Photocatalytic NO Removal Research Articles

Fabrication of core–shell nanostructure via novel ligand-defect reassembly strategy for efficient photocatalytic hydrogen evolution and NO removal

The core–shell structure often exhibits unique properties, resulting in superior physical and chemical performance distinct from individual component in the field of photocatalysis. However, traditional prepared methods such as template synthesis and layer-by-layer self-assembly are relatively complex. Therefore, it is necessary to explore an efficient and expedient approach. Here, we have proposed a convenient method to gradually destroy the terephthalic acid (BDC) of MIL-125 from the outer to inner layers through hydrothermal stirring, followed by reassembling with photosensitive 2-amino-terephthalic acid (BDC-NH2) into the exposed Ti-oxo clusters left by the BDC to create photocatalysts featuring a core–shell configuration. The special core–shell sample with the analogous mixture of MIL-125 and MIL-125-NH2 function as a high-performance dual-functional photocatalyst for hydrogen generation and NO elimination. The optimal core–shell material (M-125-45-N) exhibits an outstanding photocatalytic hydrogen production rate of 3.74 mmol·g−1·h−1 and an excellent photocatalytic NO removal rate of 70.15 %. The apparent quantum yield (AQY) value and solar-to-hydrogen energy conversion efficiency (STH) at specific wavelengths are also investigated. The Density functional theory (DFT) calculation, In-situ Fourier transform infrared (In-situ FT-IR) and Electron spin resonance (ESR) have suggested that the enhanced photocatalytic activity of optimal core–shell material arised from its stronger adsorption capacity towards reactants, promoting the production of reactive oxygen species (ROS) conducive to photocatalytic reactions. This study represents the first investigation of a dual functional core–shell MOFs formed via ligand-defect reassembly, showcasing the excellent efficacy in photocatalytic hydrogen evolution and NO removal, which contributes to the feasible development of novel dual-functional photocatalysts with core–shell structures.

Constructing dual-channel carrier transport in AgBr/BiOBr/Ag3PO4 heterojunctions for enhanced photocatalytic NO removal

Efficient and stable photocatalysts are indispensable for effectively reducing nitrogen oxide (NOx) emissions. This study presents a facile method for synthesizing AgBr/BiOBr/Ag3PO4 composites and investigates their application in photocatalytic NO removal. The optimized composite exhibited notable performance, achieving 54.95 % removal of NO (approximately 568 ppb reduced to 256 ppb) under visible light irradiation, which is about 1.6 and 2.0 times higher than single Ag3PO4 (34.95 %) and BiOBr (28.01 %), respectively. Comprehensive physicochemical characterization highlighted enhancements in light absorption and the generation of reactive radicals within the AgBr/BiOBr/Ag3PO4 composite. The favorable electronic structure, characterized by well-aligned redox band positions, facilitated efficient dual carrier transport routes, thereby promoting the separation of photo-generated charge carriers. Additionally, in-situ DRIFTS analysis revealed that the composite facilitated the conversion of intermediates into nitrates during the NO purification process. This work contributes valuable insights into designing and preparing of ternary heterojunction photocatalysts with dual carrier transport channels, advancing strategies for achieving superior photocatalytic performance.

Selective photocatalytic reduction of nitric oxide to dinitrogen via bimetallic bond incorporation

In this study, we addressed the challenge of optimizing the first rate-limiting NO adsorbate state, which has received limited attention in previous research on the photoreduction of NO. We prepared BiFeWO6 (BFWO), which improved not only the NO removal rate under illumination but also the selectivity of photocatalytic NO conversion to N2. To further optimize the performance, we introduced platinum into BFWO, achieving a 57.5 % NO conversion rate with ∼80 % N2 selectivity under 425 nm light-emitting diode illumination (50 mW/cm2), which is optimal for converting NO into less harmful compounds at low concentrations. FeOBi bonds were identified as the key active sites of the first rate-limiting NO adsorbate state in BFWO through time-resolved operando infrared (IR) spectroscopy and density functional theory (DFT) analysis. The specific adsorption configuration of NO on the FeOBi group accelerated the photoreduction reaction kinetics, resulting in superior photocatalytic NO removal performance.

Synthesis of CdS QDs/NH2-Nb2O5 via electrostatic self-assembly method for highly efficient photocatalytic removal of NO and synchronous inhibition of NO2

A two-step electrostatic self-assembly method was used to first graft –NH2 groups onto the Nb2O5 followed by loading of CdS QDs onto the NH2-Nb2O5 to obtain CdS/NH2-Nb2O5. The performance of the samples under visible light was evaluated under simulated conditions of 25 °C and varying relative humidity (RHs). The results showed that with the increase of RH, the NO removal efficiency by CdS/NH2-Nb2O5 increased first and then decreased, reaching the maximum NO removal efficiency when RH = 50 %. The selectivity of NO2 on CdS/NH2-Nb2O5 (9.01 %) was significantly lower compared to that of Nb2O5 (24.44 %) and NH2-Nb2O5 (19.72 %). The introduction of –NH2 groups and CdS QDs significantly enhanced visible light absorption and improved the separation efficiency of photogenerated charge carriers. In-situ DRIFTS analysis revealed that Cd2+ served as an additional active site for NO adsorption. Furthermore, CdS had a relatively negative conduction band position, which was conducive to the generation of O2–, further inhibiting the generation of NO2. This work provides a new approach to the design and preparation of catalysts for photocatalytic oxidation of NO.

Na-doped nitride-rich carbon nitride for efficient photocatalytic NO abatement

Nitride-rich carbon nitride (C3N5) is gaining prominence as a substantial catalyst for photocatalytic reaction because of its narrow bandgap, extensive light responsiveness, and photocatalytic stability. To enhance the efficiency of photogenerated carrier separation in C3N5, we propose a strategy for Na-doped modification. Photocatalytic NO removal efficiency of C3N5/Na achieved 73.9 % under 15 % relative humidity, which is 3.5 times higher than that of C3N5. Besides, the NO removal efficiency of C3N5/Na maintained above 70 % even after six cycles under different relative humidities. Detailed analytical characterization revealed that Na doping of C3N5 not only increased its specific surface area by 5.5-fold but also modulated its energy band structure and molecular structure, leading to improved hole-carrier separation efficiency and enhancing the photocatalytic performance of C3N5/Na. ESR and reactive species trapping experiments confirmed that electrons and superoxide are the main reactive species, and modulation of the energy band structure accelerates the reaction. This work explains the effect of Na doping on C3N5 and provides a new strategy for designing efficient for photocatalytic treatment of air pollution.

Boosting photocatalytic NO remove and H2 production by Co(ii,iii)-modified carbon dots assembly into metal–organic frameworks: The Co(ii,iii)-modified carbon dots location matters

Inhibiting electron-hole recombination and improving the utilization efficiency of photogenerated carriers perform a central role in photocatalysis. Herein, a “ship-in-a-bottle” strategy and an impregnation method were employed to incorporate highly active Co(II,III)-modified carbon dots (Co-CDs) inside or supported on a representative metal–organic framework (i.e., NH2-MIL-125), denoted as Co-CDs-N-MIL and Co-CDs/N-MIL, respectively, for photocatalytic removal of NO and H2 production. Compared with pure NH2-MIL-125, the photocatalytic activities of both Co-CDs-N-MIL and Co-CDs/N-MIL were significantly enhanced but distinctly different, suggesting that the photocatalytic efficiency closely correlates with the Co-CDs location relative to the NH2-MIL-125. A series of characterizations confirmed that Co-CDs-N-MIL shortens the electron transport distance to some extent, which is conducive to the suppression of electron-hole complexation, and thus has a better efficiency than Co-CDs/N-MIL.

Synergistic integration of metallic Bi and defective TiO2 for enhanced photocatalytic NO removal

The construction of hybrid catalysts is an effective method to enhance catalytic performance, but research on the positioning of the load is limited. In this study, we synthesized two photocatalytic materials by controlling the bismuth-titanium ratio and the site value of Bi modification in the catalyst. The surface-modified photocatalyst, namely 1:0.9 Bi/TiO2, exhibits a photocatalytic efficiency of 68.9 % for the abatement of ppb-level NO in the presence of visible irradiation. This efficiency was significantly superior to that of the corresponding one-step synthesized Bi/TiO2 (48.7 %) and the TiO2 (18.6 %). Furthermore, it promotes nitrate formation and suppresses the generation of toxic NO2. Capture experiments indicate that the same active species are involved in both surface-loaded and uniformly loaded catalysts. The differences in their performance can be attributed to the higher vacancy concentration in the surface-loaded catalysts and the different local coordination environments of vacancies in the catalysts, altering the adsorption capability of oxygen molecules. This work offers fresh perspectives for the generation of efficient photocatalysts.

Efficient photocatalytic decomposition of NO and mechanism insight enabled by NaBH4-reduced N(ligancy-3)-vacancy-rich-graphitic carbon nitride

Vacancy defect engineering is an effective means to improve the performance of g-C3N4 photooxidation for NO removal. In this paper, flake graphite-phase g-C3N4 is prepared by thermal polycondensation. Then g–C3N4–x (x = 0, 0.5, 1.0, 1.5, and 2.0) containing various amounts of vacancies of nitrogen atoms with (3 coordination number) ligancy 3 (N(ligancy-3)) was prepared by NaBH4 reduction at room temperature. The introduction of N vacancies in g-C3N4 narrowed the forbidden gap, enhanced optical absorbance, optimized photo exciton separation and migration, and functioned as traps to mitigate the recombination of photogenerated electron-hole pairs. As a result, g–C3N4–x shows a superior NO removal performance, especially g–C3N4–1.5, which exhibits a high NO removal rate of 66.7 %, excellent resistance to the by-product NO2, and excellent stability. The free-radical seizure experiments and electron paramagnetic resonance (EPR) studies proved the superiority of superoxide radicals, electrons and holes as the prominent free radicals in the photocatalytic NO removal process. In situ diffuse infrared Fourier transform spectroscopy (DRIFTS) confirmed that the cis-dimer (NO)2 produced from NO adsorption on the surface of g–C3N4–1.5 is an important intermediate. Additionally, NO2− is observed as an intermediate and a primary product, and NO3− is identified as the key product of NO photocatalytic oxidation. DFT calculations showed that the N(ligancy-3) vacancy introduces impurity energy levels in g-C3N4 and shortens the electron migration path. The adsorption calculation of NO demonstrated that g–C3N4–N(ligancy-3) exhibits good adsorption and conversion of NO. This study provides a practical defect engineering for the g-C3N4 to remediate environmental pollution.

The intense charge migration and efficient photocatalytic NO removal of the S-scheme heterojunction composites Bi7O9I3-BiOBr

For purpose of efficient photocatalytic removal of NO molecules, both components of bismuth-rich Bi7O9I3 and BiOBr were typically selected to create binary heterojunction composites Bi7O9I3-BiOBr (BI-BBX) through a facile in-situ synthetic protocol. These composites underwent thorough characterization using a range of analytical methods and were subjected to photocatalytic removal of NO at ppb level under visible light for the first time. These produced composites showed enhanced photocatalytic behavior and the best candidate BI-BB0.2 demonstrated the highest removal efficiency among all tested samples. Density-functional theory (DFT) calculations revealed the intense charge migration at the interface. In addition, the composites surface exhibited a propensity to adsorb and activate O2, H2O, and NO molecules, thus promoting the catalytic conversion of NO to NO2– and further NO3– species. Entrapping experiments and electron spin resonance (ESR) results demonstrated the increased generation of oxygen-containing species O2–, 1O2, and ·OH, which was attributed to the rational creation of heterojunctions with similar crystal structures and efficient migration and separation of generated charge carriers in an S-scheme model. This study provides insight into the design and development of Bi7O9I3-based composites for effective dislodge of NO upon the visible-light irradiation.

Atomically dispersed magnesium enhancing reactive oxygen species generation over g-C3N4 nanosheets for efficient photocatalytic NO removal

Photoinduced reactive oxygen species (ROSs)-involving nitrogen oxide (NOx) abatement offers a green way to mitigate environmental air pollution. Developing cost-effective photocatalysts remains challenging yet crucial. Herein, an atomically dispersed Mg-modified g-C3N4 nanosheet photocatalyst (xMg-CN) with excellent photoactivity is developed. The 1.0Mg-CN sample delivers a high NO removal rate of 52.3% under visible light irradiation within 30 min, far surpassing the Mg-free analog (CN, 41.2%). Moreover, a suppressed NO2 by-product discharge can be achieved. The introduction of Mg single atoms (SAs) alters the charge density distribution on the triazine ring plane of g-C3N4, inducing the formation of a built-in electric field, which improves the photoexcited charge carrier separation. Additionally, Mg SAs contribute to the adsorption and activation of O2 molecules, resulting in enhanced ROSs production, as evidenced by the experiments and theoretical simulations. The findings shed light on the role of SAs in designing highly efficient g-C3N4-based photocatalysts for air purification.

Constructing multiple active sites of Bi2WO6 for efficient photocatalytic NO removal and NO2 inhibition

Insufficient photocatalytic NOx oxidation capacity will lead to excessive toxic by-products (NO2), which still seriously restrict its practical application. Herein, the multiple active sites (Cl, Bi0 and OVs) modified Bi2WO6 has been established by in-situ synthesis method. The synergistic effect of multiple active sites greatly increased the photo-electric properties of the Bi2WO6, resulting in the boosting photocatalytic NOx deep oxidation to nitrate. The visible light driven OVs-Bi@BWO-Cl catalyst exhibited a highest NO conversion efficiency (67.3 %) with extremely low NO2 concentration (17.9 ppb). The synergism of structural regulation from the OVs with Cl-doping and surface plasmon resonance of Bi0 significantly enhanced light absorption and provided a fast charge transport channel, improving the separation efficiency of photo-generated carriers. The in-situ DRIFTS and density functional theory (DFT) results shown that the synergistic effect by multiple active sites could enhance the adsorption and activation of reactants to accelerate the processes of H2O/O2-to-ROS and decrease the energy barrier of NO removal to promote deep oxidation of NO-to-NO3−. This work can provide ideas for the design and preparation of the catalyst for safe photocatalytic environment purification.

Surface hydroxyl manipulation of BiOCl nanosheets for promoted O2 activation and photocatalytic NO removal

Surface hydroxyl manipulation of BiOCl nanosheets for promoted O2 activation and photocatalytic NO removal

Boosted photocatalytic removal of NO using direct Z-scheme UiO-66-NH2/Bi2MoO6 nanoflowers heterojunction: mechanism insight and humidity effect

Boosted photocatalytic removal of NO using direct Z-scheme UiO-66-NH2/Bi2MoO6 nanoflowers heterojunction: mechanism insight and humidity effect

Recent advances and roles of oxygen vacancies for photocatalytic nitrogen oxide removal

Air pollution has become a globally prominent environmental problem, in which nitrogen oxide (NOx, ∼ 95 % NO and NO2) is one of the most serious pollutants, how to remove low-concentered NO from the air without producing secondary pollution is becoming a challenging task. Environmental nanomaterial based photocatalytic technique is considered as a green technology for the removal of dilute NO (∼ ppb) due to its low costs, high efficiencies and environmental friendless. Photocatalysts with certain surface defects, e.g., oxygen vacancies (OVs) have attracted huge interests with appreciable effectiveness for the NO removal as they affect essential steps of the photocatalytic reactions. Considering the advantages of OV for the NO conversion, this review systematically summarizes the methods of defect creation (e.g., OVs), characterizations, detailed reaction mechanisms during the photocatalytic NO removal. This review presents the state-of-the-arts, applications and vital roles of OVs including extending light absorption, promoting carrier separation, strengthening the surface-interface reactions in the photocatalytic NO oxidations. Based on these, several challenges and prospects of surface defect engineering in semiconducting materials are proposed for the further application of OV for NO conversion as well as the removal of other potential atmospheric hazardous.

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.

2D/2D layered BiOIO3/g-C3N4 S-scheme heterojunction for photocatalytic NO oxidation

It is essential to promote interfacial separation and charge migration in heterojunctions for effectively driving surface photocatalytic reactions. In this work, we report the construction of a 2D/2D layered BiOIO3/g-C3N4 (BIO/CN) heterojunction for photocatalytic NO removal. The BIO/CN heterojunction exhibits a remarkably higher NO photo-oxidation removal rate (46.9%) compared to pristine BIO (20.1%) and CN (25.9%) under visible-light irradiation. Additionally, it effectively suppresses the formation of toxic NO2 intermediates during photocatalytic reaction. The improved photocatalytic performance of BIO/CN composite is caused by its S-scheme charge carrier transport mechanism, which is supported by Density Functional Theory simulations of work function and electron density difference, along with in-situ irradiated X-ray Photoelectron Spectroscopy and Electron Paramagnetic Resonance analyses. This S-scheme structure improves the interfacial carrier separation efficiency and retains the strong photo-redox ability. Our study demonstrates that construction of a S-scheme heterojunction is significant in the design and preparation of highly efficient photocatalysts for air purification.

In-situ fabrication of TiO2/NH2−MIL-125(Ti) via MOF-driven strategy to promote efficient interfacial effects for enhancing photocatalytic NO removal activity

In-situ fabrication of TiO2/NH2−MIL-125(Ti) via MOF-driven strategy to promote efficient interfacial effects for enhancing photocatalytic NO removal activity

Enhanced photocatalytic NO removal over AgCu alloy modified UiO-66-NH2 promoting charge transfer

Photocatalytic NO removal technology is considered as one of the most effective green methods for reducing atmospheric NO but there remains the problems of lower efficiency and poor stability of photocatalysts. Rapid recombination of photogenerated electron (e−) and holes (h+) is known as a key issue that causes low activity and poor stability of catalysts. Herein, we report a novel AgCu@UiO-66-NH2 photocatalyst (AgCu@UN) that is made up of AgCu alloy on the surface of Zr-MOF (UiO-66-NH2) by employing in-situ photodeposition method. The experimental results of photocatalytic NO removal indicated that the optimized 0.5Ag0.5Cu@UN sample with 0.5 mg of Ag and Cu exhibited the best NO removal efficiency of 63 % for ppb-level atmospheric NO, more higher than that of pure UiO-66-NH2 (38 %). The characterizations suggested that the excellent photocatalytic performance of 0.5Ag0.5Cu@UN can be ascribed to the efficient charge separation and transfer and the visible-light-harvesting ability due to benefiting electron migration process between AgCu alloys and UN. Moreover, the enriched electrons around AgCu could be transferred to O2 to generate more superoxide radicals (•O2−), which could oxidize NO to the final product, nitrate (NO3−). The present findings can provide some novel insights for the design of efficient MOF based photocatalysts to eliminate low concentrations of NOX.

Visible light photocatalytic NOx removal with suppressed poisonous NO2 byproduct generation over simply synthesized triangular silver nanoparticles coupled with tin dioxide.

The treatment or conversion of air pollutants with a low generation of secondary toxic substances has become a hot topic in indoor air pollution abatement. Herein, we used triangle-shaped Ag nanoparticles coupled with SnO2 for efficient photocatalytic NO removal. Ag triangular nanoparticles (TNPs) were synthesized by the photoreduction method and SnO2 was coupled by a simple chemical impregnation process. The photocatalytic NO removal activity results show that the modification with Ag TNPs significantly boosted the removal performance up to 3.4 times higher than pristine SnO2. The underlying roles of Ag TNPs in NO removal activity improvement are due to some advantages of Ag TNPs. Moreover, the Ag TNPs contributed photogenerated holes as the main active species toward enhancing the NO oxidation reaction. In particular, the selectivity toward green products significantly improved from 52.78% (SnO2) to 86.99% (Ag TNPs/SnO2). The formation of reactive radicals under light irradiation was also verified by DMPO spin-trapping experiments. This work provides a potential candidate for visible-light photocatalytic NO removal with low toxic byproduct generation.

Photocatalytic NO removal: complete oxidation and reduction reaction for by-product inhibition and end-product recovery

Photocatalysis is an eco-friendly and cost-effective method to realize the purification of ppb-level NO, and the end-product (nitrate/ammonia) of the photocatalytic NO complete oxidation/reduction reaction can be further recycled.