Carbocatalytic activation of persulfate for the removal of drug diclofenac from aqueous matrices

[Display omitted] •Carbon black shows good activity as a low-cost persulfate activator for diclofenac oxidation.•Complex water matrix interactions determine degradation rates.•Diclofenac adsorption on carbon black surface is pH-sensitive, but oxidation is not.•Coupling carbon black with light or ultrasound enhances degradation synergistically. In this study, carbon black (CB) was employed as a heterogeneous activator for the conversion of sodium persulfate (SPS) to reactive species for the degradation of drug diclofenac (DCF). Experiments were performed at DCF concentrations between 0.5 and 4 mg/L, CB concentrations between 25 and 75 mg/L and SPS concentrations between 25 and 200 mg/L. Degradation rates, based on pseudo-first order kinetics, generally increased with decreasing DCF and increasing CB concentrations. The rate also increased with increasing SPS concentration up to 50 mg/L and decreased at higher values due to scavenging effects. Besides experiments in ultrapure water (UPW), real matrices were tested (i.e. bottled water (BW), surface water (SW), secondary treated wastewater (WW)), as well as UPW spiked with bicarbonate (50-500 mg/L), chloride (100–500 mg/L) or humic acid (10–20 mg/L). Degradation rates decreased with increasing matrix complexity, while the addition of chloride or humic acid was detrimental to the process; on the contrary, bicarbonate at 500 mg/L enhanced DCF degradation rate nearly five-fold. The effect of initial solution pH was also studied in the range 3–9.5 showing that degradation was not pH-sensitive. Experiments were also performed activating SPS by simulated solar radiation or 20 kHz ultrasound with or without CB. Coupling activators (i.e. CB with solar light or CB with ultrasound) favored DCF degradation in a synergistic way, with the level of synergy being 45–50%.