Single‐atom CoN4 active sites have demonstrated excellent efficiency in peroxymonosulfate activation. However, the identification of CoN4 active sites and the detailed singlet oxygen generation mechanism in peroxymonosulfate activation remains ambiguous. We demonstrate a strategy to regulate the generation of reactive oxygen species by atomically dispersed cobalt anchored on nitrogen‐doped carbon. As indicated by experiment and DFT calculations, CoN2+2 was the active site and singlet oxygen was the predominant reactive oxygen species with a proportion of 98.89 %. Spontaneous dissociation of adsorbed peroxymonosulfate on the CoN2+2 active sites was energetically unfavorable because of the weakly positive Co atoms and CoN2+2 coordination, which directed PMS oxidation by a non‐radical pathway and with simultaneous singlet oxygen generation. The generated singlet oxygen degraded several organic pollutants with high efficiency across a broad pH range.
The redox behavior of metal active
sites determines the rate of
heterogeneous catalysis in peroxymonosulfate activation. Previous
reports focused on the construction of catalysts for accelerating
interfacial electron transfer. In this work, a new strategy was proposed
for facilitating valence cycles of Cu+/Cu2+ by
using pollutants. The 2.5Cu/CeO2/PMS system was capable
of achieving the efficient removal of pollutants, including tetracycline,
oxytetracycline, and rhodamine B, in a wide pH working range. In the
presence of tetracycline, a Cu–N bond was formed between the
−NH2 group of tetracycline and the Cu site of the
catalyst, showing that the coordination of Cu active sites changed
to CuO4N1. The charge of CuO4N1 active sites rearranged, making it easier to obtain electrons
and promote the PMS oxidation, thereby accelerating the reduction
of Cu2+ to Cu+ and PMS activation. The PMS activation
system showed excellent sustainability and selectivity for the removal
of organic pollutants. This study provides a novel routine to promote
peroxymonosulfate activation by utilizing pollutants to accelerate
the redox behavior of metal species.
The performance optimization of single‐atom catalysts (SACs) is important but remains challenging. Taking advantage of accompanying in situ formation of atomic clusters (ACs)/nanoparticles (NPs) during the preparation of SACs can be a promising solution. The coupled ACs/NPs and single atoms (SAs) can be highly efficient in catalyzing various reactions (e.g., oxygen reduction reaction (ORR), hydrogen evolution reaction (HER), CO2 reduction reaction (CO2RR), N2 oxidation reaction (NOR), etc), showing superior activity, selectivity, and stability. The mechanisms can be mainly categorized as ACs/NPs intensified SAs, SAs intensified ACs/NPs, and reactions proceeding on both ACs/NPs and SAs. The proposed mechanisms may be applicable to rationalize the excellent catalysts consisting of ACs/NPs and SAs. In the end, the existing issues and further development directions are put forward. This review is expected to simultaneously contribute to the development and application of highly efficient SACs and the in‐depth understanding of the single‐atom catalysis (SAC).
In the current work, a novel Co-Fe bimetallic immobilized cellulose hydrogel bead (CoFeO@CHB) was prepared via in situ chemical precipitation followed by heat treatment and applied for tetracycline (TC) degradation in the presence of peroxymonosulfate (PMS). The characterization results indicated that the Co-Fe particles were evenly distributed within the porous cellulose hydrogel beads, without affecting their morphologies or crystal structures. During the TC degradation, the CoFeO@CHB/PMS system showed a high resistance and stability to different water bodies, and the common anions and natural organic matters showed a limited effect on TC degradation. The chemical quenching experiments (using chemicals to react with specific reactive species) as well as electron paramagnetic resonance (EPR) results showed that CoFeO@CHB can effectively active PMS to generate multiple reactive oxygen species (ROS, such as SO4•−, •OH and 1O2), in which the 1O2-dominated non-radical pathway played a vital role in TC degradation. Both Co and Fe were proposed as the active sites for PMS activation, and the CoFeO@CHB/PMS system showed a high potential in practical application due to its high selectivity and robustness with much less toxic intermediate products. Furthermore, a long-term continuous home-made dead-end filtration device was constructed to evaluate the stability and application potential of the CoFeO@CHB/PMS system, in which a >70% removal was maintained in a continuous 800 min filtration. These results showed the promising potential for cellulose hydrogel beads utilized as a metal-based nanomaterial substrate for organic degradation via PMS activation.
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