Construction Of Defective Molybdenum Oxide Composites And Their Photocatalytic Water Splitting Performance

In recent years,our country has increasingly emphasized the development concept of"green water and green mountains are golden mountains and silver mountains".At the United Nations General Assembly,our country announced the emission reduction target of"carbon peak and carbon neutrality",and this year the two sessions included this target in the government work report for the first time.Therefore,it is urgently needed to develop a technology to produce high-efficiency and clean energy.Photocatalytic water splitting to produce hydrogen technology demonstrates great potential.Unfortunately,there are still some"bottlenecks"that greatly limit the practical application of photocatalytic water splitting.For example,high-speed recombination quenching of photo-generated charges,insufficient absorption range of sunlight(mainly concentrated in the ultraviolet and visible regions),and insufficient redox capabilities.Given the above shortcomings,we considered to design an S-scheme heterojunction photocatalyst containing non-metallic plasmon oxide.Non-metallic plasmon oxides will exhibit a local surface plasmon resonance(LSPR)phenomenon similar to precious metals when excited by light.The LSPR effect can expand the utilization range of sunlight,and the S-scheme heterostructure can promote the effective separation and transfer of photogenerated electron-hole pairs.By synergistically using these two effects,it is hoped to design a highly efficient new photocatalyst.In this paper,the MoO_3-x nanosheet with a strong LSPR effect was chosen as the main research object,and the MoO_3-x nanosheet was combined with three sulfide semiconductors with different morphologies.The photocatalytic performance and mechanism of photocatalytic water splitting to produce hydrogen were studied.The main research content and conclusions of this paper are as follows:(1)MoO_3-x nanosheets were successfully synthesized by the solvothermal method.XRD,XPS,SEM,and TEM tests were utilized to analyze the structure and morphology,and it was found that MoO_3-x nanosheets demonstrated an orthorhombic molybdenum oxide with a two-dimensional nanosheet morphology containing oxygen vacancies(defects).Through UV-vis spectroscopy,it is found that it has strong LSPR tail absorption in the wavelength region of 600-1400 nm.(2)The 0D Cd S nanoparticles were successfully loaded on the MoO_3?x nanosheets by the in-situ co-precipitation method.After various tests and analyses,it was proved that a 0D/2D Cd S/MoO_3?x S-scheme heterojunction was synthesized.This composite photocatalyst shows a significantly improved visible-light-driven photocatalytic hydrogen-production activity.The hydrogen production rate of the optimal ratio composite material reaches 7.44 mmol·g^?1·h^?1,and it has certain performance under single-wave light irradiation of higher wavelengths such as 550and 650 nm.Based on the results of ultraviolet-visible diffuse reflectance spectroscopy,theoretical calculations(DFT),electron spin resonance analysis,and XPS,the improvement of the photocatalytic performance of this composite material is attributed to the S-scheme heterojunction enhanced by the LSPR effect.(3)The 1D/2D Zn_0.1Cd_0.9S/MoO_3?x composite material composed of Zn_0.1Cd_0.9S nanorods and MoO_3?x nanosheets were synthesized by the interface self-assembly method.The 1D/2D Zn_0.1Cd_0.9S/MoO_3?x composite exhibited enhanced photocatalytic performance compared to the single semiconductor.The composite material containing 25%MoO_3?x nanosheets has the most excellent catalytic activity and excellent cycle stability,and the photocatalytic hydrogen production rate under visible light irradiation was as high as 149.2 mmol·g^?1·h^?1.It was found that there are two main reasons for the improved performance of this composite photocatalyst.On the one hand,the LSPR effect can broaden the range of light utilization of composite materials;on the other hand,the S-scheme heterostructure promoted the separation and transfer of photogenerated carriers.(4)When MoO_3?x nanosheets were added during the synthesis of ZnIn₂S₄,the MoO_3?x nanosheets will be partially vulcanized.At the same time,the thin layer of ZnIn₂S₄ nanosheets were grown in situ on the surface of the vulcanized MoO_3-xnanosheets to obtain a sandwich-like ZnIn₂S₄/S-MoO_3-x composite photocatalyst.The phase structure,chemical composition,microscopic morphology,energy band structure,and dynamic behavior of the generated photo-generated charges of the relevant samples were studied.Based on the analysis of these test results,the improvement of the catalytic activity of this novel photocatalyst can be attributed to the formation of a Z-scheme heterojunction,which promoted the separation and transfer of photogenerated carriers.