Preparation And Photocatalytic Degradation And Hydrogen Production Properties Of Carbon Dots Modified Semiconductor Composites

Environmental pollution and energy shortage have become the two major problems of all countries in the process of development.Semiconductor photocatalytic technology can convert light energy into other forms of energy and can directly catalyze water decomposition to produce hydrogen or to degrade organic pollutants in wastewater.It provides an effective way to solve the above two problems,which is green,environmental protection and low cost.The key of photocatalytic technology is semiconductor photocatalyst.However,most single semiconductor materials still have many disadvantages,such as weak light absorption,fast photoelectron/hole recombination rate,low specific surface area,low reactive activity sites,high price,high toxicity and poor stability and so on.Therefore,the development of high efficiency,stable and low cost visible light responsive semiconductor composite photocatalyst is a hot spot in the field of photocatalysis.As a new kind of large-scale,low-cost and non-toxic nano-functional materials,carbon dots?CDs?have been widely used in the fields of biological imaging,fluorescence detection,solar cells,luminescent devices and so on.At the same time,CDs also possess photoelectron transfer properties,which can promote light absorption,good thermal stability and chemical stability.Therefore,CDs can be used as a catalyst to improve the deficiency of semiconductor materials and improve their photocatalytic activity.However,owing to the late study of CDs during the photocatalytic field,so there are few reports on the modification of CDs-based semiconductor composite materials.In this regard,the photocatalytic activity and mechanism are systematically explored with of several representative CDs-based semiconductor composite materials.The main research contents and results are as follows:?1?CDs/ZnIn₂S₄ composites were prepared by a simple hydrothermal method for the degradation of methyl orange dye wastewater under visible light.The UV-Vis absorption spectra showed that the introduction of CDs can increase the visible light absorption of Znln₂S₄.At the same time,nitrogen adsorption desorption experiment shows that CDs can effectively improve the specific surface area of ZnIn₂S₄,and then provide more active sites.The photocatalytic results show that CDs?5?/ZnIn₂S₄ showed the highest photocatalytic activity,is 2.34 times higher than the pure phase of ZnIn₂S₄.The enhanced photocatalytic activity is attributed to the excellent catalytic activity of CDs can not only promote the light absorption of ZnIn₂S₄ and reaction activity more sites,but also CDs ZnIn₂S₄ can effectively accelerate the separation of photogenerated electrons and holes.?2?CDs/Ag/AgBr composite photocatalyst was prepared via a facile precipitation-photoreduction method.Moreover,CDs/Ag/AgBr nanocomposites show a strong absorbance in the full solar spectrum due to the interaction of Ag nanoparticles?Ag-NPs?and CDs.Meanwhile,compared with pristine AgBr and Ag/AgBr nanoparticles,a dramatic enhancement in the degradation of tetracycline under visible light irradiation is observed over the CDs/Ag/AgBr nanocomposites.Significantly,the extraordinary photocatalytic performance is attributed to the extended absorption in the full spectrum,effective charge separation,and synergistic enhancement induced by surface plasmon resonance of Ag-NPs and electron transfer properties of CDs in the complex material.?3?CDs/CoO composites were synthesized by a solvothermal method for overall water splitting under visible light irradiation.The obtained CDs/CoO composites exhibit more-efficient visible light absorption than pure CoO,leading to higher photocatalytic activity for overall water splitting.In addition,obtained CDs/CoO composites also show good photocatalytic stability.This enhanced photocatalytic activity and outstanding stability in CDs/CoO composites could be ascribed to several merits of CDs that not only improved charge separation efficiency and visible-light absorption but also effectively conducted heat generated by the photo-thermal effect of CoO.?4?A novel visible-light-driven N-doped carbon dot?N-CDs?/CBO composite was successfully synthesized by loading N-CDs nanoparticles onto the surfaces of CBO microrods via a hydrothermal method.The photocatalytic activity of the N-CDs/CBO was remarkably higher than that of CBO and CDs/CBO under visible light irradiation.The results show that N-doped CDs exhibits better photoabsorption and electron transport efficiency in composite photocatalytic materials than non-doped CDs,and thus improves the photocatalytic activity of CBO effectively.?5?N-CDs/CdS composite photocatalysts were prepared by a solvothermal method for water splitting under near-infred light.The UV-Vis absorption spectra showed that the absorption edge of N-CDs/CdS were red-shifted obviously compared with CdS.N-CDs/CdS composite photocatalysts were shown to be highly efficient in water splitting under near-infrared light irradiation with using lactic acid as a sacrificial agent.This enhanced near-infrared photocatalytic activity might have been ascribed to the up-conversion photoluminescence of N-CDs,that is,the long wavelength near-infrared light is converted into short-wavelength visible light,and the utilization of solar light by CdS is improved.