Zwitterion-based Freshwater Production:Biomimetic Designs And Applications

Freshwater is vital to human life and manufacturing.Recently,the expanding pop-ulation,booming industry and water pollution have exacerbated freshwater shortages.How to obtain more freshwater has become an urgent issue worldwide.Zwitterionic materials bearing equal positive and negative charged moieties on the same chain are featured with strong polarity but neutral charge.The neutral charge can avoid electro-static attraction-induced fouling,and the strongly polar moieties can bind abundant wa-ter molecules through ionic solvation effects,endowing zwitterions with remarkable water affinity and fouling repellence.Here,we designed and fabricated various novel zwitterionic devices for freshwater production from different water resources.The ex-cellent water affinity of zwitterions can facilitate water harvesting,and the fouling re-pellence can guarantee long-term durability of these devices in real-world conditions.On earth,available freshwater is mainly in the forms of surface water,underground water and atmospheric water.Among them,the atmospheric water is usually ignored by human and has not been widely used.This study investigated the nucleation,con-densation and transport of atmospheric water on hydrophilic and hydrophobic surfaces,respectively.A zwitterionic functionalized hydrophilic/hydrophobic hierarchical at-mospheric water collector was developed with the inspiration of beetles.Owing to the hydrophilicity-induced high nucleation density and hydrophobicity-induced rapid sur-face renewal,effective atmospheric water collection with a high rate of 1065.9 mg cm^-2 h^-1was achieved.Moreover,hydrophilic channels were built on the hydrophobic sub-strate,controllable water transport can be achieved driven by internal pressure differ-ence and gravity.In addition to the existing freshwater,more than 96.53%of global water is in the ocean,which can be desalinated into freshwater.Huge consumption of energy is gen-erally required in traditional desalination strategies such as reverse osmosis and multi-effect distillation,leading to a trade-off between energy and water.In view of this,we proposed a jellyfish-inspired zwitterionic functionalized superhydrophilic hierarchical evaporator,PU/CNT₂/ZCB,which only consumed inexhaustible solar and seawater to perform high-efficiency,energy-saving and eco-friendly freshwater production.Car-bon nanotube（CNT）in the evaporator can absorb solar influx and turn it into heat via lattice vibrations,thus the liquid seawater can be evaporated into steam.Attributing to the excellent water affinity of zwitterionic carboxybetaine（ZCB）coating,the evaporator can provide continuous water supply,achieving a high evaporation rate of～2.2 kg m^-2h^-1and solar conversion of 93.5%.Furthermore,the marine environment is complex with enormous creatures and pollutants,which can settle on the evaporator to block water and steam transport channels,increase loading,cause biocorrosion and even evaporator invalidation.To overcome this problem,a seaweed-inspired all super-hydrophilic evaporator on the basis of zwitterionic sulfobetaine（ZSB）hydrogels and hollow glass microbeads（HGB）was rationally designed.The HGB can decrease the entire density of the evaporator and localize heat where evaporation occurs.Therefore,the evaporator can float at the air/water interface and perform interfacial evaporation.Due to the antifouling capacity of ZSB,this evaporator was capable of inhibiting pro-tein adsorption,microbial adhesion,oil pollution and salt aggregation,guaranteeing its stability and durability in practical use.Besides exploring more freshwater supply,wastewater should be purified and re-cycled to conserve water resources.Therefore,solar distillation and photocatalytic deg-radation were combined to develop a catalytic evaporator,C₃M₈-ZSB,for organic wastewater purification.Fe-based metal-organic framework（Fe-MOF）particles in the evaporator were competent to generate hydroxyl radicals via photo-Fenton reaction un-der solar irradiation.The hydroxyl radicals were strongly oxidizing,enabling decom-position of organic pollutant especially volatile organic compound（VOC）in wastewater.The superhydrophilic ZSB coating not only enabled continuous water sup-ply,but also promoted mass transfer between wastewater and evaporator,leading to enhanced organic pollutant degradation.As a result,the VOC cannot evaporate with steam,avoiding the risk of organic residue and additional separation operations.