Peracetic acid activation by mechanochemically sulfidated zero valent iron for micropollutants degradation: Enhancement mechanism and strategy for extending applicability.

In this study, mechanically sulfidated microscale zero valent iron (S-ZVI) was found to effectively activate the peracetic acid (PAA) with a result of almost complete degradation of six micropollutants within 10 min under neutral conditions, and > 95% sulfamethoxazole (SMX) removal after six cycles. Reactive oxidized species (ROS) including HO•, carbon-centered radicals, and Fe(IV) were generated in the S-ZVI/PAA system, while HO• was the main contributor towards micropollutants degradation. This study clearly revealed that enhancement of the electron donating ability of ZVI by the formed conductive iron sulfides was crucial for promoted Fe(II) generation and subsequent PAA activation over several cycles, rather than the ability of sulfides to reduce Fe(III) for Fe(II) regeneration as reported previously. Interestingly, it's discovered that co-existence of Fe(III) would dramatically improve the contaminants removal efficiency of the S-ZVI/PAA system; transform the surfaced Fe(II) dominated ROS generation process to aqueous Fe(II) one; enhance the tolerance of the proposed system to water matrix. The promoting effect of predosed Fe(III) on PAA activation by S-ZVI should be mainly associated with: the greater ability of Fe(III) than H2O to accept electron from Fe0 for obtaining more active sites; slower Fe0 consumption and solid sulfur species release for elevated electron utilization efficiency and PAA activation. Considering the convenient and cost-effective access of Fe(III), the decrease of acute toxicity of treated SMX, excellent stability and good removal of various micropollutants fully demonstrate the superiority of S-ZVI/PAA system for practical application.

Sulfide-modified zero-valent iron activated periodate for sulfadiazine removal: Performance and dominant routine of reactive species production.

In this work, sulfide-modified zero-valent iron (S-Fe0) was used to activate periodate (IO4-, PI) for sulfadiazine (SDZ) removal. 60 µM SDZ could be completely removed within only 1 min by S-Fe0/PI process. Compared with other oxidants including H2O2, peroxymonosulfate (PMS), peroxydisulfate (PDS), S-Fe0 activated PI exhibited better performance for SDZ removal but with lower Fe leaching. Compared with Fe0/PI process, S-Fe0/PI process could reduce more than 80% Fe0 and PI dosage. Inorganic ions and nature organic matters had negligible effect on SDZ removal in S-Fe0/PI system inducing its good SDZ removal efficiency in natural fresh water. 80.2% SDZ still could be removed within 2 min after 7th run. S-Fe0/PI process also exhibited 2.5 - 20.1 folds enhancement for various pollutants removal compared with Fe0/PI process. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), electrochemical tests, and density functional theory (DFT) calculation were conducted to confirm the presence of sulfurs could enhance the reactivity of S-Fe0 thus increased the efficiency of PI activation for antibiotics removal. Electron paramagnetic resonance spectroscopy (EPR) tests, radical quenching experiments, quantitative detection and DFT calculation were performed to illustrate the role of multiple reactive species in SDZ removal and the dominant pathway of multiple reactive species production. IO3·, ·OH, O2-·, 1O2, FeIV, and SO4·- all participated in SDZ removal. ·OH played the major role in SDZ removal and the dominant routine of ·OH production was IO4- â†’ O2-· â†’ H2O2 â†’ ·OH. Meanwhile, S-Fe0/PI process could efficiently mineralize SDZ and reduce the toxicity. Comparison with other PI activation approaches and SDZ treatment techniques further demonstrated S-Fe0 was an efficient catalyst for PI activation and present study process was a promising approach for antibiotics removal.

Transformation of sulfamethoxazole by sulfidated nanoscale zerovalent iron activated persulfate: Mechanism and risk assessment using environmental metabolomics.

The threat caused by the misuse of antibiotics to ecology and human health has been aroused an extensive attention. Developing cost-effective techniques for removing antibiotics needs to put on the agenda. In current research, the degradation mechanism of sulfamethoxazole (SMX) by sulfidated nanoscale zerovalent iron (S-nZVI) driven persulfate, together with the potential risk of intermediates were studied. The degradation of SMX followed a pseudo-first order kinetics reaction with kobs at 0.1176 min-1. Both SO4•- and •OH were responsible for the degradation of SMX, and SO4•- was the predominant free radical. XPS analysis demonstrated that reduced sulfide species promoted the conversion of Fe (III) to Fe (II), resulting in the higher transformation rate of SMX. Six intermediates products were generated through hydroxylation, dehydration condensation, nucleophilic reaction, and hydrolysis. The risk of intermediates products is subsequently assessed using E. coli as a model microorganism. After E.coli exposure to intermediates for 24 h, the upmetabolism of carbohydrate, nucleotide, citrate acid cycle and downmetabolism of glutathione, sphingolipid, galactose by metabolomics analysis identified that SMX was effectively detoxified by oxidation treatment. These findings not only clarified the superiority of S-nZVI/persulfate, but also generated a novel insight into the security of advanced oxidation processes.

Sulfadiazine removal by peroxymonosulfate activation with sulfide-modified microscale zero-valent iron: Major radicals, the role of sulfur species, and particle size effect.

Sulfide-modified zero-valent iron (S-Fe0) is regarded as a promising method to enhance the catalytic activity of Fe0 for peroxymonosulfate (PMS) activation. However, the roles of sulfidation and the application of the sulfidation treatment method are worth to further investigation. In our study, the effects of the S/Fe ratio, Fe0 dosage, and initial pH on sulfadiazine (SDZ) removal were investigated. The characterization of S-Fe0 with SEM, XPS, contact angle and Tafel analysis confirmed that the formation of sulfur species on the Fe0 surface could enhance the catalytic performance of Fe0. S2- played the major role and SO32- played the minor role in accelerating the conversion of Fe3+ to Fe2+. EPR tests, radical quenching and quantitative determination experiments identified •OH as playing the major role and SO4•- also playing an important role in SDZ removal in S-Fe0/PMS system. Sulfidation produced no notable change in the role of •OH and SO4•-. A possible degradation pathway of SDZ was proposed. Effect of sulfidation on various sizes of Fe0 was also studied which demonstrated that the smaller sizes of Fe0 (< 8 µm) were more effective in the sulfidation method treatment. S-Fe0/PMS system also showed a good performance in removing antibiotics in natural fresh water.