Ozone Decomposition by a Manganese-Organic Framework over the Entire Humidity Range

A novel MOF-on-MOF-derived carbon-encapsulated CeO2/Co/Co3O4 humidity-resistant heterojunction with abundant oxygen vacancies for efficient ozone removal

Ground-level ozone (O3) can infiltrate indoor environments, severely impacting the environment and human health. Moisture-induced catalyst deactivation is a major challenge in catalytic ozone removal. MOF-template-derived heterojunctions supported by carbon materials can prevent chemisorption of water vapor at active sites. This paper presents a carbon-supported CeO2/Co/Co3O4 humidity-resistant heterojunction derived from a bimetallic-organic framework (Ce-BTC/Co-ZIF-67 precursor) via hydrothermal-carbonization. Instrumental characterization confirmed the successful construction of the heterojunction. The O3 removal efficiency was evaluated at the ppb level under different relative humidity conditions (RH = 0%, 50%, and 75%) at a weight hourly space velocity (WHSV) of 10,000 L g-1 h-1 and ambient temperature. The carbon-supported 20 wt% CeO2/Co/Co3O4 composite demonstrated 99 ± 0.2% O3 removal and a high reaction rate of 1.1 ± 0.06 μg.gcat-1.sec-1 for 200 ppb O3 under an RH of 50% at ambient temperature. The O3 removal rate remained at approximately 92 ± 1.2%, even in harsh environments (75% RH), indicating excellent stability and strong moisture-resistance. Oxygen vacancies and defect structures are crucial for O3 adsorption and activation processes. The optimal catalyst exhibited greater electron mobility and redox ability than the pristine materials, as confirmed by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) analyses. Furthermore, the as-synthesized catalyst is both recyclable and stable, making it suitable for practical applications. This research offers a new strategy for the fabrication of highly moisture-resistant MOF-derived heterojunctions, which will greatly facilitate the elimination of ground-level O3 in real indoor environments.

Use of In Situ X-ray Absorption to Probe Reactivity: A Catalysis Golden Rule

The decomposition of ozone on supported manganese oxide catalysts, studied here, exemplifies reactions involving electron transfer. In situ extended X-ray absorption fine-structure spectra (Mn K-edge) on in situ treated samples show that the supported phase in MnOx/SiO2 resembles Mn3O4 while that in MnOx/Al2O3 samples resembles MnO2. In situ Raman spectroscopy shows the involvement of a common peroxide surface species. Kinetic data indicate a nonuniform surface and a rate-determining step (rds) involving electron transfer from the peroxide intermediate. The activation energy for all the catalysts is the same, indicating that the pre-exponential factor controls the rate. This can be associated with the electronic partition function (unoccupied density of states (DOS)), and X-ray absorption near-edge spectroscopy duly shows that the areas of the pre-edge peaks due to 1s to 3d transitions track the reactivity trends. The relation to the unoccupied DOS is analogous to Fermi's Golden Rule for electronic transitions, and we denote the finding here, applicable to reactions involving electron transfer, as a Catalysis Golden Rule.

Mechanism for airborne ozone decomposition on X-MIL-53(Fe) (X = H, NH2, NO2)

Ground-level ozone (O3) pollution poses a significant threat to both ecosystem sustainability and human health. The catalytic decomposition of O3 presents as a promising technology to address the issues of O3 pollution. This study undertook the synthesis of various functionalized metal-organic framework (MOF) catalysts (i.e., X-MIL-53(Fe) (X = H, NH2, NO3)) to delve into the influence of ligand functional groups on skeletal structure and catalytic efficacy, particularly focusing on unraveling the mechanism of O3 catalytic decomposition under humid conditions. NH2-MIL-53(Fe) catalyst achieved complete O3 decomposition under ambient temperature and high humidity conditions (RH=75 %), exhibiting a reaction rates (mol·m-2·s-1) 129 and 10.5 times greater than that of MIL-53(Fe) and NO2-MIL-53(Fe). The NH2 group promotes electron flow within the backbone towards the hydroxyl group (OH) linked to Fe atom. In humid O3, H2O molecules augment the interaction between O3 and NH2-MIL-53(Fe), and OH is converted to·O2- after deprotonation, promoting O3 decomposition. Additionally, leveraging three-dimensional (3D) printing technology, a monolithic catalyst for O3 decomposition was prepared for application. This study not only advances understanding of the mechanisms underlying O3 decomposition but also offers practical solutions for addressing O3 pollution at humid conditions.

Investigation into the Internal Factors for the Catalytic Oxidation of Cyclohexane by Zr(IV)-Based Metal-Organic Frameworks

Three porous Zr(IV)-based MOFs, UiO-66, MOF-808 and MOF-802, were selected to catalyze cyclohexane oxidation in order to reveal the intrinsic factors of the active site and catalytic performance. It was found that reducing the number of Zr6O8 ligand linkages could improve the catalytic efficiency of cyclohexane oxidation. The main reason for this is the different enrichment abilities of MOFs with different linkage numbers for cyclohexane, which was confirmed by the TPD of cyclohexane and also by GCMC simulations. Meanwhile, the catalytic effect of MOF-802 was lower than expected due to its low porosity and narrow inner pore size. The by-products were identified in detail by GC-MS, providing evidence for this catalytic mechanism. In addition, the potential of this catalyst for industrial applications in cyclohexane oxidation was demonstrated by optimizing the catalytic conditions.

Synthesis Ag-Hollandite by mild route for highly efficient ozone decomposition

Catalytic ozone (O3) decomposition is a promising technology for curbing indoor O3 pollution, whereas its application is limited by the stability and moisture resistance of heterogeneous catalysts. Ag-Hollandite is a capable solution, but its facile synthesis still lacks systematic investigation. In this study, Ag-Hollandite catalysts were prepared using AgMnO4 as the precursor by reflux (AMO-Re), hydrothermal (AMO-HT), and homogeneous (AMO-HR) methods, respectively. The as-prepared samples showed excellent stability under moisture conditions, with the optimal one maintaining an O3 conversion rate of 99.19 % after 100 h. In the characterization results, Ramsdellite (R-MnO2) was identified as an intermediate species in the synthesis. AMO-HR exhibits higher activity due to enhanced active site exposure and weakened adsorption towards *OO species, while reduced surface hydroxyl content was a crucial factor for moisture resistance. This study aims to contribute insights for preparing catalysts by a facile method.

Optimization of Carbon-Defect Engineering to Boost Catalytic Ozonation Efficiency of Single Fe─N4 Coordination Motif

Carbon-defect engineering in single-atom metal-nitrogen-carbon (M─N─C) catalysts by straightforward and robust strategy, enhancing their catalytic activity for volatile organic compounds, and uncovering the carbon vacancy-catalytic activity relationship are meaningful but challenging. In this study, an iron-nitrogen-carbon (Fe─N─C) catalyst is intentionally designed through a carbon-thermal-diffusion strategy, exposing extensively the carbon-defective Fe─N4 sites within a micro-mesoporous carbon matrix. The optimization of Fe─N4 sites results in exceptional catalytic ozonation efficiency, surpassing that of intact Fe─N4 sites and commercial MnO2 by 10 and 312 times, respectively. Theoretical calculations and experimental data demonstrated that carbon-defect engineering induces selective cleavage of C─N bond neighboring the Fe─N4 motif. This induces an increase in non-uniform charges and Fermi density, leading to elevated energy levels at the center of Fe d-band. Compared to the intact atomic configuration, carbon-defective Fe─N4 site is more activated to strengthen the interaction with O3 and weaken the O─O bond, thereby reducing the barriers for highly active surface atomic oxygen (*O/*OO), ultimately achieving efficient oxidation of CH3SH and its intermediates. This research not only offers a viable approach to enhance the catalytic ozonation activity of M─N─C but also advances the fundamental comprehension of how periphery carbon environment influences the characteristics and efficacy of M─N4 sites.

Graphitized Carbon-Supported Co@Co3O4 for Ozone Decomposition over the Entire Humidity Range

Ground-level ozone (O3) pollution has emerged as a significant concern due to its detrimental effects on human health and the ecosystem. Catalytic removal of O3 has proven to be the most efficient and cost-effective method. However, its practical application faces substantial challenges, particularly in relation to its effectiveness across the entire humidity range. Herein, we proposed a novel strategy termed "dual active sites" by employing graphitized carbon-loaded core-shell cobalt catalysts (Co@Co3O4-C). Co@Co3O4-C was synthesized via the pyrolysis of a Co-organic ligand as the precursor. By utilizing this approach, we achieved a nearly constant 100% working efficiency of the Co@Co3O4-C catalyst for catalyzing O3 decomposition across the entire humidity range. Physicochemical characterization coupled with density functional theory calculations elucidates that the presence of encapsulated metallic Co nanoparticles enhances the reactivity of the cobalt oxide capping layer. Additionally, the interface carbon atom, strongly influenced by adjacent metallic Co nuclei, functions as a secondary active site for the decomposition of O3 decomposition. The utilization of dual active sites effectively mitigates the competitive adsorption of H2O molecules, thus isolating them for adsorption in the cobalt oxide capping layer. This optimized configuration allows for the decomposition of O3 without interference from moisture. Furthermore, O3 decomposition monolithic catalysts were synthesized using a material extrusion-based three-dimensional (3D) printing technology, which demonstrated a low pressure drop and exceptional mechanical strength. This work provides a "dual active site" strategy for the O3 decomposition reaction, realizing O3 catalytic decomposition over the entire humidity range.

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.

Stable O3 Decomposition by Layered Double Hydroxides: The Pivotal Role of NiOOH Transformation

Because ozone (O3) is a significant air pollutant, advanced O3 elimination technologies, particularly those under high-humidity conditions, have become an essential research focus. In this study, a nickel-iron layered double hydroxide (NiFe-LDH) was modified via intercalation with octanoate to develop an effective hydrophobic catalyst (NiFe-OAa-LDH) for O3 decomposition. The NiFe-OAa-LDH catalyst sustained its O3 decomposition rate of >98% for 48 h under conditions of 90% relative humidity, 840 L/(g·h) space velocity, and 100 ppm inlet O3 concentration. Moreover, it maintained a decomposition rate of 90% even when tested at a higher airflow rate of 2500 L/(g·h). Based on the changes induced by the Ni-OII to Ni-OIII bonds in NiFe-OAa-LDH during O3 treatment, catalytic O3 decomposition was proposed to occur in two stages. The first stage involved the reaction between the hydroxyl groups and O3, leading to the breakage of the O-H bonds, formation of NiOOH, and structural changes in the catalyst. This transformation resulted in the formation of abundant and stable hydrogen vacancies. According to density functional theory calculations, O3 can be effectively decomposed at the hydrogen vacancies with a low energy barrier during the second stage. This study provides new insights into O3 decomposition.

A Photoelectromagnetic 3D Metal-Organic Framework from Flexible Tetraarylethylene-Backboned Ligand and Dynamic Copper-Based Coordination Chemistry

Porous frameworks that display dynamic responsiveness are of interest in the fields of smart materials, information technology, etc. In this work, a novel copper-based dynamic metal-organic framework [Cu3TTBPE6(H2O)2] (H4TTBPE = 1,1,2,2-tetrakis(4″-(1H-tetrazol-5-yl)-[1,1″-biphenyl]-4-yl)ethane), denoted as HNU-1, is reported which exhibits modulable photoelectromagnetic properties. Due to the synergetic effect of flexible tetraarylethylene-backboned ligands and diverse copper-tetrazole coordination chemistries, a complex 3D tunneling network is established in this MOF by the layer-by-layer staggered assembly of triplicate monolayers, showing a porosity of 59%. These features further make it possible to achieve dynamic transitions, in which the aggregate-state MOF can be transferred to different structural states by changing the chemical environment or upon heating while displaying sensitive responsiveness in terms of light absorption, photoluminescence, and magnetic properties.

Precisely constructing orbital coupling-modulated iron dinuclear site for enhanced catalytic ozonation performance

The advancement of atomically precise dinuclear heterogeneous catalysts holds great potential in achieving efficient catalytic ozonation performance and contributes to the understanding of synergy mechanisms during reaction conditions. Herein, we demonstrate a "ship-in-a-bottle and pyrolysis" strategy that utilizes Fe2(CO)9 dinuclear-cluster to precisely construct Fe2 site, consisting of two Fe1-N3 units connected by Fe-Fe bonds and firmly bonded to N-doped carbon. Systematic characterizations and theoretical modeling reveal that the Fe-Fe coordination motif markedly reduced the devotion of the antibonding state in the Fe-O bond because of the strong orbital coupling interaction of dual Fe d-d orbitals. This facilitates O-O covalent bond cleavage of O3 and enhances binding strength with reaction intermediates (atomic oxygen species; *O and *OO), thus boosting catalytic ozonation performance. As a result, Fe dinuclear site catalyst exhibits 100% ozonation efficiency for CH3SH elimination, outperforming commercial MnO2 catalysts by 1,200-fold. This research provides insights into the atomic-level structure-activity relationship of ozonation catalysts and extends the use of dinuclear catalysts in catalytic ozonation and beyond.

Enhanced water resistance mechanism in Ag-Hollandite for catalytic ozone decomposition

Catalytic ozone (O3) decomposition at ambient temperature is an efficient method to mitigate O3 pollution. However, practical application is hindered by the poor water resistance of catalysts. Herein, Ag-Hollandite (Ag-HMO) with varying Ag+ content was synthesized. Catalysts with more Ag+ exhibited improved efficiency and water-resistance, with the optimal one maintaining 98% O3 conversion at 70% relative humidity (RH) within 8 h. Physicochemical characterizations revealed that Ag+ had entered the tunnel of OMS-2, facilitating oxygen species removal. Notably, enhanced H2O desorption and the complete inhibition of chemisorbed water formation on Ag-HMO were the primary reasons for its high-efficiency O3 conversion across a wide humidity range. The underlying mechanism arises from the charge redistribution induced by the Ag-O interaction within the tunnel, which reduces acidity and modulates hydrophilicity. This study aims to contribute insights for designing catalysts with higher water-resistance.

Exceptional Ozone Decomposition over δ-MnO2/AC under an Entire Humidity Environment

Ozone (O3) pollution is highly detrimental to human health and the ecosystem due to it being ubiquitous in ambient air and industrial processes. Catalytic decomposition is the most efficient technology for O3 elimination, while the moisture-induced low stability represents the major challenge for its practical applications. Here, activated carbon (AC) supported δ-MnO2 (Mn/AC-A) was facilely synthesized via mild redox in an oxidizing atmosphere to obtain exceptional O3 decomposition capacity. The optimal 5Mn/AC-A achieved nearly 100% of O3 decomposition at a high space velocity (1200 L g-1 h-1) and remained extremely stable under entire humidity conditions. The functionalized AC provided well-designed protection sites to inhibit the accumulation of water on δ-MnO2. Density functional theory (DFT) calculations confirmed that the abundant oxygen vacancies and a low desorption energy of intermediate peroxide (O22-) can significantly boost O3 decomposition activity. Moreover, a kilo-scale 5Mn/AC-A with low cost (∼1.5 $/kg) was used for the O3 decomposition in practical applications, which could quickly decompose O3 pollution to a safety level below 100 μg m-3. This work offers a simple strategy for the development of moisture-resistant and inexpensive catalysts and greatly promotes the practical application of ambient O3 elimination.

Catalytic ozonation mechanism over M1-N3C1 active sites

The structure-activity relationship in catalytic ozonation remains unclear, hindering the understanding of activity origins. Here, we report activity trends in catalytic ozonation using a series of single-atom catalysts with well-defined M1-N3C1 (M: manganese, ferrum, cobalt, and nickel) active sites. The M1-N3C1 units induce locally polarized M - C bonds to capture ozone molecules onto M atoms and serve as electron shuttles for catalytic ozonation, exhibiting excellent catalytic activities (at least 527 times higher than commercial manganese dioxide). The combined in situ characterization and theoretical calculations reveal single metal atom-dependent catalytic activity, with surface atomic oxygen reactivity identified as a descriptor for the structure-activity relationship in catalytic ozonation. Additionally, the dissociation barrier of surface peroxide species is proposed as a descriptor for the structure-activity relationship in ozone decomposition. These findings provide guidelines for designing high-performance catalytic ozonation catalysts and enhance the atomic-level mechanistic understanding of the integral control of ozone and methyl mercaptan.

Controllable Synthesis of Defective UiO-66 for Efficient Degradation and Detection of Ozone

Metal-organic framework (MOF) structures have gained significant attention for their exceptional catalytic performance in ozone degradation, even under high humidity conditions, which is attributed to the presence of unsaturated metal sites (MOF defects). However, the correlation between MOF defects and catalytic ozone remains ambiguous, and a general approach for the controllable synthesis of high-performance MOF structures is currently lacking. Herein, different defective UiO-66 materials with cluster or ligand defects were obtained by precisely controlling small molecular acid modulators. Their catalytic performance can be analyzed in real time through the specific cataluminescence (CTL) signal of ozone at the interface. The presence of ligand defects was found to be crucial for both catalytic degradation and luminescence of ozone, and the CTL signal exhibited a positive correlation with the endogenous hydroxyl group content in the material (R2 = 0.982), while external humidity further supplemented internal water molecules within the material. Furthermore, theoretical calculations were conducted to compare the adsorption behaviors of ozone on the defective UiO-66 under dry/wet conditions, leading to the proposal of two potential reaction pathways. Subsequently, UiO-66-DA with superior catalytic performance was employed to develop a highly efficient CTL sensor capable of accurately detecting ozone (LOD = 23.3 ppb). This study held significant value in elucidating the reaction site of ozone on MOFs and achieving optimal catalytic effects through the careful selection of modulators and humidity levels.

Rapid Ozone Decomposition over Water-activated Monolithic MoO3 /Graphdiyne Nanowalls under High Humidity

Catalytic ozone (O3 ) decomposition at high relative humidity (RH) remains a great challenge due to the catalysts poison and deactivation under high humidity. Here, we firstly elaborate the role of water activation and the corresponding mechanism of the promoted O3 decomposition over the three-dimensional monolithic molybdenum oxide/graphdiyne (MoO3 /GDY) catalyst. The O3 decomposition over MoO3 /GDY reaches up to 100 % under high humid condition (75 % RH) at room temperature, which is 4.0 times as high as that of dry conditions, significantly surpasses other carbon-based MoO3 materials(≤7.1 %). The sp-hybridized carbon in GDY donates electrons to MoO3 along the C-O-Mo bond, facilitating water activation to form hydroxyl species. As a result, hydroxyl species dissociated from water act as new active sites, promoting the adsorption of O3 and the generation of new intermediate species (hydroxyl ⋅OH and superoxo ⋅O2 - ), which significantly lowers the energy barriers of O3 decomposition (0.57 eV lower than dry conditions).

Accelerated Catalytic Ozonation in a Mesoporous Carbon-Supported Atomic Fe-N4 Sites Nanoreactor: Confinement Effect and Resistance to Poisoning

The design of a micro-/nanoreactor is of great significance for catalytic ozonation, which can achieve effective mass transfer and expose powerful reaction species. Herein, the mesoporous carbon with atomic Fe-N4 sites embedded in the ordered carbon nanochannels (Fe-N4/CMK-3) was synthesized by the hard-template method. Fe-N4/CMK-3 can be employed as nanoreactors with preferred electronic and geometric catalytic microenvironments for the internal catalytic ozonation of CH3SH. During the CH3SH oxidation process, the mass transfer coefficient of the Fe-N4/CMK-3 confined system with sufficient O3 transfer featured a level of at least 1.87 × 10-5, which is 34.6 times that of the Fe-N4/C-Si unconfined system. Detailed experimental studies and theoretical calculations demonstrated that the anchored atomic Fe-N4 sites and nanoconfinement effects regulated the local electronic structure of the catalyst and promoted the activation of O3 molecules to produce atomic oxygen species (AOS) and reactive oxygen species (ROS), eventually achieving efficient oxidation of CH3SH into CO2/SO42-. Benefiting from the high diffusion rate and the augmentation of AOS/ROS, Fe-N4/CMK-3 exhibited an excellent poisoning tolerance, along with high catalytic durability. This contribution provides the proof-of-concept strategy for accelerating catalytic ozonation of sulfur-containing volatile organic compounds (VOCs) by combining confined catalysis and atomic catalysts and can be extended to the purification of other gaseous pollutants.

MOF-based catalysts: insights into the chemical transformation of greenhouse and toxic gases

Metal-organic framework (MOF)-based catalysts are outstanding alternative materials for the chemical transformation of greenhouse and toxic gases into high-add-value products. MOF catalysts exhibit remarkable properties to host different active sites. The combination of catalytic properties of MOFs is mentioned in order to understand their application. Furthermore, the main catalytic reactions, which involve the chemical transformation of CH4, CO2, NOx, fluorinated gases, O3, CO, VOCs, and H2S, are highlighted. The main active centers and reaction conditions for these reactions are presented and discussed to understand the reaction mechanisms. Interestingly, implementing MOF materials as catalysts for toxic gas-phase reactions is a great opportunity to provide new alternatives to enhance the air quality of our planet.

α-Fe2O3-supported Co3O4 nanoparticles to construct highly active interfacial oxygen vacancies for ozone decomposition

Ozone pollution has become one of the most concerned environmental issue. Developing low-cost and efficient catalysts is a promising alternative for ozone decomposition. This work presents a creative strategy that using α-Fe₂O₃-supported Co₃O₄ nanoparticles for constructing interfacial oxygen vacancies (Vo) to remove ozone. The efficiency of Co₃O₄/α-Fe₂O₃ was superior to that of pure α-Fe₂O₃ by nearly two times for 200-ppm ozone removal after 6-h reaction at 25 °C, which is ascribed to the highly active interfacial Vo. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy suggest that the Fe³⁺-Vo-Co²⁺ was formed when Co₃O₄ was loaded in α-Fe₂O₃. Furthermore, the density functional theory (DFT) calculations reveal the desorption and electron transfer ability of intermediate peroxide (O₂^2-) on Fe³⁺-Vo-Co²⁺ are higher than the Vo from other regions. In situ diffuse reflectance Fourier transform (DRIFT) spectroscopy also demonstrate the higher conversion rate of O₂^2- on Co₃O₄/α-Fe₂O₃. Base on the intermediates detected, we propose a recycle mechanism of interfacial Vo for ozone removal: O₂^2- is quickly converted to O₂^- and transformed into O₂ on interfacial Vo. Moreover, O₂-temperature-programmed desorption (TPD), H₂-temperature-programmed reduction (TPR), and electrochemical impedance spectroscopy (EIS) reveal that the oxygen mobility, reducibility, and conductivity of Co₃O₄/α-Fe₂O₃ are greatly superior to those of α-Fe₂O₃, which is contributed to the conversion of O₂^2-. Consequently, our proposed strategy effectively enhances the activity and stability of the bimetallic transition oxides for ozone decomposition.

Facile Synthesis of Metal-Impregnated Sugarcane-Derived Catalytic Biochar for Ozone Removal at Ambient Temperature

This study presents the first attempt at employing catalytic biochar to remove ground-level ozone at ambient temperature. With the increase in human activity, ozone has become a critical inorganic pollutant that needs to be addressed, using more sustainable methods. Fe- and Mn-impregnated catalytic biochars were prepared from a sugarcane feedstock via the wet impregnation method and pyrolysis at various temperatures, where the optimum value was determined to be 550 °C. The metal-impregnated biochar samples demonstrated enhanced surface areas and pore volumes compared with the pristine biochar (SCB550), resulting in improved ozone-adsorption capacity. SCB550-Fe exhibited an ozone-adsorption capacity of 52.1 mg/g at 20 ppm, which was approximately four times higher than that of SCB550. SCB550-Fe demonstrated superior ozone-removal performance compared to SCB550-Mn; 122 mg/g capacity as opposed to 116.2 mg/g at 80 ppm, respectively. Isothermal and kinetic modeling are also presented to suggest a plausible mechanism of ozone removal by catalytic biochar. This includes physical adsorption, complexation, electrostatic interaction, and electron transfer during the redox reaction between ozone and metals. Overall, this study should provide preliminary insights into ozone removal using biochar and promote further research regarding material optimization and kinetic studies.

The Diverse Modes of Oxygen Reactivity in Life & Chemistry

Oxygen is a molecule of utmost importance in our lives. Beside its vital role for the respiration and sustaining of organisms, oxygen is involved in numerous chemical and physical processes. Upon combination of the different forms of molecular oxygen species with various activation modes, substrates, and reaction conditions an extremely wide chemical space can be covered that enables rich applications of diverse oxygenation processes. This Review provides an instructive overview of the individual properties and reactivities of oxygen species and illustrates their importance in nature, everyday life, and in the context of chemical synthesis.

Different degradation mechanisms of low-concentration ozone for MIL-100(Fe) and MIL-100(Mn) over wide humidity fluctuation

The synergistic control of ozone and fine particulate matter is a research hotspot in the current environmental fields. Among the ozone removal, wide humidity fluctuation and low concentration dynamic adsorption are two thorny problems. In this work, MIL-100(Fe) and MIL-100(Mn), synthesized by hydrothermal and solvothermal methods respectively, were selected to investigate the degradation of flowing ozone pollutants. The samples showed different ozone degradation mechanisms, namely photocatalytic degradation and normal temperature degradation. Notably, MIL-100(Fe) exhibited more outstanding photocatalytic activity than MIL-100(Mn), while the normal temperature catalytic efficiency of MIL-100(Mn) was much superior to MIL-100(Fe). For different humidity conditions, MIL-100(Fe) has the optimal photocatalytic performance at 10% humidity, which is 38%, while MIL-100(Mn) has basically no change in normal temperature catalytic degradation efficiency at different humidity levels of 10-90%. Furthermore, the degradation mechanism was proposed by in-situ DRIFTS and ESR, which was significantly correlated with oxygen vacancy and photogenerated electron efficiency. By the aid of Temperature Programmed Desorption (TPD), a large quantity of Lewis acid sites was detected in MIL-100(Mn), which was the critical factor that the selected materials could maintain excellent normal temperature degradation performance under high humidity. This work will expand the practical application of ozone removal and improve the degradation efficiency.

Catalytic ozone decomposition and adsorptive VOCs removal in bimetallic metal-organic frameworks

Atmospheric ozone has long been a threat to human health, however, rational design of high-performance O₃-decomposition catalysts remains challenging. Herein, we demonstrate the great potential of a series of isomorphous bimetallic MOFs denoted as PCN-250(Fe₂M) (M = Co²⁺, Ni²⁺, Mn²⁺) in catalytic O₃ decomposition. Particularly, PCN-250(Fe₂Co) showed 100% O₃ removal efficiency for a continuous air flow containing 1 ppm O₃ over a wide humidity range (0 ‒ 80% RH) at room temperature. Mechanism studies suggested that the high catalytic performance originated from the introduction of open Co(II) sites as well as its porous structure. Additionally, at low pressures around 10 Pa, PCN-250(Fe₂Co) exhibited high adsorption capacities (89 ‒ 241 mg g^-1) for most VOCs, which are not only a class of hazardous air pollutants but also the precursor of O₃. This work opens up a new avenue to develop advanced air purification materials for O₃ and VOCs removal in one.

Exploring an electric-aid ozone decomposition mode to enhance water resistance over manganese oxide monolith catalyst under high humidity

In this work, a facile, green, and effective reaction mode of electric-aid ozone decomposition (EAOD) was developed over a manganese-based monolith catalyst for eliminating ozone under high humidity. The catalyst was prepared by directly growing α-MnO₂ nanorods on Al honeycomb substrate (MnO₂/Al) via a simple hydrothermal process, and the EAOD mode was performed just by connecting the MnO₂/Al monolith catalyst with a DC power supply during ozone decomposition reaction. In the EAOD mode reaction, the MnO₂/Al catalyst exhibited a stable ozone conversion efficiency of over 82 % and excellent stability over 720 min under a relative humidity of 90%, well beyond the performance of catalyst in the conventional ozone decomposition reaction without the help of electric aid. Here, the water evaporation by the external electric field generated from the EAOD mode hinders the competitive adsorption of water vapor on the active sites of MnO₂/Al catalyst, consequently enhances its water resistance. Moreover, increasing input electric current of the DC power supply could further improve the catalytic activity and stability of the monolith catalyst for ozone decomposition in EAOD mode reaction.

Microbial Inactivation: Gaseous or Aqueous Ozonation?

For decades, ozone has been known to have antimicrobial properties when dissolved or generated in water and when utilized in its gaseous form on different substrates. This property (the ability to be used in air and water) makes it versatile and applicable to different industries. Although the medium of ozonation depends on the specific process requirements, some industries have the inherent flexibility of medium selection. Thus, it is important to evaluate the antimicrobial efficacy in both media at similar concentrations, an endeavor hardly reported in the literature. This study provides insights into ozone’s efficacy in air and water using two Gram-negative bacteria (Escherichia coli NTCC1290 and Pseudomonas aeruginosa NCTC10332), two Gram-positive bacteria (Staphylococcus aureus ATCC25923 and Streptococcus mutans), and two fungi (Candida albicans and Aspergillus fumigatus). For gaseous ozonation, we utilized a custom-made ozone chamber (equipped with ultraviolet lamps), whereas an electrolysis oxygen radical generator was applied for ozone generation in water. During gaseous ozonation, the contaminated substrates (fabric swatches inoculated with bacterial and fungal suspensions) were suspended in the chamber, whereas the swatches were immersed in ozonated water for aqueous ozone treatment. The stability of ozone nanobubbles and their resulting impact on the aqueous disinfection efficiency were studied via dynamic light scattering measurements. It was observed that ozone is more effective in air than in water on all tested organisms except Staphylococcus aureus. The presented findings allow for the adjustment of the treatment conditions (exposure time and concentration) for optimal decontamination, particularly when a certain medium is preferred for ozonation.

Ozone Decomposition below Room Temperature Using Mn-based Mullite YMn2O5

A super-low-temperature ozone decomposition is realized without energy consumption on a ternary oxide catalyst mullite YMn₂O₅ for the first time. The YMn₂O₅ oxide catalyzed ozone decomposition from a low temperature of -40 °C with 29% conversion (reaction rate: 1534.2 μmol g^-1 h^-1) and quickly reached 100% (5459.5 μmol g^-1 h^-1) when warmed up to -5 °C. The superior low-temperature performance over YMn₂O₅ could surpass that of the reported ozone decomposition catalysts. The structure and element valence characterizations confirmed that YMn₂O₅ remained the same after 100 h of room-temperature reaction, indicating excellent durability of the catalyst. O₂-TPD (O₂-temperature-programmed desorption) showed that the active sites are the Mn³⁺ sites bonded with singly coordinated oxygen on the surface. Combined with in situ Raman measurements and density functional theory calculations, we found that the ozone decomposition reaction on YMn₂O₅ showed a barrier of only 0.29 eV, following the Eley-Rideal (E-R) mechanism with a rate-limiting step of intermediate O₂^2- desorption. The low barrier minimizes the accumulation of intermediate products and realizes the fast O₃ decomposition even at super-low temperatures. Fundamentally, the moderate Mn-O bonding strength in the low-symmetry ternary oxides is crucial to produce singly coordinated active species on the surface responsible for the efficient ozone degradation at low temperatures.

A novel Fe-Co double-atom catalyst with high low-temperature activity and strong water-resistant for O3 decomposition: A theoretical exploration

Developing catalysts with high activity, durability, and water resistance for ozone decomposition is crucial to regulate the pollution of ozone in the troposphere, especially in indoor air. To overcome the shortcomings of metal oxide catalysts with respect to their durability and water resistance, Fe-Co double-atom catalyst (DAC) is proposed as a novel catalyst for ozone decomposition. Here, through a systematic study using density functional theory (DFT) calculations and microkinetic modeling, the adsorption and catalytic decomposition of O₃ on Fe-Co DAC have been examined based on adsorption configuration, orbital hybridization, and electron transfer. Based on Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) reaction mechanisms, the mechanisms of ozone decomposition on Fe-Co DAC were explored by analyzing reaction paths and energy variations. To confirm the water-resistant of Fe-Co DAC, competitive adsorption behavior between O₃ and dominant environmental gases was discussed through ab initio molecular dynamic (AIMD) simulation. The dominant reaction mechanism of ozone decomposition is L-H and the rate-determining step is the desorption of the first oxygen molecule from the surface of Fe-Co DAC which has an energy barrier of 0.78 eV. Due to this relatively low energy barrier and high turnover frequency (TOF), the optimal operation window of catalytic O₃ decomposition on Fe-Co DAC is <500 K suggesting that catalytic decomposition of O₃ on Fe-Co DAC can occur at room temperature. This theoretical study provides new insights for designing novel catalysts for ozone decomposition and fundamental guidance for subsequent experimental research.

High Water Adsorption MOFs with Optimized Pore-Nanospaces for Autonomous Indoor Humidity Control and Pollutants Removal

The indoor air quality is of prime importance for human daily life and health, for which the adsorbents like zeolites and silica-gels are widely used for air dehumidification and harmful gases capture. Herein, we develop a pore-nanospace post-engineering strategy to optimize the hydrophilicity, water-uptake capacity and air-purifying ability of metal-organic frameworks (MOFs) with long-term stability, offering an ideal candidate with autonomous multi-functionality of moisture control and pollutants sequestration. Through variant tuning of organic-linkers carrying hydrophobic and hydrophilic groups in the pore-nanospaces of prototypical UiO-67, a moderately hydrophilic MOF (UiO-67-4Me-NH₂ -38 %) with high thermal, hydrolytic and acid-base stability is screened out, featuring S-shaped water sorption isotherms exactly located in the recommended comfortable and healthy ranges of relative humidity for indoor ventilation (45 %-65 % RH) and adverse health effects minimization (40-60 % RH). Its exceptional attributes of water-uptake working capacity/efficiency, contaminants removal, recyclability and regeneration promise a great potential in confined indoor environment application.

The crystal structure of catena-poly[(1,10-phenanthroline-k2 N,N′)-(μ3-tetraoxidomoybdato(VI)-k3 O:O′:O″)manganese(II)] C12H8N2O4MoMn

C12H8N2O4MoMn, monoclinic, P21/m (no. 11), a = 8.9812(5) Å, b = 6.5212(3) Å, c = 10.6167(6) Å, β = 100.120(6)°, V = 612.13(6) Å3, Z = 2, R gt (F) = 0.0391, wR ref(F 2) = 0.0783, T = 293(2) K.