Nanosheet TiO₂ Based Catalyst For Photocatalytic Hydrogen Production And Its Interfacial Electron Transfer Mechanism

It is a sustainable energy utilization approach to convert water into clean and efficient hydrogen power by sunlight-driven photocatalysis.However,the low photoelectron utilization efficiency of photocatalysis due to fast recommbination of electron-hole hinders the further improvement of hydrogen production efficiency.Surface property of photocatalyst is important since the photoelectron transfer process involved inner electron transfer,interfacial electron transfer and interfacial electron reaction.It is an effective way to increase the photoelectron ultilizaiton efficiency by modifying the properties of photocatalyst.In this paper,TiO₂,a stable,low-cost,and non-toxicy photocatalyst,was selected as the base catalyst.Reduced grapheen oxide?RGO?,MoS₂ and transition metals?Cu,Fe,and Ni?were introduced into TiO₂ by modifing the surface properties to increase the photoelectron utilization efficiency and further improve the hydrogen production performance.?001?facet exposed two-dimension TiO₂ nanosheets were prepared by hydrothermal method.Microwave assisted hydrothermal method was further employed to reduce GO to RGO followed by depositing TiO₂ on RGO.2wt%RGO/TiO₂,showed the best hydrogen evolution rate?3.14 ?pmol/g/min?,which is 4.1 times as that of TiO₂ catalyst.The catalyst also exhibited high stability of hydrogen production.The phycial and chemical properties charatacterzation indicates that TiO₂ nanosheets were dispersed in RGO phase with intimate contact.2wt%RGO/TiO₂ exhibited increased separation of electron-hole and photocurrent density?8 ?A/cm2?,4.4 times as that of TiO₂.Interfacial charge transfer resistance of 2wt%RGO/TiO₂ was obsereved to decrease 10%.The enhanced photocatalytic performance of RGO/TiO₂ is attributed to the excellent conductivity of RGO,which accelerates electron transfer and promotes the electron-hole separation.Na₂MoO₄ and CH₃CSNH₂ were used as precursor to prepare MoS₂ modified TiO₂ nanosheets through microwave assisited hydrothermal method.The hydrogen production rate of the optimal catalyst 0.2wt%MoS₂/TiO₂ is 4.02 ?mol/g/min,which is 5.3 times as that of TiO₂.The introducing of MoS₂ results in irregular shape of nanosheet due to high temperature treatment.2wt%MoS₂/TiO₂ exhibited 1.3 times photocurrent density and similar interfical charge transfer reistance compared with TiO₂.The low hydrogen overpotential of MoS₂ is responsible for enhanced hydrogen efficiency.Under light irradiation,electrons in the CB of TiO₂ can transfer to MoS₂ due to the lower conduction band potential followed by reacting with H+ to produce H2.Cu,Fe,and Ni/TiO₂ were synthesized by a microwave assisted hydrothermal method.The hydrogen produciotn rate of 1wt%Cu?38.9 ?mol/g/min?,lwt%Ni?7.29 ?mol/g/min?,and lwt%Fe?2.35 ?mol/g/min?are 51,8.5,and 2.35 times as high as that of TiO₂,respectively.The morphology structre and crystal facet remain stable after modification.The photocurrent density of Cu,Fe,and Ni/TiO₂ is 11.4,2.8,and 3.8 times higher than that of TiO₂ and interfical charge transfer resistance decrease 51%,16%,and 16%,respectively.Cu,Fe,Ni species are believed to be grafted on TiO₂ surface and can accept electrons in TiO₂ CB under light irradiation.The electron-hole was therefore efficiently seperated and resulting in enhanced photococurrent denstity.Linear sweep voltamnetry?LSV?test indicated Cu/TiO₂ exhibhited lower hydrogen overpotential compared with the TiO₂ while a larger one for Fe,Ni/TiO₂.It concluded that fast electron transfer and lower hydrogen overpotential are the key factors acoounting for efficient photocatalytic hydrogen production for Cu/TiO₂.