Biphase Co@C core-shell catalysts for efficient Fenton-like catalysis

Nanoconfined catalytic macrostructures for advanced water remediation: From basic understanding to future application strategies

In recent years, nanoconfined catalytic macrostructures applied to advanced oxidation processes (AOPs) have been rapidly developed, effectively solving the problems of traditional heterogeneous AOPs, such as mass transfer limitation, limited diffusion of short-lived reactive oxygen species (ROS), and aggregation/leaching of catalysts. Compared with the traditional heterogeneous AOPs systems, the nanoconfined catalytic macrostructures have unique interactions between the oxidants, catalysts, ROS and micropollutants, which could significantly increase the yield and mass transfer of ROS. At present, there is a lack of comprehensive reviews on the nanoconfined catalytic macrostructures from basic theory to application performances and future development strategies. This study reviewed the preparation routines of various nanoconfined catalytic macrostructures, assessed their structural differences, catalytic properties and nanoconfined catalytic mechanisms via integrated density functional theory (DFT) and molecular dynamics (MD) stimulations. We also proposed the future strategies for nanoconfined catalytic macrostructures in combination with the machine learning, which could provide key information on the feasibility of the technology and future research directions. This review aims to enhance scholarly interest in the application of nanoconfined macrostructures in the AOPs fields, anticipating significant technical feasibilities for scale-up AOPs application of nanoconfinement.

La3+@BC500-S2O82- system for removal of sulfonamide antibiotics in water

Sulfonamide antibiotics (SAs) widely used have potentially negative effects on human beings and ecosystems. Adsorption and advanced oxidation methods have been extensively applied in SAs wastewater treatment. In this study, compared with Al3+@BC500 and Fe3+@BC500, La3+@BC500 for activating persulfate (S2O82-) had the best effect removal performance of sulfadiazine (SDZ) and sulfamethoxazole (SMX). Morphology, acidity, oxygen-containing functional groups, and loading of La3+@BC500 were analyzed by techniques, including EA, BET, XRD, XPS, FT-IR. XRD results show that with the increase of La3+ loading, the surface characteristics of biochar gradually changed from CaCO3 to LaCO3OH. Through EPR technology, it is proved that LaCO3OH on the surface of La3+@BC500 can not only activate S2O82- to generate SO4-•, but also to produce •OH. In the optimization experiment, the optimal dosage of La3+ is between 0.05 and 0.2 (mol/L)/g. SDZ had a good removal effect at pH (5-9), but SMX had a good removal effect only at pH=3. Zeta potential also proves that the material is more stable under acidic conditions. The removal process of SDZ is more in accord with pseudo-first-order kinetics (R2=0.9869), while SMX is more in line with pseudo-second order kinetics (R2=0.9926).

Magnetic cobalt nanoparticles embedded in a carbonaceous hydrogel for the activation of peroxymonosulfate to degrade azo dyes and organic pollutants

Heterogeneous cobalt-based catalysts have recently gained attention as persulfate activators to degrade dyes and organic pollutants in sulfate radical-based advanced oxidation processes (SR-AOPs). This study fabricated magnetic cobalt nanoparticles embedded in a carbonaceous hydrogel (Co@C) using high-temperature pyrolysis of the Co2+-embedded chitosan-graft-poly(acrylic acid) (Co2+-embedded CTS-g-PAA) hydrogel. Subsequently, the prepared Co@C was evaluated as a peroxymonosulfate (PMS) activator for degrading azo dyes. The catalyst showed the highest performance toward reactive red 141 (RR141) than Congo red, methyl orange, direct yellow 50, and reactive black 5. RR141 was completely degraded within 10 min, with a 3.20 min-1 pseudo-first-order rate constant. The degradation rate increased with higher catalyst dosage, PMS dosage, and temperature. The pH of the solution had a minimal effect on the degradation of RR141, indicating that the catalyst could be effective across a wide pH range. Moreover, the quenching experiment and the electron paramagnetic resonance analysis indicated that the catalytic system generated SO4•-, HO•, O2•-, and 1O2. The RR141 degradation was slightly affected by Cl-, NO3-, and SO42-. The catalyst demonstrated high efficiencies in real water samples. The catalyst could be easily recovered using a magnet and reused for ten cycles with only a 10% degradation efficiency loss. Furthermore, the catalyst could effectively degrade other organic pollutants, including tetracycline and 4-nitrophenol. This study demonstrates that the Co@C catalyst can effectively purify wastewater via SR-AOPs.

Synthesis of sewage sludge biochar in molten salt environment for advanced wastewater treatment: Performance enhancement, carbon footprint and environmental impact reduction

Sewage sludge (SS) pyrolysis to produce biochar is a vital approach for treating and utilizing SS, while reducing the carbon footprint of SS disposal. However, the high inorganic content in SS results in low carbon content and underdeveloped pore structure of biochar prepared under inert atmospheres. There is a significant risk of secondary pollutant emissions, including CO2, SO2, and NOx. In this study, we propose an innovative approach that utilizes excess molten salts, specifically a Li-Na-K molten carbonate (MC) and a Li-Na-K molten chloride (MCH), to create a medium-temperature liquid phase reaction environment (500 °C) for SS pyrolysis. This environment promotes the functional enhancement of biochar (SSB-MC and SSB-MCH) and in-situ absorption of secondary pollutants. The pore structure of SSB-MC and SSB-MCH are greatly optimized. Thanks to the dissolution of calcium-silicon-aluminum-based minerals by molten salt, the carbon content is also significantly increased. The increased specific surface area and surface-enriched functional groups (O, N, P, etc.) of SSB-MC result in greatly enhanced adsorption performance for Rhodamine B (27.9 to 89.1 mg g-1). SSB-MCH, due to the increased iron and phosphorus doping, also exhibits enhanced Fenton oxidation capability. Life cycle assessments demonstrate that the molten salt processes effectively reduce the carbon footprint, energy consumption, and environmental impact.

Electrochemical splitting of methane in melts: Producing and tuning high-value carbon materials with controllable morphology

Catalytic decomposition of methane offers a viable solution for producing pure hydrogen and nanocarbon without emitting carbon dioxide. However, conventional thermal catalytic processes and catalysts have limitations in terms of poor carbon quality and catalyst deactivation due to carbon deposition. The newly developed electrochemical splitting of methane (ESM) in molten salt has emerged as a promising alternative that allows for the separate production of hydrogen at the anode and carbon deposition at the cathode. In this study, hydrogen produced via ESM while generating nanocarbon with diverse structures through manipulations of the cathode material and kinetics. Carbon nanotubes grown on Ni cathode, possessing high specific surface area and abundant functional groups, displayed excellent adsorptive capacity for dye adsorption. The open hollow nanocarbon grown on the Ag cathode displayed good capacitance performance. ESM technology has immense potential to enhance the utilization value of carbon by-products and the commercial production of green hydrogen.

Regulation of friction pair to promote conversion of mechanical energy to chemical energy on Bi2WO6 and realization of enhanced tribocatalytic activity to degrade different pollutants

Recently, friction-induced tribocatalysis has received tremendous attention through converting mechanical energy to chemical energy. However, its efficiency is much lower than those of photocatalysis and piezocatalysis, and its environmental application is limited in dye degradation. Herein, we developed a facile approach to improve the tribocatalytic activity of Bi2WO6 via adding trace polymer powders to form friction pairs with Bi2WO6. Among various polymers, PTFE was demonstrated to be the best counterpart of Bi2WO6. Subsequently, the PTFE dosage, stirring rate, magnetic bar size and number, and stirring mode were further optimized. The PTFE-promoted Bi2WO6 tribocatalysis was verified to possess excellent performance not only for removing different dyes, but also for degrading chlorophenols that are typical persistent organic pollutants. Multiple uses of the recycled catalysts indicated its good stability and prominent tribocatalytic durability. EPR measurements suggested the generation of hydroxyl radical and superoxide radical, which were determined to be continuously generated within 12 h at the rates of 0.88 μM h-1 and 85 μM h-1, respectively. Subsequently, a possible mechanism was proposed to explain the enhanced performance of the PTFE-promoted Bi2WO6 tribocatalysis. Finally, on basis of the detected intermediates, the degradation pathways of Rhodamine B and 2,4-Dichlorophenol during tribocatalysis were suggested.

Phthalate esters: occurrence, toxicity, bioremediation, and advanced oxidation processes

Phthalic acid esters are emerging pollutants, commonly used as plasticizers that are categorized as hazardous endocrine-disrupting chemicals (EDCs). A rise in anthropogenic activities leads to an increase in phthalate concentration in the environment which leads to various adverse environmental effects and health issues in humans and other aquatic organisms. This paper gives an overview of the research related to phthalate ester contamination and degradation methods by conducting a bibliometric analysis with VOS Viewer. Ecotoxicity analysis requires an understanding of the current status of phthalate pollution, health impacts, exposure routes, and their sources. This review covers five toxic phthalates, occurrences in the aquatic environment, toxicity studies, biodegradation studies, and degradation pathways. It highlights the various advanced oxidation processes like photocatalysis, Fenton processes, ozonation, sonolysis, and modified AOPs used for phthalate removal from the environment.

New insights into engineering the core size and carbon shell thickness of Co@C core-shell catalysts for efficient and stable Fenton-like catalysis

Herein, we engineered the cobalt core size and carbon shell thickness of Co@C by molten salt electrolysis (MSE) to investigate the enhanced essence of decreasing core size as well as the shell thickness dependence-mediated transition of catalytic mechanisms. We found that the reaction activation energy (RAE) of Co@C/peroxymonosulfate (PMS) systems was intimately dependent on the core sizes for sulfamethoxazole (SMX) degradation. The smaller core size of 26 nm provided a lower RAE of 13.39 kJ mol^-1. In addition, increasing carbon shell thicknesses of Co@C altered the catalytic mechanisms from a radical pathway of SO₄^•- and •OH to to a non-radical pathway of ¹O₂ and electron-transfer process (ETP), which were verified by experimental results and density functional theory (DFT) calculations. Interestingly, increasing carbon shell thicknesses promoted the charge transfer between Co metal slab and carbon shell, increased the adsorption energy of PMS molecule on the Co@C slab, and decreased the length of OO, which favoured the occurrence of non-free radical processes.

An economic, self-supporting, robust and durable LiFe5O8 anode for sulfamethoxazole degradation

Electrochemically activating peroxydisulfate (PDS) to degrade organic pollutants is one of the most attractive advanced oxidation processes (AOPs) to address environmental issues, but the high cost, poor stability, and low degradation efficiency of the anode materials hinder their application. Herein, an economic, self-supporting, robust, and durable LiFe₅O₈ on Fe substrate (Fe@LFO) anode is reported to degrade sulfamethoxazole (SMX). When PDS is electrochemically activated by the Fe@LFO anode, the degradation rate of SMX is significantly improved. It is found that hydroxyl radicals (•OH), superoxide radical (O₂^•-), singlet oxygen (¹O₂), Fe(Ⅳ), activated PDS (PDS*), and direct electron transfer (DET) reactions synergistically contribute to the degradation of SMX, which can realize the degradation of SMX in four possible routes: cleavage of the isoxazole ring, hydroxylation of the benzene ring, oxidation of the aniline group, and cleavage of the S-N bond, as evidenced by a series of tests of radicals quenching, electron paramagnetic resonance (EPR), linear sweep voltammetry (LSV) and liquid chromatograph mass spectrometer (LC-MS). Furthermore, Fe@LFO has good structural stability, excellent cyclability and low degradation cost, demonstrating its great potential for practical applications. This work contributes to a stable and effective anode material in the field of AOPs.

Catalytic oxidation mechanism of AsH3 over CuO@SiO2 core-shell catalysts via experimental and theoretical studies

In this study, CuO@SiO₂ core-shell catalysts were successfully synthesized and applied to efficiently remove hazardous gaseous pollutant arsine (AsH₃) by catalytic oxidation under low-temperature and low-oxygen conditions for the first time. In typical experiments, the CuO@SiO₂ catalysts showed excellent AsH₃ removal activity and stability under low-temperature and low-oxygen conditions. The duration of the AsH₃ conversion rate above 90 % for the CuO@SiO₂ catalysts was 39 h, which was markedly higher than that of other catalysts previously reported in the literature. The considerable catalytic activity and stability were attributed to the protection and confinement effects of the SiO₂ shell, which resulted in highly dispersed CuO nanoparticles. Meanwhile, the strong interaction between the CuO core and SiO₂ shell further facilitated the formation of active species such as coordinatively unsaturated Cu²⁺ and chemisorbed oxygen. The accumulation of oxidation products (As₂O₃ and As₂O₅) on the interface between the CuO core and SiO₂ shell and the pore channels of the SiO₂ shell is the main cause of catalysts deactivation. Furthermore, through combined density functional theory (DFT) calculations and characterization methods, a reaction pathway including gradual dehydrogenation (AsH₃*→AsH₂*→AsH*→As*) and gradual oxidation (2As*→As*+AsO*→2AsO*→As₂O₃) for the catalytic oxidation of AsH₃ on CuO (111) surface was constructed to clarify the detailed reaction mechanism. The CuO@SiO₂ core-shell catalysts applied in this study could provide a powerful method for developing AsH₃ catalysts from multiple know AsH₃ removal systems.

A simple and green method to prepare non-typical yolk/shell nanoreactor with dual-shells and multiple-cores: Enhanced catalytic activity and stability in Fenton-like reaction

Nowadays, non-typical yolk/shell structure has drawn much attentions due to the better catalytic performance than traditional counterparts (one yolk/one shell). In this study, ZIF-67 @Co₂SiO₄/SiO₂ yolk/shell structure was prepared in one-step at room temperature, in which ZIF-67 was served as the hard-template, H₂O was served as etchant and tetraethyl orthosilicat was served as the raw material for Co₂SiO₄/SiO₂. After calcination, the non-typical Co_xO_y @Co₂SiO₄/SiO₂ yolk/shell nanoreactor with Co₂SiO₄/SiO₂ dual-shells and Co_xO_y multiple-cores was obtained. On the one hand, more active sites were exposed on multiple-cores surface and better protection were provided by dual-shells. On the other hand, the sheet-like Co₂SiO₄ inner shell not only extended the travel path and retention time of pollutants trapped in cavity, but also separated the multiple-cores from aggregation. Therefore, the nanoreactor displayed the outstanding catalytic activity and recyclability in Fenton-like reaction. Metronidazole (20 mg/L) was completely degraded after 30 min, rhodamine B (50 mg/L) and methyl orange (20 mg/L) were removed even within 5.0 min. Catalytic mechanism indicated that ¹O₂ greatly contributed to the pollutant degradation. This paper presented a simple, versatile, green and energy-saving method for non-typical yolk/shell nanoreactor, and it could inspire to prepare other catalysts with high activity and stability for environmental remediation.

Iron-doped g-C3N4 catalysts fabricated by forming Fe–N moieties with outstanding photo-Fenton activity toward tetracycline degradation

Porous Fe-doped g-C3N4 photo-Fenton catalysts are successfully prepared by a convenient one-step pyrolysis strategy and applied in the degradation of tetracycline hydrochloride.