Preparation Of Transition Metal Sulfides With High Photothermal Conversion Efficiency And Their Application In Seawater Desalination

Solar-driven steam generation is a technology to solve the current water shortage problem by using sustainable solar energy.It has shown extraordinary prospects in desalination,steam power generation,distillation,sterilization,and other aspects.However,the weak light absorption capacity of waters leads to the low water evaporation efficiency.In recent years,the proposed concept of solar heat localization interface water evaporation(SHLWE)has made it possible to greatly improve the photo-thermal efficiency and commercial applications of solar-driven steam generation.Compared with the traditional steam generation systems,SHLWE can realize liquid-gas phase transition by transporting water to the evaporation interface,and effectively avoid the unnecessary heat loss.Transition metal sulfides have attracted wide attention because of their simple preparation process,strong chemical resistance,and good absorption in UV-vis region.However,the above advantages are far from enough to meet the requirements of ideal photothermal materials.The ideal photothermal materials need to have good absorption of sunlight at all wavelengths(200-2500 nm).Meanwhile,they should exhibit excellent stability,no salt blocking,less heat loss,and other performance,when integrated into the evaporator system.In this paper,a series of transition metal sulfides with hierarchical structure were prepared.The prepared materials had excellent absorption properties to the full spectrum of sunlight.What's more,by adjusting the wettability and designing the structure of the evaporator,the problem of salt blocking in the long-term desalting process was effectively solved.Specific research contents and results are summarized as follows:1.Porous copper foam(CF)as substrat,Cu₂S as the photothermal material.Through a simple chemical bath reaction,the unique Cu₂S/Cu₂O core/shell nanowires with excellent photothermal properties were grown on the surface of CF,and the integrated Cu₂S/Cu₂O/CF nanocomposite evaporator was prepared.The results of SEM,XRD,XPS and EDS showed that the heterostructure was successfully prepared.The as-prepared Cu₂S/Cu₂O/CF nanostructure achieved a high light absorption performance(96%),a high evaporation rate of1.44 kg m^-2 h^-1 and a solar thermal conversion efficiency of 83.1%under 1 sun irradiation.At the same time,the excellent environmental stability of Cu₂S/Cu₂O/CF endows the material suitable for the treatment of a variety of contaminated solutions.In addition,its excellent hydrophilic properties provide Cu₂S/Cu₂O/CF with anti-oil capability,the evaporator can be used to treat oil/water emulsion.Cu₂S/Cu₂O/CF nanocomposites provide an effective way for the desalination of seawater driven by solar energy.2.Numerous Ni Co_xS_y nanosheets were vertically and densely grown on the polyaniline(PANI)modified glass fiber(GF)membrane to prepare an efficient solar-driven interfacial water evaporator.The Ni Co_xS_y-PANI@GF with honeycomb-like structures and rough surfaces could produce multiscattering of incident solar light.Simultaneously,the hydrophilic Ni Co_xS_y-PANI@GF modified by PANI coating could provide continuous and rapid water supply via the capillary wicking effect.The Ni Co_xS_y-PANI@GF achieves a broad spectrum light absorption rate of 96%,an evaporation rate of 1.30 kg m^-2 h^-1,and a solar-to-steam efficiency of 78.7%under one sun irradiation.The optimized size design allows the material to be used continuously for 20 h for desalination and salt collection.Meanwhile,the excellent hydrophilicity ensures the high salt-resistance ability and excellent self-cleaning performance,which ensures the subsequent efficient desalination application of the material.This kind of flexible water evaporation device provides the possibility for the practical application of this technology.3.The photothermal properties of semiconductor materials can be improved effectively by constructing hierarchitectures.In this chapter,using MOFs as template,porous copper sulfide with excellent light absorption performance was prepared by simple sulfuration.Through the adhesion of polyvinyl alcohol(PVA),Cu S is stably loaded in the porous network of melamine foam(MF),and then cross-linked with glutaraldehyde,the Cu S/MF aerogel photo-thermal evaporator is prepared.The low thermal conductivity of MF reduces the heat loss,and the PVA further improves the hydrophilicity of the material,which ensures sufficient water supply for Cu S/MF during the evaporation process.The evaporation rate of Cu S/MF reached 1.46 kg m^-2 h^-1 under one sun irradiation.In addition,the experiments of 15 times of seawater cyclic evaporation show that Cu S/MF has excellent stability.This kind of aerogel photothermal evaporator with acid and alkali resistance provides a new idea for the development of seawater desalination.