Design Of Hierarchical Three-dimensional BiOCl,SnS2 Layerd Semiconductors And Insights Into The Relationship Between The Structure And The Performances

Environmental pollution and energy shortage,which are huge challenge that we are facing and should be solved in the near future,restrict the further development of human society in the further future.The technology of semiconductor photocatalysis,which can use clean and sustainable solar energy to alleviate or even solve these problems,is considered to be one of the most potential technologies which are called‘green chemistry'.In recent decades,bismuth-based semiconductors had attracted much attention of researchers because of its high photocatalytic activity,good stability,low cost and non-toxic properties.With the efforts of numerous researchers,they are applied to the degradation of pollutants in the wastewater,the reduction of heavy metals,the oxidation of pollutants in the air,organic synthesis,hydrogen production and oxygen evolution by water splitting,the photoreduction of CO2,nitrogen fixation and so on.Bismuth oxychloride?BiOCl?,one of bismuth-based semiconductors,was reported by many researchers.BiOCl belongs to tetragonal phase with the unique layered structure characterized by[Bi2O2]slabs interleaved by double layers of Cl atoms.The layered structure makes the material form an internal electrostatic field along the[001]orientation,which is conducive to the separation and transfer of the photogenerated carriers.BiOCl,with the band gap of 3.2-3.6 eV,only responds at ultraviolet light,which limits its further application.Tin bisulfide?SnS2?,which belongs to metal sulfide semiconductors,and also has a unique layered structure.It is affluent in earth,environmentally friendly and good chemical stability.Due to its interlayer expansible accommodation space,it has been widely studied and applied to lithium ion batteries,solar cells,transistor equipment,photocatalysis and so on.However,SnS2,with the band gap of 2.2 eV,has suffered from low electrical conductivity and limited absorbance of visible light.In order to optimize the morphology and improve the photocatalytic performance for further practical applications,we design the three-dimensional hierarchical morphologies of BiOCl and SnS2 layered semiconductor materials.And we tried to get it clear what the influence factors of the morphology,growth mechanism and the photocatalytic properties are.Our work is mainly divided into the following three aspects.Firstily,3D BiOCl hierarchical microspheres with uniform morphology and self-assembled by nanoplates were prepared by simple glucose-assisted hydrothermal method.The morphology of the obtained BiOCl samples is uniform,and there are many small holes on the surface of the 3D building block nanoplates.The concentration of glucose in the hydrothermal system plays a very important role in the morphology of the samples.When the concentration is suitable,the homogeneous 3D morphology can be obtained.We also systematically studied the influence factors of the morphology of obtained BiOCl,such as the temperature and time of hydrothermal reaction,the pH of the hydrothermal system,and the calcination temperature after synthesis.When the temperature was at 140-220?,we could get 3D BiOCl;when the reaction time were 2-24 h,we could prepare 3D BiOCl;when pH=0.8-9,we could obtain3D BiOCl;and when the calcination temperature after synthesis were at 350-500?,the 3D BiOCl has no obvious change.After the photocatalytic activities test,we found many interesting things.Among the samples obtained at different pH,the sample prepared at pH=0.8 exhibited the best activity and the better activity at visible light than at UV light.Among the samples gained after calcination,the sample after calcination at 350?plays the best performance and the better performance at visible light than at UV light.We also found that the samples after calcination have the better adsorption capacity than the samples without calcination.Secondly,we demonstrated the uniform porous hierarchical plate-like BiOCl/2D networks Bi₂S₃ heterostructures realized by a facile two-step hydrothermal technique.The synthesis involved an anion exchange process by reacting pre-synthesized BiOCl irregular octagonal nanoplates with Na₂S₂O₃·5H₂O in an aqueous solution.The experiment results revealed that the 3D plate-like heterostructures were composed of internal BiOCl and outside networks interwoven by 1D Bi₂S₃ nanorods.Interestingly,the heterostructures had almost the same thickness and the bigger length compared to the precursor BiOCl.We proposed the possible formation mechanism of the composites which involved selective ion-exchange reaction,the following Ostwald ripening process and epitaxial growth.And the crystal lattice matching between the a-or b-axis of tetragonal BiOCl?a=b=3.89??and the a-axis of orthorhombic Bi₂S₃?a=3.981??could be responsible for the in-situ topotactic transformation.Due to the formation of hetero-nanostructures,the unique spatial architecture features and the existence of oxygen vacancies,the BiOCl/Bi₂S₃ composites exhibited significantly extended photo-responsive range and improved photocatalytic activity for reduction of Cr?VI?under visible-light irradiation.Moreover,the possible mechanism of photocatalysis process was investigated.Thirdly,we had prepared the 2D/0D SnS₂/Ag₂S heterojunction by in situ cation exchange method.The precursor SnS₂ hexagonal nanoplates ware synthesized by one-step hydrothermal method,which were added into the aqueous solution of AgNO₃,and the SnS₂/Ag₂S heterojunction was prepared.It was found that the SnS₂/Ag₂S heterojunction basically retained the morphology and size of the precursor SnS₂ hexagonal nanoplates,and its three-dimensional structure was composed of the internal SnS₂ and the outer Ag₂S small particles.The SnS₂/Ag₂S heterojunction samples were applied to the photocatalytic reduction of Cr?VI?under visible light.The results showed that the sample H-0.8?0.6 mmol SnS₂ and 0.8 mmol AgNO₃?was the best in visible light reduction.The characterization of the samples after catalytic reduction showed that the crystal phase stability and structural stability are very good.