Design,Preparation And Photocatalytic Properties Of Molybdenum Diselenide-Based Heterojunction Nanofibers

Photocatalysis has been considered as one of the most potential ways to solve energy crisis and environmental pollution problems.However,most photocatalysts only respond to ultraviolet and visible light.In order to make better use of the solar energy,the development of broad-spectrum-response photocatalysts has attracted more and more attention.Thus,it is necessary to find high efficient broad-spectrum-response photocatalysts.Molybdenum diselenide（MoSe2）was a narrow band gap semiconductor,which can capture a wide spectral range and was considered as a potential broad-spectrum-response photocatalyst.MoSe₂nanomaterials have higher specific surface area than bulk materials,providing more active sites to participate in photocatalytic reactions.However,MoSe₂ nanomaterials still exist some issues in practical application:Firstly,the rapid recombination of photo-generated electrons and holes of MoSe₂ result in the low quantum efficiency.Secondly,small size nanomaterials easily agglomerate,inevitably decreasingthe active sites and influcencing photocatalytic activity.Thirdly,in the practice application,nanosized photocatalysts are difficult to separate and recycle after the photocatalytic reation.In order to solve these problems,a series of MoSe₂-based heterojunctions nanofibers photocatalysts were prepared by combining electrospinning technique with solvothermal method.The as-obtained MoSe2-based heterojunction nanofibers have high photocatalytic activity and excellent reusability.The main contents are as follows:（1）Using elestrospun CNFs as supports,MoSe₂/CNFs heterojunction nanofibers have been obtained by solvothermal technique.By adjusting the concentration of precursors,MoSe₂ nanosheets with different loading amounts are evenly dispersed on CNFs,which effectively solved the problem of easy agglomeration for MoSe₂ nanoparticles.The photocatalytic degradation rate constant of RhB for the MoSe₂/CNFs heterojunctions was about 3 times of pure MoSe₂.The enhanced photocatalytic activity might be attributed to the formation of heterojunction was conducive to the separation and transfer of photogenerated electrons and holes.Further using N-CNFs as the supports of growing MoSe₂,MoSe₂/N-CNFs heterojunction nanofibers were prepared by solvothermal method.The photocatalytic degradation rate constant of RhB for the MoSe₂/N-CNFs heterojunctions was about 2.4 times of MoSe₂/CNFs heterojunctions.This is because the introduction of N increases the conductivity of CNFs and accelerates the transfer of interfacial charge,thus enhancing the photocatalytic activity of MoSe₂/N-CNFs heterojunctions.MoSe₂/CNFs and MoSe₂/N-CNFs heterojunction nanofibers self-supporting mat structure,which could be directly separated from the solution for recycling and reuse.（2）Using electrospun TiO₂ nanofibers as supports,ultrathin MoSe₂ nanosheets were uniformly grown on the TiO₂ nanofibers by solvothermal method,forming MoSe₂/TiO₂heterostructure nanofibers with hierarchical structure.The photocatalytic degradation rate constant of RhB for the MoSe₂/TiO₂ heterostructures were nearly 7 times of MoSe₂.The construction of heterostructures can effectively promote the separation and transfer of photo-generated electron-hole pairs,thus improving their photocatalytic degradation rate.Further using the Nb-TiO₂ nanofibers as supports,MoSe₂/TiO₂-Nb heterostructure nanofibers were obtained.The photocatalytic degradation rate constant of RhB for the MoSe₂/Nb-TiO₂heterostructures were nearly 6 times of MoSe₂/TiO₂ heterostructures.The introduction of Nb in TiO₂accelerates the interfacial charge transfer,more photogenerated electrons and holes are generated to participate in the photocatalytic reaction,which improves the photocatalytic reaction rate of heterostructures.MoSe₂/TiO₂ and MoSe₂/TiO₂-Nb heterostructures nanofibers have unique network structure and can be separated,recovered and reused by simple precipitation method after photocatalytic reaction.（3）TiO₂@C nanofibers were preared by a simple hydrothermal method using glucose as C source,then MoSe₂/TiO₂@C ternary heterostructure nanofibers were obtained based on TiO₂@C nanofibers as supports by solvothermal method.The photocatalytic degradation rate constant of RhB for the MoSe₂/C@TiO₂ heterostructures were nearly 3.7 times of MoSe₂/TiO₂ heterostructures.The modification of the very thin carbon layer as a good electron transport medium can further accelerate the interfacial charge transfer of the heterogeneous and improve the photocatalytic activity.Furthermore,TiO₂/Au nanofibers were acquired via in situ reduction method,MoSe₂ nanosheets were evenly grown on TiO₂/Au nanofibers,forming the MoSe₂/TiO₂/Au ternary heterostructure nanofibers.The photocatalytic degradation rate constant of RhB for the MoSe₂/TiO₂/Au heterostructures were nearly 2.1 times of MoSe₂/TiO₂ heterostructures.The enhanced photocatalytic activity might be attributed to the increases the concentration of photogenic carriers and the separation of photogenerated electrons by Au nanoparticles.Moreover,MoSe₂/C@TiO₂ and MoSe₂/TiO₂/Au ternary heterostructure nanofibers showed good separation and reusability.