The Preparation And Photocatalytic Hydrogen Evolution By Water Splitting Of TiO₂ And C Laminated Composites

The robust development of modern industry and the sharp decline in fossil energy reserves have resulted in severe environmental pollution and energy crisis.As a representative of clean and renewable,hydrogen energy has attracted extensive attention from many scientists.Converting solar energy into hydrogen production by splitting water,has been considered to be the most promising and economical approach to obtain hydrogen energy.Titanium dioxide（TiO₂）,which has the advantages of low price,rich reserves and superb chemical stability,has been admitted as one of the most potential photocatalysts.However,individual TiO₂ has several fatal weaknesses including invalid visible light absorption and low catalytic efficiency,which limit its practical industrial applications.The doping and compositing in TiO₂ are considered as exceedingly effective methods to overcome the above shortcomings.Therefore,in this article,we mainly focus on how to optimize the light absorption of intrinsic TiO₂ and its photocatalytic hydrogen evolution performance.We fabricated two different TiO₂ composites through controlling its structure and doping modification,which successfully expanded the range of light absorption and simultaneously enhanced the hydrogen evolution ability.The study delivers novel strategies for designing and preparing layered nano-heterostructures.We pre-nitrided MXene to utilize N atoms in ammonia gas remedy the carbon defects that originally existed in MXene,so that the two-dimensional structure does not dissociate during the oxidation process.Subsequently,N-MXene prepared by defect engineering is used as a precursor,and then is oxidized by carbon dioxide.After the above procedures,TiO₂ grows in situ within the MXene sheets and TiO₂/C superstructure with intercalation structure is finally synthesized,which achieves a highly orderly layer-by-layered of carbon layers and TiO₂ nanosheets.The orderly TiO₂/C superstructure dramatically accelerates separation of photocharges and simultaneously promotes photoelectron transfer,resulting in a significant improvement in hydrogen production activity.As a result,the H₂ production rates of NPT-TiO₂/C superstructure under visible light are up to 87.2μmol g^-1 h^-1.We treated MXene with high temperature under ammonia gas to prepare nitrogen doped MXene,which provides a two dimensional structure and a nitrogen source for subsequent titanium dioxide and carbon.Subsequently,as obtained nitrogen-doped MXene is used as a precursor,and then is oxidized under air condition.After above,nitrogen atoms fully entered the titanium dioxide and carbon to form the laminated heterostructure of N doped TiO₂ and N doped carbon substrate（N-TiO₂/NC）.The prepared N-TiO₂/NC composite displays greatly enhanced visible light absorption and enables photoexcited electrons to be quickly transferred to the active region owing to high conductivity by nitrogen doped carbon.Therefore,the N-TiO₂/NC laminated composite could efficiently promote water-splitting under visible-light with a satisfactory H₂ evolution rate of 102.6μmol g^-1 h^-1.