NO Removal Rate Research Articles

Efficient degradation of inorganic nitrogen in mariculture wastewater by electrochemical methods

The effective treatment of inorganic nitrogen in mariculture wastewater is important to ensure the quality and yield of cultured organisms, and protect the marine environment. The concentration of inorganic nitrogen, i.e. NO3−-N, NO2−-N and NH4+-N, reaches to the first-level of Water Drainage Standard for Seawater Mariculture (SC/T 9103–2007) after electrochemical treatment with a double-chamber cell (Ti/RuO2-IrO2 anode and Ni cathode) in this study. The results showed that the reductions of NO3−-N and NO2−-N on Ni cathode are easier than Ti and Pt cathodes. The removal rate and products (NH4+-N and NO2−-N) selectivity in degradation of NO3−-N using Pt and Ni cathodes are much higher than Ti cathode. However, the energy consumption of Pt cathode is much higher than Ti and Ni cathodes. With the potential shifted to negative using Ni cathode, both the removal rate of NO3−-N and the selectivity of NH4+-N increase, while the selectivity of NO2−-N decreases. The lowest energy consumption of Ni cathode is achieved under the potential of NO3−-N reduction peak, i.e. −1.25 V. Most of NH4+-N is oxidized indirectly on Ti/RuO2-IrO2 anode through active chlorine, and 1.30 V is the optimum potential. NO2−-N is oxidized to NO3−-N on Ti/RuO2-IrO2 anode, which can be introduced into cathode chamber again for further electrolyzing. The final product is N2 for treatment of mariculture wastewater in the double-chamber cell with Ni cathode and Ti/RuO2-IrO2 anode.

Singlet Oxygen and Mobile Hydroxyl Radicals Co-operating on Gas-Solid Catalytic Reaction Interfaces for Deeply Oxidizing NOx.

Learning from the important role of porphyrin-based chromophores in natural photosynthesis, a bionic photocatalytic system based on tetrakis (4-carboxyphenyl) porphyrin-coupled TiO2 was designed for photo-induced treating low-concentration NOx indoor gas (550 parts per billion), achieving a high NO removal rate of 91% and a long stability under visible-light (λ ≥ 420 nm) irradiation. Besides the great contribution of the conventional •O2- reactive species, a synergic effect between a singlet oxygen (1O2) and mobile hydroxyl radicals (•OHf) was first illustrated for removing NOx indoor gas (1O2 + 2NO → 2NO2, NO2 + •OHf → HNO3), inhibiting the production of the byproducts of NO2. This work is helpful for understanding the surface mechanism of photocatalytic NOx oxidation and provides a new perspective for the development of highly efficient air purification systems.

Enhanced adsorption of NO onto activated carbon by gas pre-magnetization

The NO removal efficiency was relatively low in the traditional activated carbon adsorption process. In this work, a gas pre-magnetization and activated carbon adsorption process was developed to enhance the adsorption of NO onto activated carbon. In this innovative and green process, the mixed gas was magnetized in the external magnetic field and then absorbed by activated carbon. The results indicated that the maximal removal rate of NO could be increased from 75.0% to 89.5%, and the NO adsorption capacity of commercial activated carbon in one hour elevated from 2.28 to 2.60 mg/g when the magnetic induction intensity of external magnetic field increased from 0 T to 2 T. The strengthening mechanism of the gas pre-magnetization was investigated. It was found that magnetic field could elevate the oxidation rate of NO by 11.4% and thus promote the physical adsorption of NO onto activated carbon. External magnetic field could increase the reaction activity of NO and promote the chemical reaction between NO and some functional groups (CO, CO and COOH) on the activated carbon and thus promote the chemisorption process of NO.

Long-term effects of Cu(II) on denitrification in hydrogen-based membrane biofilm reactor: Performance, extracellular polymeric substances and microbial communities

Divalent copper (Cu(II)) frequently coexists with nitrate (NO3−) in industrial wastewater and the effect of Cu(II) on the autotrophic denitrification system using H2 as the electron donor remains unknown. In this study, the hydrogen-based membrane biofilm reactor (H2-MBfR) was operated continuously over 150 days to explore the effect of Cu(II) on the performance of autotrophic denitrification system and understand the key roles of EPS and microbial community. More than 95% of 20 mg-N/L NO3− was removed at 1–5 mg/L Cu(II), and the removal rate of NO3−-N was stabilized to 82% at 10 mg/L Cu(II) after a short period, while NH4+ and NO2− in effluent were hardly detected, indicated that high concentration of Cu(II) did not permanently inhibit the denitrification performance in H2-MBfR. Colorimetric determination showed that Cu(II) stimulated the secretion of EPS, in which the protein (PN) content was much higher than polysaccharide (PS). The PN/PS ratios increased from 0.93 to 1.99, and the PN was more sensitive to copper invasion. The results of three-dimensional excitation-emission matrix illustrated that tryptophan was the main component of EPS chelating Cu(II) to reduce toxicity. The results of Fourier-transform infrared demonstrated that hydroxyl, carboxyl, and protein amide groups bound and reduced Cu(II). Furthermore, Cu(II) was effectively removed (>80%), and the results of distribution and morphology analysis of Cu(II) show that the electron-dense deposits of monovalent copper (Cu(I)) were found in EPS and biofilms and the reduction of Cu(II) to Cu(I) was an obvious self-defense reaction of biofilm to copper stress. The microbial richness and diversity decreased with the long-term exposure to Cu(II), while the relative abundance of denitrifiers Azospira and Dechloromonas increased. This study provides a scientific basis for the optimal design of treatment system for removal of nitrate and recovery of heavy metals simultaneously.

Experimental investigation of the NOx formation and control during the self-sustaining incineration process of N-containing VOCs (DIMETHYLFORMAMIDE)

An experimental investigation was conducted on N,N-dimethylformamide (DMF) pyrolysis at medium-temperature followed by extremely fuel-lean combustion. Furthermore, the NH3-SNCR (Selective non-catalytic reduction) method was studied to control NOx produced in DMF oxidation. Jet-stirred reactors (JSRs) were used in experimental investigation, because the uniform gas-phase mixing state formed by high-speed turbulence in JSR makes the validation of detailed models easier. The major gaseous species produced by pyrolysis, oxidation, and SNCR, namely H2, N2, CO, CO2, NOx, N2O, HCN, and CxHy, are quantified because the mechanism of NOx reduction will be elaborated using these species. The results show that the main nitrogen-containing pyrolysis products are HCN and N2, taking up 65% and 25% of DMF nitrogen, while carbon-containing pyrolysis products are mostly CO, CH4 and HCN. The HCN concentration increases significantly by 42.13% as pyrolysis time increases from 1.5 to 7 s. In oxidation, HCN and N2O concentration peaks are at 650 °C and 750 °C respectively, and NO concentration increases as temperature enhances when it is over 800 °C. A higher ratio of NO/N2O concentration was shown in oxidation of the higher equivalence ratio. The de-NOx efficiency of NH3-SNCR on oxidation flue gas peaked in range 825–875 °C, and as the NH3/NO ratio increased to more than 2.5, NO removal rate tended to reach the maximum of about 50%. The N2O removal rate rose significantly as temperature exceeded 900 °C in SNCR. The results shows the feasibility of NO emission control with DMF containing VOCs incineration in current industrial applications·NH3-SNCR at 825–875 °C shows significant de-NOx effect, but not a proper solution to limit N2O emission at the same time. This study could provide guidance for designing and optimizing the incinerator parameters and its de-NOx system, as well as provide validation data for future chemical kinetic model capable of predicting DMF combustion.

Exhaust gas treatment using MnO2/Mg–Al layered double hydroxide: Assessment of its mixed gas removal performance and regeneration

Combustion methods are popularly used to treat acidic exhaust gases to reduce the emission of pollutants. However, exhaust gas treatment can be difficult and expensive, rendering it essential to develop a new treatment process for acidic exhaust gases. In the present study, we investigated the removal of NO from the HCl–SO2–NO mixed gas using MnO2/Mg–Al layered double hydroxide (MnO2/Mg–Al LDH). We analyzed the influence of CO2 gas on the NO removal. Additionally, we regenerated MnO2/Mg–Al LDH after the acid gas adsorption using the wet method and examined the possibility of its cyclical use. MnO2/Mg–Al LDH could simultaneously remove HCl, SO2, and NO from the mixed gas. Because HCl and SO2 influenced the NO removal rate, we proposed a two-step treatment process with MnO2/Mg–Al LDH and CO3•Mg–Al LDH to efficiently remove HCl, SO2, and NO from the HCl–SO2–NO mixed gas. The NO removal rate decreased with an increase in the CO2 concentration, confirming the influence of CO2. Additionally, the results confirmed the possible cyclic use of MnO2/Mg–Al LDH after removing acid gases. However, the Mn elution and Mn(IV) concentration decreased the removal rates of SO2 and NO, respectively. Thus, it is necessary to develop the regeneration method further.

Sustainable treatment of nitrate-containing wastewater by an autotrophic hydrogen-oxidizing bacterium

Bacteria are key denitrifiers in the reduction of nitrate (NO3−-N), which is a contaminant in wastewater treatment plants (WWTPs). They can also produce carbon dioxide (CO2) and nitrous oxide (N2O). In this study, the autotrophic hydrogen-oxidizing bacterium Rhodoblastus sp. TH20 was isolated for sustainable treatment of NO3−-N in wastewater. Efficient removal of NO3−-N and recovery of biomass nitrogen were achieved. Up to 99% of NO3−-N was removed without accumulation of nitrite and N2O, consuming CO2 of 3.25 mol for each mole of NO3−-N removed. The overall removal rate of NO3−-N reached 1.1 mg L−1 h−1 with a biomass content of approximately 0.71 g L−1 within 72 h. TH20 participated in NO3−-N assimilation and aerobic denitrification. Results from 15N-labeled-nitrate test indicated that removed NO3−-N was assimilated into organic nitrogen, showing an assimilation efficiency of 58%. Seventeen amino acids were detected, accounting for 43% of the biomass. Nitrogen loss through aerobic denitrification was only approximately 42% of total nitrogen. This study suggests that TH20 can be applied in WWTP facilities for water purification and production of valuable biomass to mitigate CO2 and N2O emissions.

Effect of MnO2/Mg–Al layered double hydroxide preparation method on the removal of NO

In this study, we prepared Mg–Al layered double hydroxide (LDH) by anion exchange and co-precipitation methods and investigated the influence of the preparation methods on the removal of NO. MnO2/Mg–Al LDH prepared using the rehydration and anion exchange methods exhibited very high NO removal rates, removing approximately 90 % of NO even after 90 min. In contrast, MnO2/Mg–Al LDH prepared using the co-precipitation method demonstrated a poor NO removing ability. Although Mn3+ species were distributed within the LDH host layers when MnO2/Mg–Al LDH was prepared by co-precipitation, they did not affect the oxidation of NO. Conversely, MnO2 and Mn2O3 remaining in the form of bridges after the intercalation and subsequent reduction of MnO4- species contributed to NO oxidation, which was observed for MnO2/Mg–Al LDH prepared using both anion exchange and co-precipitation methods. Thus, bridging between the LDH layers by MnO2 and Mn2O3 is essential for removing NO.

Interactions between CO oxidation and selective catalytic reduction of NO with NH3 over Mn-based catalysts

The α-MnO2-Cu catalyst has a high NO and CO removal rate. CO reduced the NH3-SCR activity by inhibiting NO adsorption. NH3 negatively affected CO oxidation by minimizing the formate intermediate. NO decomposed intermediates to promote CO oxidation.

One-step calcination synthesis of accordion-like MXene-derived TiO2@C coupled with g-C3N4: Z-scheme heterojunction for enhanced photocatalytic NO removal

This work explored an effective treatment method for removing NO from simulated flue gas at normal temperature. We synthesized accordion-like MXene-derived TiO2@C coupled with g-C3N4 (TiO2@C/g-C3N4) via one-step calcination utilizing Ti3AlC2, fluoride salts and melamine as raw materials in CO2 atmosphere. One-step calcination process simultaneously achieved the etch of Al layers of Ti3AlC2 by molten fluoride salts, the generation of g-C3N4 with melamine as precursor and the oxidation of Ti3C2 by CO2. TiO2@C/g-C3N4 for photocatalytic activation of hydrogen peroxide (H2O2) had as high as 94.0% removal rate of NO at parts per million level in a normal temperature environment. This efficiency was 5.3 times and 8.0 times that of TiO2@C/g-C3N4 and H2O2 individually, due to the synergy between photocatalysis and H2O2 oxidation. Meantime, TiO2@C/g-C3N4 exhibited an enhanced performance compared with g-C3N4 (40.3%) and TiO2@C (64.1%) for Z-type heterojunction accelerating the separation of electron-hole pairs. The mechanism was proposed that Z-type TiO2@C/g-C3N4 heterojunction activated H2O2 under visible light to generate hydroxyl radical and superoxide radical for oxidation of NO.

Evaluation of NOx Reduction Effect and Impact on Asphalt Pavement of Surface Treatment Technology including TiO2 and Asphalt Rejuvenator

Nitrogen oxide (NOx), emitted at the highest rate among automobile exhaust gases, is the main cause of air pollution, and various construction technologies are being developed to reduce NOx emissions. In this study, the NOx reduction effect of surface treatment technology for road pavements, and the effect of the photocatalytic reaction on asphalt pavements, were evaluated using a photocatalyst. Three types of titanium dioxide (TiO2) were used as photocatalysts, and an asphalt rejuvenator used to recover aged asphalt was applied as a surface treatment agent. To evaluate the NOx reduction effect, a test device capable of testing large-sized specimens was manufactured and compared with the ISO method, which only allowed the testing of small specimens. In addition, the effect of TiO2 and the asphalt rejuvenator on the asphalt mixture was analyzed through chemical analysis. The test results of the newly manufactured mixed-tank photo reactor showed the same trend as the ISO test results concerning the evaluation of its NOx removal performance. As a result of the performance evaluation of the surface treatment using TiO2, the NO removal rate was up to 7.83% when Anatase-type TiO2 with excellent light efficiency was applied. In addition, when the rejuvenator was used, the oxidation of asphalt, caused by the photoreaction of TiO2, was reduced.

Study on denitration performance of mineral catalyst prepared by high energy ball milling of rare earth concentrate supported Fe2O3 for NH3-SCR

A series of mineral catalysts were prepared by soaking in ferric nitrate solution (0 mol/L, 0.1 mol/L, 0.5 mol/L, 1.0 mol/L), high-energy ball milling and microwave roasting. The denitration performance of the mineral catalyst NH3-SCR prepared by high-energy ball milling of Fe2O3 supported on rare earth concentrate was studied. XRD, SEM, EDS, NH3-TPD, H2-TPR, XPS and other means were used to characterize the mineral phase structure, surface morphology, adsorption capacity, reduction performance and surface elements of the catalyst. meanwhile, the denitration activity of the samples was evaluated and compared in the reactor of catalyst evaluation system. The results show that under the experimental conditions of ferric nitrate solution 0.5 mol/L, high-energy ball milling for 120min, ball-to-material ratio 3:1, ball milling speed 1200r/min, microwave roasting in air for 20min, and optimum reaction temperature 350 °C, the NO removal rate can reach 92%. In this paper, the key basic problems of preparing mineral catalysts by high-energy ball milling with rare earth concentrate supported Fe2O3 are revealed, which is a beneficial exploration for high-value utilization of rare earth concentrate resources.

Enhancement mechanism of full-solar-spectrum catalytic activity of g-C3N4-x/Bi/Bi2O2(CO3)1-x(Br, I)x heterojunction: The roles of plasma Bi and oxygen vacancies

In this work, plasma Bi and oxygen vacancies (OVs) co-modified g-C3N4-x/Bi/Bi2O2(CO3)1-x(Br, I)x heterojunction was prepared via solvothermal reaction. The formation of OVs was promoted induced by polarization charge transfer, while the deposition of Bi was attributed to the esterification between CH3CH2OH and NaBiO3 and subsequent anoxic thermal reduction. The increased OVs concentration improved the adsorption performance of tetracycline (TC), meanwhile promoting the separation of hot carriers of plasma Bi by trapping hot electrons. The dissociated hot holes directly drove near-infrared (NIR) photocatalytic reaction. The deactivation of OVs in Bi2O2(CO3)1-x(Br, I)x was inhibited due to the deposition of Bi, and the Z-scheme mechanism was achieved with Bi as electron mediator. Hence, g-C3N4-x/Bi/Bi2O2(CO3)1-x(Br, I)x showed enhanced full-spectrum catalytic activity and excellent stability. 84.6%/70.0% and 79.33%/70.19% of TC and total organic carbon could be removed by the optimal heterojunction under simulated sunlight/NIR light irradiation, and the NO removal rate under visible light irradiation was as high as 76.7%. This work revealed the different roles of OVs and metal in defect-mediated heterojunction, and provided a feasible method to prepare full-spectrum response photocatalysts with high activity and stability.

Oxygen vacancies in actiniae-like Nb2O5/Nb2C MXene heterojunction boosting visible light photocatalytic NO removal

Photocatalytic oxidation is a green and energy-saving technology for removing the low concentration NO in ambient atmosphere. High efficient and stable photocatalysts are essential for achieving excellent NO conversion effect. In this work, oxygen vacancy-rich Nb2O5/Nb2C heterojunction photocatalysts were prepared from Nb2C MXene by hydrothermal process and heat treatment in H2/Ar. The (001) facet-dominant Nb2O5 nanorods in-situ grown on Nb2C MXene formed an actiniae-like structure, which promotes the active site exposure and enlarges the reaction interface. Under visible light, the optimized photocatalyst exhibits excellent NO removal rates in the relative humidity range of 25–75%. Mechanism research shows that the oxygen vacancies greatly improve the photocatalytic NO oxidation capacity. Oxygen vacancies on (001) facet of Nb2O5 nanorods can boost the visible light absorption, effectively adsorb and activate the reactant gas. The separation of photogenerated carriers was synergistically enhanced by the oxygen vacancies and Nb2O5/Nb2C heterojunction.

Ultrasonication-Assisted Preparation of a Mn-Based Blast Furnace Slag Catalyst: Effects on the Low-Temperature Selective Catalytic Reduction Denitration Process.

Reducing costs and improving performance have always been hotspots in the field of catalyst research. In order to control the NOx in the low-temperature flue gas of nonpower industries, this paper studies the denitration performance of the ultrasonication-assisted preparation of Mn-based blast furnace slag selective catalytic reduction (SCR) low-temperature denitration catalysts. The catalyst was characterized by FT-IR, XRD, and SEM. The study found that ultrasound assistance can make the active components on the catalyst surface more uniformly dispersed and improve the catalytic activity of the catalyst. Under conditions of 80 W ultrasonic power and 20 min ultrasonic time, the denitration performance of the Mn-based blast furnace slag catalyst is optimal, and the NO removal rate is 2.5 times that of the unsonicated catalyst. This work clarified the mechanism of the effect of ultrasonic assistance on the Mn-based blast furnace slag catalyst and at the same time realized the utilization of solid waste resources and air pollution control.

Porphyrin-based Ti-MOFs conferred with single-atom Pt for enhanced photocatalytic hydrogen evolution and NO removal

A robust and efficient titanium metal–organic framework (TMF-Pt) with a single-atom Pt embedded PtII tetrakis(4-carboxyphenyl)porphyrins (PtTCPP) as linking groups and Ti-oxo molecular clusters as metal nodes was successfully fabricated for the first time, which have been confirmed by aberration-correction scanning transmission electron microscopy (HAADF-STEM) and synchrotron-radiation-based X-ray absorption fine-structure spectroscopy (XAFS), and was applied to photocatalytic hydrogen production and NO removal. It was worth noting that the TMF-Pt exhibited an extremely high hydrogen evolution activity (15456 µmol·g−1·h−1) and NO removal rate (70.3%) in comparison with most of the reported MOFs-based photocatalysts, which could be ascribed to the very high atom-utilization efficiency of single-atom Pt along with a high charge carriers separation efficiency and the Ti-oxo clusters as an alternative to the very famous TiO2 photocatalyst. The results provided us with a novel strategy that introducing single-atom Pt into the center of the porphyrin skeleton could integrate the broad light-harvesting porphyrin unite with the very high atom-utilization efficiency single-atom Pt to further improve the photocatalytic performance ultimately.

Insight on photocatalytic oxidation of high concentration NO over BiOCl/Bi2WO6 under visible light

The exhaust gas from an SCR (Selective Catalytic Reduction) unit still has about 100 ppm NO. BiOX/Bi2WO6 catalysts were fabricated by a one-step ultrasound-assisted method and employed for photocatalytic oxidation of NO under visible light. The bandgap energy of BiOX (Cl, Br, I)/Bi2WO6 were estimated to be 2.65 eV, 2.35 eV, and 1.75 eV, respectively. Photocurrent density and EIS curves revealed that BiOCl/Bi2WO6 had the optimal charge transfer velocity. Simulated NO removal experiments of BiOX/Bi2WO6 catalysts were carried out in a fixed bed reactor, 20–30% NO (100 ppm inlet) removal rate was achieved under visible light while promoting by H2O vapor, and the maximum NO removal rate is up to 31% on BiOCl/Bi2WO6. The fitted L-H model revealed that NO oxidation followed two-centered adsorption, and scavenger experiments confirm that the main ROS (Reactive Oxygen Species) was •OH. In situ DRIFT spectra revealed that there were bridging nitrates, monodentate and bridging nitrites, and other intermediates formed on the BiOCl/Bi2WO6, these species can be scrubbed by seawater to regenerate the catalyst. The NO photocatalytic oxidation pathway was proposed. Good activity and stability of BiOCl/Bi2WO6 provide a new approach for scale-up application of NO oxidation under visible light.

Ti3C2@TiO2/g-C3N4 heterojunction photocatalyst with improved charge transfer for enhancing visible-light NO selective removal

Control of Nitrogen dioxide (NO2) byproducts is of great importance for the photocatalytic NO removal and environmental remedy. However, individual semiconductor photocatalysts generally show limited capabilities for selective NO removal due to severe charge recombination and inadequate redox potentials. Herein, the cotton-like g-C3N4 was modified with Ti3C2@TiO2 to construct a heterojunction photocatalyst Ti3C2@TiO2/g-C3N4, which showed outperformed photocatalytic NO removal and MB degradation abilities compared to the individual photocatalysts under visible light irradiation. The UV–vis absorption spectra and photoluminescence (PL) spectra confirmed that Ti3C2@TiO2/g-C3N4 photocatalyst was endowed with superior light utilization and separation/transfer ability of charge carriers due to the presence of n-n heterojunction and Schottky barrier. Furthermore, the g-C3N4, Ti3C2, and TiO2 were closely contacted showing a high specific surface area, which promoted the charge transfer and the exposure of more active sites, further inducing the formation of more active species. Therefore, the designed photocatalyst delivered a high removal rate of NO and a suppressed discharge of NO2. Notably, the photocatalyst Ti3C2@TiO2/g-C3N4 also presented superior NO removal ability during the cycling experiment, indicating their outstanding stability and recyclability. Besides, the effects of active species were monitored using a trapping experiment to propose probable photocatalytic mechanism. This study could shed a new light to the design of photocatalyst for air purification in the future.

Sulfur-doped photocatalysts with iron-nitrogen coordination bonds by modifying graphitic carbon nitride obtained from ammonium thiocyanate pyrolysis with ferrous sulfate heptahydrate in ethanol

The photocatalytic agent graphitic carbon nitride (g-C 3 N 4 ) was synthesized by pyrolysis of ammonium thiocyanate (NH 4 SCN) which is commonly produced via extraction of desulfurization waste liquids as the main salt. The g-C 3 N 4 photocatalyst was modified by treatment with different amounts of ferrous sulfate heptahydrate in ethanol, which resulted in Fe-doping and a certain degree of S-doping of the material. According to the characterization results, the modified sample eg-C 3 N 4 /FeSO 4 -10% with superior photocatalytic efficiency exhibited the highest specific surface area and pore volume, poor crystallinity, and a good sample polymerization degree. The existence of more C defect vacancies in the modified sample structure increased the electron density around C and N atoms in the triazine ring structure and becomes the electron capture center. At the same time, the presence of ethanol solvent promotes the formation of more Fe–N coordination bonds between a large number of lone pair electrons and metal Fe ions. In addition, with the increase of the doping amount of S element, a new impurity level is introduced, and the band gap widths of the samples become narrower. The changes of surface structure and energy band structure of the modified samples led to a significantly reduced carrier recombination rate and further promoted the production of more reactive oxygen groups. In the process of Rhodamine B (RhB) degradation as organic pollutant, the degradation can reach 98% rapidly after 60 min of visible light irradiation, which is 78% higher than g-C 3 N 4 , at a simultaneous increase of the photocatalytic reaction rate constant from 0.007 to 0.305 per min. Meanwhile, the sample eg-C 3 N 4 /FeSO 4 -10% also showed excellent photocatalytic activity in the NO x removal process of air pollution. Compared with the original g-C 3 N 4 , the NO removal rate increased from 64% to 75%, and the production amount of harmful intermediate NO 2 decreased from 0.15 to 0.08 mg/m 3 . • Treatment of water and gas pollutants through waste. • Doping S element brings impurity level and band gap decreases. • The central N atom of the structure forms a Fe–N (III) coordination bond with Fe 3+ . • More Fe–N(III) can be formed by loading Fe metal ion in ethanol solvent. • The carrier compound rate of modified samples treated with ethanol solvent was lower.

Response of Nitrate Processing to Bio-labile Dissolved Organic Matter Supply Under Variable Oxygen Conditions in a Sandy Beach Seepage Face

Supply of bio-labile dissolved organic matter (DOM) has been assumed to be a key factor for the intensity of nitrate (NO3–) removal in permeable coastal sediments. In the present study, a series of flow through reactor experiments were conducted using glucose as a N-free bio-labile DOM source to permeable sediments from a sandy beach seepage face to identify its effect on benthic NO3– removal. The results revealed a shift from the dominance of NO3– production to removal processes when NO3– input concentration increased from 10 to 80 μM under oxic conditions. Sediment microbiota information suggests that nitrification (e.g., Nitrosomonas and Nitrososphaera) and denitrification (e.g., Marinobacter and Bacillus) were dominant pathways for benthic NO3– production and removal in the studied sediment. Compared with the active response of sediment microbiota to NO3– additions, the supply of glucose (approximately 300 μM final concentration added) did not significantly change the NO3– removal efficiency under aerobic conditions (dissolved oxygen saturation approximately 100%). Similarly, an insignificant increase of NO3– removal rate after glucose amendment of the circulating water was obtained when dissolved oxygen (DO) saturation decreased to approximately 70% in the input solution. When DO at the input solution was decreased to 30% saturation (sub-oxic conditions), the removal rate of NO3– in the group amended with glucose increased, suggesting that glucose stimulated denitrifiers. These results revealed that NO3– removal relied mainly on the anaerobic environment at particle surfaces, with a dependence on the sedimentary organic matter as an electron supplier under bulk aerobic conditions, while the bio-labile DOM was consumed mainly by aerobic respiration instead of stimulating NO3– reduction. However, the respiration triggered by the over-supply of bio-labile DOM reduced the DO in the porewater, likely depressing the activity of aerobic reactions in the permeable sediment. At this point, the benthic microbiota, especially potential denitrifiers, shifted to anaerobic reactions as the key to support nitrogen metabolism. The glucose amendment benefited NO3– reduction at this point, under sub-oxic conditions.