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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
Summary
Scientists have created a new water filter made entirely from non-plastic materials (ceramic and light-activated coatings) that can clean oily wastewater without breaking down into microplastic pollution—a concerning side effect of some plastic-based filters used today. The filter also "self-cleans" using light exposure to break down trapped oil, allowing it to be reused repeatedly while still removing about 99% of oil from water. This matters because it points toward more sustainable water treatment options that avoid adding more microplastics to our environment and water supply.
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.