Cr-containing wastewater treatment based on Cr self-catalysis: a critical review

Chromium (Cr), as a transition metal material with multiple redox states, has exhibited the catalysis toward Fenton-like reactions over a wide pH range. Although it is not sensible to add Cr reagents as catalysts due to its toxicity, it is highly promising to remediate Cr-containing wastewater through Cr-initiated advanced oxidation processes (Cr-initiated AOPs), which are clean and low-cost. Moreover, the widely concerned Cr-complexes, considered as obstacles in the remediation process, can be effectively destroyed by AOPs. Cr self-catalysis is defined as Cr species is both substrate and catalyst. However, the full understanding of Cr self-catalysis, including the generation of intermediates Cr(IV)/Cr(V), the synergetic effects with co-existing ions, and the accumulation of toxic Cr(VI), remains a challenge for the practical application of Cr-initiated AOPs. In this review, relevant researches on Cr self-catalysis during Cr-initiated AOPs are summarized. Specifically, the Cr-Fenton-like reaction, Cr substituted materials, and Cr-sulfite reactions are explored as key mechanisms contributing to Cr self-catalysis. Moreover, Cr transformation processes, including synchronously Cr removal, Cr redox reactions, and Cr(VI) accumulation, in AOPs-based synergistic systems are systematically analyzed. Detailed approaches for the detection of active species in AOPs-based systems are also presented. The primary objective of this review is to explore the application of AOPs for Cr-containing wastewater remediation based on Cr self-catalysis, and provide fundamental insights and valuable information for future research on Cr-initiated AOPs.

Self-Catalyzed Rechargeable Lithium-Air Battery by in situ Metal Ion Doping of Discharge Products: A Combined Theoretical and Experimental Study

Lithium-air battery has emerged as a viable electrochemical energy technology;yet a substantial overpotential is typically observed,due to the insulating nature of the discharge product Li_(2)O_(2) that hinders the reaction kinetics and device performance.Furthermore,finite solid–solid/-liquid interfaces are formed between Li_(2)O_(2) and catalysts and limit the activity of the electrocatalysts in battery reactions,leading to inadequate electrolytic efficiency.Herein,in-situ doping of Li_(2)O_(2) by select metal ions is found to significantly enhance the lithium-air battery performance,and Co^(2+)stands out as the most effective dopant among the series.This is ascribed to the unique catalytic activity of the resulting Co-O_(x) sites towards oxygen electrocatalysis,rendering the lithium-air battery self-catalytically active.Theoretical studies based on density functional theory calculations show that structural compression occurs upon Co^(2+)doping,which lowers the energy barrier of Li_(2)O_(2) decomposition.Results from this study highlight the significance of in situ electrochemical doping of the discharge product in enhancing the performance of lithium-air battery.

Self-catalyzed formation of strongly interconnected multiphase molybdenum-based composites for efficient hydrogen evolution

Molybdenum carbide(MoxC)with variable phase structure possesses flexible hydrogen-binding energy(HBE),which is a promising hydrogen evolution reaction(HER)catalyst.Herein,a hybrid multiphase MoxC freestanding film coupled with Co3Mo(CM/MoxC@NC)is synthesized through the electrospinning method supplemented by the heteroatom incorporation.CM/MoxC@NC surpasses its pure phase counterparts and exhibits remarkable catalytic activity at 114mV to deliver a current density of 10mA cm^(−2) in acid,which is among the first-rate level performance reported for MoxC-based catalysts.The subsequent ex situ and in situ characterizations reveal a phase transition mechanism based on self-catalysis that CoOx depletes the coordinated C ofα-MoC via the interaction,which realizes the assembly of weak HBEα-MoC and strong HBEβ-Mo2C,and the enhanced utilization of active materials as well.The multiple structures with optimal HBE are in favor of the stepwise reactions of HER,as the study of the correlation between HBE and phase structure revealed.This study discloses the underlying phase transition mechanism and highlights the HBE–structure relationship that should be considered for catalyst design.

Palladium/ceramic composite membranes prepared by novel electroless plating procedure

THIN films have become more and more important in advanced technology,hence attracted theresearch interest in material science and technology.In chemistry,thin films are classified intoorganic and inorganic membranes.Compared with organic membranes,inorganic membranesexhibit high-temperature stability and surface modifications,and have potential