Fabrication And Photocatalytic Properties Of Indium Sulfide Composite Nanofibers

Energy and environmental issues are two main topics of scientific research in the 21 century. Semiconductor photocatalytic materials exhibit great potentials in environmental protection and solar energy conversion. However, owing to their wide band gap, conventional photocatalysts(Such as TiO2 and ZnO) can solely absorb the UV light. Since the UV region occupies only near 4% of the entire solar spectrum, while 45% of the energy belongs to visible light, most solar energy cannot be used. Consequently, the development of efficient photocatalysts with visible-light response has become a research focus. Indium sulfide(In2S3) with a narrow band gap has been extensively studied as a potential photocatalyst for the hydrogen production reaction and degradation of pollutants. However, there still existed several major issues impeding the application of In2S3 nano-materials: Firstly, the rapid recombination of photoinduced electrons and holes greatly lowers the quantum efficiency. Secondly, nano-powders catalysts is inclined to agglomerate, inevitably reducing the photocatalytic activity. Thirdly, in the practice application, nanosized photocatalysts are difficult to separate and recycle. Thus, based on the intrinsic problem and the practical application of In2S3 nano photocatalyst, a series of In2S3 composite nanofibers photocatalysts were fabricated by combining the electrospinning technique, hydrothermal method and an in situ reduction approach. The main contents are as follows:(1) In2S3 nanosheets were assembled on electrospun TiO2 nanofibers template by a hydrothermal technique. For the obtained one-dimensional In2S3/TiO2 hierarchical heterostructures(1D In2S3/TiO2 H-HSs), the density and size of the secondary In2S3 nanosheets could be controlled by adjusting the reactant concentrations for the preparation of In2S3 in the hydrothermal process. The 1D In2S3/TiO2 H-HSs exhibited higher visible-light photocatalytic activity for the degradation of Methyl orange(MO) and the reduction of Cr(VI), as compared with the pure TiO2 nanofibers and pure In2S3 nanosheets. The enhanced visible light photocatalytic activity might be attributed to the effective photogenerated electron-hole separation based on the formation between In2S3 and TiO2. Meanwhile, the 1D In2S3/TiO2 H-HSs could be recycled easily by sedimentation due to their nanofibrous nonwoven web structure. Moreover, the mechanisms of photodegradation of MO and photoreduction of Cr(VI) were proposed through systematical investigations.(2) In2O3 nanofibers were fabricated by electrospinning technique. Using In2O3 nanofibers as both template and reactant, In2S3/In2O3 heterostructures nanofibers were fabricated by in situ ion-exchange reaction method. It is demonstrated that In2O3 can be gradually converted to In2S3 with controllable thickness determined by the reaction concentration. When the reaction concentration increased to certain value, In2O3 nanofibers would be completely converted to In2S3 nanofibers. Compared with the pure In2O3 and In2S3 nanofibers, In2S3/In2O3 heterostructures nanofibers exhibited enhanced photocatalytic activity in the decomposition of MO and reduction of Cr(VI) under visible light. The enhanced photocatalytic activity might be attributed to the effective separation of photogenerated carriers driven by the positive synergetic effect between In2S3 and In2O3 in the heterostructures.(3) The CNFs were fabricated by electrospinning technique. Next, the Au NPs were assembled on the electrospun CNFs via in situ reduction method. Finally, by using the obtained Au NPs modified CNFs(CNFs/Au) as hard template, In2S3/CNFs/Au composites were fabricated through a hydrothermal technique. Utilizing the positive synergetic effect between the In2S3, CNFs and Au components in the obtained In2S3/CNFs/Au composites, the photogenerated electrons on the conduction bands(CB) of In2S3 could easily transfer to CNFs, and then irreversibly captured by the Au NPs, realizing a more effective separation of photogenerated electron-hole pairs to get a much better performance in the photocatalytic processes compared with the pure In2S3 and In2S3/CNFs. Also, by utilizing their free-standing nanofibrous network structure, the In2S3/CNFs/Au composites could be easily recycled by sedimentation in the practical application.(4) In(NO3)3/PAN nanofibers were fabricated by electrospinning technique. Next, the In2S3/PAN flexible composite nanofibers were been successfully obtained via hydrothermal method. In2S3 nanosheets grown on the PAN nanofibers uniformly. And, the In2S3/PAN flexible composite mat due to the self-supporting property could be laid or hung conveniently anywhere under solar irradiation and recycled. The photocatalytic test results showed that the In2S3/PAN composite nanofibers exhibited strong adsorption ability towards organic dyes and shows high performance in photocatalytic degradation of the dye molecules. Comparing with the In2S3/PAN composite nanofibers obtained by the “no seed” method, adding In(NO3)3 into PAN nanofiber before hydrothermal could improve the amount of In2S3 nanosheets on the products, which could reduce the production costs. Our work provides a new strategy for the immobilization of nanosized photocatalysts.