The Synthesis Of Fluorescent Carbon Dots And Performance Study On Photocatalytic Degradation Of Composite Materials

The large-scale use of antibiotics and organic dyes has brought great convenience to the production and life of human beings,but also constitutes a serious threat to the ecological environment and human health.The traditional wastewater treatment technology can not achieve the efficient removal of organic pollutants,photocatalytic oxidation technology shows potential application prespect in wasterwater treatment by comparison.However,the narrow light response range and the recombination of photogenerated electrons and holes are prevailing problem of the photocatalyst,resulting in low photocatalytic efficiency.Most of wide bandgap photocatalysts is UV or visible light response（only in the solar spectrum 50%）,in order to broaden the range of light absorption,improve the utilization rate of light energy,carbon quantum dots（CQDs）composite photocatalyst has become a research hotspot.CQDs possess a large crossseciton of up-conversion absorption and emission,the abundant PL spectra of CQDs with upconversion properties can facilitate the matching of energy band gaps of various semicondctors with UV and visible-light photocatalytic activity.Based on the above theory,a series of CQDs composite photocatalyst was developed over the vectorial charge-transfer channel design,interfacial modification and indirect implementation of infrared light catalytic application,and the photocatlytic degradation rate and mechanism of the system were discussed from the aspects of component control,surface coating,catalysts loading and heterogeneous structure.Our works provide a basis for the realization of industrial scale-up applications.The main contents of this paper are as follows:1.We report for the first time the successful attempt at the fabrication of CQDs/Ag/Ag₂ O ternary plasmonic photocatalyst throught a facile in-situ reduction method.The in-situ growth of CQDs on Ag₂ O is important approach to achieve the robust bonding between Ag₂ O and Ag nanoparticles,which is essential for the effective charge transfer and separation during photocatalysis.Ag nanoparticles forms on photocatalyst surfaces were synthesized usually by photoreduction which is a complicated and time-consuming method due to the additional photoreduction devides such as xenon lamp.This simple synthetic route,which involves no additions photoreduction device,will offer great opportunities for the scale-up in suit preparation of other Ag-loaded Ag-based composite materials.The near-infrared photocatalytic activity is from up-converted PL properties of CQDs.Because CQDs can absorb nearinfrared light and upconverted into high-energy irradiation and it is absorbed by the neighboring Ag₂ O photocatalyst.Furthermore,photocatalytic activity and stability of the CQDs/Ag/Ag₂ O ternary plasmonic photocatlyst were significantly enhanced throught the synergetic catalytic effect of interfacial modification and vectorial chargetransfer channel design.2.Hydrogenated TiO₂ nanobelt（H-TiO₂）are prepared by the hydrogen annealing method.Hydrogenated TiO₂ nanobelts still keep the belt’s structure and get a lot of oxygen vacancies,which make them have enhanced visible photocatalytic activity.A few-layer CDs/Mo S₂ nanosheet-coated hydrogenated TiO₂ heterostructures-referred to as CDs/Mo S₂@H-TiO₂—with a flexible three-dimensional（3D）hierarchical configuration are prepared via facial hydrothermal reaction.The photocatalyst has the full solar spectrum（UV,Visble and near-infrared light）photocatalytic properties.The formation of heterojunction between H-TiO₂ and Mo S₂ bring about the transferred of photoelectrons.Meanwhile,the CQDs with upconversion properties not only realizing better utilization of NIR-light in the solar spectrum,but also bring about the vectorial transfer of photoelectrons.3.CDs and g-C₃N₄ were synthesized by a typical hydrothermal method and pyrolytic method,respectively.CDs/g-C₃N₄ composites were then prepared by hydrothermal treatment a mixture of CDs and g-C₃N₄ powder at 160 ℃.The catalyst was characterized by XRD,SEM,UV-Vis,BET,FTIR and Raman spectrum.The photodegradation experiment of CDs/g-C₃N₄ composite was carried out under visible light irradiation.New research shows that further increase of the CDs concentration could enhance the light absoption by introducing sub-band states,the maximum absorption wavelength can be reached 620 nm,which is helpful for improving light absorbanc and the photocatalytic efficiency.Experimental results show that organic dyes and medical wastewater can be effectively purified under photocatalytic oxidation.