Preparation Of Graphene-Based Composite Fiber Membranes And Photothermal/Photocatalytic Performance And Mechanism

With population growth and industrial development,water shortage has become one of the major crises facing mankind in the 21st century.High-salt wastewater contains a large amount of salt substances and complex organic pollutants,which makes the wastewater treatment more difficult,which brings great challenges for the current wastewater treatment and recycling technology.And solar photothermal desalination/photocatalysis has become a novel,effective and feasible solution for high-salt wastewater.In this study,graphene oxide/polyvinyl alcohol composite electrospun fiber membranes?GO/PVA EFMs?were developed through electrospinning technology.GO/PVA EFMs-5%could be prepared under the optimized conditions of 9%?w/v?PVA concentration,5%?w/w?GO concentration,15 kV spinning voltage,15 cm spinning spacings,and 120?m thickness.Under the illumination of one sun(1 kW m^-2),the evaporation rate of GO/PVA EFMs-5%to pure water could reach 1.40 kg m^-2h^-1 and the energy conversion efficiency could reach 90.1%.After the desalination of the yellow sea samples,the concentrations of the five main ions(Na⁺,Mg²⁺,K⁺,Ca²⁺,B³⁺)in the purified water are around 1 mg L^-1,which are far lower than the World Health Organization?WHO?drinking water standards.In addition,the material with broad spectrum absorption,high photothermal conversion,high temperature rising ability and cycle stability,and has extremely strong resistance to strong acid,strong alkali,high salty and high temperature environment.Strong hydrophilicity,conjugation effect,abundant mesoporous channels,microscopic 3D network structure,etc.contribute to continuous water supply and heat accumulation for maintain efficient evaporation.Graphene nitride?nitrogen-doped?not only has photothermal conversion performance,but also has excellent photocatalytic performance,and is a bifunctional material.Therefore,graphene nitride/polyvinyl alcohol composite electrospun fiber membranes?NG/PVA EFMs?were prepared and used for photothermal and photocatalytic treatment of high-salt wastewater.NG/PVA EFMs-5%possess high solar absorption value and very low reflectivity,its evaporation rate to pure water is1.50 kg m^-2 h^-1,and its energy conversion efficiency is 96.8%.In addition,after the desalination of simulated brine and yellow sea water,the ions concentration in the condensate are greatly reduced?four magnitude orders?,and the K⁺concentration is below the detection limit.NG/PVA EFMs-5%has more efficient solar absorption and conversion capability,and thermal positioning and water evaporation performance are also more prominent.In the investigation of the feasibility of photocatalysis,this material has certain degradation properties for dye solutions and aged landfill leachate.Under hydrophilic interaction and electrostatic interaction,the composite fiber membranes could adsorb part of the pollutants in the water to the membrane,increase the probability of contacting the pollutants with catalytic active sites,and improve the photocatalytic degradation performance of the material.The results obtained in this research have positive significance for the development of photothermal/photocatalytic dual-function potential graphene-based materials and zero-emission technology for high-salt wastewater treatment.