The role of Fe dissolution in olivine-hydroxylamine-induced Fenton reaction for enhanced oxidative degradation of organic pollutant

Decolorization and degradation of crystal violet dye by electron beam radiation: Performance, degradation pathways, and synergetic effect with peroxymonosulfate

Ionizing radiation (mainly including gamma ray and electron beam) technology provides a more efficient and ecological option for dye-containing wastewater treatment, which is supported by its successful achievements in industrial-scale applications. However, the degradation pathway of triphenylmethane dyes by radiation technology is still unclear. In this study, crystal violet (CV) was selected as representative cationic triphenylmethane dye, the decolorization and degradation performance by electron beam radiation technology was systematically evaluated. The results showed that CV can be efficiently decolorized and mineralized by radiation, and its degradation kinetics followed the first-order kinetic model. The effect of inorganic anions and chelating agents commonly existed in dye-containing wastewater on CV decolorization and total organic carbon (TOC) removal was explored. Quenching experiments, density functional theory (DFT) calculation and high performance liquid chromatography mass spectrometry (HPLC-MS) analysis were employed to reveal CV decolorization and degradation mechanism and pathway, which mainly included N-demethylation, triphenylmethane chromophore cleavage, ring-opening of aromatic products and further oxidation to carboxylic acid, and mineralization to CO2 and H2O. Additionally, electron beam radiation/PMS process was explored to decrease the absorbed dose required for decolorization and degradation, and the synergetic effect of radiation with PMS was elucidated. More importantly, the findings of this study would provide the support for treating actual dyeing wastewater by electron beam radiation technology.

Congo red dye degradation using Fe-containing mineral as a reactive material derived from waste foundry dust

This study investigated the applicability of industrial waste. The high affinity of Fe-based products is widely used for industrial effluents because of their capability to oxidize contaminants. Waste foundry dust (WFD) is an Fe oxide that has been investigated as a potential reactive material that causes the generation of reactive oxidants. We aimed to investigate the physicochemical properties of WFD and the feasibility in the Fenton oxidation process. The WFD was used as a catalyst for removing Congo red (CR), to evaluate the generation of •OH and dissolution of Fe during the oxidation process. The linkage of •OH generation by WFD with eluted Fe(II) through the Fe dissolution was found. The Fenton oxidation reaction, CR degradation was affected by H2O2 concentration, initial pH, WFD dosage, initial CR concentration, and coexisting anions. The CR degradation efficiency increased with an increase in H2O2 concentration and WFD dosage. In addition, chloride and sulfate in solution promoted CR degradation, whereas carbonate had a negative effect on the Fenton oxidation process. The elution of Fe promotes CR degradation, over three reuse cycles, the degradation performance of the CR decreased from 100 to 81.1%. For the Fenton oxidation process, •OH generation is linked to Fe redox cycling, the surface passivation and Fe complexes interrupted the release of reactive oxidants, which resulted in the degradation of the CR decreased. This study proposed that WFD can serve as catalysts for the removal of CR.

Preparation of site-specific Z-scheme g-C3N4/PAN/PANI@LaFeO3 cable nanofiber membranes by coaxial electrospinning: Enhancing filtration and photocatalysis performance

The coaxial electrospinning method for preparation of g-C₃N₄/polyacrylonitrile (PAN)/polyaniline (PANI)@LaFeO₃ cable fiber membrane (PC@PL) was designed for adsorption-filtration-photodegradation of pollutants. A series of characterization results show that LaFeO₃ and g-C₃N₄ nanoparticles (NPs) are respectively loaded in the inner and outer layers of PAN/PANI composite fibers to construct the site-specific Z-type heterojunction system with spatially separated morphologies. The PANI in cable not only possesses abundant exposed amino/imino functional groups for adsorption of contaminant molecules but also due to the excellent electrical conductivity works as a redox medium for collecting and consuming the electrons and holes from LaFeO₃ and g-C₃N₄, which can efficiently promote photo-generated charge carriers separation and improve the catalytic performance. Further investigations demonstrate that as a photo-Fenton catalyst LaFeO₃ in PC@PL catalyzes/activates the H₂O₂ generated in situ by LaFeO₃/g-C₃N₄, further enhancing the decontamination efficiency of the PC@PL. The porous, hydrophilic, antifouling, flexible and reusable properties of the PC@PL membrane significantly enhance the mass transfer efficiency of reactants by filtration effect and increase the amount of dissolved oxygen, thus producing massive •OH for degradation of pollutants, which maintains the water flux (1184 L m^-2. h^-1 (LMH)) and the rejection rate (98.5%). Profiting from its unique synergistic effect of adsorption, photo-Fenton and filtration, PC@PL exhibits wonderful self-cleaning performance and distinguished removal rate for methylene blue (97.0%), methyl violet (94.3%), ciprofloxacin (87.6%) and acetamiprid (88.9%) within 75 min, disinfection (100% Escherichia coli (E. coli) and 80% Staphylococcus aureus (S.aureus) inactivation)) and excellent cycle stability.

Challenges in Recycling Spent Lithium-Ion Batteries: Spotlight on Polyvinylidene Fluoride Removal

In the recycling of retired lithium-ion batteries (LIBs), the cathode materials containing valuable metals should be first separated from the current collector aluminum foil to decrease the difficulty and complexity in the subsequent metal extraction. However, strong the binding force of organic binder polyvinylidene fluoride (PVDF) prevents effective separation of cathode materials and Al foil, thus affecting metal recycling. This paper reviews the composition, property, function, and binding mechanism of PVDF, and elaborates on the separation technologies of cathode material and Al foil (e.g., physical separation, solid-phase thermochemistry, solution chemistry, and solvent chemistry) as well as the corresponding reaction behavior and transformation mechanisms of PVDF. Due to the characteristic variation of the reaction systems, the dissolution, swelling, melting, and degradation processes and mechanisms of PVDF exhibit considerable differences, posing new challenges to efficient recycling of spent LIBs worldwide. It is critical to separate cathode materials and Al foil and recycle PVDF to reduce environmental risks from the recovery of retired LIBs resources. Developing fluorine-free alternative materials and solid-state electrolytes is a potential way to mitigate PVDF pollution in the recycling of spent LIBs in the EV era.