Producing affordable freshwater becomes increasingly essential. Membrane separation technology offers an unprecedented opportunity, but they typically use fuel energy during the separation process. Therefore, it is a severe challenge to construct an advanced membrane for energy-free water purification. Herein, for the first time, we reported a heterogeneous membrane for pressure-free water purification. Oxidized carbon spheres (OCS) membrane was optimized by the coordinated modification of polydopamine (PDA) and tetrakis(hydroxymethyl)phosphonium chloride (THPC). Remarkably, the OCS@PDA membrane was progressively hydroxylated due to the THPC’s superb water-binding ability. Therefore, the OCS@PDA/THPC membrane demonstrated higher surface free energy and better hydrophilic capacity than the other membranes. Under the combined effect of abundant porous geometry and strong charge interaction, this membrane presented a splendid screening performance for various dye molecules without extra pressure. In addition, its separation throughput can be improved by regulating the external temperature. This work may offer a straightforward manner to handle the relationship between membrane structure and performance for pressure-free water purification.