Study On Solar Water Evaporator Constructed With Sponge Supported Graphene Oxide And Its Properties

In recent years,in order to solve the problem of fresh water shortage,people have carried out a lot of research and exploration work,among many technologies,solar driven interface water evaporation technology has been widely concerned with its high efficiency and sustainable characteristics.Carbon nanomaterials in solar thermal conversion materials are favored by researchers because of their low cost,strong solar absorption capacity,high stability and easy access.But despite great efforts,evaporators built from carbon nanomaterials still have a low rate of solar water evaporation under natural light.Under one light intensity,the water evaporation rate of carbon nanomaterials is less than 2.0 kg m^-2 h^-1,which is far from meeting the long-term demand of human beings for fresh water.Based on this background,how to improve the water evaporation rate of carbon nanomaterial evaporator becomes a major problem.Therefore,it is very important to develop a carbon nanomaterial evaporator with low cost,good light absorption ability,high photothermal conversion efficiency and highly water evaporation rate.In this paper,melamine sponge(MS)and graphene oxide(GO)were used as raw materials.AfterGO was uniformly adsorbed by MS,hydrogen iodate acid(HI)reduction and high temperature treatment,stable MS@rGO was formed.After that,two different evaporators are constructed by electrochemical oxidation MS@rGO and direct application of voltage to MS@rGO:MS@rGO-EO;MS@rGO.They exhibit extremely highly water evaporation performance.The specific research contents and conclusions are as follows:(1)An efficient solar water evaporation system was constructed using electrochemical oxidation to reconstruct the go components in sponge.Put MS into the dispersed GO solution to make it fully saturated and adsorbed evenly.Then it was dried in 60?oven for 1 h,and then it was reduced in 95?HI.After it was removed,it was repeatedly washed with anhydrous ethanol and deionized water,and then it was treated in 200?high temperature oven for 2 h to get MS@rGO.Then the sample is absorbed to a completely wet state,and the sample MS@rGO-EO evaporator is obtained after the voltage is applied to both sides of the sample for treatment.After SEM,XPS,CV,FTIR and other tests on MS@rGO-EO evaporator,it can be clearly seen that rGO is stably assembled on the surface of MS,and the increase of surface wrinkles makes it have good light absorption ability.After HI reduction,oxygen-containing functional groups are greatly reduced,and after electrochemical oxidation treatment,the functional groups on the surface are significantly different from those before.Raman spectroscopy was used to test the adsorption state of water.The proportion of intermediate water in MS@rGO-EO evaporator increased obviously,which improved the activation capacity of water and reduced the enthalpy of water evaporation.At one light intensity,the water evaporation rate of MS@rGO-EO evaporator reaches 3.47 kg m^-2 h^-1,and the solar-steam conversion efficiency reaches 97.4%,which is higher than all evaporator constructed by similar photothermal materials reported previously.The MS@rGO-EO evaporator also after 30 days of continuous brine immersion evaporation test,p H 1-13 acid and alkali environment test,three light intensity test evaporation rates can still reach 10.21 kg m^-2 h^-1,maintain a stable evaporation performance and harsh environment adaptability.(2)A high-efficiency solar water evaporation system was constructed by reducing graphene oxide with sponge load.MS@rGO is the intermediate product mentioned above.Due to its excellent light absorption and electrical conductivity,it can be used as photoelectric coupled evaporator to carry out solar water evaporation.When 10 V voltage is applied to MS@rGO at 1 sun,the difference between the photoelectric coupling minus the evaporation rate of joule hot water reaches the maximum value,which is 2.874 times that of the evaporation rate of water under the photothermal condition.When the photoelectric coupling efficiency reaches the best,the evaporation rate of the system reaches 9.02 kg m^-2h^-1,and the solar-water vapor conversion efficiency reaches 287.4%.When photothermal and Joule heat work separately,the amount of hydrogen peroxide produced is:55.2 and 132.3?M,while the amount of hydrogen peroxide produced by photoelectric coupling is 419?M,which is more than the sum of hydrogen peroxide produced by photo-thermal and Joule heat alone,indicating that the water evaporation caused by photoelectric coupling is more than that produced by the other two alone.During evaporating brine,MS@rGO can also efficiently catalyze oxygen reduction for the sustainable production of H₂O₂ to serve as the broad-acting disinfecting agent in the condensed water.which is due to the disappearance of a large number of oxygen-containing functional groups after HI reduction and heat treatment at200?,and the formation of many obvious expansions on the surface of the whole material and the close arrangement between the layers.Many fractured parts form edge fault defects,and more ether bonds are formed at the edges.These ether bonds are the active sites for hydrogen peroxide generation,which provides a basis for H₂O₂ generation at the same time as photoelectric coupling water evaporation.During evaporating brine,MS@rGO can also efficiently catalyze oxygen reduction for the sustainable production of H₂O₂ to serve as the broad-acting disinfecting agent in the condensed water.This work has built a bridge between photothermal,photocatalysis and electrocatalysis,and opened up a new way and laid a theoretical foundation for the collaboration of the three.In addition,when 3.5 wt%Na Cl solution and real sea water were respectively used as body phase water,the content of H₂O₂ in collected water was basically the same,indicating that hydrogen peroxide can be directly prepared by using sea water as reaction source.This provides an important theoretical basis for the realization of the combined operation of photothermal and photovoltaic in the sea.