Preparation And Properties Of Graphene-based Composites For Solar Photothermal Conversion

In twenty-first century,human beings are facing increasingly serious problems such as energy crisis and environmental pollution.It is urgent for mankind to expedite the development and utilization of clean and renewable resources.As a representative of these energy sources,solar energy has been extensively explored by scientific researchers and some significant progress has been made in recent years.However,the practical application scale of solar energy is still small and the application efficiency is also low.For example,photothermal technology can heat liquid medium by absorbing solar radiation,and this technology can be used for solar steam generation and desalination.However,this conventional photothermal technology suffers from low efficiency and high energy consumption due to the requirement for heating the bulk liquid.As a different method to convert solar energy to heat energy,the surface plasmon resonance effects of nanoparticles can enhance light absorption and reduce heat conduction,turning it into an ideal nanoscale heat to realize the highly efficient conversion of solar energy and generation of solar steam.The difficulty of realizing this technology lies in the design and preparation of highly efficient and stable photothermal conversion materials.This thesis based on the existing technology,uses graphene oxide and reduced graphene oxide to design and prepare novel macro nano designs and assembly systems,and deeply studies and analyses their characteristics of light absorption and ability of photothermal conversion.The main tasks include:1.Investigation on the preparation and photothermal effect of reduced graphene oxide based double layer system:The double-layer graphene oxide based system prepared by chemical crosslinking and vacuum filtration method,and then get the reduced graphene oxide based system by microwave assisted chemical reduction method.Contrast experiments on the same light intensity show that the reduced graphene oxide has better photothermal conversion performance than graphene oxide,and their macro system has better photothermal conversion performance than the counterparts of their nanofluids.Under a light density of 4 kW/m2,the rGO/MCE membrane achieved the evaporation efficiency of approximately 71.8%,and its evaporation rate is 4.3 times higher than that of pure water.The structural characterization and cyclic stability test showed that the reduced graphene oxide based double-layer system had excellent chemical and mechanical stability,and could remain a stable performance over 15 cycles under the same illumination conditions.Excellent mechanical stability,low cost,simple preparation and reusability of the double-layer system are suitable for a wide range of practical applications in large-scale solar steam generation,sterilization of waste,seawater desalination.2.Investigation on the preparation and photothermal effect of reduced graphene oxide-polyurethane nanocomposite foam(rGO/PU):Graphene oxide-polyurethane nanocomposite foam(GO/PU)prepared by in-situ polymerization method,and then get rGO/PU by microwave assisted chemical reduction method.This novel photothermal conversion system utilize reduced graphene oxide as light absorption materials,which can effectively absorb solar light from ultraviolet to near infrared regions and efficiently convert light energy into localized heat energy,and utilize porous polyurethane as matrix,providing self-floating and heat conduction inhibition ability as well as acting as water channels for replenishment of surface water evaporated.In addition,the reduced graphene oxide sheets are connected with the polyurethane matrix by covalent binding,giving the system excellent chemical and mechanical stability.The evaporation test showed that rGO/PU achieved about 81%evaporation efficiency under a light density of 10 kW/m2.The stability test results showed that rGO/PU could maintain stable structure in acidic and alkaline environment,and maintained stable performance after repeated evaporation test for 20 times.This photothermal conversion foam can directly convert solar energy into steam energy and has the advantages of high efficiency,simple preparation process,low cost,excellent stability and reusability,which can provide certain reference value for industrial application.