Radiofrequency-triggered surface-heated laser-induced graphene membranes for enhanced membrane distillation

Abstract

Membrane distillation (MD) has attracted significant research interest for desalinating hypersaline brine. However, the lack of robust hydrophobic membranes and lower energy efficiency requirements restrict its true potential. Designing and fabricating a hydrophobic membrane that enables surface heating at the mass transfer interface provides a potential route for efficient desalination with MD. This study aims to study a new class of surface-heated membranes that can be triggered by radiofrequency (RF) electromagnetic waves. We developed hydrophobic membranes that were prepared by CO₂ laser ablation of a polyethersulfone (PES) membrane substrate. The proposed single-step laser modification converts the PES membrane surface to laser-induced graphene (LIG), which is hydrophobic and electroconductive, making it suitable for surface heating. The hydrophobic nature of the prepared PES–LIG membrane is confirmed from the surface water contact angle (143.7°), and the surface heating potential is studied by investigating the thermal response of the membrane exposed to RF fields. The membrane surface average temperature can reach up to ∼140 °C with optimized RF frequency and power. The PES–LIG membrane's mechanical and thermal properties are characterized to investigate its feasibility for MD application. In this work, vacuum MD (VMD) is studied by integrating with RF heating and a permeate flux of up to 13.5 L m⁻² h⁻¹ with >99% salt rejection is reported. Cyclic thermal and mechanical stability tests and long-term VMD tests show the stable performance of the PES–LIG membranes. This work demonstrates a novel MD strategy that can potentially address challenges impeding its commercialization.