Study On Photothermal Devices Based On Three-dimensional Graphene Film

Solar-driven interfacial evaporation is a promising technique in response to drinking water scarcity.The development of efficient solar photothermal conversion materials and devices is the key to realize practical interface water evaporation.Due to their merit of wide spectrum absorption,low-cost and easy composite with other functional materials,carbon-based materials,especially graphene-based materials,are great candidates for solar absorber.Great progress has been made in the research of photothermal conversion materials based on carbon materials.However,it is still a great challenge to develop solar photothermal conversion materials with high water evaporation rate and solar-to-vapor conversion efficiency.In this paper,three-dimensional graphene films with hydrophilic-hydrophobic dual characteristics were prepared by interfacial solvothermal method.Then the performance of such three-dimensional graphene films in solar-driven interfacial water evaporation and seawater desalination was further studied.The research results are as follows:1.Preparation and characterization of graphene films.Graphene films were prepared from graphene oxide/ethylene glycol solution-glycerol by interfacial solvothermal method.SEM analysis shows that the graphene film has a three-dimensional porous structure.It is worth noting that the upper and lower surfaces of the film have different morphological characteristics.The upper surface is a relatively dense structure with sparse pores,while the lower surface has micro continuous pore structures of different sizes.The porous lower surface has abundant pores that provide effective channels for water transport.What is more,the lower surface is hydrophobic,which is conducive to the rapid evaporation of liquid water into steam.Therefore,the graphene film has the Janus characteristics of hydrophilic and hydrophobic coexistence.The thickness of graphene film can be effectively controlled by adjusting the volume ratio of graphene oxide/ethylene glycol solution and glycerol.And the thickness of the graphene film was controlled from 300μm to 2 mm.The absorption spectrum test showed the thickness of 300μm graphene film has optical absorbance>91%in UV band,>85%in visible band,and>80%in IR band.2.Photothermal properties of graphene films.We used polyethylene,absorbent cotton and graphene film to build a group of photothermal devices.The device has a water evaporation rate of 1.36 kg m^-2h^-1,and the solar-to-vapor conversion efficiency is as high as 85.33%under one sun irradiation(1 k W m^–2).Under the continuous one sun irradiation for up to 4 hours,the solar-to-vapor conversion efficiency is still about85%.3.Seawater desalination.We try to study the performance of our 3D graphene film based photothermal device in the application of seawater desalination.The results show that the device has a seawater evaporation rate of 1.3 kg m^-2h^-1under one sun irradiation,and the solar-to-vapor conversion efficiency is as high as 81.6%,which is similar to that of fresh water evaporation data.The device still maintains a solar-to-vapor conversion efficiency of more than 80%for 4 h sun irradiation.There is no salt crystallization on the upper and lower surfaces of the films after several hours of seawater evaporation.This result indicates that the graphene film has excellent salt resistance.Meanwhile,we used ICP-MS to test the concentration of ions before and after desalination.The salt contents in water were reduced after desalination(1.9044mg/m L,0.0372 mg/m L,2.3412 mg/m L and 0.3724 mg/m L for Na⁺,Mg²⁺,K⁺,Ca²⁺,respectively)which met the drinking water standards of the World Health Organization（WHO）.