Activation of sodium persulfate by magnetic carbon xerogels (CX/CoFe) for the oxidation of bisphenol A: Process variables effects, matrix effects and reaction pathways

• Published in: Water research (Oxford) Vol. 124; pp. 97 - 107
• Main Authors: Outsiou, Alexandra, Frontistis, Zacharias, Ribeiro, Rui S., Antonopoulou, Maria, Konstantinou, Ioannis K., Silva, Adrián M.T., Faria, Joaquim L., Gomes, Helder T., Mantzavinos, Dionissios
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01-11-2017
• Subjects: Benzhydryl Compounds - chemistry; Carbon; Chloride; Endocrine disruptors; Fenton-like; Intermediates; Operating parameters; Oxidation-Reduction; Phenols - chemistry; Radicals; Sodium Compounds; Sulfates; Water Pollutants, Chemical - chemistry; Endocrine disruptors; Fenton-like; Chloride; Operating parameters; Radicals; Intermediates
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/j.watres.2017.07.046

An advanced oxidation process comprising sodium persulfate (SPS) and a novel magnetic carbon xerogel was tested for the degradation of bisphenol A (BPA), a model endocrine-disrupting compound. The catalyst, consisting of interconnected carbon microspheres with embedded iron and cobalt microparticles, was capable of activating persulfate to form sulfate and hydroxyl radicals at ambient conditions.
The pseudo-first order degradation rate of BPA in ultrapure water (UPW) was found to increase with (i) increasing catalyst (25–75 mg/L) and SPS (31–250 mg/L) concentrations, (ii) decreasing BPA concentration (285–14,200 μg/L), and (iii) changing pH from alkaline to acidic values (9–3).
Besides UPW, tests were conducted in drinking water, treated wastewater, groundwater and surface water; interestingly, the rate in UPW was always lower than in any other matrix containing several organic and inorganic constituents. The effect of natural organic matter (in the form of humic acids) and alcohols was detrimental to BPA degradation owing to the scavenging of radicals. Conversely, chlorides at concentrations greater than 50 mg/L had a positive effect due to the formation and subsequent participation of chlorine-containing radicals.
Liquid chromatography time-of-flight mass spectrometry was employed to identify major transformation by-products (TBPs) of BPA degradation in the absence and presence of chlorides; in the latter case, several chlorinated TBPs were detected confirming the role of Cl-related radicals. Based on TBPs, main reaction pathways are proposed.
•Bimetallic Fe and Co carbon xerogels activate persulfate to sulfate radicals.•BPA decomposition in environmental matrices is faster than in pure water.•Chloride ion promotes degradation through the formation of chloride radicals.•Catalyst/oxidant/substrate concentrations, pH and radical scavengers affect rates.•Polymerization, bimolecular radical coupling and hydroxylation reactions dominate.