2D MOF derived cobalt and nitrogen-doped ultrathin oxygen-rich carbon nanosheets for efficient Fenton-like catalysis: Tuning effect of oxygen functional groups in close vicinity to Co-N sites

High-performance nitrogen-doped carbon catalyst with Co-Cu-CuxO interfaces via bimetallic ion exchange-carbonization: Synergistic Co/Cu interactions and nonradical activation mechanism for micropollutant removal

Mono-metal active sites, with their restricted electron transfer ability, typically lead to lower redox reaction efficiency, which hampers peroxymonosulfate (PMS) activation and reduces antibiotic degradation effectiveness. In this work, a novel nitrogen-doped carbon catalyst with Co-Cu-CuxO interfaces was synthesized by pyrolyzing a Zn-based elliptical two-dimensional template through a Co2+/Cu2+ bimetallic ion exchange process. The synthesized samples were comprehensively characterized using a range of physicochemical analysis techniques. Furthermore, the catalytic performance was systematically evaluated under varying conditions, including peroxymonosulfate dosage, tetracycline concentration, solution pH, and the influence of co-existing ions and organic matter in water. The results indicated that the optimized 1:1-950 catalyst achieved over 96 % degradation of tetracycline (TC) through PMS activation, with a reaction rate constant (k) of 0.038 min-1, significantly outperforming both the mono-metal ion exchange group and the non-metal ion exchange group. This improvement was attributed to the synergistic effects of Co(II)/Co(III) and Cu(I)/Cu(II) redox reactions at the Co-Cu-CuxO interfaces. Quenching experiments, electron spin resonance (ESR), and electrochemical analyses revealed that non-radical reactive oxygen species (ROS), such as singlet oxygen (1O2) and high-valent metal-oxo species (e.g., Cu(III)-oxo and Co(IV)-oxo), played a key role in the degradation process. The degradation pathways for TC were proposed using high-performance liquid chromatography-mass spectrometry (HPLC-MS), and the environmental safety of the catalytic system was confirmed through physiological testing on mung bean growth. This work presents an efficient approach for PMS activation in TC degradation, using nitrogen-doped carbon catalysts with Co-Cu-CuxO interfaces synthesized via bimetallic ion exchange and carbonization strategy, with promising applications in advanced wastewater treatment.

Machine learning-driven simultaneous quantification of Cd(II) and Cu(II) on Co2P/CoP heterostructure: enhanced electrochemical signals via activated Co-P electron bridge

Simultaneous quantification of multiple heavy metal ions remains a significant challenge in electrochemical methods, as complex high-throughput data from signal interference cannot be accurately analyzed through individual expertise and calibration curves. In this study, machine learning techniques were introduced to co-detect Cd(II) and Cu(II), with their electrochemical interference mechanisms explored on highly active Co2P/CoP heterostructures. The random forest (RF) model initially identified key feature variables in response currents, which were subsequently input into the convolutional neural network (CNN) to uncover the relationship between electrochemical signals and ion concentrations, demonstrating excellent reliability with R2 values of 0.996 for both Cd(II) and Cu(II). The root mean square error (RMSE) values for Cd(II) and Cu(II) were 0.0177 and 0.0206 μM, respectively, indicating high predictive accuracy. The experiments and theory calculations revealed that Cu(II) preferentially bonded with P sites over Cd(II). Enhanced electron transfer from Co to P atoms and weakened Cu-P bonds facilitated Cu(II) reduction and desorption from Co2P/CoP, thereby boosting electrochemical signals, while Cd(II) signals were inhibited due to active site loss. Herein, the integration of machine learning provides robust support for simultaneous detection of multiple analytes, accelerating the practical application of electrochemical methods in environmental monitoring.

The chitosan confined pyrolysis strategy enhances the catalytic performance of a carbon material based on a novel carboxyl functionalized MOF

A carboxyl functionalized metal-organic framework [Co(TPT)2/3(bptc)]·3H2O (Co-MOF (-COOH)) was designed with the aim of grafting protective CTS onto the surface as a precursor. Compared with direct carbonization and physical mixing carbonization, (Co-MOF-g-CTS)-900 prepared by confined pyrolysis shows excellent catalytic reduction performance.

Improvement Catalytic Efficiency of the Fenton-Like Reaction via the Interaction among Fe Species Encapsulated in N-Doped Carbon Materials

The Fenton-like reaction has been widely used for environmental modification. However, improvement of the catalytic efficiency is still a challenge. In this study, a series of core-shell-shaped catalysts (FeNC-x, x presents the calcination temperature) for the Fenton-like reaction was fabricated through the pyrolysis of the Fe-based metal-organic frameworks (Fe-MOF). The Fe species were encapsulated by the N-doped carbon materials and changed from Fe3O4 to Fe3C, α-Fe, and Fe-N4 with the temperature increasing from 500 to 800 °C. Simultaneously, the electron density of the Fe atom obviously increased. FeNC-650 exhibited high efficiency, as more than 85.6% TC (40 mg/L) instantaneous removal through the H2O2-based Fenton-like reaction. The turnover number is about 70 and 64 times higher than that of Fe-MOF and FeNC-500. The synergistic interaction among Fe3C, α-Fe, and Fe-N4 induced electron distribution around the Fe atom and excellent catalytic performances. Moreover, FeNC-650 exhibited excellent interference resistance toward different anions and humic acid. The toxicity of intermediate products decreased during the TC degradation. This research may give a strategy for the synthesis of catalysts used in wastewater purification.

Oxygen-containing functional groups in Fe3O4@three-dimensional graphene nanocomposites for enhancing H2O2 production and orientation to 1O2 in electro-Fenton

In electro-Fenton (EF), development of a bifunctional electrocatalyst to realize simultaneous H2O2 generation and activation efficiently for generating reactive species remains a challenge. In particular, a nonradical-mediated EF is more favorable for actual wastewater remediation, and deserves more attention. In this study, three-dimensional graphene loaded with Fe3O4 nanoparticles (Fe3O4@3D-GNs) with abundant oxygen-containing functional groups (OFGs) was synchronously synthesized using a NaCl-template method and served as a cathode to establish a highly efficient and selective EF process for contaminant degradation. The amounts of OFGs can be effectively modulated via the pyrolysis temperature to regulate the 2e- oxygen reduction reaction activity and reactive oxygen species (ROS) production. The optimized Fe3O4@3D-GNs synthesized at 750 °C (Fe3O4@3D-GNs-750) with the highest -C-O-C and -C꞊O group ratios exhibited the maximum H2O2 and 1O2 yields during electrocatalysis, thus showing remarkable versatility for eliminating organic contaminants from surface water bodies. Experiments and theoretical calculations have demonstrated the dominant role of -C-O-C in generating H2O2 and the positive influence of -C꞊O sites on the production of 1O2. Moreover, the surface-bound Fe(II) favors the generation of surface-bound •OH, which steers a more favorable oxidative conversion of H2O2 to 1O2. Fe3O4@3D-GNs were proven to be less pH-dependent, low-energy, stable, and recyclable for practical applications in wastewater purification. This study provides an innovative strategy to engineer active sites to achieve the selective electrocatalysis for eliminating pollution and reveals a novel perspective for 1O2-generation mechanism in the Fenton reaction.

Double pyramid stacked CoO nano-crystals induced by graphene at low temperatures as highly efficient Fenton-like catalysts

Transition metal oxides are widely used as Fenton-like catalysts in the treatment of organic pollutants, but their synthesis usually requires a high temperature. Herein, an all-solid-state synthesis method controlled by graphene was used to prepare a double pyramid stacked CoO nano-crystal at a low temperature. The preparation temperature decreased by 200 °C (over 30% reduction) due to the introduction of graphene, largely reducing the reaction energy barrier. Interestingly, the corresponding degradation rate constants (kobs) of this graphene-supported pyramid CoO nano-crystals for organic molecules after their adsorption were over 2.5 and 35 times higher than that before adsorption and that of free CoO, respectively. This high catalytic efficiency is attributed to the adsorption of pollutants at the surface by supporting graphene layers, while free radicals activated by CoO can directly and rapidly contact and degrade them. These findings provide a new strategy to prepare low carbon-consuming transition metal oxides for highly efficient Fenton-like catalysts.

Coordination-Polymer-Derived Cu-CoO/C Nanocomposite Used in Fenton-like Reaction to Achieve Efficient Degradation of Organic Compounds

In this paper, carbon-matrix-supported copper (Cu) and cobaltous oxide (CoO) nanoparticles were obtained by using coordination polymers (CPs) as a precursor. The aqueous solutions of copper methacrylate (CuMA) and cobalt methacrylate (CoMA) were preferentially prepared, which were then mixed with anhydrous ethanol to fabricate dual metal ion coordination polymers (CuMA/CoMA). After calcination under an argon atmosphere, the Cu-CoO/C nanocomposite was obtained. Scanning electron microscope (SEM) and transmission electron microscope (TEM) showed that the material has banded morphology, and the dual functional nanoparticles were highly dispersed in the carbon matrix. The prepared material was used in a heterogeneous Fenton-like reaction, with the aim of replacing traditional ferric catalysts to solve pH constraints and the mass production of ferric slime. The obtained nanocomposite showed excellent catalytic performance on the degradation of methylene blue (MB) at near-neutral conditions; the discoloration efficiency is about 98.5% within 50 min in the presence of 0.15 mmol/mL H2O2 and 0.5 mg/mL catalyst. And good reusability was verified via eight cycles. The plausible pathway for MB discoloration and the possible catalytic mechanism was also proposed.

Mechanisms of interaction between metal-organic framework-based material and persulfate in degradation of organic contaminants (OCs): Activation, reactive oxygen generation, conversion, and oxidation

Metal-organic frameworks (MOFs)-based materials have been of great public interest in persulfate (PS)-based catalytic oxidation for wastewater purification, because of their excellent performance and selectiveness in organic contaminants (OCs) removal in complex water environments. The formation, fountainhead and reaction mechanism of reactive oxygen species (ROSs) in PS-based catalytic oxidation are crucial for understanding the principles of PS activation and the degradation mechanism of OCs. In the paper, we presented the quantitative structure-activity relationship (QSAR) of MOFs-based materials for PS activation, including the relationship of structure and removal efficiency, active sites and ROSs as well as OCs. In various MOFs-based materials, there are many factors will affect their performances. We discussed how various surface modification projects affected the characteristics of MOFs-based materials used in PS activation. Moreover, we revealed the process of ROSs generation by active sites and the oxidation of OCs by ROSs from the micro level. At the end of this review, we putted forward an outlook on the development trends and faced challenges of MOFs for PS-based catalytic oxidation. Generally, this review aims to clarify the formation mechanisms of ROSs via the active sites on the MOFs and the reaction mechanism between ROSs and OCs, which is helpful for reader to better understand the QSAR in various MOFs/PS systems.

Gravity-driven rattan-based catalytic filter for rapid and highly efficient organic pollutant removal

Metal organic frameworks hold great promise as heterogeneous catalysts in sulfate radical (SO₄^∙-) based advanced oxidation. However, the aggregation of powdered MOF crystals and the complicated recovery procedure largely hinder their large-scale practical applications. It is important to develop eco-friendly and adaptable substrate-immobilized metal organic frameworks. Based on the hierarchical pore structure of the rattan, gravity-driven metal organic frameworks loaded rattan-based catalytic filter was designed to degrade organic pollutants by activating PMS at high liquid fluxes. Inspired by the water transportation of rattan, ZIF-67 was in-situ grown uniformly on the rattan channels inner surface using the continuous flow method. The intrinsically aligned microchannels in the vascular bundles of rattan acted as reaction compartments for the immobilization and stabilization of ZIF-67. Furthermore, the rattan-based catalytic filter exhibited excellent gravity-driven catalytic activity (up to 100 % treatment efficiency for a water flux of 10173.6 L·m^-2·h^-1), recyclability, and stability of organic pollutant degradation. After ten cycles, the TOC removal of ZIF-67@rattan was 69.34 %, maintaining a stable mineralisation capacity for pollutants. The inhibitory effect of the micro-channel promoted the interaction between active groups and contaminants, increasing the degradation efficiency and improving the stability of the composite. The design of a gravity-driven rattan-based catalytic filter for wastewater treatment provides an effective strategy for developing renewable and continuous catalytic systems.