Preparation Of Monolithic Porous Carbons And Application In Atmospheric Water Harvesting

Lack of fresh water resources is a serious resource issue in the world at present.The lack of water resources threatens the health and survival of humans,thus affecting the development of society.There is a considerable amount of water vapor in the atmosphere,which is a huge reservoir of freshwater resources.If it is harvested,it may be an effective solution to the lack of water resources.Adsorption-based atmospheric water harvesting（AWH）is considered to be a promising technology to address the issue of global water shortage,showing the advantages of the simple device structure,low energy consumption,and wide application range.One of the key issues is to find high-performance porous adsorbents.The monolithic porous carbons have the advantages of high porosity,good compressive strength,easy mass synthesis,and relatively low cost,making them a promising adsorbent for AWH.In this thesis,monolithic porous carbons for solar-driven adsorption-based AWH were focused on,and their water vapor adsorption capacity was improved through the strategy of modification regulation and in situ growth of hydrophilic polar sites.A solar-driven AWH device was built,and then the AWH effect of several porous adsorbents was tested.The energy efficiency of the device was also roughly evaluated.（1）A high-strength micro-meso-macroporous hierarchical porous monolithic carbon was prepared with resorcinol-formaldehyde-hexanediamine by a benzoxazine sol-gel polymerization method.The specific surface area can reach 569 m²/g.The total pore volume is0.365 cm³/g.The compressive strength exceeds 10 MPa.The water vapor adsorption performance of carbons was improved through the control of pore structure and surface chemistry without affecting the compressive strength.The adsorption capacity of water vapor can reach 12 mmol/g at 70%of relative humidity after adjustment.Inorganic salts are loaded into the pores of carbons to form composite materials,which can also greatly improve the water vapor adsorption capacity.（2）Adopting a composite hydrophilic strengthening strategy,a class of monolithic porous carbons was prepared by interpenetrating metal-organic frameworks into resorcinol-formaldehyde resin networks,in which the metal-organic parts evolved into polar sites in the formaldehyde-resorcinol polymer cross-linked framework as carbon precursors.The specific surface area can reach 705 m²/g,and the water vapor adsorption capacity could reach 8 mmol/g at 30%of relative humidity.By adjusting the addition amount of Cu²⁺and 4,4′-bipyridine and the pyrolysis temperature during the synthesis,the pore structure and surface hydrophilicity of the samples were adjusted.The surface hydrophilic sites formed by removal of metallic copper and copper oxides and the oxygen-containing functional groups generated by oxidation on the surface of the carbon material jointly improved the hydrophilicity of the monolithic porous carbons.（3）An AWH device was set up and several porous adsorbents were applied to AWH,all of which can harvest water vapor in the air.Taking two commercial porous solid adsorbents as examples,the energy efficiency of the device was roughly evaluated,reaching 20.3%.Considering the reachable temperature and energy efficiency of the adsorbent when irradiated by sunlight,it is concluded that carbons are suitable adsorbents for solar-driven adsorption-based AWH.