Ultrafast degradation of contaminants in a trace cobalt(II) activated peroxymonosulfate process triggered through borate: Indispensable role of intermediate complex

Among all homogeneous catalysts, cobalt ions show the highest catalytic performance for the activation of peroxymonosulfate (PMS). Herein, we report a Co2+/PMS/H3BO3 system that can effectively generate reactive oxygen species (ROS) with ultra–low Co2+ dosage (5 μg/L). Co2+/PMS/H3BO3 system showed ultrafast reactivity and wide applicability for various pollutants. Sulfamethoxazole (SMX, 2 mg/L) could be completely removed within 5 min, and the corresponding kobs reached up to 1.1239 min−1. The introduction of H3BO3 significantly promoted the generation of ROS. The turnover frequency (TOF) calculated through dividing kobs by the cobalt ions concentration is as high as 224.78 min−1, which is much higher than most of the current research. Through a series of theoretical and experimental analyses, the complex of H2BO3−–MS (HSO5B(OH)3–) was inferred to be the key substance that led to the excellent performance of the system. This work provides new insights into the Co2+/PMS system in the presence of borate buffer.