Fabrication of a photocatalytic self-cleaning all-inorganic membrane by depositing GO/TiO2 nanocomposite active layer on alumina substrate for sustainable separation of emulsified oil from water

Recent discovery and potential inclusion of important membrane-fabrication polymers, such as polyvinylidene difluoride (PVDF), among microplastics/micropollutants have spurred the development of new and efficient membranes for wastewater treatment. The objective of the current work was to develop an all-inorganic membrane as a sustainable solution for the treatment of wastewater, such as oily wastewater. A photocatalytic self-cleaning inorganic membrane was developed by initially synthesizing the GO/TiO 2 (TiO 2 nanoparticles decorated graphene oxide nanosheets) photocatalytic nanocomposite by ultrasonication-assisted synthesis. The GO/TiO 2 nanocomposite was deposited as an active layer on a ceramic alumina support by a simple drop-casting approach, followed by thermal annealing, yielding a self-cleaning photocatalytic inorganic membrane. The GO/TiO 2 coated alumina membrane possessed special wettability of being superhydrophilic in air and superoleophobic underwater, owing to a water contact angle of 0° in air and an oil contact angle of ∼160° underwater. This feature preferentially allowed water to permeate through the membrane, and oil was retained, resulting in excellent separation of emulsified oil from water. The GO/TiO 2 -coated alumina membrane exhibited a permeate flux of 1183 L m -2 h -1 at a transmembrane pressure of 4 bar when distilled water was used as the feed. The permeate flux decreased when crude oil was used in a water emulsion, to 676.1 L m -2 h -1 at 4 bar, indicating the formation of a fouling layer on the membrane surface. However, the photocatalytic self-cleaning potential of the GO/TiO 2 nanocomposite active layer effectively removed the fouling layer and restored the membrane's permeability to a greater extent. The GO/TiO 2 coated alumina membrane regained a normalized flux of ∼0.88 upon photocatalytic self-cleaning. It is also important to note that the GO/TiO 2 -coated alumina membrane retained a separation efficiency of nearly 99% before and after cleaning, indicating that the membrane structure remained intact and could be reused for subsequent cycles. Therefore, the strategy of fabricating inorganic membranes with photocatalytic self-cleaning properties is highly promising for applications in treating complex feeds such as stabilized/emulsified oil from water.