Photocatalytic NO Oxidation Research Articles

Atomic interfacial structure and charge transfer mechanism on in-situ formed BiOI/Bi2O2SO4 p–n heterojunctions with highly promoted photocatalysis

Developing novel and highly efficient Bi-based photocatalysts induced by visible light, and determining their interfacial mechanism represent two significant challenges in the environmental catalysis field. Herein, the preparation of bismuth oxysulfate, Bi2O2SO4, and in-situ couping with BiOI to form a novel BiOI/Bi2O2SO4 p–n heterojunction are described. The optimized BiOI/Bi2O2SO4 heterojunction exhibits remarkable photocatalytic NO oxidation under visible-light irradiation, with multifold higher activities than pristine BiOI or Bi2O2SO4. The BiOI/Bi2O2SO4 heterojunction enforces a directional charge transfer induced by the internal electric field, and substantially boosts the charge separation of photogenerated electron-hole pairs at the Bi2O2SO4 and BiOI interface. The electron-rich interfacial environment promotes reactant activation and reactive oxygen species generation, and prevents the formation of toxic NO-derived by-products, resulting in superior photocatalytic activity. Considered in its entirety, the current work introduces a promising Bi-based photocatalyst and provides guidance for the rational design of highly efficient heterojunction photocatalysts.

New Insights on Competitive Adsorption of NO/SO2 on TiO2 Anatase for Photocatalytic NO Oxidation.

Here, we investigate competitive adsorption and photocatalytic reaction over TiO2@SiO2: NO conversion efficiency decreases by 29.1%, and the adsorption capacity decreases from 0.125 to 0.095 mmol/g due to the influence of SO2. According to identification and comparative analysis of the IR signal, SO2 has little effect on the NO conversion route and intermediates (adsorbed NO → nitrite → nitrate), but accelerates the deactivation of catalysts. The electronic interaction scheme from density functional theory (DFT) confirms that surface hydroxyls create an unsaturated coordination of neighboring Ti or O atoms, which is favorable for NO/SO2 adsorption on anatase (101). In addition, the lone pair electrons of N or S atoms prefer to be delocalized and form covalent bonds with active surface-O on the (101) facet with terminal hydroxyls. However, preadsorbed SO2 could offset the increase of hydroxyls and strongly inhibit NO adsorption, which is consistent with the result performance evaluation. A possible reaction mechanism characterized by oxygen vacancies and·O2- is proposed, while the essential reason of catalyst deactivation and regeneration is theoretically analyzed based on the experimental and DFT calculation.

In situ synthesis of an advanced Z-scheme Bi/BiOI/black TiO2 heterojunction photocatalysts for efficient visible-light-driven NO purification

Limited light absorption and severe charge recombination have been widely acknowledged as the two main obstacles restricting the application of P25 in NO photocatalytic conversion. In this work, an advanced heterojunction photocatalyst of Bi/BiOI/black TiO2 was synthesized via an in-situ solid-state chemical reduction method. The black TiO2 extended the light absorption to the full spectral region. It constructed a direct Z-scheme heterojunction with BiOI nanosheets, not only promoting the charge separation, but also preserving the strong oxidation ability of photogenerated holes in black TiO2 and strong reducing ability of photogenerated electrons in BiOI. Thus, more •O2− and •OH radical could form when Bi/BiOI/black TiO2 was subjected to visible light irradiation. Besides, the introduced Bi metal nanoparticles could also enhance the light utilization and served as a cocatalyst to accept the electrons. Therefore, enhanced NO photocatalytic oxidation activity was obtained, with the optimal sample Bi/BiOI/black TiO2 exhibiting a high NO conversion efficiency of ~70% and NOx removal of ~45%. This work may provide a refreshing perspective for the design of heterojunction photocatalysts for efficient NO photocatalytic purification and other photocatalytic applications.

ZIF-67/CoOOH cocatalyst modified g-C3N4 for promoting photocatalytic deep oxidation of NO

The removal of nitrogen oxides (NOX) by semiconductor photocatalysis is an emerging technology in recent years. However, due to incomplete oxidation, the photocatalytic oxidation of NOX is usually accompanied by the generation of toxic intermediate by-products nitrogen dioxide (NO2), which causes secondary pollution and seriously limits its practical application. To tackle the issue, ZIF-67/CoOOH (ZIF-CH) cocatalyst was constructed via flexible strongly alkali oxidation treatment to modify g-C3N4, in which ZIF-67 was selected as a cobalt source of CoOOH. XRD, SEM, TEM and XPS demonstrated the ZIF-CH was successfully synthesized and anchored on CN. UV–vis, PL, EIS, transfer photocurrent response and DFT indicated that the introduction of ZIF-CH enlarged the response range to visible light, favored the separation and transfer of carriers and improved NO/NO2 adsorption ability. Consequently, the optimized ZIF-67/CoOOH/g-C3N4 (ZIF-CH/CN) exhibited a superior NO removal efficiency of 52.5% without any generation of toxic by-product NO2, and the cycling tests indicated the high stability of ZIF-CH/CN was obtained. In-suit DRIFTS and ESR were used to investigate the reaction pathway by comparing adsorption energy and detecting the reaction intermediates and products. More importantly, this result reveal that amount of hydroxyl radical (·OH) increased after introducing ZIF-CH cocatalyst, which promotes the deep oxidation of NO. These findings could supply a convenient and effective strategy for the design of a cocatalyst to enhance the photocatalytic oxidation performance of NO and inhibit the production of toxic by-product NO2.

Amorphous Carbon Nitride with Three Coordinate Nitrogen (N3C) Vacancies for Exceptional NOx Abatement in Visible Light

AbstractOver the past several decades, much effort has been applied to atmospheric nitrogen oxide (NOx) abatement. The current techniques require high energy consumption and result in secondary pollution. Particularly, the removal of low dose (<200 ppm) of NOx has been very challenging. Though graphitic carbon nitride (g‐CN), an eco‐friendly and sustainable material was tried as a promising metal‐free photocatalyst for NOx abatement. Herein, a one‐step, energy efficient calcination approach is developed to prepare amorphous carbon nitride (ACN) with N3C‐site vacancies. The visible‐light responsive range is expanded and the activation barrier of NO triple bonds is sharply decreased by one order of magnitude; 0.19 eV when compared to the 2.22 eV of g‐CN. These modifications allow the NOx removal efficiency of ACN to reach 57.1% which is among the highest in visible light. The unique N3C‐site vacancies are well maintained after photocatalytic NO oxidation, which shows an exceptional structural stability. This boosts the generation of singlet oxygen (1O2) and superoxide radical (•O2−) for complete NO removal. This study sheds light on the active site design and photocatalytic performance enhancement of g‐CN based materials by vacancy engineering.

In situ loading of MoO3 clusters on ultrathin Bi2MoO6 nanosheets for synergistically enhanced photocatalytic NO abatement

Synthesis of high-efficiency photocatalysts and revealing of the interfacial reaction mechanism are two major prerequisites for the commercial application of photocatalytic technology. Herein, the ultrathin Bi2MoO6 nanosheets modified by MoO3 clusters are synthesized through a surfactant-assisted one step hydrothermal process. The ultrathin two-dimensional (2D) structure shortens the carrier transmission distance, thereby reducing the recombination probability during the transport process. The surface clusters highly favor the interfacial charge transfer via giving a fire-new electron migration pathway from Bi2MoO6 nanosheets to MoO3 clusters directly. With the pivotal effect of directed electrons migration, the separation efficiency of carriers could be largely enhanced. The Bi2MoO6 nanosheets loaded with MoO3 clusters demonstrated highly efficient photocatalytic performance for NO removal under relative humidity from 25 to 100% due to the synergistic strategy of ultrathin structure and clusters. This work can provide a novel synergistic strategy for efficient carrier transfer, and also can put forward deep insights into the photocatalytic NO oxidation mechanism.

Photocatalytic oxidation of NO on reduction type semiconductor photocatalysts: effect of metallic Bi on CdS nanorods.

We report the first visible light photocatalytic oxidation of NO on CdS nanorods (CdS-NRs), one of the typical reduction type semiconductor photocatalysts. The NO removal rate in a continuous reactor sharply increases from 44% to 58% after in situ deposition of Bi nanoplates on CdS-NRs. The LSPR effect of metallic Bi causes the dramatic production of superoxide radicals (˙O2-) and singlet oxygen (1O2) that are responsible for the oxidation of NO.

B doped Bi2O2CO3 hierarchical microspheres: Enhanced photocatalytic performance and reaction mechanism for NO removal

Challenges are remaining in preparation of photocatalysts with efficient separation of charge carriers and utilization of visible light, and understanding of the reaction mechanism. In this work, B-doped Bi2O2CO3 hierarchical microspheres were prepared by one-step hydrothermal treatment using bismuth citrate and sodium tetraborate as precursors. Compared with pure Bi2O2CO3, the B-doped Bi2O2CO3 exhibited high visible-light photocatalytic activity of removing NO to achieve efficient air purification. Combined with experiments and DFT calculations, the doped-B could induce the formation of the intermediate level near the valence band, thus increasing the visible light absorption. The B-doping could also promote the separation of electron-hole pairs and enhance the activation of reactants. Therefore, plentiful reactive could be generated and detected by ESR via the reaction between the activated small reactant molecules and separated photogenerated carriers. To reveal the reaction mechanism of photocatalytic NO oxidation, the in-situ DRIFTS method was used to study the reaction processes, and an important intermediate NO2+ was found. The presence of NO2+ participated in the reaction enabled favorable formation for the final product of nitrates. This work could provide a new strategy for the improvement of photocatalytic efficiency.

Motivated surface reaction thermodynamics on the bismuth oxyhalides with lattice strain for enhanced photocatalytic NO oxidation

Understanding and establishing a specific relationship between modified structures and photocatalytic reaction process has a profound significance for designing catalysts with preferable activity. In this study, we have favorably synthesized the bismuth oxyhalides (BiOClxBr1-x, 0 ≤ x ≤ 1) photocatalysts by utilizing the ethylene glycol assisted solvothermal method and the calcination procedure for photocatalytic nitric oxide oxidation. By regulating the halogen proportion in anions layer, the lattice strain has been induced in the structure, specifically the tensile strain in c axis. By virtue of in situ DRIFTS and DFT calculation, we found that the optimized surface reaction thermodynamic process should be the main factors response for prominent enhanced photocatalytic activity, rather than the light absorption and separation of carriers. The bismuth oxyhalides with Cl/Br ratios of 3:1 (BiOClxBr1-x-3:1) possess the lowest thermodynamic energy barrier for photocatalytic nitric oxide oxidation reaction, whilst both associative and dissociative reaction process exist in the initial elementary reaction about oxygen reduction. Finally, we develop a feasible strategy to depress thermodynamic energy barriers via tuning the ratio of halogen in anions layer and bringing the lattice strain, as well build relationship between the adjusted structures and surface reaction process.

Fe1 /TiO2 Hollow Microspheres: Fe and Ti Dual Active Sites Boosting the Photocatalytic Oxidation of NO.

Recently, single-atom catalysts have aroused extensive attention in fields of clean energy and environmental protection due to their unique activity and efficient utilization of the active atoms. It is of great importance but still remains a great challenge to unveil the effect of single atoms on precise catalysis. Herein, it is reported that doping TiO2 hollow microspheres (TiO2 -HMSs) with single atomic Fe can boost the photoreactivity of TiO2 -HMSs towards NO oxidation due to the synergistic effects of atomically dispersed Fe and bonded Ti atom which act as dual active sites. The atomically dispersed Fe atoms occupy the subsurface Ti vacancies, and the interaction between Ti 3d and Fe 3d orbitals result in the formation of FeTi bond. Single atomic Fe modulates the electronic structure of the bonded Ti atoms by electron transfer, which facilitates the adsorption and activation of NO and O2 at Fe and bonded Ti sites, respectively. In addition, the introduction of single atomic Fe sharply suppresses the production of toxic NO2 byproduct. The synergistic effects of the dual active sites then cause a drastic promotion in photocatalytic oxidation of NO.

Core‐crown Quantum Nanoplatelets with Favorable Type‐II Heterojunctions Boost Charge Separation and Photocatalytic NO Oxidation on TiO2

AbstractFunctionalization of TiO2 (P25) with oleic acid‐capped CdSe(core)/CdSeTe(crown) quantum‐well nanoplatelets (NPL) yielded remarkable activity and selectivity toward nitrate formation in photocatalytic NOx oxidation and storage (PHONOS) under both ultraviolet (UV‐A) and visible (VIS) light irradiation. In the NPL/P25 photocatalytic system, photocatalytic active sites responsible for the NO(g) photo‐oxidation and NO2 formation reside mostly on titania, while the main function of the NPL is associated with the photocatalytic conversion of the generated NO2 into the adsorbed NO3− species, significantly boosting selectivity toward NOx storage. Photocatalytic improvement in NOx oxidation and storage upon NPL functionalization of titania can also be associated with enhanced electron‐hole separation due to a favorable Type‐II heterojunction formation and photo‐induced electron transfer from the CdSeTe crown to the CdSe core of the quantum well system, where the trapped electrons in the CdSe core can later be transferred to titania. Re‐usability of NPL/P25 system was also demonstrated upon prolonged use of the photocatalyst, where NPL/P25 catalyst surpassed P25 benchmark in all tests.

Modelling of NO photocatalytic degradation in an experimental chamber

“Almost real-life” experiments of abatement of a pollutant, actually nitrogen monoxide, were carried out in a 10-m3 chamber, the walls of which were covered with plasterboard samples, themselves coated with a photocatalytic dispersion. The experimental protocol consisted in first injecting NO polluted air into the chamber to a certain level, then maintaining a steady level of pollution by tuning the flow rate to balance the leaks and, finally, illuminating the chamber. In a first stage of analysis, a three-flow (injection, leakage and renewal flows) model was used in order to characterize the leakage flow rate. This model was based on the difference of NO concentration between the interior and the exterior rather than on a pressure difference. A two-parameter empirical law was specially formulated for this purpose. In a second stage, the photocatalytic phenomenon was described by a four-flow model completing the previous one, the fourth flow being associated with the photocatalytic oxidation of NO. This flow was described by a rate law derived from the Langmuir-Hinshelwood (L-H) law, which was generalized to the experimental chamber. The parameters K (adsorption constant) and k (abatement kinetics constant) of the rate law were identified using a standardized lab-scale reactor. The equations, integrated by finite differences, fitted the experimental results correctly. The “diffusive zone thickness” was introduced as the thickness of the air layer potentially concerned by the photocatalysis and was quantified. This first attempt to model photocatalysis on a large scale was promising. However, further research work is needed to enable the model to take more parameters into account.

In situ construction of oxygen-vacancy-rich Bi0@Bi2WO6-x microspheres with enhanced visible light photocatalytic for NO removal

Surface oxygen vacancy defects and metal deposition on semiconductor photocatalysts play a critical role in photocatalytic reactions. In this work, oxygen-deficient Bi2WO6 microspheres have been prepared by a facile ethylene glycol-assisted solvothermal method. Bi0 nanoparticles were reduced by in situ thermal-treatment on Bi2WO6 microspheres to obtain Bi0@Bi2WO6-x as well as maintaining the oxygen vacancies (OVs) under N2 atmosphere. Afterwards, photocatalytic NO oxidation removal activities of these photocatalysts were investigated under visible light irradiation and Bi0@Bi2WO6-x shows the best NO removal activity than other samples. The photogenerated charge separation and transfer are promoted by Bi0 nanoparticles deposited on the surface of semiconductor catalysts. OVs defects promote the activation of reactants (H2O and O2), thereby enhancing the formation of the active substance. Moreover, both OVs defects and Bi0 metal have the characteristics of extending light absorption and enhancing the efficient utilization of solar energy. Besides, the photocatalytic NO oxidation mechanism of Bi0@Bi2WO6-x was investigated by in situ FTIR spectroscopy for reaction intermediates and final products. This work furnishes insight into the synthesis strategy and the underlying photocatalytic mechanism of the surface-modified Bi0@Bi2WO6-x composite for pollutants removal.

Mechanisms of Interfacial Charge Transfer and Photocatalytic NO Oxidation on BiOBr/SnO2 p-n Heterojunctions.

In this work, hydrothermally prepared p-n heterojunction BiOBr/SnO2 photocatalysts were applied to eliminate NO in visible light. The as-synthesized BiOBr/SnO2 photocatalysts exhibit superior photocatalytic activity and stability through the establishment of a p-n heterojunction, resulting in a significant improvement in charge separation and transfer properties. The morphological structure and optical property of the BiOBr/SnO2 heterojunction were also investigated comprehensively. Extended light absorption into the visible range was achieved by SnO2 coating on the surface of the BiOBr microsphere through the constructed heterojunction between BiOBr and SnO2, thus achieving efficient NO removal. Moreover, the transfer channels and directions of charge at the BiOBr/SnO2 interface were determined by a combination of theoretical calculations and experimental studies. Within this p-n heterojunction, the charge in SnO2 migrates into BiOBr through the preformed electron transfer channels, thus generating an internal electric field (IEF) between SnO2 and BiOBr. Under the influence of IEF, the photogenerated electrons of BiOBr migrate from the conduction band (CB) to the CB of SnO2, thus promoting the separation of electrons (e-)-holes (h+) pairs. The intermediates and final products were monitored by the in situ DRIFTS technology in the process of removal of NO in visible light; hence, the oxidation pathways of NO were reasonably proposed. Meanwhile, the construction of the heterojunction not only achieves more efficient NO photocatalytic oxidation but also inhibits the production of more toxic NO2. This work provides mechanistic insights into the interfacial charge transfer for heterojunction photocatalysts and reaction mechanism for efficient air purification.

Simultaneous deSOx and deNOx of marine vessels flue gas on ZnO-CuO/rGO: Photocatalytic oxidation kinetics

Marine Pollution Convention has been updated to prevent the excessive emissions from diesel machine. For high concentrated, large fluxed SO2 and NO photocatalytic oxidation, a novel dual stages oxidation-scrubbing process was proposed. The p–n junction ZnO-CuO/rGO ternary catalysts were prepared via the co-precipitation route and supported on reduced graphene oxide (rGO). The UV–vis spectra showed that the bandgap Eg of ZnO-CuO/rGO was notably narrowed to 2.3–2.6eV for facilitating electron transfer, and its flat band potential of was −0.54V versus Ag/AgCl. The PL spectra and photocurrent curves revealed that the formation of heterojunctions and the introduction of graphene promoted an efficient separation of the photo-induced charge carriers. The photocatalytic activity of the ZnO-CuO/rGO with 5wt% GO was evaluated for simultaneous DeSOx and DeNOx, and 97% desulfurization rate and 64% denitration rate could be reached under GHSV 2000h−1 for 270min. In seawater scrubber, ZnO-CuO/rGO(5%) addition made SO32− conversion was 80.72%. The radical scavenging experiments demonstrated that holes (h+) and superoxide radicals (•O2−) contributed most to SO32− photocatalytic oxidation. Kinetic studies showed that SO32− oxidation on ZnO-CuO/rGO fitted the L-H model. The mechanism of photocatalytic oxidation in gas and liquid phases were also proposed to address the reaction pathway.

In-situ generation of oxygen vacancies and metallic bismuth from (BiO)2CO3 via N2-assisted thermal-treatment for efficient selective photocatalytic NO removal

In this study, a N2-assisted thermal treatment method is proposed for in-situ formation of a series of oxygen vacancies (OVs)-rich Bi0/Bi-based photocatalysts, including OVs-(BiO)2CO3, Bi0/OVs-(BiO)2CO3, Bi0/OVs-(BiO)2CO3/β-Bi2O3, Bi0/OVs-β-Bi2O3, Bi0/OVs-β-Bi2O3/α-Bi2O3 and Bi0/α-Bi2O3. Mechanisms of in-situ formation of Bi0 nanoparticles and generation of OVs in Bi-based photocatalysts are clarified. Apart from their contribution to the effective separation of photogenerated charge carriers and enhancement of light absorption, the effects of Bi0 nanoparticles and OVs on selective photocatalytic oxidation of NO are also investigated. Among the synthesized Bi-based photocatalysts, Bi0/OVs-(BiO)2CO3 shows the best photocatalytic activity and stability for photo-oxidative removal of NO. The systematic study of photocatalytic mechanism demonstrated that the Ohmic contact between OVs-(BiO)2CO3 and Bi0 gradually promote the formation of •O2– and •OH species. It is found that •O2– plays an important role in the photocatalytic NO removal process, while •OH species can effectively inhibit the formation of NO2 during the NO removal process. The new approach demonstrated in this study can be applied for the in-situ formation of wide-solar-spectrum-responsive photocatalysts with efficient photocatalytic activity.

Nanoscale SrFe0.5Ta0.5O3 double perovskite photocatalyst: Low-temperature solvothermal synthesis and photocatalytic NO oxidation performances

As a kind of the promising photocatalyst, double pervoskite oxides have the excellent light adsorption performance, highly stability, and favorable electronic property, but fabricating nanoscale double perovskite with high crystallinity and purity under facile preparation conditions is an attractive challenge. In this work, the low-temperature solvothermal method was introduced to fabricating double perovskite oxide SrFe0.5Ta0.5O3 at 100 °C. The as-prepared SrFe0.5Ta0.5O3 had the high crystallinity with particle size of ca. 31 nm. Under visible light irradiation, the pure SrFe0.5Ta0.5O3 photocatalyst exhibited the photocatalytic NO removal efficiency of ca. 35.1% which is much higher than that of Sr2FeTaO6. We found that the nanoscale size, high crystallinity, and purity of as-prepared SrFe0.5Ta0.5O3 particle can significantly increase the transfer and separation efficiency of the photogenerated charges from the bulk phase to surface. We also confirmed that the interaction between precursor cations and oleate ion was the key factor to decrease the solvothermal temperature and control the particle size. This work provided a novel strategy for preparing the Ta-containing perovskite photocatalyst under mild conditions.

Facile synthesis of Bi2O3 nanocrystals for photocatalytic NO oxidation and its conversion pathway via in situ DRIFTS

In this work, the two different polymorphs of Bi2O3, including α-Bi2O3 and β-Bi2O3, were fabricated by the post-calcined the precursor at 300 and 500 °C respectively. The pathway of photocatalytic NO oxidation over the as-prepared photocatalyst (β-Bi2O3) was explored. The results showed that NO removal ratio on as-synthesis samples followed the order: β-Bi2O3 (32 %) > the precursor (13 %) > α-Bi2O3 (5 %). The ESR and in situ DRIFTS demonstrated that the superoxide (O2−), as the main radical, can react with the absorbed NO on the surface of β-Bi2O3 to generate the final products NO3− and NO2−. Therefore, such findings reveal the possible photocatalytic pathway of NO oxidation on β-Bi2O3 based on in situ DRIFTS and give insight into understanding the polymorphism of Bi2O3 in efficient photocatalytic NO oxidation under the visible light.

Surface hydrogen bond network spatially confined BiOCl oxygen vacancy for photocatalysis

Rational engineering of oxygen vacancy (VO) at atomic precision is the key to comprehensively understanding the oxygen chemistry of oxide materials for catalytic oxidations. Here, we demonstrate that VO can be spatially confined on the surface through a sophisticated surface hydrogen bond (HB) network. The HB network is constructed between a hydroxyl-rich BiOCl surface and polyprotic phosphoric acid, which remarkably decreases the formation energy of surface VO by selectively weakening the metal–oxygen bonds in a short range. Thus, surface-confined VO enables us to unambiguously distinguish the intrafacial and suprafacial oxygen species associated with NO oxidation in two classical catalytic systems. Unlike randomly distributed bulk VO that benefits the thermocatalytic NO oxidation and lattice O diffusion by the dominant intrafacial mechanism, surface VO is demonstrated to favor the photocatalytic NO oxidation through a suprafacial scheme by energetically activating surface O2, which should be attributed to the spatial confinement nature of surface VO.

La-doping induced localized excess electrons on (BiO)2CO3 for efficient photocatalytic NO removal and toxic intermediates suppression

Photocatalysis technology has been extensively adopted to abate typical air pollutants. Nevertheless, it is a challenge to develop photocatalysts aiming to simultaneously improve photocatalytic selectivity and efficiency. In this study, to improve the photocatalytic selectivity and the performance of (BiO)2CO3 in the oxidation of NO to target products (NO2− /NO3−), we developed a novel method to construct La-doped (BiO)2CO3 (La-BOC) for forming localized excess electrons (Ex) on (BiO)2CO3 surface. The results indicate that the Ex could effectively accelerate the activation of reactants and promote charge separation and transfer. Under visible light, the gas molecules could capture the Ex and get activated to produce reactive oxygen species (ROS) with high oxidation ability, which enables complete oxidation of NO to target products instead of producing other toxic by-products. Due to the functionality of the Ex, the photocatalytic selectivity and efficiency of La-BOC have been synchronously improved. Combining experimental and theoretical methods, this work unravels the pathway of charge carriers transportation/transformation and elucidates the photocatalytic NO oxidation mechanism. The present work could provide a novel method to improve photocatalytic selectivity and activity for safe air pollutant abatement.