Degradation of Rhodamine B by activation of peroxymonosulfate using Co₃O₄-rice husk ash composites

Rice husk is an agricultural residue in rice producing process with a worldwide annual output of more than 190 million tons. To investigate the possibility of disposal method, rice husk ash (RHA) derived from the rice husk residue was treated as a support material thus synthesizing a Co-based heterogeneous catalyst for peroxymonosulfate activation. The interconnected architecture of the Co₃O₄ nanoflakes grown vertically on the surface of RHA provided high surface area and structure stability. The as-synthesized heterogeneous catalyst exhibited enhanced ability for peroxymonosulfate activation towards Rhodamine B degradation. Degradation efficiency of Rhodamine B achieved 96.3% within 60 min by using Co₃O₄-0.5 RHA catalyst, while only 44.1% Rhodamine B was degraded for bare Co₃O₄. The effects of pH, catalyst dosage, peroxymonosulfate dosage, Rhodamine B concentration, inorganic ions and temperature were evaluated. Radical scavenging experiments revealed that ¹O₂ and O₂^•- other than SO₄^•- and •OH were the main active species. Furthermore, the addition of rice husk ash proved to be capable of reducing the dissolution of Co and extended the lifetime of the catalyst. This study elucidated a new opportunity for both utilizing agricultural residue and reducing contaminants in wastewater.