A new insight into mass and heat transfer for Janus membranes in MD/PMD and its implication for membrane selection

Although the Janus membrane has been widely used in membrane distillation (MD) and photothermal membrane distillation (PMD), the mass and heat transfer mechanisms are still unclear. This study constructed and verified a numerical model based on the MXene based membranes and revealed that the thermal conductivity of the hydrophilic layer has a negligible effect on MD performance. The highly hydrophilic MXene membrane demonstrated superior suitability for low feed temperature, exhibiting a rapid decrease in simulated diffusion coefficient from 2.59 × 10 −5  m 2 /s to 1.68 × 10 −5  m 2 /s between 303.2 K and 309.7 K. In contrast, the MX-CNT membrane showed a linear increase from 2.18 × 10 −5  m 2 /s at 303 K to 2.67 × 10 −5  m 2 /s at 333 K. A mass transfer mechanism was proposed wherein water molecules transport to the hydrophilic/hydrophobic interface, with the effective evaporation area decreasing as temperature rises. The temperature polarization coefficient (TPC) under low-temperature PMD conditions was significantly higher than in conventional MD. The TPC can be significantly affected by the diffusion coefficient of the membrane. This work provides critical insights into Janus membrane transport mechanisms, which with great significance to its development.