Two-dimensional (2D) catalytic ultrafiltration membranes, tightly assembled with MXene (Ti3C2Tx) lamellae and significantly dispersed Co single atoms (∼ 2.4 wt%), were prepared by a simple solvothermal and low-temperature reduction method. The Co-MXene membrane overcomes the conventional trade-off between selectivity and permeability, and demonstrated an instant water purification (100 % carbamazepine degradation within 240 ms) and a high membrane permeability (∼900 LMH/bar). It has been confirmed that coordinatively unsaturated Co-N1O2 accelerated electron transfer and activated the formation of 1O2 and high-valent Co-oxo species. Nano-confinement channels assembled by the small-sized lamellae facilitated the transport of water molecules. A stable treatment performance with natural surface water was achieved at 3000 L/m2. Good anti-fouling capabilities were also demonstrated with a 96 % alleviation of membrane fouling in the presence of Pseudomonas aeruginosa. These comprehensive mechanistic investigations and stable performances provide a valuable basis for preparing SACs-catalyzed membranes with highly dispersed single atoms and high permeability.