Facet Engineered α-MnO2 for Efficient Catalytic Ozonation of Odor CH3SH: Oxygen Vacancy-Induced Active Centers and Catalytic Mechanism

Oxygen Vacancy-Rich Manganese Nanoflowers as Ferroptosis Inducers for Tumor Radiotherapy

The combination of ferroptosis and innovative tumor therapy methods offers another promising answer to the problem of tumors. In order to generate effective ferroptosis in tumor cells, iron-based nanomaterials are commonly utilized to introduce foreign iron as a trigger for ferroptosis. However, this usually necessitates the injection of larger doses of iron into the body. These exogenous iron increases are likely to create concealed concerns for symptoms such as liver damage and allergy. Herein, an iron-free radiosensitizer is introduced, oxygen-vacancy-rich MnO2 nanoflowers (ovs-MnO2), that promotes ferroptosis and modifies the tumor microenvironment to assist radiotherapy. ovs-MnO2 with enriched oxygen vacancies on the surface induces the release of intracellular free iron (Fe2+), which functions as an activator of Fenton reaction and enhances the accumulation of intracellular reactive oxygen species. On the other hand, Fe2+ also triggers the ferroptosis and promotes the accumulation of lipid peroxides. Subsequently, the depletion of glutathione and accumulation of lipid peroxidation in tumor cells leads to the inactivation of glutathione peroxidase 4 (GPX4) and ferroptosis, thereby enhancing the therapeutic efficacy of radiotherapy. The nanoplatform provides a novel strategy for generating novel nanomedicines for ferroptosis-assisted radiotherapy.

Structure and molecular-level transformation for oxidation of effluent organic matters by manganese oxides

As important organic components in water environments, effluent organic matters (EfOMs) from wastewater treatment plants are widely present in Mn-rich environments or engineered treatment systems. The redox interaction between manganese oxides (MnOx) and EfOMs can lead to their structural changes, which are crucial for ensuring the safety of water environments. Herein, the reactivities of MnOx with EfOMs were evaluated, and it was found that MnOx with high specific surface area, active high-valent manganese content and lattice oxygen content (i.e., amorphous MnO2) possessed stronger oxidizing ability towards EfOMs. Accompanying by EfOMs oxidation, Mn(IV) and Mn(III) were reduced into Mn(II), with Mn(III) as the significant active species. Through molecular-level transformation analysis by ultrahigh mass spectrometry (FT-ICR MS), the highly reactive compounds in EfOMs were clearly determined to be that with more aromatic and unsaturated structures, especially lignin-like compounds (the highest content in EfOMs (over 60 %)). EfOMs were oxidized by amorphous MnO2 into products with lower humification index (0.60 vs. 0.46), smaller apparent molecular weight (388.17 Da vs. 369.31 Da), and higher biodegradability (BOD5/COD: 0.12 vs. 0.78). This finding suggested that redox reactions between MnOx and EfOMs might alter their abiotic and biotic behaviors in receiving water environments.

Transforming Plain LaMnO3 Perovskite into a Powerful Ozonation Catalyst: Elucidating the Mechanisms of Simultaneous A and B Sites Modulation for Enhanced Toluene Degradation

Herein, we propose preferential dissolution paired with Cu-doping as an effective method for synergistically modulating the A- and B-sites of LaMnO3 perovskite. Through Cu-doping into the B-sites of LaMnO3, specifically modifying the B-sites, the double perovskite La2CuMnO6 was created. Subsequently, partial La from the A-sites of La2CuMnO6 was etched using HNO3, forming novel La2CuMnO6/MnO2 (LCMO/MnO2) catalysts. The optimized catalyst, featuring an ideal Mn:Cu ratio of 4.5:1 (LCMO/MnO2-4.5), exhibited exceptional catalytic ozonation performance. It achieved approximately 90% toluene degradation with 56% selectivity toward CO2, even under ambient temperature (35 °C) and a relatively humid environment (45%). Modulation of A-sites induced the elongation of Mn-O bonds and decrease in the coordination number of Mn-O (from 6 to 4.3) in LCMO/MnO2-4.5, resulting in the creation of abundant multivalent Mn and oxygen vacancies. Doping Cu into B-sites led to the preferential chemisorption of toluene on multivalent Cu (Cu(I)/Cu(II)), consistent with theoretical predictions. Effective electronic supplementary interactions enabled the cycling of multiple oxidation states of Mn for ozone decomposition, facilitating the production of reactive oxygen species and the regeneration of oxygen vacancies. This study establishes high-performance perovskites for the synergistic regulation of O3 and toluene, contributing to cleaner and safer industrial activities.

Management of methyl mercaptan contained in waste gases - an overview

Methyl mercaptan is a typical volatile organosulfur pollutant contained in many gases emitted by urban waste treatment, various industries, natural gas handling, refining processes, and energy production. This work is a comprehensive overview of the scientific and practical aspects related to the management of methyl mercaptan pollution. The main techniques, including absorption, adsorption, oxidation, and biological treatments, are examined in detail. For each method, its capability as well as the technical advantages and drawbacks have been highlighted. The emerging methods developed for the removal of methyl mercaptan from natural gas are also reviewed. These methods are based on the catalytic conversion of CH3SH to hydrocarbons and H2S.

Portable hydrogel kit driven by bimetallic carbon dots nanozyme for H2O2-self-supplying dual-modal monitoring of atmospheric CH3SH

Due to the typical volatility of gaseous pollutant methyl mercaptan (CH3SH), the development of a facile, reliable, and accurate onsite environmental surveillance of highly toxic CH3SH faces many challenges, but it is critical to environmental atmosphere assessment and safeguarding public health. Here, we prepared a novel bimetallic carbon dots (Fe&Cu@CDs) nanozyme with high peroxidase-mimicking activity to design a portable hydrogel kit for onsite visual H2O2-self-supplying enzymatic cascade catalytic colorimetric and photothermal signal synergistic amplification dual-modal monitoring of CH3SH in atmospheric environment. Assisted by alcohol oxidase (AOX), CH3SH could be specifically converted into H2O2 for oxidizing chromogenic substrate 3,3',5,5'-tetramethylbenzidine (TMB) catalyzed by Fe&Cu@CDs to produce dark blue ox-TMB with absorption at 652 nm and photothermal characters. Consequently, a CH3SH concentration-dependent change both in naked-eye color and photothermal effect-triggered temperature were observed. By hybridizing AOX-assisted Fe&Cu@CDs + TMB with agarose, a H2O2-self-supplying colorimetric and photothermal signal synergistic amplification sensory hydrogel kit integrated with Color Picker APP-installed smartphone and 660 nm laser-equipped handheld thermal imager for CH3SH was proposed with acceptable results in atmospheric environment around wastepile (e.g., solid waste and food waste piles), which exhibited great potentials to further develop commercial onsite monitoring platforms in warning-early abnormal atmospheric CH3SH for safeguarding environmental health.

Can xenobiotics support the growth of Mn(II)-oxidizing bacteria (MnOB)? A case of phenol-utilizing bacteria Pseudomonas sp. AN-1

Biogenic manganese oxides (BioMnOx) produced by Mn(II)-oxidizing bacteria (MnOB) have garnered considerable attention for their exceptional adsorption and oxidation capabilities. However, previous studies have predominantly focused on the role of BioMnOx, neglecting substantial investigation into MnOB themselves. Meanwhile, whether the xenobiotics could support the growth of MnOB as the sole carbon source remains uncertain. In this study, we isolated a strain termed Pseudomonas sp. AN-1, capable of utilizing phenol as the sole carbon source. The degradation of phenol took precedence over the accumulation of BioMnOx. In the presence of 100 mg L-1 phenol and 100 µM Mn(II), phenol was entirely degraded within 20 h, while Mn(II) was completely oxidized within 30 h. However, at the higher phenol concentration (500 mg L-1), phenol degradation reduced to 32% and Mn(II) oxidation did not appear to occur. TOC determination confirmed the ability of strain AN-1 to mineralize phenol. Based on the genomic and proteomics studies, the Mn(II) oxidation and phenol mineralization mechanism of strain AN-1 was further confirmed. Proteome analysis revealed down-regulation of proteins associated with Mn(II) oxidation, including MnxG and McoA, with increasing phenol concentration. Notably, this study observed for the first time that the expression of Mn(II) oxidation proteins is modulated by the concentration of carbon sources. This work provides new insight into the interaction between xenobiotics and MnOB, thus revealing the complexity of biogeochemical cycles of Mn and C.

Boosting the Energy Density of Bowl-Like MnO2@Carbon Through Lithium-Intercalation in a High-Voltage Asymmetric Supercapacitor with "Water-In-Salt" Electrolyte

Highly concentrated "'water-in-salt"' (WIS) electrolytes are promising for high-performance energy storage devices due to their wide electrochemical stability window. However, the energy storage mechanism of MnO2 in WIS electrolytes-based supercapacitors remains unclear. Herein, MnO2 nanoflowers are successfully grown on mesoporous bowl-like carbon (MBC) particles to generate MnO2/MBC composites, which not only increase electroactive sites and inhibit the pulverization of MnO2 particles during the fast charging/discharging processes, but also facilitate the electron transfer and ion diffusion within the whole electrode, resulting in significant enhancement of the electrochemical performance. An asymmetric supercapacitor, assembled with MnO2/MBC and activated carbon (AC) and using 21 m LiTFSI solution as the WIS electrolyte, delivers an ultrahigh energy density of 70.2 Wh kg-1 at 700 W kg-1, and still retains 24.8 Wh kg-1 when the power density is increased to 28 kW kg-1. The ex situ XRD, Raman, and XPS measurements reveal that a reversible reaction of MnO2 + xLi+ + xe-↔LixMnO2 takes place during charging and discharging. Therefore, the asymmetric MnO2/MBC//AC supercapacitor with LiTFSI electrolyte is actually a lithium-ion hybrid supercapacitor, which can greatly boost the energy density of the assembled device and expand the voltage window.

Switching reactive oxygen species reactions derived from Mn-Pt anchored zeolite for selective catalytic ozonation

Rationally switching reactive oxygen species (ROS) reactions in advanced oxidation processes (AOPs) is urgently needed to improve the adaptability and efficiency for the engineering application. Herein we synthesized bimetallic Mn-Pt catalysts based on zeolite to realize the switching of ROS reactions in catalytic ozonation for sustainable degradation of organic pollutants from water. The ROS reactions switched from singlet oxygen (1O2, 71.01%) to radical-dominated (93.79%) pathway by simply introducing defects and changing Pt/Mn ratios. The oxygen vacancy induced by anchoring Mn-Pt species from zeolite external surface (MnPt/H-Beta) to internal framework (MnPt@Si-Beta) exposes more electron-rich Pt2+/Pt4+ redox sites, accelerating the decomposition of O3 to generate •OH via electron transfer and switching ROS reactions. The Mn site acted as a bridge plays a critical role in conducting electrons from organic pollutants to Pt sites, which solidly solves the electron loss of catalysts, facilitating the efficient degradation of pollutants. A 34.7-fold increase in phenol degradation compared with the non-catalytic ozonation and an excellent catalytic stability are achieved by MnPt@Si-Beta/O3. The 1O2-dominated ROS reaction originated from MnPt/H-Beta/O3 exhibits superior performances in anti-interference for Cl-, HCO3-, NO3-, and SO4-. This work establishes a novel strategy for switching ROS reactions to expand the targeted applications of O3 based AOPs for environmental remediation.

S vacancies-introduced chalcopyrite switch radical to non-radical pathways via peroxymonosulfate activation: Vital roles of S vacancies

Regulation of peroxymonosulfate (PMS) activation from radical to non-radical pathways is an emerging focus of advanced oxidation processes (AOPs) due to its superiority of anti-interference to complex wastewater. However, the detailed correlation mechanism between the defect structure of the catalyst and the regulation of radicals/non-radicals remains unclear. Herein, natural chalcopyrite (CuFeS2) with different levels of S vacancies created by a simple NaBH4 reduction process was employed to explore the above-mentioned underlying mechanism for constructing high efficiency and low cost of catalyst towards AOPs. With the assistance of simulated solar light, S-deficient chalcopyrite (Sv-NCP) exhibited prominent performance for PMS activation. More interestingly, the different degrees of S vacancies regulated the active species from radicals to non-radical 1O2, thus showing excellent purification of complex wastewater as well as actual pharmaceutical wastewater. Mechanistic analysis reveals that PMS tends to loss electrons on S vacancies sites and is dissociated into 1O2 rather than ·OH/SO4·- due to electron deficiency. Meanwhile, the improved adsorption performance makes the degradation sites of pollutants change from solution to surface. Most importantly, Sv-NCP presented excellent detoxication for antibiotic wastewater due to the high selectivity of 1O2. This work provides novel insights into the regulation of active species in Fenton-like reactions via defect engineering for high efficiency of pollutant degradation.

Structural/surface characterization of transition metal element-doped H-ZSM-5 adsorbent for CH3SH removal: identification of active adsorption sites and deactivation mechanism

CH3SH is a potential hazard to both chemical production and human health, so controlling its emissions is an urgent priority. In this work, a series of transition metal-loaded H-ZSM-5 adsorbents (Si/Al = 25) (Cu, Fe, Co, Ni, Mn, and Zn) were synthesized through the wet impregnation method and tested for CH3SH physicochemical adsorption at 60 °C. It was shown that the Cu-modified H-ZSM-5 adsorbent was much more active for CH3SH removal due to its abundant strong acid sites than other transition metal-modified H-ZSM-5 adsorbents. The detailed physicochemical properties of various modified H-ZSM-5 adsorbents were characterized by SEM, XRD, N2 physisorption, XPS, H2-TPR, and NH3-TPD. The effects of metal loading mass ratio, calcination temperature, and acid or alkali modification on the performance of the adsorbent were also investigated, and finally 20% Cu/ZSM-5 was found to have the best adsorption capacity after calcined at 350 °C. Additionally, the Cu/ZSM-5 adsorbent modified by sodium bicarbonate could expose more active components, which improved the adsorbent's stability. However, the consumption and reduction of the active component Cu2+ and the accumulation of sulfate during the adsorption process are the main reasons for the deactivation of the adsorbent. In addition, the simultaneous purging of N2 + O2 can effectively restore the adsorption capacity of the deactivated adsorbent and can be used as a potential strategy to regenerate the adsorbent.

Synergically regulated silver species and surface oxygen on manganese oxide for promoted activity of formaldehyde oxidation

Formaldehyde (HCHO) is a common indoor pollutant that is detrimental to human health. Its efficient removal has become an urgent demand to reduce the public health risk. In this work, Ag-MnOx-based catalysts were prepared and activated under different atmosphere (i.e., air, hydrogen (H2) and carbon monoxide (CO)) for efficient oxidation of HCHO. The catalyst activated with CO (Ag/Mn-CO) displayed the highest activity among the tested samples with 90% conversion at 100°C under a gas space velocity of 75,000 mL/(gcat·hr). Complementary characterizations demonstrate that CO reduction treatment resulted in synergically regulated content of surface oxygen on support to adsorb/activate HCHO and size of Ag particle to dissociate oxygen to oxidize the adsorbed HCHO. In contrast, other catalysts lack for either abundant surface oxygen species or metallic silver with the appropriate particle size, so that the integrate activity is limited by one specific reaction step. This study contributes to elucidating the mechanisms regulating the oxidation activity of Ag-based catalysts.

Promoted catalytic performance of Ag-Mn bimetal catalysts synthesized through reduction route

VOCs can exert great harm to both human and environment, and catalytic oxidation is believed to be an effective technique to eliminate these pollutants. In this paper, Ag-Mn bimetal catalysts with 10 wt.% of silver were synthesized using doping, impregnation, and reduction methods respectively, and then they were applied to the catalytic oxidation of benzene. Through series of characterizations it showed that the loading of silver using reduction method significantly resulted in improved physico-chemical properties of manganese oxides, such as larger surface area and pore volume, higher proportion of surface Mn3+ and Mn4+, stronger reducibility and more active of surface oxygen species, which were all beneficial to its catalytic activity. As a result, the Ag-Mn catalysts synthesized by reduction method showed a lower T90 value (equals to the temperature at which 90% of initial benzene was removed) of 203°C. Besides, both the used and fresh Ag-Mn catalysts synthesized by reduction method showed preferable stability in this research.

Effective degradation of quinoline by catalytic ozonation with MnCexOy catalysts: performance and mechanism

Quinoline inevitably remains in the effluent of coking wastewater treatment plants due to its bio-refractory nature, which might cause unfavorable effects on human and ecological environments. In this study, MnCexOy was consciously synthesized by α-MnO2 doped with Ce3+ (Ce:Mn = 1:10) and employed as the ozonation catalyst for quinoline degradation. After that, the removal efficiency and mechanism of quinoline were systematically analyzed by characterizing the physicochemical properties of MnCexOy, investigating free radicals and monitoring the solution pH. Results indicated that the removal rate of quinoline was greatly improved by the prepared MnCexOy catalyst. Specifically, the removal efficiencies of quinoline could be 93.73, 62.57 and 43.76%, corresponding to MnCexOy, α-MnO2 and single ozonation systems, respectively. The radical scavenging tests demonstrated that •OH and •O2- were the dominant reactive oxygen species in the MnCexOy ozonation system. Meanwhile, the contribution levels of •OH and •O2- to quinoline degradation were about 42 and 35%, respectively. The abundant surface hydroxyl groups and oxygen vacancies of the MnCexOy catalyst were two important factors for decomposing molecular O3 into more •OH and •O2-. This study could provide scientific support for the application of the MnCexOy/O3 system in degrading quinoline in bio-treated coking wastewater.

Integrated Optimization of Crystal Facets and Nanoscale Spatial Confinement toward the Boosted Catalytic Performance of Pd Nanocrystals

Tuning the surface chemical property and the local environment of nanocrystals is crucial for realizing a high catalytic performance in various reactions. Herein, we aim to elucidate the structure sensitivity of Pd facets on the surface catalytic hydrogenation reaction and to identify what role the nanoconfinement effect plays in the catalytic properties of Pd nanocrystal catalysts. By controlling the coating structures of mesoporous silica (mSiO2) on Pd nanocrystals with different exposed facets that include {100}, {111}, and {hk0}, we present a series of Pd@mSiO2 nanoreactors in core-shell and yolk-shell structures and the discovery of a partial-coated structure, which can provide different types of nanoconfinement, and we propose a seed size-dominated growth mechanism. We demonstrate that a superior activity was exhibited in Pd nanocrystals enclosed by the {hk0} facet as compared to the Pd{100} and Pd{111} facets, and substantially enhanced efficiency and stability were achieved in Pd@mSiO2 particles with yolk-shell structures, indicating a crucial superiority of optimizing the configuration of crystal facets and nanoconfinement. Our study provides an efficient strategy to rationally design and optimize nanocatalysts for promoting catalytic performance.

Selective Synergistic Catalytic Elimination of NOx and CH3SH via Engineering Deep Oxidation Sites against Toxic Byproducts Formation

NOx and CH3SH as two typical air pollutants widely coexist in various energy and industrial processes; hence, it is urgent to develop highly efficient catalysts to synergistically eliminate NOx and CH3SH. However, the catalytic system for synergistically eliminating NOx and CH3SH is seldom investigated to date. Meanwhile, the deactivation effects of CH3SH on catalysts and the formation mechanism of toxic byproducts emitted from the synergistic catalytic elimination reaction are still vague. Herein, selective synergistic catalytic elimination (SSCE) of NOx and CH3SH via engineering deep oxidation sites over Cu-modified Nb-Fe composite oxides supported on TiO2 catalyst against toxic CO and HCN byproducts formation has been originally demonstrated. Various spectroscopic and microscopic characterizations demonstrate that the sufficient chemisorbed oxygen species induced by the persistent electron transfer from Nb-Fe composite oxides to copper oxides can deeply oxidize HCOOH to CO2 for avoiding highly toxic byproducts formation. This work is of significance in designing superior catalysts employed in more complex working conditions and sheds light on the progress in the SSCE of NOx and sulfur-containing volatile organic compounds.

Engineering the Crystal Facet of Monoclinic NiO for Efficient Catalytic Ozonation of Toluene

Modulating oxygen vacancies of catalysts through crystal facet engineering is an innovative strategy for boosting the activity for ozonation of catalytic volatile organic compounds (VOCs). In this work, three kinds of facet-engineered monoclinic NiO catalysts were successfully prepared and utilized for catalytic toluene ozonation (CTO). Density functional theory calculations revealed that Ni vacancies were more likely to form preferentially than O vacancies on the (110), (100), and (111) facets of monoclinic NiO due to the stronger Ni-vacancy formation ability, further affecting O-vacancy formation. Extensive characterizations demonstrated that Ni vacancies significantly promoted the formation of O vacancies and thus reactive oxygen species in the (111) facet of monoclinic NiO, among the three facets. The performance evaluation showed that the monoclinic NiO catalyst with a dominant (111) facet exhibits excellent performance for CTO, achieving a toluene conversion of ∼100% at 30 °C after reaction for 120 min under 30 ppm toluene, 210 ppm ozone, 45% relative humidity, and a space velocity of 120 000 h-1. This outperformed the previously reported noble/non-noble metal oxide catalysts used for CTO at room temperature. This study provided novel insight into the development of highly efficient facet-engineered catalysts for the elimination of catalytic VOCs.

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.

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.

Engineering the crystal facets of α-MnO2 nanorods for electrochemical energy storage: experiments and theory

Crystal facet engineering is an effective strategy for precisely regulating the orientations and electrochemical properties of metal oxides. However, the contribution of each crystal facet to pseudocapacitance is still puzzling, which is a bottleneck that restricts the specific capacitance of metal oxides. Herein, α-MnO2 nanorods with different exposed facets were synthesized through a hydrothermal route and applied to pseudocapacitors. XRD and TEM results verified that the exposure ratio of active crystal facets was significantly increased with the assistance of the structure-directing agents. XPS analysis showed that there was more adsorbed oxygen and Mn3+ on the active crystal facets, which can provide strong kinetics for the electrochemical reaction. Consequently, the α-MnO2 nanorods with {110} and {310} facets exhibited much higher pseudocapacitances of 120.0 F g-1 and 133.0 F g-1 than their α-MnO2-200 counterparts (67.5 F g-1). The theoretical calculations proved that the {310} and {110} facets have stronger adsorption capacity and lower diffusion barriers for sodium ions, which is responsible for the enhanced pseudocapacitance of MnO2. This study provides a strategy to enhance the electrochemical performance of metal oxide, based on facet engineering.

Controlled synthesis of Fe3O4/MnO2 (3 1 0)/ZIF-67 composite with enhanced synergetic effects for the highly selective and efficient adsorption of Cu (II) from simulated copperplating effluents

This study designed a composite material with internal synergistic effects among multiple components to achieve highly selective adsorption of Cu (II). Through controlled synthesis, the Fe3O4/MnO2(3 1 0)/ZIF-67 composite was successfully fabricated, leading to significant improvement in adsorption selectivity, capacity, and adsorption rate. The experimental results showed that the composite is of outstanding selectivity in the adsorption of Cu (II), with a partition coefficient K of Cu (II) that was 2.2-5.3 times higher than that of other coexisting ions. Moreover, the composite exhibited a remarkable adsorption capacity of 1261.0 mg g-1 and a fast adsorption rate of 840.7 mg g-1 h-1 at 298 K. Additionally, its magnetic property facilitated easy separation from wastewater, thereby enhancing its potential for commercial applications. The synergetic effect mechanism was analyzed through characterizations and DFT calculations. Furthermore, the recyclability of the composite was investigated, which showed that after seven cycles, the adsorption efficiency remained at 85% of its initial efficiency. It can be concluded that Fe3O4/MnO2(3 1 0)/ZIF-67 has potential to address challenges posed by heavy metal pollution in copperplating effluents.

Oxygen doped graphite carbon nitride as efficient metal-free catalyst for peroxymonosulfate activation: Performance, mechanism and theoretical calculation

In this study, oxygen-doped graphitic carbon nitride (g-C3N4), named O-g-C3N4, was successfully fabricated and characterized, and its performance in activating peroxymonosulfate (PMS, HSO5-) for the removal of phenol, 2,4-dichlorophenol (2,4-DCP), bisphenol A (BPA), rhodamine B (RhB), reactive brilliant blue (RBB) and acid orange 7 (AO7) was evaluated. The catalytic performance of O-g-C3N4 for AO7 removal increased by 14 times compared to g-C3N4. In the presence of 0.2 g L-1 O-g-C3N4, 3.5 mM PMS at natural pH 5.8, 96.4% of AO7 could be removed in 60 min, reduced toxicity of the treated AO7 solution was obtained, and the mineralization efficiency was 47.2% within 120 min. Density functional theory (DFT) calculations showed that the charge distribution changed after oxygen doping, and PMS was more readily adsorbed by O-g-C3N4 with the adsorption energy (Eads) of -0.855 kcal/mol than that of the pristine g-C3N4 (Eads: -0.305 kcal/mol). Mechanism investigation implied that AO7 was primarily removed by the sulfate radicals (SO4•-) and hydroxyl radicals (•OH) on the surface of O-g-C3N4, but the role of singlet oxygen (1O2) to AO7 elimination was negligible. The results of cyclic experiments and catalyst characterization after reaction confirmed the favorable catalytic activity and structural stability of O-g-C3N4 particles. Furthermore, the O-g-C3N4/PMS system was very resistant to most of the environmental impacts, and AO7 removal was still acceptable in natural water environment. This study may provide an efficient metal-free carbonaceous activator with low dosage for PMS activation to remove recalcitrant organic pollutants (ROPs).

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.

In Situ Regulation of MnO2 Structural Characteristics by Oxyanions to Boost Permanganate Autocatalysis for Phenol Removal

Oxyanions, a class of constituents naturally occurring in water, have been widely demonstrated to enhance permanganate (Mn(VII)) decontamination efficiency. However, the detailed mechanism remains ambiguous, mainly because the role of oxyanions in regulating the structural parameters of colloidal MnO2 to control the autocatalytic activity of Mn(VII) has received little attention. Herein, the origin of oxyanion-induced enhancement is systematically studied using theoretical calculations, electrochemical tests, and structure-activity relation analysis. Using bicarbonate (HCO3-) as an example, the results indicate that HCO3- can accelerate the degradation of phenol by Mn(VII) by improving its autocatalytic process. Specifically, HCO3- plays a significant role in regulating the structure of in situ produced MnO2 colloids, i.e., increasing the surface Mn(III)s content and restricting particle growth. These structural changes in MnO2 facilitate its strong binding to Mn(VII), thereby triggering interfacial electron transfer. The resultant surface-activated Mn(VII)* complexes demonstrate excellent degrading activity via directly seizing one electron from phenol. Further, other oxyanions with appropriate ionic potentials (i.e., borate, acetate, metasilicate, molybdate, and phosphate) exhibit favorable influences on the oxidative capability of Mn(VII) through an activation mechanism similar to that of HCO3-. These findings considerably improve our fundamental understanding of the oxidation behavior of Mn(VII) in actual water environments and provide a theoretical foundation for designing autocatalytically boosted Mn(VII) oxidation systems.

Nanozyme Rich in Oxygen Vacancies Derived from Mn-Based Metal-Organic Gel for the Determination of Alkaline Phosphatase

Vacancy engineering as an effective strategy has been widely employed to regulate the enzyme-mimic activity of nanomaterials by adjusting the surface, electronic structure, and creating more active sites. Herein, we purposed a facile and simple method to acquire transition metal manganese oxide rich in oxygen vacancies (OVs-Mn2O3-400) by pyrolyzing the precursor of the Mn(II)-based metal-organic gel directly. The as-prepared OVs-Mn2O3-400 exhibited superior oxidase-like activity as oxygen vacancies participated in the generation of O2•-. Besides, steady state kinetic constant (Km) and catalytic kinetic constant (Ea) suggested that OVs-Mn2O3-400 had a stronger affinity toward 3,3',5,5'-tetramethylbenzidine and possessed prominent catalytic performance. By taking 2-phospho-l-ascorbic acid as the substrate, which can be converted into reducing substance ascorbic acid in the presence of alkaline phosphatase (ALP), OVs-Mn2O3-400 can be applied as an efficient nanozyme for ALP colorimetric analysis without the help of destructive H2O2. The colorimetric sensor established by OVs-Mn2O3-400 for ALP detection showed a good linearity from 0.1 to 12 U/L and a lower limit of detection of 0.054 U/L. Our work paves the way for designing enhanced enzyme-like activity nanozymes, which is of significance in biosensing.

S modified manganese oxide for high efficiency of peroxydisulfate activation: Critical role of S and mechanism

Mn₂O₃ as a typical Mn based semiconductor has attracted growing attention due to its peculiar 3d electron structure and stability, and the multi-valence Mn on the surface is the key to peroxydisulfate activation. Herein, an octahedral structure of Mn₂O₃ with (111) exposed facet was synthesized by a hydrothermal method, which was further sulfureted to obtained a variable-valent Mn oxide for the high activation efficiency of peroxydisulfate under the light emitting diode irradiation. The degradation experiments showed that under the irradiation of 420 nm light, S modified manganese oxide showed an excellent removal for tetracycline within 90 min, which is about 40.4% higher than that of pure Mn₂O₃. In addition, the degradation rate constant k of S modified sample increased 2.17 times. Surface sulfidation not only increased the active sites and oxygen vacancies on the pristine Mn₂O₃ surface, but also changed the electronic structure of Mn due to the introduce of surface S^2-. This modification accelerated the electronic transmission during the degradation process. Meanwhile, the utilization efficiency of photogenerated electrons was greatly improved under light. Besides, the S modified manganese oxide had an excellent reuse performance after four cycles. The scavenging experiments and EPR analyses showed that •OH and ¹O₂ were the main reactive oxygen species. This study therefore provides a new avenue for further developing manganese-based catalysts towards high activation efficiency for peroxydisulfate.

Redox-Induced In Situ Growth of MnO2 with Rich Oxygen Vacancies over Monolithic Copper Foam for Boosting Toluene Combustion

Catalytic combustion has been known to be an effective technique in volatile organic compound (VOC) abatement. Developing monolithic catalysts with high activity at low temperatures is vital yet challenging in industrial applications. Herein, monolithic MnO₂-O_v/CF catalysts were fabricated via the in situ growth of K₂CuFe(CN)₆ (CuFePBA, a family of metal-organic frames) over copper foam (CF) followed by a redox-etching route. The as-synthesized monolith MnO₂-O_v-0.04/CF catalyst displays a superior low-temperature activity (T_90% = 215 °C) and robust durability for toluene elimination even in the presence of 5 vol % water. Experimental results reveal that the CuFePBA template not only guides the in situ growth of δ-MnO₂ with high loading over CF but also acts as a source of dopant to create more oxygen vacancies and weaken the strength of the Mn-O bond, which considerably improves the oxygen activation ability of δ-MnO₂ and consequently boosts the low-temperature catalytic activity of the monolith MnO₂-O_v-0.04/CF toward toluene oxidation. In addition, the reaction intermediate and proposed mechanism in the MnO₂-O_v-0.04/CF mediated catalytic oxidation process were investigated. This study provides new insights into the development of highly active monolithic catalysts for the low-temperature oxidation of VOCs.

Performance of nitrification-denitrification and denitrifying phosphorus removal driven by in-situ generated biogenic manganese oxides in a moving bed biofilm reactor

Simultaneous removal of NH₄⁺-N, NO₃^--N, COD, and P by manganese redox cycling in nutrient wastewater was established with two moving bed biofilm reactors (MBBRs) with in-situ generated biogenic manganese oxides (BioMnOx) and non-BioMnOx. In-situ generated BioMnOx preferentially promoted the denitrification, and the average removal of NO₃^--N, NH₄⁺-N, and TN in the experimental MBBR with BioMnOx increased to 89.00%, 70.64%, and 76.06% compared with the control MBBR with non-BioMnOx. The relevant enzymes activity, extracellular polymeric substance (EPS), electron transport system activity (ETSA), and reactive oxygen species (ROS) were investigated. The element valence and morphology of purified BioMnOx were characterized by X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM), as well as the effect of BioMnOx on nitrogen and phosphorus removal. The results suggested that BioMnOx could improve nitrogen conversion. Electrochemical characteristic and microbial community were detected. This study provided a new strategy for nutrients removal in BioMnOx-mediated wastewater treatment.

Catalytic Ozonation of Polluter Benzene from -20 to >50 °C with High Conversion Efficiency and Selectivity on Mullite YMn2O5

Catalytic decomposition of aromatic polluters at room temperature represents a green route for air purification but is currently challenged by the difficulty of generating reactive oxygen species (ROS) on catalysts. Herein, we develop a mullite catalyst YMn₂O₅ (YMO) with dual active sites of Mn³⁺ and Mn⁴⁺ and use ozone to produce a highly reactive O* upon YMO. Such a strong oxidant species on YMO shows complete removal of benzene from -20 to >50 °C with a high CO_x selectivity (>90%) through the generated reactive species O* on the catalyst surface (60 000 mL g^-1 h^-1). Although the accumulation of water and intermediates gradually lowers the reaction rate after 8 h at 25 °C, a simple treatment by ozone purging or drying in the ambient environment regenerates the catalyst. Importantly, when the temperature increases to 50 °C, the catalytic performance remains 100% conversion without any degradation for 30 h. Experiments and theoretical calculations show that such a superior performance stems from the unique coordination environment, which ensures high generation of ROS and adsorption of aromatics. Mullite's catalytic ozonation degradation of total volatile organic compounds (TVOC) is applied in a home-developed air cleaner, resulting in high efficiency of benzene removal. This work provides insights into the design of catalysts to decompose highly stable organic polluters.

Boosting Ozone Catalytic Oxidation of Toluene at Room Temperature by Using Hydroxyl-Mediated MnOx/Al2O3 Catalysts

Ozone catalytic oxidation (OZCO) has gained great interest in environmental remediation while it still faces a big challenge during the deep degradation of refractory volatile organic compounds (VOCs) at room temperature. Hydroxylation of the catalytic surface provides a new strategy for regulating the catalytic activity to boost VOC degradation. Herein, OZCO of toluene at room temperature over hydroxyl-mediated MnO_x/Al₂O₃ catalysts was originally demonstrated. Specifically, a novel hydroxyl-mediated MnO_x/Al₂O₃ catalyst was developed via the in situ AlOOH reconstruction method and used for toluene OZCO. The toluene degradation performance of MnO_x/Al₂O₃ was significantly superior to those of most of the state-of-the-art catalysts, and 100% toluene was removed with an excellent mineralization rate (82.3%) and catalytic stability during OZCO. ESR and in situ DRIFTs results demonstrated that surface hydroxyl groups (HGs) greatly improved the reactive oxygen species generation, thus dramatically accelerating the benzene ring breakage and deep mineralization. Furthermore, HGs provided anchoring sites for uniformly dispersing MnO_x and greatly enhanced toluene adsorption and ozone activation. This work paves a way for deep decomposition of aromatic VOCs at room temperature.

Photo-sterilization of groundwater by tellurium and enhancement by micro/nano bubbles

In rural areas where low-temperature groundwater is used as a drinking water source, cost-effective sterilization techniques are needed to prevent groundwater consumers from the disease risks triggered by pathogenic microorganisms like Escherichia coli and fungal spores. In this study, micro/nano bubbles (MNBs) coupled with the tellurium (Te)-based catalysts were used to considerably enhance the solar disinfection (SODIS) efficiency while overcoming the intrinsic defects of SODIS, particularly in low-temperature. Sterilization tests showed that 6.5 log₁₀ cfu/mL of E. coli K-12 and 4.0 log₁₀ cfu/mL of Aspergillus niger spores were completely inactivated within 5 min while applying this novel process for disinfection of raw groundwater, even in low-temperature. The underlying mechanisms of the extraordinary sterilization efficiency were revealed through comprehensive characterization of the catalysts and the physiological changes of the microorganisms. The localized surface plasmon resonance (LSPR) effect of the Te catalysts was identified to take advantage of photothermal synergism to achieve cell death. The integration of MNBs with the facet-engineered Te catalysts improved the photothermal catalytic effect and extracellular electron transfer, which substantially strengthened disinfection efficiency. This study provides a targeted solution into microbial inactivation in groundwater and emphasizes a cost-effective groundwater sterilization process.

Ultrafast short-range catalytic pathway modified peroxymonosulfate activation over CuO with surface oxygen defects for tetracycline hydrochloride degradation

The presence of antibiotics in water bodies seriously threatens the ecosystem and human health. Advanced oxidation processes (AOPs) based on peroxymonosulfate (PMS), an effective method to remove antibiotics, have a bottleneck problem that the low oxidant utilization is attributed to the hindered electron transfer between metal oxides and peroxides. Here, CuO with rich oxygen vacancies (OVs), MSCuO-300, was synthesized to efficiently degrade tetracycline hydrochloride (TTCH) (k = 0.095 min^-1). The dominant role of direct adsorption and activation of OVs and its regulated Cu-O, rather than surface hydroxyl adsorption, mediated a short-range catalytic pathway. The shortened catalytic pathway between active sites and PMS accelerated the charge transfer at the interface, which promoted PMS activation. Compared with Cu_xO-500 and Commercial CuO, the activation rate of PMS was increased by 11.97, and 12.64 times, respectively. OVs contributed to the production of ¹O₂ and O₂^•-, the main active species. In addition, MSCuO-300/PMS showed excellent adaptability to real water parameters, such as pH (3-11), anions, and continuous reactor maintained for 168 h. This study provides a successful case for the purification of antibiotic-containing wastewater in the design of efficient catalysts by oxygen defect strategies.

Volatile organic compound removal by post plasma-catalysis over porous TiO2 with enriched oxygen vacancies in a dielectric barrier discharge reactor

Non-thermal plasma (NTP) degradation of volatile organic compounds (VOCs) into CO₂ and H₂O is a promising strategy for addressing ever-growing environment pollution. However, its practical implementation is hindered by low conversion efficiency and emissions of noxious by-products. Herein, an advanced low-oxygen-pressure calcination process is developed to fine-tune the oxygen vacancy concentration of MOF-derived TiO₂ nanocrystals. Vo-poor and Vo-rich TiO₂ catalysts were placed in the back of an NTP reactor to convert harmful ozone molecules into ROS that decompose VOCs via heterogeneous catalytic ozonation processes. The results indicate that Vo-TiO₂-5/NTP with the highest Vo concentration exhibited superior catalytic activity in the degradation of toluene compared to NTP-only and TiO₂/NTP, achieving a maximum 96% elimination efficiency and 76% CO_x selectivity at an SIE of 540 J L^-1. Mechanistic analysis reveals that the ¹O₂, ˙O₂^- and ˙OH species derived from the activation of O₃ molecules on Vo sites contribute to the decomposition of toluene over the Vo-rich TiO₂ surface. With the aid of advanced characterization and density functional theory calculations, the roles of oxygen vacancies in manipulating the synergistic capability of post-NTP systems were explored, and were attributed to increased O₃ adsorption ability and enhanced charge transfer dynamics. This work presents novel insights into the design of high-efficiency NTP catalysts structured with active Vo sites.

Oxygen vacancy regulation strategy in V-Nb mixed oxides catalyst for enhanced aerobic oxidative desulfurization performance

Bimetallic oxide is a potential catalyst for oxidative desulfurization of fuel. Thus, an appropriate method is needed to improve its catalytic performance. Manufacturing defect is an effective means. In this contribution, an oxygen vacancies (OVs) regulation strategy for enhancing the catalytic activity of bimetallic oxide is proposed. Density functional theory (DFT) calculations show that the crystal phase has a huge influence on the generation energy of oxygen vacancies, so a series of V-Nb mixed oxide with different crystal phases are synthesized. Detailed characterizations show that the as-prepared tetragonal V-Nb mixed oxide (T-VNbO_x) has lower OVs formation energy and larger OVs concentration (compared to orthorhombic V-Nb mixed oxides, O-VNbO_x). Owing to the activation of OVs, the catalytic activity of T-VNbO_x was significantly enhanced to form ultra-deep oxidative desulfurization. In addition, T-VNbO_x can be cycled eight times without significantly degrading the desulfurization performance.

The increased oxygen vacancy by morphology regulation of MnO2 for efficient removal of PAHs in aqueous solution

Manganese dioxide (MnO₂) is considered to have a promising future in degrading polycyclic aromatic hydrocarbons (PAHs) in aqueous phase because of its low cost and environmental friendliness. In this study, various MnO₂ morphologies were prepared, and their removal performance and mechanism were evaluated using benzo(a)pyrene (B[a]P) as model molecule. Results showed that nanoflower MnO₂ with higher concentration of oxygen vacancies exhibited better oxidative and easier oxygen migration properties, and thus enhanced PAHs removal by 14.28%-43.21% compared with other MnO₂ samples. Additionally, the transformation rate of PAHs is correlated with their ionization potential (IP) values. Further mechanism studies showed that the degradation of B[a]P by MnO₂ process was first to form a combination and then oxidized by non-radical Mn species and superoxide radical (O₂^-•) to produce degradation product (B[a]P-6-one and B[a]P-6,12-quinone). The specific surface area was not the main factor affecting the removal of B[a]P by MnO₂ and oxidation was the main removal mechanism of degrading B[a]P by MnO₂. Mn³⁺ and absorbed oxygen (O_abs) played an important role in the process of removing PAHs by MnO₂. Additionally, synergistic effects of oxygen vacancy and Mn³⁺could be benefit for transforming O_abs to O₂^-•, leading to the efficient degradation of PAHs.

Effective Toluene Ozonation over δ-MnO2: Oxygen Vacancy-Induced Reactive Oxygen Species

To improve the reactivity and lifetime of catalysts in the catalytic ozonation of toluene, a simple strategy was provided to regulate the morphology and microstructure of δ-MnO₂ via the hydrothermal reaction temperature. The effects of the reaction temperature and the ozone to toluene concentration ratio on the catalyst performance were investigated. The optimized MnO₂-260 catalyst prepared at the limiting hydrothermal temperature (260 °C) showed high catalytic activity (X_Tol = 95%) and excellent stability (1200 min) at the approximately ambient temperature of 40 °C, which was superior to the results in previous studies. The structure and morphology of δ-MnO₂ were characterized by extended X-ray absorption fine structure, X-ray diffraction, scanning electron microscopy, positron annihilation lifetime spectroscopy, electron spin resonance, and other techniques. Experimental results and density functional theory calculations were in agreement that surface oxygen vacancy clusters, especially surface oxygen dimer vacancies, are critical in ozone activation. Oxygen vacancies can facilitate the adsorption and activation of O₃ to generate reactive oxygen species (ROS, including ¹O₂, O₂^-, and ^•OH), leading to superior ozonation activity to degrade toluene and intermediates. Meanwhile, free radical detection and scavenger tests indicated that ^•OH is the primary ROS during toluene ozonation rather than ¹O₂ or O₂^-.

Enhanced H2O2 utilization efficiency in Fenton-like system for degradation of emerging contaminants: Oxygen vacancy-mediated activation of O2

Hydrogen peroxide (H₂O₂) is the most commonly used oxidant in advanced oxidation processes for emerging organic contaminant degradation. However, the activation of H₂O₂ to generate reactive oxygen species is always accompanied by O₂ generation resulting in H₂O₂ waste. Here, we prepare a Ti doped Mn₃O₄/Fe₃O₄ ternary catalyst (Ti-Mn₃O₄/Fe₃O₄) to create abundant oxygen vacancies (OVs), which yields electron delocalization impacts on enhancing the electrical conductivity, accelerating the activation of O₂ to produce H₂O₂. In Ti-Mn₃O₄/Fe₃O₄/H₂O₂ system, OVs-mediated O₂/O₂^•-/H₂O₂ redox cycles trigger the activation of locally generated O₂, boost the regeneration of O₂^•- and on site produce H₂O₂ for replenishment. This leads to a 100% removal of tiamulin in 30 min at an unprecedented H₂O₂ utilization efficiency of 96.0%, which is 24 folds higher than that with Fe₃O₄/H₂O₂. Importantly, further integration of Ti-Mn₃O₄/Fe₃O₄ catalysts into membrane filtration achieved high rejections of tiamulin (> 83.9%) from real surface water during a continuous 12-h operation, demonstrating broad pH adaptability, excellent catalytic stability and leaching resistance. This work demonstrates a feasible strategy for developing OVs-rich catalysts for improving H₂O₂ utilization efficiency via activation of locally generated oxygen during the Haber-Weiss reaction.

Thermal Annealing Induced Surface Oxygen Vacancy Clusters in α-MnO2 Nanowires for Catalytic Ozonation of VOCs at Ambient Temperature

Catalytic ozonation has gained considerable interest in volatile organic compound (VOC) elimination due to its mild reaction conditions. However, the low activity and mineralization rate of VOCs over catalysts hinder its practical application. Herein, a series of α-MnO2 nanowire catalysts were prepared via thermal annealing treatment at various temperatures to tailor defect species. Numerous characterization techniques were used and combined to investigate the relationship between activity and microstructure. PALS and XAFS indicated that more unsaturated manganese and oxygen vacancies, especially surface oxygen vacancy clusters, were produced in α-MnO2 under the optimal high calcination temperature. As a result, MnO2-600 was found to exhibit the best-ever performance in toluene conversion (95%) and mineralization rate (89.5%) at 20 °C, making it a promising candidate for practical use. The roles of these defects in manipulating the reactive oxygen species of α-MnO2 were clarified by quantifying the amounts of reactive oxygen species by quenching experiments and density functional theory calculations. 1O2 and ·OH species generated in the vicinity of oxygen vacancy clusters, especially the dimer oxygen vacancy cluster, were identified as key oxygen species in the abatement of toluene. This study provides a facile method to engineer the microstructure of MnO2 by means of the manipulation of oxygen vacancies and an in-depth understanding of their roles in the catalytic ozonation of VOC.

New insight into the enhanced ozonation of malodorous compounds by Cu(II): Inhibiting the formation of free radicals to promote ozone utilization

Metal-enhanced ozonation can greatly improve the decay of organic matter; however, whether this method benefits the decay of malodorous compounds or not and the possible mechanism are not well understood. In this study, nine typical malodorous compounds were selected to reveal that Cu(II)-enhanced ozonation can greatly promote the decay of fatty amines because of the direct ozone oxidation, which was enhanced to promote ozone utilization. Moreover, trace Cu(II) can amplify the observed rate constants of dimethylamine and trimethylamine for 48.9% and 155.7%, respectively, and Cu(II) dosage was the determining factor using response surface methodology to investigate the interactions between initial pH, Cu(II) dosage and ozone dosage. These results demonstrated that the formation of ^•OH and O₂^•- was inhibited rather than promoted, which was quite different from some previously reported Cu(II)-enhanced ozonation counterparts. Moreover, the enhanced effect of trace Cu(II) was exhibited in both single and complex malodorous compounds. The conversion pathway of nitrogen and sulfur elements was clarified, with the targeted mineralization of nitrogen of nitrogen-containing malodorous compounds into NO₃-N and the odor characteristics of sulfur-containing malodorous compounds disappeared. These findings provided new insight for utilizing metal ions to enhance the direct ozone oxidation capacity of malodorous compounds.

Insights into the influence of water molecules on selective catalytic ozonation of gaseous ammonia into nitrogen on cryptomelane-type manganese oxide using in-situ DRIFTS

Catalytic ozonation is an environmentally friendly technology for the removal of gaseous NH₃ due to high NH₃ conversion and high N₂ selectivity at ambient temperature. However, the influence mechanism of ubiquitous water vapor on catalytic ozonation of NH₃ is unclear. In this study, cryptomelane-type manganese oxide (OMS-2) catalyst was prepared and tested for catalytic ozonation of NH₃ in different relative humidity. The results showed that water vapor significantly decreased the catalytic activity, which was due to the inhibition of water on NH₃ adsorption on Lewis acid sites and O₃ decomposition on oxygen vacancies, as well as the combination of water with active oxygen species (O₂^2- and O_atom). And the effect of water vapor on NH₃ conversion was more significant than O₃ decomposition because more Mn-OH were involved in the O₃ decomposition under humid conditions. Combining in-situ DRIFTS results with the performance of NH₃ oxidation, it is found that L-2 acid sites (the peak of NH₃ adsorption on Lewis acid sites at 1188 cm^-1) were the main active sites for adsorption and activation of NH₃ in the early stage of catalytic reaction; as the reaction progressed, L-2 acid sites were gradually occupied by water and more Brønsted acid sites participated in the catalytic reaction. This work deepened the understanding of the reaction process for selective catalytic ozonation of NH₃, and provided theoretical guidance for the design of efficient hydrophobic catalysts to eliminate gaseous NH₃ pollution.

Cordierite and citric acid regulate crystal structure of manganese oxide for effective selective catalytic reduction of nitrogen oxide

Catalyst is the key to effective selective catalytic reduction of nitrogen oxide, and developing catalyst is always one of the hottest topics in both field of industry and academy. In order to realize an industrial application, one catalyst must grow on a specific support. However, seldom work compared the difference of catalyst growth with or without support. In this work, Mn²⁺ growth on cordierite (a typical commercial catalyst support) was investigated. The formed active species were detailedly characterized. As a result, orthorhombic cordierite guided Mn²⁺ to form orthorhombic oxide (γ-MnO₂). In comparison, Mn²⁺ preferred to form tetragonal β-MnO₂ without the guide of cordierite. During the synthesis, cordierite and citric acid promoted γ-MnO₂ dispersion, increased growth of exposed (301) facet, and created lattice distortion between (301) and (101) planes. β-MnO₂ mainly exposed (101) facet. The best catalyst was γ-MnO₂, which was mostly dominated by (301) facet and had an obvious lattice distortion from 75° to 78° between (301) and (101) planes. In comparison, 0.1 g of the γ-MnO₂ reached a catalytic conversion rate 1.6 times bigger than 1.0 g of β-MnO₂ at 250 °C. This work helps to understand guiding effect of support on formed catalytic species, which is in favor of developing effective commercial catalysts for environmental pollutants.

Engineering an Enzymatic Cascade Catalytic Smartphone-Based Sensor for Onsite Visual Ratiometric Fluorescence-Colorimetric Dual-Mode Detection of Methyl Mercaptan

Precise and reliable onsite detection of methyl mercaptan (CH₃SH) is of great significance for environmental surveillance. Here, we synthesized a novel blue fluorescence nanozyme CeO₂@TPE with high peroxidase-like activity by employing aggregation-induced emission (AIE) tetraphenylethene (TPE) to embed into hollow CeO₂ nanospheres. In the presence of ethanol oxidase (AOX) and o-phenylenediamine (OPD), we engineered an enzymatic cascade activation ratiometric fluorescence-colorimetric dual-mode system AOX/CeO₂@TPE + OPD toward CH₃SH. In this design, CH₃SH initiated AOX catalytic activity to convert it into H₂O₂ for activating the peroxidase-like activity of CeO₂@TPE, producing ^•OH for oxidizing the naked-eye colorless OPD into deep yellow 2,3-diaminophenazine (DAP) with an absorption enhancement at ∼425 nm, companied by a new emission peak at ∼550 nm to match with the intrinsic emission at ∼441 nm for observing ratiometric fluorescence response, enabling a ratiometric fluorescence-colorimetric dual-mode analysis. Interestingly, both the ratiometric fluorescence and colorimetric signals could be gathered for being converted into the hue parameter on a smartphone-based sensor, achieving the onsite visual fluorescence-colorimetric dual-mode detection of CH₃SH in real environmental media with acceptable results. This study gave a novel insight into designing target-responsive enzymatic cascade activation system-based efficient and reliable dual-mode point-of-care sensors for safeguarding environmental health.

Revealing the crystal facet effect on N2O formation during the NH3-SCR over α-MnO2 catalysts

The detailed atomic-level mechanism of the effect induced by engineering the crystal facet of α-MnO₂ catalysts on N₂O formation during ammonia-selective catalytic reduction (NH₃-SCR) was ascertained by combining density functional theory (DFT) calculations and thermodynamics/kinetic analysis. The surface energies of α-MnO₂ with specific (100), (110), and (310) exposed planes were calculated, and the adsorptions of NH₃, NO, and O₂ on three surfaces were analyzed. The adsorption energies showed that NH₃ and NO molecules could be strongly adsorbed on the surface of the α-MnO₂ catalyst, while the adsorption of O₂ was weak. Moreover, the key steps in the oxidative dehydrogenation of NH₃ and the formation of NH₂NO as well as dissociation of NH₂ were studied to evaluate the catalytic ability of NH₃-SCR reaction and N₂ selectivity. The results revealed that the α-MnO₂ catalyst exposed with the (310) plane exhibited the best NH₃-SCR catalytic performance and highest N₂ selectivity, mainly due to its low energy barriers in NH₃ dehydrogenation and NH₂NO generation, and difficulty in NH₂ dissociation. This study deepens the comprehension of the facet-engineering of α-MnO₂ on inhibiting N₂O formation during the NH₃-SCR, and points out a strategy to improve their catalytic ability and N₂ selectivity for the low-temperature NH₃-SCR process.

Catalysts for gaseous organic sulfur removal

Organic sulfur gases (COS, CS₂ and CH₃SH) are widely present in reducing industrial off-gases, and these substances pose difficulties for the recovery of carbon monoxide and other gases. The reaction pathways and reaction mechanisms of organic sulfur on different catalyst surfaces have yet to be fully summarized. The literature shows that many factors, such as catalyst synthesis method, loaded metal composition, number of surface hydroxyl groups, number of acid-base sites and methods of surface modification, have important effects on the catalytic performance of metal catalysts. Therefore, this paper presents a comprehensive review of the research on the application of catalysts such as zeolites, metal oxides, carbon-based materials, and hydrotalcite-like derivatives in the field of organic sulfur removal. Future research prospects are summarized, more in situ characterization experiments and theoretical calculations are needed for the catalytic decomposition of methanethiol to analyze the coke generation pathways at the microscopic level, while the simultaneous removal of multiple organic sulfur gases needs to be focused on. Based on previous catalyst research, we propose possible innovations in catalyst design, desulfurization technology and organic sulfur resource utilization technology.

Promoting the Catalytic Ozonation of Toluene by Introducing SO42- into the α-MnO2/ZSM-5 Catalyst to Tune Both Oxygen Vacancies and Acid Sites

Mn-based catalysts hold the promise of practical applications in catalytic ozonation of toluene at room temperature, yet improvement of toluene conversion and CO_x selectivity remains challenging. Here, an innovative α-MnO₂/ZSM-5 catalyst modified with SO₄^2- was successfully prepared, and both characterizations and density functional theory (DFT) calculations showed that SO₄^2- introduction facilitated the formation of oxygen vacancies, Lewis and Brönsted acid sites, and active oxygen species and enhanced the adsorption ability of toluene on α-MnO₂/ZSM-5. Characterizations also showed that SO₄^2- introduction made the catalyst possess larger specific surface area, superior reducibility, and stronger surface acidity. As a result, α-MnO₂/ZSM-5 with a S/Mn molar ratio of 0.019 exhibited the best toluene conversion and CO_x selectivity, 87 and 94%, respectively, after the reaction for 8 h at 30 °C under an initial concentration of 5 ppm toluene and 45 ppm ozone, relative humidity of 45%, and space velocity of 32,000 h^-1, far superior to those of non-noble catalysts reported to date under comparable reaction conditions. The synergistic role of increased oxygen vacancies and acid sites of α-MnO₂/ZSM-5 modified with SO₄^2- resulted in excellent toluene conversion and CO_x selectivity. The findings represented a critical step toward the rational design and synthesis of highly efficient catalysts for catalytic ozonation of toluene.

Tuning the Micro-coordination Environment of Al in Dealumination Y Zeolite to Enhance Electron Transfer at the Cu-Mn Oxides Interface for Highly Efficient Catalytic Ozonation of Toluene at Low Temperatures

The development of stable, highly active, and inexpensive catalysts for the ozone catalytic oxidation of volatile organic compounds (VOCs) is challenging but of great significance. Herein, the micro-coordination environment of Al in commercial Y zeolite was regulated by a specific dealumination method and then the dealuminated Y zeolite was used as the support of Cu-Mn oxides. The optimized catalyst Cu-Mn/DY exhibited excellent performance with around 95% of toluene removal at 30 °C. Besides, the catalyst delivered satisfactory stability in both high-humidity conditions and long-term reactions, which is attributed to more active oxygen vacancies and acidic sites, especially the strong Lewis acid sites newly formed in the catalyst. The decrease in the electron cloud density around aluminum species enhanced electron transfer at the interface between Cu-Mn oxides. Moreover, extra-framework octahedrally coordinated Al in the support promoted the electronic metal-support interaction (EMSI). Compared with single Mn catalysts, the incorporation of the Cu component changed the degradation pathway of toluene. Benzoic acid, as the intermediate of toluene oxidation, can directly ring-open on Cu-doped catalysts rather than being further oxidized to other byproducts, which increased the rate of the catalytic reaction. This work provides a new insight and theoretical guidance into the rational design of efficient catalysts for the catalytic ozonation of VOCs.

Review on Catalytic Oxidation of VOCs at Ambient Temperature

As an important air pollutant, volatile organic compounds (VOCs) pose a serious threat to the ecological environment and human health. To achieve energy saving, carbon reduction, and safe and efficient degradation of VOCs, ambient temperature catalytic oxidation has become a hot topic for researchers. Firstly, this review systematically summarizes recent progress on the catalytic oxidation of VOCs with different types. Secondly, based on nanoparticle catalysts, cluster catalysts, and single-atom catalysts, we discuss the influence of structural regulation, such as adjustment of size and configuration, metal doping, defect engineering, and acid/base modification, on the structure-activity relationship in the process of catalytic oxidation at ambient temperature. Then, the effects of process conditions, such as initial concentration, space velocity, oxidation atmosphere, and humidity adjustment on catalytic activity, are summarized. It is further found that nanoparticle catalysts are most commonly used in ambient temperature catalytic oxidation. Additionally, ambient temperature catalytic oxidation is mainly applied in the removal of easily degradable pollutants, and focuses on ambient temperature catalytic ozonation. The activity, selectivity, and stability of catalysts need to be improved. Finally, according to the existing problems and limitations in the application of ambient temperature catalytic oxidation technology, new prospects and challenges are proposed.