Surfactant-regulated electrospray printing PEI-TMC nanofiltration membrane for efficient separation of Mg²⁺/Li

Nanofiltration (NF) offers an energy-efficient approach for lithium recovery from brines. Conventional NF membranes rely on the positively charged polyamide layer formed via interfacial polymerization (IP) of polyethyleneimine (PEI) and trimesoyl chloride (TMC) to repel Mg²⁺ more strongly than Li⁺, but their Mg²⁺/Li⁺ selectivity remains constrained by limited control over pore size distribution. Here, we develop polyamide (PA) layers using amphiphilic dioctyl sulfosuccinate sodium (DOSS)-mediated electrospray interfacial polymerization (DEIP). Electrospray-assisted polymerization at the interfaces of abundant immiscible microdroplets produces thinner PA layers with reduced transport resistance and accelerates monomer diffusion in a non-selective manner. Molecular dynamics (MD) simulation and density function theory (DFT) calculations further reveal that DOSS selectively regulates the diffusion behavior of PEI and TMC within microdroplets, enabling the formation of PA layers with uniform pore structures and a positively charged surface. These structural advantages deliver precise ion sieving for lithium extraction, achieving a Mg²⁺/Li⁺ selectivity of 142 and water permeance of 13.45 L·m^-2·h^-1·bar^-1. The DEIP membrane also demonstrates stable Mg²⁺/Li⁺ separation over seven days of continuous NF operation. This work underscores the promise of DEIP membranes for high-efficiency lithium extraction and highlighted their potential for practical brine-based lithium recovery.