Preparation And The Study On The Photocatalytic Hydrogen Performance Of Molybdenum Disulfide Based Photocatalysis

With the growing global environmental problems and growing energy demand,the production of clean and renewable energy has been recognized as one of the most important and promising strategies.There is tremendous potential for replacing fossil fuels by decomposing water photocatalytic hydrogen production?PHR?to produce clean,sustainable hydrogen.The development of the number and quality of active sites and the efficient separation of photogenerated carri ers are important means for achieving efficient photocatalysis.This paper explores and constructs the control of the morphological structure,exposes the edge and edge effects of the active semiconductor,and activates the semi-conductive inert surface to exploit the active site of the catalyst.At the same time,functionally oriented multi-stage nanostructures are grown,and low-resistance interfaces enable efficient spatial separation of photogenerated carriers.In this dissertation,2D layered sulphides are used as the main method to construct multi-stage nanostructured composite materials.Methods including the design and construction methods of composite materials are studied.The behavior of photoelectron electrons is studied by means of transient flu orescence attenuation spectroscopy.Physical theory simulation calculations explore the mechanism of PHR.The full-scale analysis of photogenerated carrier generation-efficient migration-interface transfer-reaction was revealed.details as follows:?1?Morphology structure controls the exposure of co-catalyst active sites:By assembling CdS nanoparticles onto multi-stage nanostructures of MoS₂ and N-doped graphene,a variety of active materials are integrated into one and the overall composition of the components Configured and optimized for efficient PHR.The unique vertical orientation structure promotes efficient light capture and absorption and provides an unobstructed electronic rapid separation/transport pathway to suppress charge recombination.Its high surface area and density of highly active sites lead to efficient use.Notably,visible light-irradiated photocatalysts showed hydrogen generation rates of up to 5.01 mmol h^-1 g^-1,25 times that of CdS nanoparticles alone,without the use of a precious metal as a co-catalyst.After a 30-hour stability test,it shows extremely high performance and stability.?Chapter 2??2?Exposure of semiconductor active edge and edge effects:For 2D semiconductor materials,active sites exist at their edges,corners,t wists,and creases.MoS₂QDs?MoS₂ quantum dot?enhance the hydrogen evolution activity by enhancing edge effects and electrical/optical properties to create more active sites.In addition,the edge interface has a lower interface resistance,and the design of the edge-based heterostructure can maximize the use of edges.The difficulty in constructing a 2D semiconductor-based photocatalyst is to deposit the co-catalyst onto the active sites of the semiconductor to enhance its activity more effectively through a clever structural design.By preparing closely-linked ZnIn₂S₄ floral structures,their structural spaces are closely linked to form a huge flower network structure,and the light absorption intensity is higher than that of monodisperse and independent ZnIn₂S₄ nanospheres.MoS₂QDs occupy the edge of the petal of the ZnIn₂S₄ compact nanoflower net due to the exposure of the active sites of the marginalization,fully functioning as an edge effect,with the edges as active sites,successfully building the e dge of the MoS₂QDs deposited to the edge active sites of ZnIn₂S₄.Heterogeneous structure,more reasonable use of ZnIn₂S₄ lamellar active sites.The PHR performance of the composite system has been greatly improved to 2.2378 mmol h^-1g^-1.?Chapter 3??3?3D spatial compounding for omni-directional light capture:In order to seek greater sustainability of water management,this study proposes a new line for wastewater purification while producing clean energy.Photocatalytic purification of wastewater while simultaneously converting solar energy into clean hydrogen energy is attractive.However,due to the relatively low photocatalytic efficiency of photocatalysts,this work remains a challenge.In this study,we used a simple solvothermal method to synthesize 3D nanostructured ZnIn₂S₄ and RGO?reduced graphene oxide?photocatalyst composites-MoS₂QDs@ZnIn₂S₄@RGO modified by MoS₂QDs.RGO promotes electron transfer and the highly dispersed MoS ₂QDs provides many H₂ generation sites.RhB?rhodamine B?,EY?potato Y?,FA?rich acid?,MB?methylene blue?and PNP?p-nitrophenol?were purified by photocatalysis in simulated wastewater.Degradation efficiency and TOC removal rate were 91%and75%for PNP,92.2%and 72%for FA,98.5%and 80%for MB,98.6%and 84%for EY,and 98.8%and 88%for RhB,respectively.In these tests,the highest H ₂ yield?45?mol?was achieved during degradation of RhB.Experiments and calculations have shown that the more negative LUMO levels of organic molecules can be used to transfer electrons to the catalyst,thereby experimentally purifying wastewater while producing H₂.Importantly,the removal efficiency of real river water in natural organic matter reached 76.3%⁹8.4%,COD decreased from 32 to 16 mg/L,and produced 12.8?mol H₂ after 12 hours.The results confirmed that organic contaminants in the wastewater can act as electron donors for the PHR.Solar-driven photocatalysts have good resistance to toxicity and good circulation in the presence of organic pollutants.Importantly,the organic matter in the natural river water can be used effectively as an electron donor to obtain a considerable H ₂ yield.Photocatalytic processes have the potential to purify wastewater while converting solar energy to clean hydrogen energy.?Chapter 4??4?Activate the semi-conductor inert basal plane to construct a low-resistance and high-efficiency interface to achieve high-efficiency space separation of photo-generated carriers:Realization of an effective PHR reaction requires highly efficient adjustment of the flow of photo-generated carriers.In this study,we developed an intelligent strategy to place MoS₂QDs on S defects in the Zn plane in monolayer ZnIn₂S₄?Vs-M-ZnIn₂S₄?to produce 2D atomic-level heterostructure MoS₂QDs@Vs-M-ZnIn₂S₄.This work provides a prototype material for the study of the role of defects between electronic structure and activity,as well as atomic level understanding of photocatalytic systems based on 2D photocatalytic materials.The results showed that the PHR activity of optimized MoS₂QDs@Vs-M-ZnIn₂S₄ was as high as 6.884 mmol g^-1 h^-1,which was 11 times higher than that of the bulk ZnIn₂S₄PHR activity of 0.623 mmol g^-1 h^-1.Apparent quantum yield reached to 63.87%?420nm?.This work provides a prototype material for the study o f the role of defects between electronic structure and activity,as well as atomic level understanding of photocatalytic systems based on 2D photocatalytic materials.?Chapter 5?...