3D-printed MoS_(2)/Ni electrodes with excellent electro-catalytic performance and long-term stability for dechlorination of florfenicol

Here,we report the production of 3D-printed MoS_(2)/Ni electrodes(3D-MoS_(2)/Ni)with longterm stability and excellent performance by the selective laser melting(SLM)technique.As a cathode,the obtained 3D-MoS_(2)/Ni could maintain a degradation rate above 94.0%for forfenicol(FLO)when repeatedly used 50 times in water.We also found that the removal rate of FLO by 3D-MoS_(2)/Ni was about 12 times higher than that of 3D-printed pure Ni(3D-Ni),attributed to the improved accessibility of H^(*).In addition,the electrochemical characterization results showed that the electrochemically active surface area of the 3D-MoS_(2)/Ni electrode is about 3-fold higher than that of the 3D-Ni electrode while the electrical resistance is 4 times lower.Based on tert-butanol suppression,electron paramagnetic resonance and triple quadrupole mass spectrometer experiments,a“dual path”mechanism and possible degradation pathway for the dechlorination of FLO by 3D-MoS_(2)/Ni were proposed.Furthermore,we also investigated the impacts of the cathode potential and the initial pH of the solution on the degradation of FLO.Overall,this study reveals that the SLM 3D printing technique is a promising approach for the rapid fabrication of high-stability metal electrodes,which could have broad application in the control of water contaminants in the environmental field.

New insights into FeS/persulfate system for tetracycline elimination:Iron valence,homogeneous-heterogeneous reactions and degradation pathways

In this study,complete tetracycline(TTC)and above 50%of total organic carbon(TOC)were removed by Fe S/PS after 30 min under optimized conditions.Although free radicals and high-valent iron ions were identified to generate in the process,the apparent similarity between intermediate products of Fe S/PS,Fe/PS,and UV/PS systems demonstrated that the degradation of TTC was due to sulfate radicals(SO_(4)·^(-))and hydroxyl radicals(·OH).Based on the reaction between free radicals and organic matter,we speculated that TTC in the Fe S/PS system was decomposed and mineralized by dehydration,dehydrogenation,hydroxyl addition,demethylation,substitution,E-transfer,and ring-opening.Furthermore,a new understanding of Fe S-mediated PS activation based on stoichiometry and kinetic analysis showed that there were both homogeneous and heterogeneous reactions that occurred in the entire progress.However,due to the effect of p H on the dissolution of iron ions,the homogeneous reaction became the principal process with iron ions concentration exceeding 1.35 mg/L.This work provides a theoretical basis for the study of the degradation of TTC-containing wastewater by the iron-based advanced oxidation process.

Formation and transformation of schwertmannite in the classic Fenton process

The massive amount of sludge generated by the classic Fenton process, which has often been hypothesized to consist of ferric hydroxide, remains a major obstacle to its large-scale application. Therefore, reutilization of Fenton sludge has recently gained more attention.Understanding the formation, transformation, and properties of Fenton sludge combined with the stages of the Fenton reaction is pivotal, but not well illustrated yet. In this study,SEM-EDS, FT-IR, XRD, and XPS were applied to study the morphology, crystallinity,elemental composition, and valence state of Fenton sludge. The authors report that schwertmannite and 2-line ferrihydrite were generated and transformed in the oxidation phase and the neutralization phase of the Fenton process. SO_4^(2-) in the solution decreased by8.7%–26.0% at different molar ratios of Fe(II) to H_2 O_2; meanwhile, iron ion precipitated completely at pH 3.70 with the formation of schwertmannite containing sulfate groups in the Fenton sludge. The structural sulfate(Fe-SO_4) in schwertmannite was released from the precipitate with the addition of OH-, and the production of Fenton sludge decreased with increasing pH when pH > 3.70. Goethite was found to form when the final p H was adjusted to 12 or at a reaction temperature of 80°C. Moreover, the possible thermal transformation to goethite and hematite indicated that Fenton sludge can be reused as a raw material for synthesizing more stable iron(hydro)oxides. The results provide useful insights into the formation and transformation of Fenton sludge, with implications for regulating the crystal type of Fenton sludge for further reuse.