Biocatalytic degradation of perfluoroalkyl substances from water using multi-walled carbon nanotube/laccase polyamide thin film nanocomposite membranes

Biocatalytic membranes have emerged as a sustainable approach for removing and degrading detrimental pollutants from water. This research introduces a uniquely engineered biocatalytic PA-TFC membrane synthesised through in-situ incorporation of an MWCNTs/laccase nanocomposite, offering a new integration strategy that enhances catalytic stability, membrane performance, and pollutant degradation. The study distinguishes itself by demonstrating simultaneous removal and enzymatic degradation of PFOA, supported by multi-technique characterisation and superior functional metrics compared to conventional membranes. The Attenuated Total Reflectance Fourier Infra-Red spectroscopy confirmed the successful synthesis of modified PA-TFC membranes, revealing the presence of an amide band at 1610 cm⁻¹, which is a characteristic of the polyamide thin film layer. Additionally, the scanning electron microscopy and correlative light electron microscopy showed green fluorescence under confocal microscopy, validating the presence of laccase enzyme aggregates. The modified PA-TFC membranes exhibited enhanced hydrophilicity, as evidenced by reduced water contact angle of 42.07° ± 6.89 and high-water flux of 37.40 ± 1.07 L m⁻² h⁻¹. Conversely, the pristine PA-TFC exhibited low hydrophilicity, characterised by an elevated contact angle of 54.42° ± 6.89° and a reduced water flux of up to 9.36 ± 9.36 L m⁻² h⁻¹. This was accompanied by enhanced antifouling properties of the modified membranes, with a flux recovery ratio of over 80 %, compared to 72.55 % for the unmodified membrane. Furthermore, the modified membranes achieved the perfluorooctanoic acid (PFOA) removal efficiencies of 65.33 % ± 3.52, whereas the unmodified membranes exhibited the removal of 55.06 % ± 0.80. Perfluorooctanoic acid was degraded into less toxic by-products such as perfluorohexanoic acid, perfluoroheptanoic acid, perfluorobutanoic acid, and formic acid. The in-situ modified MWCNTs/laccase-PA-TFC membranes exhibited enhanced efficacy compared to other conventional biocatalytic membranes, highlighting their potential in advancing sustainable water treatment applications due to their self-cleaning properties and longevity in degrading the PFOA contaminant.