Constructing oxidized carbon spheres-based heterogeneous membrane with high surface energy for energy-free water purification

[Display omitted] •An advanced energy-free separation membrane was presented for the first time.•It endowed with a high surface free energy due to the functionalization of THPC.•It presented low roughness and superhydrophilicity because of the PDA and THPC.•It showed a splendid energy-free screening performance for various dye molecules. 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.