Solar-driven high efficiency air water harvesting study of covalent organic framework
Capturing water from air is an effective method to solve the current fresh water shortage crisis because of its low construction cost,ease of use and flexibility,as well as the abundance of fresh water resources in the atmosphere.The sorption-absorption method of AWH is the most promising method with stable efficiency and green features.Insufficient water sorption capacity and high desorption temperature of hygroscopic materials are the core problems which limit the wide application of air extraction technology.Covalent organic framework is a new porous crystalline material with large specific surface area and permanent porosity,which is achieved wide attention in the field of gas sorption and storage.The β-ketoenamine COFs:TpPa-1 with high crystallinity and good water stability are prepared by the solvothermal method.The specific surface area of TpPa-1 is 502 m2/g,and the pore size is distributed at 1.26 nm,which makes TpPa-1 have excellent water adsorption ability at low relative humidity.TpPa-1 exhibits an S-shaped sorption isotherm with a steep increase in water sorption capaci-ty from 0.08 g/g to 0.27 g/g under 20％-30％RH.In the sorption kinetics test,TpPa-1 reaches the sorption e-quilibrium within 2 h at 15 ℃ and 30％RH.Meanwhile,TpPa-1 has a low desorption temperature and may reach 91％desorption efficiency under a standard sunlight(AM 1.5 G),indicating that TpPa-1 may fully drive the desorption process by sunlight irradiation without any energy input.Especially,TpPa-1 exhibits excellent cycling stability after 10 sorption-desorption cycles(1 400 min)under humid conditions(60％RH),and the water absorption rate only decreases by 1.48％.A simple AWH device is designed filling with TpPa-1,and AWH tests are conducted under simulated laboratory conditions.It is observed that 0.225 g/g fresh water may be collected in one cycle under 60％RH condition.This work implies that the porous TpPa-1 may provide a sta-ble strategy for adsorption-assisted air collection with high efficiency and fast cycling.
air water harvestingcovalent organic frameworkrelative humiditysorption
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