How Nitrogen and Sulfur Doping Modified Material Structure, Transformed Oxidation Pathways, and Improved Degradation Performance in Peroxymonosulfate Activation.

Current research has widely applied heteroatom doping for the promotion of catalyst activity in peroxymonosulfate (PMS) systems; however, the relationship between heteroatom doping and stimulated activation mechanism transformation is not fully understood. Herein, we introduce nitrogen and sulfur doping into a Co@rGO material for PMS activation to degrade tetracycline (TC) and systematically investigate how heteroatom doping transformed the activation mechanism of the original Co@rGO/PMS system. N was homogeneously inserted into the reduced graphene oxide (rGO) matrix of Co@rGO, inducing a significant increase in the degradation efficiency without affecting the activation mechanism transformation. Additionally, S doping converted Co3O4 to Co4S3 in Co@rGO and transformed the cooperative oxidation pathway into a single non-radical pathway with stronger intensity, which led to a higher stability against environmental interferences. Notably, based on density functional theory (DFT) calculations, we demonstrated that Co4S3 had a higher energy barrier for PMS adsorption and cleavage than Co3O4, and therefore, the radical pathway was not easily stimulated by Co4S3. Overall, this study not only illustrated the improvement due to the heteroatom doping of Co@rGO for TC degradation in a PMS system but also bridged the knowledge gap between the catalyst structure and degradation performance through activation mechanism transformation drawn from theoretical and experimental analyses.

Why the cooperation of radical and non-radical pathways in PMS system leads to a higher efficiency than a single pathway in tetracycline degradation.

Current research focused on developing multiple active species in peroxymonosulfate (PMS) system to degrade contaminants, but deepening concern lacks over why cooperation of those active species facilitated a faster degradation. Here, we employed Co3O4, rGO and Co3O4@rGO composite to activate PMS for tetracycline (TC) degradation, and detected crucial factors toward highest performance of Co3O4@rGO/PMS system. Batch experiments exhibited a satisfactory TC degradation efficiency under Co3O4@rGO/PMS, complete degraded 50 mg/L TC within 20 min. Analytical tests discovered that radical active species generated by Co3O4/PMS and non-radical species by rGO/PMS were successfully co-existed in Co3O4@rGO/PMS system, significantly improving the performance of TC removal. Subsequently, a combination of density functional theory (DFT) calculation and intermediates analysis revealed that, in Co3O4@rGO/PMS system, the cooperation rather than independent effect of radical and non-radical active species expanded TC degradation pathways, enhancing the degradation performance. Furthermore, decent adaptability, stability, and recyclability toward affecting factors variation of Co3O4@rGO/PMS demonstrated it as a potent and economical system to degrade TC. Overall, this study developed a novel Co3O4@rGO/PMS system with a cooperative oxidation pathway for highly efficient TC removal, and managed to clarify why this oxidation pathway achieved high efficiency through a combination of theoretical and experimental method.

Transfer characteristic of fluorine from atmospheric dry deposition, fertilizers, pesticides, and phosphogypsum into soil.

Fluorine (F) is widely dispersed in the environment and frequently used in industry and agriculture with a high migration ability. Thus, it is essential to understand the leaching characteristic of F in soil from industry and agriculture sources. Several sources of F pollutants in soil, including fertilizers, pesticides, phosphogypsum, and atmospheric deposition, were selected to investigate leaching characteristics of F in soil by leaching experiments. The addition of phosphate fertilizer and compound fertilizer (N:P:K = 20:10:15) enhanced the leachability of F in soil and the proportion of F leached out from soil treated by these fertilizers were 0.25% and 0.24%, respectively. However, unanticipated lower leachability of F appeared in compound fertilizer (N:P:K = 17:17:17), nitrogen fertilizer, dipterex, fluoroglycofen, fluopimomide, simulative dry deposition (YF3), and phosphogypsum loaded soils compared with additive-absent treatment. Although phosphogysum had a high F concentration, minimum proportion of F released (0.18%) was observed in phosphogypsum-coverd soil. The amounts of F leaching-out from surface soils (0-25 cm) treated with nitrogen fertilizer decreased 1.03 kg ha-1 comparing with blank control. Soil with phosphate fertilizer leached 5.47 kg F ha-1 a year, having the highest environment risk to deeper soil and groundwater. However, phosphogypsum and dry deposition of airbone F chemical had few effects on F leaching in soil. F-containing materials from agricultural process may leach more F from surface soils than industrial sources.