Nitric Oxide Removal Research Articles

Photocatalytic property of cement mortars coated with graphene/TiO2 nanocomposites synthesized via sol–gel assisted electrospray method

Titanium dioxide (TiO2) photocatalyst coatings on cement material surfaces of buildings or structures that require high mechanical integrity, such as tunnel walls and pedestrian roads, can directly utilize solar energy for self-cleaning surfaces and removing air pollutants in the environment. However, TiO2 can utilize only ultraviolet (UV) light, which accounts for only 5% of sunlight. To improve photocatalytic efficiency, graphene/TiO2 nanocomposites are prepared by a sol-gel assisted electrospray method and characterized by various instrumental analysis methods. Photocatalytic cement mortars are prepared by incorporating the as-prepared nanocomposites and commercial TiO2 into cement mortar. The self-cleaning and air purifying properties of the cement mortars are evaluated by the discoloration of rhodamine B (RhB) and the removal of nitric oxide (NO). As desired, cement mortar coated with graphene/TiO2 nanocomposites expresses high photocatalytic effectiveness on both RhB and NO. In addition, the regeneration of graphene/TiO2 nanocomposite photocatalysts has also been studied. The results show that the photocatalytic activity can be effectively regenerated by UV irradiation, with good repeatability and stability. Therefore, graphene/TiO2-coated cement mortar is a potential candidate for effective building self-cleaning and air purification through the use of solar irradiation.

Photocatalytic performance of doped TiO2/AC coating and its UV stability research

Based on the porous structure of activated carbon (AC) and the photo-oxidation behavior of TiO2, a visible-light-responsive photocatalytic coating with UV stability was constructed by loading Fe/N/Co-TiO2@AC (DTC) on waterborne acrylic coating. The DTC with adsorption and degradation synergistic effect was prepared by a simple mechanochemistry method and characterized by UV–vis, SEM, XRD, and BET. The nitric oxide (NO) removal efficiency of DTC was 51.6 % under visible light in 2 h. Besides, under the same conditions, the NO removal efficiency of the DTC coating still reached 45.8 %. Further, to investigate the UV stability of DTC coating, different coatings were prepared with the same dosage of DTC, TiO2@AC (TC), and TiO2. The UV stability of the coatings was tested with a color difference, degree of chalking, adhesion strength, hardness, and impact resistance as evaluation indicators. The results showed that the DTC coating exhibited the best UV stability. The photooxidation of organic binder on the coating surface before and after aging was micro-characterized by SEM and FT-IR, and the UV stability improvement mechanism was revealed.

Resistive Oxidation Kinetics of Iron(II) Thiochelate used as a Nitric Oxide Absorbent in Flue Gas

Iron(II) thiochelates, especially iron(II) 2,3-bis(sulfanyl)propane-1-sulfonate (Fe(II)(DMPS)2), have received particular attention as nitric oxide (NO) absorbents because they maintain high NO removal efficiency even in the presence of O2 in flue gases. Herein, we explored the O2-inducing oxidation kinetics of Fe(II) and thiol groups (R–SH) in Fe(II)(DMPS)2 and analyzed the resultant products to understand the resistive behavior toward O2. Quantitative analysis revealed that 4 mM of Fe(II) in 10 mM Fe(DMPS)2 solution was maintained without further oxidation even after 12 h under 5% O2, but instead thiol group concentration continued to decrease. In comparison to the commonly used Fe(II)(EDTA) absorbent, in which all the 10 mM Fe(II) was fully oxidized within 40 min reaction by 5% O2, this distinctive oxidative behavior of iron(II) thiochelate was attributed to the self-sacrificing thiol-containing ligands. This phenomenon was verified by the rapid and almost complete redox reaction between the oxidized Fe(III) and thiol groups in DMPS. Fourier transform infrared spectra indicated that the oxidation products of thiols were disulfide (S–S) and some sulfonates (−SO3–). Finally, based on all the experimental data, possible oxidation pathways of Fe(II)(DMPS)2 by O2 were proposed. This study provides both fundamental and applied insights of harnessing iron(II) thiochelate as a competitive NO absorbent for mitigating air pollution.

Novel process of NO removal from simulated flue gas using a Fe/Gr periodically reversing electro-activated peroxymonosulfate system

Nitric oxide (NO) emissions seriously threaten the atmospheric ecology and cause air quality degradation, and the acid rain type has gradually changed from sulfuric acid to nitric acid in some areas of China. To this end, an efficient, facile, innovative strategy of NO removal from simulated flue gas using Fe/Gr periodically reversing electro-activated peroxymonosulfate (PMS) system is proposed for the first time. Encouragingly, we find that the graphite (Gr) electrode has the similar electrochemical property to those of the boron-doped diamond (BDD) and platinum (Pt) electrodes, converting SO42- to sulfate radicals (SO4·-), and provide direct spectroscopy evidence for the theory that the electron e- can activate PMS to generate SO4·- and hydroxyl radicals (OH) via the electron-paramagnetic resonance (ESR) tests. In addition to the two free radicals mentioned above the singlet oxygen (1O2) is detected synchronously in the electrical-activated PMS system. And the signal intensity of the radicals detected increases with increasing current intensity correspondingly. Addition of excess methanol has a greater effect on the NO removal than tert-butanol and sodium azide, demonstrating that SO4·- dominates the NO removal. Furthermore, the results show PMS concentration, current intensity, pH, in-situ generated Fe2+ and O2 concentration have the distinct effect on the NO removal. Compared with different electro-activation systems of Fe/Fe and Gr/Gr and BDD/Gr, Fe/Gr achieves the optimum NO removal effect. Finally, the reaction mechanism is proposed: direct electrode oxidation, non-radical oxidation, and radical oxidation are combined to remove NO in the electro-activated PMS reaction system.

Simultaneous Removal of NO and SO2 with a Novel Oxidation-Absorption Process Based on Air Microbubble Water System

Microbubbles (MBs) can spontaneously generate hydroxyl radicals (·OH) with high oxidizing capacity. In this study, a novel oxidation-absorption process based on a microbubble system in the indirect removal mode was proposed for the simultaneous removal of nitric oxide (NO) and sulfur dioxide (SO2). In this process, an air microbubble water system (AMBW) was produced by a microbubble generator (MBG) inhaling air and tap water and injected into an oxidation-absorption column reactor by the MBG, meanwhile the mixed gas composed of NO and SO2 passed through a micron-sized gas distributor at the bottom of the reactor and flowed into the AMBW. Important parameters including initial pH and temperature of tap water, operation time, NO concentration, SO2 concentration, and NaCl concentration were assessed to investigate the feasibility of the AMBW for the simultaneous removal of NO and SO2. The results showed that ·OH generated from the collapsed MBs played a critical role in the removal and the simultaneous removal of NO and SO2 was successfully achieved with the AMBW. Even with only tap water used as the absorbent, the removal efficiencies of NO and SO2 reached 92.7% and above 99%, respectively, when the experiment conditions were initial water pH 11.5, initial water temperature 298 K, 600 ppm NO, and 3,000 ppm SO2. Compared with the microbubble system in the direct removal mode, this new system is more suitable for the treatment of flue gases with low NO concentration and high volume. Moreover, this novel process should have a good prospect of industrial application in the flue gas treatment due to its high efficiencies of desulfurization and denitration and some advantages such as low usage cost of the reagents, simple system, and small occupation space.

Supersensitive test of photocatalytic activity based on ISO 22197-1:2016 for the removal of NO

A supersensitive test (SST) for photocatalytic activity is described, based on ISO 22197-1:2016 for the removal of NO, i.e. the standard NO removal ISO. The key reaction is the photocatalysed oxidation of nitric oxide (NO) to nitrogen dioxide (NO2) by oxygen, which, for most materials, is the dominant reaction at the end of the 5 h irradiation period employed in the standard ISO. The SST uses the same photoreactor as the standard NO ISO, but with 3 (instead of 1) sample pieces and a flow rate of 0.25 L min−1 (instead of 3 L min−1) and, as a consequence, is 36 x’s more sensitive than the standard ISO. The SST is used to assess the activities of materials that show little if any activity when tested using the standard ISO, such as commercial self-cleaning samples (such as glass (Activ™), paint and plastic), as well as bank notes. An expression is derived, and verified using films of P25 powder, which relates rate, and so photocatalytic activity, directly to the average %NO removed, measured under either standard ISO or SST conditions, in the last 15 min of irradiation, i.e. %NOrem, where the latter value is directly related to the photocatalytic area, A, and the reciprocal of the flow rate, 1/f. This relationship allows all %NOrem values < 25 %, measured using either standard ISO or SST conditions, to be combined to create a universal scale of photocatalytic activity. The universal scale of activity is illustrated using the calculated %NOrem values for high, medium and low activity materials which spans over 3 orders of magnitude of activity. The possible uses of this scale are discussed briefly.

Performance, optimization, and mechanism of nitric oxide removal by thiourea dioxide/FeIIEDTA reaction systems

In this work, a new innovative absorption system containing both thiourea dioxide (TD) and FeIIEDTA was used to NO removal. The independently influences of O2 volume concentration, TD concentration, original pH value and absorbent temperature on NO removal in bubbling device were examined preliminarily. The results revealed that the NO removal efficiency firstly increased and then decreased with the increasing of the three independent variables (O2 volume concentration, TD concentration and temperature). However, the NO removal efficiency monotonously increased to some extent with pH value increasing from 6.5 to 10.5. In addition, the respective effects of the four variables and the interactive function of them on NO removal were checked with the response surface methodology (RSM) by central composite design (CCD). The calculative model showed that pH value possessed a main positive independent impact on NO removal. Furthermore, the interactive effects between any two factors were expounded by the 3D surface and counter plots. Finally, the optimum absorption conditions for the maximum NO removal at 94.3% experimentally and 95.8% statistically were obtained in O2 volume content of 6.0%, TD concentration of 0.02 mol·L−1, original pH value of 10.5 and absorption temperature of 42 °C.

Nitric oxide reduction by microbial fuel cell with carbon based gas diffusion cathode for power generation and gas purification

Nitric oxide (NO) from anthropogenic emission is one of the main air contaminants and induces many environmental problems. Microbial fuel cells (MFCs) with gas diffusion cathode provide an alternative technology for NO reduction. In this work, pure NO as the sole electron acceptor of MFCs with gas diffusion cathode (NO−MFCs) was verified. The NO−MFCs obtained a maximum power density of 489 ± 50 mW/m2. Compared with MFCs using O2 in air as electron acceptor (Air−MFCs), the columbic efficiency increased from 23.2% ± 4.3% (Air−MFCs) to 55.7% ± 4.6% (NO−MFCs). The NO removal rate was 12.33 ± 0.14 mg/L/h and N2 was the main reduction product. Cathode reduction was the dominant pathway of NO conversion in NO−MFCs, including abiotic electrochemical reduction and microbial denitrification process. The predominant genera in anodic microbial community changed from exoelectrogenic bacteria in Air−MFCs to denitrifying bacteria in NO−MFCs and effected the power generation.

Surface modification to control the secondary pollution of photocatalytic nitric oxide removal over monolithic protonated g-C3N4/graphene oxide aerogel

Recently, photocatalytic NOx treatment has attracted great attention on account of the use of environmental-friendly and tremendous energy source. However, the difficult recovery of most reported powdery photocatalysts and the high generation rate of toxic NO2 byproduct limit its application. Here, we designed a novel monolithic protonated g-C3N4/graphene oxide aerogel through a direct frozen-drying method. A remarkable surface electric charge change of negative g-C3N4 to positive protonated g-C3N4 can be observed after the protonating treatment, which connects with negative graphene oxide nanosheets through the formation of strong electrostatic self-assembly to accelerate the photogenerated charge carriers transfer. Graphene oxide aerogel acts as a monolithic substrate, which provides abundant porous structure, enhanced visible-light absorption, and electrons transport pathway to improve photocatalytic activity. Importantly, the introduction of H atoms on the N atoms of p-C3N4 promotes the activation of oxygen atoms, thus improving the oxidization of NO2 to nitrate. As a result, protonated g-C3N4/graphene oxide aerogel reveals an excellent NO removal ratio (46.1%) and low NO2 generation (2.4%), demonstrating its excellent promising for air pollution purification. Our current work affords novel innovative insight for the construction of monolithic photocatalysts to control the secondary pollution for environmental remediation.

Ti3C2 MXene modified g-C3N4 with enhanced visible-light photocatalytic performance for NO purification

As for photocatalytic oxidation of nitric oxide (NO), the low NO oxidation activity and generation of by-products (cf. NO2) are the urgent challenge. To tackle these issues, a simple in-situ growing stragegy was employed to constructe Ti3C2/g-C3N4 system. The fabricated Ti3C2/g-C3N4 composite (TC-CN) presented enhanced photocatalytic NO removal efficiency and inhibited toxic NO2 generation. Density functional theory (DFT) calculations and experimental characterizations were combined to demonstrate the presence of strong interface effect between Ti3C2 and g-C3N4, which could greatly improve photo-generated charge carrier separation via the construction of electron transfer channels, and further activate oxygen molecules adsorbed on the side of Ti3C2 layer. As a result, nitrite and nitrate instead of NO2 were the final products during the photocatalytic reaction process through the monitoring by in situ diffuse reflectance infrared spectroscopy (DRIFTS).

Influence of Hydrogen Pre-treatment at Different Temperatures on Copper Oxide Supported on Carbonised Oil Palm Empty Fruit Bunch (CuO/EFBC) for Low-Temperature Nitric Oxide Removal

Influence of Hydrogen Pre-treatment at Different Temperatures on Copper Oxide Supported on Carbonised Oil Palm Empty Fruit Bunch (CuO/EFBC) for Low-Temperature Nitric Oxide Removal

Removal of nitric oxide from flue gas using novel microwave-activated double oxidants system

A novel microwave-activated H2O2/PS (persulfate) double oxidants system was developed for NO removal from flue gas. Several experiments and characterization were conducted to study several fundamental issues of NO removal using the developed microwave-activated H2O2/PS oxidation system (e.g., optimizing technological parameters, determining free radicals and products, and revealing NO removal mechanism). Free radical identification experiments showed that several synergistic activation effects were found in the developed microwave-activated H2O2/PS oxidation system. SO4−·, ·OH, HO2·, H2O2 and PS were considered to be the active species for the NO removal , and ·OH played a leading role. The product and by-product such as nitrate, sulfate and NO2 from tail gas were determined quantitatively. Increasing microwave power, concentration of H2O2 and PS, and O2 content enhanced the NO removal. Increasing NO and SO2 concentration, solution pH value, and flue gas flow rate weakened the NO removal. Reaction temperature and reagent flow rate showed a double effect on the NO removal.

Photocatalytic oxidation of nitric oxide over AgNPs/TiO2-loaded carbon fiber cloths

Series of AgNPs/TiO2-loaded carbon fiber cloth (CFC) composites were prepared by incorporation of pristine TiO2 and three AgNPs-modified TiO2 additives onto the surface of four commercial CFCs. AgNPs/TiO2 photocatalysts were synthesized by the wet impregnation method, including NaBH4 reduction of silver ions. The silver content in the modified photocatalyst was assessed by inductively coupled plasma optical emission spectrometry (ICP‐OES) as well as XRD analysis. It can be indicated that silver was successfully reduced to Ag nanoparticles what was confirmed by UV–Vis/DRS as well as XRD methods. The photocatalytic activity of the AgNPs/TiO2-loaded CFCs was evaluated during the photocatalytic oxidation (PCO) tests of nitric oxide (NO) acting as a model air contaminant under UV light. It was found that the highest NO removal rate was observed for the AgNPs/TiO2-loaded CFC material containing 3.70 wt% of AgNPs. Modification of TiO2 with AgNPs stabilized the photocatalytic efficiency of the composites during 5 as well as 24 consecutive NO photooxidation cycles. It was also concluded that the presence of AgNPs was a key factor responsible for hindering NO2 formation.

Energy efficiency improvement in nitric oxide reduction by packed DBD plasma: optimization and modeling using response surface methodology(RSM).

The non-thermal plasma (NTP) is a superior proposed method for nitric oxide removal because of operation at atmospheric pressure and ambient temperature. The energy consumption is the main challenge of using this technology. The packed plasma reactor with dielectric materials has been extensively investigated; it has higher energy efficiency. In this study, the energy efficiency and the other effectiveness factors in nitric oxide removal by NTP reactor packed with ceramic and glass beads optimized and modeled using Response Surface Methodology. The findings showed the maximum energy efficiency was 132.69g/J in the optimal conditions of initial concentration, gas flowrate, and duty cycle(voltage) equal to 1050 ppm, 2.5 L/min, and 9%(22KV), respectively in the packed reactor with ceramic beads by 1.7 times than the empty reactor. It is concluded that the use of ceramic beads as a dielectric material in the discharge space significantly increased energy efficiency in the removal of nitric oxide.

Utilization of domestic wastewater as a water source of Tetradesmusobliquus PF3 for the biological removal of nitric oxide

The reduction of nitrogen oxide (DeNOx) from flue gas by microalgae is a promising technology that has attracted increasing attention. Because the water source is a major limitation of microalgae application in the DeNOx from flue gas, we investigated the feasibility of using domestic wastewater (WW) as a water source. As a result, a biomass accumulation rate of 0.27 ± 0.01 mg L−1 d−1 was achieved by Tetradesmusobliquus PF3 cultivated in WW for 8 d, and 30 mg L−1 of nitrate nitrogen was added to the WW to fulfill the nutrient requirements of the microalgae cells. The ammonium (NH4+) nitrogen present in WW exerted inhibitory effects on the removal of nitric oxide (NO), thereby leading to 8% decrease removal efficiency in comparison with that using clean water and nutrients (BG11 medium). However, these inhibitory effects disappeared following the exhaustion of NH4+ by T. obliquus PF3 after 1 d. To overcome the inhibition of NH4+ and to achieve a high NO removal efficiency, a strategy of connecting two reactors in series was presented. The removal efficiency of NO by the two series reactors reached up to 71.2 ± 2.9%, which was significantly higher than that obtained by a single reactor (43.1 ± 3.6%). In addition, 70.9 ± 4.8% of the supplied NO was fixed into microalgae cells in the two reactors, which was 1.75 times higher than that in the single reactor (40.6 ± 5.1%), thereby suggesting that connecting two reactors in series rendered effective recovery of NO from flue gas using WW as a water source. In this study, we provided an economically viable water source for the application of microalgae in the biological DeNOx from flue gases.

Green fabrication of AuNPs/CMTKP/g-C3N4 nanocomposites with enhanced photocatalytic activity for the removal of nitric oxide under visible-light irradiation

A facile and green method of in-situ photo-reduction was developed to fabrication the AuNPs/CMTKP/g-C3N4 nanocomposites catalyst. Carboxymethyl tamarind kernel polysaccharide (CMTKP) was used to regulate and stabilize the monodispersed AuNPs onto g-C3N4 NSs surface. The morphology, microstructure and composition of the Au-CMTKP-g-C3N4 nanosheets hybrids were systematically characterized. The NO removal experiments showed that AuNPs/CMTKP/g-C3N4 nanocomposites exhibited excellent visible-light response and enhanced photo-oxidization ability to inhibit the generation of NO2. Compared with g-C3N4 NSs, the removal efficiency of 4 wt% Au-CMTKP-g-C3N4 NSs was increased by 27.5%. Reactive radicals during the photocatalysis processes were identified by electron spin resonance (ESR) study. As identified by ESR, ·O2−, ·OH and photogenerated holes could be considered as the main activated species involved in NO removal. The possible mechanism for photocatalytic NO oxidation was also proposed. Meanwhile, this photocatalyst also demonstrates suitable stability, showing good potential in practical applications.

Surface Engineering of g-C3 N4 by Stacked BiOBr Sheets Rich in Oxygen Vacancies for Boosting Photocatalytic Performance.

BiOBr containing surface oxygen vacancies (OVs) was prepared by a simple solvothermal method and combined with graphitic carbon nitride (g-C3 N4 ) to construct a heterojunction for photocatalytic oxidation of nitric oxide (NO) and reduction of carbon dioxide (CO2 ). The formation of the heterojunction enhanced the transfer and separation efficiency of photogenerated carriers. Furthermore, the surface OVs sufficiently exposed catalytically active sites, and enabled capture of photoexcited electrons at the surface of the catalyst. Internal recombination of photogenerated charges was also limited, which contributed to generation of more active oxygen for NO oxidation. Heterojunction and OVs worked together to form a spatial conductive network framework, which achieved 63 % NO removal, 96 % selectivity for carbonaceous products (that is, CO and CH4 ). The stability of the catalyst was confirmed by cycling experiments and X-ray diffraction and transmission electron microscopy after NO removal.

Surface Engineering of g‐C3N4 by Stacked BiOBr Sheets Rich in Oxygen Vacancies for Boosting Photocatalytic Performance

AbstractBiOBr containing surface oxygen vacancies (OVs) was prepared by a simple solvothermal method and combined with graphitic carbon nitride (g‐C3N4) to construct a heterojunction for photocatalytic oxidation of nitric oxide (NO) and reduction of carbon dioxide (CO2). The formation of the heterojunction enhanced the transfer and separation efficiency of photogenerated carriers. Furthermore, the surface OVs sufficiently exposed catalytically active sites, and enabled capture of photoexcited electrons at the surface of the catalyst. Internal recombination of photogenerated charges was also limited, which contributed to generation of more active oxygen for NO oxidation. Heterojunction and OVs worked together to form a spatial conductive network framework, which achieved 63 % NO removal, 96 % selectivity for carbonaceous products (that is, CO and CH4). The stability of the catalyst was confirmed by cycling experiments and X‐ray diffraction and transmission electron microscopy after NO removal.

Evaluation of FeIIEDTA‐NO reduction by thiourea dioxide in NO removal with FeIIEDTA

AbstractReducing FeIIEDTA‐NO is key for NO absorption with FeIIEDTA absorbent. In this work, the reducing agent thiourea dioxide (TD) was for the first time employed for reducing FeIIEDTA‐NO. The behavior and kinetics of reducing FeIIEDTA‐NO with TD had been examined with different pH value, varied TD concentrations, and various temperatures. The results investigated that FeIIEDTA‐NO reducing rate rose with pH value increasing as well as elevated temperature. The reaction order of FeIIEDTA‐NO by TD was proved to be 2 on FeIIEDTA‐NO. Meanwhile, activating energy, activating entropy, and activating enthalpy of reducing FeIIEDTA‐NO by TD were separately calculated to be 49.583 kJ mol−1, −64.956 J k−1 mol−1, and 46.943 kJ mol−1. The simultaneous reduction of FeIIIEDTA and FeIIEDTA‐NO by TD was investigated. Results showed that TD was more powerful in reducing FeIIIEDTA and FeIIEDTA‐NO compared with other reduction systems. Finally, nitric oxide removal experiment illustrates that TD can remarkably strengthen the NO removal with FeIIEDTA solution. These theoretical findings could provide constructive suggestions for industrial tail gas denitrification employing associative FeIIEDTA and TD system.

La0.75Sr0.25Cr0.5Mn0.5O3-δ-Ce0.8Sm0.2O1.9 as composite electrodes in symmetric solid electrolyte cells for electrochemical removal of nitric oxide

Symmetric solid electrolyte cells with La0.75Sr0.25Cr0.5Mn0.5O3-δ (LSCM)-Ce0.8Sm0.2O1.9 (SDC) composite electrodes are employed for nitric oxide (NO) removal. The LSCM powders are synthesized and the cells with LSCM-SDC composite electrodes are fabricated successfully. The results show that moderate SDC addition in LSCM electrode improves the cell performance due to the expansion of three phase boundaries (TPBs). The electrode with 30 wt% SDC has the highest NO conversion of 69.2% and the lowest polarization resistance at 750 °C in 1000 ppm NO. The cathodic polarization activates the cathode because of the Cr/Mn ions reduction, more surface oxygen vacancies and Cr metal exsolution. The cell has good tolerances for H2O, CO2, and SO2, but excess O2 competes with NO for TPBs seriously. The sufficient stability and flexible operation mode of the cell are also proved. Finally, the NO adsorption mechanism on LSCM surface is revealed by density functional theory (DFT) calculations.