NO Removal Rate Research Articles

Enhanced adsorption and reduction performance of nitrate by Fe–Pd–Fe3O4 embedded multi-walled carbon nanotubes

Multi walled carbon nanotubes (MWCNTs) have attracted more and more attention as adsorbents due to their excellent adsorption properties. By loading metal particles on MWCNTs, the chemical reduction ability of adsorbed pollutants could be provided, so as to achieve the purpose of adsorption and degradation of pollutants. Therefore, the removal process of NO3−-N by Fe–Pd–Fe3O4/MWCNTs was studied, including rapid adsorption of initial pollutants, gradual reduction of intermediate products and re-adsorption of final products. The results showed that Fe–Pd–Fe3O4/MWCNTs completely removed NO3−-N within 2 h, 39% and 25% of which were converted into NO2−-N and NH4+-N. The adsorption efficiency, kinetics, capacity and adsorption energy all followed the order of NH4+-N > NO2−-N > NO3−-N. With the recoverability and reusability of Fe–Pd–Fe3O4/MWCNTs having been confirmed in 5 consecutive cycles, the removal rate of NO3−-N still reached 43%. It has been shown that MWCNTs prolonged the reducing power for NO3−-N, due to avoiding the aggregation of metal particles. The rapid adsorption of initial pollutants, effective stepwise reduction and convenient recovery processes were of great value for the rehabilitation of polluted water.

Realization of nitrite accumulation in a sulfide-driven autotrophic denitrification process: Simultaneous nitrate and sulfur removal

The study was based on the removal of nitrate and sulfide, and aimed to nitrite accumulation. The process of autotrophic denitrification driven by sulfide as an electron donor was investigated in a sequencing batch reactor. The research showed that autotrophic denitrification successfully started on day 22, and the removal rates of NO3−-N and S2--S were 95.8% and 100%, respectively, when the S/N molar ratio was 1.45. When the S/N ratio was reduced to 0.94, the phenomenon of NO2−-N accumulation was observed. NO2−-N continuously accumulated, and the maximum accumulation rate was 55.3% when the S/N ratio was 0.8. In the batch test, the study showed that NO2−-N accumulation was optimal when the S/N ratio was 0.8, and the NO2−-N concentration increased with increasing NO3−-N concentration at the same S/N ratio. Microbial communities also changed based on the high-throughput analysis, and Proteobacteria (59.5%–84%) was the main phylum. Arenimonas (11.4%–28.2%) and uncultured_f_ Chromatiaceae (5.7%–27.5%) were the dominant bacteria, which complete denitrification and desulfurization throughout the operating system. Therefore, this study provided a theoretical basis for the simultaneous removal of NO3−-N and S2--S, as well as the accumulation of nitrite, and provided material support for anaerobic ammonia oxidation technology.

Ammonia storage/release behaviors of the CeSn0.2Mo0.6Ox/TiO2 catalyst in selective catalytic reduction of NO

• CeSnMoO x /TiO 2 obtained stable NO removal due to ammonia storage/release. • Excess NO induced ammonia release, the amount reached maximum during 250−300 °C. • Ammonia was mainly stored in physical form and partly by chemical adsorption. • High temperature enhanced ammonia activation and improved ammonia release. This work explored the ammonia storage/release behaviors of the CeSn 0.2 Mo 0.6 O x /TiO 2 catalyst in selective catalytic reduction of NO. Results displayed that the CeSn 0.2 Mo 0.6 O x /TiO 2 performed much higher NO removal rate than the theoretical maximum if the NH 3 /NO ratio was lower than one, which was due to the ammonia storage/release behaviors. The ammonia storing was more likely to occur at low temperatures, and the storage capacity of the catalyst reached 27 μmol m −2 at 50 °C. Moreover, ammonia exists mainly on physical form of temperatures below 250 °C and is adsorbed in weakly acidic sites; while high temperature strengthen activation of strong acid sites, resulting in increasing the ammonia storage at 350 °C. NH 3 -TPD results showed two peaks of ammonia desorption, indicating the weak and strong acid sites of the catalyst. The ammonia storage/release curves at Constant Temperature Flow Field were asymmetric and BET isotherm showed Type H3 hysteresis loop, which was caused by mass transfer in the plate-like pore structure formed by the particle polymerization. The porous structure and highly dispersed active components were beneficial for storing ammonia. The effective utilization ratio of the stored ammonia decreased with the increasing temperature and GHSV.

Effect of Co/Ce ratio on NO reduction by petroleum gas over Co-Ce-Ti oxide catalyst

Co-Ce-Ti composite oxide catalysts with TiO2 as support and different loadings and molar ratios of Co/Ce were prepared by a sol–gel method. The conversion efficiency of NOx was inspected on a fixed bed with liquefied petroleum gas as reducing agent, and decoupling experiments were performed in a simulated rotary reactor to investigate the adsorption and reduction efficiency of NOx. The experiments founded that CeTi, Co0.5CeTi, and CoCe0.5Ti had poor nitrogen oxide conversion efficiency, and the effects of CoTi and CoCeTi above 300 °C were relatively good and acceptable. The CoCeTi catalyst showed excellent NO adsorption performance in the simulated rotary reactor, and the removal rate of NO exceeded 95% above 300 °C. Through characterization methods such as BET, TPR, XPS, XRD, and in situ DRIFT, it could be known that Co element in the catalyst was the main factor for NO reduction and Ce element played an important role in the adsorption process, but it had little effect when acting alone. In the case of proper metal ratio, the interaction of two elements reduce the surface oxygen vacancy formation energy and change the pore structure of the catalyst surface. The formed surface synergetic oxygen vacancies promoted the reaction rate for NO removal by liquefied petroleum gas, and effectively improved the catalytic reduction efficiency.

Neodymium oxide (Nd2O3) coupled tubular g-C3N4, an efficient dual-function catalyst for photocatalytic hydrogen production and NO removal

Graphitic carbon nitride (g-C3N4) has emerged as a most promising photocatalyst, non-toxicity and low density, but it is plagued by low activity due to the small specific surface area and poor quantum efficiency. Morphological engineering and coupling with other materials to form hybrids have proven to be effective strategies for enabling high photocatalytic performances. Here, neodymium oxide (Nd2O3) coupled tubular g-C3N4 composites had been facilely synthesized by a solvent evaporation and high-temperature calcination method to realize efficient photocatalytic activity of hydrogen production and NO removal. A series of characterizations, such as XRD, ESR, in-situ DRIFTS, etc., were used to analyze the physical and chemical properties of the bifunctional photocatalyst, which demonstrated that the composite material had more active sites and a faster electron transfer rate. The optimal sample (1 wt% Nd2O3/CN-T) had a H2 generation rate of 4355.34 μmol·g−1·h−1, which was 9.46 times than that of original g-C3N4 obtained through heating melamine (CN-M). In addition, the NO removal rate was also 32.32% higher than that of original CN-M. On the basis of the above photocatalytic experimental results and characterizations, a possible mechanism or pathway was proposed and illustrated. This work could provide a feasible strategy to fabricate tubular g-C3N4-based composites with rare earth metal oxides (dual-factor regulation) to simultaneously enhance photocatalytic hydrogen production and NO removal efficiently (double application).

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

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

Facile synthesis of the Z-scheme graphite-like carbon nitride/silver/silver phosphate nanocomposite for photocatalytic oxidative removal of nitric oxides under visible light

In this study, a novel ternary Z-scheme Graphite-like Carbon Nitride (g-C3N4)/Silver (Ag)/Silver Phosphate (Ag3PO4) photocatalyst was designed and prepared using a two-step method (sodium chloride (NaCl) template-assisted strategy plus selective deposition). Its photocatalysts performance against removing 400 ppm of Nitric Oxides (NOx) was then investigated. We found 50 wt% g-C3N4/Ag/Ag3PO4(AP-CN 2:1) catalyst removes up to 74% of NO in 90 min under the illumination of visible light (>420 nm), which is respectively 3.5 and 1.8 times higher than using g-C3N4 or Ag3PO4, alone. This improved performance was attributed to the formation of Z-scheme g-C3N4/Ag/Ag3PO4 heterojunction, driven by the built-in electric field across the g-C3N4/Ag/Ag3PO4 interface. These separated the electron-hole but enhanced the original strong oxidation and reduction performance of related components. The superior performance is also attributed to the improved surface area, enhanced hydrophilicity (H2O2) and better visible-light-harvesting capability of the composite compound. More importantly, the AP-CN 2:1 sample maintained a NO removal rate of more than 73% even after four rounds of recycling. The photocatalytic oxidation removal mechanism was evaluated using the radical-capture experiments, electron spin resonance (ESR) and ion-exchange high-performance liquid chromatography (HPLC) analysis. The findings of this work offer a simple but effective design of a highly reactive and practical ternary Z-scheme heterojunction photocatalysts for the removal of toxic NO.

Defects and internal electric fields synergistically optimized g-C3N4−x/BiOCl/WO2.92 heterojunction for photocatalytic NO deep oxidation

In this work, g-C3N4−x/BiOCl/WO2.92 heterojunction with “N-O” vacancies was prepared using NaBiO3 and WCl6 as raw materials and non-metal plasma of WO2.92 grew in-situ on the surface of BiOCl, resulting in the enhanced photocatalytic NO deep oxidation. XPS tests and DFT calculation indicated the formation of internal electric fields from g-C3N4−x to BiOCl, BiOCl to WO2.92, which induced the transition from Ⅱ-Ⅱ-type to double Z-scheme hetero-structure. High separation efficiency, prolong lifetime and strong redox ability of photo-generated electron-hole pairs were simultaneously achieved due to the charge capture effect of defects and double Z-scheme mechanism. Therefore, g-C3N4−x/BiOCl/WO2.92 exhibited the significantly increased NO removal rates from 21.17% (BiOCl/WO2.92) and 36.52% (g-C3N4−x) to 68.70% and the main oxidation product of NO was NO3−. This study revealed that the carrier dynamics of heterojunction photocatalysts could be optimized by the synergistic effect of defects and internal electric fields to achieve photocatalytic NO deep oxidization.

Parametric study and mechanism analysis of NO removal by cobalt ethylenediamine

Nitrogen oxides (NOx) are one of the major air pollutants, causing many environmental problems, NO being the main component of NOx. In the present work, the solution of cobalt ethylenediamine was used to removal NO via the wet denitrification method. For industrial applications, this experiments was carried out in the packing tower and the influence of CO2 and SO2 on the removal rate of NO also was analyzed. It found that the concentration of [Co(en)3]2+, pH, gas flow rate, the liquid-gas ration, the concentration of NO and O2 strongly affected the denitrification efficiency at a different rate. More precisely, the concentration of 0.025 mol/L of [Co(en)3]2+, pH of 13.0, low gas flow rate, high liquid-gas ratio, and high concentration of NO and O2 was proved to be recommendable for the highest efficiency. Furthermore, a reduced amount of CO2 and SO2 in the flue gas would be a recommended method for NO removal. Although three different reaction paths have been proposed by previous studies, they are still controversial. To determine which is the most accurate, three different reaction paths were checked by experiments in this work. The results implied that the cobalt ethylenediamine was complexed with NO and O2 to produce [Co(en)2(NO)(OH−)]+ and [Co2(en)4O2(OH)]3+, and then these products reacted each other to regenerate the [Co(en)3]2+. As a summary, we can affirm that the present work can guide toward the industrialization of wet denitrification using cobalt ethylenediamine.

Performance of transition metal (Cu, Fe and Co) modified SCR catalysts for simultaneous removal of NO and volatile organic compounds (VOCs) from coal-fired power plant flue gas

Emissions of NO and Volatile Organic Compounds (VOCs) in China are growing rapidly, thus it is necessary to develop a catalyst that can simultaneously remove them. In this study, a series of new V-W/Ti SCR catalysts modified by Cu, Fe and Co were prepared by wet impregnation method, which was used to simultaneously remove NO and typical VOCs (benzene and toluene) from coal-fired power plant flue gas. The catalyst activity evaluation was studied in selective catalytic reduction temperature window (260 °C, 300 °C, 340 °C, 380 °C and 420 °C) by a self-built device. Simulated flue gas was composed of 100 ppm benzene, 100 ppm toluene, 500 ppm NO, 1000 ppm SO2, 500 ppm NH3, 3.33% O2, and balanced N2, whose total flow was 750 mL/min. Characterization techniques such as SEM-EDS, XRD, XPS, and NH3-TPD were used to analyze the effect of Cu, Fe and Co loading on the catalyst's surface properties, physical structure, valence, and acid site, which further explained the removal efficiency result. The experimental results indicated that Cu0.1-V-W/Ti had the best denitration performance at low temperature and reached a maximum NO removal rate of 86.4% at 340 °C. All prepared catalysts had over 90% benzene removal and over 95% toluene removal rate. Cu0.1-V-W/Ti shows certain SO2 tolerance and has the potential to be used for simultaneous removal of NO and VOCs at SCR area of coal-fired power plants without extra capital cost.

NH2-MIL-125(Ti) encapsulated with in situ-formed carbon nanodots with up-conversion effect for improving photocatalytic NO removal and H2 evolution

The bifunctional photocatalyst [email protected]2-MIL-125(Ti), carbon nanodots (CDs) encapsulated in NH2-MIL-125(Ti), was constructed in situ by a simple and convenient low-temperature calcination approach, which exhibited great capacity in NO removal (at air level) and H2 evolution simultaneously under visible-light irradiation. The NO removal rate of [email protected]2-MIL-125(Ti) (10 mM) reached 53%, which was 28.4% higher than pristine NH2-MIL-125(Ti). Moreover, the H2 production rate was 5820.95 μmol g−1, which was 5.34 times higher than that of original NH2-MIL-125(Ti). The corresponding optical and electrical performances of [email protected]2-MIL-125(Ti) characterized by UV–Vis, UCPL, ESR, and in situ DRIFTS, etc. indicated that the encapsulated CDs uniformly dispersed in the pores of NH2-MIL-125(Ti) could improve the visible light utilization via the up-conversion effect and photosensitization, and serve as an electron-receiver to significantly prolong the lifetime of the photogenerated charge carriers, thus enhancing the photocatalytic performance. The results revealed that fabricating CDs with metal-organic frameworks (MOFs) could be an available strategy for us to boost the photocatalytic NO elimination and H2 evolution activity simultaneously.

Bismuth nanoparticles and oxygen vacancies synergistically attired Zn2SnO4 with optimized visible-light-active performance

As for the common synthesis methods of ameliorated Zn2SnO4 (ZSO), additional oxides refer to Zn or Sn or Zn/Sn would be introduced into the doped system synchronously, thereby the achievement of doped pure ZSO appears particularly difficult. In this study, a novel bismuth (Bi) nanoparticles modified ZSO composite with oxygen vacancies (OVs-BZSO) was fabricated via a facile one-pot hydrothermal approach. According to XRD and XPS analysis results, it was found that the metallic Bi nanoparticles were successfully introduced into ZSO. In addition, based on the results of XPS and EPR measurements, the existence of OVs in the ZSO was also affirmed. On this basis, the DFT calculation was employed to reveal the position of OVs, the electronic structure and charge transport properties of the interface between Bi and ZSO. Furthermore, it was observed that the introduction of OVs not only diminishes the bandgap induced by an intermediate gap but also services as active centers to favor the adsorptions of small molecules such as NO, O2 and H2O as revealed by DFT simulations to promote the formation of reactive species. While the addition of metallic Bi nanoparticles into ZSO for one thing enhances the light harvesting capacity endowed by SPR effect as evidenced by UV–vis DRS result, for another accelerates the separation of photo-generated carriers by virtue of Schottky barrier formed at the metallic Bi and ZSO interface. Therefore, the synergistic effect of OVs and Bi nanoparticles can thermodynamically drive the adsorption/activation of NO molecules, benefitting the directional migration and effective separation of electrons in OVs-BZSO, all of which serviced the efficient NO removal rate with the illumination of visible light. Meanwhile, for OVs-BZSO, in-situ infrared spectroscopy results indicated that the formation of toxic by-products was greatly bridled, thus a fresh charge transfer path: Bi nanoparticles → ZSO → gas molecules and a unique NO reaction path were proposed accordingly. This study can provide new insights on controllable preparation and reaction mechanism of ZSO-based photocatalysts.

Removal of nitrogen from rainwater runoff by bioretention cells filled with modified collapsible loess

The construction of bioretention facilities in collapsible loess areas faces some problems such as low infiltration rate of rainwater runoff and system blockage, which seriously affect the treatment effect of bioretention cell on rainwater runoff. According to the different filler matrix, three bioretention cells with improved filler were constructed, the 1# bioretention system was filled with 50% of the construction waste mixed with 50% loess, and the 2# bioretention system was filled with 50% concrete sand mixed with 50% loess, the 3# bioretention system was filled with 45% concrete sand +10% wood chips +45% loess mixed in the bioretention cell. The results show that the removal rate of NH4+-N is the highest when the height of the inundation zone of the bioretention cell is 600 mm (more than 98%). The change of hydraulic load and submerged zone height had a significant effect on the removal rate of NO3−-N in bioretention cell (P < 0.05). The removal rate of NO3−-N in the bioretention cell decreased with the increase of hydraulic load, and the bioretention cell had the highest removal rate of NO3−-N (48.85%) under low hydraulic load conditions. The removal rate of NO3−-N in the bioretention cell increased with the increase of the height of the inundation area, and the removal rate of NO3−-N was the highest when the inundation area height of the bioretention cell was set at 600 mm (98.33%). The improved bioretention cell has a better effect on NH4+-N treatment during the wet period, and the NH4+-N concentration of the effluent is below 0.4 mg/L. The NO3−-N concentration in the effluent of the three improved bioretention cells during the wet period differed greatly. Among them, the bioretention cells using sawdust modified fillers had the highest removal rate of NO3−-N. The collapse amount of the three improved bioretention cells was below 0.5 cm, and the permeability coefficients were above 2 cm/h. The experiment proves that the three methods to improve the collapsible loess filler can be applied to the construction of the bioretention cell in the collapsible loess area so that the bioretention technology can be effectively promoted in the loess area. This experiment has great significance to the construction of bioretention cells in the loess area.

Nitrogen-rich g-C3N4@AgPd Mott-Schottky heterojunction boosts photocatalytic hydrogen production from water and tandem reduction of NO3− and NO2−

Developing an effective photocatalytic denitrification technology for NO3− and NO2− in water is urgently needed. In this paper, we synthesized a nitrogen-rich g-C3N4, and in-situ grown AgPd nanowires (NWs) on the surface of nitrogen-rich g-C3N4 to build AgyPd10−y/g-CxN4 Mott-Schottky heterojunction. Compared with g-CxN4, AgyPd10−y/g-CxN4 exhibits the enhanced photocatalytic hydrogen production from water and tandem reduction of NO3− and NO2− without the addition of other hydrogen source under 365 nm irradiation. The catalytic activity and selectivity of AgyPd10−y/g-CxN4 were studied by combination of the nitrogen-rich g-C3N4 and the different component of AgyPd10−y nanowires (NWs). Among the AgyPd10−y/g-CxN4 catalyst, the Ag3Pd7/g-C1.95N4 catalyst exhibited the highest photocatalytic activity and selectivity for photocatalytic reduction of NO3− and NO2−, and the removal rate of NO3− and NO2− are 87.4% and 61.8% under 365 nm irradiation at 25 °C, respectively. The strategy opens a new way for making the photocatalytic hydrogen production in tandem with reduction of NO3− and NO2− in water, also extending it to remove metal ion.

Desulfurization and Denitrification of Ship Exhaust Gas with Low Temperature Plasma

In order to reduce the emission of pollutants such as sulfur oxides and nitrogen oxides in ship exhaust gas, the principles and experimental methods of desulfurization and denitrification with low temperature plasma with dielectric barrier discharge were introduced in this study. The impacts of reactor voltage and reactor frequency of low temperature plasma, humidity and oxygen content of ship exhaust gas on the efficacy of desulfurization and denitrification were also explored by experiments in this study. It was revealed that the low temperature plasma technology could desulfurize and denitrify the ship exhaust gas better. The efficacy of desulfurization and denitrification would be increased when the voltage increases. At a voltage of 20 kV, the removal rates of NO and SO2 reached 59% and 52% respectively. When the reactor voltage was maintained at 15 kV, the removal rates of NO and SO2 would rise at the beginning and decrease later with increase of the frequency. The highest removal rates of NO and SO2 were 55% and 42% respectively when the frequency was 10 kHz. The efficacy of desulfurization and denitrification can be affected by humidity and oxygen content of the ship exhaust gas. Researches in this study provided a crucial reference for the application of low temperature plasma technology in the desulfurization and denitrification of ship exhaust gas.

Self-cleaning and de-pollution efficacies of photocatalytic architectural membranes

Photocatalytic self-cleaning “cool” roofs and walls can maintain high albedos, saving building cooling energy, reducing peak power demand, and mitigating the urban heat island effect. Other environmental benefits result from their de-polluting properties. Specimens from two different photocatalytic architectural membranes and a non-photocatalytic control were exposed alongside vertically, facing west, for two years at three California sites, and retrieved quarterly for testing. Photocatalytic materials showed excellent self-cleaning performance, retaining albedos of 0.74 – 0.75. By contrast, the control material exhibited an albedo loss of up to 0.10, with appreciable soiling observed by scanning electron microscopy. De-pollution capacity was assessed by quantifying NO removal and NOx deposition rates at 60 °C. Efficacy varied with exposure location, weather conditions, and the nature of the photocatalytic material. Seasonal effects were observed, with partial inhibition during the dry season and reactivation during the rainy season.

G‐C3N4/TiO2 Composite Film in the Fabrication of a Photocatalytic Air‐Purifying Pavements

The fabrication of a photocatalytic air‐purifying pavement with a facile loading route, long depolluting period, and excellent deNOx activity under weak solar irradiation is essential for ambient air purification. Herein, a promising methodology is developed relying on the exploitation of a graphitic carbon nitride/TiO2 (g‐C3N4/TiO2) composite hydrosol at room temperature. The TiO2 hydrosol can act as a source of photocatalyst and dispersant for g‐C3N4 during loading. The photoinduced hydrophilicity, adhesive force, and regeneration tests in the laboratory show the long‐term deNOx application potential of g‐C3N4/TiO2 coatings. Field studies indicate that the NO removal rate is 70.7% of g‐C3N4/TiO2‐coated pavement in the morning (07:00–10:00) and afternoon (17:00–19:00), at which times solar radiation is weakest. The deNOx efficiency is influenced by solar irradiation and traffic volume. The latter exerts a more significant influence on deNOx efficiency than the former. A desirable route in fabricating a photocatalytic air‐purifying pavement is provided and offers a promising photocatalyst suitable for outdoor environmental remediation.

TiO2 with exposed (001) facets/Bi4O5Br2 nanosheets heterojunction with enhanced photocatalytic for NO removal

A TiO2 with exposed (001) facets/Bi4O5Br2 nanosheets heterojunction (TNS/BOB) was fabricated via a hydrothermal and electrostatic self-assembly method. The photocatalytic activity for NO removal was evaluated under simulated solar light irradiation. Through optimizing the content of TNS nanosheets, the photo-oxidative NO removal rate of 15% TNS/BOB was increased by up to 54.3%. This value is much higher than that of the individual components TNS (31.1%) and BOB (37.7%). Through capturing experiments and electron spin resonance (ESR) measurements, the main active species in the photocatalytic process were identified as · and ·OH. Discrete Fourier transform computation results and ESR tests revealed that the photo-induced electrons in TNS should recombine with the holes in BOB, leading to effectively promoted charge separation at the TNS/BOB interface through the Z-type charge transfer. This work showed that with appropriate facet control and heterojunction design TiO2 can be used as an effective visible-light photocatalyst material.

Removal of high concentrations of NO3− from nuclear industrial wastewater by using a fixed-bed bioreactor

In this work, a down-flow fixed bed anaerobic biofilm reactor filled by biological ceramsites were prepared to remove the high concentration of NO3− (> 20 g/L) from nuclear industry wastewaters. The effects of hydraulic retention time, the concentration of NO3−, the molar ratio of C/N and temperature on the removal efficiencies of NO3− were investigated. The results showed that the removal rate of NO3− with the initial concentration of 6 g/L can reach 99% or more by controlling the hydraulic retention time at 0.75 h, the molar ratio of C/N at 1.5 and the temperature over 18 °C. In the process, the NO2− was not accumulated, and the autotrophic denitrifying bacteria grow well in anaerobic biofilm reactors, proving a usable method for removing the high concentration NO3− from nuclear industrial wastewaters.

C3N4 with engineered three coordinated (N3C) nitrogen vacancy boosts the production of 1O2 for Efficient and stable NO photo-oxidation

The introduction of nitrogen vacancy to C3N4 holds promise in the photocatalytic behavior improvement. Yet, minimal literatures on reaction and stability mechanisms are presently available in the NO-oxidation reaction of C3N4. Here C3N4 with three coordinated (N3C) nitrogen vacancy was prepared by directly calcining the mixture of azodicarbonamide and melamine. Unlike previously reported C3N4 that exhibits an obvious deactivation beyond 30 min (>10% loss of reactivity after one cycle) and high in-situ formed NO2 concentration (>100 ppb), the C3N4 with three coordinated (N3C) nitrogen vacancy exerts increased NO-oxidation performance (40.3%, ~2.28 times higher than that of pristine C3N4 with a NO-removal rate of 17.7%) and suppressed in-situ produced NO2 (36.3 ppb, decreased by 76.6 ppb compared to pure C3N4) as well excellent stability (<2% loss of activity after a 5 h cycling test). DFT calculations reveal that, intermediates (NO2) and end-products (NO2– and NO3–) can weakly adsorp on the surface of C3N4 with three coordinated (N3C) nitrogen vacancy, thus rendering a well maintained activity. Based on the time-dependent ESR measurements, the 1O2 generation, which achieving from the O2 activation process, can compensate for the consumption of major reactive species and thus support the remarkable reusability. Therefore, this study provides a potential and sustainable route for the steady and efficient NO-oxidation.