C3N4 composite which was synthesized by a simple mixing and calcination method. The synthesized composite was applied in photocatalytic degradation of rhodamine B solution under visible light irradiation. Results indicated that the Bi3O4Cl/g-C3N4 showed higher activity than pure g-C3N4 or Bi3O4Cl. The optimal sample presents a degradation rate of 0.019 min−1, which is 1.9 and 3.8 times of Bi3O4Cl and g-C3N4, respectively. Various techniques including thermogravimetric analysis (TG), N2 adsorption, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), UV–vis diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and photoluminescence spectroscopy (PL) were applied to investigate the characters of the composite and reveal the origin of the high photocatalytic activity. It is found that the coupling of Bi3O4Cl on g-C3N4 slightly increased the BET surface area of the photocatalyst. However, the main reason for the enhanced photoactivity could be ascribed to the synergetic effect between Bi3O4Cl and g-C3N4 in separating electron and hole pairs.

•Fe2(MoO4)3/g-C3N4 composite was prepared by a mixing-calcination method.•Fe2(MoO4)3/g-C3N4 showed high efficiency in RhB degradation.•The degradation rate of Fe2(MoO4)3/g-C3N4 is 7.8 times faster than that of g-C3N4.•Fe2(MoO4)3/g-C3N4 can generate hydrogen 6.6 time faster than g-C3N4.•The influence factors on the photoactivity of Fe2(MoO4)3/g-C3N4 were investigated.Novel Fe2(MoO4)3/g-C3N4 composites were synthesized by a facile mixing-calcination method. The photocatalytic activity of the Fe2(MoO4)3/g-C3N4 hybrid was evaluated via RhB degradation and H2-production under visible light irradiation. Results indicated that the Fe2(MoO4)3/g-C3N4 binary composite exhibited excellent photocatalytic activity. The optimal hybrid could produce hydrogen 6.6 times faster than pure g-C3N4 from water-methanol solution under visible light irradiation. For the photocatalytic degradation of RhB, it showed a degradation rate of 0.070 min−1, which was 7.8 times higher than that of pure g-C3N4. Moreover, the composite showed high stability and extensive adaptability in degradation of other organic pollutants. The N2 physical absorption measurement and UV–visible diffuse reflection spectroscopy suggested that the coupling of Fe2(MoO4)3 increased the BET specific surface area and visible light absorption, both of which favored the photocatalytic reaction. However, the main reason of the enhanced activities were attributed to the interfacial transfer of photogenerated electrons and holes between Fe2(MoO4)3 and g-C3N4, leading to the effective charge separation in the composite, which were evidenced by photoluminescence spectroscopy and photocurrent analysis. This work may provide some useful information for the future design and practical application of multifunctional hybrids photocatalysts in water purification.

•Novel CdV2O6/g-C3N4 composites are prepared via mixing-calcination method.•CdV2O6/g-C3N4 composite degrades RhB 4.5 × times faster than g-C3N4.•The influence factors on the photoactivity of CdV2O6/g-C3N4 are investigated.Novel CdV2O6/g-C3N4 hybrid system was synthesized by a facile mixing-calcination method. The photocatalytic test indicated that the decoration of CdV2O6 nanorods on g-C3N4 can significantly promote the photocatalytic activity in RhB degradation under visible light. The optimal CdV2O6/g-C3N4 sample exhibited a degradation rate of 0.041 min−1, which is 4.5 times higher than that of pure g-C3N4. Various techniques including N2 adsorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectroscopy (DRS), and photoluminescence (PL) spectroscopy were applied to investigate the origin of the enhanced photoactivity of CdV2O6/g-C3N4. The results indicated that the enhanced activities were mainly attributed to the interfacial transfer of photogenerated electrons and holes between CdV2O6 and g-C3N4, leading to the effective charge separation in the composite, which were evidenced by photoluminescence spectroscopy and photocurrent analysis. This work may provide some useful information for the future design and practical application of multifunctional hybrids photocatalysts in water purification.

•Novel Z-scheme SnO2−x/g-C3N4 composites are prepared and tested.•SnO2−x/g-C3N4 composite degrades RhB 8.8 times faster than g-C3N4 under visible light.•SnO2−x/g-C3N4 composites also show high activity in photocatalytic CO2 reduction.•The Z-scheme mechanism is verified by reactive species trapping experiment.Highly efficient SnO2−x/g-C3N4 composite photocatalysts were synthesized using simple calcination of g-C3N4 and Sn6O4(OH)4. The synthesized composite exhibited excellent photocatalytic performance for rhodamine B (RhB) degradation under visible light irradiation. The optimal RhB degradation rate of the composite was 0.088 min−1, which was 8.8 times higher than that of g-C3N4. The SnO2−x/g-C3N4 composite also showed high photocatalytic activity for CO2 reduction and photodegradation of other organic compounds. Various techniques including Brunauer–Emmett–Teller method (BET), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectroscopy (DRS), photoluminescence spectroscopy (PL) and an electrochemical method were applied to determine the origin of the enhanced photoactivity of SnO2−x/g-C3N4. Results indicated that the introduction of SnO2−x on g-C3N4 increased its surface area and enhanced light absorption performance. More importantly, a hetero-junction structure was formed between SnO2−x and g-C3N4, which efficiently promoted the separation of electron–hole pairs by a direct Z-scheme mechanism to enhance the photocatalytic activity. This study might represent an important step for the conversion of solar energy using cost-efficient materials.

A novel FeVO4/g-C3N4 composite photocatalyst was synthesized via a simple mixing-calcination method and characterized by various techniques including the Brunauer–Emmett–Teller method, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, UV-vis diffuse reflectance spectroscopy, photoluminescence spectroscopy, and an electrochemical method. The photocatalytic activity was evaluated by degradation of rhodamine B (RhB). Results indicated that the FeVO4/g-C3N4 composite exhibited a much higher photocatalytic activity than pure g-C3N4 under visible light illumination. The rate constant of RhB degradation for the optimal FeVO4/g-C3N4 composite (5.0% FeVO4/g-C3N4) is approximately 2.2 times that of pure g-C3N4. The formation of a heterojunction structure between FeVO4 and g-C3N4 which efficiently promoted the separation of electron–hole pairs was believed to be the origin of the enhanced photoactivity.

The visible-light-driven ZrO2/g-C3N4 hybrid photocatalysts were prepared by direct heating of ZrO2 and melamine. Compared to pure g-C3N4 or ZrO2, the synthesized ZrO2/g-C3N4 exhibited much higher photocatalytic activity for rhodamine (RhB) degradation under visible light irradiation. In order to reveal the origin of the high photoactivity, the ZrO2/g-C3N4 composites were characterized by various techniques including N2 adsorption, thermogravimetric analysis (TG), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance spectroscopy (DRS), photoluminescence spectroscopy (PL), and electrochemical methods. The characterization results demonstrated that ZrO2 nanoparticles were well distributed on the surface of g-C3N4. Although the anchoring of ZrO2 on g-C3N4 increased the surface area and light absorption ability, the hetero-junctions formed between the two semiconductors which retarded the recombination of electrons and holes were believed to result in the enhanced photoactivity of the ZrO2/g-C3N4 composite. In addition, it was found that holes and ˙O2− generated in the photocatalytic process played a key role in RhB degradation over the ZrO2/g-C3N4 hybrids.

The objective of this research was to prepare, characterize, and evaluate two new composite photocatalysts: t-LaVO4/g-C3N4 and m-LaVO4/g-C3N4. The two catalysts were synthesized with m-LaVO4 or t-LaVO4 and g-C3N4, and characterized by various techniques including Brunauer–Emmett–Teller method (BET), thermogravimetric analysis (TGA), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), ultraviolet–visible-light (UV-vis) diffuse reflectance spectroscopy (DRS), and photoluminescence (PL) spectroscopy. The structure characterizations indicate that the two composites have similar phase composition. Both of them consist of LaVO4 and g-C3N4. Meanwhile, their photoabsorption performance is also similar. The photocatalytic test indicates that both m-LaVO4 and t-LaVO4 can effectively promote the photoactivity of g-C3N4, as demonstrated with the PL and photocurrent–time experiments, although the optimal concentrations of LaVO4 in the two catalysts are different. Both LaVO4/g-C3N4 and t-LaVO4/g-C3N4 are promising photocatalysts for degradation of RhB.

•Novel SiO2/g-C3N4 composite was synthesized by a simple mixing-calcination method.•The SiO2/g-C3N4 composite degraded RhB 2.5× faster than g-C3N4 under visible light.•The origin of the increased photoactivity was discussed.•The addition of SiO2 decreased the aggregation of g-C3N4 stack layers.A visible-light driven SiO2/g–C3N4 composite was prepared by heating a mixture of SiO2 and melamine. The products were characterized by X-ray diffraction, Brunauer–Emmett–Teller analysis, transmission electron microscopy, and ultraviolet–visible diffuse reflectance spectroscopy. Results indicate that the composite only contained SiO2 and g-C3N4. The addition of SiO2 had minimal influence on light absorption, but the specific surface area was increased. In addition, the aggregation of g-C3N4 in the SiO2/g-C3N4 composite was weakened. The increased surface area and decreased aggregation of g-C3N4 are considered as the cause of the strong activity of the SiO2/g-C3N4 composite in RhB photodegradation.

•Novel graphene/SmVO4 composite is prepared and tested.•Graphene/SmVO4 composite degrades RhB 4×times faster than SmVO4 under visible light.•The promotion effect of graphene was investigated.Graphene(GR)/SmVO4 composite was prepared by a facile mixing-calcination method and characterized by X-ray diffraction (XRD), Raman spectroscopy, N2 adsorption, and transmission electron microscopy (TEM) techniques. Results showed that SmVO4 nanoparticle adhered on graphene sheet in GR/SmVO4 composite. The photoactivity of the synthesized composite was evaluated by the photodegradation of Rhodamine (RhB). In comparison with pure SmVO4, the graphene/SmVO4 system illustrated much higher photocatalytic activity due to the contribution of GR in RhB adsorption and charge separation. 2% GR/SmVO4 exhibited the highest photocatalytic efficiency with a degradation rate of 0.62 h−1, which is 4 and 1.6 times higher than that of SmVO4 and N–TiO2, respectively.

DyVO4/graphitic carbon nitride (DyVO4/g-C3N4) composite photocatalyst with visible-light response was prepared by a milling and heating treatment method. The synthesized powder was characterized by X-ray diffraction, thermogravimetry/differential thermal analysis, N2 adsorption, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, and UV–vis diffuse reflection spectroscopy. The activity of composite photocatalyst DyVO4/g-C3N4 for photodegradation of rhodamine B is much higher than that of either single-phase g-C3N4 or DyVO4. The obviously increased performance of DyVO4/g-C3N4 is mainly ascribed to the electron–hole separation enhancement at the interface of the two semiconductors, as proven by photoluminescence spectroscopy and photocurrent measurement. In addition, it is found that holes and •O2– are the main active species in the photocatalytic oxidation of RhB solution in the presence of DyVO4/g-C3N4 composite.

The present paper reports a novel visible light-driven photocatalyst, Sr0.25Bi0.75O1.36 prepared by a simple impregnation–calcination method. Brunauer–Emmett–Teller analysis, scanning electron microscopy, X-ray diffraction, Raman spectroscopy, diffuse reflectance spectroscopy and density functional theory were applied to investigate the physical/photophysical properties and electronic structure of the catalyst. The photocatalytic activity of Sr0.25Bi0.75O1.36 was evaluated by the decomposition of methylene blue (MB) in an aqueous solution under visible light irradiation (λ > 420 nm). Pure Sr0.25Bi0.75O1.36 is found to possess an optical band gap of 2.43 eV and exhibit excellent photocatalytic activity for MB photodegradation. The theoretical calculations show that the electronic structure of the photocatalyst favors the mobility of photo-generated charge carriers and positively contributes to the photocatalytic reaction. The good photoabsorption and special electronic structure are believed to be the origin of the high activity of the photocatalyst.Highlights► Pure Sr0.25Bi0.75O1.36 crystal is synthesized by impregnation–calcination method. ► Sr0.25Bi0.75O1.36 crystal is found to possess an optical band gap of 2.43 eV. ► Sr0.25Bi0.75O1.36 shows excellent activity for methylene blue degradation. ► The electronic structure of Sr0.25Bi0.75O1.36 is the origin of the high activity.

This paper presents a novel visible-light-driven catalyst, a SO42–/MoOx/MgF2 composite, which was synthesized by a simple solution method. Multiple techniques, including Brunauer-Emmett-Teller (BET), scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and diffuse reflectance spectroscopy (DRS) were applied to investigate the physical and photophysical properties of the catalysts. The photocatalytic activities were evaluated in the degradation of acetone in gas phase. In the photodegradation of acetone, the highest conversion was obtained over a catalyst containing 5 mol % molybdenum. The XRD and Raman characterizations indicate that the molybdenum oxide was highly dispersed in the MgF2 matrix. These MoOx species might be the active sites of the catalysts, which is the reason for the visible-light response of the composite catalyst. The MgF2 matrix acts to isolate the MoOx species and retard the electron–hole pair recombination. When the molybdenum concentration is >5 mol %, crystalline MoO3 phase was observed. The large MoO3 particle would decrease the separation efficiency. Thus, the photocatalytic activity was reduced. Besides the molybdenum concentration, the calcination temperature also shows a great effect on the activity. A sulfated 5 mol % MoOx/MgF2 catalyst that was calcined at 350 °C showed the highest photocatalytic activity. Based on the results of the characaterization, the origin of the high activity was discussed. The light absorption ability and the MoOx size effect are considered as the key factors.

This article presents a novel visible-light-driven catalyst, an LaVOx composite that was prepared from La(NO3)3 and NH4VO3 solutions. The visible-light-induced photocatalytic activity of this composite was evaluated by the degradation of acetone. Results indicate that the LaVOx composite exhibits high activity for acetone photodegradation. The highest acetone conversion (93.1%) was obtained with the La1V1.5Ox catalyst. Its photo-activity and ability for complete oxidation could be enhanced further by doping with a small amount of the metal platinum. Physical and photophysical properties of the LaVOx composite catalysts were evaluated by X-ray diffraction (XRD), the Brunauer–Emmett–Teller (BET) method, Raman spectroscopy (Raman), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), UV–vis diffuse reflectance spectroscopy (DRS), and photoluminescence (PL) spectroscopy. Based on the results of this investigation, the coupling effect of m-LaVO4 and V2O5 was identified as generating the high activity in catalysis.Graphical abstractResearch highlights► V2O5–LaVO4 composite is a novel visible-light driven catalyst. ► The LaVOx composite shows high activity for acetone degradation under visible light irradiation. ► The coupling effect of m-LaVO4 and V2O5 is the origin of the high activity.

A series of MoTeOx/SiO2 and MoBiTeOx/SiO2 catalysts was prepared and catalytic performance of propane partial oxidation to acrolein was tested. The addition of low amount of Bi component to MoTeOx/SiO2 catalysts was found to significantly promote acrolein selectivity. The catalyst structure and redox properties were investigated by means of X-ray powder diffraction, Raman spectroscopy, in situ Raman spectroscopy, X-ray photoelectron spectroscopy, and H2-TPR techniques. Results indicate that the Bi promotive effect can be attributed to two possible reasons. One is that the Bi component promotes the dispersal of MoO3. The isolation effect results in acrolein selectivity increase. Another reason is that Bi doping enhances lattice oxygen diffusion and increases the amount of surface active oxygen, which is responsible for the oxidation of intermediate propylene to acrolein.The doping of Bi promoted the dispersal of MoO3 and enhanced lattice oxygen diffusion, the catalytic performance of MoBiTeOx/SiO2 was thus increased.

This paper presents the synergetic effect of Te2MoO7 and MoO3 (WO3) in the partial oxidation of propylene to acrolein. The study found that the addition of MoO3 (or WO3) to Te2MoO7 greatly promoted the propylene conversion and acrolein yield. As the results of the investigation revealed, the higher catalytic performance could be attributed to the increased acidity, which is beneficial for the adsorption of propylene.

AbstractA detailed study on the synergetic effect of TeMo5O16 and MoO3 phases in the MoTeOx catalysts for the partial oxidation of propylene to acrolein has been reported in this work. It was found that both propylene conversion and acrolein selectivity increased with the addition of MoO3 to TeMo5O16. Based on the results of N2 adsorption-desorption, XRD, XPS, in-situ XRD, O2-TPO, and 2-propanol decomposition reaction, the higher catalytic performance and synergetic effect could be attributed to the enhancement of acidity and the oxygen transfer from TeMo5O16 to MoO3 phase.

•Novel AgBr/Bi3O4Br composite was prepared via an ion-exchange method.•AgBr/Bi3O4Br composite degrades RhB 2.5× times faster than Bi3O4Br does.•The origin of the high activity of AgBr/Bi3O4Br was investigated.AgBr/Bi3O4Br composite was successfully prepared via one-step ionic reaction between Bi3O4Br and AgNO3 solution, and characterized by multi techniques including XRD, Raman, XPS, DRS, PL and transient photocurrent response. Results indicate the synthesized AgBr/Bi3O4Br composite is actually a ternary system of Ag/AgBr/Bi3O4Br, which displays excellent photocatalytic activity in Rhodamine B degradation due to the contribution of AgBr and Ag in charge separation. 5% AgBr/Bi3O4Br composite has the highest photocatalytic efficiency with a degradation rate of 0.032 min−1, which is 2.5 times higher than that of pure Bi3O4Br.