Constructing High Performance Photocatalytic Hydrogen Production Catalyst Based On Two-dimensional Layer Material And Its Role Mechanism Research

With the rapid economic development and the continuous improvement of people’s living standards,the demand for energy continues to grow.The development of clean,pollution-free,renewable,and highenergy-density hydrogen energy is essential to solve current energy and environmental problems.Photocatalytic water splitting can utilize abundant and clean solar energy,has the characteristics of environmental friendliness and low energy consumption.Therefore,it is a hydrogen energy production method with broad application prospects.However,traditional semiconductor catalysts often involve shortcomings such as low conductivity,narrow visible light absorption range,high photoelectronhole recombination rate.Therefore,the design and synthesis of photocatalysts with strong light response capability and high electron-hole separation efficiency are important for improving photocatalytic water splitting and hydrogen production.Performance,so as to achieve highefficiency energy conversion is of great significance.In addition,in the photocatalytic water splitting hydrogen production reaction,light excites electrons to reduce protons to produce H2,but the oxidizing ability of excited holes is not fully utilized.Therefore,if the abundant and easily available raw materials(such as biomass and its derivatives)are used to capture and excite holes,the photocatalytic aquatic hydrogen production reaction and the biomass oxidation reaction can be coupled to promote the increase in the efficiency of hydrogen production.High-value-added downstream products can not only effectively promote solar energy utilization efficiency,but also achieve high-value conversion of renewable resources.This thesis takes the photocatalytic decomposition of water to produce hydrogen and the photocatalytic water production of hydrogen-biomass oxidative coupling reaction as the target reactions,and two twodimensional layers of graphite phase carbon nitride(g-C3N4)and layered composite metal hydroxides(LDHs)The shape material is the catalyst carrier or precursor,and the control of the energy band structure,defect structure and electronic structure of the supported catalyst is focused on,thereby achieving the enhancement of catalytic performance.Specifically,in view of the unsatisfactory performance of traditional semiconductor catalysts for photocatalytic hydrogen production,it is proposed to use Sdoped C3N4 as a carrier to construct a supported sulfide catalyst rich in defect sites by means of photo-induced reduction method to enhance the light A new method for catalytic decomposition of water to produce hydrogen performance;in response to the problem that the half-reaction efficiency of 5-hydroxymethylfurfural(5-HMF)oxidation in the coupling reaction needs to be improved,a specific alloy with LDHs as the precursor was created and based on the topological reduction method.The structure of the bimetallic catalyst is a new strategy to enhance the performance of photocatalytic water production of hydrogen-5-HMF oxidative coupling reaction.(1)Taking the photocatalytic water splitting hydrogen production performance enhancement as the starting point,the S-doped layered material g-C3N4 is used as the carrier,and Ni(dmgH)2 is loaded on the surface as the precursor,and it is prepared by the light-induced reduction method.Supported NiS photocatalysts rich in defect sites,systematically explored the effects of dopant atoms and promoter types on the structure and electronic structure of active site defects,and studied the structureactivity relationship based on the difference in the performance of each catalyst.The results of spherical aberration electron microscopy,XAFS,EPR,and XPS show that after light-induced reduction,the structure of the catalyst changes,from atomically dispersed Ni(dmgH)2 to lowcoordination NiS with an average size of about 12.5 nm,and A large number of Ni+ and S vacancies are generated.The study found that the hydrogen production performance of the NiS/SCN catalyst is greatly improved compared with the non-doped NiO/CN,the NiS/CN prepared by the chemical deposition method and the NiO/SCN comparison sample obtained by the light-induced reduction method.The average hydrogen production rate after 15h was 414.5 μmol·g-1·h-1,which was 3.9 times,30.5 times,and 2.4 times that of the other three,respectively.In addition,after 5 cycles of experiments,the hydrogen production performance of the catalyst did not decrease,and it had good photocatalytic stability.The reason for the improved performance can be attributed to:the doping of S atoms and the existence of S vacancies broaden the light absorption range,improve the visible light absorption capacity,and promote the separation of photogenerated carriers.The low-coordination Ni species acts as the active site.Therefore,the activation energy of the hydrogen evolution reaction is reduced,so that the NiS/SCN catalyst obtained based on the light-induced method exhibits the best hydrogen production performance.(2)Starting from the enhancement of the photocatalytic water production of hydrogen-5-HMF oxidative coupling reaction performance,the photosensitive ions Cu2+and Co2+are introduced into LDHs at the same time,with CuCo3Al2-LDHs,CuCo4Al2-LDHs,CuCo5Al2-LDHs as precursors,and high temperature topology Three kinds of bimetallic CuCo catalysts were prepared by reduction.The study found that in this series of catalysts,the bimetallic particles present a core-shell structure of Co@CuCo alloy and are evenly dispersed on the amorphous Al2O3 carrier.Compared with other catalysts,the CuCo5/Al2O3 catalyst with a Cu/Co ratio of 1:5 has the highest hydrogen production performance,and its hydrogen production rate can reach as high as 888.3 μmolh-1g-1.And it shows a high conversion rate of 5-HMF and a yield of 2,5furandicarboxylic acid(FDCA),which realizes the high-efficiency directional conversion from 5-HMF to FDCA under neutral conditions.The reason for the improved performance can be attributed to:CuCo5/Al2O3 catalyst has stronger light absorption ability,higher photogenerated electron-hole separation ability and stronger driving force for hydrogen evolution reaction,so that it has higher photocatalysis Hydrogen production from water-5-HMF oxidative coupling reaction performance.