NO Removal Efficiency Research Articles

Synthesis of CdS QDs/BaSnO3 nanocomposites via electrostatic self-assembly for visible light photocatalytic deep oxidation of NO

A BaSnO3 sample loaded with CdS quantum dots (CdS QDs/BaSnO3) was prepared by an electrostatic self-assembly method. The obtained CdS QDs/BaSnO3 nanocomposites exhibited an efficient visible light utilization and photocatalytic NO oxidation activity. The experimental results revealed that the loading of CdS QDs tremendously improved the light absorption range and the separation efficiency of photogenerated electron-hole pairs. In-situ DRIFTS tests demonstrated that the introduced Cd2+ could provide new active sites for NO adsorption and activation. Simultaneously, the EPR test showed that the introduction of CdS QDs induced the generation of ·O2–, which was conducive to promoting the deep oxidation of NO. This study provides a facile and effective synthesis method and strategy for improving the photocatalytic NO removal efficiency while significantly suppressing the NO2 concentration.

Establishment of a novel Fenton-like enhanced low-temperature selective catalytic reduction over FeVO4 catalysts

Deep NO removal technology for low-temperature flue gas is urgently needed in tail gas purification. This work proposes an efficient Fenton-like enhanced SCR reaction for NO removal. The SCR, Fenton-like, and Fenton-like enhanced SCR reactions were systematically studied with Fe2O3, V2O5, and FeVO4 as catalysts. The results showed that the FeVO4 exhibited an excellent NO removal performance in Fenton-like enhanced SCR reactions at low temperatures. Hydroxyl radicals (•OH) were demonstrated to perform a pivotal role in the NO removal from the radical tests. Moreover, H2O2 vapor inhibited the formation of N2O and improved the N2 selectivity. When the reaction temperature was 175 ℃, and the molar ratio of H2O2 and NO was 6, the NO removal efficiency researched 95.3%, which was 5.5 times higher than that with FeVO4 in SCR reactions. Further, the stability of FeVO4 was verified via the H2-TPR, Raman, FTIR, and SEM characterizations. The XPS results indicated that the regeneration of Fe3+ in Fenton-like enhanced SCR reactions had also positively influenced NO removal. Finally, the rate-determined steps were obtained via kinetic studies so that the mechanism of Fenton-like enhanced SCR reactions were speculated. This study provided a comprehensive view of the structure-activity relationships of FeVO4 catalyst in Fenton-like enhanced SCR reactions and was conducive to promoting potential applications.

Bi12TiO20-TiO2 S-scheme heterojunction for improved photocatalytic NO removal: Experimental and DFT insights

The fabrication of step-scheme (S-scheme) photocatalysts with superior redox ability for air purification is very important but remains a challenge. In this study, an S-scheme Bi12TiO20-TiO2 heterojunction is prepared for photocatalytic NO removal. The optimized Bi12TiO20-TiO2 heterojunction shows higher NO removal efficiency (42.6 %) than that of pristine Bi12TiO20 (8.7 %) and TiO2 (21.4 %) under simulated solar light irradiation. The enhanced photocatalytic activity can be attributed to the efficient separation and transfer efficiency of photoinduced electrons-hole pairs, enhanced redox ability, and increased NO adsorption capacity induced by S-scheme heterojunction between Bi12TiO20 and TiO2. The S-scheme charge transfer mechanism on Bi12TiO20-TiO2 heterojunction is proposed based on characterizations and theoretical calculations. The NO conversion process is investigated using in-situ Fourier transform infrared spectroscopy (in-situ FTIR). This study provides new insights for exploring highly efficient photocatalysts for NO removal.

Removal of NO at low concentration from air in urban built environments by activated miscanthus biochar

This work presents an innovative and sustainable approach to remove NO emissions from urban ambient air in confined areas (underground parking areas or tunnels) using low-cost activated carbons obtained from Miscanthus biochar (MSP700) by physical activation (with CO2 or steam) at temperatures ranging from 800 to 900 °C. The NO removal capacity of the activated biochars was evaluated under different conditions (temperature, humidity and oxygen concentration) and compared against a commercial activated carbon. This last material showed a clear dependence on oxygen concentration and temperature, exhibiting a maximum capacity of 72.6% in air at 20 °C, whilst, its capacity notably decreased at higher temperatures, revealing that physical NO adsorption is the limiting step for the commercial sample that presents limited oxygen surface functionalities. In contrast, MSP700-activated biochars reached nearly complete NO removal (99.9%) at all tested temperatures in air ambient. Those MSP700-derived carbons only required low oxygen concentration (4 vol%) in the gas stream to achieve the full NO removal at 20 °C. Moreover, they also showed an excellent performance in the presence of H2O, reaching NO removal higher than 96%. This remarkable activity results from the abundance of basic oxygenated surface groups, which act as active sites for NO/O2 adsorption, along with the presence of a homogeneous microporosity of 6 Å, which enables intimate contact between NO and O2. These features promote the oxidation of NO to NO2, which is further retained over the carbon surface. Therefore, the activated biochars studied here could be considered promising materials for the efficient removal of NO at low concentrations from air at moderate temperatures, thus closely approaching real-life conditions in confined spaces.

Dry Emission Control Technology for Glass Melting Furnace by Plasma-Chemical Hybrid Processing

To use the continuous combustion of fossil fuels as a sustainable energy source, a low-cost and energy-saving exhaust gas treatment for NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> , SO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> , and suspended particulate matter is required. The plasma hybrid exhaust gas treatment technology proposed by the authors is not only a method of plasma treatment, but also a method that combines it with a chemical process, such as chemical solution stabilizer, to clean exhaust gas. This study reports the simulation and application of glass melting furnace exhaust gas treatment as a practical result of the plasma chemical hybrid process (PCHP). In the experiment, higher removal efficiencies of NO, NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> , and SO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> (33, 16, and 55%, respectively) were obtained. The energy efficiency of NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> removal by evaluating the electrical power using the cost of NaOH and the power of ozonizers was measured to be 23 g(NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> )/kWh. From comparison, the simulated and experimental temperature distributions and NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> concentration were found to be in good agreements. This indicates that numerical design simulation produces a satisfactory result. PCHP can potentially be the most suitable method for exhaust gas treatment in glass melting furnaces.

Simultaneous removal of SO2, NO and Hg0 using porous carbon/heat-coactivated persulfate system

A novel simultaneous removal technique of SO2, NO, and Hg0 using porous carbon/heat-coactivated persulfate (PS) system was proposed. A series of experiments and theoretical analysis were conducted to explore simultaneous removal process of Hg0, SO2, and NO. Study demonstrates that the developed porous carbon/heat-coactivated PS system gains larger free radical yield and higher pollutants simultaneous removal efficiency than other comparison systems, which are associated with the synergism between porous carbon and heat. High temperature plays a vital role in this co-activation system. Both SO4−· and ·OH play an important role in NO and Hg0 removal, but ·OH is more important for NO removal while SO4−· is more important for Hg0 removal. Both NO and Hg0 removal processes meet pseudo-first-order rapid reaction kinetics, and their removal processes are controlled by mass transfer. Removal efficiencies of NO and Hg0 are increased first and then are decreased with increasing PS concentration, temperature and porous carbon concentration. Increasing pH and concentrations of SO2, NO and Hg0 reduce the NO and Hg0 removal efficiencies. The highest simultaneous removal efficiency of Hg0, SO2, and NO is up to 98.4% for Hg0, 100% for SO2, and 89.3% for NO under an optimized test condition.

Insights into the role of C-S-C bond in C3N5 for photocatalytic NO deep oxidation: Experimental and DFT exploration

Non-stoichiometric polymer carbon nitride of C3N5 is becoming an important visible-light-type catalyst due to the narrow bandgap, non-toxicity, and thermal stability. Here, we report a sulfur doping strategy for upgrading the photogenerated carriers’ dynamics of C3N5. Studies on the transient diffuse reflectance spectra prove that the lifetime of photogenerated carriers of sulfur-doped C3N5 (S-C3N5) increases 61.6 %. The widened visible-light responsive range and enhanced structural defects are also confirmed by UV–vis DRS and ESR characterizations. DFT calculations also verify the better NO adsorption and activation as well as give an insight into the mechanism of NO conversion from the molecule level. Such unique properties endow S-C3N5 with a 4.9- and 5.1-fold increase in photocatalytic NO removal efficiency and rate respectively compared to C3N5. In-situ DRIFTS tests demonstrate the excellent NO deep-oxidation capability of S-C3N5. Ten-cycle NO removal experiments prove its reusability and durability.

Indirect catalytic oxidation of multi-pollutants in diesel exhaust by ozone/micro-nano bubbles system

ABSTRACT Wet oxidation absorption is an efficient and promising method of exhaust gas treatment. When the micro-nano bubbles collapse, they can generate hydroxyl radicals with strong oxidising ability, which can oxidise a variety of pollutants in diesel exhaust. Ozone has strong oxidising properties, and the coupling of ozone and micro-nano bubbles can improve the oxidation and removal effects of polluted gases. In this study, the ozone micro-nano bubbles system was used to oxidise NO x , SO2, and CO to gases that were more readily dissolved in water, such as NO2, SO3, and CO2, and the gases were removed through the absorbent solution. The effects of surfactant, catalyst, urea, pH value, and salinity on the removal efficiency of NO x , SO2, and CO from diesel exhaust were investigated. Through experiments, it was found that the removal efficiency of pollutants was enhanced and then weakened with the increasing concentrations of surfactants, catalysts, and salinity, and continued to decrease with increasing concentrations of urea. When the pH value was < 7, the removal efficiency increased first and then weakened with the increase of the pH value. When the pH value was > 7, it mainly depended on the absorption of acid gas by the alkali solution. Under optimal conditions, the removal efficiencies were 86.3% for NO, 92.1% for SO2, and 65.4% for CO. This study could provide important theoretical support for the industrial application of this technology.

Simultaneous removal of NO and SO2 by Fe(II)/peracetic acid oxidation system: Operating conditions, removal efficiency and removal mechanism

The request of synergistic control of PM2.5 and O3 pollution has made NO and SO2 emission control a hot topic again in the field of atmospheric environment. An advanced oxidation process (AOPs) for simultaneous removal of SO2 and NO from the flue gas of small and medium-sized boilers and kilns by Fe(II) activated peracetic acid (PAA) was investigated. The influences of operating parameters like reaction temperature, initial pH, concentrations of PAA and Fe(II) on SO2 and NO removal efficiency in Fe(II)/PAA system were studied. The NO removal efficiency was increased with higher PAA concentration and lower initial pH. Changes in reaction temperature and Fe(II) concentration had a dual effect on NO removal efficiency. The SO2 removal efficiency can be stably maintained above 99 % under all operating conditions, which is of great significance for practical engineering applications. Results indicated that the maximum removal efficiency of 92.3 % for NO and 99.5 % for SO2 were obtained under the optimal conditions of 100 mM PAA, 10 mM Fe(II), operating temperature 45 °C and initial solution pH 2.4. PAA was confirmed to play a major role in NO removal rather than coexistent H2O2. According to the electron paramagnetic resonance (EPR) technology, methyl phenyl sulfoxide (PMSO)-based probe experiments and radicals quenching experiments, reactive oxidizing species such as CH3C(O)O·, CH3C(O)OO·, ·OH and FeIVO2+ were generated in the Fe(II)/PAA system, where organic radicals (R-O•) were confirmed to be the major ones affecting NO oxidation. Ion chromatographic analysis revealed that SO42- and NO3- were the main products of SO2 and NO removal, and the mechanism of SO2 and NOx oxidation and removal by Fe(II)/PAA system was thus elucidated, which would promote the industrial application of this novel method.

Noble Metal Nanoparticles Decorated Boron Nitride Nanotubes for Efficient and Selective Low-Temperature Catalytic Reduction of Nitric Oxide with Carbon Monoxide

Parallel to CO2 emission, NOx emission has become one of the menacing problems that seek a simple, durable, and high-efficiency deNOx catalyst. Herein, we demonstrated simple syntheses of platinum group metal nanoparticle-decorated f-BNNT (PGM = Pd, Pt, and Rh, and f-BNNT stands for -OH-functionalized boron nitride nanotubes) as a catalyst for efficient and selective reduction of NO by CO at low-temperature conditions. PGM/f-BNNT with a low amount of noble metal nanoparticles (0.7-0.8 wt %) presents very efficient catalytic activity for NO reduction as well as CO oxidation during their removal process. The removal efficiencies of NO and CO with Pd/f-BNNT, Pt/f-BNNT, and Rh/f-BNNT catalysts were investigated under various temperatures, flow rates, and reaction times, respectively. For most cases, NO catalytic reduction with CO reaction was >99% at a temperature as low as ∼200 °C. The catalyst robustness and efficiency were also verified by presenting almost 100% conversion of NO using a Rh/f-BNNT catalyst, which was aged under humid air at 600 and 700 °C for 24 h, respectively. The synergic effect of the catalytic efficacy of the well-dispersed noble metal nanoparticles and the excellent surface properties of BNNT are reasons for the high selectivity and catalytic property at a low temperature. On the basis of this investigation, we demonstrated that the noble metal nanoparticle-decorated f-BNNT catalysts are possible to save expensive PGM catalysts, such as Pt, Pd, and Rd, as much as 100 times while presenting similar or better catalytic performance for simultaneous NO and CO removals.

La2Ti2O7 nanosheets modified by Pt quantum dots for efficient NO removal avoiding NO2 secondary pollutant

Two-dimensional La2Ti2O7 nanosheets with regular morphology and good dispersion were prepared by the hydrothermal method under a magnetic field. Zero-dimensional Pt quantum dots (Pt-QDs) were loaded on the La2Ti2O7 nanosheets. The electron-hole separation and carrier transfer in the Pt-loaded La2Ti2O7 nanosheets were significantly enhanced. The La2Ti2O7 nanosheets loaded with 3 wt% Pt-QDs exhibit the largest NO removal efficiency of 51% and less than 3.2 ppb NO2 intermediate pollutant in 30 min. The high photocatalytic ability was attributed to the surface plasmon resonance in Pt-QDs and the enhanced electron-hole separation. A large number of e−, h+, •OH and •O2− active species were formed on the surface of Pt-loaded La2Ti2O7 nanosheets under light irradiation. The conversion pathway from NO to NO3− was verified by the in situ diffuse reflectance infrared Fourier-transform spectroscopy and DFT calculation. This work supplies a feasible approach to responsive photocatalysts for efficient, stable, and selective NO removal avoiding the NO2 secondary pollutant.

Photodegradation of NO with minimal NO2 secondary pollution by La2Ti2O7 nanosheets loaded with Ag particles

Lanthanum titanate (LTOM) nanosheets with regular morphology and good dispersion were prepared by a hydrothermal method under magnetic field of 240 mT. Ag particles with different sizes from several nanometers to tens of nanometers were loaded on the LTOM surface to be Schottky contact. The LTOM nanosheets loaded with 7 wt% Ag exhibit the largest NO removal efficiency of about 46 % and produce only 6.0 ppb NO2 secondary pollution in 15 min, which increases by 48% and reduces by 88% in comparison with the pure LTOM. The improved photocatalytic performance is attributed to the broadened light harvest in the visible range, enhanced spatial separation of photoinduced charge carriers by the Schottky contact and surface plasmon resonance in zero-dimensional Ag nanoparticles. A large number of e−, h+, ·OH, ·O2− and 1O2 radicals are generated as active reaction sites under light irradiation, playing key roles in the NO photodegradation reaction. Moreover, the composite photocatalysts enjoy good stability and repeatability without obvious photodegradation reduction after several cycles of photocatalytic reaction. The photocatalysis mechanism is eventually proposed on the basis of trapping experiments and in situ DRIFTS measurements.

Optimization and comprehensive mechanism of environment-friendly bimetal oxides catalysts for efficient removal of NO in ultra-low temperature flue gas

The catalytic purification of NOx at ultra-low temperature (less than100 °C) is still a significant challenge so far. In this work, a new UT-USCR (ultra-low temperature SCR with urea) technology scheme is adopted to directly utilize the amino –NH2 in urea to carry out the catalytic reduction of NOx, thus realizing the efficient removal of NOx at 50 ∼ 100 °C and saving the energy consumption required for urea decomposition in the industrial NH3-SCR process. Specifically, novel binary UT-USCR nanocatalysts preloaded with reducing agent were successfully synthesized by simple solvent evaporation-induced assembly method and systematically optimized. The catalysts were characterized in detail by FESEM, EDS, TEM, XRD, XPS, AAS, TPD, H2-TPR, in-situ DRIFTS, etc. The activity results showed that the optimized catalyst could achieve over 95 % NOx removal at 50 ∼ 100 °C and had good cycle stability. Through the research path of “exclusion-verification-thermodynamic theoretical analysis-transient &in-situ experimental analysis”, the rate-limiting step and specific reaction path on the surface of UT-USCR catalyst were expounded in detail for the first time. The specific synergistic path between the two active metal elements was revealed and the modified catalyst enhanced the chemical adsorption of NO, promoted the direct reaction of NO with reductant urea and the formation of NO2, thus promoting the UT-USCR reaction. More interestingly, the SCR catalyst in this work is a new type of catalyst that does not require acid sites, and the research of UT-USCR catalyst can provide ideas for the future development of anti-poisoning SCR catalysts in environments prone to acid site poisoning.

Simultaneous oxidation and absorption of nitric oxide and sulfur dioxide by peroxymonosulfate activated by bimetallic metal-organic frameworks

SO2 and NO from coal combustion are the main precursors of acid rain, regional haze, and photochemical smog. Advanced oxidation strategies can be used to simultaneously remove SO2 and NO from flue gas under a low temperature. Two metal-organic frameworks (MOFs), FeBDC and CuFeBDC, were synthesized and used to activate peroxymonosulfate (PMS) for the oxidation and absorption of flue pollutants. The characterization results revealed that MOFs contained the redox pairs Fe(II)/Cu(I) and Fe(III)/Cu(II). Fe(II)/Cu(I) initiated firstly the PMS activation. Then, the Fe(II-III-II) and Cu(I-II-I) redox cycles continuously activated PMS and generated reactive species. MOFs-PMS removed 76.6 % and 86.5 % of NO in the presence of FeBDC and CuFeBDC catalysts, respectively. 100 % of SO2 was removed. CuFeBDC exhibited the efficient catalytic properties for the removal of NO and SO2 in PMS solution, and could be recycled and regenerated. After five cycles, the removal efficiencies of NO and SO2 were 71.2 % and 100 %, respectively, and NO and SO2 emissions in the outlet were lower than the emission limit when using CuFeBDC-PMS. During the oxidation and absorption process, NO and SO2 were first oxidized to NO2- and SO32- as intermediates, then formed the final products of NO3- and SO42-. Radical scavenging experiments and electron paramagnetic resonance measurements revealed that both radical (SO4-•, •OH) and non-radical pathways (1O2) contributed to the efficient oxidation of NO/ SO2. 1O2 was the predominant reactive oxygen species for the removal of NO, while SO4-• and •OH were responsible for the removal of SO2.

Simultaneous oxidation absorption of NO and Hg0 using biomass carbon-activated Oxone system under synergism of high temperature

Compared with the heterogeneous activation technology activated by transition metal oxides, the biomass carbon-activated Oxone technology receives extensive attention because it does not produce metal ion leakage (no secondary pollution). Here a biomass carbon-activated Oxone system under synergism of high temperature was designed to achieve simultaneous oxidation absorption of NO and Hg0 from simulated flue gas. The feasibility, mechanism, products and main technical influencing factors of NO and Hg0 simultaneous removal using this system were explored. The developed removal technique gains a high simultaneous removal efficiency of NO and Hg0 (respectively reaching 91.5% and 98.8%). Based on removal efficiency comparison, free radicals determination and sacrificial agent experiment, hydroxyl radical is proved to be a dominant oxidant for NO removal, and sulfate radical is the second important oxidant for NO removal. Sulfate radical is found to be a dominant oxidant for Hg0 removal, and hydroxyl radical is the second important oxidant for Hg0 removal. Synergistic effect of high temperature and biomass carbon plays a vital role in efficient removal of NO and Hg0. Increasing Oxone concentration, temperature and biomass carbon concentration enhance simultaneous oxidation absorption process of NO and Hg0. However, increasing pH and concentrations of NO and Hg0 reduces simultaneous removal efficiency of NO and Hg0. The main products of NO and Hg0 simultaneous oxidation absorption are NO3– and Hg2+, which can be recycled through the proposed product post-treatment route.

2D/3D g-C3N4/BiOI heterostructure catalyst for efficient and robust photocatalytic NO removal

Developing visible light responsive photocatalysts with strong light capture ability for catalytic NO removal is of great significance. In this work, we coupled the narrow-gap semiconductor BiOI with graphite-like carbon nitride (g-C3N4) to construct 2D/3D heterostructure and applied it for efficient photocatalytic elimination of NO under visible light irradiation. At relative humidity (RH) of 15 %, g-C3N4/BiOI achieves remarkable NO removal activity (80.5 %) under a gas hourly space velocity (GHSV) of 1,740,000 mL h−1 g−1. Outstanding durability was realized that the NO removal efficiency of g-C3N4/BiOI after 6 consecutive runs. Even at high RH of 50 % and 80 %, g-C3N4/BiOI still exhibited excellent NO removal performances of 80.3 % and 78.5 %, respectively. The heterostructure of g-C3N4/BiOI endowed the enhanced light harvesting, efficient charge separation and rapid charge transfer, which enables sufficient superoxide radicals (O2−) production to improve the efficiency and strengthen the durability of photocatalytic NO removal. This work provides insights into the rational design of heterostructure photocatalyst toward air purification.

Studies on the preparation of fly ash-derived Fe-SSZ-13 catalysts and their performance in the catalytic oxidation of NO by H2O2

SSZ-13 zeolite was synthesized from fly ash using a combined alkali fusion hydrothermal method. The optimal synthesis parameters are as follows: NaOH/FA=1.4, SiO2/Al2O3=50, H2O/SiO2=1800, TMAda-OH/Al2O3=7, the amount of SSZ-13-seed=10%, and crystallization time and temperature were 160 °C and 40 h. Based on this, a series of fly ash-based Fe-SSZ-13 catalysts were prepared using three different methods and tested in catalytic oxidation with H2O2 for NO removal. The experiment results showed that the NO removal efficiency catalyzed by Fe-SSZ-13-SSIE, Fe-SSZ-13-LIE and Fe-SSZ-13-IM were 78%, 87% and 84%, respectively. ESR was used to detect hydroxyl radicals, UV-vis, XPS and H2-TPR were applied to test the composition, state and distribution of iron species, while NH3-TPD and Py-FTIR were performed to analyze the intensity and type of acidic sites, and finally to determine the relationship between catalyst structure, active species and catalytic performance in combination with NO removal experiments. The catalytic oxidation mechanism analysis revealed that the excellent catalytic performance can be attributed to the dual function of strong Brønsted acidity on the surface and isolated Fe3+ with high dispersion, which can rapidly decompose H2O2 into ·OH and efficiently achieve NO oxidation. In conclusion, the preparation of fly ash catalysts has great potential for achieving the dual function of waste utilization and pollutant removal.

Solar-driven photocatalytic removal of NO over a concrete paving eco-block containing black TiO2

The as-prepared black TiO2-based concrete paving eco-block exhibits outstanding photocatalytic NO removal efficiency without harmful by-products and an enhanced binding force between the photocatalyst and concrete matrix.

Oxygen-vacancy-rich Ag/Bi5O7Br nanosheets enable improved photocatalytic NO removal and oxygen evolution under visible light exposure

Photocatalytic NO removal is a green and sustainable alternative to the conventional thermocatalysis in the conversion of NO to nitrates. However, the efficiency of photocatalytic NO removal is restricted by weak NO adsorption and high charge recombination on photocatalyst. Herein, we report on one-step synthesis of Ag/Bi5O7Br nanosheets with rich oxygen vacancies (OVs) by a facile liquid phase reduction method. Under visible light irradiation on oxygen-vacancy-rich Ag/Bi5O7Br for 50 min the photocatalytic NO removal ratio is up to 64.65%, which is about 1.6 times higher than that by using pristine Bi5O7Br. The average oxygen production rate is 823 μmol·g−1·h−1, which is nearly 10 times higher than that of Bi5O7Br. Density functional theory (DFT) calculations reveal that OVs incorporation and plasmonic Ag can synergistically strengthen NO adsorption on Bi5O7Br. This work highlights the great potential of defects and plasmonic metals on synergistic enhancement in photocatalytic NO removal and oxygen evolution.

Photocatalytic-treated asphalt road in Copenhagen for urban text{NO}_{x} removal

Atmospheric nitrogen oxides (hbox {NO}_{x} = hbox {NO}+hbox {NO}_{2}) are key pollutants and short-lived climate forcers contributing to acid rain, photochemical smog, aerosol formation and climate change. Exposure to nitrogen dioxide (hbox {NO}_{2}) emitted mainly from transportation, causes adverse health effects associated with respiratory illnesses and increased mortality even at low concentration. Application of titanium dioxide (hbox {TiO}_{2})-based photocatalysis in urban environment is a new air cleaning solution, activated by sunlight and water vapour to produce OH radicals, able to remove hbox {NO}_{x} and other pollutants from the planetary boundary layer. This study is a large-scale evaluation of hbox {NO}_{x} removal efficiency at a near-road environment with applied photocatalytic NOxOFF™ technology on an urban road west of Copenhagen, thus supporting local municipality in meeting their clean-air Agenda 2030. The photocatalytic NOxOFF™ granulate containing hbox {TiO}_{2} nanoparticles was applied on an asphalt road in July 2020 and ambient hbox {NO}_{x} was measured during a six-month monitoring campaign. It is the first hbox {NO}_{x} monitoring campaign carried out at this road and specific efforts have been devoted to evaluate the reduction in ambient hbox {NO}_{x} levels with NOxOFF™-treated asphalt. Several methods were used to evaluate the photocatalytic effect, taking into account analysis limitations such as the short reference period prior to application and the highly uncertain measurement period during which SARS-CoV-2 lockdown measures impacted air quality. There was no statistically significant difference in hbox {NO}_{x} concentrations between the reference period and the photocatalytic active period and NO removal efficiency resulted in -,0.17 (± 1.27). An upper limit removal of 17.5% hbox {NO}_{x} was estimated using a kinetic tunnel model. While hbox {NO}_{2} comparison with COPERT V street traffic model projection was roughly estimated to decrease by 39% (± 38%), although this estimate is subject to high uncertainty. The observed annual mean hbox {NO}_{2} concentration complies with Frederiksberg clean-air Agenda 2030 and air quality standards.Graphical abstractA graphical abstract illustrating the air cleaning properties of hbox{TiO}_{2}-based photocatalytic-treated asphalt