Preparation Of TiO₂/SiC Heterojunction Nanofibers And Their Photocatalytic Properties

In recent years,the development of science and technology lead to many problems such as environmental pollution and energy shortages.Photocatalytic technology has become the key to solving the problems of environmental pollution and energy shortage due to its advantages of environmental protection,high efficiency,low cost and no secondary pollution to the environment.Silicon carbide（SiC）has excellent photocatalytic performance and extremely stable characteristics.So the development of SiC-based composite photocatalysts with high catalytic activity has become an important research direction in the field of photocatalysis in recent years.Nano-scale SiC have high specific surface area,which is conducive to improving photocatalytic activity,but the single SiC nano powders as photocatalyst still face the following problems: 1.The photo-generated electrons and holes of pure SiC powder are easy to recombine which like other single-component semiconductor photocatalysts,resulting in a low photon yield;2.The SiC powders is hydrophobic,it is not easy to contact with the reactants in the liquid environment,which affects the progress of the photocatalytic reaction;3.The SiC powders with high surface energy causes to agglomerate easily.A number of particles agglomerated together,the specific surface area was reduced,resulting in a reduction of the active sites;4.Nano-powders are difficult to recover in the liquid phase reaction,resulting in waste of catalyst and it is not conducive to recycling.In order to solve these problems,we prepared TiO₂/SiC heterojunction nanofibers by electrospinning technology.Using the built-in electric field of the heterojunction to improve the separation of photogenerated electrons and holes.Using the fiber structure to promote one-dimensional axial transmission and transfer of carriers.At the same time,the combination of hydrophobic SiC powder and hydrophilic TiO₂ is used to improve the hydrophilicity of the composite catalyst.Using the high specific surface area of nanofibers and net felt structure to promote surface reaction and sedimentation separation.The specific research contents are as follows:（1）Add SiC nano powders with different contents to the mixed solution of high molecular polyvinyl pyrrolidone（PVP）,glacial acetic acid,tetra-n-butyl titanate and ethanol.Different ratios of TiO₂/SiC heterojunction nanofiber materials can be obtained through electrostatic spinning technology and high-temperature calcination process.The detailed characterization and analysis of TiO₂/SiC heterojunction nanofibers have shown a lot of features.TiO₂/SiC heterojunction nanofibers have a one-dimensional ultra-long nanostructure,and the specific surface area is significantly higher than TiO₂ nanofibers,SiC nanopowders,mechanical mixtures of them and TiO₂/SiC heterojunction nanopowders.The spatial distribution of the components is relatively uniform.There were obvious lattice boundaries between TiO₂and SiC.In addition,TiO₂/SiC heterojunction nanofibers are hydrophilic.But the hydrophilicity becomes poorer as the content of SiC added increases.Photocurrent response and luminescence spectrum test show that TiO₂/SiC heterojunction nanofibers have a stronger photocurrent response compare with single-component TiO₂ and SiC.The response intensity of different component ratios TiO₂/SiC heterojunction nanofibers was different.When the molar ratio of TiO₂ and SiC is 1:1,the photocurrent is the strongest and the luminous intensity is the weakest.The energy band structure of the interface between TiO₂ and SiC was analyzed,that provide a basis for further understanding of their photocatalytic principles.（2）In order to explore the catalytic performance,the photocatalytic activity of TiO₂/SiC heterojunction nanofibers was first studied with rhodamine B（RhB）as the target pollutant.The photocatalytic activity of TiO₂/SiC heterojunction nanofibers is significantly higher than that of single-component TiO₂,SiC and their mechanical mixtures,indicating that a heterostructure is formed between TiO₂and SiC,which promotes the separation of electrons and holes and inhibits the recombination process of carriers.In addition,the photocatalytic activity of TiO₂/SiC heterojunction nanofibers is higher than that of its powder,this is because the structure of the fiber is conducive to the transport and transfer of electrons and holes,and the specific surface area of the fiber is conducive to increase the active site of the reaction.When the molar ratio of TiO₂ and SiC is 1:1,the photocatalytic performance was best.The low content of SiC cause the number of heterojunctions formed was little,which is not conducive to the transport of electrons and holes.When the SiC content was high,local agglomeration of the SiC powder happened,which cause the recombination of electrons and holes.That reduce the hydrophilicity of the composite material,which is not conducive to the photocatalytic reaction in the liquid environment.Further,a hydrogen production experiment was conducte.The research results show that the hydrogen production efficiency of TiO₂/SiC heterojunction nanofibers is higher than that of pure TiO₂,SiC and their mechanical mixture.When the molar ratio of TiO₂ to SiC is 1:1,the effect of hydrogen production is the best.In addition,cyclic experimental studies of degrading RhB and decomposing water to produce hydrogen have shown that TiO₂/SiC heterojunction nanofibers are easy to settle and separate from the mixed solution.The above research provides some new ideas and experimental basis for improving the photocatalytic performance of nano-SiC materials.