Preparation Of Biomass Carbon And CuO-based Photothermal Material And Its Application In Seawater Desalination

Solar energy is a green,safe,and universal renewable energy with the characteristics of broad spectrum and large area.At present,the utilization of solar energy mainly includes photoelectric conversion,photochemical conversion and photothermal conversion.Among them,photothermal conversion has been widely used in the fields of solar thermal power generation,solar thermal energy storage and solar sea water desalination.Especially in the field of seawater desalination,this technology has received great attention due to the use of solar energy without the need to consume other types of energy.The key of solar desalination technology is the development of photothermal materials.At present,several photothermal materials(such as gold nanoparticles,graphene and carbon nanotubes)have been prepared and successfully used for efficient photothermal evaporation of seawater.However,there are still two problems.The first problem is high cost,since the synthesis of photothermal materials requires complicated steps and expensive raw materials.The second problem is the easy appearance of solid-salt accumulation during the evaporation process.To solve the above problems,in this thesis two new low-cost photothermal conversion materials have been developed,and the hanging mode is used to avoid the precipitation of solid salt.The main results include the following two points:(1)Fabrication of porous carbon aerogels with natural watermelon as precursors for evaporation of seawaterVarious photothermal materials have been developed for seawater desalination,but their practical applications have been limited due to their complex synthesis methods and high cost.To solve this problem,watermelon has been chosen as a cheap,abundant,green and pollution-free precursors to prepare porous carbon aerogels for seawater desalination.Firstly,the porous carbon hydrogels have been synthesized by a simple one-pot hydrothermal method(at 180?for 12 h)with watermelon soft tissue as raw material.Then it is freeze-dried to remove the water to obtain porous carbon aerogel.The aerogel consists of both carbon network and cross-linked carbon nanospheres network,with an average pore size of 31.97 nm.There are also large amount functional group in this aerogel.This carbon aerogel exhibits strong photoabsorbtion property in a wide range(the absorbance in range of visible light reaches?95%),conferring high photothermal conversion property.The heat-loss and evaporation performance of aerogel have been investigated by adjusting its height.The results reveal that aerogel with 3-cm height has the highest evaporation rate which reaches 2.34 kg m^-2 h^-1 under the irradiation of the simulated sunlight(1 k W m^-2),and the photothermal efficiency is 86.3%.Importantly,no obvious decline of evaporation rate can be found after 60 h continuous experiments.Therefore,this porous carbon aerogel has great potential in large-scale solar seawater desalination.(2)Preparation of porous Cu@CuO photothermal foam sheet for evaporation of seawater with hanging modeIn the previous studies,the photothermal films have been directly floated on the water surface to evaporate the seawater.After the long time evaporation,the soluble salt in the seawater will be accumulated on the photothermal film surface,which induces the decrease of the evaporation rate.To solve this problem,a porous and soft Cu@CuO foam sheet has been prepared and then been hanging to evaporating seawater.Firstly,Cu foam sheet(thickness:1.5 mm)has been used as substrates to grow Cu(OH)₂nanowires(length 5-10?m)by chemical oxidation method,and then Cu(OH)₂nanowires can be converted into CuO nanowires by heating,resulting in the formation of Cu@CuO foam sheet.This Cu@CuO foam sheet has strong photoabsorbtion property in a wide range(the absorbance in range of visible light reaches?93%),conferring high photothermal conversion property.Then the Cu@CuO foam is fixed on two water containers,where the high container is filled full with seawater while the low one is empty.Cu@CuO foam sheet can absorb the seawater from the higher water container,and then seawater can flow along the foam to the lower container due to the capillary action,siphon effect of the Cu@CuO foam and gravity of water.By adjusting the relative height between the two water containers,the inclination angle of Cu@CuO foam can be adjusted.Under the irradiation of the simulated sunlight(1 k W m^-2),Cu@CuO foam with the inclination angle of 20°exhibits the highest evaporation of 2.06 kg m^-2 h^-1,and the solar efficiency is 86.3%.Especially,during the evaporation process,the high concentration brine will flow to the lower water container,which will prevent the solid salt accumulated on the surface of Cu@CuO foam sheet.After 12 h continuous evaporation,the evaporation rate of the Cu@CuO foam sheet has no obvious change.Therefore,this hanging mode has great potential in practical solar seawater desalination.This thesis reports the preparation of biomass carbon porous aerogel and porous Cu@CuO foam sheet as new photothermal materials.A hanging mode has been developed to evaporate seawater.These results provide some ideas for subsequent large-scale applications and the design of new evaporators.