Study On Photoelectrochemical Properties Of Bismuth Tungstate Nanocomposites

The development of visible light driven photocatalysts has attracted much attention in the past few decades.A large amount of research has focused on semiconductor photocatalysts,mainly involving water decomposition and degradation of organic pollutants under ultraviolet or visible light irradiation.Titanium dioxide?TiO₂?is found to be the most effective photocatalyst under ultraviolet light and is therefore the most commercially available.However,TiO₂ can only be excited by ultraviolet light irradiation corresponding to 3-4%of the solar spectrum.The use of visible light-driven photocatalysts not only increases outdoor photocatalytic activity,but also extends indoor applications where there is little exposure to ultraviolet light.There are two main strategies for developing new visible light catalysts.The first is the doping of TiO₂,which is intended to extend its absorption into the visible range.However,the methods used for doping element introduction are not fully controlled,and the low thermal stability of these compounds limits their application.The second strategy is to use other materials that absorb in the visible range.Bismuth tungstate?Bi₂WO₆?appears to be a good candidate for photoelectrocatalysis because it has a band gap in the visible range,due to the interaction between the 6s Bi and 2p O orbitals at the top of the valence band.In addition,it is chemically and thermally stable and non-toxic.Bi₂WO₆ is a promising photocatalyst with excellent stability,efficient electron transport properties,and high photocatalytic activity under visible light.Here,we show a simple template-assisted route for the vertical growth of Bi₂WO₆ nanosheet arrays on a conductive glass substrate by combining hydrothermal reaction with annealing.These Bi₂WO₆ nanosheet arrays show much higher photocurrent densities than conventional particle photoanodes because of their unique vertical sheet structure for fast charge transport.In this paper,Bi₂WO₆ nanosheets are the core,supplemented by noble metal,sulfides and in-situ growth methods,focusing on improving their photoelectrochemical performance.The combination of ultraviolet-visible source and scanning electrochemical microscope?UV-vis/SECM?is a platform for in-depth exploration of photoelectrochemical performance of bismuth tungstate-based nanocomposites from the perspective of micro-interface dynamics.This work mainly has the following three aspects,the specific research content is as follows:1.Multichannel charge-carrier transfer in Z-scheme Bi₂WO₆/Au/Bi₂S₃ heterostructure with enhanced photoelectrochemistry performance.We designed a Z-scheme Bi₂WO₆/Au/Bi₂S₃ heterostructure with anion exchange and in-situ growth amorphous Bi₂S₃ on Bi₂WO₆ nanosheets.When the Au NPs are embedded the contact interface between Bi₂WO₆ and Bi₂S₃,the photoelectrochemical performance was significantly improved compared to its case on the amorphous Bi₂S₃ surface.The Au NPs modified between the two have two effects,one is the S-Au bond,and the other is the role of S-Bi bond between newly formed Bi₂S₃,the Au NPs only have the former effect on the surface.In addition,highly dispersed gold nanoparticles act as a recombination center to promote the transfer efficiency of photogenerated electrons.We used a self-built ultraviolet-visible/scanning electrochemical microscope?UV-vis/SECM?platform to characterize the kinetic constant of electron transfer at the microinterface of four materials in-situ from the microinterface angle.It was found that Bi₂WO₆/Au/Bi₂S₃ exhibited faster interfacial electron transfer behavior than Bi₂WO₆/Bi₂S₃/Au.2.Convert the surface bismuth enrichment layer into a favorable Bi₂WO₆/BiOCl heterojunction to improve its photoelectrochemical performance.BiOI nanosheets were first transformed into Bi₂WO₆ nanosheets,and then Bi₂WO₆/BiOCl heterojunction was obtained by handling the surface of Bi₂WO₆nanosheets with dilute hydrochloric acid.Bi₂WO₆ nanosheets grown vertically on a conductive glass substrate exhibit a much higher photocurrent density than conventional particle photoanodes because of their unique vertical sheet structure,which facilitates rapid charge transfer.Thus,Bi₂WO₆/BiOCl heterojunction photoelectric chemical properties comparsion with merely some Bi₂WO₆ performance has been significantly increased.Furthermore,the kinetic parameters of microinterface electron transfer were characterized by UV-vis/SECM platform established by our laboratory,found that Bi₂WO₆/BiOCl has more active sites than Bi₂WO₆ surface and exhibits faster interface electron transfer behavior.3.Photoelectrochemical performance of molybdenum disulfide double-sensitized by porphyrin and grapheme.The porphyrin and graphene sensitized molybdenum disulfide?MoS₂?composites were successfully prepared by hydrothermal reaction.After the sensitization of MoS₂,the active sites of MoS₂ exposure were increased,and increased contact between electrons and active sites,ultimately results in a catalyst with high chemical activity.In addition,RGO can affect the adsorption behavior of porphyrins and the interaction between porphyrins and MoS₂/RGO composites.This interaction is critical and may affect the following interface electron transfer between the excited porphyrin and/or reduced porphyrin species and RGO.Simple characterization of SEM,UV-vis,PL,etc.are performed,while introducing UV-vis/SECM to further characterize and study its active sites and performance from a microscopic perspective,in order to more accurately and effectively reflect excellent performance of MoS₂ after double sensitization.