Photocatalytic And Photoelectrochemical Properties Of TaWO₆Nanosheet And Its Composite Electrodes

Nowadays, the solar-light utilization and its conversion efficiency greatlyinfluence the sustainable development of society and economy. The semiconductor-based photocatalytic/photoelectrocatalytic and photoelectric conversion technologies,grounded on the redox performance of photocarriers, can be employed to directlydegrade the organic pollutants in the environment, and to convert solar energy intoelectrical energy, hydrogen energy and other forms of energy, which can therebyalleviate the global energy crisis.Lithium tantalotungstate （LiTaWO₆）, a semiconductor with a lamellar structure,was prepared by high temperature solid state reaction in this dissertation. Throughacid exchange, the layered HTaWO₆was exfoliated into an aqueous colloidcontaining single-molecular nanosheets. The multilayer-film electrode materials,（TaWO₆）n,（G/TaWO₆）nand （SnO₂/G/TaWO₆）n, were fabricated by the layer-by-layerself-assembly technology using the indium-tin-oxide （ITO）-coated glass as substrates.XRD, AFM, UV-vis, Raman, electrochemical and photoelectrochemicalmeasurements have been carried out to analysis the membrane materials’ structure,band position and photoelectric catalytic activities, and the photocatalitic mechanismsunder different contions have been explored.AFM showed that TaWO₆nanosheet has an extremely ultrathin thickness of0.84nm and a lateral size about microns. Due to the quantum size effect, the bandgap of TaWO₆nanosheet was determined to be increased to3.48eV, and the lowedge of conduction band was obtained as-0.57V （vs SHE） throughphotoelectrochemical experiments. As the CB position is higher than redox potentialof O₂, the electrons will be easily captured by the dissolved oxygen and form O₂–free radicals, while the hole in valence band will oxidize hydroxyl or water moleculesform OH, promoting the separation of electrons and holes, enhancing the catalyticactivity. In the photoelectrocatalytic degradation experiment, under an applied biaspotential, the photoelectrons were quickly migrated to the external circuit in visible orUV irradiation, the recombination of photo-generted carrieries was suppressed. TaWO₆nanosheet catalysis in the photo-degradation of Rhodamine B follows theband-excition mechanism under UV irradiation and the dye-sensitized path undervisible irradiation.It was revealed that all of the composite electrode materials containing graphenenanosheet exhibit a red-shift absorption band. The absorption setups of （G/TaWO₆）n,（SnO₂/G/TaWO₆）nand （TaWO₆）nare550,539and310nm, respectively. It was foundthat, through electrochemical and photoelectrochemical experiments, the employedgraphene benefits the rapid migration of the photo-generated electrons. The thephotoelectric conversion efficiency of the as-prepared （G/TaWO₆）nwas the best,compared from the IPCE data. And its resistance was also the smallest from the EISdata. This study demonstrates that a film composite, which is consisted of two ormore semiconductor building compositions including graphene, can improve thetransfer way of the electrons, and thus enhance the electron transfer efficiency, whichleads to a good photocatalytic activity for a material. Under visible light irradiationfor60min, the degradation efficiency of （G/TaWO₆）nwas70.4%, those of（SnO₂/G/TaWO₆）nand （TaWO₆）nunder the same conditions were49.7%and28.5%,respectively.（G/TaWO₆）nhas an excellent photoelectrocatalytic and electrocatalyticbehaviors.