Study On Desalination And Water Purification Based On Interfacial Photothermal Effect Of Solar Energy

Human society is facing the severe problem of the shortage of fresh water resources,and desalination technology has gradually become one of the important means for obtaining clean water in the field of water treatment.Traditional energy-driven desalination technologies such as thermal-driven and membrane-driven desalination processes have several disadvantages such as high consumption of fossil energy and pollution to the environment.Compared with traditional energy,solar energy,as a green and sustainable resource,can provide a new type of energy source for desalination technology of water treatment and has been widely concerned.Based on the interfacial heating technology,the problem of salt crystal pollution in solar direct-driven evaporation and desalination has been solved and the evaporation efficiency has been improved through the construction of the new photothermal evaporation systems,and to achieve solar photothermal activating the microbial electrochemical system through the development of asymmetric photothermal Janus anode electrode to generate bioelectricity and drive capacitive deionization(CDI)system to carry out innovative research on organic wastewater treatment while desalting low brine.The research results obtained of the thesis are as follows:First,to address the problem of salt deposition of photothermal film materials in the process of solar evaporation and desalination,a graphite felt with 3D macroporous structure was selected as the photothermal material substrate,and the simple polydopamine(PDA)interfacial deposition method was used to make it hydrophilic.The treatment improves its wettability and realizes the preparation of macroporous super-hydrophilic photothermal felt(PFF).Thanks to the high light absorption rate(93.6%)and good wetting performance of PFF,and heat loss management control of the photothermal system,and the evaporation rate was 1.48kgm^-2h^-1,and the photothermal conversion efficiency was 87.4%,showing good evaporation performance.The results of evaporation and desalination showed that even when the salt ion concentration is as high as 10 wt%,the good 3D macroporous network structure of the hydrophilic photothermal felt can provide sufficient space for the migration and transportation of salt ions,which ensures the migration and circulation of the upward transportation and downward diffusion of salt ions during the evaporation process,thereby showing the ability to resist salt deposition of the PFF surface.Due to the cohesive energy of water molecules,it is difficult to further improve the evaporation performance of solar evaporation desalination technology.Based on the theory of surface activity,an interconnected porous photothermal matrix(IPPM)with confined interfacial activation effect through the one-step water bath method.IPPM had good surface wetting properties and its light absorption rate was as high as 97.7%.The dark state evaporation experiment proved that IPPM can reduce the evaporation enthalpy of its interfacial water molecules to 1.5kJg^-1.Molecular dynamics simulation results showed that both the r GO framework of IPPM and the PDA with outward indole structure can promote the evaporation of water molecules at the interface of IPPM.Due to the decrease of the evaporation enthalpy of the water molecules at the interface,the evaporation rate of IPPM under one solar intensity was 2.2kgm^-2h^-1,and its photothermal conversion efficiency was 86.3%.In addition,it could reach an evaporation level of 11.5kgm^-2h^-1 under 5 solar intensities.In addition,the existence of the interconnected porous pore structure also ensured that the IPPM showing good resistance to salt deposition while the interfacial evaporation was enhanced.In addition to achieve the desalination of relatively clean brine-containing bodies to obtain purified water through the use of solar energy,driving the purification of sewage and wastewater by the utilization of solar energy also has important value and significance.Here,the innovative research of solar photothermal activating microbial fuel cell(MFC)coupling capacitive deionization(CDI)for the treatment of low brine and the purification of organic wastewater in low temperature environments has been realized through the solar interfacial heating technology.First,we rationally designed and prepared asymmetric photothermal Janus anode electrode(PTJA).By optimizing the structure of the non-porous layer of the Janus anode electrode,it was proved that when the concentration of carbon black was 20 wt%,PTJA had the best light absorption capacity(96.3%)and remarkable waterproof performance,which can avoid photosynthetic toxicity during the photothermal process.The maximum power density of the photothermal system based on PTJA was 678.3mWm^-2,and the maximum open circuit voltage could reach 773.4mV.By setting the light/dark cycle period of 10/14h,the maximum power density of the PTJA-based photothermal MFC was about 646.9mWm^-2,which was only 4.6% lower than the system operating during continuous irradiation,indicating that it had the resistance ability to the low temperature environment in the absence of light.Under the premise of the successful startup and operation of the PTJA-based photothermal MFC system,the salt removal rates of the PTJA-based photothermal MFC system was 60.6%;the organic matter removal rate of the PTJA-based photothermal MFC system has reached more than 80%,while driving the CDI desalination for water purification.Through the analysis of the microbial community composition,it was found that the anaerobic electricity-producing bacteria Geobacter is the main electricity-producing microorganism in the PTJA-based photothermal system,accounting for 76.4% of the biofilm components.The results showed that the PTJA electrode could ensure the growth and reproduction of the electrogenic bacteria in the conductive porous layer while avoiding the growth of photosynthetic microorganisms,and degrade organic matter for the production of bioelectricity.The research topic of the thesis is based on the interfacial photothermal technology with solar energy as the total input energy,purifying seawater through evaporation and desalination directly driven by solar energy,and achieving low temperature photothermal MFC coupling CDI desalination system through the indirect method of solar photothermal activating the production of bioelectricity of MFC for the purification of low brine and the treatment of organic wastewater at the same time.The research results have significance and value for promoting and enriching the development of solar desalination technology in the field of water treatment.