Facilitation effects of trace metals on the photosensitive pollutant self-activating persulfate process: An enhanced "using waste to treat waste" way

Photosensitive pollutants, such as dyes, can self-activate peroxymonosulfate (PMS) or persulfate (PS) to degrade themselves under light irradiation, presenting a promising "waste-as-catalyst"paradigm in wastewater treatment, which is characterized by low energy consumption and minimal secondary pollution compared with traditional PMS or PS oxidation processes. The findings of this study indicated that trace metal ions, particularly Fe3 +, significantly enhanced the dye self-activating PS process. To investigate the underlying mechanisms, a visible-light catalytic system comprised by Fe3+, Rhodamine B (RhB) and PS was developed. 10 μM Fe3+ facilitated the complete degradation of 100 mL 10 mg/L of RhB within an hour. The efficiencies for total organic carbon removal and 1 mM PS decomposition were respectively 52.5 % and 24 %, three and two times higher than those of the RhB/PS system. The formation of Fe-N bond between Fe3+ and the RhB molecule was responsible for this improvement, which enhanced the light absorption capability of RhB, benefiting for more photoinduced electrons generation and fast transmission. Some of the electrons were directly transferred to PS, while the remainder were captured by Fe3+, subsequently reduced to Fe2+. Both pathways initiated the efficient decomposition of PS. The resulting oxidizing species of •OH, SO4•-, O2•- and 1O2 attacked the RhB molecules with varying degrees of contribution, which ultimately led to N-deethylation, chromophore cleavage, ring-opening and finally mineralization. This study presents a method that fully leverages the trace metal ions in wastewater to substantially enhance the performance of the "using waste to treat waste"water purification system.