Preparation And Properties Of Hierarchically Porous Photothermal Conversion Hydrogels

With the increase of industrialization and population,the shortage of freshwater resources has become an urgent problem for mankind.Desalination is currently one of the most effective methods to solve the shortage of fresh water resources.Solar-driven water evaporation uses inexhaustible solar energy for light-to-heat conversion to heat water and promote water evaporation.This technology is energy-saving and environmentally friendly,and is the general direction of the future development of seawater desalination technology.The water evaporation material is mainly composed of two parts:a photothermal conversion material and a hydrophilic skeleton material.In this paper,copper sulfide(CuS),reduced graphene oxide(rGO)and copper sulfide/reduced graphene oxide(CuS/rGO)are used as light-to-heat conversion materials,and polyvinyl alcohol(PVA)is used as the skeleton to prepare a hierarchical pore structure.Hydrogel is used for high-efficiency solar water evaporation,and the influence of light-to-heat conversion materials and hydrogel structure on water evaporation performance is explored.Firstly,rGO is obtained by reducing graphene oxide(GO),then it is used as a photothermal conversion material and blended with PVA and then chemically cross-linked to prepare rGO/PVA photothermal conversion hydrogel(TLPSH)with hierarchical pore structure,Explored the effect of rGO/PVA solid content on evaporation rate.The study found that TLPSH exhibits excellent solar light absorption performance,with an absorbance of as high as 98.2%,and the evaporation surface temperature can quickly increase by about 20?within 5 minutes.TLPSH₂ with a solid content of 10wt%exhibits the best evaporation performance due to its unique hierarchical pore structure(which can reduce water evaporation enthalpy),suitable porosity(80%)and excellent water transport rate(1.3 g/min);Through simulated seawater evaporation experiment,under 1 sunlight,the seawater evaporation rate is as high as 1.65 kg m^-2 h^-1,which is 5.5 times of its self-evaporation rate(0.3 kg m^-2 h^-1).The conversion efficiency can reach 107.2%.Use rGO as a dopant to prepare CuS/rGO,and use it as a photothermal conversion material to blend and crosslink with PVA to prepare CuS/rGO/PVA photothermal conversion hydrogel(SCr)with a hierarchical pore structure.The influence of the amount of photothermal conversion material,the thickness of the hydrogel and the solid content on the evaporation rate of SCr.Studies have shown that the solar energy absorption performance(95.4%)of CuS/rGO obtained by doping is greatly improved compared to CuS(89.6%).Through simulated seawater evaporation experiments on the prepared different CuS/rGO loadings,CuS/rGO/PVA content and different thickness of SCr,it is found that the CuS/rGO loading is 0.2wt%(compared to the quality of PVA),and CuS/When the rGO/PVA content is 10wt%and the thickness is 3 mm,it has the best water evaporation performance.Under 1 sunlight,the corresponding simulated seawater evaporation rate is 1.59 kg m^-2 h^-1,and the energy conversion efficiency can reach 103.3%.