Copper embedded in nitrogen-doped carbon matrix derived from metal-organic frameworks for boosting peroxide production and electro-Fenton catalysis

Enhanced mineralization of pharmaceutical residues at circumneutral pH by heterogeneous electro-Fenton-like process with Cu/C catalyst

Conventional electro-Fenton (EF) process at acidic pH ∼3 is recognized as a highly effective strategy to degrade organic pollutants; however, homogeneous metal catalysts cannot be employed in more alkaline media. To overcome this limitation, pyrolytic derivatives from metal-organic frameworks (MOFs) have emerged as promising heterogeneous catalysts. Cu-based MOFs were prepared using trimesic acid as the organic ligand and different pyrolysis conditions, yielding a set of nano-Cu/C catalysts that were analyzed by conventional methods. Among them, XPS revealed the surface of the Cu/C-A2-Ar/H2 catalyst was slightly oxidized to Cu(I) and, combined with XRD and HRTEM data, it can be concluded that the catalyst presents a core-shell structure where metallic copper is embedded in a carbon layer. The antihistamine diphenhydramine (DPH), spiked into either synthetic Na2SO4 solutions or actual urban wastewater, was treated in an undivided electrolytic cell equipped with a DSA-Cl2 anode and a commercial air-diffusion cathode able to electrogenerate H2O2. Using Cu/C as suspended catalyst, DPH was completely degraded in both media at pH 6-8, outperforming the EF process with Fe2+ catalyst at pH 3 in terms of degradation rate and mineralization degree thanks to the absence of refractory Fe(III)-carboxylate complexes that typically decelerate the TOC abatement. From the by-products detected by GC/MS, a reaction sequence for DPH mineralization is proposed.

A new and highly efficient CuMOF-based nanoenzyme and its application to the aptamer SERS/FL/RRS/Abs quadruple-mode analysis of ultratrace malachite green

Malachite green (MG) is highly toxic, persistent, and carcinogenic, and its widespread use is a danger to the ecosystem and a threat to public health and food safety, making it necessary to develop new sensitive multimode molecular spectroscopy methods. In this work, a new copper-based nanomaterial (CuNM) was prepared by a high-temperature roasting using a copper metal-organic framework (CuMOF) as precursor. The as-prepared CuNM was characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy, transmission electron microscopy (TEM), and BET surface area analysis. CuNM was found to catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) by H2O2 to produce the oxidation product TMBOX; however, subsequently, the MG aptamer (Apt) could be adsorbed on the CuNM surface by intermolecular interaction, which would inhibit the catalytic performance. After the addition of MG to be tested, the CuNM previously adsorbed by the Apt was transformed into its free state, thus restoring its catalytic activity. This new nanocatalytic indicator reaction could be monitored by surface-enhanced Raman scattering (SERS)/resonance Rayleigh scattering (RRS)/fluorescence (FL)/absorption (Abs) quadruple-mode methods. The SERS determination range was 0.004-0.4 nmol L-1 MG, with a limit of detection of 0.0032 nM. In this way, a rapid, stable, and sensitive method for the determination of MG residues in the environment was established.

Electrochemical detection of enrofloxacin in meat using bimetallic organic framework-derived NiCo2O4@NiO

A novel electrochemical aptasensor based on a bimetallic organic frame-derived carbide nanostructure of Co and Ni (NiCo₂O₄@NiO) was prepared for rapid and sensitive enrofloxacin (ENR) detection of sheep and pork liver meats. The composite was fabricated by solvothermal and direct pyrolysis methods and dropped onto a modified electrode to improve the electron transfer efficiency. Furthermore, different techniques such as scanning electron microscopy and X-ray photoelectron spectroscopy were used to characterize the morphology and structure of the materials. Electrochemical impedance spectroscopy and cyclic voltammetry were used to evaluate the performance of the electrochemical sensor. As a result, the electrochemical aptasensor based on NiCo₂O₄@NiO exhibited excellent sensing performances for ENR with an extremely low detection limit of 1.67 × 10^-2 pg mL^-1 and a broad linear range of 5 × 10^-2 to 5 × 10⁴ pg mL^-1, as well as great selectivity, excellent reproducibility, high stability and applicability. In addition, the relative standard deviation for real samples was in the range of 93.83 to 100.09% and 94.95 to 100.01% for sheep and pork liver. The results showed that the composite can be expected to greatly facilitate ENR detection and practical applications in harmful food due to the advantages of simple fabrication, controllable, large-area uniformity, environmental friendliness, and trace detection.

Recent advances in application of heterogeneous electro-Fenton catalysts for degrading organic contaminants in water

Over the last decades, advanced oxidation processes (AOPs) have been widely used in surface and ground water pollution control. The heterogeneous electro-Fenton (EF) process has gained much attention due to its properties of high catalytic performance, no generation of iron sludge, and good recyclability of catalyst. As of October 2022, the cited papers and publications of EF are around 1.3 × 10^-5 and 3.4 × 10^-3 in web of science. Among the AOP techniques, the contaminant removal efficiencies by EF process are above 90% in most studies. Current reviews mainly focused on the mechanism of EF and few reviews comprehensively summarized heterogeneous catalysts and their applications in wastewater treatment. Thus, this review focuses on the current studies covering the period 2012-2022, and applications of heterogeneous catalysts in EF process. Two kinds of typical heterogeneous EF systems (the addition of solid catalysts and the functionalized cathode catalysts) and their applications for organic contaminants degradation in water are reviewed. In detail, solid catalysts, including iron minerals, iron oxide-based composites, and iron-free catalysts, are systematically described. Different functionalized cathode materials, containing Fe-based cathodes, carbonaceous-based cathodes, and heteroatom-doped cathodes, are also reviewed. Finally, emphasis and outlook are made on the future prospects and challenges of heterogeneous EF catalyst for wastewater treatments.

Micro/macrostructure and multicomponent design of catalysts by MOF-derived strategy: Opportunities for the application of nanomaterials-based advanced oxidation processes in wastewater treatment

Advanced oxidation processes (AOPs) have demonstrated an effective wastewater treatment method. But the application of AOPs using nanomaterials as catalysts is challenged with a series of problems, including limited mass transfer, surface fouling, poor stability, and difficult recycling. Recently, metal-organic frameworks (MOFs) with high tunability and ultrahigh porosity are emerging as excellent precursors for the delicate design of the structure/composition of catalysts and many MOF-derived catalysts with distinct physicochemical characteristics have shown optimized performance in various AOPs. Herein, to elucidate the structure-composition-performance relationship, a review on the performance optimization of MOF-derived catalysts to overcome the existing problems in AOPs by micro/macrostructure and multicomponent design is given. Impressively, MOF-derived strategy for the design of catalyst materials from the aspects of microstructure, macrostructure, and multicomponent (polymetallic, heteroatom doping, M/C hybrids, etc.) is firstly presented. Moreover, important advances of MOF-derived catalysts in the application of various AOPs (Fenton, persulfate-based AOPs, photocatalysis, electrochemical processes, hybrid AOPs) are summarized. The relationship between the unique micro/macrostructure and/or multicomponent features and performance optimization in mass transfer, catalytic efficiency, stability, and recyclability is clarified. Furthermore, the challenges and future work directions for the practical application of MOF-derived catalysts in AOPs for wastewater treatment are provided.

Graphite felt modified by nanoporous carbon as a novel cathode material for the EF process

Nanoporous carbon prepared by carbonizing ZIF-8@MWCNTs can greatly improve the performance of graphite felt as an electro-Fenton cathode.

The Surge of Metal-Organic-Framework (MOFs)-Based Electrodes as Key Elements in Electrochemically Driven Processes for the Environment

Metal–organic-frameworks (MOFs) are emerging materials used in the environmental electrochemistry community for Faradaic and non-Faradaic water remediation technologies. It has been concluded that MOF-based materials show improvement in performance compared to traditional (non-)faradaic materials. In particular, this review outlines MOF synthesis and their application in the fields of electron- and photoelectron-Fenton degradation reactions, photoelectrocatalytic degradations, and capacitive deionization physical separations. This work overviews the main electrode materials used for the different environmental remediation processes, discusses the main performance enhancements achieved via the utilization of MOFs compared to traditional materials, and provides perspective and insights for the further development of the utilization of MOF-derived materials in electrified water treatment.