Low Concentrations Of NO Research Articles

Photocatalytic NO Removal by Ternary Composites Bi12GeO20/BiOCl/W18O49 Using a Waste Reutilization Strategy

Heterojunction creation is demonstrated as an effective strategy to enhance the transfer and separation of charge carriers, which is beneficial for subsequent photocatalytic reactions. In this study, “sea urchin-like” W18O49 was in situ-grown on the surface of Bi12GeO20 through a hydrothermal process, and the released Cl− anions tended to produce BiOCl simultaneously. Systematical characterizations confirmed the construction of ternary composites Bi12GeO20/BiOCl/W18O49 (GBW), in which Type I and Z-scheme models were integrated to promote charge carrier migration and separation by combining the structural merits of both models. Under UV–visible light, the catalytic performance of the as-synthesized samples was tested in terms of NO oxidation removal. Compared to pure Bi12GeO20, the composite GBW5 showed the highest NO photocatalytic removal efficiency of 42%, which was nearly four times that of pure Bi12GeO20. These improvements were mainly due to enhanced light absorption, suitable morphological features, effective separation of charge carriers, and the boosted generation of reactive species in the GBW series. This study paves the way for the construction of Bi12GeO20-based ternary composites using a comprehensive utilization of waste method and the employment of the composites for the photocatalytic removal of low concentrations of NO at the ppb level.

A photocatalytic superhydrophobic coating with p-n type BiOBr/α-Fe2O3 heterojunctions applied in NO degradation.

Coal combustion generates soot-type air pollution, and NO, as a typical pollutant, is the main haze-causing pollutant. The degradation of NO by means of photocatalytic superhydrophobic multifunctional coatings is both durable and economical. The precipitation method was employed to create a p-n type BiOBr/α-Fe2O3 photocatalytic binary system. BiOBr/α-Fe2O3 nanoparticles were combined with polydimethylsiloxane (PDMS) in a butyl acetate solution to produce a BiOBr/α-Fe2O3/PDMS/butyl acetate emulsion, and photocatalytic superhydrophobic coatings were then prepared using a one-step cold-spraying method. Photocatalytic oxidation experiments were conducted using a low concentration of NO as the targeted degradant. The results indicate that BiOBr/α-Fe2O3 photocatalytic heterojunctions were successfully prepared with NO removal up to 65%, indicating that the formation of p-n type heterojunctions enhances the light absorption range and improves the separation of photogenerated charge carriers. Furthermore, when the mass ratio of photocatalytic material to PDMS is 30 : 1, the photocatalytic superhydrophobic coating exhibits optimal performance, attaining a contact angle of 159.55° and NO degradation rate of 70.9%. The study also found that the photocatalytic superhydrophobic coating remained stable after undergoing cyclic degradation, acid and alkali resistance tests, and self-cleaning tests. The mechanism of photocatalytic superhydrophobic coatings was further explored, which provided new insights and a theoretical foundation for the development of self-cleaning urban environments.

Room Temperature NO2-Sensing Properties of N-Doped ZnO Nanoparticles Activated by UV-Vis Light.

Zinc oxide nanoparticles (ZnO NPs) with varying levels of nitrogen (N) doping were synthesized using a straightforward sol-gel approach. The morphology and microstructure of the N-doped ZnO NPs were examined through techniques such as SEM, XRD, photoluminescence, and Raman spectroscopy. The characterization revealed visible changes in the morphology and microstructure resulting from the incorporation of nitrogen into the ZnO lattice. These N-doped ZnO NPs were used in the fabrication of conductometric gas sensors designed to operate at room temperature (RT) for detecting low concentrations of NO2 in the air, under LED UV-Vis irradiation (λ = 400 nm). The influence of nitrogen doping on sensor performance was systematically studied. The findings indicate that N-doping effectively enhances ZnO-based sensors' ability to detect NO2 at RT, achieving a notable response (S = R/R0) of approximately 18 when exposed to 5 ppm of NO2. These improvements in gas-sensing capabilities are attributed to the reduction in particle size and the narrowing of the optical band gap.

Highly Sensitive and Selective SnO2-Gr Sensor Photoactivated for Detection of Low NO2 Concentrations at Room Temperature.

Chemical nanosensors based on nanoparticles of tin dioxide and graphene-decorated tin dioxide were developed and characterized to detect low NO2 concentrations. Sensitive layers were prepared by the drop casting method. SEM/EDX analyses have been used to investigate the surface morphology and the elemental composition of the sensors. Photoactivation of the sensors allowed for detecting ultra-low NO2 concentrations (100 ppb) at room temperature. The sensors showed very good sensitivity and selectivity to NO2 with low cross-responses to the other pollutant gases tested (CO and CH4). The effect of humidity and the presence of graphene on sensor response were studied. Comparative studies revealed that graphene incorporation improved sensor performance. Detections in complex atmosphere (CO + NO2 or CH4 + NO2, in humid air) confirmed the high selectivity of the graphene sensor in near-real conditions. Thus, the responses were of 600%, 657% and 540% to NO2 (0.5 ppm), NO2 (0.5 ppm) + CO (5 ppm) and NO2 (0.5 ppm) + CH4 (10 ppm), respectively. In addition, the detection mechanisms were discussed and the possible redox equations that can change the sensor conductance were also considered.

The influence of NOx, temperature, wind and total radiation on the level of ozone concentration in the Upper Silesian agglomeration

In 2019, ozone was responsible for about 365,000 premature deaths worldwide (6.21 million healthy life years lost) and acute ozone exposure led to 16,800 premature deaths in the European Union. The aim of the study was to estimate the influence of NO, NO2, wind direction (WD) wind speed (WS), air temperature (TA), and total radiation (GLR) on ozone concentration levels. Data provided by 3 automatic air quality monitoring stations of the Regional Environmental Protection Inspectorate in Katowice, were used in this study. The measurements were conducted in from January 1 2009 to December 31 2017. The data obtained from the measuring stations were statistically analysed. The study showed that the strongest influencing factors for O3 values are air temperature and total radiation, with each showing a high correlation with ozone concentration. NO and NO2 had a dual effect on O3 concentration, causing an increase in ozone concentration at low NO and NO2 concentrations and a decrease in ozone concentration at higher NO and NO2 concentrations. We noted that the direction of the wind had very little effect on the concentration of O3. The influence of wind speed on the O3 level was also small, but stronger than that of the wind direction. The research shows that in the analysed years for selected measuring stations the strongest factors influencing O3 concentration are air temperature and total radiation, the NO and NO2 concentrations had a dualistic effect on the O3 concentration.

Engineering an Ultrafast Ambient NO2 Gas Sensor Using Cotton-Modified LaFeO3/MXene Composites.

This work presents a room-temperature (RT) NO2 gas sensor based on cotton-modified LaFeO3 (CLFO) combined with MXene. LaFeO3 (LFO), CLFO, and CLFO/MXene composites were synthesized via a hydrothermal method. The fabricated sensor, utilizing MXene/CLFO, exhibits a p-type behavior and fully recoverable sensing capabilities for low concentrations of NO2, achieving a higher response of 14.2 times at 5 ppm. The sensor demonstrates excellent performance with a response time of 2.7 s and a recovery time of 6.2 s, along with notable stability. The sensor's sensitivity is attributed to gas interactions on the material's surface, adsorption energy, and charge-transfer mechanisms. Techniques such as in situ FTIR (Fourier transform infrared) spectroscopy, GC-MS (gas chromatography-mass spectroscopy), and near-ambient pressure X-ray photoelectron spectroscopy were employed to verify gas interactions and their byproducts. Additionally, finite-difference time-domain simulations were used to model the electromagnetic field distribution and provide insight into the interaction between NO2 molecules and the sensor surface at the nanoscale. A prototype wireless IoT (Internet of Things)-based NO2 gas leakage detection system was also developed, showcasing the sensor's practical application. This study offers valuable insight into the development of room-temperature NO2 sensors with a low detection limit.

Plasmonic Au-enabled photoenhanced room temperature NO2 sensing of 2D SnS2-heterostructure via single-step mechanochemical synthesis

The development of high-performance gas sensors for NO2 detection is critical due to its harmful effects on human health and environment. Tin disulfide (SnS2), with its layered structure akin to transition metal dichalcogenides (TMDs), shows potential for NO2 sensing. However, SnS2-based sensors typically exhibit weak response and incomplete recovery at room temperature. In this study, we propose 2D SnS2 nanosheets modified with gold nanoparticles (Au-NPs) by a single-step mechanochemical synthesis, in which photoelectric sensors depend on the light absorption properties of the sensitive material, thus Au-NPs with LSPR effect coupled with SnS2 can enhance the absorption capacity of the composite in the UV light band. The higher light absorption efficiency means that more electrons and holes can be produced under light excitation, and the holes can react with the NO2 adsorbed on the surface of the material, speeding up the desorption of NO2. As compared to the unmodified SnS2 sensor, the response values of Au/SnS2 sensor to 10 ppm NO2 at room temperature increased from 7.74 to 16.01, while the response/recovery time reduced from 169/201 s to 98/154 s. Moreover, the Au/SnS2 sensor can detect low concentrations of NO2 (50 ppb) with excellent repeatability, selectivity, and long-term stability at room temperature. This study demonstrates that integrating Au-NPs modification with UV photo-assistance is a viable strategy for developing high-performance room temperature gas sensors.

Indoor Air Quality Monitoring System with High Accuracy of Gas Classification and Concentration Prediction via Selective Mechanism Research.

The efficacy of sensors, particularly sensor arrays, lies in their selectivity. However, research on selectivity remains notably obscure and scarce. In this work, indoor pollutants (C7H8, HCHO, CH4, and NO2) were chosen as the target gas. Following the screening of six oxides from previous work, temperature-programmed desorption/reduction experiments were conducted to delve into the origins of selectivity. The results explicate the superiority of NiO in detecting toluene and unveil the distinctive NO2 sensing mechanism of WO3 sensors. Based on the sensor array comprising these oxides, it can clearly detect low concentrations of C7H8 (S = 1.6 to 50 ppb), HCHO (S = 1.4 to 50 ppb), and NO2 (S = 3.3 to 50 ppb), which satisfies the requisites of indoor air monitoring. Meanwhile, three machine learning models (Extreme Gradient Boosting, Support Vector Machine, and Back Propagation Neural Network) are employed for gas classification. The classification accuracies of these models are 95.45%, 100%, and 100%, while the R2 values of the concentration prediction are 99.65%, 94.9%, and 98.04%, respectively, indicating the rationality of material selection. Furthermore, it can still achieve relatively high accuracy in gas classification (94.12%) and concentration prediction (89.36%), even for gas mixtures of four gases. Finally, an indoor air quality monitoring system is developed, which enables real-time monitoring of indoor gas quality through the Internet of Things.

Insights into the enhancement of trace level NO2− on 2,4,6-tribromophenol degradation in UV/PS process: Experimental study and theoretical calculation

Sulfate radical (SO4−)-based UV/persulfate (PS) process is extensively studied to remove organic pollutants in water, while the wide presence of nitrite (NO2−) in natural water can quickly react with SO4− and hydroxyl radicals (OH) to form reactive nitrogen species (RNS). In this study, the degradation of 2,4,6-tribromophenol (TBP) in UV/PS process in the presence of low concentration of NO2− was systematically investigated through experimental studies and theoretical calculations. The introduction of trace NO2− enhanced the TBP degradation by UV/PS process due to the formation of RNS (such as NO2 and BrNO2) and both RNS and SO4− played the important role in the pH range of 6.0–8.0. TBP was more easily photolyzed under alkaline conditions due to higher photodegradation coefficient at pH 8.0. When TBP underwent deprotonation, the reaction energy barrier of TBP with SO4−, OH and NO2 significantly decreased and subsequent debromination may be more likely to occur. Additionally, NO2 attacked ionized TBP at relatively high rate mainly through electron transfer. The degradation pathways of TBP mainly involved in the debromination, hydroxylation and nitrosylation and the generated products all presented lower toxicity than TBP. Moreover, the effects of PS dosage, NO2− concentration, humic acid, bicarbonate and chloride on TBP elimination also were thoroughly assessed. The presence of low concentration of NO2− reduced the toxicity risk caused by the formation of trihalomethanes (THMs) and haloacetic acids (HAAs) during the chlorination process after UV/PS pre-oxidation. This study broadens the knowledge of trace NO2− enhancing organic pollutants degradation by UV/PS process.

Graphene oxide-mediated polymorphic engineering of In2O3 for boosted NO2 gas sensing performance

Nitrogen dioxide (NO2) is a serious menace to human health and the environment, it is of great practical meaning to develop a fast and accurate gas sensor for monitoring low-concentration NO2 at near room temperature (RT). Here, the polymorphism of In2O3 was regulated with controllable mixed-phase ratios of hexagonal In2O3 (h-In2O3) and cubic In2O3 (c-In2O3) via a graphene oxide (GO)-mediated solvothermal approach and annealing treatment. The GO-mediation markedly promoted the formation of h-In2O3 and defect content. The morphology, specific surface area, surface chemical state and activation energy were roundly analyzed. The NO2-sensing performance results showed that the sensor based on an 8 wt% GO-mediated In2O3 sample (In2O3-8) exhibited an ultrahigh response of 1021 towards 1 ppm NO2 at 30℃, which was 2.3 times higher than that of In2O3 without GO-mediation. At the same time, the response/recovery time of In2O3-8 was significantly shorter than other sensors. Additionally, the In2O3-8 sensor possessed good repeatability and long stability. In2O3-8 with an appropriate GO-mediated content provided a suitable h-In2O3/c-In2O3 phase junction interface, abundant oxygen vacancies and elevated Fermi energy levels of In2O3, which activated the surface sites and ultimately enhanced the sensing performance.

Flexible, Breathable and Hydrophobic SnO2–SnS2–SiO2/SiO2 All‐Inorganic Self‐Supporting Nanofiber Membrane for Ultralow‐Concentration NO2 Sensing Under High Humidity

AbstractInorganic semiconductor gas sensors, being widely utilized in gas‐sensing applications, face significant challenges in attaining mechanical flexibility and humidity resistance in wearable sensing fields. Herein, a highly flexible, breathable, and hydrophobic all‐inorganic self‐supporting nanofiber (NF) gas sensor is developed using electrospinning combined with thermal sulfidation approach. This innovative sensor features a bilayer configuration, with an amorphous SiO2 nanofiber substrate layer and an interwoven SiO2 and SnO2–SnS2 nanofiber active layer. The relatively low elastic modulus of the amorphous SiO2 nanofibers, combined with the three‐dimensional network interwoven structure, endow the SnO2–SnS2–SiO2/SiO2 sensor with superior mechanical flexibility. The sensor exhibits excellent sensitivity, selectivity, moisture resistance, and cycling stability (>10 000 cycles at 140° bending) to both high and low concentration NO2. Notably, an excellent flexible detecting capability of the sensor to NO2, an asthma‐related biomarker, is demonstrated at ultralow concentrations (≈25 ppb) in simulated exhaled breath environments. The enhanced moisture resistance is attributed to the effective inhibition of hydrogen bond formation from H2O molecules by the Sn─S bonds formed through sulfidation of SnO2 nanofibers. This work represents a substantial advancement in the universal fabrication of flexible, breathable and moisture‐resistant inorganic semiconductor sensors for wearable breath sensing applications.

Nitrite sensitized photolysis of ibuprofen in the liquid and ice phases: Roles of reactive species and influences of the main dissolved components

This study evaluated the kinetics, mechanisms, toxicity assessment, and influencing factors of ibuprofen (IBP) photolysis induced by nitrite (NO2–) in the liquid and ice phases. The photon-flux-normalized rate constant for IBP photolysis (kIBP*) increased monotonically with increasing NO2– concentrations in the liquid and ice phases. kIBP* in the ice phase was decreased by 21.5–29.9 %, as compared with those obtained with the same NO2– concentration in the liquid phase. Reactive nitrogen species (RNS) contributed more to NO2–-sensitized photolysis of IBP than hydroxyl radicals (•OH) in the liquid and ice phases, and the contributions of RNS to IBP degradation in the ice phase were higher than those in the liquid phase. The NO2–-sensitized photolysis mechanisms of IBP in the ice phase seemed to be similar to those in the liquid phase, including hydroxylation, nitration, nitrosation, decarboxylation, side-chain cleavage and ketonization. The reactions of IBP with RNS were more favored in the ice phase due to higher photon flux, leading to greater generation of photoproducts with higher toxicity. Bicarbonate (HCO3–) inhibited NO2–-sensitized photolysis of IBP. Although dissolved organic matter (DOM) itself could induce IBP photolysis, it exhibited an inhibitory effect on NO2–-sensitized photolysis of IBP. For the real water and ice samples containing low NO2– concentrations (≤ 3.6 μM) and medium DOM concentrations (2.6–5.1 mg C/L), DOM played a more important role in IBP photolysis than NO2– in the liquid phase and particularly in the ice phase. kIBP* for the real samples in the ice phase were 32.1–136.4 % higher than those in the liquid phase.

Integrated electrocatalytic synthesis of ammonium nitrate from dilute NO gas on metal organic frameworks-modified gas diffusion electrodes

The electrocatalytic conversion of NO offers a promising technology for not only removing the air pollutant but also synthesizing valuable chemicals. We design an integrated-electrocatalysis cell featuring metal organic framework (MOF)-modified gas diffusion electrodes for simultaneous capture of NO and generation of NH4NO3 under low-concentration NO flow conditions. Using 2% NO gas, the modified cathode exhibits a higher NH4+ yield and Faradaic efficiency than an unmodified cathode. Notably, the modified cathode shows a twofold increase in NH4+ production with 20 ppm NO gas supply. Theoretical calculations predict favorable transfer of adsorbed NO from the adsorption layer to the catalyst layer, which is experimentally confirmed by enhanced NO mass transfer from gas to electrolyte across the modified electrode. The adsorption layer-modified anode also exhibits a higher NO3− yield for NO electro-oxidation compared to the unmodified electrode under low NO concentration flow. Among various integrated-cell configurations, a single-chamber setup produces a higher NH4NO3 yield than a double-chamber setup. Furthermore, a higher NO utilization efficiency is obtained with a single-gasline operation mode, where the NO-containing gas flows sequentially from the cathode to the anode.

Development of a rapid NO2 gas sensor based on SnO2 nanoparticles synthesized with glycine

Amino acids, as naturally occurring small molecules, have shown potential as materials for gas sensor-assisted synthesis. In this study, we present a novel method based on amino acid templates for the assisted synthesis of small-sized SnO2 nanoparticles at a low temperature of 140℃. Specifically, the Gly/SnO2-2 sample, synthesized with 20 % wt glycine incorporation, exhibited a sensitivity of 22.74 towards a low concentration (3 ppm) of NO2 under UV irradiation at 365 nm, with a rapid response/recovery time of 12/11 s. Remarkably, even under UV-free room-temperature conditions, the sensor continued to respond to NO2. Crystal structure analysis of the material was conducted through scanning electron microscopy (SEM) and transmission electron microscopy (TEM), revealing excellent crystallinity with a particle size of approximately 10 nm. Additionally, BET characterization indicated a well-defined spatial structure with a specific surface area of 58.17 m2/g. Experimental data further demonstrated that the Gly/SnO2-2 displayed good selectivity, reproducibility, and stability. These findings underscore the potential of amino acid templating in advancing gas sensing technologies, offering avenues for the development of highly efficient sensing materials.

Xerogel mesoporous materials based on ultrastable Blatter radicals for efficient sorption of nitric oxide

The reduction of hazardous nitric oxide emissions remains a significant ecological challenge. Despite the variety of possibilities, sorbents able to capture low concentrations of NO from flue gas with high selectivity are still in demand. In this work a new type of mesoporous xerogel material highly loaded with ultrastable Blatter radicals (BTR, >60 % by mass) that act as selective NO sorption sites is developed. Electron Paramagnetic Resonance (EPR) spectroscopy evidences reversible NO sorption in nanometer-scale pores of BTR-based xerogels and indicates the high NO capacity of such radical-rich sorbent. Efficient NO capture from model flue gas mixture is also evidenced in experiments with a fixed bed reactor. Such advanced properties of new materials as selectivity, strong binding with NO and an ability for mild regeneration via thermodesorption promote them for future ecological applications.

Identification of response regulation governing ozone formation based on influential factors using a random forest approach

The pursuit of enhanced scientific, refined, and precise ozone and air quality control continues to pose significant challenges. Using data visualization techniques and random forest (RF) algorithms, the temporal distribution of atmospheric pollutants and the interrelationship between O3 concentration and its influential factors were investigated with one-year monitoring data in Deqing county in 2021. The local atmospheric conditions predominantly belonged to NOx-sensitive and transition zone. Extremely high O3 concentration were primarily observed when temperatures (T) exceeded 30 °C, with relative humidity (RH) ranging between 30 and 60 %. NO2, RH and T were identified as the top 3 important factors, and O3 concentration have stronger linearly relationship to RH and T, while stronger nonlinearly relationship to NO2. By employing an optimized RF model, controlling consistent mild and high reaction atmospheric conditions, the O3 concentration response to the change of individual influencing factors was acquired. The O3 concentration increased and then decreased in response to the increasing NO2 concentration, displaying a characteristic inflection point at 10 μg m−3. More reactive radicals produced at higher VOCs concentration and continuing NOx cycle at lower NO2 concentration, resulting in the acceleration in the direction of producing more O3. Therefore, the significant different O3 response to variation of VOCs and NOx concentration between mild and high reaction atmospheric conditions, as well as the existing of oxidant elevation should be considered in local air quality control. This study demonstrates the efficacy of ML methods in simulating nonlinear response of O3, supports the understanding of local O3 formation and quick guidance for precise local O3 pollution control and the related strategies.

A room temperature NO2 gas sensor based on Rb-doped ZnO/In2O3 nano-heterojunction with high performance

In this study, we prepared Rb-doped ZnO/In2O3 n-n nano-heterojunction, which functioned as highly responsive gas sensors for NO2 at room temperature. The experiments demonstrated a significant enhancement in the gas-sensing capabilities for low concentrations of NO2 at room temperature. ZnO/In2O3 NO2 gas sensors were synthesized with varying concentrations of Rb-doped using a two-step method. Gas-sensing experiments showed that the sensor with 6 mol% Rb-doped exhibited excellent selectivity and remarkable response values to NO2. At a NO2 concentration of 1 ppm, the response value was ten times greater than that of the undoped ZnO/In2O3 sensor, reaching a value as high as 119.5. This exceptional NO2 detection performance can be attributed to several factors. The presence of Rb-doped increased the concentration of oxygen vacancies on the material's surface, leading to a 14 % increase in adsorbed oxygen content compared to the undoped material. Additionally, Rb-doped resulted in a thicker depletion layer on the material's surface, which enhanced charge-transfer density. The band gap of Rb-doped ZnO/In2O3 decreased by 0.21 eV compared to the undoped ZnO/In2O3, enhancing the electron-leaping capability. The combined effects of these sensitization phenomena resulted in a significant improvement in the NO2 detection performance of the Rb-doped ZnO/In2O3 gas sensor.

NO Formation in Combustion Engines Fuelled by Mixtures of Hydrogen and Methane

The present work addresses the production of nitrogen oxides in ICEs burning hydrogen mixed with methane. A mathematical model that allows the calculation of nitrogen oxide emissions from such combustion was built; this model uses the extended chemical kinetic mechanism of Zeldovich. Numerical simulations were carried out on the production of NO, varying the following variables: proportion of H2 to CH4, the equivalence ratio of the reactant mixture, the compression ratio, and the engine speed. The essential purpose was to assess how NO production is affected by the mentioned variables. The main assumptions were (i) Otto cycle; (ii) instantaneous combustion; (iii) chemical equilibrium reached just at the end of combustion; (iv) the formation of NO only during the expansion stroke of pistons. Results were obtained for various proportions of hydrogen and methane, various equivalence ratios, speeds of rotation, and compression ratios of an engine. In short, the results obtained in the current work show that the lowering of the equivalence ratio leads to a lower concentration of NO; that increasing the compression ratio also lowers the concentration of NO; that NO production occurs until shortly after the beginning of the expansion stroke; and finally, that the NO concentration in the engine exhaust is not very sensitive to the H2/CH4 ratio in the fuel mixture.

Study of pyrene-based covalent organic frameworks for efficient photocatalytic oxidation of low-concentration NO

This research presents the development of innovative pyrene-based COFs aimed at enhancing photocatalytic oxidation of low-concentration nitrogen oxide. By precisely modifying the structural length and incorporating additional functional groups into pyrene-based COFs, we identified TAPPy-DMTP-COF as the most effective performer. This COF, characterized by its shortest length and the presence of -OCH3 functional groups, demonstrated superior performance, likely due to reduced electron transfer resistance and the presence of additional oxygen active sites. Building on the potential of TAPPy-DMTP-COF, we developed a covalently linked Type-II heterostructure with g-C3N4. The resulting heterostructure, 40TAPPy-DMTP-COF/g-C3N4, with a 40 % mass fraction of TAPPy-DMTP-COF, was confirmed using SEM, XRD, and other techniques. It exhibited an exceptional photocatalytic efficiency of 45.8 % and NO3- selectivity of 97.4 %. This remarkable performance can be attributed to improved electron communication facilitated by chemical bonding, as confirmed by XPS results. Additionally, the optimized heterostructure interface not only improved electron transfer but also inhibited the recombination of electron-hole pairs. The growth of TAPPy-DMTP-COF on the surface of g-C3N4 significantly enhanced visible light absorption, as confirmed by UV–vis spectroscopy. This study not only underscores the importance of precise control over the structural features of pyrene-based COFs but also introduces a novel approach for enhancing NO oxidation. By constructing a covalently linked Type-II heterostructure, we have significantly enhanced the interface interaction within the heterostructure, leading to superior photocatalytic performance.

Controllable synthesis of heterostructured CuO–ZnO microspheres for NO2 gas sensors

Nitrogen dioxide (NO2) sensors experience the drawback of requiring high operating temperatures because of the low charge transfer ability of gas-sensing materials. Herein, an advanced NO2 sensor resistant to interference is designed using the interfacial energy barriers of a hierarchical CuO/ZnO composite. With the benefits of abundant desirable defect features, and the amplification effect of heterojunctions, the sensor based on CuO/ZnO composite with 10% Cu(CH3COO)2·H2O (S2) shows outstanding performance in terms of faster response and recovery time (1.8-fold/1.1-fold), higher response (3.1-fold), and lower power consumption (140℃ decrease) compared to the pristine ZnO sensor. Furthermore, the composite sensor exhibits long-term stability and reproducibility, indicating the potential promise of CuO/ZnO heterojunctions in interference-resistant detection of low-concentration NO2 in real applications. This study not only provides a rational solution to designing advanced gas sensors by tuning the interfacial energy barriers of heterojunctions, but also provides a fundamental understanding of CuO structures in the gas-sensing field.