Performance And Mechanism Of G-C₃N₄/Transition Metal Sulfide Photocatalytic Reduction Of Hexavalent Uranium

Graphite-phase carbon and nitrogen compounds（g-C₃N₄）,as a novel metal-free polymer n-type semiconductor,have many promising properties,making g-C₃N₄-based materials a new class of multifunctional nanoscilloplatform for electronic,catalytic,and energy applications.Although g-C₃N₄has many advantages and bright prospects in a variety of photocatalytic applications,its narrow visible light absorption range,low quantum yield,and easy combination of photoelectron-holes limit its effectiveness in a practical applications.Constructing heterojunction has been proved to be an effective strategy,and the purpose of this paper is to solve the above problems by constructing heterostructure of transition metal sulfide and g-C₃N₄.In addition,the remediation of U（VI）is also a concerned issue.Although it has been reported in previous studies that photocatalytic technology can effectively reduce U（VI）to U（IV）,the final reduction morphology,reduction mechanism,influencing factors and practical application efficiency remain to be further explored.Therefore,In paper we not only studies the photoelectric properties and photocatalytic properties of materials,but also pays attention to the above problems.Main tasks include:（1）Two-dimensional g-C₃N₄nanosheets（g-CNNS）and flower-like Mo S₂were successfully synthesized by calcination and hydrothermal method.The Mo S₂/g-C₃N₄nanosheet（FMCN）was successfully matched by water bath,ultrasonic and calcination.By XRD,FT-IR,SEM and TEM,the interface between g-CNNS and Mo S₂was well matched.The photocatalytic reduction of U（VI）showed that FMCN had a good catalytic reduction efficiency on U（VI）in visible light.At 75 min,the reduction rate of 0.05-FMCN at p H=5.5was 86.8%.UV-vis,PL and other characterization results confirmed that FMCN obtained stronger visible light absorption,faster separation and transmission of photogenerated charges,which significantly enhanced the photocatalytic performance.The band gap position was measured by XPS-VB and Mott-Schottky curves.Finally,it is proved that h⁺,·O₂^-and·OH are all active substances in U（VI）reduction through the capture experiment of active species.（2）2D g-CNNS and hexagonal Sn S₂nanosheets were successfully synthesized by thermal oxidation method and hydrothermal method,respectively.The composite of 2D structure and 2D structure can maximize the specific surface area and expose more active sites providing better conditions of U（VI）reduction.Sn S₂/g-CNNS（abbreviated to Sn CN）was successfully synthesized by a simple heat treatment method.XRD,FT-IR,SEM and TEM confirmed that the interface between g-CNNS and Sn S₂is well matched.U（VI）photocatalytic reduction test showed that Sn CN has excellent catalytic reduction effect on U（VI）under visible light,and the reduction rate of U（VI）was 98.39%in 90 min.The optimal reducing conditions of the materials were studied by changing the experimental conditions such as p H,uranium solution concentration,solid-liquid ratio,and methanol content,that is,at p H=5,C_U（VI）=100 ppm,solid-liquid ratio is 1 g.L^-1and 3.5 m L of methanol added,the catalyst has the best catalytic reduction performance for U（VI）.In addition,the photocatalytic performance of the photocatalytic performance under actual conditions was studied under sunlight.Characterization methods such as UV-vis and photocurrent response confirm that Sn CN has stronger absorption of visible light and faster separation and transmission of photo-generated charges,thereby significantly enhancing photocatalytic performance.Mott-Schottky and XPS valence band spectra accurately show the material band gap.The intrinsic electron-hole transport mechanism and the valence state of uranium were explored by XPS.The surface morphology changes of the material after photocatalysis were explored by TEM,and the final deposited form of uranium was（UO₂）O₂.2H₂O by XRD.Finally,through active species capture experiments,it was proved that h⁺,·O₂^-and·OH are all active substances in U（Ⅳ）reduction.