Hierarchical underwater oleophobic electro-ceramic/carbon nanostructure membranes for highly efficient oil-in-water separation

Fouling is major concern in several industries involving separation of heavy oil components such as crude and motor oils. In this work, a novel free-standing, conductive ceramic membrane, made from nanozeolite and carbon nanostructures (CNS) was fabricated. Various nano-zeolite: CNS ratios were studied. The membranes were tested for oil/water separation with oil concentration of 600 ppm using a dead-end filtration setup under an applied vacuum of 70 kPa on the permeate side. The zeolite nanoparticles provide excellent underwater oleophobicity and a hydrophilic interface, resulting in efficient oil/water separation with a high rejection of 98% for crude oil. The role of CNS in the composite membrane is three-fold; acting as a binder for zeolite nanoparticles, to provide flexibility and to make the membrane conductive. The hierarchical membrane structure formed from hydrophilic zeolite nanoparticles embedded with the CNS greatly facilitates the rapid permeation of water with a high flux of ˃400 L/m² h for oil/water separation. With increasing zeolite composition relative to CNS, membrane separation performance was observed to increase till 60 wt. % zeolite content. However, higher percentage decreased the flux considerably while keeping the oil rejection constant. Membrane repeatability was studied by performing 10 filtration cycles, where a decrease in flux to about 50% was observed by the end of the 5th cycle. The conductive nature of the membrane (electrical conductivity = 4.9 × 10³ S/m) allowed periodic electrolysis of the membrane, hence recovering the flux considerably after each cycle, and reaching about 80% by the end of the 10th cycle. This work provides a new way to develop ceramic based self-cleaning membranes which are applicable in various industries where fouling in ceramic membranes is a major drawback.