Preparation Of Carbon Quantum Dots And Semiconductor Photocatalyst With Enhanced Visible-light Irradiation Photocatalytic Activity Toward Dye Waste-water Degradation And Hydrogen Production

Semiconductor photocatalytic technology has unique advantages in the degradation of organic pollutants in sewage,and is an effective method in environmental treatment.In addition,in recent years,the application of photocatalytic technology to clean energy generation?H₂?from water decomposition has also attracted great attention.Nowadays,photocatalytic technology has been wide application prospects for degradation of organic pollutant and water splitting?When organic pollutants are used as sacrificial agents and appropriate photocatalysts are selected,the degradation of pollutants can be realized and hydrogen can be produced at the same time.Photocatalytic technology can not only restore the environment,but also produce clean energy and alleviate the energy crisis.In order to make photocatalytic degradation of organic pollutants and produce hydrogen efficiently and orderly,we choose to use wide band semiconductor photocatalyst,which has strong redox ability.However,in practical application,this kind of photocatalyst has some defects and shortcomings:First of all,because of the wide band gap of this kind of photocatalyst,the photocatalyst can be stimulated only under high energy ultraviolet light,thus redox reaction is carried out.However,ultraviolet light accounts for only 5.0 percent of the solar light,most of the visible light is difficult to use,and the utilization rate of solar light is low.After the photocatalyst is excited,photogenerated electrons and photogenerated holes are produced in the conduction band and valence band respectively.Because of the activity of electrons and holes,it is easy to compound,which affects the efficiency of photocatalytic reaction.Therefore,we choose carbon quantum dots?CQDs?with upconversion luminescence and electron transport function to recombine with wide band semiconductor to improve the utilization ratio of solar light and the efficiency of photocatalytic reaction.In this work,a novel visible-light driven photocatalyst,CQDs/KNbO₃ composite,is successfully prepared via hydrothermal and mixed-calcination methods.Multipletechniques,such as X-ray diffraction?XRD?spectroscopy,scanning electron microscope?SEM?,transmission electron microscopy?TEM?,X-ray photoelectron spectroscopy?XPS?,energy dispersive X-ray?EDX?spectroscopy,fourier-transform infrared?FT-IR?spectroscopy,UV–vis diffuse reflectance spectroscopy and photoluminescence?PL?spectroscopy,are applied to investigate the morphologies,structures and optical properties of the prepared CQDs/KNbO₃ composites.The photocatalytic activity of CQDs/KNbO₃ composites is evaluated via degradation of crystal violet dye as target organic pollutant with simultaneous hydrogen production under visible-light irradiation.The results show that the CQDs/KNbO₃ composites exhibit much higher photocatalytic activity than the KNbO₃.It is ascribed to the presence of the CQDs as co-catalyst on the surface of KNbO₃ particles,forming much more active sites for trapping electrons and promoting the separation of photo-generated electron-hole pairs.In addition,the CQDs can absorb visible-lights and emit the ultraviolet-lights to activate the wide band-gap KNbO₃.The study of reusability shows that the CQDs/KNbO₃ can be effectively recycled for four repetitive cycles and maintain a higher level of photocatalytic activity.In conclusion,the present work designs an effectively visiblelight driven photocatalyst,which can be applied in photocatalytic degradation of organic pollutants with simultaneous hydrogen evolution.It is of great significance to solve environmental problems and generate clean energy.