Janus resorcinol-formaldehyde-based membrane with opposite wettability for efficient separation of oil and water emulsion

Abstract

A resorcinol-formaldehyde (RF)-based Janus membrane was fabricated by casting graphene oxide (GO)-dispersed RF solution on Janus-B side and Cu salt-RF solution on the opposite Janus-A side of an activated carbon fibre (ACF) substrate, and then subjecting the composite material to chemical vapor deposition to form a web of carbon nanofiber (CNF) on the Janus-A side. CNF imparted the super-hydrophobic (water contact angle WCA ∼151°) and super-oleophilic (oil contact angle OCA ∼0°) characteristics, while GO-RF imparted the hydrophilic (WCA 30°) and olephobic (OCA ∼121°) characteristics to the membrane. The microfiltration tests were carried out under different conditions of oil and water feed concentrations (0–15% v/v) and operating pressure (1–3 bar). The super-hydrophobic side showed 99.75% water rejection efficiency and the initial permeate flux of 1020 Lm−2h−1 for a 5% (v/v) water-in-oil (W/O) emulsion, while the hydrophilic side showed 99.96% oil rejection efficiency and the initial permeate flux of 380 Lm−2h−1 for 5% (v/v) oil-in-water (O/W) emulsion. The material showed good chemical stability in acidic, basic and corrosive media as well as an excellent repeatability under the repeated alternate cycles of pure diesel/water and emulsion post- simple ethanol wash. Considering that the method of fabrication is simple, fast, and scalable, the comparative performance data clearly pitch CNF-RF/ACF/GO-RF ahead of the other membranes discussed in the literature for oil-water emulsion.