Preparation Of Carbon Nanomaterial-Sodium Alginate Based Solar Evaporator And Its Water Purification Efficiency

Water scarcity is one of the major problems facing mankind today,and to obtain more water resources people have started desalination and reuse of wastewater,but these technologies require a lot of energy.To reduce carbon emissions,people have started to focus on using clean energy sources.Solar energy,as a safe and sustainable green energy source,offers a new way to develop new,environmentally friendly water purification solutions.The solar evaporator is to absorb sunlight through photo-thermal conversion material to convert it into heat energy to heat water body,and then realize the evaporation and collection of water.Solar evaporators can be effective for desalination and water purification,and have broad application prospects,especially in remote areas with long light hours.However,at present.the preparation process of the solar evaporators is complicated,the preparation is difficult,the raw material is expensive and the crystallization of evaporator surface produces pollution when applied,which hinders the application of evaporator in actual water treatment.To address these problems,based on a comprehensive amount of relevant literature at home and abroad,this thesis uses sodium alginate(SA)biomass hydrogel as a carrier and prepares safe,environmentally friendly and simple CNT-SA hydrogel and aerogel solar evaporator and Graphene-SA hydrogel and aerogel solar evaporator by doping carbon nanotubes(CNT)and graphene as photothermal conversion materials,respectively.The performance differences between hydrogel evaporator and aerogel evaporator and the effects of different photothermal conversion materials on evaporation performance were comparatively studied.The main studies are as follows:(1)A shape-controlled,environmentally friendly,and economical CNT-SA hydrogel solar evaporator(CSH)was developed by immobilizing CNT into the SA hydrogel network.Characterization of the CSH shows that the CSH was internally porous and has an extremely high hydrophilicity as well as a high absorption of light(94.3%),and the SA hydrogel can significantly reduce the evaporation enthalpy of water in the evaporator.The increase of both S A and CNT content in the evaporator can improve the evaporation rate of the evaporator,and the CSH prepared under the optimal economic and performance ratios(SA concentration of 4 wt%and CNT concentration of 0.05 wt%)reached an evaporation rate of 1.70 kg m-2 h-1 under 1 sun irradiation,with a maximum photothermal conversion efficiency of 86%,and it can effectively avoid salt crystallization in the process of seawater desalination or evaporation of high salt wastewater.In the long-time cycle evaporation experiment,CSH still maintains stable evaporation,and the ion removal rate of seawater and brine reaches more than 99%.In addition,CSH also shows excellent performance for decolorization of organic dye wastewater.(2)To investigate the performance difference between hydrogel and aerogel evaporators under the same material,CNT-SA aerogel evaporator(CSA)was prepared by freeze-drying on the basis of CSH.The characterization shows that CSA also has extremely hydrophilic properties and causes a significant decrease in the evaporation enthalpy of water,but the absorption of light by CSA was lower than that of CSH,which was only 82.7%.The comparison study with CSH shows that the evaporation rate of CSA was lower than that of CSH,and the highest evaporation efficiency and photothermal conversion efficiency were 1.62 kg m-2 h-1 and 68%,respectively.CSA also has excellent ion removal effect on brine and seawater,but the evaporation rate of CSA decays during the long-time evaporation process,and the stability of the evaporator was poor.(3)To investigate the effects of different carbon nanomaterials on evaporation performance,Graphene-S A hydrogel evaporators(GSH)and Graphene-S A aerogel evaporators(GSA)were prepared by immobilizing graphene into SA hydrogels.The characterization tests showed that both GSH and GSA have excellent hydrophilicity and strong light absorption properties,and the average light absorption of the two evaporators was 88.8%and 76.6%,respectively.Both evaporators have a reduced enthalpy of water evaporation,and GSH exhibits a higher evaporation rate than CSH in the evaporation process,and the evaporation rate of GSH reaches equilibrium(1.82 kg m-2 h-1)when the graphene content was 0.01 wt%,and the rate of GSA(1.73 kg m-2 h-1)was slightly lower than that of GSH.Ion removal experiments show that both GSH and GSA have excellent.The ion removal experiments showed that both GSH and GSA had excellent ion removal ability,but the stability of GSA was poor.