Photocatalytic self-cleansing ZnO-coated ceramic membranes for preconcentrating microalgae

Abstract

Microalgae present strong potential for biofuel and bioproduct production; however, efficient harvesting methods remain a critical challenge to enhancing the economic competitiveness of microalgal products. This study introduces a simple approach for fabricating self-cleaning microfiltration membranes tailored for Scenedesmus sp. microalgae solutions by coating alumina substrates with ZnO. The ZnO layer was deposited using reactive magnetron sputtering and the functional properties of the membrane were tailored through controlled coating thicknesses. Surface characterization confirmed the formation of a uniform, crystalline ZnO layer. The solar light absorption of the ZnO-coated membrane was found to vary with coating thickness. The water contact angle of the membrane decreased from 80° to 42° after ZnO coating, demonstrating a substantial increase in hydrophilicity. While both uncoated and ZnO-coated alumina membranes initially exhibited a permeate flux of about 55 L·m⁻ 2 ·h⁻ 1 (LMH), the ZnO-coated membranes demonstrated superior fouling resistance, with only a 5% flux decline after three filtration cycles compared to a 32% reduction in uncoated membranes. Under optimal conditions, the ZnO-coated membranes achieved full flux recovery within 30 minutes of solar simulator exposure, highlighting their excellent photocatalytic self-cleaning capabilities. The performance of the ZnO-coated membranes remained stable over three repetitive filtration cycles and membrane recovery, with the standard deviation of <5%, confirming the durability of the ZnO coatings. These findings highlight the potential of ZnO-coated ceramic membranes as a cost-effective solution for sustainable microalgae harvesting. • Facile method to prepare self-cleansing ZnO-coated alumina membranes • ZnO coating enhanced hydrophilicity & reduced fouling during microalgae filtration • ZnO-coated membrane had less flux decrease (5%) than the uncoated membrane (32%) • Self-cleansing by 30 min solar irradiation resulted in complete flux recovery

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