Increasing the activity and stability of chemi-deposited palladium catalysts on nickel foam substrate by electrochemical deposition of a middle coating of silver

Microenvironment Engineering of Heterogeneous Catalysts for Liquid-Phase Environmental Catalysis

Environmental catalysis has emerged as a scientific frontier in mitigating water pollution and advancing circular chemistry and reaction microenvironment significantly influences the catalytic performance and efficiency. This review delves into microenvironment engineering within liquid-phase environmental catalysis, categorizing microenvironments into four scales: atom/molecule-level modulation, nano/microscale-confined structures, interface and surface regulation, and external field effects. Each category is analyzed for its unique characteristics and merits, emphasizing its potential to significantly enhance catalytic efficiency and selectivity. Following this overview, we introduced recent advancements in advanced material and system design to promote liquid-phase environmental catalysis (e.g., water purification, transformation to value-added products, and green synthesis), leveraging state-of-the-art microenvironment engineering technologies. These discussions showcase microenvironment engineering was applied in different reactions to fine-tune catalytic regimes and improve the efficiency from both thermodynamics and kinetics perspectives. Lastly, we discussed the challenges and future directions in microenvironment engineering. This review underscores the potential of microenvironment engineering in intelligent materials and system design to drive the development of more effective and sustainable catalytic solutions to environmental decontamination.

Enhanced dehalogenation of brominated DBPs by catalyzed electrolysis using Vitamin B12 modified electrodes: Kinetics, mechanisms, and mass balances

Vitamin B₁₂ (VB₁₂) modified electrodes were prepared for the electrocatalytic reductive debromination of tribromoacetic acid (TBAA). Under galvanostatic conditions set as 5 mmol/L VB₁₂ loading, 20 mmol/L Na₂SO₄ as electrolyte, 10.0 mA/cm² current density, pH 3, and 298 K, the degradation efficiency of 200 μg/L TBAA at the VB₁₂ modified electrode could reach 99.9 % after 6 h. The debromination of TBAA followed the first-order kinetic model. The masses of carbon and bromine elements were conserved before and after the reaction, together with the qualitative analysis of the degradation products showed the likely degradation pathways as TBAA→dibromoacetic acid (DBAA)→monobromoacetic acid (MBAA)→acetic acid (AA). ESR detection and quenching experiments confirmed the role of atomic H* in TBAA debromination. In-situ Raman spectroscopy showed that the Co-Br bond was strongly enriched to the electrode surface, accelerating the electron transfer. The H₂O dissociation performance and transition states searching catalyzed by VB₁₂ were calculated by Density Functional Theory (DFT) and proved that the composite electrode can effectively promote atomic H* generation. Material characterization and electrochemical performance tests showed that the VB₁₂ modified electrode had excellent stability and atomic H* catalytic activity. The electrocatalytic debromination of TBAA at VB₁₂ modified electrodes mainly involves two mechanisms, direct reduction by electron transfer and indirect reduction by the strongly reducing atom H*. The results provide an efficient way to achieve safe removal of brominated DBPs from drinking water after chlorination and before human consumption.

Enhanced electrocatalytic hydrodechlorination of 2,4-dichlorophenoxyacetic acid by a Pd-Co3O4/Ni foam electrode

A new Pd-Co3O4/Ni foam electrode was synthesized by a facile two-step method comprising co-electrodeposition and calcination. Compared with Ni foam-supported Pd electrodes obtained by electrodeposition or chemical deposition, the new Pd-Co3O4/Ni foam electrode exhibited greatly enhanced catalytic hydrodechlorination activity. The introduction of Co3O4 reduced the amount of Pd required. For the same degree of dechlorination of 2,4-D, only 25% of the Pd was required in the Pd-Co3O4/Ni foam electrode compared with the Ni foam electrode prepared by chemical deposition. Various characterizations indicated that Co3O4 on the surface of the Ni foam enhanced catalytic performance through accelerated generation of atomic H*. In addition, the good distribution of macropores, providing a larger specific surface area and lower electron transfer impedance, enabled more adsorption of atomic .

Preparation of Conductive Polyester Fibers Using Continuous Two-Step Plating Silver

Polyester fibers are used in various fields, due to their excellent mechanical and chemical stability. However, the lack of conductivity limits their application potential. In order to prepare conductive polyester fibers, silver is one of the most widely used materials to coat the surface of the fibers. This work aimed to prepare silver-coated polyester fibers by a continuous two-step method, which combined the operations of continuous electroless plating and electroplating. Meanwhile, we designed specialized equipment for the continuous plating of silver on the polyester fibers under a dynamic condition. The mechanical property, washability, electrical resistivity, and electrical conductivity of the resultant conductive polyester fibers obtained from different silver-plating conditions were also characterized. The results demonstrated that the conductive fibers prepared by continuous two-step silver plating equipment, had good electrical conductivity with better mechanical properties and washability.

Interaction of nickel with carbon dioxide in [Ni(CO2)(n)](-) clusters studied by infrared spectroscopy

We present infrared photodissociation spectra of [Ni(CO2)n](-) clusters (n = 2-8) in the wavenumber region of 1000-2400 cm(-1) using the antisymmetric stretching vibrational modes of the CO2 units in the clusters as structural probes. We use density functional theory to aid in the interpretation of our experimental results. The dominant spectral signatures arise from a core ion composed of a nickel atom and two CO2 ligands bound to the Ni atom in a bidentate fashion, while the rest of the CO2 molecules in the cluster play the role of solvent. Other core structures are observed as well but as minor contributors. The results for [Ni(CO2)n](-) clusters are discussed in the context of other anionic transition- metal complexes with CO2.

Effect of silver or copper middle layer on the performance of palladium modified nickel foam electrodes in the 2-chlorobiphenyl dechlorination

To enhance the activity of chemi-deposited palladium/nickel foam (Pd/Ni) electrodes used for an electrochemical dechlorination process, silver or copper was deposited electrochemically onto the nickel foam substrate (to give Ag/Ni or Cu/Ni) before the chemical deposition of palladium. The physicochemical properties of the resulting materials (Pd/Ni, Pd/Ag/Ni and Pd/Cu/Ni) were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), and their electrochemical catalytic activities were evaluated by monitoring the electrochemical dechlorination of 2-chlorobiphenyl (2-CB) in strongly alkaline methanol/water solution. The results show that the Pd/Ag/Ni and Pd/Cu/Ni electrodes had consistently higher electrocatalytic activities and current efficiencies (CEs) compared with the untreated Pd/Ni electrode. The Pd/Ag/Ni electrode exhibited the highest activity. The dechlorination was also studied as a function of Pd loading, the Ag or Cu interlayer loadings, and the current density. The Pd loading and the interlayer loadings both had positive effects on the dechlorination reaction. Increasing the current density increased the reaction rate but reduced the CE. The improvement of the electrocatalytic activities of the Pd/Ni electrode by applying the interlayer of Ag or Cu resulted from the enlargement of the effective surface area of the electrode and the adjustment of the metal-H bond energy to the appropriate value, as well as the effective adsorption of 2-CB on Ag. Moreover, the high catalytic activity of the Pd/Ag/Ni electrode was maintained after six successive cyclic experiments, whereas Pd/Cu/Ni electrodes deactivate severely under the same conditions.

Complete dechlorination of 2,4-dichlorophenol in aqueous solution on palladium/polymeric pyrrole-cetyl trimethyl ammonium bromide/foam-nickel composite electrode

The electrochemically reductive dechlorination of 2,4-dichlorophenol (2,4-DCP) in aqueous solution on palladium/polymeric pyrrole-cetyl trimethyl ammonium bromide/foam-nickel electrode (Pd/PPy-CTAB/foam-Ni electrode) was investigated in this paper. Pd/PPy-CTAB/foam-Ni electrode was prepared and characterized by cyclic voltammetry (CV), scanning electron microscope (SEM), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) adsorption and inductively coupled plasma-atomic emission spectroscopy (ICP-AES). The influences of some experimental factors such as the dechlorination current, dechlorination time and the initial pH on the removal efficiency and the current efficiency of 2,4-DCP dechlorination on Pd/PPy-CTAB/foam-Ni electrode were studied. Complete removal of 2,4-DCP was achieved and the current efficiency of 47.4% could be obtained under the conditions of the initial pH of 2.2, the dechlorination current of 5 mA and the dechlorination time of 50 min when the initial 2,4-DCP concentration was 100 mg L(-1). The analysis of high performance liquid chromatography (HPLC) identified that the intermediate products were 2-chlorophenol (2-CP) and 4-chlorophenol (4-CP). The final products were mainly phenol. Its further reduction product cyclohexanone was also detected. The electrocatalytic dechlorination pathways of 2,4-DCP on Pd/PPy-CTAB/foam-Ni electrode were discussed. The stability of the electrode was favorable that it could keep dechlorination efficiency at 100% after having been reused 10 times. Results revealed that the stable prepared Pd/PPy-CTAB/foam-Ni electrode presented a good application prospect in dechlorination process with high effectiveness and low cost.