New insight into peroxymonosulfate activation by CoAl-LDH derived CoOOH: Oxygen vacancies rather than Co species redox pairs induced process

Cobalt oxyhydroxide (CoOOH) has received much attention as a environmental friendly mineral for activating peroxymonosulfate (PMS) for organics elimination in environment remediation. Yet, it suffered from unsatisfactory catalytic activity. This work presents a facile self-sacrifice method to synthesize highly effective hexagonal CoOOH microplate (B-CoOOH) from cobalt aluminum layered double hydroxide (CoAl-LDH). 40 μM of sulfamethoxazole (SMX) was 100% eliminated in 6 min in the presence of 0.1 g/L B-CoOOH and 0.3 mM PMS. B-CoOOH/PMS system achieved a high degradation (0.60 min−1), which was 12 times higher than CoOOH/PMS system (0.05 min−1). Besides, B-CoOOH also displayed satisfactory recyclability during the repeating tests, excellent physicochemical stability with low cobalt ions leaching (0.05 mg/L), and high mineralization efficiency (97.5% of TOC removal). Quenching tests signified the dominant role of 1O2 in SMX degradation. Mechanisms exploration revealed that the abundant oxygen vacancies (OV) on B-CoOOH acted as the electron donator in PMS activation process, which differed from previous report, in which Co species redox pairs was responsible for activating PMS and producing reactive oxygen species. In the initial stage of PMS activation, the dissolved oxygen in solution contributed to the generation of 1O2, while in the later stage PMS was regarded as the main precursor for the 1O2 formation. This study provides a convenient approach for the synthesis of cobalt oxyhydroxide with excellent catalytic activity, and sheds a new insight into the indispensable role of OV in heterogeneous catalysis.