Catalyst-free photodegradation of ethylparaben on surface-engineered PBT membranes: a coupled adsorption–photolysis mechanism

Abstract

In the face of the growing threat posed by ethylparaben (EP), a persistent endocrine disruptor, this study introduces an effective catalyst-free approach (i.e., relying solely on UV-driven photolysis without embedded semiconductor or metallic photocatalysts such as TiO₂, ZnO, or MOFs) for its removal. Commercial polybutylene terephthalate (PBT) nonwoven membranes were transformed into active purification platforms via an adsorption-assisted photolysis mechanism. By applying simple and targeted surface treatments—including hydrogen peroxide (H₂O₂) etching, ultraviolet (UV) irradiation, and sodium hydroxide (NaOH) hydrolysis—we successfully grafted oxygen-containing functional groups (–OH, CO, –COO⁻) onto the membrane surface. Quantitative FTIR analysis showed treatment-specific changes: UV irradiation decreased ester carbonyl groups by 76.9%, H₂O₂ etching achieved a 99.8% reduction at 30% concentration, and NaOH hydrolysis resulted in an 87.4% decrease with formation of carboxylate. Under optimized conditions, modified membranes achieved removal efficiencies of 84% (15% H₂O₂, 30 min), 85% (UV, 60 min), and 86% (1.0 M NaOH, 20 min)—representing 24–26% absolute improvement over UV photolysis alone (60%). Kinetic modeling confirmed that 80–90% of EP removal occurs via a rapid interfacial pathway (k₁ = 0.049–0.068 min⁻¹), while bulk photolysis contributed negligibly (k₂ → 0). SEM imaging confirmed preservation of the microfibrous structure (79–90% porosity) throughout all treatments. This work demonstrates that controlled surface oxidation transforms standard polymers into an effective, quantifiably superior platform for water purification, offering a catalyst-free solution based on industrially relevant surface-engineering techniques that addresses key practical barriers (such as complex fabrication and catalyst leaching) to emerging contaminant removal.