Micrometer-sized NiOOH hierarchical spheres for enhanced degradation of sulfadiazine via synergistic adsorption and catalytic oxidation in peroxymonosulfate system

As an antibiotic, sulfadiazine has posed a serious threat to humans and ecosystems due to its chronic toxicity. The advanced oxidation processes (AOPs) via heterogeneous catalytic activation of peroxymonosulfate (PMS) have significant potential for the degradation of antibiotics. However, there are multiple restrictions including non-specifically binding to target contaminants, which would deplete oxidation capacity, and lacking energy effectiveness due to inefficient utilization of reactive oxygen species (ROS). To overcome these obstacles, we adopted the “bait-hook & destroy” strategy in this study. Herein, we synthesized a novel micrometer-sized NiOOH hierarchical spheres assembled from nanosheets, which have relatively large specific surface areas and yield specified cavities to “bait-hook” sulfadiazine and PMS onto the surface cavities. This process was further conductive to effective generation of ROS and subsequently “destruction” of sulfadiazine with elevated mass transformation rate. 20.4% of sulfadiazine can adsorb to NiOOH surface in less than 30 min (0.0051 min−1), and then sulfadiazine was completely degraded in 90 min intervals in the NiOOH/PMS system. The degradation rate constant (k = 0.0537 min−1) was about 5.3, 2.5 and 2.2 times higher than that in Ni2O3/PMS, NiO/PMS and Ni(OH)2/PMS system, respectively. This was ascribed to the synergistic catalytic oxidation and adsorption process occurred on the surface of NiOOH. Appreciably, there were both non-radicals (1O2) and radicals (O2•− and SO4•−) involved in the NiOOH/PMS system, and 1O2 was distinguished as the dominated ROS for degradation of sulfadiazine. This study provides a novel strategy via synergistic adsorption and catalytic oxidation, and indicates that the micrometer-sized NiOOH hierarchical sphere as heterogeneous catalyst is an attractive candidate for potential application of the SR-AOPs technology in water treatment.