Roles of oxygen vacancies in layered double hydroxides-based catalysts for wastewater remediation: fundamentals and prospects

Wastewater globally is a significant concern for environmental health and for the sustainable management of water resources. Catalysed based advanced oxidation processes (AOP), as a relatively low operation cost and high removal efficiency of pollutants method, has a promising potential to treat the wastewater. Among the numerous catalysts, Layered Double Hydroxides (LDHs) stands out for lamellar structure, high charge density, and tuneable properties. Meanwhile, oxygen vacancies engineering could modulate the electronic properties of materials and create active centres to regulate the poor charge transfer capability of LDHs. In this regard, this review is focused on how to create and confirm the oxygen vacancies, as well as the applications of the wastewater treatment from different AOPs. It starts with the synthesized of oxygen vacancies via chemical reduction method, plasma etching method, hydrothermal treatment method, ion doping strategy. Followed by the description of characterization methods, including EPR, XPS, XAS, Raman. Finally, the role of oxygen vacancies in LDHs for contaminant removal across various systems, including photocatalysis, electrocatalysis, Fenton reactions, and sulfate radical-based processes, was thoroughly examined and analyzed.

Enhancing hydrogen peroxide activation of CuCo layered double hydroxide by compositing with biochar: Performance and mechanism

In this study, CuCo layered double hydroxide/biochar composite (CuCo LDH/BC) was prepared and employed for activating H₂O₂ to degrade ciprofloxacin (CIP), a common fluroquinolone antibiotic detected in water environment. The as-synthesized catalysts were also comprehensively characterized to study the physiochemical properties. For the catalytic activity, the degradation rate of CuCo LDH/BC to CIP was approximately 1.5 times higher than that of CuCo LDH. The improved catalytic activity can be ascribed to the synergistic effect between CuCo LDH and BC, such as more functional groups, accelerated electron transfer, and varied charge distribution. Meanwhile, CuCo LDH/BC/H₂O₂ could degrade CIP efficiently in a wider pH range comparing with CuCo LDH/H₂O₂, and the efficiency was approximately 84.7% at neutral pH within 90 min. The generation of OH, O₂^- and ¹O₂ in CuCo LDH/BC/H₂O₂ system were then verified by electron spin resonance (ESR) technology. The quenching experiments indicated that both non-radical pathway (¹O₂) and radical pathway (OH, O₂^-) led to CIP degradation, in which O₂^- and ¹O₂ made major contribution. Then, the intermediate products of CIP during catalytic reaction were monitored by high-performance liquid chromatography-mass spectrometry (HPLC-MS), and the environmental risk of these degradation intermediates was tested through seed germination experiments. This study tends to provide valuable information for LDH/BC application in heterogeneous Fenton-like reaction.

Ag+ significantly promoted the biofilm formation of thermoacidophilic archaeon Acidianus manzaensis YN-25 on chalcopyrite surface

Silver ion (Ag⁺) is an important catalyst to improve chalcopyrite bio-dissolution, but its effects on initial adhesion behaviors and biofilm formation of acidophiles onto metal sulfide were still unknown. In this study, initial attachment behavior and adhesion force in the presence of Ag⁺ (0, 1, 2, 5, 10 and 20 mg/L) were comparatively analyzed for Acidianus manzaensis YN-25. Biofilm was observed by fluorescent images in the presence of 0, 1 and 2 mg/L Ag⁺. X-ray photoelectron spectroscopy (XPS) corroborated the catalytic mechanisms of Ag⁺ to biofilm formation. Results showed that Ag⁺ could significantly promote the attachment of cells on chalcopyrite, and the optimum concentration of Ag⁺ was 2 mg/L with the biggest percentage of attached cells (74%), followed by 5 mg/L (71%), whereas that for the control (0 mg/L) was only 61%. Ag⁺ significantly increased the interaction force between A. manzaensis YN-25 and chalcopyrite. Compared with the control, larger coverage of biofilm (up to 40% versus 32%) and more corrosion pits were observed on chalcopyrite in the presence of 2 mg/L Ag⁺. Moreover, Ag⁺ catalyzed chalcopyrite corrosion and accelerated biofilm formation by producing a loose porous Ag₂S layer and Ag⁰ to decrease the resistivity. The live/dead ratio was small with a range of 0.31-1.38, suggesting that dead cells were a great slice during the whole life-cycle of biofilm on chalcopyrite. This report offers a profound insight into the promotion mechanism of Ag⁺ on adhesion behaviors and biofilm formation by thermoacidophilic archaeon under extremely acidic conditions.