Novel 3D spherical CoN4-based alginate beads towards efficient activation peroxymonosulfate for anti-inflammatory drug degradation in a continuous flow column

Abstract

The rapid increase in global pharmaceutical consumption has raised concerns over environmentally persistent drug residues. Herein, a monoatomic-planar phthalocyanine cobalt complex/calcium alginate bead composite (CoN4/Alg) was synthesized and applied as a peroxymonosulfate (PMS) activator for diclofenac sodium (DCF) degradation. CoN4 was immobilized into alginate beads at varying loadings (4, 10, and 25 wt%), with 25% showing the highest catalytic activity. Under optimal conditions, 98% DCF removal was achieved within 30 min using 0.65 mM PMS. Beyond DCF, the 25-CoN4/Alg composite efficiently degraded Rhodamine B (92% in 30 min) and ciprofloxacin (91% in 35 min). In a continuous flow system, 83% pollutant removal was sustained over 48 h. Radical quenching experiments identified singlet oxygen and superoxide radicals as the primary reactive species, while hydroxyl and sulfate radicals played negligible roles. Mechanistic analysis confirmed that Co(II) sites in CoN4 facilitated electron transfer to PMS, driving reactive oxygen species generation. Phytotoxicity tests further demonstrated that DCF solutions treated with the CoN4/Alg/PMS system exhibited markedly reduced toxicity, with degraded 7.5 ppm DCF showing no inhibitory effect on wheat seed germination (80%), in contrast to untreated DCF. These findings underscore the synergistic role of heteroatom doping in enhancing PMS activation and highlight the potential of CoN4/Alg as a practical and sustainable catalyst for the removal of persistent pharmaceutical pollutants in wastewater treatment.