The Construction And Mechanism Study Of TiO₂ Based Heterostructure Photocatalytic Materials

In view of the narrow photoresponse range of TiO₂ and the easy recombination of electron-holes,the author constructed three heterostructure material to optimize the catalytic performance of TiO₂,including that the coupling of TiO₂ nanotubes with reduced graphene oxide and FTO;the coupling of TONT:Nb with rGO;the coupling of TiO₂:?Mo,C?with FTO.Besides,the catalytic mechanism involved in the heterostructure materials was studied and explained through various characterization methods.The main innovations and research contents are as follows:One-step hydrothermal method was used to synthesize the rGO-TONT complex,which was then deposited on FTO to construct a rGO-TONT/FTO heterostructure photocatalyst.Photocatalytic degradation of methylene blue?MB?under ultraviolet light irradiation showed that the photocatalytic activity of rGO-TONT/FTO was 3 times that of pure TONT.The structural characterization shows that the TONT is disorderly distributed on the rGO surface and forms a chemically bonded heterostructure with it.Due to the lower Fermi energy level of rGO,and the biased effect between FTO and TiO₂,the photoinduced electrons of the TiO₂ conduction band can transfer to rGO and FTO under the drive of the built-in potential,thus greatly promoting the separation of the photoinduced electron hole,and then enhances its photocatalytic performance.?TONT:Nb?-rGO heterostructure photocatalyst was synthesized by two hydrothermal processes.The structural characterization indicates that the dopant Nb in TiO₂ was existed as Nb⁵⁺state.In addition,the defect states of Ti³⁺and oxygen vacancies have also been formed.These Nb⁵⁺donor states and Ti³⁺,oxygen vacancies defect states stable in TiO₂and result in the formation of localized mid-bandgap states,which rendering a bandgap reduce of 0.46 eV and extending the optical absorption to visible light region.Meanwhile,the electron transfer channels were formed in the heterostructure interface,which greatly promotes the transfer of photoinduced electrons.The results of photocatalytic degradation of MB under visible light irradiation showed that the?TONT:Nb?-rGO catalyst was four times more efficient in MB degradation than pure TONT.TiO₂:?Mo,C?was synthesized by hydrothermal process,and then deposited it onto FTO to construct TiO₂:?Mo,C?/FTO heterojunction photocatalyst.The results of catalytic degradation show that the catalytic performance of TiO₂:?Mo,C?/FTO is significantly improved compared to single-doped or undoped TiO₂.The band structure characterization shows that the Mo-C co-doping reduces the bandgap of TiO2 by 1.0eV,and the decrease of the bandgap is mainly attributed to the formed band tail at the valence band edge as a result of doping.DFT calculation manifest that co-doping effectively increases the charge density at the TiO₂ conduction band edge.Photoinduced carrier dynamics investigation shows that co-doping induces deep electron trap state in TiO₂:?Mo,C?,which enables accumulate long-lived photoinduced electrons and effectively suppresses the radiative electron-hole recombination,thus enhance the photocatalytic performance.