Study On Photocatalytic Bromate Reduction By Ti₃C₂ MXene Doped TiO₂

As a common disinfection by-product in drinking water,bromate has been identified as a 2B potential carcinogen by the International Agency for Cancer.Therefore,it is necessary to develop technologies for the efficient removal of bromate.Among numerous technologies,titanium dioxide（TiO₂）photocatalytic removal technology has been one of research hotspots,due to its advantages of environmental protection and high efficiency.In this study,two series of Ti₃C₂-doped TiO₂photocatalysts were prepared,with the two-dimensional material Ti₃C₂ MXene used as a non-noble metal cocatalyst:TiO₂/TC prepared by Ti₃C₂-doped TiO₂,TBR prepared by Bi and Ti₃C₂ co-doped TiO₂.They were used to study the efficiency of photocatalytic bromate reduction under UV light and visible light,respectively.The morphology,optical and electrochemical properties of the photocatalysts were investigated through characterization tests.And the relationship between the enhanced photocatalytic performance and their properties was identified.Furthermore,the mechanisms of photocatalytic bromate reduction by photocatalysts were explored.Meanwhile,the effects of main factors such as p H,temperature,coexisting anions,and humic acid on the TiO₂/TC photocatalytic reaction system were studied.Both TiO₂/TC and TBR showed excellent efficiency of photocatalytic bromate reduction.More than 98%of bromate with an initial concentration of 200μg/L could be removed by 0.075 g/L TiO₂/TC composite（Ti₃C₂:TiO₂=1 wt%）in 15 min under UV light irradiation at an intensity of 10 W,26μW/cm².Bromate with an initial concentration of 200μg/L could be completely removed by 0.075 g/L TBR composite（Ti₃C₂:TiO₂=10 wt%,Bi:TiO₂=20 wt%）in 60 min under visible light irradiation at an intensity of 50 W.In addition,TiO₂/TC and TBR had good stability and reusability in photocatalytic removal of bromate.The efficiency of photocatalytic bromate reduction by TiO₂/TC only decreased by 6%after four consecutive cycles,and bromate could be completely removed by TBR after four consecutive cycles.The boosted photocatalytic performance of TiO₂/TC and TBR photocatalysts was attributed to the doping of Ti₃C₂.On the one hand,due to its properties of excellent electrical conductivity and low Fermi energy level,Ti₃C₂ functioned as“an electron sink”to accelerate the migration of photoinduced carriers and accumulate photoinduced electrons on its surface.On the other hand,the Schottky barrier formed in the tight Ti₃C₂-TiO₂ interface provided a unidirectional channel for electron transfer,which facilitated the separation of electron-hole pairs.Moreover,the band gap of photocatalysts was narrowed with the doping of Ti₃C₂,which was beneficial for enhancing the light absorption capacity and improving the density of photo-carriers.Furthermore,the excellent visible-light photocatalytic activity of TBR was benefited from the doping of Bi.Due to the surface plasmon resonance（SPR）effect of Bi,the band gap of the photocatalyst was narrowed from 2.88 e V to 2.50 e V,and the light response range of the photocatalyst was broadened to the visible light region.In result,TBR performed high removal efficiency of bromate under visible light.In a word,TiO₂/TC and TBR photocatalysts shows great properties such as excellent photocatalytic activity,good stability and low cost,which highlight the potential of Ti₃C₂ as a noble-metal-free photocatalytic cocatalyst and explore the possible expansion of the application of MXene.