Preparation,Characterization and Photocatalytic Performances Study of SnS2-based Heterojunctions Photocatalysts

Author:Feng Juan

Supervisor:hu xiao yun


Degree Year:2019





Nowadays,with the rapid development of contemporary economy and science technology,the subsequent environmental pollution and energy demands have seriously affected the health and subsistence of human beings.Semiconductor photocatalytic technology with the advantages of economic security and green environment can solve environmental problems using new energy materials.The core of the photocatalytic technology is high-efficient and stable semiconductor photocatalyst.SnS2 has special physical/chemical properties and suitable bandgap,which has drawn much attention in the field of photocatalysis.However,the photocatalytic efficiency of single photocatalyst is low,duing to that the charge carriers may recombine easily and quickly.In this thesis,with SnS2 as the objiect,we focus on the improvement of photocatalytic efficiency by constructing SnS2-based heterjunction,and investigate their morphologies,structures,properties and phtocatalytic activities in detail.Besides,we also investigate the seperation transfer of photo-generated charge carriers,and discuss the synergistic enhanced mechanism.The main contents are as follow:(1)2D SnS2 nanomaterials with size of 3 um and thickness of 20 nm were successfully synthesized by a hydrothermal method,which is used for photocatalytic degradation and hydrogen evolution.The effects of raw material ratio,solvent,reaction temperature and time on the morphologies of products were also discussed,and the parameters were optimized.The morphologies,structure and compositions were characterized by XRD,SEM,XPS,TEM,Raman and BET techniques.PL spectra were used to characterize the combination of photoelectron and hole.The photocatalytic degradation of MB can reach 81.53%after 3h illumination.These high photocatalytic properties are probably due to that the ultrathin SnS2 nanosheets can effectively reduce the distance and time for photogenic carriers which migrate from the body phase to surface and inhibit the combitination of photogenic carriers.(2)Au/SnS2 composites were fabricated by a rapid microwave-assisted synthesis,which are used for photocatalytic degradation of MB and hydrogen evolution.TEM images show that the load mass and size of Au can be controlled by changing the volume of chloroauric acid aqueous solution.The addition of Au can greatly improve the photocatalytic performance of SnS2.When the volume of aqueous chloro-auric acid solution is 4 ml,the Au/SnS2 composites have a specific surface of 28.47 m2/g and show the best photocatalytic performance,in which the size of Au nanoparticles is 20 nm.After1 h,the photodegradation efficiency of MB reaches 92.90%,and the hydrogen production rate is 85.6μmol/(h·g).The composites also reveal good stability.The first principle calculation show that electrons transfer from SnS2 to Au and accumulate at the interface.Compared with the pure SnS2,the introduction of Au nanoparticles provides thermal electron effect and local surface plasmon resonance effect.The formation of schottky between them will promote the separation and migration of photogenic carriers,and improve their photocatalytic capacity.(3)0D-2D ZnO/SnS2 heterojunction composites were fabricated by a hydrothermal method for photocatalytic degradation and hydrogen evolution.TEM reveals that the monodisperse ZnO nanoparticles recrystallize during this process,during which the small particles with size of 16 nm aggregate into large particles with size of about 100 nm.When the mass fraction of ZnO in the composites is 2%,the degradation efficiency of MB could reach 94.47%after 3 h of illumination.The hydrogen production rate is 346.1μmol/(h·g),which is 2.7 time higher than the pure SnS2.The addition of ZnO broadens the absorption range of spectrum and the heterojunction is formed with SnS2.The synergistic effect can promote the effective separation of photogenic carriers.(4)g-C3N4/SnS2 heterojunction composites were prepared by solvent thermal method for photocatalytic degradation and hydrogen evolution.The g-C3N4 nanosheets were in situ modified on the SnS2 nanosheets.The photocatalytic results demonstrate the addition of g-C3N4 can effectively improve the photocatalytic performance,and the load mass of g-C3N4 can affect the photocatalytic properties.When the load mass fraction of g-C3N4 is 15%,the g-C3N4/SnS2 composites show the best photodegradation efficiency.The degradation efficiency of MB can reach 88.01%after 3 h illumination,and the hydrogen production rate is 115.3μmol/(h·g).Compared with bare SnS2 nanosheets,the enhancement of photocatalytic efficiency is ascribed to the constructed P-N type heterogeneous structure between g-C3N4 and SnS2.The built-in electric field and synergy effect between them can accelerate the transfer of carriers and promote separation of photogenic electrons and holes.(5)Binary ZnFe2O4/SnS2 heterojunction composites were prepared by polyol method.TEM shows that ZnFe2O4 nanoparticles are mainly dispersed at the edge of SnS2nanosheets.The XPS results indicate that there is an interaction between ZnFe2O4 and SnS2.The degradation efficiency of RBh could reach 94.47%under 3 h of illumination,and the hydrogen production rate is 491.7μmol/(h·g).On the above basis,the ternary rGO/ZnFe2O4/SnS2 composites were formed by combining rGO into ZnFe2O4/SnS2heterojunction.In comparison with pure SnS2 and ZnFe2O4/SnS2,ternary composites can be recycled better and their photocatalytic performances have been significantly optimized.The hydrogen production rate of 7%rGO/ZnFe2O4/SnS2 can reach 609.3μmol/(h·g),which is 4.78 times higher than that of SnS2 and 1.24 times larger than that of binary hybrids.This improvement is mainly attributed to the interaction between heterogeneous junction,which makes the electrons and holes of composite material more active.Besides,the addition of rGO can promote the separation of photogenic electrons and holes.In addition,after introduction of magnetic materials,it can provide a possibility for the reuse of catalysts.It also provides a new research idea for the preparation and modification of novel,high efficiency,recyclable multivariate heterojunction photocatalyst.