Interfacial Evaporation Of Carbon-based Functional Materials And Structures

High efficient and fast evaporation is of great significance in the fields of chemical separation,material preparation,distillation purification and seawater desalination,and is the direction people have been pursuing.In recent years,new materials such as nano particles,carbon nano materials,metal oxides and aerogels have been adopted to enhance the thermal interfacial evaporation powered by solar energy.The efficient absorption and conversion of solar interfacial evaporation were improved by adjusting the micro-nano structure of materials,by designing new structures for thermal management and by concentrate the solar energy to localize the heat energy.At present,some achievements have been made in this field,but from the perspective of practical engineering applications in the future,there are still many challenges in the field of interface evaporation:low cost,enveromentally friendly,anti-weathering,all-weather stable output,higher evaporation rates and higher efficiency.Porous carbon is the best choice,as carbon can be prepared from a wide range of sources,carbon has strong light absorption,rich pore structures and large specific surface area,carbon is conducitive thus can be used as Joule heater.More importantly,carbon can simultaneously exert solar,wind and electrical energy to promote the evaporation.Aiming at tackling the key challenges,this thesis explores the interfacial evaporation behavior,key influencing factors and the science in various materials and structures and obtained the following results:A"mushroom"-like structure(GMPCC)with a composite material composed of biomass monolithic porous carbon and geopolymer was designed and fabricated.Both the hydrophilic biomass carbon and geopolymer are low cost,mechanically robust and environmentally friendly.The"mushroom"handle composed of geopolymers is hydrophilic,heat-insulating and durable.Based on the connected macroporous structure and polar functional groups,water can be delivered to the"mushroom"umbrella surface through the capillary action.The porous carbon coated on the umbrella can efficiently absorb the broadband solar energy,localize the heat on the surface,and power the water evaporation.MPC with mesoporous structure can absorb 90-95%of solar light over a wide range of spectrum(250 nm-2500 nm)before and after wetting.The geopolymers have low thermal conductivity(0.26 W m^-1 K^-1),which can effectively limit the heat to the umbrella evaporation layer.Under the solar of 1 k W m^-2,the water interface evaporation rate reached 1.58 kg m^-2 h^-1,and the photothermal-steam conversion efficiency reached84.95%.Wind(light breeze,1-3 m s^-1)is used to improve the water vapor mass transfer conditions on the upper part of the composite structure and reduce the local pressure.Experimental shows that the wind can increase the solar interface evaporation rate by 5times(up to 7.55 kg m^-2 h^-1).In order to meet the requirements of all-weather stable output and obtain higher evaporation rate,we first proposed the idea of using Joule heating combined with the micro-nano structured materials to achieve faster interfacial evaporation.A three-layer floating structure with monolithic porous carbon(MPC),hydrophilic fiber cloth and polystyrene foam has been proposed and fabricated.The 2D hydrophilic carbon fiber cloth has micron-level macropore structure and strong hydrophilicity,which can effectively supply water.The MPC has excellent electrothermal performance and rich pore structure,and can be used as a carrier for Joule heat generation and interface evaporation.By controlling the structure of the fiber cloth and the insulation foam,the heat is limited to the MPC evaporation layer,and a stable local heat zone is quickly formed to achieve thermal management.At the same time,the synergy of physical fields such as Joule heat,solar heat,wind/negative pressure,etc.can be realized through the absorption and conversion of MPC to solar and the change of mass transfer conditions.Compared with traditional Joule heating materials,this structure can directly avoid the energy loss of the preheated water body,directly realize the high-rate interfacial evaporation,and greatly improve the energy utilization efficiency.By increasing the input power,the interfacial evaporation rate can reach up to 112.2 kg m^-2 h^-1.The application of Joule heat to micro-nano structures greatly expands the application range of interfacial evaporation and provides conditions for stable and high-rate interface evaporation.During the interfacial evaporation,the mass transfer play an important role.The mass transfer have been inhibited by the micro pore structures,as a result the energy conversion efficiency of MPC decreased under stronger solar light irradiation.In order to study the influence of the pore structures of carbon materials on the mass transfer process and interfacial evaporation,hierarchical porous carbon(HPC)was prepared by mechanochemical method by using industrial waste polyvinyl chloride(PVC)as the raw material.The HPC has a high broad-spectrum solar absorption(?91%,250-2500 nm),which can harvest more energy to supply heat to realize faster water evaporation.The HPC whose specific surface area reaches up to 1740 m² g^-1contains micropores,mesopores and macropores.With the increase of solar intensity,the conversion efficiency of HPC composite structure gradually increased to a higher level(>95%),which confirmed the promotion effect of the hierarchical pore structure on interfacial evaporation(7.87 kg m^-2h^-1,5 k W m^-2).In addition,the surface chemical properties of the material,such as hydrophilicity/hydrophobicity,also have a great impact on the mass transfer and thermal management of the interfacial evaporation.Carbon based composite structures with different hydrophility through commercial carbon cloth and 2D reduced graphene(r GO)by electrochemistry deposition were prepared.With the three-layer structure of carbon cloth(CC)and graphene's composite material-hydrophilic fiber cloth-polystyrene foam,the GO-CC,r GO-CC and CC modified with nitric acid are hydrophilic,which exhibit similar interfacial evaporation performance.It is mainly due to strong hydrophilicity,which absorbs a large amount of water and causes more heat loss.The hydrophobic carbon cloth shows better interfacial evaporation due to its good gas diffusion performance.In summary,a serious of weather-resistant and stable porous carbon based materials,composites and structures has been designed and prepared in this thesis.The interfacial evaporation systems using photothermal,wind,Joule heat and wind and negative pressure,as well as comprehensive utilization of renewable energy have been realized and studied.The influence of chemical properties on mass transfer and heat management lays a good foundation towards low cost,stable and high-speed interfacial evaporation and practically useful systems for energy harvest,water purifications and drinking water preparation from sea water.