Heterogeneous Oxidation Research Articles

Heterogeneous Nickel Molybdenum Oxide Nanorods Conjugated Graphitic Carbon Nitride: A Bifunctional Electrocatalyst for Overall Water Splitting.

The pursuit of sustainable energy solutions has driven extensive research into efficient and cost-effective water-splitting techniques. This study introduces a straightforward method employing nickel molybdenum oxide NiMoO4 (NMO) nanorods integrated with graphitic carbon nitride (g-CN) sheets as promising catalysts for water splitting. The integrated coupling between NMO nanorods and g-CN leverages the distinctive properties of both materials to boost robustness as well as effectiveness in catalysis for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). We systematically optimized the nanostructure by adjusting the reduction annealing temperature during calcination to improve HER and OER activities. The NMO@g-CN-600 nanostructured catalyst demonstrates exceptional electrochemical HER activity in acidic media, with an overpotential of 148 mV at 10 mA cm-2 current density, which is approximately 2.72 times lower than that of bare NMO and 2.97 times lower than pristine g-CN catalysts. Under alkaline conditions, the NMO@g-CN-600 nanostructured catalyst exhibited superior OER activity with an overpotential of 252 mV to reach a current density of 10 mA cm-2, outperforming bare NMO and pristine g-CN catalysts. Additionally, the nanostructured catalyst demonstrated excellent long-term electrochemical stability with chronoamperometric testing over 50 h in both basic and acidic environments, showing low Tafel slopes for the OER and HER of 97 and 98 mV dec-1, respectively. Various analytical methods confirmed the successful synthesis and structural stability of prepared catalysts. The outstanding electrocatalytic properties of the NMO@g-CN-600 nanostructured catalyst position it as a feasible choice to platinum-group-based catalysts for overall water electrolysis.

Mechanistic insight into heterogeneous electro-Fenton oxidation of reactive dyes with typical iron-based particle electrodes

Mechanistic insight into heterogeneous electro-Fenton oxidation of reactive dyes with typical iron-based particle electrodes

Advances and challenges in the application of confined catalysts in heterogeneous advanced oxidation processes: A review

Advances and challenges in the application of confined catalysts in heterogeneous advanced oxidation processes: A review

Heterogeneous Fenton oxidation of aniline aerofloat catalyzed by Fe/Mn binary oxides supported on activated carbon: Performance and mechanism

Heterogeneous Fenton oxidation of aniline aerofloat catalyzed by Fe/Mn binary oxides supported on activated carbon: Performance and mechanism

Harvesting ionic power from a neutralization reaction through a heterogeneous graphene oxide membrane.

Nanofluidics is a system of fluid transport limited to a nano-confined space, including the transport of ions and molecules. The use of intelligent nanofluidics has shown great potential in energy conversion. However, ion transport is hindered by homogeneous membranes with uniform charge distribution and concentration polarization, which often leads to an undesirable power conversion performance. Here, we demonstrate the feasibility of a neutralization reaction-enhanced energy conversion process based on heterogeneous graphene oxide (GO) nanofluidics with a bipolar structure. The asymmetric charge distribution inherent to the heterogeneous nanofluidics facilitates a complementary two-way ion diffusion process, which in turn promotes efficient charge separation and superposed ionic diffusion. An output power density of up to 29.58 W m-2 is achieved with 0.1 M HCl/NaOH as the acid-base pair (ABP), which is about 712% and 117% higher than using symmetric unipolar pGO and nGO membranes. Both experiments and theoretical simulations indicate that the tunable asymmetric heterostructure contributes to regulating diffusion-based ion transport and enhancing the ion flux. This work not only establishes a significant paradigm for the utilization of chemical reactions within nanofluidic systems but also opens up new avenues for ground-breaking discoveries in the fields of chemistry, nanotechnology, and materials science.

Heterogeneous Fenton-type oxidative degradation of low-density polyethylene to valuable acid products using a nanostructured Fe–CeO2 solid solution catalyst

A study of the synergistic effect of Fe and Ce in the microwave-assisted heterogeneous Fenton-type oxidation of low-density polyethylene to value-added chemicals over a Fe–CeO2 catalyst.

Sustained Tl(I) removal by α-MnO2: Dual role of tunnel structure incorporation and surface catalytic oxidation.

Manganese oxide-based filtration technologies are considered cost-effective for thallium (Tl) removal in engineered systems. However, current gaps in understanding the heterogeneous adsorption and oxidation mechanisms of typical tunneled α-MnO2 may lead to a serious underestimation of its long-term Tl removal potential. In this study, α-MnO2 could continuously remove Tl(I) during the 584-h reaction, with its irreversible removal eventually increasing to 81 %-95 % in different anionic environments. The adsorbed low-loaded Tl(I) is preferentially oxidized, whereas the high-loaded Tl tends to be adsorbed in a nonoxidative pathway by α-MnO2. The nonoxidized Tl(I) was gradually immobilized in the stable thalliomelane-like tunnel structure. More importantly, the synergism of surface Mn(III)-oxygen vacancies (Ov) on α-MnO2 could catalyze the oxidation of Tl(I). Furthermore, the oxidized Tl(III) was bound to the tunnel surface via double edge-sharing and double corner-sharing. In addition, the phosphate anion occupied the surface active site and inhibited the oxidation of Tl(I), thereby reducing the binding strength of Tl. This study provides a new perspective on the effectiveness and stability of Tl(I) removal by MnO2 and highlights the neglected mechanism of Mn(III)-Ov mediating Tl(I) oxidation, which expands our understanding of the removal and transformation fate of Tl in MnO2-engineered systems.

Design and Synthesis of Mn-Fe-Cu Multi-Metal Oxide Catalysts for Efficient Degradation of Organic Pollutants

ABSTRACT Heterogeneous ozone-catalyzed oxidation technology is one of the effective ways of wastewater treatment, and the development of efficient ozone oxidation catalyst is the key to this process. Herein, this work proposes the design and synthesis of an efficient multi-metal composite oxide catalyst by metal salt precursor mixing-direct granulation. The successful loading of the main active metal components, such as Mn, Cu, Fe, etc. was clarified by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and other systematic characterizations, the specific surface area of the catalyst spheres produced by pelletizing could reach 231.699 m2/g, and the pore volume was 0.414 cm3/g. And after the optimization of the catalyst preparation conditions and oxidation process conditions, the removal rate of COD could reach more than 50% for the simulated wastewater, and the catalytic activity was basically kept stable in a long-cycle operation of 1000 h, which indicated that the prepared multi-metal composite oxide catalyst had good catalytic activity and stability. Finally, the EPR characterization clarified that the degradation of organic pollutants in the catalytic process was mainly dominated by the singlet oxygen and proposed a possible catalytic oxidation mechanism, which provided a reference for the synthesis of new high-efficiency ozone oxidation catalysts.

Balance of Unimolecular and Bimolecular Pathways Control the Temperature-Dependent Kinetics of Ozonolysis in Aerosols.

To better understand the key kinetic mechanisms controlling heterogeneous oxidation in organic aerosols, submicron particles composed of an alkene and a saturated carboxylic acid are exposed to ozone in a variable-temperature flow tube reactor. Effective uptake coefficients (γeff) are obtained from the multiphase reaction kinetics, which are quantified by Vacuum Ultraviolet Photoionization Aerosol Mass Spectrometry. For aerosols composed of only of alkenes, γeff doubles (from 6 × 10-4 to 1.2 × 10-3) when the temperature is decreased from 293 to 263 K. Alternatively, for an alkene particle doped with a carboxylic acid, an efficient scavenger of stabilized Criegee Intermediates (sCI), γeff is observed to be weakly temperature dependent. A kinetic model, benchmarked to literature data, explains these results as arising from the temperature dependent competition between unimolecular pathways of sCI that promote radical chain cycling and those bimolecular pathways that form stable chain termination products (i.e., α-acyloxyalkyl hydroperoxides). The implication of these results for the kinetics of aerosol aging at low temperatures is discussed.

Temperature-Dependent Water Oxidation Kinetics: Implications and Insights.

As a vital process for solar fuel synthesis, water oxidation remains a challenging reaction to perform using durable and cost-effective systems. Despite decades of intense research, our understanding of the detailed processes involved is still limited, particularly under photochemical conditions. Recent research has shown that the overall kinetics of water oxidation by a molecular dyad depends on the coordination between photocharge generation and the subsequent chemical steps. This work explores similar effects of heterogeneous solar water oxidation systems. By varying a key variable, the reaction temperature, we discovered distinctly different behaviors on two model systems, TiO2 and Fe2O3. TiO2 exhibited a monotonically increasing water oxidation performance with rising temperature across the entire applied potential range, between 0.1 and 1.5 V vs the reversible hydrogen electrode (RHE). In contrast, Fe2O3 showed increased performance with increasing temperature at high applied potentials (>1.2 V vs RHE) but decreased performance at low applied potentials (<1.2 V vs RHE). This decrease in performance with temperature on Fe2O3 was attributed to an increased level of electron-hole recombination, as confirmed by intensity-modulated photocurrent spectroscopy (IMPS). The origin of the differing temperature dependences on TiO2 and Fe2O3 was further ascribed to their different surface chemical kinetics. These results highlight the chemical nature of charge recombination in photoelectrochemical (PEC) systems, where surface electrons recombine with holes stored in surface chemical species. They also indicate that PEC kinetics are not constrained by a single rate-determining chemical step, highlighting the importance of an integrated approach to studying such systems. Moreover, the results suggest that for practical solar water splitting devices higher temperatures are not always beneficial for reaction rates, especially under low driving force conditions.

Heterogeneous Catalytic Oxidations with In Situ-Generated Hypervalent Iodine-Based Porous Organic Polymers.

Porous organic polymers (POPs) are novel emergent materials for heterogeneous organocatalysis owing to their remarkable physicochemical stabilities. Through a bottom-up approach entailing diligent design of twisted biaryl building blocks with in-built o-iodobenzoic acid (IA) moieties, a series of POP precatalysts, p-OMeIA-POP, DiMeIA-POP, and m-OMeIA-POP, were synthesized by employing Friedel-Crafts alkylation. These IA-POP precatalysts can undergo in situ oxidation in the presence of Oxone® to generate hypervalent iodine(V) species (λ5-iodanes), in particular, modified o-iodoxybenzoic acid, popularly termed IBX, which mediates diverse oxidative transformations. The applications of m-OMeIA-POP as a heterogeneous precatalyst in the presence of Oxone® are demonstrated for facile oxidation of i) primary and secondary alcohols to carbonyl compounds, ii) cleavage of olefins, vicinal diols, and acyloins into carboxylic acids and iii) oxidation of diols to lactones; the in situ formation of the λ5-iodane species in catalytic amounts precludes potential explosive attributes of IBX. It is shown that the IA-precatalyst (m-OMeIA-POP) can be easily recycled without any loss of catalytic activity. The results constitute the first demonstration of the development of IA-bearing POP precatalysts for in situ generation of hypervalent iodine(V) species and various heterogeneous oxidations mediated therefrom.

Enhanced oxidative potential and SO2 heterogeneous oxidation on candle soot after photochemical aging: Influencing mechanisms of different irradiation wavelengths.

Photochemistry plays a significant role in the atmospheric aging processes of soot. However, the physicochemical properties and changes in environmental and health effects of soot particles from sacrificial sources after photochemical aging remain unclear. The reaction mechanisms of soot under different irradiation wavelengths require further investigation. In this study, candle soot from sacrificial sources was subjected to photochemical aging using ultraviolet (UV) and visible light. The experimental results of oxidation potential (OP) and heterogeneous oxidation of sulfur dioxide (SO2) indicated that both UV and visible light promoted the photooxidation of candle soot, leading to significant increases in oxygen-containing functional groups, environmentally persistent free radicals, and negative charges on soot surfaces. After photochemical aging, candle soot exhibited higher OP values and enhanced SO2 oxidation and sulfate formation. UV light had a stronger photooxidation ability on candle soot than visible light. Mechanistic analysis revealed that the photochemical aging mechanisms driven by reactive oxygen species were different under these two wavelengths. Photosensitive aging induced by organic carbon under UV light was stronger than the photocatalytic oxidation induced by element carbon under visible light. Our research findings provided new insights into the photochemical aging mechanisms and health impacts of soot.

Intensive electron transfer of a single-atom Fe-based catalytic ceramic membrane for municipal wastewater treatment: The synergistic effects of nitrogen vacancy defect and ultrathin nanostructure.

The integration of membrane separation with heterogeneous advanced oxidation processes is a prospective strategy for the elimination of contaminants during wastewater treatment. Fe-based catalysts and the green oxidant peracetic acid (PAA) are desirable candidates for the development of catalytic membranes because they are environmentally friendly. However, the construction of catalytic ceramic membranes (CMs) modified with efficient Fe-based catalysts that generate increased amounts of high-valent Fe-O species during PAA activation for the degradation of specific pollutants, especially during instantaneous membrane filtration, remains challenging. Herein, a single-atom Fe-based catalytic CM was fabricated and further optimized via the "electron enrichment + electron-transfer enhancement" method, which specifically refers to the simultaneous introduction of nitrogen vacancy (Nv) defects and the construction of ultrathin nanostructures. The CM-UCNv-Fe/PAA system exhibited outstanding bisphenol A (BPA) removal performance, with a first-order rate constant of 0.078 ms-1 (4680 min-1), which was 37 times greater than that of CM-BCN-Fe/PAA system (126 min-1). In addition, the remarkable environmental adaptability, stability and low Fe leakage underscored its practical application potential. Mechanistic investigations revealed that Fe(V)=O was the predominant reactive oxygen species. Multi-scaled characterization and theoretical calculations confirmed that engineered Nv defects facilitated the construction of electron-rich single-atom Fe sites, which had the potential to supply more electrons. Porous ultrathin nanosheets exposed more Fe active sites, and many microinterfaces within the catalytic layers of the CM increased the possibility of contact between the Fe sites and PAA. The synergy of them enabled intensive electron transfer from Fe sites to PAA, which was the driving force for Fe(V)=O conversion during transient membrane filtration. In addition, the efficacy of the catalytic CM in municipal wastewater treatment and membrane fouling control were investigated. This work expands the research on the intensive electron transfer of a single-atom Fe-based catalytic CM for increased Fe(V)=O conversion via Nv defect introduction and ultrathin nanostructure construction.

Research and perspective of heterogeneous catalytic oxidation by ozone in the removal of pollutants from industrial wastewater: A review

Research and perspective of heterogeneous catalytic oxidation by ozone in the removal of pollutants from industrial wastewater: A review

Insights into pore structure-activity relationships of iron catalysts supported on fluorine–cerium nanosheets for heterogeneous Fenton oxidation

Two-dimensional (2D) structural materials as catalyst supports is crucial for improving the heterogeneous catalytic activity, while the relationships between their porous structure and catalytic performance are still not very clear. Herein, four kinds of porous 2D Fluorine-Cerium (F-Ce) nanosheets were fabricated and used as catalyst support, aiming to investigate the effect of porous structure on the catalytic properties by heterogeneous Fenton oxidation and unveil the structure-activity relationships. Compared with 2D non-porous GO, Ti3C2, and porous g-C3N4, F-Ce nanosheets exhibited superior catalytic activity. Specifically, FeOOH/F-Ce-3 catalysts achieved 95.5 % phenol removal within 40 minutes, with the deposition sites and electronic structures of the loaded Fe-active species being modulated by tuning the pore structures. In addition, we demonstrated that large pore size and high pore volume are more conducive to high catalytic performance, as well as the uniform pore shape and well-ordered pore distribution are more favorable for mass transfer during catalysis. This work emphasizes the great advantage of using porous 2D F-Ce nanosheets as support in the construction of heterogeneous Fenton catalysts while elaborating the relationship between pore structure and catalytic activity.

Shape-Controlled Iridium Catalysts for OER in PEM Electrolysis

Hydrogen is a clean energy carrier that holds the potential to power future transportation.1 One way to generate green hydrogen is proton exchange membrane (PEM) electrolysis with renewable electricity, but this process is limited by the sluggish oxygen evolution reaction (OER).2, 3 Iridium (Ir) catalysts have balanced activity and durability for OER.4, 5 However, due to the scarcity and high cost, the structures of the Ir catalysts must be properly controlled to improve the catalyst performance and reduce Ir loading.6, 7 Currently, most Ir catalysts are nanoparticles without well-defined crystal facets, and it remains largely unknown what Ir surface structure is the most effective for OER.4 Here, we present the facet-selective growth of Ir catalysts by using various shape-controlled seeds. These shape-controlled Ir catalysts exhibit high Ir atom usage efficiency due to the formation of only a few atomic layers of Ir shells. The activity and durability of these shape-controlled Ir catalysts towards OER are evaluated by rotating disk electrode measurements and tested in a PEM electrolyzer. This work demonstrates the possibility to further improve Ir catalyst performance by precise control over the arrangements of catalyst surface atoms. Acknowledgments We acknowledge the funding support from the Laboratory Directed Research and Development (LDRD) program at Los Alamos National Laboratory (LANL) (20240061DR) and the Hydrogen and Fuel Cell Technologies Office (HFTO), Office of Energy Efficiency and Renewable Energy, US Department of Energy (DOE). References (1) Debe, M. K. Electrocatalyst approaches and challenges for automotive fuel cells. Nature 2012, 486, 43-51.(2) Wang, Y.; Pang, Y.; Xu, H.; Martinez, A.; Chen, K. S. PEM Fuel cell and electrolysis cell technologies and hydrogen infrastructure development – a review. Energy Environ. Sci. 2022, 15, 2288-2328.(3) An, L.; Wei, C.; Lu, M.; Liu, H.; Chen, Y.; Scherer, G. G.; Fisher, A. C.; Xi, P.; Xu, Z. J.; Yan, C.-H. Recent Development of Oxygen Evolution Electrocatalysts in Acidic Environment. Adv. Mater. 2021, 33, 2006328.(4) Wang, S.; Shen, T.; Yang, C.; Luo, G.; Wang, D. Engineering Iridium-Based Oxygen Evolution Reaction Electrocatalysts for Proton Exchange Membrane Water Electrolyzers. ACS Catal. 2023, 13, 8670-8691.(5) Gao, J.; Liu, Y.; Liu, B.; Huang, K.-W. Progress of Heterogeneous Iridium-Based Water Oxidation Catalysts. ACS Nano 2022, 16, 17761-17777.(6) Alia, S. M.; Pylypenko, S.; Neyerlin, K. C.; Kocha, S. S.; Pivovar, B. S. Activity and durability of iridium nanoparticles in the oxygen evolution reaction. ECS Trans. 2015, 69, 883-892.(7) Alia, S. M.; Shulda, S.; Ngo, C.; Pylypenko, S.; Pivovar, B. S. Iridium-Based Nanowires as Highly Active, Oxygen Evolution Reaction Electrocatalysts. ACS Catal. 2018, 8, 2111-2120.

Investigating the Kinetics of Heterogeneous Lipid Ozonolysis by an Online Photoionization High-Resolution Mass Spectrometry Technique.

Lipid oxidation-induced imbalance in the redox system is one of the key causative factors leading to accelerated aging in living organisms and related diseases. Online sampling and analysis of the heterogeneous ozonolysis kinetics of lipid aerosols are highly important in revealing the oxidation-driven aging process of lipids. In this paper, an online detection method based on atmospheric pressure photoionization combined with ultrahigh resolution mass spectrometry (APPI-HRMS) is developed for real-time analysis of the heterogeneous reactions between lipid particles (oleic acid and squalene) and ozone. The online APPI-HRMS technique serves as an ideal platform for analyzing the heterogeneous oxidation of particles, exhibiting remarkable stability, sensitivity, and responsiveness across a wide range of particle concentrations. Owing to the distinctive characteristics of soft ionization, the heterogeneous effective oxidation rate of lipid aerosols was quantitatively measured. This has facilitated the detection of a series of fingerprint particle-phase products, including aldehydes, secondary ozonides, and hydroperoxides. Additionally, the kinetics evolution of these products with the ozone concentration was captured. Consequently, the ability of this online APPI-HRMS technique in assessing the multiphase oxidation of organic particles has been demonstrated, positioning it as a promising and feasible tool for revealing the heterogeneous reactions of particles.

NO₂-mediated voloxidation for iodine separation from cesium iodide surrogates

ABSTRACT Heterogeneous NO2-mediated oxidation of uranium, also known as advanced voloxidation, is a proposed head-end reprocessing method for used nuclear fuel. An advantage of advanced voloxidation is the removal of volatile fission products, which complicate downstream separation and containment challenges leading to increased processing economics. Iodine, one of the volatile species of interest, has exhibited varied results in this process. Using CsI as a surrogate material, this work mimics the effect of NO2-based voloxidation on iodine and sheds light on the factors that influence the solid–gas phase reaction. Solid-state analysis using Fourier transform infrared attenuated total reflectance spectroscopy and scanning electron microscopy with energy-dispersive X-ray spectroscopy confirmed the conversion of CsI to CsNO3. Iodine separation ranged from 46% to 100% across multiple tests. Iodine separation was most effective when multiple recharges of NO2 were administered. At the bench scale, liberating iodine from CsI appears to occur within 1 h, but the presence of surface H2O and the composition of the NO x reagent mixtures greatly influence its success.

Interfacial and electronic dual regulation of metal organic frameworks for enhanced catalytic oxidation of peroxymonosulfate into dyes

In heterogeneous advanced oxidation processes, it is important to improve the catalytic performance, which can be achieved by increasing the mass transfer of catalysts and utilization efficiency of reactive oxygen species (ROSs). Herein, the functional groups, amino group (NH2) and hydroxyl group (OH), were introduced onto the surface of metal organic frameworks (MOFs), FeBDC (Iron terephthalate) by ligand exchange. The synthesized MOFs were used as catalysts to activate peroxymonosulfate (PMS) for the efficient removal of dye from wastewater. The NH2/-OH groups accumulated at the surface of MOFs to significantly enhanced their hydrophilicity, which favored dye adsorption efficiency on the surface of MOFs from aqueous solution. This dye enrichment was benefited to the high utilization of ROSs due to the shorter transfer distance in solution. Additionally, the introduction of NH2/OH favored the reduction in electrochemical resistance both within the bulk and at the interface of the MOFs, thereby facilitating the electron transfer from the MOFs to PMS. The efficient utilization of ROSs (the radicals (SO4− and O2−) and non-radical (1O2)) generated by PMS removed nearly all RB171 (96.2–98.5 %) by oxidation reaction. The azo bonds and aromatic rings of dye molecules were susceptible to the attack by these ROSs. At the utilization of 5 cycles, iron leaching from MOFs/PMS was very low, satisfying the value of discharge standards. This work demonstrates that the functional groups presented in MOFs effectively facilitate the dual regulation of dye enrichment and catalytic activity in heterogeneous advanced oxidation processes.

Homogeneous and heterogeneous selective oxidation of ethyl lactate regulated by a novel vanadium complex

As a green and sustainable alternative for producing ethyl pyruvate (EP), the selective aerobic oxidation of ethyl lactate (EL) is still facing issues such as low catalytic efficiency, harsh reaction conditions and catalyst instability. Herein, a novel crystalline vanadium-based coordination compound (VTC=VPTPYCl2(H2O), PTPY = 4′-phenyl-2,2′:6′,2′’-terpyridine) has been designed and synthesized. A highly efficient homogeneous catalytic system (VTC-400-O2-CH3CN, 400 represents the activation temperature) and a recyclable heterogeneous system (VTC-500-O2-CH3CN) for the liquid-phase conversion of EL to EP are developed using molecular oxygen as oxidant through activating VTC at different temperature. In VTC-400-O2-CH3CN system, EL can be completely converted within 4 h, and the yield of EP is 77.8 %, which outperforms the state-of-art reported catalytic system. Meanwhile, the heterogeneous VTC-500 catalyst can also promote the full conversion of EL within 4 h, and its activity remains basically unchanged after being used for 10 times. Structural characterization reveals that the soluble VTC breaks the weak coordination V-Cl bonds at a lower activation temperature of 400 ° C to expose more vanadium-based catalytic sites, but the framework of ligand remains intact. However, the organic derived carbon skeleton at higher temperature of 500 ° C can effectively confine the V-based active species and prevent the dissolution of the catalyst, which impels the transition of the homogeneous to heterogeneous catalytic system.