Kinetic-Thermodynamic Coupling for Enhanced Water Isotopologue Separation Via Solar-Powered Diffusion-Evaporation.

Separating water isotopologues is highly energy-intensive because the nearly identical physicochemical properties of H2O and D2O impose intrinsically small thermodynamic differences, limiting the efficiency of conventional thermal separation processes. Here, we report a solar-powered diffusion-evaporation coupling (SDEC) strategy that integrates nonequilibrium transport with interfacial phase transition to enable efficient H2O/D2O separation. The proof-of-concept separator comprises a photothermal two-dimensional nanofluidic membrane constructed from cellulose-nanofibril-intercalated porous MXene nanosheets. In the SDEC separator, solar-powered transpiration drives directional flow through confined nanochannels, and the local temperature increase amplifies the kinetic diffusion differences between H2O and D2O, achieving high selectivity. Selectivity at the evaporation interface is further enhanced by nanoconfinement-induced modulation of isotopologue evaporation enthalpies. Under one-sun illumination, the SDEC separator achieves a separation factor of 1.84. A five-stage SDEC device further reduces the D2O concentration from 10 vol % to 0.45 vol %, sustaining a stable daily condensate yield of 4.3 kg·m-2.