Cobalt sulfide nanosheets derived from sulfurization of Prussian blue analogue as an enhanced catalyst for activating monopersulfate to degrade caffeine

Abstract

As caffeine (CAF) is extensively consumed as food additives and medication, CAF has been continuously released into aquatic environment, causing threats to ecology because of its high solubility and persistency. While cobalt sulfides have received increasing attention for activating monopersulfate (MPS), almost no studies have been conducted to investigate cobalt sulfides to degrade CAF. Thus, the aim of this study is to investigate cobalt sulfide for activating MPS to degrade CAF. Specifically, a unique cubic cluster of cobalt sulfide nanosheets (CoSNS) is developed through a simple sulfurization of cobaltic Prussian Blue Analogue (Co-PBA) (Co3[Co(CN)6]2) under very mild condition (25 °C) to convert Co-PBA to CoSNS. CoSNS could exhibit much higher catalytic activities than its precursor Co-PBA, and the benchmark catalyst of MPS activation, Co3O4, for activating MPS to degrade CAF in 45 min. Ea of CAF degradation (24.3 kJ/mol) by CoSNS+MPS is also significantly lower than many reported Ea values, validating that CoSNS is an advantageous and highly-efficient catalyst for MPS activation to degrade CAF. The activation mechanism of CoSNS towards MPS activation is also realized using electron spin resonance. Degradation pathway of CAF degradation by CoSNS+MPS is also investigated by mass spectrometry to provide insights into degradation behaviors.