All-in-one fabrication of NiO nanorods/carbon-containing porous catalytic polymer membranes for persulfate-facilitated oxidation-adsorption of diclofenac in flow–through

We introduce a novel all-in-one fabrication method for porous catalytic polyethersulfone (PES) membranes containing NiO nanorods and carbon nanoparticles. This method is based on the sonochemical in situ solidification of a metal salt with NaBH4 in presence of carbon particles in a PES-containing casting-reaction solution, directly followed by membrane preparation via film casting cum phase separation. In the catalytic flow-through degradation of 20 mg/L aqueous diclofenac with persulfate as oxidant, an as-prepared NiO-carbon-PES membrane achieved a 99 % aromatic content removal degree at a residence time of only 1.6 s. In comparison, NiO and CuO membranes without carbon particles exhibited < 40 % aromatic removal degrees. The high performance was attributed to a degradation-induced adsorption, with a diclofenac removal capacity of 950 mg/g of incorporated carbon particles. We demonstrated that diclofenac is catalytically mineralized in the membrane at incorporated NiO nanorods, followed by adsorption of remaining degradation products at nearby carbon particles. Our data further suggests that reducing NiO to Ni(0) via a membrane pretreatment shifts the catalytic persulfate activation from a radical to a non-radical pathway, and that HCO3– can function as sacrificial electron donor for Ni(0). This completely mitigated nickel leaching from the membrane in contact to persulfate. Moreover, even in the presence of NaHCO3 and NaCl, a Ni(0)–carbon–PES membrane consistently eliminated ∼ 90 % of the total organic carbon (TOC) from a 2 mg/L diclofenac feed containing persulfate in single-pass flow-through mode (continuously for 5 h, respectively for 500 L/m2 permeate volume), with no detectable release of degradation products or any nickel leaching.