Preparation Of Carbon Dot-based Photothermal Conversion System And Research On Its Solar-driven Water Evaporation

Faced with increasingly severe water pollution,severe shortages of fresh water resources and energy shortages,to solve the problem of global water shortages,the majority of scientific researchers have developed various advanced materials and technologies to obtain high-quality fresh water from salt water or even polluted water.However,current water purification technologies,such as reverse osmosis or low temperature low temperature distillation techniques,mainly have problems such as high energy consumption,complex production processes and low evaporation rate.Solar-powered evaporating water has the advantages of low energy consumption,small size,simple production and high evaporation speed.Therefore,it is considered to be one of the most sustainable technologies.In this paper,based on the advantages of carbon dots(CDs)as a conversion material from light to heat at low cost,easy formation and environmental friendliness,binary and ternary carbon dot-based photothermal conversion materials have been designed and synthesized,and they have been tested through solar-driven water evaporation tests.The specific research contents of the light-to-heat conversion characteristics of the composite structure are as follows:First,based on the broad spectrum absorption characteristics of polydopamine(PDA),CDs were added during the polymerization of dopamine(DA)to generate PDA,and a low-cost,environmentally friendly PDA-modified CDs photothermal conversion material(CDs/PDA)was synthesized.The results show that the functional groups on the surface of CDs and DA interact.This interaction not only greatly accelerates the oxidative polymerization of DA and the deposition of PDA formed by oxidation on the surface of CDs,but also effectively promotes the efficient separation of photogenerated electrons and holes.Inhibits the recombination of photogenerated electrons and holes to radiation,thereby improving the photothermal conversion performance of CDs/PDA.Under 1 k W m^-2 simulated sunlight,the water evaporation rate of CDs/PDA can reach 1.82 kg m^-2 h^-1,and the efficiency is 74.4%,which is about 15.9%higher than the water evaporation rate of pure CDs,which is higher than that of pure PDA.An increase of about 15.2%.Second,based on the visible light of CDs,copper phosphate(Cu₃(PO₄)₂)has good absorption properties in the near-infrared region.We designed and synthesized the CDs/Cu₃(PO₄)₂ photothermal conversion material by hydrothermal method.The water evaporation rate was tested under 1 k W m^-2simulated sunlight,and the results showed that the water evaporation rate of CDs/Cu₃(PO₄)₂ could reach 1.64 kg m^-2 h^-1.Compared with pure CDs,it increased by about 11.6%;compared with Cu₃(PO4)₂,it increased by about 10.1%.Based on the consideration that hydroxyapatite(HA)has good thermal insulation properties,HA fibers are introduced in the process of preparing CDs/Cu₃(PO₄)₂.However,the solar-driven water evaporation test showed that the photothermal performance of the synthesized HA/CDs/Cu₃(PO₄)₂ composite sample was not significantly improved.We guess that although the introduction of HA can increase the surface roughness of the composite structure and by reducing heat loss,it also reduced the absorption of light in the sample,so that the evaporation of moisture in the samples received did not significantly increase.How to effectively design the composition to obtain a photothermal conversion material with high photothermal conversion efficiency will be further developed in the follow-up research.