Microstructure Regulation And Photocatalytic Property Of ? Phase Stannous Tungstate

The narrow band gap(an indirect band gap at around 1.7 eV)and strong UV-vis absorption capacity of?-SnWO₄ make it be a potential sunlight-driven photocatalyst.However,the photogenerated electrons and holes of?-SnWO₄ are easy to recombine,which will significantly reduce the photocatalytic activity of?-SnWO₄ and limit its practical applications in photocatalytic field.Aiming at the current problem that photogenerated electrons and holes are easy to recombine in?-SnWO₄,this paper adopted morphological control,heterostructure construction and ion doping to realize the regulation and optimization of microstructures.The photocatalytic properties of?-SnWO₄ under different microstructure regulation were studied with methyl orange(MO),rhodamine B(RhB)and tetracycline hydrochloride(TC)as target pollutants.The results proved that the three microstructure regulation methods all achieved the purpose of improving the photocatalytic property of?-SnWO₄.The research results are as follows:(1)Using ethylene glycol(EG)as the solvent,the morphology of?-SnWO₄ was transformed from nanostrip to nanosheet and its size was controlled by adjusting the water contents in EG.In the solvothermal process,the nucleation and growth rates of?-SnWO₄were controlled by the slow release of stannous alkoxide formed by the chelation of EG and Sn²⁺and the mass transfer capacity of the solvent.The photocatalytic results showed that?-SnWO₄(?-SW-10)prepared with a water content of 10 vol%had a photodegradation efficiency of 90.4%for MO in 30 min,exhibiting the good photocatalytic activity.(2)Ag nanoparticles(Ag-NPs)were modified on the surfaces of?-SnWO₄nanosheets to construct the Ag-NPs/?-SnWO₄ heterostructures.Good dispersion of Ag-NPs on?-SnWO₄ nanosheets was achieved by adjusting the concentration of silver ammonia solution.The photodegradation efficiencies of all Ag-NPs/?-SnWO₄heterostructures for MO were higher than that of pure?-SnWO₄.The heterojunction with a Ag⁺/Sn²⁺molar ratio of 5%had the best photocatalytic property,and the photodegradation efficiency reached 97.1%after 70 min.It was concluded that the surface plasmon resonance(SPR)effect produced by Ag-NPs enhanced the visible light absorption capacity of heterojunctions;the Schottky barrier formed between Ag-NPs and?-SnWO₄ nanosheets facilitated the separation of photogenerated carriers and thus improved the photocatalytic properties of Ag-NPs/?-SnWO₄ heterostructures.(3)Using?-SnWO₄ as a template and taking advantage of the negatively charged characteristic of its precursor,SnS quantum dots(QDs)were in-situ anchored on the surface of?-SnWO₄ by a one-pot hydrothermal process to form a direct Z-scheme heterojunction with intimate contact.The size and dispersion of SnS QDs were controlled by changing the molar ratios of S^2-/W⁶⁺,and the average particle size of SnS QDs with good dispersion was 2.2 nm.In the photodegradation of MO,RhB and TC,the photocatalytic properties of SnS QDs/?-SnWO₄ heterojunctions were better than that of pure?-SnWO₄.The sample with a S^2-/W⁶⁺molar ratio of 2%showed best photodegradation efficiencies,which were 95.6%(90 min),97.6%(240 min)and 57.0%(180 min)for MO,RhB and TC,respectively.The direct Z-scheme heterojunction formed by SnS QDs and?-SnWO₄ not only improved the separation ability of photogenerated carriers,but also accelerated the migration of carriers,effectively solving the problem of high recombination rate of photogenerated electrons and holes in?-SnWO₄.(4)The photocatalytic property of?-SnWO₄ was optimized by doping La³⁺into the crystal lattice of?-SnWO₄ to form specific defect energy levels such as La_Sn^· and V_Sn^''.The sample doped with 1 mol%La³⁺had photodegradation efficiencies of 94.9%(20 min),98.6%(300 min)and 53.9%(180 min)for MO,RhB and TC,respectively,and exhibited the excellent photocatalytic property.The improved photocatalytic property of?-SnWO₄was related to the defect La_Sn^· which was near the bottom of the conduction band.The photoinduced electrons were captured and transferred to O₂ by La_Sn^·,which effectively separated the photogenerated electrons and holes.In this paper,the photocatalytic property of?-SnWO₄ had been significantly improved by means of solvent effect,heterostructure construction and doping,and the corresponding enhancement mechanism of photocatalytic property had been analyzed based on the microstructure level.In particular,the preliminary studies on the degradation of pharmaceutical pollutants(TC)showed that?-SnWO₄ had the ability of photodegradation of pharmaceutical pollutants,and the photocatalytic property may be further improved.This laid a solid foundation for the future application of?-SnWO₄ in the treatment of medical pollutants.