Preparation Of Cu/Graphene Aerogel And Research On Its Photothermal Seawater Desalination Characteristics

With the increasing scarcity of potable fresh water resources,the treatment and application of seawater resources,which account for more than 70%of the earth's surface,has attracted more and more attention.Traditional seawater desalination technology consumes too much energy and high investment cost,and the energy consumed for desalination treatment mainly comes from fossil fuels such as coal and petroleum that are non-renewable,have limited reserves,and emit large amounts of greenhouse gases into the air when burned,not only caused environmental pollution,but also brought about an energy crisis again,hindering the further development and application of seawater desalination technology.In order to alleviate the double pressure of the deterioration of the ecological environment and the shortage of conventional energy,people have begun to look for new renewable energy.Solar energy stands out among many energy sources due to its unique advantages of cleanliness and unlimited reserves.It also has the advantages of low cost,no fossil energy consumption,and no secondary pollution.The use of solar energy for desalination of seawater has become a consensus among people.Therefore,in order to meet the basic domestic water demand in developing countries and remote areas,most of the seawater desalination treatment is carried out by preparing solar-driven light-to-heat conversion functional materials.Among the many unique photothermal conversion materials,graphene and copper nanoparticle materials have been studied and applied in seawater desalination due to their full-spectrum absorption characteristics and localized surface plasmon resonance(LSPR)effects,respectively.In this paper,copper nitrate solid powder and graphene oxide dispersion are used as raw materials,and graphene-based aerogel photothermal composite materials loaded with copper nanoparticles are successfully prepared through hydrothermal,freeze-drying and high-temperature reduction.In the hydrothermal reaction,the graphene oxide nanosheets self-assemble and connect under the action of high temperature to form a three-dimensional graphene hydrogel with a spatial network structure.The freeze-drying process allows the graphene hydrogel to successfully maintain the original three-dimensional porous structure,and the high-porosity porous structure enables the material to float on the water surface to achieve interfacial heating.Subsequent high-temperature reduction successfully prepared copper nano-particle graphene-based aerogel photothermal composite material.In order to explore the photothermal properties of graphene-based aerogel composites,five groups of photothermal materials with copper nanoparticle loadings of 2wt%,4wt%,6wt%,8wt%,and 10wt%were prepared in this paper,then float them on the water surface to test the water evaporation experiment.The experimental results show that as the loading of copper nanoparticles increases,the water evaporation rate of the graphene-based aerogel photothermal composite material first increases and then decreases under the irradiation of a sunlight intensity.When the load is 6wt%,the material water evaporation rate and efficiency are the highest,1.40 kg m^-2 h^-1 and 87.82%are respectively,it is 2.09 times the efficiency of simulated seawater directly under the same light intensity.The efficient water evaporation rate of the composite material is due to the synergy of the full spectrum absorption of the graphene black carbon material and the unique LSPR effect of copper nanoparticles,at the same time,the spatial network pore structure of the three-dimensional graphene not only enables the material to float on the water surface to achieve interfacial heating,but also provides a channel for the transportation of the bottom water body and the escape of steam,which further promotes the evaporation of water.Both graphene and metallic copper have high thermal conductivity,so the heat loss caused by the heat conduction of the water body can not be ignored.In order to further improve the thermal insulation performance of the material,the experiment introduced a melamine sponge placed at the bottom of the material to isolate the heat conduction of the water body and reduce the heat loss.In the experiment,five groups of melamine sponges with different thicknesses(1mm,2 mm,3 mm,4 mm,5 mm)were placed on the bottom of the composite material for water evaporation test.The experiment shows that when the thickness of the sponge is 2 mm,the water evaporation rate and efficiency of the composite material are the highest,reaching 1.49kg m^-2 h^-1 and 93.08%,respectively,it is 2.22 times the efficiency of simulated seawater directly under the same light intensity.When the water evaporation test is carried out under higher light intensity(2 sun,3 sun),the water evaporation rate of the material can reach 2.68 kg m^-2 h^-1 and4.49 kg m^-2 h^-1,respectively,it shows that the material can maintain a stable and efficient water evaporation rate under higher light intensity.In order to test the cyclic stability and durability of the material,a graphene-based aerogel photothermal composite material with a copper nano-particle load of 6wt%and a melamine sponge thickness of 2 mm was tested for 12 times of circulating water evaporation under one solar illumination intensity.The experimental results show that the evaporation rate of the material is stable between 1.47 kg m^-2 h^-1 and 1.52 kg m^-2h^-1,which indicates that the thermal insulation graphene-based aerogel photothermal composites have good cycle stability and durability.