Urchin-like nano lawn of cobalt-iron/nitrogen-carbon activating peroxymonosulfate forced by ultrasonic action: Selective oxidation from pollutant structure

Abstract

Selective oxidation in heterogeneous activation of persulfate has attracted much interest, however, the current research focuses more on the active species and less on the pollutant structure itself. In this study, the novel composite-materials, Co-Fe/N-C nanowires (CFNC-Nws), the C/N combined Co-Fe bimetallic carbonate hydroxide nano-lawn, were synthesized as activators of peroxymonosulfate (PMS). Subsequently, a representative oxidation system, CFNC-Nws (0.02 g L⁻¹) activating PMS under ultrasonic (US, 28 kHz) mechanochemical action (the surface mechanochemical roles of dilatational wave-US driving the CFNC-Nws accompanied by particle motions), was constructed for exploring the effects of removing the different structures of pollutants including triphenylmethane-, azo-, and xanthene-compounds. It was found that without additional pH adjustment required, the coupling US/CFNC-Nws/PMS system itself could generate hydroxyl radical (•OH), sulfate radicals (SO₄^•−), superoxide radical (O₂^•−), singlet oxygen (¹O₂), and high-valent-metal oxidizing species (HVM) in the absence of pollutants. However, upon introducing model pollutants, although over 90% removal of them can be obtained within 15–30 min apparently, the kinds of dominant active species and their contributions for the removals of the above pollutants were widely varied, which indicated the selective oxidation from the pollutant structure. It was because of that the variations in the affinity of pollutant structures for different active species resulted in distinct removal processes and pathways. Our study provided novel insights that could be served as a foundation for selecting, designing, and implementing appropriate advanced oxidation technologies at the pollutant structure level to enhance their practical effectiveness in water treatment.