The Study Of The Modification Of ZnIn₂S₄ Photocatalyst And Its Construction Of Z Scheme System For The Hydrogen Evolution From Water Under Visible-light

Solar energy is one of the most important renewable energy. Hydrogen is an ideal form of solar energy for its high energy density, convenience of storage and transport,and eco-friendly nature. Therefore, the transformation of solar energy into hydrogen by using water as raw materials is a strategy of sustainable development, which has great social and economic value. In this work, the hydrogen production photocatalyst ZnIn₂S₄ has been modified first, then the new style Z scheme photocatalyst has been constructed to produce H₂ from water steady without a sacrifice agent, and finally, the Z scheme photocatalyst has been used on the photocatalytic degradation of organic pollutant and H₂ evolution from water. Meanwhile, a series of characterization methods such as XRD,SEM, EDS, BET, DSR and UV-vis have been used to determine the composition and structure of the catalyst, the main research contents are as follows:The effect of the rare earth elements on the performance of ZnIn₂S₄ has been studied. The results indicate that the RE element exists as the oxide RE2O3 and their modification can reduce the ZnIn₂S₄ crystallite size, inhibit ZnIn₂S₄ grain growth,promote ZnIn₂S₄ crystallite self-organized into a micro-sphere flower-like morphology,increase BET surface area and total pore volume, and bring rich defects to ZnIn₂S₄. The photocatalytic activity is enhanced with the increase of the RE3+ radius and the decrease of the number of electrons of RE 4f shell and the La show the best effect. The effects of the amount of La on the performance of the catalyst have also been studied. The morphology, BET surface area, and pore structure of the catalyst have be affected by the La amount. 1.0 wt% La-ZnIn₂S₄ show the best activity, the apparent quantum yields and the energy conversion efficiency was determined to be 8.83 % and 5.06 %.The effects of the treatment manner of the oxidized graphene and the amount of GO on the performance of the photocatalyst have also been studied. The morphology and the reduction degree of the RGO which decide the separation efficiency of the photogenerated electron-hole pairs could be affected by the treatment manner of GO and the solution method show the best effect. Regarding the synergistic effect of RGO and La on the performance of ZnIn₂S₄, studies have shown the separation efficiency of the photogenerated electron-hole pairs could be improved by the adding of RGO and the morphology and pore structure of the catalyst could be affected by the addition of La.The activity reached its peak when both of the La and RGO amount reached 1.0 wt%,and the apparent quantum yields and energy conversion efficiency were determined to be 29.45 % and 18.79 %.The Z scheme photocatalyst has been constructed in three ways: discrete contact,simple contact, and contact by RGO. It is found that the Z scheme photocatalyst just beconstructed by RGO own good activity. The catalyst optimization experiment show that when the proportion of the two ends is 5:1, the amount of the hole trap RuO2 is 1.0 wt%,the amount of the RGO is 1.5 wt%, and the amount of the electron trap Pt is 1.0 wt%,the catalyst shows the best activity. The mechanism of the Z scheme photocatalyst is that both the two ends of the catalyst is inspired by the visible light and generate electron-hole pairs. The electron on the surface of ZnIn₂S₄ will be trapped by the Pt and will reduce water to produce H₂. The RuO2 will trap the hole on the surface of BiVO4.The electron on the surface of BiVO4 will be transferred to the RG, which will surround the surface of BiVO4. Then, the RGO will pass the electron to the ZnIn₂S₄ and recombine with the ZnIn₂S₄ hole so as to realize the charge recycle of the whole Z scheme system. The optimized Z scheme photocatalyst has been used on the photocatalytic degradation of organic pollutant and H₂ evolution from water. The results show that when formaldehyde is added, the catalyst concentration is 1.5 g·L^-1 and the solution pH is 13, it achieves its best performance. The H₂ evolution efficiency is raised with the rising of the concentration of formaldehyde. The activity reached the best when the formaldehyde concentration is 5 mol·L^-1. The apparent quantum yields and the energy conversion efficiency were determined to be 22.91 % and 13.31 %. The H₂ production efficiency is also very high when the mixed compound organic pollutants acted as the sacrificial agent.The photocatalyst ZnIn₂S₄ has been modified by the rare earth elements and graphene together, the activity of photocatalytic decomposition of water into hydrogen under visible light has achieved remarkable results. On this basis, the Z scheme photocatalyst ZnIn₂S₄-graphene-BiVO4 has been constructed, the hydrogen production from photocatalytic decomposition of water has been realized under visible light without sacrificial agent. This study will provide a new way for the photocatalytic decomposition of water under visible light, and it will lay the foundation for the development of Z scheme photocatalytic theory.