Peroxymonosulfate activation by three-dimensional cobalt hydroxide/graphene oxide hydrogel for wastewater treatment through an automated process

Abstract

Sulfate radical (SO4−) produced by peroxymonosulfate (PMS) activation has been extensively studied due to the excellent oxidation ability in organic pollutants decomposition. PMS can be activated by various transition metal ions to generate active radicals, and Co2+ shows the best activation ability for PMS. However, the secondary pollution of cobalt ions (Cox+) limits the application of Co2+/PMS system. In this work, the three-dimensional (3D) cobalt hydroxide (CoOOH)/graphene oxide (GO) hydrogel was prepared as a catalyst through graft polymerization reaction between CoOOH/GO composite and acrylamide monomer. The 3D composite hydrogel has multiple advantages in wastewater treatment application. It could be packed into the degradation columns of the equipment to achieve automatic treatment of wastewater under laboratory conditions, which is helpful to promote the large-scale treatment of industrial wastewater. The Co2+ loaded inside 3D hydrogel could efficiently activate PMS to generate active species. The quencher experiments and electronic paramagnetic resonance (EPR) spectra proved that SO4− and 1O2 are the main oxidation species in CoOOH/GO hydrogel/PMS system for the remediation of organic pollutants, including rhodamine B, phenol, p-chlorophenol, bisphenol A, sulfadiazine, norfloxacin, and tetracycline hydrochloride. The existing GO and hydrogel could effectively inhibit the dissolution of Cox+, reduce the secondary pollution, and prolong the service time of the catalyst, which showed good catalytic activity even after ten cycles. Under the flow reaction system, the mineralization rate of organic molecules such as sulfadiazine can reach more than 40% after two cyclic reactions. The dissolution of Cox+ was measured by inductively coupled plasma-atomic emission spectroscopy (ICP-AES), which met the national standards after the second cyclic test. In the automated process, the dissolved Cox+ can also be used in the next cycles to further promote the decomposition of PMS. In a word, this work provides a new way for the industrial application of Cox+/PMS system for the remediation of wastewater.