Analytical approaches to track nylon 6 microplastic fiber degradation using HKUST-1(Cu/Fe)-derived CuO/TiO2 photocatalyst

Abstract

Nylon 6 microplastic (MP) degradation was performed for the first time by photocatalysis using HKUST-1(Cu/Fe)-derived CuO/TiO₂ (TCFH). The TCFH composites with 5, 10, and 15 wt % of HKUST-1(Cu/Fe) were synthesized using the solvothermal method, followed by calcination, and deposited on borosilicate glass. The prepared materials were analyzed using TGA/DSC, UV–Vis/DRS, PL spectroscopy, XRD, XPS, FTIR, N₂ physisorption, and SEM-EDS techniques to confirm their crystallinity, chemical bonding, porosity, thermal, optical, and morphological properties. With an increase in HKUST-1(Cu/Fe) content in TiO₂, the crystallite size, surface area, and pore size increased, whereas the bandgap energy and the recombination rate of photogenerated e⁻/h⁺ pairs decreased compared to TiO₂, favoring nylon 6 MP degradation. The TCFH (15 wt %) displayed optimal MP degradation performance, degrading MPs at pH 7 under UV–Vis light, showing an increase in TOC content during MP degradation (11.42 mg L⁻¹), related to the presence of soluble by-products, a decrease in turbidity associated with the reduction in particle size and MP concentration, and a decrease in amide signal intensity at 3090 cm⁻¹ compared with values observed during photolysis and TiO₂ photocatalysis. SEM and XPS analyses confirmed the oxidation and breakage of the MP polymeric chain. Soluble organic compounds such as aldehydes, amides, and carboxylic acids generated during MP degradation were detected by GC–MS. Thus, photocatalysis using the bimetallic MOF HKUST-1(Cu/Fe)-derived CuO/TiO₂ is a promising treatment for eliminating polyamide MPs in water effluents, where reactive oxygen species (^•OH and O₂⁻) contribute to their degradation.