Nitric Oxide Removal Research Articles

Enhanced Photocatalytic Activity of Nickel(II)‐Doped Bi2O2CO3 Nanosheets for Efficient Nitric Oxide Removal

AbstractBi2O2CO3 is a typical bismuth‐based semiconductor photocatalyst that has attracted much attention because of layered structure and polarization characteristics. However, the wide bandgap of Bi2O2CO3 limits its practical applications in photocatalysis. In this study, the nickel (II)‐doped Bi2O2CO3 (Ni2+‐Bi2O2CO3) with oxygen vacancies was prepared by adding a controllable amount of nickel ions. The photocatalytic efficiency of the optimized sample for ppb‐grade NO under visible light irradiation is 59.4 %, which is 2.8 times than that of its counterpart, Bi2O2CO3 (21.2 %). Based on experiments and characterizations, Introduction of nickel ions and oxygen vacancies improves the photocatalytic performance of Ni2+‐Bi2O2CO3, which not only lowered the bandgap from 3.25 eV to 2.92 eV, but also reduced the recombination of photogenerated carriers by formation of the impurity level. Furthermore, the adsorption and photocatalytic conversion pathway of NO was explored by in situ DRIFTS, the principal byproducts of photocatalytic oxidation of NO are NO3− and NO2−. This work offers a new perspective to improve the photocatalytic activity by doping mothed for air purification.

Oxygen Vacancy Sites Enable Efficient Photocatalytic Oxidation of Nitric Oxide: The Role of W/Mo Valence Transition in Bi2W(Mo)O6‐x

AbstractOxygen vacancy (Ov) sites play a critical role in the activation and deep oxidation of nitric oxide (NO). However, controlling the concentration and type of Ov remains a significant challenge. In this study, Bi2W(Mo)O6‐x is investigated as a model system and demonstrates that increasing the concentration of Ov substantially enhances the efficiency of air NO removal. Increasing the Ov concentrations in Bi2WO6‐x and Bi2MoO6‐x improves NO removal efficiency ≈12‐ and 11‐fold, respectively, compared to their low‐Ov counterparts. This enhancement is attributed to improved adsorption and activation of NO/O2 molecules, better separation and transfer of photogenerated carriers, and increased visible light absorption. Notably, Bi2WO6‐x remains highly stable over ten recycling tests for continuous air NO deep photooxidation, while Bi2MoO6‐x shows a 43.5% decrease in efficiency after ten runs. This sustained performance is attributed to stable Ovs without changes in metal ion valence, unlike Bi2MoO6‐x, where instability arises from the reduction of Mo6+ to Mo4+. In situ DRIFTS reveals possible pathways for the deep photooxidation of NO to nitrate (NO3−). This study provides valuable insights into designing high‐performance, durable catalysts by effectively controlling Ov concentration and type, paving the way for efficient photocatalytic air purification technologies.

A natural polyphenolic nanoparticle--knotted hydrogel scavenger for osteoarthritis therapy

Exploring highly efficient and cost-effective biomaterials for osteoarthritis (OA) treatment remains challenging, as current therapeutic strategies are difficult to eradicate the excessive reactive oxygen species (ROS) and nitric oxide (NO) at damaged sites. Tea polyphenol (TP) nanoparticles (NPs), a nature-inspired antioxidant in combination with 2-(4-Carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (carboxy-PTIO), a NO scavenger, could provide maximized positive therapeutic effects on OA by eradicating both ROS and NO. Notably, this combination not only improves the half-life of the TP monomer and the drug loading efficiency of carboxy-PTIO but also prevents nitrite from being harmful to tissue. Moreover, the protonation ability of carboxy-PTIO allows smart acid-responsive release in response to environmental pH, which provides conditioned treatment strategies for OA. In in vitro experiments, TP/PTIO NPs downregulated proinflammatory cytokine release via synergistic removal of ROS and NO and suppression of ROS/NF-κB and iNOS/NO/Caspase-3 signaling. For in vivo experiments, NPs were cross-linked with 4-arm-PEG-SH to form an injectable hydrogel system. The release of TP and carboxy-PTIO from the system efficiently prevents cartilage inflammation and damage via similar signaling pathways. Overall, the proposed system provides an efficient approach for OA therapy.

Preparation of gray ZnO1−x photocatalyst containing oxygen vacancies for the highly efficient removal of nitric oxide and acetaminophen

Preparation of gray ZnO1−x photocatalyst containing oxygen vacancies for the highly efficient removal of nitric oxide and acetaminophen

Hydrogen Peroxide Heterolytic Cleavage Induced Gas Phase Photo-Fenton Oxidation of Nitric Oxide.

Nitric oxide (NO) is one of the major air pollutants that may cause ecological imbalance and severe human disease. However, the removal of NO faces challenges of low efficiency, high energy consumption, and production of toxic NO2 byproducts. Herein, we report an efficient *OOH intermediate-involved NO oxidation route with high NO3- selectivity via a gas phase photo-Fenton system. Fe single atoms (Fe SAs)-anchored NH2-UiO-66(Zr) (Fe SAs@NU) was synthesized. The five-coordinated Fe SAs undergo a transient structure reconstitution during the photo-Fenton process, which enables a novel heterolytic cleavage pathway of H2O2 to derive specific ·OOH/·O2- radicals as reactive oxygen species. Therefore, a high NO (550 parts per billion) removal rate of 81% (NO3- selectivity up to 99%) is achieved under visible-light irradiation (>420 nm). This study provides new insight for the high-performance photo-Fenton process via a transient structure reconstitution pathway for the removal of gas phase NOx pollutants.

Built-in electric field mediated S-scheme charge migration and Co-N4(II) sites in cobalt phthalocyanine/MIL-68(In)-NH2 heterojunction for boosting photocatalytic nitric oxide oxidation

The efficiency of photocatalytic Nitric Oxide(NO) oxidation is limited by the lack of oxygen(O2) active sites and poor charge carrier separation. To address this challenge, we developed a molecular Cobalt Phthalocyanine modified MIL-68(In)–NH2 photocatalyst with a robust Built-in electric field(BIEF). In the 2 % CoPc-MIN sample, the BIEF strength is increased by 3.54 times and 5.83 times compared to pristine CoPc and MIL-68(In)–NH2, respectively. This BIEF facilitates the efficient S-scheme charge transfer, thereby enhancing photogenerated carrier separation. Additionally, the Co-N4(II) sites in CoPc can effectively trap the separated photoexcited electrons in the S-scheme system. In addition, the Co-N4(II) sites can also serve as active sites for O2 adsorption and activation, promoting the generation of superoxide radical (O2–), thereby driving the direct conversion of NO to nitrate(NO3–). Consequently, the 2 % CoPc-MIN sample exhibits a remarkable photocatalytic NO removal efficiency of 79.37 % while effectively suppressing the formation of harmful by-product nitrogen dioxide(NO2) to below 3.5 ppb. This study provides a feasible strategy for designing high-efficiency O2 activation photocatalysts for NO oxidation.

Engineering the defect distribution via boron doping in amorphous TiO2 for robust photocatalytic NO removal

Nitric oxide (NO) pollutant can threaten the regional environment and human health. Solar-powered photocatalytic oxidation method is desirable for NO removal (ppb level) at ambient conditions, but suffers from the unsatisfactory activity and poor selectivity due to the sluggish molecular oxygen activation. Herein, we demonstrate that efficient photocatalytic NO removal can be realized by modulating the defects distribution of amorphous TiO2 via boron doping. Theoretical calculations and experimental results reveal that H3BO3 modification can refine the structure of surface oxygen vacancies, promoting electron-rich molecular oxygen activation to •OH. Meanwhile, bulk-phase oxygen defects can be filled by free-state B atoms, accelerating the electron transfer via Ti-O-B bonding. Homogeneous boron-doped amorphous TiO2 achieves about 5 times higher NO removal efficiency (∼50%) than that of amorphous TiO2 (∼9%) without releasing remarkable NO2 (selectivity, ∼97%). This study provides a state-of-the-art approach for robust photocatalytic NO removal by engineering the defect distribution.

Oxidation-complexation removal of nitric oxide by anatase titanium dioxide with exposed (0 0 1) facets ultraviolet-induced ferrous ethylenediaminetetraacetate

Ferrous ethylenediaminetetraacetate (Fe(II)EDTA) accompanied by regeneration is thought to be a very efficient method to remove nitric oxide (NO) from flue gas. However, Fe(II)EDTA regeneration requires a large amount of regenerant consumption. For this purpose, anatase titanium dioxide with exposed (001) facets by fluorination (nF-TiO2) was synthesized and combined with Fe(II)EDTA solution for NO removal with ultraviolet light (UV). The result showed that 5F-TiO2 with approximately 30 % (001) facets exposed can significantly promote NO removal of Fe(II)EDTA under UV irradiation, with an average removal efficiency of up to 94.83 % over a 60-minute period. The mechanism study indicated that the excellent removal performance of 5F-TiO2 was mainly because the moderate co-exposure of its (001) and (101) facets could greatly suppress the electron hole recombination rate, accelerate the Fe(Ⅱ)EDTA/Fe(III)EDTA cycle, and form catalytic oxidation-complexation synergism denitrification. Under this synergistic effect, NO from simulated flue gas was mainly transformed to NO3–, NO2–, NH4+, N2, and N2O. Subsequently, NO removal performance using UV/Fe(Ⅱ)EDTA/5F-TiO2 under different parameters demonstrated that appropriate oxygen concentration (3 vol%), suitable 5F-TiO2 mass (0.5 g), low temperature (30 ℃), and weak acidic environment (pH = 4) were favorable for NO removal. The kinetics demonstrated that NO removal by the UV/Fe(Ⅱ)EDTA/5F-TiO2 system was a pseudo-first-order process. Finally, UV/Fe(II)EDTA/5F-TiO2 denitrification technology shows great potential in practical applications. This work offers a new route for the greenandlow-costapplication of Fe(Ⅱ)EDTA denitrification in flue gas treatment.

S-Scheme heterojunction of Cs2SnBr6/C3N4 with interfacial electron exchange toward efficient photocatalytic NO abatement

Photocatalytic technology is of great significance in environmental purification due to its eco-friendly and cost-effective operations. However, low charge-transfer efficiency restricts the photocatalytic activity of the catalyst. Herein, we report Cs2SnBr6/C3N4 composite catalysts that exhibit a robust interfacial electron exchange thereby enhancing photocatalytic nitric oxide (NO) oxidation. A comprehensive study has demonstrated the S-scheme electron transfer mechanism. Benefiting from the interfacial internal electric field, the C-Br bond serves as a direct electron transfer channel, resulting in enhanced charge separation. Furthermore, the S-scheme heterojunction effectively traps high redox potential electrons and holes, leading to the production of abundant reactive oxygen radicals that enhance photocatalytic NO abatement. The NO removal rate of the Cs2SnBr6/C3N4 heterogeneous system can reach 86.8 %, which is approximately 3-fold and 18-fold that of pristine C3N4 and Cs2SnBr6, respectively. The comprehensive understanding of the electron transfer between heterojunction atomic interfaces will provide a novel perspective on efficient environmental photocatalysis.

Effect of Nitrogen, Carbon Dioxide, and Air Activation on the Low-Temperature Ammonia Removal Performance of Activated Carbon during Nitric Oxide Removal

Effect of Nitrogen, Carbon Dioxide, and Air Activation on the Low-Temperature Ammonia Removal Performance of Activated Carbon during Nitric Oxide Removal

Micro-Spherical BiOI Photocatalysts for Efficient Degradation of Residual Xanthate and Gaseous Nitric Oxide.

BiOI microspheres were synthesized using the solvothermal method for the degradation of residual xanthate and gaseous nitric oxide (NO) under visible light irradiation. The as-prepared BiOI nanomaterials were then characterized using various technologies, including XRD, FE-SEM, TEM, UV-Vis DRS, and XPS. The photodegradation results show that the removal efficiency of isobutyl sodium xanthate can reach 98.08% at an initial xanthate concentration of 120 mg/L; that of NO is as high as 96.36% at an inlet NO concentration of 11 ppm. Moreover, the effects of operational parameters such as catalyst dosage, initial xanthate concentration, and pH value of wastewater on the removal of xanthate were investigated. The results of scavenging tests and full-spectrum scanning indicate that ·O2- radicals are the main active species in xanthate degradation, and peroxide xanthate is an intermediate. The reusability of BiOI was explored through cyclic experiments. Furthermore, the reaction path and the mechanism of NO removal using BiOI were analyzed, and the main active species was also ·O2-. It is concluded that BiOI photocatalysts have high potential for wastewater treatment and waste gas clean-up in the mineral industry.

One-step in-situ construction engineering of ZnO-Zn2SnO4 heterojunction for deeply photocatalytic oxidation of nitric oxide

The generation of hazardous intermediates during the process of photocatalytic nitric oxide (NO) oxidation presents a tough issue. Herein, a one-step microwave strategy was employed to introduce oxygen vacancies (OVs) into zinc oxide-zinc stannate (ZnO-Zn2SnO4) heterojunction, resulting in an improvement in the photocatalytic efficiency for NO removal. The construction ZnO-Zn2SnO4 heterojunction with the OVs (ZSO-3) owns a significant contribution towards highly efficient electron transfer efficiency (99.7%), which renders ZSO-3 to exert a deep oxidation of NO-to-nitrate (NO3−) rather than NO-to-nitrite (NO2−) or NO-to-nitrogen dioxide (NO2). Based on the solid supports of experimental and simulated calculations, it can be found that OVs play an irreplaceable role in activating small molecules such as NO and O2. Moreover, the enhanced adsorption capacity of small molecules, which guarantees the high yield of active radical due to the formation of S-scheme heterojunction. This work illuminates a novel viewpoint on one-step in-situ route to prepare Zn2SnO4-based heterojunction photocatalyst with deep oxidation ability of NO-to-NO3−.

Selective Electrocatalytic Conversion of Nitric Oxide to High Value-Added Chemicals.

The artificial disturbance in the nitrogen cycle has necessitated an urgent need for nitric oxide (NO) removal. Electrochemical technologies for NO conversion have gained increasing attention in recent years. This comprehensive review presents the recent advancements in selective electrocatalytic conversion of NO to high value-added chemicals, with specific emphasis on catalyst design, electrolyte composition, mass diffusion, and adsorption energies of key intermediate species. Furthermore, the review explores the synergistic electrochemical co-electrolysis of NO with specific carbon source molecules, enabling the synthesis of a range of valuable chemicals with C─N bonds. It also provides in-depth insights into the intricate reaction pathways and underlying mechanisms, offering valuable perspectives on the challenges and prospects of selective NO electrolysis. By advancing comprehension and fostering awareness of nitrogen cycle balance, this review contributes to the development of efficient and sustainable electrocatalytic systems for the selective synthesis of valuable chemicals from NO.

Experimental and computational study on removal of nitric oxide using NH2-MIL-125: Revisiting removal mechanism

The NH2-MIL-125 (NM-125) or modified NM-125 materials are used for photocatalytic removal of nitric oxide (NO). Most researchers attributed few NO2 emission during NO photocatalysis to high selectivity towards the formation of nitrate ions due to the neglect of the principle of electroneutrality and pore structure of NM-125. This may cause misleading photocatalytic mechanism of NO removal. Herein, this work proposes a new mechanism behind NO removal using NM-125 based on experimental investigations and theoretical calculations. First, experimentally, the highest NO removal efficiency of 88.54 % with negligible NO2 emission occurs at the anhydrous condition. In addition, in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements verify the presence and accumulation of NO2 as product during photocatalytic conversion of NO. Furthermore, density functional theory (DFT) calculations and grand canonical Monte Carlo (GCMC) computations demonstrate that there exist strong interactions between NO2 and -NH2 group within pores. Few NO2 is detected during experiments is probably due to its subsequent adsorption in the pores of NM-125. The new NO removal mechanism including photocatalytic conversion NO into NO2 and subsequent NO2 adsorption in the pores of NM-125 is thus proposed. This work provides a deeper insight into photocatalytic NO removal over NM-125 and its variants.

Removal of nitric oxide in bioreactors: a review on the pathways, governing factors and mathematical modelling.

The constant surge in nitric oxide in the atmosphere results in severe environmental degradation, negatively impacting human health and ecosystems, and is presently a global concern. Widely used physicochemical technologies for nitric oxide (NO) removal comes with high installation and operational costs and the production of secondary pollutants. Thus, biological treatment has been emphasized over the last two decades, but the poor solubility of NO in water makes it a challenging issue. The present article reviews the various technical aspects of biological treatment of nitric oxide, including the removal pathways and reactor configurations involved in the process. The most widely used technologies in this regard are chemical adsorption processes followed by biological reactors like biofilters, biotrickling filters and membrane bioreactors that enhance NO solubility and offer the flexibility and scope of further improvement in process design. The effect of various experimental and operational parameters on NO removal, including pH, carbon source, gas flow rate, gas residence time and presence of inhibitory components in the flue gas, is also discussed along with the developed mathematical models for predicting NO removal in a biological treatment system. There is an extensive scope of investigation regarding the development of an economical system to remove NO, and an exhaustive model that would optimize the process considering maximum practical parameters encountered during such operation. A detailed discussion made in this article gives a proper insight into all these areas.

Nitric oxide removal from flue gas coupled with the FeIIEDTA regeneration by ultraviolet irradiation

Nitric oxide removal from flue gas coupled with the FeIIEDTA regeneration by ultraviolet irradiation

Streamlining manufacture of high-performance SiC catalytic membrane using bifunctional precursors for multipollutant control

SiC catalytic membrane holds great promise in controlling high-temperature nitric oxide (NO) and particulate matter (PM), but its complex fabrication process limits its potential for practical application. We present a novel, rapid fabrication route, based on co-sintering and acid treatment (CSAT), for the fabrication of Co3O4-loaded SiC (A-Co-SiC) catalytic membranes. Our approach involves using functional activated carbons and Co2O3 for the simultaneous sintering of both the support and separation layers at a lower temperature. The CSAT approach eliminates particle penetration into the support layer and accelerates the generation of active Co3O4 nanoparticles on Co2SiO4. This reduces the number of fabrication steps from 9 to 5, resulting in over a 50% reduction in both energy consumption and sintering time. The resulting A-Co-SiC catalytic membrane exhibits remarkable gas permeance of 224.51 m3 m−2 h−1·kPa−1, superior NO oxidation efficiency (85% at 280 °C), and a high PM2.5 filtration efficiency of 99.97% - the highest simultaneous removal of NO and PM2.5 reported to date. The manufacturing method developed in our work offers a practical and efficient solution for producing SiC catalytic membranes that can be utilized in various integrated emission filtration systems in industrial settings, with the potential to be adapted to other ceramic systems.

Breaking the Selectivity Barrier: Reactive Oxygen Species Control in Photocatalytic Nitric Oxide Conversion

AbstractSemiconductor photocatalytic technology holds promise in efficiently reducing low concentrations of gaseous nitric oxide (NO). However, the suboptimal selectivity in NO removal, leading to the undesired production of NO2 byproducts, poses a challenge. In this study, a defective CdS/Na2Ti3O7 heterostructure is rationally designed with strong electronic interaction and intimate interface contact for promoting charge transfer kinetics. This design refines reactive oxygen species (ROS) generation, resulting in an impressive 81% NO elimination and 99.7% selectivity toward nitrates. Detailed mechanistic studies reveal an intriguing catalysis scenario in which reactant molecules are selectively adsorbed and activated at different sites. Anionic vacancies on the CdS/Na2Ti3O7 surface render the activation of molecular O2 to reactive superoxide radicals (O2 −) species. Furthermore, intrinsic surface basicity and O vacancy sites of the Na2Ti3O7 cocatalyst facilitate the capture and activation of acidic nitrogen oxides (NOx) molecules as nitrate species, contributing to enhanced catalytic activity and selectivity. As a result, anionic vacancies and basic sites over CdS/Na2Ti3O7 heterostructure synergistically regulate the NOx oxidation pathway, refining the products toward nitrate with remarkable selectivity. These insights guide the development of advanced photocatalytic systems for environmental remediation, highlighting the importance of managing ROS production for efficient pollutant removal.

Nitric oxide removal by synergistic photooxidation and adsorption using Pd1/g-C3N4-UiO-66-NH2 P-A heterojunction

Simultaneous avoidance of secondary air pollution and catalyst deactivation remains a challenge for existing photocatalytic removal of nitric oxide (NO). Herein, a photocatalysis-adsorption (P-A) heterojunction is synthesized for eco-friendly NO removal by facilely grinding Pd single atoms (Pd1) anchored g-C3N4 (48CN/Pd) with UiO-66-NH2 (UION). Under visible-light irradiation, the 40UION-CN/Pd composite shows 93.91 % of NO removal efficiency with only 2.73 % of NO2 emissions and negligible catalyst deactivation. The DeNOx index increases remarkably from −0.66 for 48CN/Pd to 0.86 for 40UION-CN/Pd. Furthermore, the synthesized P-A heterojunction efficiently removes NO from real flue gases produced by a domestic coal-fired stove and from SO2-rich flue gases. The mechanism exploration based on experimental investigations and density functional theory (DFT) calculations reveals that UION captures the NO2 selectively produced by 48CN/Pd, simultaneously suppressing NO2 emissions and refreshing active sites for NO photooxidation. Moreover, the results of X-ray photoelectron spectroscopy (XPS), charge density difference calculation, energy-resolved distribution of electron traps (ERDT) and in-situ Kelvin probe force microscopy (KPFM) reveal that the built-in electric field and Type-II heterojunction formed between 48CN/Pd and UION promote the separation of photogenerated carriers, enhancing the catalytic activity of the composite. This work provides an innovative strategy to avoid NO2 emission and catalyst deactivation during photocatalytic NO removal.

Mass transfer vectors for nitric oxide removal through biological treatments

The reduction of nitric oxide (NO) emissions to atmosphere has been recently addressed using biological technologies. However, NO removal through bioprocesses is quite challenging due to the low solubility of NO in water. Therefore, the abatement of NO emissions might be improved by adding a chelating agent or a mass transfer vector (MTV) to increase the solubility of this pollutant into the aqueous phase where the bioprocess takes place. This research seeks to assess the performance of different non-aqueous phase liquids (NAPs): n-hexadecane (HEX), diethyl sebacate (DSE), 1,1,1,3,5,5,5-heptamethyl-trisiloxane (HTX), 2,2,4,4,6,8,8-heptamethylnonane (HNO), and high temperature silicone oil (SO) in chemical absorption–biological reduction (CABR) integrated systems. The results showed that HNO and HTX had the maximum gas-liquid mass transfer capacity, being 0.32 mol NO/kmol NAP and 0.29 mol NO/kmol NAP, respectively. When an aqueous phase was added to the system, the mass transfer gas–liquid of NO was increased, with HTX reaching a removal efficiency of 82 ± 3% NO with water, and 88 ± 6% with a phosphate buffer solution. All NAPs were tested for short-term toxicity assessment and resulted neither toxic nor inhibitory for the biological activity (denitrification). DSE was found to be biodegradable, which could limit its applicability in biological processes for gas treatment. Finally, in the CABR system tests, it was shown that NO elimination improved in a short time (30 min) when the three mass transfer vectors (HEX, HTX, HNO) were added to enriched denitrifying bacteria.