Utilization of Janus membranes and low-grade thermal energy for sustainable desalination

Abstract

Harvesting low-grade thermal energy for eco-friendly desalination represents an important and advantageous effort to address the challenges of energy shortages and freshwater scarcity. This work reports a system for producing fresh water using a hydrophilic composite Janus membrane. Based on the hydrophilic composite Janus membrane, the thermo-osmosis phenomenon is employed to supply a driving force in desalination. Low-grade thermal energy can provide the necessary condition (temperature difference) of thermo-osmosis. This work establishes an experimental system for seawater desalination using a Janus membrane combined with Low-grade thermal energy utilization, and the microscopic mechanism is verified by molecular dynamics simulations. The experimental results indicate that the water production rate of the hydrophilic composite Janus membranes is 39.48 % higher compared to that of the widely used purely hydrophobic membranes currently in membrane distillation. The ion concentration and conductivity of the freshwater produced by the system are measured. It successfully desalinated the seawater, reducing all four ions (Ca²⁺, K⁺, Mg²⁺, Na⁺) by 99.99 %, and the ion concentration of the freshwater, as measured by the conductivity, remained at a low level (well below the WHO standard) over a long term. Generally, this work integrates seawater desalination with low-grade thermal energy recovery, which can improve the water production rate of membrane distillation. It paves the way for broader applications of low-grade thermal energy and facilitates the development of low-carbon or even zero-carbon seawater desalination processes.