Preparation Of ZnIn₂S₄-Based Heterojunction Composite Photocatalyst And Performance For Hydrogen Production Under Visible Light

The technology of semiconductor photocatalytic water splitting has been considered as one of the most important approaches to achieve the conversion from solar energy to hydrogen energy.Because of its potential for solving environmental and energy problems,it has received widespread attention.For the application of technology,it is a key is to develop visible-light-driven semiconductor photocatalyst with high activity and stability.The ternary sulfide ZnIn₂S₄ has the advantages of low toxicity,good crystallinity,and considerable chemical stability.It is a promising semiconductor photocatalyst material water-splitting into hydrogen.However,its photocatalytic H₂ evolution activity in visible light regeion is low.The construction of heterojunctions is an effective method for the modification of semiconductor photocatalysts and can broaden the visible light absorption range of the catalysts.In this thesis,the ZnIn₂S₄-based heterojunction composite catalyst was synthesized by hydrothermal method,and its visible light photocatalytic hydrogen production performance was studied.My thesis is divided into two parts:???The Zn_mIn₂S₃₊m/In₂S₃ J type heterojunction composite catalyst was synthesized by oxalic acid assisted one-step hydrothermal method.The morphology of the photocatalyst is a flower-like hollow microsphere composed of flakes.The prepared photocatalysts were characterized by X-ray diffraction?XRD?,UV-vis diffuse reflectance spectra?Uv-vis DRS?,scanning electron microscope?SEM?and transmission electron microscope?TEM?,High-resolution transmission electron microscopy?HRTEM?and scanning transmission electron microscopy?STEM?.The formation mechanism of J-heterojunction and flower-like hollow microspheres of Znm In₂S_3+m/In₂S₃ photocatalyst was also discussed.The oriented grown J-heterostructures in the catalyst promote the efficient transport and separation of photogenerated carriers and show high photocatalytic activity under visible light irradiation.When the Pt loading was 1wt%,the Zn_mIn₂S₃₊m/In₂S₃ photocatalyst achieved a maximum activity of 330 ?mol/h,about four times that of a single ZnIn₂S₄ photocatalyst,and far greater than that of the pure In2S3.The apparent quantum efficiency of Znm In₂S₃₊m/In₂S₃ photocatalyst reaches 32% under a single wavelength of 420 nm,and it has obvious activity in the long wavelength range.???A precursor was obtained by adding Na₂S which is less than the stoichiometric ratio into the solution of In³⁺ and Zn²⁺.The precursor was transformed into the ZnIn₂S₄/In?OH?y Sz heterojunction composite photocatalyst by a one-step hydrothermal method.The ZnIn₂S₄/In?OH?y Sz heterojunction composite photocatalyst formed when the addition amount of S^2- is 10% less than the stoichiometric ratio,shows the highest hydrogen evolution activity and good stability under visible light irradiation.Compared with ZnIn₂S₄ alone,the ZnIn₂S₄/In?OH?_yS_z heterojunction composite shows an hydrogen evolution activity.When the Pt content was 0.5 wt%,the ZnIn₂S₄/In?OH?_yS_z photocatalyst achieved the highest activity of 169 mol/h,which was 2 time higher than that of single ZnIn₂S₄,and the apparent quantum efficiency at wavelength of 420 nm is 31.5%.