Construction Of Graphene Two-dimensional Layered Film And Its Solar Water Evaporation/power Generation Performance

Traditional desalination technology plays an important role in alleviating the growing freshwater shortage crisis.But high cost,high energy consumption and environmental pollution have hindered its development.With the advantages of high efficiency,sustainability,and no pollution,solar interfacial evaporation technology become one of the most promising means of desalination.Especially when combined with other technologies（such as triboelectric,thermoelectric,piezoelectric and salinity gradient effect）,a solar hybrid system with dual functions is formed,which can simultaneously solve the dual problems of fresh water and energy shortages.The design of photothermal materials and evaporation devices has been at the heart of research in this field.Graphene,an excellent photothermal material,suffers from agglomeration in the process of building thin films.The compact structure thus formed violates the vapor transport and light absorption in interfacial evaporation,which further limits the efficiency of seawater desalination.In addition,during the evaporation process,the salt accumulation on the evaporator surface will hinder the service life of the evaporator.To address the above problems,a multi-stage assembly strategy is proposed in this thesis to prepare lamellar membranes with two-dimensional material reduced graphene oxide as a substrate.And the type of one-dimensional material,carrying functional groups,hydrophilicity and water transport path of the evaporator are tuned around the problems faced by the mechanical properties,light absorption,water transport and salt discharge characteristics of the photothermal evaporator.The integration of the advantages of 1D and 2D materials,the synergistic production of fresh water and electricity,and the efficient salt harvesting are achieved through an interlaced network constructed of 1D and 2D materials to enhance vapor transmission and the use of multiple reflections to enhance light trapping.The main research contents of the thesis are as follows:（1）A multistage assembly strategy was proposed.Multi-walled carbonnanotubes（MWCNTs）werecoatedwith poly（diallyldimethylammonium）chloride（PDDA）to form a one-dimensional assembly（PDDA@CNT）,and then combined with reduced graphene oxide（r GO）to construct a two-dimensional layered porous membrane on the nano scale.The experimental results show that the evaporation rate of a single 10-PDDA@CNT/r GO optimized sample as an evaporator reaches 1.97 kg·m^-2·h^-1under the solar light intensity of1 k W·m^-2.Meanwhile,stable evaporation of 10-PDDA@CNT/r GO films was achieved at three different light intensities(1,2,and 3 k W·m^-2)in five cycles.The output voltage of the 10-PDDA@CNT/r GO film reaches0.40 V in 1 k W·m^-2and 10 wt%Na Cl solution.This work revolves around the design and light absorption performance of photothermal materials,and proposes a strategy of multi-stage assembly to construct laminates with porous network structure.The light absorption is enhanced and an excellent photothermal layer is formed.Solar energy-driven evaporation and power generation are realized,opening up a new way to alleviate energy and environmental crises.（2）Based on the above multi-stage assembly strategy,in order to solve the problem of salt accumulation,this chapter uses in situ synthesis to realize the in situ growth of silver nanoparticles on cellulose and combine them with r GO by vacuum filtration to construct Ag@CNC/r GO layered films with good hydrophilic and self-cleaning properties.The test results show that the optimized 1%-Ag@CNC/r GO film has fast water transport properties and high light absorption properties（85.93%light absorption in the wavelength range of 250-2500 nm）.Its photothermal evaporation rate was 1.92 kg·m^-2·h^-1under solar illumination conditions of 1 k W·m^-2.The output voltage of the 1%-Ag@CNC/r GO films reached0.44 V in 3.5 wt%Na Cl solution under the same light conditions.Meanwhile,the film has a desalination rate of over 97%for artificial simulated seawater,and the salt crystals accumulated by evaporation during the day can be removed automatically by diffusive reflux at night.This work revolves around regulating the type and hydrophilicity of one-dimensional materials and constructing laminar films with good hydrophilicity and self-cleaning ability.The capacity of electron and heat generation performance transmission is enhanced,the rapid water transmission is realized,and the salt discharge capacity of the evaporator is improved.（3）Based on the above work,this chapter constructs two-dimensional layered films with excellent mechanical properties and high energy conversion efficiency using Chiber,MWCNTs and r GO to address the problems of salt crystallization on the evaporator surface limiting its effective operation time during daytime and the cost and stability of precious metals.The results show that the optimized sample Chibers@CNT/r GO-60%has a water evaporation rate of 2.10 kg·m^-2·h^-1and a photothermal conversion efficiency of 73.50%under the sunlight of1 k W·m^-2.The evaporator was modified by simulating the principle of tree transpiration,and the stable evaporation and fixed-point collection of salts were realized in 3.5 wt%Na Cl solution for 300 h continuously.Furthermore,based on the energy harvesting strategy of the flow current,the output voltage of Chibers@CNT/r GO-60%film increased from 0.26V to 0.45 V in distilled water to saturated Na Cl solution.The work in this chapter focuses on the mechanical properties of the film and the water transport pathway of the evaporator,enhancing the film tensile strength and constructing a restricted transport water pathway.Synergistic production of freshwater and electricity and efficient salt harvesting are achieved.The insight that increasing salt concentration improves power generation efficiency was also successfully confirmed at the molecular level using molecular dynamics simulation analysis.