(554g) Super-Hydrophobic Laser-Induced Graphene Membranes for Membrane Distillation of Complex Wastewater Treatment

Membrane distillation (MD) is an emerging desalination technology with a high potential for addressing water scarcity issues. However, traditional MD membranes often suffer from wetting, fouling, low selectivity, and inadequate performance in rejecting various contaminants including volatile compounds. To overcome these limitations, there is a need for the development of advanced membranes with enhanced hydrophobicity, electrical conductivity, and resistance to fouling. This study aims to address the shortcomings of conventional MD membranes by developing superhydrophobic laser-induced graphene (LIG) flat sheet membranes. Laser-induced graphene (LIG) is a three-dimensional porous carbon material generated by direct laser scribing with a 10.6 µm CO₂ laser on a polymeric substrate in an ambient atmosphere, leading to electrically conductive, low-fouling surfaces. Recently, LIG has been fabricated on porous supports, which led to highly permeable and porous separation filters, and making them superhydrophobic is appropriate for the membrane distillation application.

First, dual-layer polymeric membranes were gently prepared using the phase inversion technique. Briefly, 22 wt% of PVDF-co-HFP polymeric membrane was prepared by phase inversion, and a 20% PES polymeric layer was coated on the adjacent side of the PVDF film carefully. The PES side of the membrane is converted to graphene using a 10.6 µm CO2 laser. Optimal parameters of laser power, frequency, and speed were used, at focus length. These finely tuned parameters ensured the fabrication of LIG with exceptional characteristics, achieving the required features for the membrane distillation process. Further silane coating was used to enhance the super-hydrophobicity of the membrane surface. These membranes are then comprehensively characterized to evaluate their surface morphology, porosity, wettability, liquid entry pressure, hydrophobicity, thermal stability, and electrical conductivity. Furthermore, the performance of the LIG membranes is assessed in terms of contaminant rejection and permeability rate, particularly in direct contact membrane distillation (DCMD) applications. The study also investigates the anti-biofouling properties of LIG membranes under challenging biofilm development conditions, including the application of an electric field.

The reported LIG membrane demonstrated exceptional performance in rejecting various contaminants, including NaCl (>99.5%), seawater (>99.5%), produced water from oil and gas industry (99.8%), PFAS (>99.45%), textile dyes (>99.9%), carbamazepine (>99.8%), hexavalent chromium (>99.35%), and arsenic (98.86%), all while maintaining a high permeability rate of >8.5 LMH. Furthermore, this innovative LIG membrane exhibited remarkable antibiofouling properties, particularly when subjected to an electric field under challenging biofilm development conditions. These outstanding rejection properties, coupled with the electrically conductive and superhydrophobic nature of the LIG membranes, position them as promising candidates for future fouling-free membrane distillation applications. Additionally, their potential for solar energy harvesting makes them a suitable choice for solar-driven membrane distillation processes.