Research On The Application Of Seawater Desalination And Resource Utilization

More than a quarter of the world's population lives in an environment with severe water shortages,and nearly half of the population suffers from severe water shortages for at least one month each year.In order to solve this widespread and destructive problem,researchers have turned their attention to desalination,because about 97.5%of the world's total water is not directly drinkable seawater.Therefore,it is very urgent to seek efficient,large-scale and sustainable desalination technology.Traditional desalination technologies,including multi-stage flash evaporation(MSF),reverse osmosis(RO),vapor compression distillation(VCD)and multi-effect distillation(MED),not only require expensive and complex infrastructure and equipment,but also consume a lot of traditional energy.For poor areas,this is an insurmountable obstacle.In addition,these technologies at the expense of energy and the environment run counter to global sustainable development.Inspired by natural evaporation,an important part of terrestrial fresh water supply,solar water evaporation using solar energy as the only energy source to produce fresh water is a promising strategy with negligible environmental impact.However,the natural evaporation efficiency is low due to poor light absorption capability and severe heat loss,which cannot meet the actual demand for fresh water.On the other hand,there are many pollutants in sea water,such as volatile organic compounds,heavy metal ions and so on.To solve above problems,we propose a method of interfacial heating for desalination to produce fresh water.At the same time,pollutants in seawater are removed by photocatalysis,adsorption and other methods during the seawater desalination process.In addition,a new type of material has been developed for solar water evaporation to prevent the precipitation of crystalline salt during seawater evaporation.The main research contents of the paper are as follows:1.Self-suspended photothermal micro-reactor for water desalination and integrated VOCs removing.After loading the photocatalyst P25(commercial TiO₂)on the surface of the biomass waste(the roots of Flammulina velutipes),the roots of Flammulina velutipes are carbonized to obtain TiO₂-loaded porous clustered carbon array foams(PPC-array foams).Due to its low mass density and clustered porous structure,this self-supporting PPC-array foams float on the water.In addition,many channels are produced in PPC-array foams during the carbonization process,which can not only greatly enhance the light trapping ability to improve the light and heat efficiency,but also provide an effective way to accelerate the transmission of water from the bottom to the surface of the materials.In addition,the TiO₂ nanocrystals loaded on PPC-array foams can also degrade VOCs at the same time during the evaporation of seawater,so as to realize the removal of VOCs during solar water evaporation.2.Bifunctional photothermal membranes for clean water generation by solar steam generation and heavy metal ions adsorption.In this research,we developed a photothermal film in which TNC composite material(titanate nanotube-carbon nanotube)can be used for solar seawater evaporation and wastewater purification for the first time.Using P25 and multi-walled carbon nanotubes as the original materials,the microwave-assisted alkali heating method was used to synthesize titanate nanotube-carbon nanotube composite,then the composite is uniformly dispersed in deionized water,and then vacuum filtered through the PTFE membrane,forming a photothermal film.Because TNC composite material has excellent photothermal performance and heavy metal ion adsorption capacity,it can achieve high evaporation rate and high energy conversion efficiency under the irradiation of simulated solar light.In addition to excellent evaporation efficiency,this TNC composite material can efficiently adsorb and remove various heavy metal ions(Cu²⁺,Cd²⁺and Pb²⁺)from polluted seawater during solar seawater evaporation.In addition,vacuum filtration of the dispersion onto the PTFE membrane can fix the adsorbent,solve the problem of adsorbent recovery,and make full use of solar energy.TNC composite materials have good light absorption capacity and can adsorb heavy metal ions,which can effectively solve the problem of water shortage.3.Preparation and performance study of polypyrrole/melamine sponge-based solar interface evaporation materials.With melamine sponge as the substrate,a polypyrrole(PPy)coating is in-situ synthesized on the sponge to provide photothermal materials for solar seawater desalination.The fast capillary transmission through the microchannels of polypyrrole/melamine sponge and the effective transport of water between the large channels of the evaporator facilitate the rapid replenishment of vaporized water on the surface to ensure rapid and continuous production of clean water vapor.The polypyrrole/melamine sponge-based solar interface evaporation material prepared by this method is an efficient,stable,low-cost and environmentally friendly solar evaporator.