NO Oxidation Research Articles

High-temperature selective reduction of NOx into N2 catalyzed by different ion-doped titania

The active titanium-based composite oxide carrier with strong thermal stability and surface acidity is the key to ensure the steady operation of high-temperature deNOx catalyst for gas-fired exhaust. In this paper, W6+, Zr4+, Mo6+, Al3+, Si4+, Cu2+, Co2+, Mn2+, Fe3+ doped titanium-based composite oxides were synthesized by sol–gel method. The effects of ion species, doping amount, calcination temperature on NH3-SCR deNOx efficiency and resistance to water vapor and SO2 poisoning were investigated. Results showed that the Cu2+, Co2+, Mn2+, Fe3+ doped titanium-based composite oxides calcined at 630 °C had negligible deNOx activity, while the doping of W6+, Zr4+, Mo6+, Al3+ and Si4+ improved the NH3-SCR activity and anti-water vapor and SO2 poisoning of titanium-based composite oxide. The deNOx efficiency of the best compatibility of the five ions doping was TiW0.1Ox-630 > TiMo0.12Ox-630 > TiAl0.11Ox-487 > TiZr0.06Ox-538 ≈ TiSi0.04Ox-582, which was consistent with the order of total acid amount. The order of resistance to water vapor and SO2 poisoning and resistance to high temperature thermal shock was TiW0.1Ox-630 ≈ TiMo0.12Ox-630 > TiSi0.04Ox-582 > TiZr0.06Ox-538 > TiAl0.11Ox-487. Doping of five ions inhibited the transformation of anatase TiO2 to rutile TiO2 in different degrees. Among them, W6+ doping had the best inhibitory effect and the exposure ratio of TiO2 (101) crystal plane in TiW0.1Ox-630 was the highest, which was beneficial to NH3-SCR of NOx. Furthermore, the concentration of chemisorbed oxygen Oα was in the order of TiW0.1Ox-630 > TiMo0.12Ox-630 > TiAl0.11Ox-487 > TiZr0.06Ox-538 > TiSi0.04Ox-582. The higher the concentration of Oα is, the more conducive to the oxidation of NO to NO2 and the promotion of NH3 adsorption and dehydrogenation oxidation.

Microbial Sources and Sinks of Nitrous Oxide during Organic Waste Composting.

Composting is widely used for organic waste management and is also a major source of nitrous oxide (N2O) emission. New insight into microbial sources and sinks is essential for process regulation to reduce N2O emission from composting. This study used genome-resolved metagenomics to decipher the genomic structures and physiological behaviors of individual bacteria for N2O sources and sinks during composting. Results showed that several nosZ-lacking denitrifiers in feedstocks drove N2O emission at the beginning of the composting. Such emission became negligible at the thermophilic stage, as high temperatures inhibited all denitrifiers for N2O production except for those containing nirK. The nosZ-lacking denitrifiers were notably enriched to increase N2O production at the cooling stage. Nevertheless, organic biodegradation limited energy availability for chemotaxis and flagellar assembly to restrain nirKS-containing denitrifiers for nitrate reduction toward N2O sources but insignificantly interrupt norBC- and nosZ-containing bacteria (particularly nosZ-containing nondenitrifiers) for N2O sinks by capturing N2O and nitric oxide (NO) for energy production, thereby reducing N2O emission at the mature stage. Furthermore, nosZII-type bacteria included all nosZ-containing nondenitrifiers and dominated N2O sinks. Thus, targeted strategies can be developed to restrict the physiological behaviors of nirKS-containing denitrifiers and expand the taxonomic distribution of nosZ for effective N2O mitigation in composting.

Electron mobility of SnO2 from first principles

The transparent conducting oxide SnO2 is a wide bandgap semiconductor that is easily n-type doped and widely used in various electronic and optoelectronic applications. Experimental reports of the electron mobility of this material vary widely depending on the growth conditions and doping concentrations. In this work, we calculate the electron mobility of SnO2 from first principles to examine the temperature and doping concentration dependence and to elucidate the scattering mechanisms that limit transport. We include both electron–phonon scattering and electron-ionized impurity scattering to accurately model scattering in a doped semiconductor. We find a strongly anisotropic mobility that favors transport in the direction parallel to the c-axis. At room temperature and intrinsic carrier concentrations, the low-energy polar-optical phonon modes dominate scattering, while ionized-impurity scattering dominates above 1018 cm−3.

Neural network potential-based molecular investigation of pollutant formation of ammonia and ammonia-hydrogen combustion

This study developed neural network potentials (NNPs) specifically designed for ammonia and ammonia-hydrogen combustion systems for the first time. The NNPs were employed to perform reactive molecular dynamics (RMD) simulations, combining the precision of density functional theory (DFT) calculations with the efficiency of empirical force fields. NNP-based RMD simulations provide a more detailed and comprehensive understanding of chemical reaction mechanisms. The impacts of different equivalence ratios and hydrogen addition on ammonia combustion as well as NOX and N2O formation were analysed. The results indicate that both the addition of hydrogen and the reduction of equivalence ratios contribute to enhancing ammonia combustion. The primary reason is the enhancement of the oxidative environment within the system, leading to a significant increase in the frequency of reactions associated with oxidising radicals such as OH, O, and HO2. This is also the cause for the increased production of NO and NO2, because the formation of NO depends on the oxidation of NH and NH2, while NO2 is formed through the oxidation of NO. An interesting finding is that the addition of hydrogen decelerates the generation of N2O, while reducing the equivalence ratio promotes N2O production. This phenomenon is attributed to the additional H radicals generated during hydrogen decomposition, which hinders the binding between NH and NO, resulting in a reduction in the formation of the precursor HN2O required for N2O formation.

Electrical and Optical Properties of Thin-Film Wide-Gap Metal Oxides Sno 2, In 2 O 3 , Ito , Cdo , Moo 3

The electrical properties of the created doped and undoped wide-gap layers of metal oxides SnO 2, In 2 O 3 , ITO , CdO , MoO 3 were studied. Depending on technological factors. The optimal growth conditions for these semiconductor materials have been determined. The study of the electro physical and optical properties of the resulting oxide films confirmed the stability of the operational parameters of oxide materials SnO 2, In 2 O 3 , ITO , CdO , MoO 3 . The AFM method showed, along with the oxides SnO 2, In 2 O 3 , ITO , CdO , the oxide of pure MoO3 has The highest transmittance is in the visible region of the spectrum , where the absorption edge shifts toward higher wavelengths.

Technical Note: A technique to convert NO2 to NO2− with S(IV) and its application to measuring nitrate photolysis

Abstract. Nitrate photolysis is a potentially significant mechanism for “renoxifying” the atmosphere, i.e., converting nitrate into nitrogen oxides – nitrogen dioxide (NO2) and nitric oxide (NO) – and nitrous acid (HONO). Nitrate photolysis in the environment occurs through two channels which produce (1) NO2 and hydroxyl radical (⚫OH) and (2) nitrite (NO2-) and an oxygen atom (O(3P)). Although the aqueous quantum yields and photolysis rate constants of both channels have been established, field observations suggest that nitrate photolysis is enhanced in the environment. Laboratory studies investigating these enhancements typically only measure one of the two photo-channels, since measuring both channels generally requires separate analytical methods and instrumentation. However, measuring only one channel makes it difficult to assess whether secondary chemistry is enhancing one channel at the expense of the other or if there is an overall enhancement of nitrate photochemistry. Here, we show that the addition of S(IV), i.e., bisulfite and sulfite, can convert NO2 to NO2-, allowing for measurement of both nitrate photolysis channels with the same equipment. By varying the concentration of S(IV) and exploring method parameters, we determine the experimental conditions that quantitatively convert NO2 and accurately quantify the resulting NO2-. We then apply the method to a test case, showing how an ⚫OH scavenger in solution prevents the oxidation of NO2- to NO2 but does not enhance the overall photolysis efficiency of nitrate.

Impact of mild hydrothermal aging on kinetics of NH[formula omitted], NO, SO[formula omitted] and CO oxidation reactions on Cu/SSZ-13 catalyst

Cu/SSZ-13 is a catalyst commonly used for selective catalytic reduction (SCR) of nitrogen oxides (NOx) in diesel engine exhaust. Standard configurations are based on SCR preceded by an oxidation catalyst, however, a close-coupled SCR configuration appears relevant for upcoming regulations addressing cold-start emissions. Two often discussed ion-exchanged Cu sites in Cu/SSZ-13 are denoted ZCuOH and Z2Cu, where Z represents an Al atom in the zeolite framework. Mild hydrothermal aging (HTA) causes Cu redistribution within the catalyst; ZCuOH sites transform into more stable Z2Cu species. In this work, the effect of mild HTA on NH3, NO, SO2, and CO oxidation is studied on a commercial Cu/SSZ-13 sample. Temperature-programmed reaction experiments, performed in a lab reactor, and previously published catalyst characterization data using H2-TPR, NH3-TPD, and DRIFTS were used to build and validate a mathematical model. It couples the kinetics of the oxidation reactions with ZCuOH and Z2Cu concentration evolution during mild HTA. The model uses two distinct rate coefficients for ZCuOH and Z2Cu sites, allowing prediction of the catalyst activity during aging. The results suggest that the rate coefficients for the studied reactions on Z2Cu are effectively nil, so the observed activity in NH3, NO, SO2, and CO oxidation can be attributed solely to ZCuOH sites.

Application of TiO2 Supported on Nickel Foam for Limitation of NOx in the Air via Photocatalytic Processes.

TiO2 was loaded on the porous nickel foam from the suspended ethanol solution and used for the photocatalytic removal of NOx. Such prepared material was heat-treated at various temperatures (400-600 °C) to increase the adhesion of TiO2 with the support. Obtained TiO2/nickel foam samples were characterized by XRD, UV-Vis/DR, FTIR, XPS, AFM, SEM, and nitrogen adsorption at 77 K. Photocatalytic tests of NO abatement were performed in the rectangular shape quartz reactor, irradiated from the top by UV LED light with an intensity of 10 W/m2. For these studies, a laminar flow of NO in the air (1 ppm) was applied under a relative humidity of 50% and a temperature of 28 °C. Concentrations of both NO and NO2 were monitored by a chemiluminescence NO analyzer. The adsorption of nitrogen species on the TiO2 surface was determined by FTIR spectroscopy. Performed studies revealed that increased temperature of heat treatment improves adhesion of TiO2 to the nickel foam substrate, decreases surface porosity, and causes removal of hydroxyl and alcohol groups from the titania surface. The less hydroxylated surface of TiO2 is more vulnerable to the adsorption of NO2 species, whereas the presence of OH groups on TiO2 enhances the adsorption of nitrate ions. Adsorbed nitrate species upon UV irradiation and moisture undergo photolysis to NO2. As a consequence, NO2 is released into the atmosphere, and the efficiency of NOx removal is decreasing. Photocatalytic conversion of NO to NO2 was higher for the sample heated at 400 °C than for that at 600 °C, although coverage of nickel foam by TiO2 was lower for the former one. It is stated that the presence of titania defects (Ti3+) at low temperatures of its heating enhances the adsorption of hydroxyl groups and the formation of hydroxyl radicals, which take part in NO oxidation. Contrary to that, the presence of titania defects in TiO2 through the formation of ilmenite structure (NiTiO3) in TiO2/nickel foam heated at 600 °C inhibits its photocatalytic activity. No less, the sample obtained at 600 °C indicated the highest abatement of NOx due to the high and stable adsorption of NO2 species on its surface.

Surface fluorinated anatase TiO2 nanosheets for NO deep oxidation in O3/H2O2 system: Enhanced mechanism and oxidation characteristics

O3 technology has exhibited promise in removing NO at low-temperature. However, challenges of high NO2 concentration that are difficult to absorb due to insufficient O3 oxidizing capacity remains. Herein, we reported an efficient strategy to generate oxygen-containing radicals for NO deep oxidation via fluorine and {001} facets modulated anatase TiO2 triggering highly activity sites that catalyzed O3/H2O2 to address the above issue. The strong electron withdrawing effect of F sites enhanced the deprotonation of H2O2, while Ti5c on {001} surface exhibited strong Lewis acid to activate O3, thermal stabilization treatment of the catalyst strengthened the synergistic effect of F and Ti5c, resulting in a 97 % NO deep oxidation efficiency at 100 °C with 3 % water vapor content. Additionally, the oxidation characteristics of the radicals was carefully discussed by occupying NO adsorption sites on TiO2 surface, the result revealed that radicals could remarkably react with gas-phase NO. Finally, the synergistic effect and oxidation properties would possess guiding significance for improving NO oxidation and applications.

Steady-State and transient kinetic investigations of the oxidation of NO over Pt/SiO2

The reaction mechanism of the oxidation of NO under conditions of high NO concentration over a 2 wt% Pt/SiO2 was studied using both kinetic and transient isotopic tracing experiments. The reaction mechanism was found to involve both NO adsorption and oxygen adsorption, contrary to the situation under low NO concentration where NO reacts from the gas phase. The kinetic rate data could be fitted to the Langmuir-Hinshelwood model permitting the estimation of rate and equilibrium constants of elementary steps. These steps were investigated using transient responses following independent reactant gas isotopic switches for tracing the nitrogen path and the oxygen path during NO oxidation. These transients could be sufficiently described by a microkinetic model based on two pools of NO intermediates, one pool each for the adsorbed molecular oxygen and atomically adsorbed oxygen. Surface atomic oxygen was found to be formed by two different routes: via a direct dissociation of molecularly adsorbed oxygen and also via an assisted pathway that leads to NO2 formation. The latter surface reaction between adsorbed NO and adsorbed molecular oxygen comprised the kinetically relevant step. Insights from the two experimental and model approaches were in good agreement and provided a coherent reaction mechanism for NO oxidation under high NO reactant concentration.

NOx Storage and Reduction (NSR) Performance of Sr-Doped LaCoO3 Perovskite Prepared by Glycine-Assisted Solution Combustion

Here, we successfully synthesized Sr-doped perovskite-type oxides of La1−xSrxCo1−λO3−δ, “LSX” (x = 0, 0.1, 0.3, 0.5, 0.7), using the glycine-assisted solution combustion method. The effect of strontium doping on the catalyst structure, NO to NO2 conversion, NOx adsorption and storage, and NOx reduction performance were investigated. The physicochemical properties of the catalysts were studied by XRD, SEM-EDS, N2 adsorption–desorption, FTIR, H2-TPR, O2-TPD, and XPS techniques. The NSR performance of LaCoO3 perovskite was improved after Sr doping. Specifically, the perovskite with 50% of Sr doping (LS5 sample) exhibited excellent NOx storage capacity within a wide temperature range (200–400 °C), and excellent stability after hydrothermal and sulfur poisoning. It also displayed the highest NOx adsorption–storage capacity (NAC: 1889 μmol/g; NSC: 1048 μmol/g) at 300 °C. This superior performance of the LS5 catalyst can be attributed to its superior reducibility, better NO oxidation capacity, increased surface Co2+ concentration, and, in particular, its generation of more oxygen vacancies. FTIR results further revealed that the LSX catalysts primarily store NOx through the “nitrate route”. During the lean–rich cycle tests, we observed an average NOx conversion rate of over 50% in the temperature range of 200–300 °C, with a maximum conversion rate of 61% achieved at 250 °C.

Decoding the Reactivity Enhancement of Ln2Ce2O7 Compounds (Ln = Yb, Y, Tb, and Gd) for Soot Combustion: The Remarkable Contribution of Variable Valence A-Sites.

The impact of variable valence A-sites on the redox property and reactivity of Ln2Ce2O7 compounds in soot particulate combustion has been investigated. It was observed that Yb2Ce2O7, Y2Ce2O7, and Gd2Ce2O7 formed a rare earth C-type phase, while Tb2Ce2O7 formed a solid solution phase. Both Tb2Ce2O7 and Yb2Ce2O7 possess dual valence state A-sites, resulting in significantly more surface vacancies. Additionally, the advantageous solid solution phase structure of Tb2Ce2O7 leads to even more surface vacancies than Yb2Ce2O7, which is crucial to generate active oxygen sites. Moreover, the introduction of NO into the reaction feed enhances combustion activity by producing active surface monodentate nitrates. A catalyst with higher numbers of surface vacancies exhibits improved NO oxidation ability and better NO2 utilization efficiency. Consequently, the Tb2Ce2O7 compound demonstrates not only the best soot combustion activity, but also an optimal NOx-assistance effect. Therefore, it is concluded that variable valence A-site is the intrinsic factor to improve the reactivity of Ln2Ce2O7 catalysts.

An organic/inorganic Z-scheme heterojunction Yb-MOF/BiOBr for efficient photocatalytic removal of NO

The advantages of visible light-driven catalysts with good light absorption, fast charge separation rate and high redox capacity are compelling. However, conventional inorganic semiconductor, such as pure BiOBr (BOB), showed a rapid photogenerated carriers recombination rate and low solar energy utilization ability, which limited the practical application of its photocatalytic performance. In this work, a novel organic/inorganic interleaved (Z-scheme) heterojunction Yb-MOF/BiOBr (Yb-MOF/BOB) photocatalyst was successfully synthesized. Compared with a single component, the Yb-MOF/BOB heterojunction exhibited significantly enhanced performance in photocatalytic oxidation of NO under visible light. Among them, Yb-MOF/BOB-20 had the best photocatalytic NO removal effect, up to 6424 ppb/g, which was 2.8 times and 4.2 times that of BOB and Yb-MOF, respectively. Photoelectrochemical characterization confirmed that the formation of heterojunctions broadened the absorption sidebands and increased the charge transfer at the interfacial junction of Yb-MOF/BOB. Combined with UPS, ESR and in-situ DRIFTS analysis, possible photocatalytic mechanisms were revealed, in which the formation of the Yb-MOF/BOB heterostructure endowed its high charge mobility and strong redox ability. Therefore, this work provided an effective way for photocatalytic removal of NO, and offered new ideas for developing heterogeneous photocatalysts.

High-temperature calcination dramatically promotes the activity of Cs/Co/Ce-Sn catalyst for soot oxidation

Catalytic oxidation of soot is of great importance for emission control on diesel vehicles. In this work, a highly active Cs/Co/Ce-Sn catalyst was investigated for soot oxidation, and it was unexpectedly found that high-temperature calcination greatly improved the activity of the catalyst. When the calcination temperature was increased from 500 °C to 750 °C, T50 decreased from 456.9 °C to 389.8 °C in a NO/O2/H2O/N2 atmosphere. Characterization results revealed that high-temperature calcination can promote the ability to transfer negative charge density from Cs to other metal cations in Cs/Co/Ce-Sn, which will facilitate the production of more oxygen defects and the generation of more surface-active oxygen species. Surface-active oxygen species are beneficial to the oxidation of NO to NO2, leading to the high yield of NO2 exploitation. Therefore, the Cs/Co/Ce-Sn catalyst calcined at 750 °C demonstrated higher activity than that calcined at 500 °C. This work provides a pathway to prepare high efficiency catalysts for the removal of soot and significant insight into the effects of calcination on soot oxidation catalysts.

Improved continuous measurement system for atmospheric total peroxy and total organic nitrate under the high NOx condition.

We improved the thermal dissociation cavity attenuated phase shift spectroscopy (TD-CAPS) instrument to measure atmospheric total peroxy nitrates (PNs) and organic nitrates (ONs) continuously under the condition of high NOx. In TD-CAPS, PNs and ONs are dissociated in heated quartz tubes to form NO2, and the NO2 concentration is measured by cavity attenuated phase shift spectroscopy (CAPS). The original TD-CAPS system overestimates PN and ON concentrations in the presence of high NO concentrations. Our laboratory experiments and numerical simulations showed that the main cause of the overestimation was NO oxidation to NO2 by peroxy radicals generated in the heated quartz tubes. In the improved system, NO was converted to NO2 by adding excess O3 after the quartz tubes so that CAPS detected NOx (NO and NO2) instead of NO2. The uncertainty of the improved system was less than 20% with ∼15 parts per billion by volume (ppbv) NO and ∼80ppbv NO2. The estimated detection limit (3σ) was 0.018ppbv with an integration time of 2minin the presence of 64ppbv NO2. The improved system was tested for measurement of PNs and ONs in an urban area, and the results indicated that interference from NO was successfully suppressed.

Impact of atmospheric O3 and NO2 on the secondary sulfates in real atmosphere

As an important component of secondary aerosols, sulfate plays a crucial role in regulating atmospheric radiative balance and influencing the secondary formation of ozone (O3). In real atmosphere, atmospheric oxidants NO2 and O3 can promote the oxidation of SO2 to form sulfate (SO42−) through multiphase chemistry that occur at different time scales. Due to the combined impact of meteorology, pollution sources, atmospheric chemistry, etc., time-scale dependence of SO2-SO42− conversion makes the impact of NO2/O3 on it more complex. In this study, based on long-term time series (2013-2020) of air pollution variables from seven stations in Hong Kong, the Multifractal Detrended Cross-Correlation Analysis (MFDCCA) method has been employed to quantify the cross-correlations between SO2 and SO42− in real atmosphere at different time scales, for examining the time-scale dependence of SO2-SO42− conversion efficiency. Furthermore, the Pearson correlation analysis has been used to study the influence of NO2/O3 on SO2-SO42− conversion, and the regional and seasonal differences have been analyzed by considering factors such as meteorology, pollution sources, and regional transport. Changes in the main components of secondary aerosols are closely linked with the co-control of regional PM2.5 and O3. Therefore, the exploration of the impact of co-existing NO2/O3 gases on the secondary formation of sulfates in real atmosphere is significant.

The fabrication of Mn single atoms/clusters on Al2O3 for enhanced catalytic NO oxidation

The exploitation of transitional metal catalysts for high-efficient conversion of NO to NO2 still persists as an imperative issue due to the high cost of currently used Pt–based catalysts. Herein, we report a TEA-modification strategy to anchor Mn single atoms/clusters on Al2O3 (Mn/Al2O3-T) for NO oxidation. Activity tests show that Mn/Al2O3-T (T83 = 275 °C) displays a superior NO-to-NO2 capacity compared with the unmodified Mn nanoparticle on Al2O3 (Mn/Al2O3-B, T66 = 300 °C) and Pt/Al2O3 (T43 = 350 °C) counterparts. Comprehensive characterization and DFT calculations discover that the effective adjustment of TEA can promote the generation of coordination unsaturated Mn sites with elongated Mn-O bonds, which can improve the mobility of surface lattice oxygen and facilitate the activation of molecular oxygen. Additionally, reducing Mn size from nanoparticles to single atoms/clusters favors the formation of labile nitrate species and facile desorption of NO2, thereby regenerating active sites and accelerating overall NO oxidation reaction.

Elucidating the role and enhancement mechanisms of CH4 on the coupling abatement of N2O & NO over Fe-SSZ-13 catalysts

CH4 + NH3 + NOx + N2O coupling system was proposed for high-effective simultaneous catalytic reduction of both NO and N2O from flue gas generated by nitric or adipic acid industries. The Fe-SSZ-13 catalyst performed both elegant activity for NOx and N2O at 400–600 °C. Based on experimental studies, the active Fe species were illustrated and the transforming of Fe species during the N2O decomposition (deN2O) and selective catalytic reduction (SCR) processes was clarified. It found that deN2O could cause the main active sites of [Fe-O2-Fe]2+ transform to [Fe-O-Fe]2+ and consequently inhibited the NH3-SCR process over the Fe-SSZ-13 catalyst. Meanwhile, the αO* generated via N2O decomposition would strengthen NO oxidation to NO2, which is advantageous to NH3-SCR. More importantly, the functions of CH4 for deN2O and NH3-SCR were also investigated. CH4 could work as reductant to convert N2O over the Fe-SSZ-13. CH4 could also facilitate the reduction of NO; however, NH3 has stronger activity to NO than that of CH4. And CH4 was easily oxidized by O2 rather than N2O or NO, which significantly limit the CH4-SCR for N2O with present of O2. At the same time, CH4 can also accelerate αO* consumption that somehow enhance deN2O efficiency. Moreover, the consumption of αO* by CH4 prevent the transforming of [Fe-O2-Fe]2+ to [Fe-O-Fe]2+, and CH4 play an important role on turnover rates of [Fe-O2-Fe]2+ and [Fe-O-Fe]2+ active sites, guaranteeing both satisfactory purifying efficiency for NO and N2O. This work reveals the positive promoting effect of CH4 on simultaneous reduction of NOx and N2O, and proposes a potential catalyst for implementation.

Regulation of oriented NO photooxidation to circumvent NO2 with high-coordinated M–N5 (M = Fe, Co, Mn, Ti) sites and far–carbon defects

The targeted oxidization of trace NO to NO3- instead of toxic NO2via photocatalytic process represents one of the promising protocols for assuring environmental benefits. A novel type of graphite carbon nitride (CN) photocatalysts with high coordination sites (M–N5; M = Fe, Co, Mn, Ti) and far–carbon defects were manufactured by reconstructing the low coordination structure (M–N4). The mingled characterizations and theoretical calculations demonstrated that the reconstructed sites could improve the charge and energy transfer process of the exciton to precisely regulate the activation process of O2, while inhibiting the activation of adsorbed H2O. Superior orientation to form superoxide radical and singlet oxygen, rather than hydroxyl radical, showed excellent NO removal rates (68.6%) and superior NO3- selectivity (about 100%) under visible–light irradiation. This work proposes a unique mechanism via tailored construction of highly coordinated structures for selective NO oxidation to achieve the goal of atmospheric purification.

Boosting photocatalytic NO oxidation mediated by high redox charge carriers from visible light-driven C3N4/UiO-67 S-scheme heterojunction photocatalyst

The construction of CN/UiO-67 (CNU) S-scheme heterojunction composites through in situ formation of UiO-67 on carbon nitride (C3N4) helps to address the limitations of carbon nitride (CN) in photocatalytic NO elimination. The optimized CNU3 demonstrates superior photocatalytic efficiency, which is attributed to electronic channels constructed by Zr-N bonds and S-scheme electron transport mechanism, effectively promoting the efficient separation of photogenerated charge carriers with high redox potentials. Density Functional Theory (DFT) calculations reveal redistributed electronic orbitals in CNU3, with progressive and continuous energy levels near the Fermi level, which bolsters electronic conduction. Comprehensive quenching experiments, Electron Paramagnetic Resonance (EPR), and in situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) analyses highlight a synergistic interplay of electrons, holes, and superoxide radicals in CNU3, inhibiting the generation of toxic nitrogen oxide intermediates and culminating in highly efficient photocatalytic NO oxidation. This study not only elucidates the mechanisms underpinning the enhanced performance of CNU3 heterojunctions but also offers new perspectives on the preparation and interfacial charge separation of heterojunction photocatalysts.