Development of robust and superamphiphobic membranes using reduced graphene oxide (rGO)/PVDF-HFP nanocomposite mats for membrane distillation

Abstract

Membrane distillation (MD) has attracted significant attention owing to its unique advantages in desalination of hypersaline water. However, commercially available membranes used for MD desalination face fouling and wetting issues in treating wastewater containing low surface tension contaminants (e.g., oil and alcohol) and surface-active agents (e.g., surfactants). Herein, a superamphiphobic (i.e., superhydrophobic and near-superoleophobic) MD membrane was fabricated using the electrospinning technique followed by a simple surface modification step for treating challenging wastewater containing low surface tension substances. In order to fabricate a superamphiphobic membrane, a highly hydrophobic nanofibrous mat was first prepared by electrospinning a mixture of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP, also refers to PH) and reduced graphene oxide (rGO). Surface superamphiphobicity was then supplemented by a facile one-step grafting of low surface energy fluoroalkylsilane POTS. The influence of this one-step surface modification on the morphology and physicochemical properties of the membranes was investigated, revealing the altered elemental composition and enhanced hydrophobicity of the electrospun nanofiber mats. The resulting membranes demonstrated superamphiphobicity, confirmed by their wetting resistance evaluated with water and low surface tension liquids. The anti-wetting performance of the membrane was tested through desalinating 35 g L⁻¹ sodium chloride solution in the presence of a surfactant (sodium dodecyl sulfate, SDS) in the direct contact membrane distillation (DCMD) unit. Membranes modified with fluoroalkylsilane (PH–rGO–POTS) exhibited enhanced stability and durability in terms of both permeation flux (∼27.94 kg m⁻² h⁻¹) and salt rejection (∼100%), while control membranes suffered from severe wetting problems.