Reactive Oxygen Species and Catalytic Active Sites in Heterogeneous Catalytic Ozonation for Water Purification

Polarized electric field induced by piezoelectric effect of ozone micro-nano bubbles/spontaneously polarized ceramic to boost ozonolysis for efficient fruit sterilization

Ozone (O3) treatment is an environmentally friendly fruit sterilization strategy. However, the low O3 utilization rate and long-term oxidation lead to O3 waste and fruit damage, respectively. Herein, a sterilization system based on the synergy of O3 micro-nano bubbles (OMNB) and spontaneously polarized ceramic (SPC) was developed to piezoelectrically catalyze ozonolysis for efficient fruit sterilization. OMNB/SPC showed excellent sterilizing activity with 7 lg CFU/mL of E. coli and S. aureus inactivation within 20 min, together with significantly improved fruit quality in Kyoho grapes preservation. The excellent sterilizing performance of OMNB/SPC is attributed to that the piezoelectric SPC (d33 = 103.4 pm/V) formed a strong polarized electric field and rich reactive oxygen species (ROS) under OMNB collapse resulting in O3 absorption/decomposition. The electric field and rich ROS caused membranes in-situ electroporation and irreversible inactivation to the microorganisms on fruits successively. This system is important for more efficient long-term preservation of fruits.

Reversible Sol-Gel Transitions Mediated Organics Selective Uptake and Release for Simultaneous Water Purification and Chemicals Recovery

The separation and recovery of useful organics from wastewater have been a promising alternative to tackling water pollution and resource shortages, while strategies that truly work have rarely been explored. Herein, a reversible CO2 triggered sol-gel state transformation mediated selective organics uptake-release system using a surface modified carbonitride (S-CN) is proposed and exhibits remarkable organics recovery performance from wastewater. Results show that CO2 can serve as a cross-linker for linking S-CN particles to form a hydrogel by electrostatic interaction and hydrogen bonding, which can be recycled to the pristine sol state simply by removing the cross-linked CO2 with Ar purging. The reversible sol-gel transformation achieves nearly complete uptake of valuable organics from wastewater with high selectivity at the first sol-to-gel stage through electrostatic interaction, hydrogen bonding, and π-π interactions together, and it recovers 90% of the organics uptaked by releasing them into a concentrated solution at the second gel-back-to-sol stage.

Electrolyte reactivity on electrode surfaces for active species formation and Reactive Red X-3B degradation in electrochemical treatment of dyeing wastewater

The pivotal role of electrolytes such as Na2SO4 and NaCl in electrochemical treatment of dyeing wastewater was investigated by comparing recalcitrant Reactive Red X-3B (RRX-3B) degradation rates, active species formation and intermediates generation in a double-chamber cell. It was found that similar reactive oxygen species (ROS) formed in the anodic chamber are •OH and 1O2, in the cathodic chamber is •O2- with different electrolytes, while this is not the case for ROS contribution, RRX-3B degradation kinetic and intermediates. NaCl favored the generation of 1O2, faster decolorization (-N=N- cleavage), and organic intermediates degradation in the anodic chamber. A comparatively faster hydrogenation reduction of -N=N- and higher COD removal with fewer organic categories in Na2SO4 cathodic chamber outperformed those in NaCl cathodic chamber. The RRX-3B degradation pathways were proposed in both chambers based on GC-MS investigations and Fukui function calculations. Atoms Cl, S and N in RRX-3B molecule removals were in the order of R-S > R-N > R-Cl.

Catalytic ozonation of dimethyl phthalate by Ti-MCM-41 in water

A Ti-MCM-41 mesoporous molecular sieve catalyst was prepared by a hydrothermal method. Nitrogen adsorption desorption, XRD, TEM and SEM characterization results showed that the catalyst had a large specific surface area, a regular hexagonal pore structure, and titanium doping was uniformly dispersed in MCM-41 molecular sieves. The amount of titanium doping, reaction temperature, and the initial solution pH had important effects on the catalytic ozonation of dimethyl phthalate (DMP) by Ti-MCM-41. In comparison to ozonation alone and MCM-41/O3, Ti-MCM-41/O3 exhibited the most effective degradation and mineralization of DMP, with a Si/Ti ratio of 80, a reaction temperature of 25 °C, and an initial solution pH of 5.4. Ozonation alone, MCM-41/O3, and Ti-MCM-41/O3 removed 94%, 96%, and 100% of DMP after 15 min of reaction. At 60 min of reaction, the TOC removal rate of the Ti-MCM-41/O3 process reached 36%, which was 2.4 times that of the O3 process and 1.9 times that of the MCM-41/O3 process. The experimental results of initial solution pH and hydroxyl radical capture showed that Ti-MCM-41 had the highest catalytic activity near the zero-charge point, and hydroxyl radicals were active oxygen species. Ti-MCM-41 catalytic ozonation of DMP had synergistic effects and is a promising environmental catalytic material.

Rerouting charge transfer for pharmaceutical wastewater electrochemical treatment via interfacial cocatalyst modification

Electrochemical oxidation stands as a pivotal technology for refractory wastewater treatment. However, the high cost and low elemental abundance of commercial electrodes limit its widespread application. This work tries to address this by introducing a charge-transfer rerouting strategy via cocatalyst modification using earth-abundant elements. Here, we uncover the role of the cocatalyst in enhancing electrode performance. The in-situ reconstructed cocatalyst induces a substantial rerouting of the charge transfer pathway, facilitating the mass/charge transfer of organics while concurrently suppressing the oxygen evolution side reaction. The Ti-Fe2O3 electrode, loaded with the cocatalyst PbO2, exhibits both high current efficiency (∼45.4 %) and low energy requirement (∼31.8 kW h kg-1 COD), surpassing other reported electrodes and displaying great versatility in various scenarios with good stability and reusability. Moreover, this charge-transfer rerouting strategy holds promise for synergy with other methodologies, such as nanostructure engineering and molecular imprinting, to further enhance the reactivity and selectivity of electrocatalysts in environment and energy-related domains.

Mass Transfer-Enhanced Photothermal Membranes with Synergistic Light Utilization for High-Turbidity Wastewater Purification

The photo-Fenton process faces significant limitations in treating high-turbidity, colored wastewater due to light attenuation and impurity interference (blocked mass transfer). To address these issues, we developed a suspended photothermal Fenton membrane by loading a photothermal catalyst on a hydrophobically modified cotton filter paper, enabling precise suspension 1 mm below the water surface. This design achieved 89.49 % light utilization and high chemical oxygen demand (COD) removal, even in wastewater with extreme chromaticity (10 multiples) and turbidity (703 NTU). The enhanced photothermal conversion accelerated molybdenum co-catalyzed Fenton reactions and improved peroxymonosulfate (PMS) activation, maintaining over 90 % phenol removal for 15 days. Mechanistic simulations revealed improved mass transfer of reactive oxygen species (ROS) and pollutants at the solid-liquid interface, with PMS diffusion identified as the rate-limiting step. The membrane resisted fouling from suspended solids and maintained stable operation in soil-containing solutions for 10 days. This innovative approach offers an efficient solution for degrading pollutants in dark-colored, high-turbidity wastewater, overcoming traditional process limitations.

Three-dimensionally structured MoS2@biochar breaks through the bottleneck in antibiotic wastewater treatment: Greater efficiency and self-motivated oxidation pathway

Two-dimensional (2D) MoS2 has been widely used to remove antibiotics. However, low selectivity for antibiotic pollutants, dependence on applied energy and oxidant, and secondary contamination are still the bottlenecks of this system for treating antibiotic wastewater. In this study, we proposed a three-dimensional (3D) material (3MoS2/BMBC@MF) based on MoS2 and biochar with melamine sponge as the backbone. Compared with the 2D material (MoS2/BMBC), 3MoS2/BMBC@MF performed significantly better in enrofloxacin (ENR) removal, with an increase in the removal degree from 60.8 % to 88.1 %, and acted mainly through the degradation pathway rather than relying solely on the adsorption effect. It was shown that the direct oxidation process (DOP) behind the 3D materials is the key to the self-activated oxidation pathway. The three-dimensional structure enhances the generation and transfer pathways of persistent free radicals (PFRs) and electrons, realizing a multi-dimensional activation mechanism through its unique three-dimensional network, which greatly improves the redox capacity of the material. Upon exposure to pollutants, 3MoS2/BMBC@MF generates carbon-centered radicals of PFRs, which degrade ENR through mediated electron transfer. Coupled with the three-dimensional structure that contributes to the homogeneous dispersion of the active substances, dense steric active centers are formed in the grid skeleton by redox cycling of Mo ions to degrade antibiotics via DOP. Meanwhile, 3MoS2/BMBC@MF possesses good recyclability and maintains high efficiency in recycling. The structural design of this material not only enhances the removal efficiency and reduces the environmental impact, but also provides new potentials and solutions for practical water treatment of antibiotic contaminants.

Comparative study on CeO2 catalysts with different morphologies and exposed facets for catalytic ozonation: performance, key factor and mechanism insight

Morphology and facet effects of metal oxides in heterogeneous catalytic ozonation (HCO) are attracting increasing interests. In this paper, the different HCO performances for degradation and mineralization of phenol of seven ceria (CeO2) catalysts, including four with different morphologies (nanorod, nanocube, nanooctahedron and nanopolyhedron) and three with the same nanorod morphology but different exposed facets, are comparatively studied. CeO2 nanorods with (110) and (100) facets exposed show the best performance, much better than that of single ozonation, while CeO2 nanocubes and nanooctahedra show performances close to single ozonation. The underlying reason for their different HCO performances is revealed using various experimental and density functional theory (DFT) calculation results and the possible catalytic reaction mechanism is proposed. The oxygen vacancy (OV) is found to be pivotal for the HCO performance of the different CeO2 catalysts regardless of their morphology or exposed facet. A linear correlation is discerned between the rate of catalytic decomposition of dissolved ozone (O3) and the density of Frenkel-type OV. DFT calculations and in-situ spectroscopic studies ascertain that the existence of OV can boost O3 activation on both the hydroxyl (OH) and Ce sites of CeO2. Conversely, various facets without OV exhibit similar O3 adsorption energies. The OH group plays an important role in activating O3 to produce hydroxyl radical (∙OH) for improved mineralization. This work may offer valuable insights for designing Facet- and OV-regulated catalysts in HCO for the abatement of refractory organic pollutants.

Progress and limitations in reactive oxygen species quantitation

Reactive oxygen species (ROS) are a set of oxygen- and nitrogen-containing radicals. They are produced from a wide range of sources. In biological contexts, cellular stress leads to an overproduction of ROS, which can lead to genetic damage and disease development. In industry, ROS are often productively used for water purification or for analyzing the possible toxicity of an industrial process. Because of their ubiquity, detection of ROS has been an analytical goal across a range of fields. To understand complicated systems and origins of ROS production, it is necessary to move from qualitative detection to quantitation. Analytical techniques that combine quantitation, high spatial and temporal resolution, and good specificity represent detection methods that can fill critical gaps in ROS research. Herein, we discuss the continued progress and limitations of fluorescence, electrochemical, and electron paramagnetic resonance detection of ROS over the last ten years, giving suggestions for the future of the field.

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.

Quantification of the Contribution of Heterogeneous Surface Processes to Pollutant Abatement during Heterogeneous Catalytic Ozonation

Heterogeneous surface processes such as adsorption and oxidation with surface-adsorbed reactive oxygen species (ROSad, e.g., adsorbed oxygen atom (*Oad) and hydroxyl radicals (•OHad)) have been suggested to play an important role in pollutant abatement during heterogeneous catalytic ozonation (HCO). However, to date, there is no reliable method to quantitatively evaluate the contribution of heterogeneous surface processes to pollutant abatement (fS) during HCO. In this study, we developed a method by combining probe compound-based experiments with kinetic modeling to distinguish heterogeneous surface processes from homogeneous bulk reactions with aqueous O3 and ROS (•OH and superoxide radicals (O2•-) in the abatement of various pollutants (e.g., atrazine, ibuprofen, tetrachloroethylene, and perfluorooctanoic acid) during HCO with reduced graphene oxide. The results show that the pollutants that have a low affinity for the rGO surface (e.g., ibuprofen and tetrachloroethylene) were essentially abated by homogeneous bulk reactions, while the contribution of heterogeneous surface processes was negligible (fS < 5%). In contrast, heterogeneous surface processes played an important or even dominant role in the abatement of pollutants that have a high surface affinity (e.g., fS = 32-82% for atrazine and perfluorooctanoic acid). This study is a critical first step in quantitatively evaluating the role of heterogeneous surface processes for pollutant abatement during HCO, which is crucial to understanding the mechanism of HCO and designing catalysts for effective pollutant abatement.

Non-radical oxidation driven by iron-based materials without energy assistance in wastewater treatment

Chemical oxidation is extensively utilized to mitigate the impact of organic pollutants in wastewater. The non-radical oxidation driven by iron-based materials is noted for its environmental friendliness and resistance to wastewater matrix, and it is a promising approach for practical wastewater treatment. However, the complexity of heterogeneous systems and the diversity of evolutionary pathways make the mechanisms of non-radical oxidation driven by iron-based materials elusive. This work provides a systematic review of various non-radical oxidation systems driven by iron-based materials, including singlet oxygen (1O2), reactive iron species (RFeS), and interfacial electron transfer. The unique mechanisms by which iron-based materials activate different oxidants (ozone, hydrogen peroxide, persulfate, periodate, and peracetic acid) to produce non-radical oxidation are described. The roles of active sites and the unique structures of iron-based materials in facilitating non-radical oxidation are discussed. Commonly employed identification methods in wastewater treatment are compared, such as quenching, chemical probes, spectroscopy, mass spectrometry, and electrochemical testing. According to the process of iron-based materials driving non-radical oxidation to remove organic pollutants, the driving factors at different stages are summarized. Finally, challenges and countermeasures are proposed in terms of mechanism exploration, detection methods and practical applications of non-radical oxidation driven by iron-based materials. This work provides valuable insights for understanding and developing non-radical oxidation systems.

Self-supporting three-dimensional CuNi-Sb-SnO2 anode with ultra-long service life for efficient removal of antibiotics in wastewater

Electrochemical ozone production (EOP) is a promising technology for the removal of contaminants in wastewater. However, traditional two-dimensional anodes for EOP are restricted by their reliance on substrates and limited surface area, thus exhibiting poor stability and efficiency. Herein, a novel three-dimensional Sb-SnO2 with Cu and Ni co-doped (3D CuNi-ATO) was synthesized via a facile pressing-sintering method without the Ti substrate. 3D CuNi-ATO had a specific surface area two orders of magnitude higher than conventional CuNi-ATO/Ti, as well as the significant capability of EOP that differs from intrinsic 3D ATO. This endowed 3D CuNi-ATO with the capability to remove tetracycline with a pseudo-first-order rate constant of 0.033 min-1 under a low current density of 5 mA cm-2 within 120 min, which was far more efficient than that by 3D ATO and other two-dimensional anodes reported. The 3D CuNi-ATO was confirmed stable in 100 cycles and had an accelerated service lifetime of over 1100 h versus 83 h of CuNi-ATO/Ti. The degradation of tetracycline in complex matrix and flow-through reactors further revealed the promising potential of 3D CuNi-ATO to be applied in scenarios of practical application and continuous high-rate treatment.

Mn-Fe Dual-Metal Assemblages on Carbon-Coated Al2O3 Spheres for Catalytic Ozonation Oxidation: Structure, Performance, and Reaction Mechanism

Catalysts with high catalytic activity and low production cost are important for industrial application of heterogeneous catalytic ozonation (HCO). In this study, we designed a carbon-coated aluminum oxide carrier (C-Al2O3) and reinforced it with Mn-Fe bimetal assemblages to prepare a high-performance catalyst Mn-Fe/C-Al2O3. The results showed that the carbon embedding significantly improved the abundance of surface oxygen functional groups, conductivity, and adsorption capacity of γ-Al2O3, while preserving its exceptional mechanical strength as a carrier. The prepared Mn-Fe/C-Al2O3 catalyst exhibited satisfactory catalytic ozonation activity and stability in the degradation of p-nitrophenol (PNP). Electron paramagnetic resonance (EPR) and quenching experiments reveal that radical ( ⋅ OH and ⋅ O2 ⋅ ) and nonradical oxidation (1O2) dominated the PNP degradation process. Theoretical calculations corroborated that the anchored atomic Fe and Mn sites regulated the local electronic structure of the catalyst. This modulation effectively promoted the activation of O3 molecules, resulting in the generation of atomic oxygen species (AOS) and reactive oxygen species (ROS). The economic analysis on Mn-Fe/C-Al2O3 revealed that it was a cost-competitive catalyst for HCO. This study not only deepens the understanding on the reaction mechanism of HCO with transition metal/carbon composite catalysts, also provides a high-performance and cost-competitive ozone catalyst for prospective application.

High-efficient M-NC single-atom catalysts for catalytic ozonation in water purification: Performance and mechanisms

Heterogeneous catalytic ozonation (HCO) holds promise in water purification but suffers from limited accessible metal sites, metal leaching, and unclear structure-activity relationships. This work reported M-NC (M=Co, Ni, Fe, and Mn) single-atom catalysts (SACs) with high atomic efficiency and minimal metal release. The new HCO systems, especially the Co-based system, exhibited impressive performance in various refractory contaminant removal, involving various reactive species generation, such as •OHads, •OHfree, *O, and 1O2. For sulfamethoxazole removal, the normalized kobs for Co-NC, Ni-NC, Fe-NC, and Mn-NC were determined as 13.53, 3.94, 3.55, and 4.13 min-1·mMmetal-1·g·m-2 correspondingly, attributed to the abundant acid sites, faster electron transfer, and lower energy required for O3 decomposition and conversion. The metal atoms and hydroxyl groups, individually serving as Lewis and Bronsted acid sites (LAS and BAS), were the primary centers for •OH generation and O3 adsorption. The relationships between active sites and both O3 utilization and •OH generation were found. LAS and BAS were responsible for O3 adsorption, while strong LAS facilitated O3 conversion into •OH. Theoretical calculations revealed the catalytic mechanisms involved O3→ *O→ *OO→ O3•-→ •OH. This work highlights the significance of SAC design for HCO and advances the understanding of atomic-level HCO behavior.

Enhanced Photocatalytic Ozonation Using Modified TiO2 With Designed Nucleophilic and Electrophilic Sites

Photocatalytic ozonation is considered to be a promising approach for the treatment of refractory organic pollutants, but the design of efficient catalyst remains a challenge. Surface modification provides a potential strategy to improve the activity of photocatalytic ozonation. In this work, density functional theory (DFT) calculations were first performed to check the interaction between O3 and TiO2-OH (surface hydroxylated TiO2) or TiO2-F (surface fluorinated TiO2), and the results suggest that TiO2-OH displays better O3 adsorption and activation than does TiO2-F, which is confirmed by experimental results. The surface hydroxyl groups greatly promote the O3 activation, which is beneficial for the generation of reactive oxygen species (ROS). Importantly, TiO2-OH displays better performance towards pollutants (such as berberine hydrochloride) removal than does TiO2-F and most reported ozonation photocatalysts. The total organic carbon (TOC) removal efficiency reaches 84.4 % within two hours. This work highlights the effect of surface hydroxylation on photocatalytic ozonation and provides ideas for the design of efficient photocatalytic ozonation catalysts.

MgO-loaded tubular ceramic membrane with spatial nanoconfinement for enhanced catalytic ozonation in refractory wastewater treatment

Heterogeneous catalytic ozonation (HCO) enables the destruction of organic pollutants in wastewater via oxidation by powerful hydroxyl radicals (·OH). However, the availability of short-lived ·OH in aqueous bulk is low in practical treatment scenarios due to mass transfer limitations and quenching of water constituents. Herein, we overcome these challenges by loading MgO catalysts inside the pores of a tubular ceramic membrane (denoted as CCM) to confine ·OH within the nanopores and achieve efficient pollutant removal. When the pore size of the membrane was reduced from 1000 to 50 nm, the removal of ibuprofen (IBU) by CCM was increased from 49.6 % to 90.2 % due to the enhancement of ·OH enrichment in the nanospace. In addition, the CCM exhibited high catalytic activity in the presence of co-existing ions and over a wide pH range, as well as good self-cleaning ability in treating secondary wastewater. The experimental results revealed that ·OH were the dominant reactive oxygen species (ROS) in pollutant degradation, while surface hydroxyl groups were active sites for the generation of ·OH via ozone decomposition. This work provides a promising strategy to enhance the utilization of ·OH in HCO for the efficient degradation of organic pollutants in wastewater under spatial confinement.

Design and synthesis of LDH nano composite functionalized with trimesic acid and its environmental application in adsorbing organic dyes indigo carmine and methylene blue

This work designed and prepared an organic-inorganic nanocomposite using layered double hydroxide (LDH) inorganic substrate and trimesic acid (TMA) as chelating agent. Subsequently, the synthesized organic-inorganic nanocomposite was assessed using multiple identification methods, including FTIR, EDX, XRD, TGA, and FESEM, and the outcomes demonstrated that the intended structure was successfully prepared. Also, in order to investigate the efficiency of the Mg-Al LDH-TMA nanocomposite as an efficient nano adsorbent, it was used for removal of indigo carmine (IC) and methylene blue (MB) from aqueous solutions. This synthetic nanocomposite showed a high adsorption capacity. The efficiency of the produced nanocomposite in the adsorption of selected dyes was investigated with the help of batch adsorption studies performed in a variety of experimental settings, including dye concentration, adsorbent dose, pH, adsorption temperature and contact time. Furthermore, the produced Mg-Al LDH-TMA nanocomposite exhibits strong stability and can be recycled and reused five times in a row, which is well consistent with the principles of green chemistry.

Nanoscale Sequential Reactor Design Achieves Effective Removal of Disinfection Byproduct Precursors in Catalytic Ozonation

Transforming dissolved organic matter (DOM) is a crucial approach to alleviating the formation of disinfection byproducts (DBPs) in water treatment. Although catalytic ozonation effectively transforms DOM, increases in DBP formation potential are often observed due to the accumulation of aldehydes, ketones, and nitro compound intermediates during DOM transformation. In this study, we propose a novel strategy for the sequential oxidation of DOM, effectively reducing the levels of accumulation of these intermediates. This is achieved through the development of a catalyst with a tailored surface and nanoconfined active sites for catalytic ozonation. The catalyst features a unique confinement structure, wherein Mn-N4 moieties are uniformly anchored on the catalyst surface and within nanopores (5-20 Å). This design enables the degradation of the large molecular weight fraction of DOM on the catalyst surface, while the transformed smaller molecular weight fraction enters the nanopores and undergoes rapid degradation due to the confinement effect. The generation of *Oad as the dominant reactive species is essential for effectively reducing these ozone refractory intermediates. This resulted in over 70% removal of carbonaceous and nitrogenous DBP precursors as well as brominated DBP precursors. This study highlights the importance of the nanoscale sequential reactor design and provides new insights into eliminating DBP precursors by the catalytic ozonation process.

Efficient Ozone Elimination Over MnO2 via Double Moisture-Resistance Protection of Active Carbon and CeO2

The widespread ozone (O3) pollution is extremely hazardous to human health and ecosystems. Catalytic decomposition into O2 is the most promising method to eliminate ambient O3, while the fast deactivation of catalysts under humid conditions remains the primary challenge for their application. Herein, we elaborately developed a splendidly active and stable Mn-based catalyst with double hydrophobic protection of active carbon (AC) and CeO2 (CeMn@AC), which possessed abundant interfacial oxygen vacancies and excellent desorption of peroxide intermediates (O22-). Under extremely humid (RH = 90%) conditions and a high space velocity of 1200 L h-1 g-1, the optimized CeMn@AC achieved nearly 100% O3 conversion (140 h) at 5 ppm, showing unprecedented catalytic activity and moisture resistance toward O3 decomposition. In situ DRIFTS and theory calculations confirmed that the exceptional moisture resistance of CeMn@AC was ascribed to the double protection effect of AC and CeO2, which cooperatively prevented the competitive adsorption of H2O molecules and their accumulation on the active sites of MnO2. AC provided a hydrophobic reaction environment, and CeO2 further alleviated moisture deterioration of the MnO2 particles exposed on the catalyst surface via the moisture-resistant oxygen vacancies of MnO2-CeO2 crystal boundaries. This work offers a simple and efficient strategy for designing moisture-resistant materials and facilitates the practical application of the O3 decomposition catalysts in various environments.

Ferromanganese oxide-functionalized TiO2 for rapid catalytic ozonation of PPCPs through a coordinated oxidation process with adjusted composition and strengthened generation of reactive oxygen species

Ferromanganese oxide (MFOx) was first utilized to functionalize TiO2 and an MFOx@TiO2 catalyst was developed for catalytic ozonation for rapid attack of pharmaceutical and personal care products (PPCPs) with adjusted reactive oxygen species (ROSs) composition and strengthened ROSs generation. Unlike Al2O3, which strongly relied on adsorption and was significantly influenced by MFOx loading, synergistic catalytical effects of MFOx and TiO2 were observed, and optimal MFOx doping of 2 wt% and MFOx@TiO2 dosage of 500 ppm were obtained for catalyzing ozonation. In ibuprofen (IBP) degradation, MFOx@TiO2-catalyzed ozonation (MFOx@TiO2/O3) obtained 2.0-, 4.7- and 6.9-folds the kobs of TiO2/O3, MFOx/O3 and bare ozonation (B/O3). Stronger O3 decomposition was observed by MFOx@TiO2 over bare TiO2 with the participation of redox pairs Fe(II)/Fe(III) and Mn(II)/Mn(III)/Mn(IV) and increased surface oxygen vacancies (SOVs) from 9.8 % to 33.7 % was detected. The results revealed that Fe(II), Mn(II) and Mn(III) with low valance accelerated Ti(III) generation from Ti(VI), obtaining an unprecedented high Ti(III) composition occupying 35.3 % of the total Ti atoms. Ti(III) catalyzed the direct reduction of SOVs-O2 to •O2-, and it accelerated the formation of Ti(VI)-OH and Ti(VI)-O which catalyzed O3 decomposition into •O2-. •O2- was found to primarily initiate IBP degradation with nucleophilic addition and dominated over 66 % IBP removal. The enhanced •O2- generation further strengthened •OH and 1O2 production. MFOx@TiO2/O3 obtained 17 %, 21 % and 30 % higher TOC removal over TiO2/O3, MFOx/O3 and B/O3, respectively. Acute toxicity tests confirmed the effective toxicity control of organics by MFOx@TiO2/O3 process (inhibition rate: 10.9 %). Degradation test of atenolol and sulfamethoxazole confirmed the catalytic effects of MFOx@TiO2. MFOx@TiO2 performed strong resistance to water matrix in application test and showed good stability and reusability. The study proposed an effective catalyst for strengthening the ozonation process on PPCPs degradation and provided an in-depth understanding of the mechanisms and characteristics of the MFOx@TiO2 catalyst and MFOx@TiO2/O3 process.

Catalytic ozonation of reverse osmosis concentrate from coking wastewater reuse by surface oxidation over Mn-Ce/γ-Al2O3: Effluent organic matter transformation and its catalytic mechanism

Degradation of organics in high-salinity wastewater is beneficial to meeting the requirement of zero liquid discharge for coking wastewater treatment. Creating efficient and stable performance catalysts for high-salinity wastewater treatment is vital in catalytic ozonation process. Compared with ozonation alone, Mn and Ce co-doped γ-Al2O3 could remarkably enhance activities of catalytic ozonation for chemical oxygen demand (COD) removal (38.9%) of brine derived from a two-stage reverse osmosis treatment. Experimental and theoretical calculation results indicate that introducing Mn could increase the active points of catalyst surface, and introducing Ce could optimize d-band electronic structures and promote the electron transport capacity, enhancing HO• bound to the catalyst surface ([HO•]ads) generation. [HO•]ads plays key roles for degrading the intermediates and transfer them into low molecular weight organics, and further decrease COD, molecular weights and number of organics in reverse osmosis concentrate. Under the same reaction conditions, the presence of Mn/γ-Al2O3 catalyst can reduce ΔO3/ΔCOD by at least 37.6% compared to ozonation alone. Furthermore, Mn-Ce/γ-Al2O3 catalytic ozonation can reduce the ΔO3/ΔCOD from 2.6 of Mn/γ-Al2O3 catalytic ozonation to 0.9 in the case of achieving similar COD removal. Catalytic ozonation has the potential to treat reverse osmosis concentrate derived from bio-treated coking wastewater reclamation.

In-situ growth of Mn-Ni3S2 on nickel foam for catalytic ozonation of p-nitrophenol

In this study, a new catalyst for catalytic ozonation was obtained by in-situ growth of Mn-Ni3S2 nanosheets on the surface of nickel foam (NF). The full degradation of p-nitrophenol (PNP) was accomplished under optimal conditions in 40 min. The effects of material dosage, ozone dosage, pH and the presence of inorganic anions on the degradation efficiency of PNP were investigated. ESR analysis showed that singlet oxygen (1O2) and superoxide radical (O2•-) are the main contributors of PNP degradation. This study offers a new combination of supported catalysts with high efficiency and easy recovery, which provides a new idea for wastewater treatment.

Synergetic Manipulation Mechanism of Single-Atom M-N4 and M-OH (M = Mn, Fe, Co, Ni) Sites for Ozone Activation: Theoretical Prediction and Experimental Verification

Carbon-based single-atom catalysts (SACs) have been gradually introduced in heterogeneous catalytic ozonation (HCO), but the interface mechanism of O3 activation on the catalyst surface is still ambiguous, especially the effect of a surface hydroxyl group (M-OH) at metal sites. Herein, we combined theoretical calculations with experimental verifications to comprehensively investigate the O3 activation mechanisms on a series of conventional SAC structures with N-doped nanocarbon substrates (MN4-NCs, where M = Mn, Fe, Co, Ni). The synergetic manipulation effect of the metal atom and M-OH on O3 activation pathways was paid particular attention. O3 tends to directly interact with the metal atom on MnN4-NC, FeN4-NC, and NiN4-NC catalysts, among which MnN4-NC has the best catalytic activity for its relatively lower activation energy barrier of O3 (0.62 eV) and more active surface-adsorbed oxygen species (Oads). On the CoN4-NC catalyst, direct interaction of O3 with the metal site is energetically infeasible, but O3 can be activated to generate Oads or HO2 species from direct or indirect participation of M-OH sites. The experimental results showed that 90.7 and 82.3% of total organic carbon (TOC) was removed within 40 min during catalytic ozonation of p-hydroxybenzoic acid with MnN4-NC and CoN4-NC catalysts, respectively. Phosphate quenching, catalyst characterization, and EPR measurement further supported the theoretical prediction. This contribution provides fundamental insights into the O3 activation mechanism on SACs, and the methods and ideals could be helpful for future studies of environmental catalysis.

Tailored Metal-Organic Frameworks for Water Purification: Perfluorinated Fe-MOFs for Enhanced Heterogeneous Catalytic Ozonation

An industrially viable catalyst for heterogeneous catalytic ozonation (HCO) in water purification requires the characteristics of good dispersion of active species on its surface, efficient electron transfer for ozone decay, and maximum active species utilization. While metal-organic frameworks (MOFs) represent an attractive platform for HCO, the metal nodes in the unmodified MOFs exhibit low catalytic activity. Herein, we present a perfluorinated Fe-MOF catalyst by substituting H atoms on the metalated ligands with F atoms (termed 4F-MIL-88B) to induce structure evolution. The Lewis acidity of 4F-MIL-88B was enhanced via the formation of Fe nodes, tailoring the electron distribution on the catalyst surface. As a result of catalyst modification, the rate constant for degradation of the target compounds examined increased by ∼700% compared with that observed for the unmodified catalyst. Experimental evidence and theoretical calculations showed that the modulated polarity and the enhanced electron transfer between the catalyst and ozone molecules contributed to the adsorption and transformation of O3 to •OH on the catalyst surface. Overall, the results of this study highlight the significance of tailoring the metalated ligands to develop highly efficient and stable MOF catalysts for HCO and provide an in-depth mechanistic understanding of their structure-function evolution, which is expected to facilitate the applications of nanomaterial-based processes in water purification.

Application of catalytic ozonation using Y zeolite in the elimination of pharmaceuticals in effluents from municipal wastewater treatment plants

Catalytic ozonation using faujasite-type Y zeolite with two different SiO2/Al2O3 molar ratios (60 and 12) was evaluated for the first time in the removal of 25 pharmaceutical compounds (PhCs) present in real effluents from two municipal wastewater treatment plants both located in the Mediterranean coast of Spain. Additionally, control experiments including adsorption and direct ozonation, were conducted to better understand the fundamental aspects of the different individual systems in wastewater samples. Commercial zeolites were used in sodium form (NaY). The results showed that the simultaneous use of ozone and NaY zeolites significantly improved the micropollutants degradation rate, able to degrade 95 % of the total mixture of PhCs within the early 9 min using the zeolite NaY-12 (24.4 mg O3 L-1 consumed), while 12 min of reaction with the zeolite NaY-60 (31 mg O3 L-1 consumed). In the case of individual experiments, ozonation removed 95 % of the total mixture of PhCs after 25 min (46.2 mg O3 L-1 consumed), while the direct adsorption, after 60 min of contact time, eliminated 30 % and 44 % using the NaY-12 and NaY-60 zeolites, respectively. Results showed that the Brønsted acid sites seemed to play an important role in the effectiveness of the treatment with ozone. Finally, the environmental assessment showed that the total risk quotients of pharmaceuticals were reduced between 87 %-99 % after ozonation in the presence of NaY-60 and NaY-12 zeolites. The results of this study demonstrate that catalytic ozonation using NaY zeolites as catalysts is a promising alternative for micropollutant elimination in real-world wastewater matrices.

Insight into roles of carbon anodes for removal of refractory organic contaminants in electro-peroxone system: Mechanism, performance and stability

Electro-peroxone (EP) is a novel technique for the removal of refractory organic contaminants (ROCs), while the role of anode in this system is neglected. In this work, the EP system with graphite felt anode (EP-GF) and activated carbon fiber anode (EP-ACF) was developed to enhance ibuprofen (IBP) removal. The results showed that 91.2% and 98.6% of IBP was removed within 20 min in EP-GF and EP-ACF, respectively. Hydroxy radical (O⋅H) was identified as the dominant reactive species, contributing 80.9% and 54.0% of IBP removal in EP-ACF and EP-GF systems, respectively. The roles of adsorption in EP-ACF and direct electron transfer in EP-GF cannot be ignored. Due to the differences in mechanism, EP-GF and EP-ACF systems were suitable for the removal of O⋅H-resistant ROCs (e.g., oxalic acid and pyruvic acid) and non-O⋅H-resistant ROCs (e.g., IBP and nitrobenzene), respectively. Both systems had excellent stability relying on the introduction of oxygen functional groups on the anode, and their electrolysis energy consumption was significantly lower than that of EP-Pt system. The three degradation pathways of IBP were proposed, and the toxicity of intermediates were evaluated. In general, carbon anodes have a good application prospect in the removal of ROCs in EP systems.

Activation of peroxymonosulfate with natural pyrite-biochar composite for sulfamethoxazole degradation in soil: Organic matter effects and free radical conversion

Peroxymonosulfate (PMS)-based advanced oxidation processes (AOPs) represent an effective method for the remediation of antibiotic-contaminated soils. In this study, a natural pyrite-biochar composite material (FBCx) was developed, demonstrating superior activation performance and achieving a 76% removal rate of SMX from soil within 120 min. There existed different degradation mechanisms for SMX in aqueous and soil solutions, respectively. The production of 1O2 and inherent active species produced by soil slurry played an important role in the degradation process. The combination of electron paramagnetic resonance (EPR) and free radical probe experiments confirmed the presence of free radical transformation processes in soil. Wherein, the·OH and SO4·- generated in soil slurry did not directly involve in the degradation process, but rather preferentially reacted with soil organic matter (SOM) to form alkyl-like radicals (R·), thereby maintaining a high concentration of reactive species in the system. Furthermore, germination and growth promotion of mung bean seeds observed in the toxicity test indicated the environmental compatibility of this remediation method. This study revealed the influence mechanism of SOM in the remediation process of contaminated soil comprehensively, which possessed enormous potential for application in practical environments.

Performance evaluation and optimization of a suspension-type reactor for use in heterogeneous catalytic ozonation

Packed fixed-bed reactors are traditionally used for heterogeneous catalytic ozonation. However, a high solid-to-liquid requirement, poor ozone dissolution, ineffective utilization of catalyst surface area, and production of large amounts of catalyst waste impede application of such reactors. In this study, we designed a suspension catalytic ozonation reactor and compared the performance of this reactor with that of a traditional fixed-bed catalytic ozonation reactor employing oxalic acid (OA) as the target contaminant. Our results showed that total O3 dissolved into the suspension reactor (117-134 mg.L-1) was much higher compared to that measured in the fixed-bed reactor (53 mg.L-1) due to a higher O3(g) interphase mass transfer rate in the suspension reactor. In accordance with the higher O3(g) interphase mass transfer, we observed a much higher proportional OA removal (32 %) compared to that achieved in the fixed-bed reactor (10%) employing an Fe-oxide catalyst supported on Al2O3 (Fe-oxide@Al2O3) in both reactors. Use of a double-layered Cu-Al hydroxide (Cu-Al LDHs) catalyst in the suspension reactor further enhanced the performance with nearly 90 % OA removal observed. Given the superior performance of the suspension reactor, we investigated the impact of operating conditions (catalyst dosage, hydraulic retention time and ozone dosage) employing Cu-Al LDHs as the catalyst. We also developed a mathematical kinetic model to describe the performance of the suspension reactor and, through use of the kinetic model, showed that O3(g) interphase transfer rate was the rate-limiting step in OA removal. Thus, improvement in ozone gas diffuser design is required to improve the performance of the suspension reactor. Overall, the present study demonstrated that suspension reactors were more effective than fixed-bed reactors for oxidation of surface-active organic compounds such as OA due to the higher ozone interphase mass transfer rate and effective utilization of the catalyst surface area that can be achieved. As such, further research on suspension reactor design and development of catalysts suitable for use in suspension reactors should facilitate large-scale application of catalytic ozonation processes by the wastewater treatment industry.

Effect of pH on the ozonolysis degradation of p-nitrophenol in aquatic environment and the synergistic effect of hydroxy radical

Density functional theory (DFT) was employed to elucidate the mechanisms for ozonolysis reaction of p-nitrophenol (PNP) and its anion form aPNP. Thermodynamic data, coupled with Average Local Ionization Energies (ALIE) analysis, reveal that the ortho-positions of the OH/O- groups are the most favorable reaction sites. Moreover, rate constant calculations demonstrate that the O3 attack on the C2-C3 bond is the predominant process in the reaction between neutral PNP and O3. For the aPNP + O3 reaction, the most favorable pathways involve O3 attacking the C1-C2 and C6-C1 bonds. The rate constant for PNP ozonolysis positively correlates with pH, ranging from 5.47 × 108 to 2.86 × 109 M-1 s-1 in the natural aquatic environment. In addition, the formation of hydroxyl radicals in the ozonation process of PNP and the mechanisms of its synergistic reaction of PNP with ozone were investigated. Furthermore, the ozonation and hydroxylation processes involving the intermediate OH-derivatives were both thermodynamically and kinetic analyzed, which illustrate that OH radicals could promote the elimination of PNP. Finally, the toxic of PNP and the main products for fish, daphnia, green algae and rat were assessed. The findings reveal that certain intermediates possess greater toxicity than the original reactant. Consequently, the potential health risks these compounds pose to organisms warrant serious consideration.

Defluorination of perfluorooctanoic acid and perfluorooctane sulfonic acid by heterogeneous catalytic system of Fe-Al2O3/O3: Synergistic oxidation effects and defluorination mechanism

In this study, catalytic ozonation by Fe-Al2O3 was used to investigate the defluorination of PFOA and PFOS, assessing the effects of different experimental conditions on the defluorination efficiency of the system. The oxidation mechanism of the Fe-Al2O3/O3 system and the specific degradation and defluorination mechanisms for PFOA and PFOS were determined. Results showed that compared to the single O3 system, the defluorination rates of PFOA and PFOS increased by 2.32- and 5.92-fold using the Fe-Al2O3/O3 system under optimal experimental conditions. Mechanistic analysis indicated that in Fe-Al2O3, the variable valence iron (Fe) and functional groups containing C and O served as important reaction sites during the catalytic process. The co-existence of 1O2, OH, O2- and high-valence Fe(IV) constituted a synergistic oxidation system consisting of free radicals and non-radicals, promoting the degradation and defluorination of PFOA and PFOS. DFT theoretical calculations and the analysis of intermediate degradation products suggested that the degradation pathways of PFOA and PFOS involved Kolbe decarboxylation, desulfonation, alcoholization and intramolecular cyclization reactions. The degradation and defluorination pathways of PFOA and PFOS consisted of the stepwise removal of -CF2-, with PFOS exhibiting a higher defluorination rate than PFOA due to its susceptibility to electrophilic attack. This study provides a theoretical basis for the development of heterogeneous catalytic ozonation systems for PFOA and PFOS treatment.

Ozone-Induced Rapid and Green Synthesis of Polydopamine Coatings with High Uniformity and Enhanced Stability

The development of green, controllable, and simplified pathways for rapid dopamine polymerization holds significant importance in the field of polydopamine (PDA) surface chemistry. In this study, a green strategy is successfully devised to accelerate and control the polymerization of dopamine through the introduction of ozone (O3 ). The findings reveal that ozone serves as an eco-friendly trigger, significantly accelerating the dopamine polymerization process across a broad pH range, spanning from 4.0 to 10.0. Notably, the deposition rate of PDA coatings on a silicon wafer reaches an impressive value of ≈64.8 nm h-1 (pH 8.5), which is 30 times higher than that of traditional air-assisted PDA and comparable to the fastest reported method. Furthermore, ozone exhibits the ability to accelerate dopamine polymerization even under low temperatures. It also enables control over the inhibition-initiation of the polymerization process by regulating the "ON/OFF" mode of the ozone gas. Moreover, the ozone-induced PDA coatings demonstrate exceptional characteristics, including high homogeneity, good hydrophilicity, and remarkable chemical and mechanical stability. Additionally, the ozone-induced PDA coatings can be rapidly and effectively deposited onto a wide range of substrates, particularly those that are adhesion-resistant, such as polytetrafluoroethylene (PTFE).

3D Carbon Microspheres with a Maze-Like Structure and Large Mesopore Tunnels Built From Rapid Aerosol-Confined Coherent Salt/Surfactant Templating

Hierarchically porous carbons with tailor-made properties are essential for applications wherein rich active sites and fast mass transfer are required. Herein, a rapid aerosol-confined salt/surfactant templating approach is proposed for synthesizing hierarchically porous carbon microspheres (HPCMs) with a maze-like structure and large mesopore tunnels for high-performance tri-phase catalytic ozonation. The confined assembly in drying microdroplets is crucial for coherent salt (NaCl) and surfactant (F127) dual templating without macroscopic phase separation. The HPCMs possess tunable sizes, a maze-like structure with highly open macropores (0.3-30 µm) templated from NaCl crystal arrays, large intrawall mesopore tunnels (10-45 nm) templated from F127, and rich micropores (surface area >1000 m2 g-1 ) and oxygen heteroatoms originated from NaCl-confined carbonization of phenolic resin. The structure formation mechanism of the HPCMs and several influencing factors on properties are elaborated. The HPCMs exhibit superior performance in gas-liquid-solid tri-phase catalytic ozonation for oxalate degradation, owing to their hierarchical pore structure for fast mass transfer and rich defects and oxygen-containing groups (especially carbonyl) for efficient O3 activation. The reactive oxygen species responsible for oxalate degradation and the influences of several structure parameters on performance are discussed. This work may provide a platform for producing hierarchically porous materials for various applications.

Singlet oxygen: Properties, generation, detection, and environmental applications

Singlet oxygen (1O2) is molecular oxygen in the excited state with high energy and electrophilic properties. It is widely found in nature, and its important role is gradually extending from chemical syntheses and medical techniques to environmental remediation. However, there exist ambiguities and controversies regarding detection methods, generation pathways, and reaction mechanisms which have hindered the understanding and applications of 1O2. For example, the inaccurate detection of 1O2 has led to an overestimation of its role in pollutant degradation. The difficulty in detecting multiple intermediate species obscures the mechanism of 1O2 production. The applications of 1O2 in environmental remediation have also not been comprehensively commented on. To fill these knowledge gaps, this paper systematically discussed the properties and generation of 1O2, reviewed the state-of-the-art detection methods for 1O2 and long-standing controversies in the catalytic systems. Future opportunities and challenges were also discussed regarding the applications of 1O2 in the degradation of pollutants dissolved in water and volatilized in the atmosphere, the disinfection of drinking water, the gas/solid sterilization, and the self-cleaning of filter membranes. This review is expected to provide a better understanding of 1O2-based advanced oxidation processes and practical applications in the environmental protection of 1O2.

Redox property of coordinated iron ion enables activation of O2 via in-situ generated H2O2 and additionally added H2O2 in EDTA-chelated Fenton reaction

The Fenton system was a generation system of reactive oxygen species via the chain reactions, which employed H2O2 and O2 as radical precursors and Fe2+/Fe3+ as electron-donor/acceptor for triggering or terminating the generation of radicals. Recent work mainly emphasized the Fe2+- activated H2O2 and the application of in-situ generated •OH, while neglecting other side-reactions. In this work, EDTA (Ethylene diamine tetraacetic acid) was employed as a chelating agent of iron ions, which simultaneously changed the redox property of coordinated iron. The Fe2+-EDTA complexes in the presence of dissolved oxygen enabled the two-electron transfer from Fe2+ to O2 and the in-situ production of H2O2, which further activate H2O2 for yielding •OH. Meanwhile, coordinated Fe3+ exhibited non-negligible reactivity toward H2O2, which was higher than that of free Fe3+ in the traditional Fenton system. The complexation of EDTA with Fe3+ could enhance the Fe2+ generation reaction by the H2O2, accompanied by the O2•- formation. The enhancement of O2•- formation and Fe2+-EDTA regeneration induced the subsequent H2O2 activation by Fe2+-EDTA, thus accelerating the Fe3+-EDTA/Fe2+-EDTA cycle for simultaneously producing O2•- and •OH. To sum up, the EDTA-chelated Fenton system extended the applicable pH range to circumneutral/alkaline level and tuned the redox property of coordinated iron for diversifying the •OH production routes. The research reinterpreted the chain reactions in the Fenton system, revealing another way to enhance the radical production or other property of the Fenton/Fenton-like system.

Unveiling the traits of dry and wet pre-magnetized zero-valent iron-activated peroxymonosulfate: Degradation of oxytetracycline

It has been previously reported that pre-magnetization could enhance the efficacy of zero-valent iron (ZVI) in removing contaminants. However, little is known about the effects and persistence of different magnetization methods on pre-magnetized ZVI (Pre-ZVI) when used in advanced oxidation processes (AOPs). Gaining a comprehensive understanding of the durability of various pre-magnetization methods in enhancing the removal efficiency of different pollutants will significantly impact the widespread utilization of Pre-ZVI in practical engineering. Herein, we investigated the efficiency of dry and wet Pre-ZVI-activated peroxymonosulfate (PMS) in eliminating oxytetracycline (OTC) and evaluated the durability of Pre-ZVI. Additionally, we examined several factors that influence the degradation process's efficiency. Our results found that the reaction constant k values corresponding to the dry Pre-ZVI/PMS system at the pH values of 3, 7, and 9 varied from approximately 0.0384, 0.0331, and 0.0349 (day 1) to roughly 0.0297, 0.0278, and 0.0314 (day 30), respectively. Meanwhile, the wet Pre-ZVI/PMS system exhibited k values ranging from approximately 0.0392, 0.0349, and 0.0374 (day 1) to roughly 0.0380, 0.0291, and 0.0322 (day 30), respectively. Moreover, we proposed four OTC degradation pathways using LC-MS/MS and density functional theory calculations. The toxicity of the degradation products was assessed using the ecological structure activity relationship and the toxicity estimation software tool. Overall, this study provides insights into the application of Pre-ZVI/PMS that can be selectively used to eliminate tetracycline antibiotics from water.

Advanced oxidation process for the treatment of industrial wastewater: A review on strategies, mechanisms, bottlenecks and prospects

Due to its complex and, often, highly contaminated nature, treating industrial wastewater poses a significant environmental problem. Many of the persistent pollutants found in industrial effluents cannot be effectively removed by conventional treatment procedures. Advanced Oxidation Processes (AOPs) have emerged as a promising solution, offering versatile and effective means of pollutant removal and mineralization. This comprehensive review explores the application of various AOP strategies in industrial wastewater treatment, focusing on their mechanisms and effectiveness. Ozonation (O3): Ozonation, leveraging ozone (O3), represents a well-established AOP for industrial waste water treatment. Ozone's formidable oxidative potential enables the breakdown of a broad spectrum of organic and inorganic contaminants. This paper provides an in-depth examination of ozone reactions, practical applications, and considerations involved in implementing ozonation. UV/Hydrogen Peroxide (UV/H2O2): The combination of ultraviolet (UV) light and hydrogen peroxide (H2O2) has gained prominence as an AOP due to its ability to generate hydroxyl radicals (ȮH), highly efficient in pollutant degradation. The review explores factors influencing the efficiency of UV/H2O2 processes, including H2O2 dosage and UV radiation intensity. Fenton and Photo-Fenton Processes: Fenton's reagent and Photo-Fenton processes employ iron ions and hydrogen peroxide to generate hydroxyl radicals for pollutant oxidation. The paper delves into the mechanisms, catalyst selection, and the role of photoactivation in enhancing degradation rates within the context of industrial wastewater treatment. Electrochemical Advanced Oxidation Processes (EAOPs): EAOPs encompass a range of techniques, such as electro-Fenton and anodic oxidation, which employ electrode reactions to produce ȮH radicals. This review explores the electrochemical principles, electrode materials, and operational parameters critical for optimizing EAOPs in industrial wastewater treatment. TiO2 Photocatalysis (UV/TiO2): Titanium dioxide (TiO2) photocatalysis, driven by UV light, is examined for its potential in industrial wastewater treatment. The review investigates TiO2 catalyst properties, reaction mechanisms, and the influence of parameters like catalyst loading and UV intensity on pollutant removal. Sonolysis (Ultrasonic Irradiation): High-frequency ultrasound-induced sonolysis represents a unique AOP, generating ȮH radicals during the formation and collapse of cavitation bubbles. This paper delves into the physics of cavitation, sonolytic reactions, and optimization strategies for industrial wastewater treatment. This review offers a critical assessment of the applicability, advantages, and limitations of these AOP strategies in addressing the diverse challenges posed by industrial wastewater. It emphasizes the importance of selecting AOPs tailored to the specific characteristics of industrial effluents and outlines potential directions for future research and practical implementation. The integrated use of these AOPs, when appropriately adapted, holds the potential to achieve sustainable and efficient treatment of industrial wastewater, contributing significantly to environmental preservation and regulatory compliance.

Regulating oxygen vacancies and hydroxyl groups of α-MnO2 nanorods for enhancing post-plasma catalytic removal of toluene

Although nonthermal plasma (NTP) technology has high removal efficiency for volatile organic compounds (VOCs), it has limited carbon dioxide (CO2) selectivity, which hinders its practical application. In this study, α-MnO2 nanorods with tunable oxygen vacancies and hydroxyl groups were synthesized by two-step hydrothermal process to enhance their activity for deep oxidation of toluene. Hydrochloric acid (HCl) was used to assist in synthesis of α-MnO2 nanorods with tunable oxygen vacancies, furtherly, more hydroxyl groups were introduced to HCl-assisted synthesized α-MnO2 by K+ supplement. The results showed that the as-synthesized nanorods exhibited superior activity, improved by nearly 30% removal efficiency of toluene compared to pristine MnO2 at SIE = 339 J/L, and reaching high COx selectivity of 72% at SIE = 483 J/L, successfully promoting the deep oxidation of toluene. It was affirmed that oxygen vacancies played an important role in toluene conversion, improving the conversion of ozone (O3) and resulting in higher mobility of surface lattice oxygen species. Besides, the enhancement of deep oxidation performance was caused by the increase of hydroxyl groups concentration. In-situ DRIFTS experiments revealed that the adsorbed toluene on catalyst surface was oxidized to benzyl alcohol by surface lattice oxygen, and hydroxyl groups were also found participating in toluene adsorption. Overall, this study provides a new approach to designing catalysts for deep oxidation of VOCs.

Construction of highly dispersed iron active sites for efficient catalytic ozonation of bisphenol A

The essential factor of catalytic ozonation technology relies on an efficient and stable catalyst. The construction of highly dispersed active sites on heterogeneous catalysts is an ideal strategy to combine the merits of homogeneous and heterogeneous catalysis with high activity and stability. Herein, an iron-containing mesoporous silica material (Fe-SBA15) with sufficient iron site exposure and enhanced intrinsic activity of active sites was employed to activate ozone for bisphenol A (BPA) degradation. Approximately 100% of BPA and 36.6% of total organic carbon (TOC) removal were realized by the Fe-SBA15 catalytic ozonation strategy with a reaction constant of 0.076 min-1, well beyond the performance of FeOx/SBA15 mixture and Fe2O3. Radical quenching experiments and electron paramagnetic resonance (EPR) analysis demonstrated that the hydroxyl radicals (HO•) and superoxide radicals (O2•-) played an important role in the degradation process. The iron sites with recyclable Fe(III)/Fe(II) pairs act as both the electron donors and active sites for catalytic ozonation. The mesoporous framework of SBA15 in Fe-SBA15 stabilizes the iron sites that enhance its stability. With high catalytic performance and high reusability for catalytic ozonation of BPA, the Fe-SBA15 is expected to be a promising catalyst in catalytic ozonation for wastewater treatment.

Heterogenous Iron Oxide Assemblages for Use in Catalytic Ozonation: Reactivity, Kinetics, and Reaction Mechanism

Heterogeneous catalytic ozonation (HCO) has gained increasing attention as an effective process to remove refractory organic pollutants from industrial effluents. However, widespread application of HCO is still limited due to the typically low efficacy of catalysts used and matrix passivation effects. To this end, we prepared an Al2O3-supported Fe catalyst with high reactivity via a facile urea-based heterogeneous precipitation method. Due to the nonsintering nature of the preparation method, a heterogeneous catalytic layer comprised of γ-FeOOH and α-Fe2O3 is formed on the Al2O3 support (termed NS-Fe-Al2O3). On treatment of a real industrial effluent by HCO, the presence of NS-Fe-Al2O3 increased the removal of organics by ∼100% compared to that achieved with a control catalyst (i.e., α-Fe2O3/Al2O3 or γ-FeOOH/Al2O3) that was prepared by a conventional impregnation and calcination method. Furthermore, our results confirmed that the novel NS-Fe-Al2O3 catalyst demonstrated resistance to the inhibitory effect of high concentration of chloride and sulfate ions usually present in industrial effluent. A mathematical kinetic model was developed that adequately describes the mechanism of HCO process in the presence of NS-Fe-Al2O3. Overall, the results presented here provide valuable guidance for the synthesis of effective and robust catalysts that will facilitate the wider industrial application of HCO.

Revisit the Role of Salinity in Heterogeneous Catalytic Ozonation: The Trade-Off between Reaction Inhibition and Mass Transfer Enhancement

Heterogeneous catalytic ozonation (HCO) is an effective technology for advanced wastewater treatment, while the influence of coexisting salts remains unclear and controversial. Here, we systematically explored the influence of NaCl salinity on the reaction and mass transfer of HCO through lab experiments, kinetic simulation, and computational fluid dynamics modeling, and proposed that the trade-off between reaction inhibition and mass transfer enhancement would affect the pollutants degradation pattern under varying salinity. The increase of NaCl salinity decreased ozone solubility and accelerated the futile consumption of ozone and hydroxyl radicals (•OH), and the maximum •OH concentration under 50 g/L salinity was only 23% of that without salinity. However, the increase of NaCl salinity also significantly reduced the ozone bubble size and enhanced the interphase and intraliquid mass transfer, with the volumetric mass transfer coefficient being 130% higher than that without salinity. The trade-off between reaction inhibition and mass transfer enhancement shifted under different pH values and aerator pore sizes, and the oxalate degradation pattern would change correspondingly. Besides, the trade-off was also identified for Na2SO4 salinity. These results emphasized the dual influence of salinity and offered a new theoretical perspective on the role of salinity in the HCO process.

Enhanced Mass Transfer of Ozone and Emerging Pollutants through a Gas-Solid-Liquid Reaction Interface for Efficient Water Decontamination

Ozone (O3), as an environmentally friendly oxidant, is widely used to remove emerging pollutants and ensure the safety of the water supply, whereas the restricted accessibility of O3 and limited collision frequency between pollutants and O3 will inevitably reduce the ozonation efficiency. To promote the chemical reactions between O3 and target pollutants, here we developed a novel gas-solid-liquid reaction interface dominated triphase ozonation system using a functional hydrophobic membrane with an adsorption layer as the O3 distributor and place where chemical reactions occurred. In the triphase system, the functional hydrophobic membrane simultaneously improved the interface adsorption performance of emerging pollutants and the access pathway of O3, leading to a marked enhancement of interfacial pollutant concentration and O3 levels. These synergistic qualities result in high ciprofloxacin (CIP) removal efficiency (94.39%) and fast apparent reaction rate constant (kapp, 2.75 × 10-2 min-1) versus a traditional O3 process (41.82% and 0.48 × 10-2 min-1, respectively). In addition, this triphase system was an advanced oxidation process involving radical participation and showed excellent degradation performance of multiple emerging pollutants. Our findings highlight the importance of gas-solid-liquid triphase reaction interface design and provide new insight into the efficient removal of emerging pollutants by the ozonation process.

Salinity-mediated water self-purification via bond network distorting of H2O molecules on DRC-surface

High salinity has plagued wastewater treatment for a long time by hindering pollutant removal, thereby becoming a global challenge for water pollution control that is difficult to overcome even with massive energy consumption. Herein, we propose a novel process for rapid salinity-mediated water self-purification in a dual-reaction-centers (DRC) system with cation-π structures. In this process, local hydrogen bond networks of H2O molecules can be distorted through the mediation of salinity, thereby opening the channels for the preferential contact of pollutants on the DRC interface. As the result, the elimination rate of pollutants increased approximately 32-fold at high salinity (100 mM) without any external energy consumption. Our findings provide a novel technology for high-efficiency and low-consumption water self-purification, which is of great significance in environmental remediation and even fine chemical industry.

Enhancing water purification through F and Zn-modified Fe-MCM-41 catalytic ozonation

Due to its low interfacial electron migration ability and highly hydrophilic, Fe-MCM-41 (FeM) had poor activity and stability during catalytic ozonation. To this end, the secondary metal Zn and Si-F group were introduced into the framework of FeM to create surface potential difference and hydrophobic sites. Comparative characterizations showed that there existed rich acid sites with great potential difference on F-Fe-Zn-MCM-41 (FFeZnM). Additionally, because of the existence of hydrophobic and electron-withdrawing Si-F unit, the electron migration ability, hydrophobicity and acidity of FFeZnM were enhanced. The greater O3 mass transfer was induced by Si-F group and O3 was directly activated at Fe and Zn Lewis acid sites into •OH, •O2- and 1O2. With •OH acting as main species, FFeZnM/O3 achieved the superior IBP removal (93.4%, 30 min) and TOC removal (46.6%, 120 min) over those of sole O3 and F-FeM/O3 processes, respectively. HCO3-, Cl-, NO3- and SO42- hindered IBP degradation by FFeZnM/O3, but high concentration humic acid (HA) exhibited promotion by forming HA-IBP complex. IBP degradation by FFeZnM/O3 was enhanced with tap water, river water, and effluent from the secondary sedimentation tank of the sewage plant acting as medium. This study proposed an innovative approach to catalyst design for catalytic ozonation.

Mn-doped carbon-Al2SiO5 fibers enable catalytic ozonation for wastewater treatment: Interface modulation and mass transfer enhancement

Heterogeneous catalytic ozonation is an efficient approach to remove hazardous and refractory organic contaminants in wastewater. It is crucial to design an ozone catalyst with high catalytic activity, high mass transfer and facile separation properties. Herein, easily separable aluminosilicate (Al2SiO5) fibers were developed as carriers and after interface modulation, Mn-doped carbon-Al2SiO5 (Mn-CAS) fibrous catalysts were proposed for catalytic ozonation. The growth of carbon shells on Al2SiO5 fiber surface and the introduction of metal Mn provided abundant Lewis acid sites to catalyze ozone. The Mn-CAS fiber/O3 system exhibited superior reactivity to degrade oxalic acid with a rate constant of 0.034 min-1, which was about 19 times as high as Al2SiO5/O3. For coal gasification wastewater treatment, Mn-CAS fibers also demonstrated high catalytic activity and stability and the COD removal was over 56%. Computational fluid dynamic simulations proved the high mass transfer properties of fibrous catalysts. Hydroxyl radicals (•OH) were identified as the predominant active species for organic degradation. Particularly, the catalytic pathways of O3 to •OH on Mn-O4 sites were revealed by theoretical calculations. This work provides a novel fibrous catalyst with high reactivity and mass transfer as well as easy separation characteristics for catalytic ozonation and wastewater purification.

Carbon-based electrocatalytic dual-membrane system bolsters singlet oxygen production for ultrafast water decontamination

Reactive electrochemical membranes (REMs) are promising technologies in treating pharmaceuticals and personal care products (PPCPs) in water. Herein, a novel carbon-based electrocatalytic dual-membrane system was designed to exploit the whole redox process of electrodes, in which the membrane cathode and anode were formed by carbon fibers doped with Fe and metal organic frameworks derived SnO2, respectively. Propranolol (PRO) was used as a representative of PPCPs. The system bolstered singlet oxygen (1O2) production by the synergy of two REM electrodes, further improving the removal rate constant of PRO compared with single-electrode-dominant modes. 97.5 ± 1.7% of PRO removal was achieved in a single-pass electro-filtration at a residence time of ∼2.9 s. The generation of 1O2 and its reaction with pollutants were systematically and thoroughly explored via experiments coupled with theoretical calculation. The toxicity of the decomposition products was predicted to be reduced compared with PRO. These findings suggested that the carbon-based electrocatalytic dual-membrane system could effectively promote 1O2 production for ultrafast catalytic oxidation of PRO, providing a cost-effective solution for the development of an efficient and stable technology for PPCPs removal.

Highly efficient catalytic ozonation degradation of levofloxacin by facile hydrogenation-modified red mud wastes

Iron-rich red mud (RM) is a potential catalyst. However, as industrial waste, is strongly alkaline, low effectiveness, and safety concerns are problems that cannot be ignored, it is urgent to mine out a reasonable disposal and utilization technology for the waste. In this study, an effective catalyst (H-RM) was obtained by facile hydrogenation heating modification of red mud. Then above-prepared H-RM was applied in the catalytic ozonation degradation of levofloxacin (LEV). The H-RM exhibited more remarkable catalytic activities than the RM in terms of LEV degradation, and the optimal efficiency can reach over 90% within 50 min. The mechanism experiment proved that the concentration of dissolved ozone and hydroxyl radical (•OH) significantly increased, which enhanced the oxidation effect. Hydroxyl radical played a dominant role in the degradation of LEV. In the safety test, it is concluded that the concentration of total hexavalent chromium (total Cr(Ⅵ)) in the H-RM catalyst decreases and the leaching concentration of water-soluble Cr(Ⅵ) in aqueous solution is low. The results indicated that the hydrogenation technique is an available Cr (Ⅵ) detoxification method for RM. Moreover, the H-RM has excellent catalytic stability, which is beneficial to recycling and maintains high activity. This research provides an effective means to fulfill the reuse of industrial waste as an alternative to standard raw materials, and comprehensive utilization of the waste to attain the purpose of treating pollution with wastes.

Selective Removal of Organic Pollutants in Groundwater and Surface Water by Persulfate-Assisted Advanced Oxidation: The Role of Electron-Donating Capacity

The efficiency of persulfate-assisted advanced oxidation processes (PS-AOPs) in degrading organic pollutants is affected by the electron-donating capability of organic substances present in the water source. In this study, we systematically investigate the electron-donating capacity (EDC) difference between groundwater and surface water and demonstrate the dependence of removal efficiency on the EDC of target water by PS-AOPs with carbon nanotubes (CNTs) as a catalyst. Laboratory analyses and field experiments reveal that the CNT/PS system exhibits higher performance in organic pollutant removal in groundwater with a high concentration of phenols, compared to surface water, which is rich in quinones. We attribute this disparity to the selective electron transfer pathway induced by potential difference between PS-CNT and organic substance-CNT intermediates, which preferentially degrade organic substances with stronger electron-donating capability. This study provides valuable insights into the inherent selective removal mechanism and application scenarios of electron transfer process-dominated PS-AOPs for water treatment based on the electron-donating capacity of organic pollutants.

Performance of alkali and Cu-modified ZSM-5 during catalytic ozonation of polyvinyl alcohol in aqueous solution

A novel hierarchical Cu/ZSM-5 was prepared over alkaline treatment and incipient wet impregnation method for the catalytic ozonation of polyvinyl alcohol (PVA). Under the optimum preparation conditions, hierarchical Cu/ZSM-5 exhibited an excellent mineralization performance during the PVA degradation process, and the removal rate of TOC after 60 min of reaction was 47.86%, much higher than that of ozonation alone (5.40%). Its high catalytic activity could attribute to the large pore volume (0.27 cm³/g) and pore size (6.51 nm) which are beneficial for the distribution of loaded copper and adsorption performance for PVA. Compared to ·OH, ¹O₂ (2.66 times in 10 min) contributed more to the removal of PVA. The degradation of PVA was a combined process of direct ozone oxidation, catalytic ozonation and adsorption. With its high catalytic performance and stability, hierarchical Cu/ZSM-5 has a very broad application prospect in the process of catalytic ozonation of refractory pollutants.