Efficient Light-Driven\nIon Pumping for Deep Desalination\nvia the Vertical Gradient Protonation of Covalent Organic Framework\nMembranes

Traditional desalination methods face criticism due to\nhigh energy\nrequirements and inadequate trace ion removal, whereas natural light-driven\nion pumps offer superior efficiency. Current synthetic systems are\nconstrained by short exciton lifetimes, which limit their ability\nto generate sufficient electric fields for effective ion pumping.\nWe introduce an innovative approach utilizing covalent-organic framework\nmembranes that enhance light absorption and reduce charge recombination\nthrough vertical gradient protonation of imine linkages during acid-catalyzed\nliquid–liquid interfacial polymerization. This technique creates\nintralayer and interlayer heterojunctions, facilitating interlayer\nhybridization and establishing a robust built-in electric field under\nillumination. These improvements enable the membranes to achieve remarkable\nion transport across extreme concentration gradients (2000:1), with\na transport rate of approximately 3.2 × 10<sup>12</sup> ions\nper second per square centimeter and reduce ion concentrations to\nparts per billion. This performance significantly surpasses that of\nconventional reverse osmosis systems, representing a major advancement\nin solar-powered desalination technology by substantially reducing\nenergy consumption and secondary waste.