Preparation And Photocatalytic Properties Of Molybdenum Selenide Composite Photocatalyst

With the rapid development of industry and agriculture the problem of water pollution becomes more and more serious.Ammonia nitrogen is one of the main pollutants leading to the water eutrophication.The development of solar photocatalytic technology for the removal of ammonia nitrogen has become a hot issue in the field of environmental protection.In the solar spectrum,infrared light?760-3000 nm?is 53%,UV light??<400nm?is only 4%,and visible light?400-760 nm?is 43%.In the past few decades,people's research has focused on ultraviolet and visible light.Therefore,it is of great significance to develop semiconductor materials with near-infrared light response for making full use of solar energy.In this paper,molybdenum selenide?MoSe₂?was used as the main material and the composite photocatalyst was prepared with activated carbon?AC?,fullerenes(C₆₀),graphene?rGO?,and nitrogen-doped graphene?NG?.Their photocatalytic performances for the degradation of ammonia nitrogen upon near-infrared light were studied,respectively.The main content is as follows:First,MoSe₂/AC material was synthesized through the hydrothermal method.X-ray powder diffraction?XRD?,scanning electron microscope?SEM?,high-resolution transmission electron microscope?HRTEM?,raman spectroscopy?Raman?,ultraviolet visible near infrared diffuse reflection spectroscopy?UV-VIS-INF-DRS?were used for the characterization of the morphology and structure of MoSe₂/AC.The composite materials were used as photocatalysts to degrade ammonia upon near infrared light.Experiment showed that MoSe₂/AC was produced by hydrothermal method with using sodium molybdate?Na₂MoO₄·2H₂O?and selenium?Se?,hydrazine hydrate?H₄N₂·H₂O?as reducing agent and AC at 180?,under 48 h.The degradation efficiency of ammonia reached 95.7%using 2 g/L MoSe₂/AC?AC 5.0 wt%?composite as the photocatalyst in the100.0 mg/L ammonia-nitrogen solution with pH 10.5 under near-infrared light irradiation for 11 h,while the degradation ratio was only 68.0%using the pure MoSe₂ as the photocatalyst under similar conditions.Its degradation rate increased by 27.7%.The kinetics study showed that ammonia degradation followed the first-order reaction kinetics equation,and the average value of its apparent chemical rate constant was 0.1882 h^-1.Seven runs of photocatalytic degradation experiments showed that the composite materials of MoSe₂/AC had relatively stable photocatalytic activity and could be recycled and reused.The results of gas chromatography showed that the degradation product of ammonia nitrogen is nitrogen and the near infrared radiation denitrification was realized.Second,MoSe₂/C₆₀0 material was synthesized through the hydrothermal method.The morphology of composite materials was characterized by XRD,SEM,TEM,Raman,UV-VIS-INF-DRS.It was used as photocatalyst to degrade ammonia nitrogen in near infrared light.The experiment showed that MoSe₂/C₆₀0 was produced by hydrothermal method with using Na₂MoO₄·2H₂O and Se,H₄N₂·H₂O as reducing agent and C₆₀0 at 180?,under 48 h.The degradation efficiency of ammonia reached 93.7%using 3 g/L MoSe₂/C₆₀(C₆₀0 5.0 wt%)composite as the photocatalyst in the 100.0 mg/L ammonia-nitrogen solution with pH 10.0 under near-infrared light irradiation for 9 h,while the degradation ratio was only 59.3%using the pure MoSe₂ as the photocatalyst under similar conditions.The kinetics study showed that ammonia degradation followed the first-order reaction kinetics equation,and the average value of its apparent rate constant was 0.2095 h^-1.Seven runs of photocatalytic degradation experiments showed that the photocatalytic performance of MoSe₂/C₆₀0 was stable.The results of gas chromatography showed that the degradation product of ammonia nitrogen is nitrogen and the near infrared radiation denitrification was realized.Third,MoSe₂/rGO material was synthesized through the hydrothermal method.The morphology of composite materials was characterized by XRD,SEM,TEM,Raman,UV-VIS-INF-DRS.Then MoSe₂/rGO material was used as photocatalyst to degrade ammonia upon near infrared light.The experiment showed that MoSe₂/rGO was produced by hydrothermal method with using Na₂MoO₄·2H₂O and Se,H₄N₂·H₂O as reducing agent and rGO at 180?,under 48 h.The degradation efficiency of ammonia reached 94.8%using 3 g/L MoSe₂/rGO?rGO 5.0 wt%?composite as the photocatalyst in the 100.0 mg/L ammonia-nitrogen solution with pH 10.5 under near-infrared light irradiation for 9 h,while the degradation ratio was only 60.0%using the pure MoSe₂ as the photocatalyst under similar conditions.The degradation rate increased by 34.8%.The kinetics study showed that ammonia degradation followed the first-order reaction kinetics equation,and the average value of its apparent rate constant was 0.2161 h^-1.Five runs of photocatalytic degradation experiments showed that the photocatalytic activity of MoSe₂/rGO was stable and it could be recycled.Fourth,MoSe₂/NG material was synthesized through the hydrothermal method.The morphology of composite materials was characterized by XRD,SEM,TEM,Raman,UV-VIS-INF-DRS,X-ray photoelectron spectroscopy?XPS?.Then MoSe₂/NG materials were used as photocatalysts to degrade ammonia upon near infrared light.The experiment showed that MoSe₂/NG was produced by hydrothermal method with using Na₂MoO₄·2H₂O and Se,H₄N₂·H₂O as reducing agent and NG at 180?,under 48 h.The degradation efficiency of ammonia reached 95.6%using 3 g/L MoSe₂/NG?NG 5.0 wt%?composite as the photocatalyst in the 100.0 mg/L ammonia-nitrogen solution with pH 10.0under near-infrared light irradiation for 8 h,while the degradation ratio was only 53.0%using the pure MoSe₂ as the photocatalyst under similar conditions.The kinetics study showed that ammonia nitrogen degradation followed the first-order reaction kinetics equation,and the average value of its apparent rate constant was 0.2340 h^-1.Seven runs of photocatalytic degradation experiments showed that MoSe₂/NG was stable.The reaction mechanism indicated the ammonia was converted into nitrogen gas.Fifth,the apparent rate constants of MoSe₂/AC,MoSe₂/C₆₀,MoSe₂/rGO,and MoSe₂/NG were respectively 0.1882 h^-1,0.2095 h^-1,0.2161 h^-1,and 0.2340 h^-1.The photocatalytic activity order of MoSe₂ composites were MoSe₂/NG>MoSe₂/rGO>MoSe₂/C₆₀>MoSe₂/AC by comparison.Obviously,the photocatalytic activity of MoSe₂/NG was the highest,possibly because the nitrogen atoms in NG and ammonia components have the high electronegativity.Therefore,it was easy to form hydrogen bonds with NH₃,which increased the concentration of ammonia on the surface of the composite material,and eventually improved the efficiency of ammonia degradation.In addition,NG had faster electron transport capacity,which could greatly reduce the composite rate of photogenerated electrons and holes.