Synthesis And Photocatalytic Performance Of Multi-vanadate Heterojunction Photocatalyst

Semiconductor-based heteronanostructures with high carriers-flow steering,high activity and high stability in visible-light-driven multi-component photocatalytic system have been of great concern due to its long-standing demand in the wide application of environmental protection and energy conversion.However,the construction of multi-component nanocrystals usally undergos multiple complex steps,which restricts its application.In this paper,the one-step preparation of zinc vanadate heterojunction photocatalyst based on phase transition strategy was discussed,and the photocatalytic performance of zinc vanadate heterojunction for photocatalytic degradation of phenols and other organic pollutants under visible light was studied in depth and systematically.It is worth further exploring the preparation,modification and application of zinc vanadate catalysts.1.We successfully reported the facile design and synthesis of a novel double Z-scheme Zn₃?VO₄?₂/Zn₂V₂O₇/ZnO ternary heteronanostructure system?THS?via self-phase transition on basis of heating the Zn₃?OH?₂V₂O₇·2H₂O precursor synthesized by a low-cost microwave hydrothermal assistant,which exhibited excellent photocatalytic performances.In this case,the employment of Zn₃?OH?₂V₂O₇·2H₂O acted as the heteronanostructure precursor was the key for fabricating the THS material,which not only boosted the interaction within its structure and but also maintained the mesoporous nanosheet structure.It had been proved that Zn₃?OH?₂V₂O₇·2H₂O firstly lost its H₂O and then the partial Zn₃?VO₄?₂ underwent the self-phase transition process to produce Zn₂V₂O₇ and ZnO?Zn₃?OH?₂V₂O₇·2H₂O?Zn₃?VO₄?₂?Zn₂V₂O₇+ZnO?,which obtained the double Z-scheme THS.Accordingly,the interfacial-dominated photocatalysis reactivities such as the removal of phenols and dyes were applied as ideal experiments to verify the photocatalytic performance of the constructed double Z-scheme THS material.It was proved that the narrow band gap,intimate contact interface,the wider visible light absortion and more efficient charge carriers transfer and separation played important role in high visible-light photocatalytic ability and stable cycling.Moreover,PL spectra,radicals trapping experiments and ESR tests confirmed that the nontraditional transport of photoinduced h⁺and e^-caused by double Z-scheme mechanism played important role in efficiently removing target pollutants.In which the sample roasted at 700 ? had the best photocatalytic degradation over phenols.Within 150 minutes,the degradation rates of bisphenol A,phenol and p-chlorophenol were 77%,75%and 98%,respectively.Such a synthetic approach maybe render double Z-scheme THS to promote the development and large-scale applications of the hetero-transition metal vanadates.2.It is important to further explore the influence of pH on the morphology,structure,surface states,crystalline phase and the optimum pH condition of Z-scheme TSH materials.The morphology and photocatalytic performance were successfully optimized via adjusting the pH condition during the synthesis of Zn₃?OH?₂V₂O₇·2H₂O precursor.In which the experimental results showed that with increasing synthesized pH could promote the transformation of Zn₃?OH?₂V₂O₇·2H₂O from micron-sized bulk to nanosheet and improve the crystallinity of prepared samples,which enhanced the absorption of ultraviolet light by THS materials and promoted the separation of photoinduced electrons-hole pairs.The dye degradation experiments showed that THS material synthesized at pH=10 has the best photocatalytic performance at the same calcination temperature?700 ??.The samples synthesized at pH>6 had excellent photocatalytic activity,and with the increase of pH,the photocatalytic performance first enhanced and then weakened.The performance of photocatalytic degradation of dyes followed the pattern:pH=10/T=700 ?>pH=8/T=700?>pH=12/T=700 ?>pH=6/T=700 ?.3.To further improve the visible light harvesting and the utilization of photoinduced electron-hole pairs,a novel Ag₃VO₄/Zn₃?VO₄?₂/Zn₂V₂O₇/ZnO quaternary heterojunction?Ag₃VO₄/Zn-V-O?was constructed via a phase transformation and in-situ precipitation process.The well matched band structure among Ag₃VO₄,Zn₃?VO₄?₂ and Zn₂V₂O₇semiconductors greatly enhanced the light harvesting and suppressed the recombination of photoinduced electron-hole pairs in Ag₃VO₄/Zn-V-O quaternary heterojunction,producing more·OH and·O₂^- radicals to participate in decomposing the organic pollutants.Under visible light irradiation,Ag₃VO₄/Zn-V-O quaternary heterojunction exhibited excellent photocatalytic performance for phenols degradation.Within 25 minutes,50% Ag₃VO₄/Zn-V-O had the most excellent photocatalytic performance on bisphenol A and the degradation rate was 85.91%.Within 50 minutes,the degradation rates of phenol and p-chlorophenol by 50% Ag₃VO₄/Zn-V-O were 70.39%and 79.68%,respectively,indicating that Ag₃VO₄/Zn-V-O had good application prospects on phenols degradation,especially for the degradation of bisphenol A.