Screening of GO-coated microporous polymeric filters for efficient paraquat removal: effect of support surface on membrane roughness and flux stability.

We report the fabrication and systematic evaluation of three thin-layer graphene oxide (GO) composite membranes prepared by vacuum-filtering a GO dispersion (nominal loading 0.42 mg cm-2) onto low-cost microporous supports (mixed cellulose ester, nylon, PVDF; 0.45 µm pore, 12 cm2). The membranes (M-GO, N-GO, P-GO) were characterized by AFM, SEM, XPS, and contact angle measurements to reveal support-dependent GO morphology and surface chemistry. At low (0.2 bar) transmembrane pressure (TMP), M-GO exhibited the highest steady-state water flux (425 ± 10 L m-2 h-1, n = 3), followed by N-GO and P-GO, while all GO-coated membranes achieved near-complete paraquat rejection (≤ LOD = 0.04 ppm) for feed concentrations of 0.1-1.0 ppm. Reusability tests on M-GO demonstrated ≥95% removal over five consecutive 1 h cycles with a flux recovery ratio (FRR) ≥ 65% after hydraulic flushing. In a 42 h continuous stability test at 0.2 bar, M-GO retained 66% of its initial flux and maintained ≥ 99% paraquat rejection. Tests in a simulated agricultural matrix (paraquat 5 ppm, 100 mM NaCl, 10 ppm humic acid) show a moderate flux decline (stabilizing at ∼55-60% of initial flux) with paraquat rejection > 90%, indicating robustness to ionic strength and natural organic matter. The head-to-head comparison isolates the decisive role of support surface roughness and porosity in governing GO layer formation, flux stability, and antifouling behavior, a pathway to low-pressure, high-flux membranes for cationic pesticide removal.