Preparation Of Mesoporous Titania Nanotube Heterojunction And Study Of Visible Light Photocatalytic Performance

Due to the rapid development of the national economy and society,the increasing consumption of energy and the constant pollution of the environment have forced people to start working on solutions.Over the years,researchers have been working on photocatalytic semiconductor materials.In particular,titanium dioxide has attracted attention for its excellent chemical stability,cheapness,non-toxicity and environmental friendliness.However,two problems limit their photocatalytic performance:one is the low efficiency of harnessing solar energy,which can only absorb UV light,and the other is the rapid compounding of photogenerated electrons-hole(P es-hs).Therefore,controlling the mesoporous titanium dioxide band gap to improve the efficient use of light at wavelengths other than UV and improving the separation of P es-hs remains a challenging topic at present.In this paper,a mesoporous titanium dioxide nanotubes(TNs)photocatalyst was synthesised by a one-step hydrothermal method and heterojunction photocatalysts were prepared by compounding with other materials to improve the photoresponse and P es-hs separation efficiency.In addition,precious metals were introduced as co-catalysts to further enhance the solar photocatalytic performance.The main content of this paper is divided into three parts as follows:1.Mesoporous titanium dioxide nanotubes(TNs)were synthesised in a mixture of anhydrous ethanol,anhydrous ether and glycerol using titanium oxide sulphate as a precursor,which has the characteristics of porosity and large specific surface area.The p-n heterojunction photocatalytic material(NiO/TNs)was then prepared by impregnation and high temperature heat treatment.The presence of NiO reduced the band gap of TNs from 3.2 e V to 2.9 e V,and the visible photocatalytic hydrogen production performance was improved by a factor of 4(228?mol g^-1h^-1).It was demonstrated that the introduction of surface NiO resulted in a reduced band gap with increased visible light absorption,while the p-n heterojunction formed a built-in electric field that promoted the transport of P es-hs between NiO and TNs through the heterogeneous interface.2.Pt-loaded mesoporous titanium dioxide nanotubes(Pt/TNs)were synthesized by photodeposition using TNs as the substrate.Pt nanoparticles grown on the surface of TNs could accelerate and direct P es-hs transport.The Pt₁/TNs with the best photocatalytic hydrogen production performance were prepared by controlling the amount of Pt loading,which further improved the photocatalytic hydrogen production performance due to the formation of a heterogeneous structure on the surface of TNs by Pt loading,resulting in a large accumulation of electrons(es)at the interface and an increase in the efficiency of P es-hs involved in the reaction of photocatalytic hydrogen production.Thus the visible photocatalytic hydrogen production performance of Pt₁/TNs is increased by a factor of 9(512?mol g^-1-h^-1)compared to that of TNs.3.Pt-loaded Pt/NiO/TNs were synthesised by photodeposition using NiO/TNs as the substrate.Pt/NiO/TNs significantly promoted the transport and separation efficiency of P es-hs under the synergistic effect of the built-in electric field formed by the p-n heterostructure and the Pt co-catalyst.The absorption range of the material is extended to the visible range and the photocatalytic hydrogen production performance is enhanced.As a result,the photocatalytic hydrogen production performance of Pt/NiO/TNs was improved by a factor of 4 and 2(1000?mol g^-1h^-1)compared to NiO/TNs and Pt₁/TNs,respectively.With the heterogeneous structure and the co-catalyst of Pt,the photocatalytic hydrogen production performance is enhanced as it is no longer limited by UV light and its own defects and can absorb visible light.