Persulfate activation by reduced graphene oxide membranes: Practical and mechanistic insights concerning organic pollutants abatement

Abstract

The catalytic activity of membranes produced with commercial unmodified reduced graphene oxide (rGO) was demonstrated for the first time in persulfate (PS) activation through experiments performed in continuous mode. Phenol (Ph; C0 = 5 mg L−1) and venlafaxine (VFX; C0 = 250 µg L−1) were employed as model compounds. The influence of the main operation parameters was first investigated considering an operation period of 24 h. For a rGO membrane with an effective area of 2.1 cm2, contaminant removal is favored at lower flow rates (0.1 mL min−1) and higher catalyst loads (15 mg). Assays carried out under these conditions yielded average removals of 90 and 94% for Ph and VFX, respectively, corresponding to normalized removal rates in the range of 1.71-1.79 L m−2 h−1 mgcat−1. Membrane stability tests were conducted in continuous mode for 1 week, allowing to observe a significant catalyst deactivation after 2-3 d of operation, although the catalytic activity could be recovered through simple thermal regeneration procedures. Batch mode oxidation tests employing powder rGO treated at different temperatures (500, 850 and 1000 °C) and materials characterization data allowed to conclude that a shift of the surface chemistry character from acidic to basic enhances the catalytic performance. Moreover, scavenging tests indicated that singlet oxygen (1O2), apparently generated by nucleophilic attack of PS to C = O in pyrone-like functionalities, is the main oxidizing species in the rGO-PS system.