Preparation And Photocatalytic Properties Of Amino Modified Carbon Quantum Dots And Their Composites

BackgroundCarbon quantum dots?CQDs?is a new type of green carbon nanomaterials,C is its main component.It has a number of excellent photophysical and chemical properties,such as the light-induced electron transfer capacity,photo-proton capability,up-conversion and down-conversion luminescence properties,wide UV-Vis spectrum absorption,which makes it possible to improve the catalytic performance of photocatalysis as semiconductor material.However,the pure CQDs have low fluorescence efficiency,weak visible light absorption,poor stability in photocatalysis and low photocatalytic efficiency.Therefore,it is extremely important to prepare high-performance fluorescent carbon quantum dots.ObjectiveThe amino modified,water-soluble carbon quantum dots with excellent optical properties were prepared by a simple operation method.Prepared the amino modified carbon quantum dots/titanium dioxide?NCDs/TiO₂?and the amino modified carbon quantum dots/graphite phase carbon nitride/copper oxide?NCDs/g-C₃N₄/CuO?composite photocatalytic materials with sunlight spectral response by combined with other materials.To explore the different experimental parameters on the photocatalytic performance,revealed the mechanism of MB degradation of these two composites under visible light,provide a theoretical basis for the application of these type of catalysts.Methods1.The amino modified fluorescent CQDs were prepared by hydrothermal method using folic acid as carbon source and ammonia as modifier.The CQDs were purified by dialysis,and then they were characterized by UV,fluorescence,infrared and X ray photoelectron spectroscopy.2.Titanium dioxide nanoparticles were prepared by sol-gel method using four butyl titanate as titanium source,and then NCDs/TiO₂ composite photocatalyst was prepared by ultrasonic method combined with titanium dioxide and NCDs.The morphology,crystal structure,elemental composition and content of the composite photocatalyst were characterized by scanning electron microscopy?SEM?,X-ray diffraction?XRD?and X-ray photoelectron spectroscopy?XPS?.Taking decolorization rate and reaction rate constant as the main indexes,the effects of different experimental parameters(such as reaction time,amount of catalyst,pH,amount of NCDs on the degradation efficiency and reaction kinetics characteristics of MB were investigated.3.As the three element composite photocatalyst NCDs/g-C₃N₄/CuO was prepared by in situ composite of NCDs with visible light catalyst graphite nitride and metal ion Cu²⁺.The influence of the amount of carbon quantum dots and Cu²⁺doping on the photocatalytic activity of the composites was investigated.The photodegradation mechanism of MB with NCDs/g-C₃N₄/CuO and H₂O₂ was studied.Results1.NCDs prepared in this experiment has wide spectrum ultraviolet absorption,excitation wavelength dependence,upconversion fluorescence properties,salt resistant stability and photoelectric conversion properties;It was shown that the surface of NCDs contains-OH,-NH₂,C=O and other functional groups,and has good water solubility.It can be applied to detect metal ions,such as Zn²⁺,Fe³⁺,Co²⁺,Ni²⁺and Cu²⁺.2.The NCDs/TiO₂ composite photocatalyst has better morphology and crystallinity,and the activity of TiO₂ was increased with the doping of NCDs in the degradation of MB under visible light.3.With the doping of NCDs and Cu²⁺,the photogenerated electrons and holes of g-C₃N₄ were effectively separated,thus the photocatalytic efficiency of g-C₃N₄ by visible light was increased obviously.With the addition of H₂O₂,the degradation rate of MB can be reached more than 90%catalyzed by NCDs/g-C₃N₄/CuO under light irradiation for30 min.Conclusion1.The aminated NCDs with excellent optical properties have been successfully prepared by a simple method.With the doping of NCDs,the spectral range of TiO₂ was extended,and the catalytic efficiency of TiO₂ under visible light was appropriate increased,too.2.NCDs/g-C₃N_4/CuO as a new three element composite photocatalytic material has been prepared,and good photocatalytic activity for MB under visible light was shown.Superoxide anion radical(O₂^·-)and photohole?h⁺?played an important role in the process of photocatalytic degradation of MB.