NO Removal Rate Research Articles

Selective photocatalytic reduction of nitric oxide to dinitrogen via bimetallic bond incorporation

In this study, we addressed the challenge of optimizing the first rate-limiting NO adsorbate state, which has received limited attention in previous research on the photoreduction of NO. We prepared BiFeWO6 (BFWO), which improved not only the NO removal rate under illumination but also the selectivity of photocatalytic NO conversion to N2. To further optimize the performance, we introduced platinum into BFWO, achieving a 57.5 % NO conversion rate with ∼80 % N2 selectivity under 425 nm light-emitting diode illumination (50 mW/cm2), which is optimal for converting NO into less harmful compounds at low concentrations. FeOBi bonds were identified as the key active sites of the first rate-limiting NO adsorbate state in BFWO through time-resolved operando infrared (IR) spectroscopy and density functional theory (DFT) analysis. The specific adsorption configuration of NO on the FeOBi group accelerated the photoreduction reaction kinetics, resulting in superior photocatalytic NO removal performance.

Research on smoke cleaning based on Mg(OH)2/NaClO2 seawater solution

Abstract Ship exhaust emissions contain a large amount of sulfur oxides and nitrogen oxides, which have attracted widespread attention from the international community for their pollution of the atmospheric environment. In order to reduce the emissions of these pollutants, the International Maritime Organization (IMO) and other national institutions have established strict emission standards and promoted the research and application of ship exhaust desulfurization and denitrification technology. Experimental and simulation analyses were conducted on the denitrification effect of Mg(OH)2/NaClO2 solution using a cyclic spray method. Simulation analysis was carried out using cyclic spraying. The experiment compared the reaction degree and reaction time of NO in NaClO2 seawater, NaClO2 water, and Mg(OH)2/NaClO2 marine solution. The experimental result is that in the process of cyclic spray, the removal rate of NO by these three solutions can reach 100%. The reaction time of NO is 71, 86, and 90 minutes, respectively. Under the same conditions, the simulation results showed that the reaction rate of NaClO2 water solution with NO was faster, followed by NaClO2 seawater solution. The reaction rate of Mg(OH)2/NaClO2 seawater solution with NO was the slowest of the three. When the pH value exceeds 7, it effectively inhibits the production of ClO2 gas by NaClO2. The removal rate of Mg(OH)2/NaClO2 seawater solution is directly proportional to the initial concentration of NaClO2. In addition, it could be seen from the simulation cloud diagram that the removal speed of NO in the spray reactor slows down as the concentration of NO increases.

MXene quantum dots decorated g-C3N4/BiOI heterojunction photocatalyst for efficient NO deep oxidation and CO2 reduction

The photocatalytic performance of g-C3N4 is greatly limited by the severe charge recombination due to its s-triazine unit structure. Hence, enhancing the separation of photogenerated carriers is the pivotal factor for high-efficiency photocatalysis of g-C3N4. In this work, we construct a MXene quantum dots (MQDs) decorated BiOI/g-C3N4p-n heterojunction photocatalyst. The interfacial charge separation and transfer are substantially promoted, due to the synergistic effect of the internal electric field (IEF) of BiOI/g-C3N4 heterojunction and strong electron-withdrawing capability of MQDs. Furthermore, the introduction of BiOI with a low band gap and MQDs with large specific areas and rich surface terminals lead to enhanced light absorption and active sites. As a result, the ternary g-C3N4/MQDs/BiOI photocatalyst achieves a much higher NO removal rate of 42.23 % and discharges less NO2 intermediate than the individual and binary ones. Meanwhile, the g-C3N4/MQDs/BiOI photocatalyst also exhibits the most effective CO2 photoreduction, with a CO production rate of 57.8 μmol·g−1·h−1 and a CH4 production rate of 3.6 μmol·g−1·h−1, surpassing all other photocatalysts in this study. In addition, the designed composite photocatalyst shows remarkable stability. The photocatalytic mechanisms are studied by the trapping experiment and in-situ Fourier Transform Infrared (FTIR) Spectra. This work paves a new avenue for enhancing charge separation and thus improving performances of g-C3N4-based photocatalysts by integrating a p-n heterojunction and a co-catalyst, which would accelerate commercial deployment of emerging photocatalysts.

The in-situ fabricated Bi nanoparticles on the BiOBr efficiently inhibit the production of toxic by-product NO2 during the photocatalytic NO oxidation

In this study, bismuth nanoparticles (NPs) are reduced in-situ on the BiOBr surface to enhance the electron transfer rate. The formation of Bi NPs is directly confirmed by characterizations such as XRD, TEM and XPS. Meanwhile, UV–Vis, PL characterization analysis and DFT theoretical calculation suggest that Bi NPs not only broaden the photoresponse range but also form a fast charge-transfer channel with the BiOBr. The results demonstrate that the NO removal rate of the optimal sample (BiOBr-1.5) is about 48.93%, which is 6.5 times that of the original BiOBr, and almost no toxic by-product NO2 is produced. This study provides a valuable strategy for designing photocatalysts that remove NO while effectively suppressing toxic by-products.

Remarkable improvement in photocatalytic activity of g-C3N4 for NO oxidation through surface hydroxylation

The nitrogen oxide emissions originating from combustion pose significant risks to the environment. Photocatalysis is considered an efficient and environmentally friendly strategy to alleviate this problem. Graphitic carbon nitride (g-C3N4) is regarded as one of the most promising organic photocatalytic materials for environmental purification. However, its small specific surface area, weak adsorption and high recombination rate of charge carriers result in low intrinsic photocatalytic activity. To overcome these obstacles, a hydrothermal treatment of dicyandiamide-derived g-C3N4 (DCN) at different temperatures (140–200 °C) was employed to enhance the photocatalytic activity for NO oxidation. The experimental results demonstrated a significant improvement in the photocatalytic oxidation removal rate of NO after a hydrothermal treatment. The optimal photocatalyst, DCN-180, treated at 180 °C, demonstrated the highest NO removal efficiency (65.0 %), which is twice the value of pristine DCN (32.5 %). Additionally, the formation of the toxic intermediate NO2 was effectively suppressed during the reaction. Photoelectrochemical tests revealed that DCN-180 exhibited higher photocurrent density and smaller impedance radius compared to the untreated g-C3N4 sample. Moreover, density functional theory (DFT) calculations confirmed that the DCN-180 sample showed a stronger ability to adsorb O2 and NO. The enhanced photocatalytic NO oxidation performance of DCN-180 has been primarily attributed to its enlarged specific surface area (from 10.7 to 35.5 m2 g−1), local polarization effect, reduced interfacial charge transfer resistance, and improved adsorption abilities for NO and O2 molecules. This study provides valuable insights for designing and preparing highly efficient g-C3N4 based photocatalysts through surface modification for photocatalytic NO purification.

Efficient photocatalytic decomposition of NO and mechanism insight enabled by NaBH4-reduced N(ligancy-3)-vacancy-rich-graphitic carbon nitride

Vacancy defect engineering is an effective means to improve the performance of g-C3N4 photooxidation for NO removal. In this paper, flake graphite-phase g-C3N4 is prepared by thermal polycondensation. Then g–C3N4–x (x = 0, 0.5, 1.0, 1.5, and 2.0) containing various amounts of vacancies of nitrogen atoms with (3 coordination number) ligancy 3 (N(ligancy-3)) was prepared by NaBH4 reduction at room temperature. The introduction of N vacancies in g-C3N4 narrowed the forbidden gap, enhanced optical absorbance, optimized photo exciton separation and migration, and functioned as traps to mitigate the recombination of photogenerated electron-hole pairs. As a result, g–C3N4–x shows a superior NO removal performance, especially g–C3N4–1.5, which exhibits a high NO removal rate of 66.7 %, excellent resistance to the by-product NO2, and excellent stability. The free-radical seizure experiments and electron paramagnetic resonance (EPR) studies proved the superiority of superoxide radicals, electrons and holes as the prominent free radicals in the photocatalytic NO removal process. In situ diffuse infrared Fourier transform spectroscopy (DRIFTS) confirmed that the cis-dimer (NO)2 produced from NO adsorption on the surface of g–C3N4–1.5 is an important intermediate. Additionally, NO2− is observed as an intermediate and a primary product, and NO3− is identified as the key product of NO photocatalytic oxidation. DFT calculations showed that the N(ligancy-3) vacancy introduces impurity energy levels in g-C3N4 and shortens the electron migration path. The adsorption calculation of NO demonstrated that g–C3N4–N(ligancy-3) exhibits good adsorption and conversion of NO. This study provides a practical defect engineering for the g-C3N4 to remediate environmental pollution.

Ammonia-free selective catalytic reduction of NO by coal-based activated carbon supported Cu-Mn oxides at low temperature

Selective catalytic reduction of ammonia is the most widely technology for removing NOx, but there were serious ammonia leakage and high temperature reaction. To overcome these limitations, a series of Cu and Mn metals supported on coal-based activated carbon (CuxMny/CAC) were synthesized, for ammonia-free catalytic reduction of NO at low temperature. The results demonstrated that Cu and/or Mn catalysts significantly improved low-temperature SCR performance and char-NO reaction selectivity when combined with CAC. In particular, Cu6Mn4/CAC showed excellent NO removal rate (100 %) and higher char-NO selectively (111.21 mg/g) at 290 ℃ under O2-rich condition. Characterization analyses revealed that Cu6Mn4/CAC had a larger BET surface area and preferable pore structure, and the synergistic effect mainly came from the redox cycle between CuOx and MnOy, as well as the interaction between Cu-Mn oxides and the CAC support. Cu-Mn metals promote the adsorption of NO and O2 in the char-NO process, leading to the generation of abundant surface adsorption oxygen species (O2-, O22-, and O-) and C(O) complex, which facilitated the char-NO reaction. Therefore, a mechanism for ammoniac-free selective catalytic reduction of NO by Cu6Mn4/CAC was proposed. These finding provide new insights for developing low-temperature ammonia-free denitrification technology and improving high-value utilization of coal resources.

Atomically dispersed magnesium enhancing reactive oxygen species generation over g-C3N4 nanosheets for efficient photocatalytic NO removal

Photoinduced reactive oxygen species (ROSs)-involving nitrogen oxide (NOx) abatement offers a green way to mitigate environmental air pollution. Developing cost-effective photocatalysts remains challenging yet crucial. Herein, an atomically dispersed Mg-modified g-C3N4 nanosheet photocatalyst (xMg-CN) with excellent photoactivity is developed. The 1.0Mg-CN sample delivers a high NO removal rate of 52.3% under visible light irradiation within 30 min, far surpassing the Mg-free analog (CN, 41.2%). Moreover, a suppressed NO2 by-product discharge can be achieved. The introduction of Mg single atoms (SAs) alters the charge density distribution on the triazine ring plane of g-C3N4, inducing the formation of a built-in electric field, which improves the photoexcited charge carrier separation. Additionally, Mg SAs contribute to the adsorption and activation of O2 molecules, resulting in enhanced ROSs production, as evidenced by the experiments and theoretical simulations. The findings shed light on the role of SAs in designing highly efficient g-C3N4-based photocatalysts for air purification.

Efficient adsorption of NO onto K, Na-embedded porous carbon material prepared by using zinc-bearing dust as activator

The increasingly generation of NO-containing flue gases and zinc-bearing dusts has posed huge pressure to the environment. A green process of integration of reduction of zinc-bearing dusts and preparation of porous carbon material with high NO adsorption capacity was developed and its mechanism was clarified in this paper. The reduced dusts with high content of iron (70.52 %) and low contents of harmful elements (0.017 % Zn, 0.015 % K and 0.026 % Na) could be used as high-quality raw material for ironmaking while the K, Na-embedded porous carbon material (APC) with surface area of 390.38 m2/g can be used as effective adsorbent for NO pollution control. The adsorption property and mechanism of NO on APC was investigated. It was found that the maximal removal rate of NO could reach 96.15 %, and the K, Na on porous carbon material could promote the chemisorption process of NO and increase the NO adsorption efficiency of APC. The hazardous waste was successfully utilized to treat the flue gas in this work.

Strongly reducing NaHS regenerates Fe(II)EDTA for efficient NO removal with high cycling performance under high oxygen conditions

Fe(II)EDTA can remove NO efficiently, but it has not been industrially applied. This is because the oxygen present in the flue gas will oxidize Fe(II)EDTA and Fe(II)EDTA-NO to Fe(III)EDTA and deactivate them. In order to solve this problem, this paper innovatively proposes to use NaHS to reduce Fe(III) EDTA, because NaHS has high reducing ability and low price. Therefore, a series of experimental conditions were explored in order to obtain the best reaction setup. The results indicate that increasing the concentrations of NaHS, temperature, and pH enhances the rate of NaHS reduction. The mechanism of the increase in reduction rate was studied in depth using potentiometric titration. It was found that an increase in OH- concentration will generate S8 precipitate, which is beneficial to the forward progress of the reaction and promotes the large-scale production of the active component Fe2+. Oxygen is an inevitable factor in actual flue gas, so this study innovatively proposed a kinetic model under aerobic conditions and used this model to predict the trend of Fe(III)EDTA reduction by NaHS. On this basis, NO removal experiments were conducted under high oxygen conditions. After 15 cycles, the reduction performance of NaHS was still very high, and the NO removal rate was higher than 70%. The reason for this phenomenon is that the stabilizer exists in a form that is conducive to the removal of NO by the active component Fe2+. Therefore, this study provides theoretical guidance for promoting the industrial application of Fe(II) EDTA technology for NO removal.

Regulation of oriented NO photooxidation to circumvent NO2 with high-coordinated M–N5 (M = Fe, Co, Mn, Ti) sites and far–carbon defects

The targeted oxidization of trace NO to NO3- instead of toxic NO2via photocatalytic process represents one of the promising protocols for assuring environmental benefits. A novel type of graphite carbon nitride (CN) photocatalysts with high coordination sites (M–N5; M = Fe, Co, Mn, Ti) and far–carbon defects were manufactured by reconstructing the low coordination structure (M–N4). The mingled characterizations and theoretical calculations demonstrated that the reconstructed sites could improve the charge and energy transfer process of the exciton to precisely regulate the activation process of O2, while inhibiting the activation of adsorbed H2O. Superior orientation to form superoxide radical and singlet oxygen, rather than hydroxyl radical, showed excellent NO removal rates (68.6%) and superior NO3- selectivity (about 100%) under visible–light irradiation. This work proposes a unique mechanism via tailored construction of highly coordinated structures for selective NO oxidation to achieve the goal of atmospheric purification.

Remarkable Enhancement of Photocatalytic Activity of High-Energy TiO2 Nanocrystals for NO Oxidation through Surface Defluorination.

The superior photocatalytic activity of TiO2 nanocrystals with exposed high-energy (001) facets, achieved through the use of hydrofluoric acid as a shape-directing reagent, is widely reported. However, in this study, we report for the first time the detrimental effect of surface fluorination on the photoreactivity of high-energy faceted TiO2 nanocrystals towards NO oxidation (resulting in a NO removal rate of only 5.9%). This study aims to overcome this limitation by exploring surface defluorination as an effective strategy to enhance the photocatalytic oxidation of NO on TiO2 nanocrystals enclosed with (001) facets. We found that surface defluorination, achieved through either NaOH washing (resulting in an improved NO removal rate of 23.2%) or calcination (yielding an enhanced NO removal rate of 52%), leads to a large increase in the photocatalytic oxidation of NO on TiO2 nanocrystals with enclosed (001) facets. Defluorination processes stimulate charge separation, effectively retarding recombination and significantly promoting the production of reactive oxygen species, including superoxide radicals (·O2-), singlet oxygen (1O2), and hydroxyl radicals (·OH). Both in situ diffuse reflectance infrared Fourier-transform spectroscopy and density functional theory calculations confirm the higher adsorption of NO after defluorination, thus facilitating the oxidation of NO on TiO2 nanocrystals.

Performance and microbial response to nitrate nitrogen removal from simulated groundwater by electrode biofilm reactor with Ti/CNT/Cu5-Pd5 catalytic cathode.

To enhance the removal of nitrate nitrogen (NO3 - -N) in groundwater with a low C/N ratio, electrocatalytic reduction of NO3 - -N has received extensive attention since its electrons can be directly produced in situ while simultaneously providing a clean electronic donor of hydrogen for denitrifying bacteria. In this study, Ti/CNT/CuPd bimetallic catalytic electrodes with different copper-palladium (CuPd) ratios were prepared by electrodeposition onto carbon nanotube (CNT) using titanium (Ti) plates. The results showed that the NO3 - -N conversion rate by Ti/CNT/Cu5-Pd5 electrode was the highest (53.60%) compared with other CuPd electrode ratios because of the combined role of the copper's high NO3 - -N catalytic activity and the palladium's high N2 selectivity. A new type of electrode biofilm reactor (EBR) with Ti/CNT/Cu5-Pd5 cathode, biochar substrate was constructed to explore the removal ability of NO3 - -N in simulated low C/N groundwater. When the influent NO3 - -N concentration was 30 mg/L, under the condition of a 30 mA electronic current and hydraulic retention time (HRT) of 12 h, the removal rate of NO3 - -N could reach as high as 78.1 ± 1.2%, and the N2 conversion rate was 99.7%. The horizontal distribution of microbial communities in EBR showed that the denitrification capacity was significantly improved through the electrochemical catalytic reduction of the Ti/CNT/Cu5-Pd5 cathode and the supply of the hydrogen electron donor to autotrophic denitrogenerating microbes such as Anaerobacillus, Thauera, and Hydrophaga. This study provides a new bimetallic catalytic cathode to enhance the removal of NO3 - -N in groundwater with a low C/N ratio. PRACTITIONER POINTS: The Cu5Pd5/CNTs/Ti electrode is beneficial to the adsorption and reduction of NO3 - -N to N2 . The production of hydrogen electron donors by cathode promoted nitrogen degradation. Activated electrodes together with denitrifying microorganisms contributed to the improved N removal rate.

A novel method for enhancing nitrogen removal from wastewater treatment plant tailwater by zeolite-supported nano zero-valent iron substrate constructed wetland

The discharge of tailwater from wastewater treatment plants can cause pollution to receiving water bodies. Constructed wetlands (CWs) provide an economical approach to tailwater treatment. However, biological denitrification is limited due to the low bioavailability of carbon (C) relative to nitrogen (N) for denitrification in tailwater. Zeolite-supported nano zero-valent iron (Z-nZVI) and montmorillonite-supported nano zero-valent iron (Mt-nZVI) were prepared and used as substrates in CWs to evaluate their efficiency and mechanism of nitrogen removal from low C:N ratio tailwater. The results suggest that Z-nZVI can convert different forms of inorganic nitrogen to ammonium nitrogen (NH4+–N),which can be subsequently removed by the adsorption via zeolite or montmorillonite. The conversion rate for nitrate (NO3−–N) reached a maximum of 76.5%, electron transfer occurred during the reduction of NO3−–N by Z-nZVI. The removal rates of NO3−–N, NH4+–N, and total nitrogen by the Z-nZVI-substrate CW were 66.42 ± 1.33%, 86.56 ± 0.93%, and 69.92 ± 0.56%, which were, on average, 40.77%, 18.34%, and 35.73% higher than those observed in the CW with traditional gravel substrate. This presents a practical method for improving nitrogen reduction in CWs.

Effect of phosphorus on the performance of sulfur autotrophic denitrification

Autotrophic denitrification, recognized as a biological denitrification method, has garnered increasing interest in the field of ecological water environment denitrification technology. This study focuses on the utilization of the sulfur autotrophic denitrification process for the deep denitrification treatment of wastewater. Furthermore, it investigates the impact of phosphorus on nitrogen removal efficiency and bacterial community structure of sulfur autotrophic denitrification. In the experiment, a column containing an autotrophic denitrification filter with a carbon-sulfur filler was constructed. This study aimed to examine the impact of phosphorus on the initiation and denitrification efficiency of the autotrophic denitrification filter column. High-throughput sequencing was used to examine alterations in the structure of the bacterial community. The experimental findings indicated that the absence of phosphorus in the influent considerably extended the initiation period of the autotrophic denitrification filter column. The average Total Inorganic Nitrogen (TIN) removal rate was determined to be 80.26%, while the effluent exhibited an accumulation concentration of NO2−-N ranging from 7 to 11 mg/L. After the addition of phosphate, the removal rate of NO3−-N in the autotrophic denitrification process increased to more than 97%, with no2−-N accumulation. As the influent phosphorus concentration increased, the ability of the sulfur autotrophic denitrification filter column to resist hydraulic impact load improved. At a NO3−-N concentration of 30 mg/L and Hydraulic Retention Time (HRT) = 2 h, the mean NO3−-N removal rate increased from 73.22% to 81.71%. The concentration of phosphorus affected the quantity and variety of primary bacteria in the sulfur autotrophic denitrification system, as their domination changed from Pseudomonas to Ferritrophicum and Thiobacillus, and from a mixed culture to complete autotrophy.

Establishing rapid charge channel via synergism of oxygen vacancy and interfacial effect to promote stable photocatalytic NO purification

Developing efficient and economical photocatalysts is critical to the practical application of nitrogen oxide (NOx) photocatalytic purification technology. At the same time, the spatial separation and migration of charges were extremely limited by the energy band mismatch and limited adaptability of the heterojunction. Herein, the interfacial effect of AgBr/Bi4O5Br2 heterojunctions with oxygen vacancies (OVs) was established to modify the interface and surface properties for enhance the photocatalytic performance. As a result, the optimal OVs-Bi4O5Br2/AgBr composite exhibited a maximum NO removal rate of 66.4 % (728 ppb → 245 ppb) and high stability for 600 min under visible light. The results show that an internal electric field could be formed by the synergism of the oxygen vacancy and interfacial effect to provide a rapid charge transport channel, which improved the separation efficiency of photo-generated carriers. It also generated abundant reactive oxygen species (ROS), which enhanced the photocatalytic NO purification performance. The present work provided a valuable design strategy for rapid charge transfer-based photocatalysts for pollutant treatment.

Efficient photocatalytic NO removal with inhibited NO2 formation and catalyst loss over sponge-supported and functionalized g-C3N4

Though photocatalytic purification of NO has been widely studied, how to avoid secondary pollution during gas-solid reaction is still a challenge, especially in inhibiting the formation of toxic intermediates (NO2) and avoiding the blow away of powdery photocatalyst. Herein, we proposed a one-step solvothermal method to prepare melamine sponge (MS) supported and functionalized g-C3N4 (CN), which simultaneously realizes the inhibition of NO2 formation and catalyst loss. Sodium hydroxide, which plays a dual role, has been introduced during the preparation of supported photocatalyst. Specifically, sodium atom, as the modifier of performance, could facilitate the randomly distributed charge of pristine CN to be converged, which accelerates the adsorption/activation of reactants for efficient and deep NO oxidation. Hydroxyl group, as the binder between CN and MS, induces the interaction by forming hydrogen bonds, which contributes to the firm immobilization of powdery photocatalyst. The supported sample exhibits outstanding NO removal rate (58.90%) and extremely low NO2 generation rate (1.41%), and the mass loss rate of photocatalyst before and after reaction is less than 1%. The promotion mechanism of performance also has been elaborated. This work takes environmental risks as a prerequisite to propose a feasible strategy for perfecting the practical application of photocatalytic technology.

Removal of Nitrate Nitrogen from Municipal Wastewater Using Autotrophic Denitrification Based on Magnetic Pyrite

As the problem of eutrophication of water bodies and nitrate pollution of surface and groundwater is becoming more and more prominent, deep denitrification of wastewater can effectively reduce the amount of nitrate nitrogen (NO3−-N) discharged into natural water bodies. To solve this problem, in this research, the autotrophic denitrifying bacteria were incorporated in an autotrophic denitrification simulator equipped with magnetic pyrite to remove NO3−-N and total nitrogen (TN) from wastewater. The purified strains were inoculated into municipal sewage. When the ratio of magnetic pyrite to quartz sand was 1:1 and the particle size of the filler was 0.5–1 mm, the removal rate of NO3−-N and TN was optimized, at 93.52% and 83.22%, respectively. Sulphate (SO42−) concentrations will level off during stable system operation, and SO42− concentrations show a positive correlation with NO3−-N and TN removal. The 16s rDNA sequencing analysis of the screened sludge showed that the main phyla in the screened and purified sludge were Epsilonbacteraeota and Proteobacteria, with an abundance of 65.83% and 26.88%, and the final enriched products were dominated by Sulfurimonas and Thiobacillus, with an abundance of 64.91% and 9.32%, respectively. The results showed that autotrophic denitrifying bacteria could be screened and purified using thiosulfate as a substrate, and that the use of magneto pyrite as an electron donor reduced most of the NO3−-N to N2, while reducing the TN content.

Promoting the photocatalytic NO oxidation activity of hierarchical porous g-C3N4 by introduction of nitrogen vacancies and charge channels

Sluggish charge kinetics and moderate adsorption–desorption ability of gas molecules are major limitations for photocatalytic NOx elimination of bulk g-C3N4. A hierarchical porous g-C3N4 photocatalyst modified with N vacancies and charge channels (KCNN) was prepared by thermal polymerisation in KCl medium followed by quenching to increase the photocatalytic efficiency. The optimized KCNN sample exhibits highly enhanced photocatalytic NO removal rate (70.5%), which is superior to those of bulk g-C3N4 (38.1%), porous g-C3N4 (54.5%) and K-doped g-C3N4 (58.6%), respectively. X-ray photoelectron spectroscopy and electron paramagnetic resonance data reveal the successful formation of N vacancy in g-C3N4 framework. The enhanced activity of KCNN is ascribed to the enlarged surface area, expanded light absorption, low charge recombination efficiency and strong oxidation capability, respectively. In situ DRIFTS and density functional theory results suggest that the introduction of N vacancies and K+ ions enable control over NO adsorption and activation, leading to the implementation of a preferred pathway (NO → NO+ → NO3‾) and reduction in the emission of toxic intermediates. This work presents a potential idea for improving the charge transfer of layered materials and optimising the diffusion/adsorption/activation of gas molecules for photocatalytic NO oxidation.

W18O49/crystalline g-C3N4 layered heterostructures with full solar energy harvesting towards efficient H2O2 generation and NO conversion

The photocatalytic performance of graphitic carbon nitride (g-C3N4) heterostructures related to the charge carrier separation and transport efficiency is often governed by the interfaces. Herein, in-situ growth of W18O49 nanobelts is attained on amorphous and crystalline g-C3N4 nanosheets to study the effects of the interfaces on photocatalytic oxidation activities. The horizontal growth of W18O49 on g-C3N4 nanosheets is the key in formation of two dimensional (2D)/2D W18O49/g-C3N4 heterostructures. The growth of W18O49 nanobelts on crystalline g-C3N4 nanosheets shows well-developed interfaces (sample W18O49-CCN) in comparison with heterostructures constructed using amorphous g-C3N4 base (sample W18O49-ACN). Characterizations on the structure, components, and properties of the samples demonstrate that these heterostructures reveal extended photo-absorption in visible to near infrared region, with sample W18O49-CCN showing much higher photogenerated charge carrier separation and transport efficiency. A H2O2 evolution rate of 5550 µMg−1h−1 is observed for sample W18O49-CCN under full solar-spectrum illumination (and 398 µMg−1h−1 observed for pristine crystalline g-C3N4), which is ∼ 2.4 times of that of sample W18O49-ACN prepared using amorphous g-C3N4. In addition, a NO removal rate of 72.1% is observed for sample W18O49-CCN with a NO2 selectivity of 6.2%. These results provide inspiration for construction of g-C3N4 homojunctions for practical photo-redox reaction applications.