Chemisorbed Oxygen Research Articles

Unveiling the promoting mechanism of Mo on the performance of CuCeOx catalyst for simultaneously NH3-SCR denitration and CO oxidation under oxygen-rich conditions

NOx and CO coexisted in numerous actual industrial flue gases. The simultaneous removal of NOx and CO had great potential for application but remained still a challenge. Herein, a series of Mo-modified CuCeOx catalyst was developed to simultaneously achieve NH3-SCR denitration and CO oxidation. The results indicated that the CCM3 catalyst displayed the optimal performance with 91.2 % NOx conversion and 100 % CO conversion as well as excellent long-time stability and SO2 or/and H2O tolerance at 225 ℃. It was found that the strong interaction between Cu, Ce and Mo oxides resulted in the particles highly dispersed with smaller size on catalyst surface, which could provide abundant active sites to decreasing the competitive adsorption among reactive gases. Furthermore, the Mo modification promoted the production of more oxygen vacancies, Ce3+ and Oα species, which facilitated the redox recycle and the generation of intermediates. Moreover, the H2-TPR and NH3/CO/O2-TPD analysis illustrated that the reducibility and the capacity for reaction gas adsorption and activation were enhanced, which improved low-temperature activity. The in situ DRIFTS experiment revealed that the E-R and L-H mechanism were existed in NH3-SCR process on CC and CCM3 catalysts. What’s more, the stronger acidity and strengthened E-R mechanism on CCM3 catalyst hindered the adsorption of SO2 and weakened the inhibition effect of competitive adsorption among SO2 and NO. Additionally, both surface lattice oxygen and chemisorbed oxygen could react with Cu+–CO species to produce CO2, the pathway obeyed L-H and MvK mechanism. This work may provide a novel strategy for the treatment of CO and NOx pollutants in industrial flue gas.

Effect of modified Ca-Al adsorbents on heavy metal fixation during co-combustion of coal and coconut shells: Experiments and simulations

As an alternative fuel, bio-waste coconut shells have shown promise in reducing pollution during the co-combustion process. In this study, a novel metal-mineral adsorbent, Ca-Al (Ca5Al6O14), was prepared and physically (ultrasonic) and chemically (ethylene glycol) modified to enhance its adsorption properties. Thermal adsorption experiments investigated the effect of the adsorbents on the fixation of six heavy metals (HMs): Cr, Cu, Mn, Ni, Pb, and Zn. XRD, SEM, BET, and XPS were used to analyze the adsorbents and the adsorption mechanism was investigated by combining lattice oxygen concentration and Factsage simulation calculations. The ecological risk assessment of heavy metals was used to comprehensively evaluate the fixation effects of the three Ca-Al adsorbents at different additive levels. The results showed that the modification significantly changed the morphological characteristics and oxygen activity of the Ca-Al adsorbents, increased the lattice oxygen and chemisorbed oxygen concentration, and laid the foundation for promoting the chemisorption process in the fixation of heavy metals. In combination with the Er (environmental risk factors), adding all three adsorbents reduced Ri (Risk index). Among them, Ca-Al (EG) at 3% had the best effect on Ri. 3% Ca–Al (EG) reduced the Er value of Ni by 49.02%. 5% Ca–Al (EG) reduced the Er value of Cr by 86.01%. 5% Ca–Al (UM) had the best effect on Mn, with a reduction of 46.13%. The addition of 10% Ca–Al (UM) reduced Er of Ni by 50.43%. Considering the practical application in coal-fired power plants, Ca-Al(EG), which exhibits a higher fixation rate at small additions, is more suitable.

Strong interaction between promoter and metal in Pd-Ba/TiO2 catalysts for formaldehyde oxidation

As our previous works found, alkali metals have a common promotion effect on supported noble metals catalysts for formaldehyde (HCHO) oxidation. As second-group elements, alkaline earth metals (AEMs) are neighbors to the first-group elements and share some properties in common. However, detailed investigations into the specific mechanisms underlying AEMs’ effects on HCHO oxidation remain limited. In this study, we found that Ba addition showed a similar promotion effect on HCHO oxidation for Pd/TiO2. Ba species stabilized Pd groups, improved the dispersion, and even caused a large number of monatomic-like Pd sites to appear, which may be attributed to the electronic interaction between promoter and metal (EIPM) between Ba and Pd. Besides, AEM loading had the important effect of increasing the electron density of metallic Pd nanoparticles, which further improved the ability for O2 activation and so enhanced the mobility of chemisorbed oxygen on the catalyst surface. For Pd/TiO2, the HCHO oxidation path is mainly HCHO→HCOOH→HCOO→H2O+CO2. By contrast, for Pd-Ba/TiO2, with more surface-active species, the formate intermediate was more likely to be directly oxidized into H2O and CO2, which is a more effective reaction pathway. The details of the EIPM between Pd and Ba were investigated by GPAW (DFT calculation module) in ASE (Atomic Simulation Environment). The AEM Ba acted as an electron donor and could interact with Pd d orbital electrons through BaO sp orbital electrons. Ba species were highly dispersed on the carrier due to the Ba-Ti interaction. Ba species dispersed over large areas stabilized the Pd particles and donated electrons to Pd. Therefore, adding an AEM is an efficacious strategy to improve the performance of the catalytic oxidation of HCHO.

Regulation of surface oxygen (OV, OC) and enhancement of triethylamine sensing performance of MOF-derived Co3O4 hollow nanocubes by g-C3N4 coupling

The regulation of oxygen defects and chemisorbed oxygen plays an essential role in the sensing behavior of oxide semiconductor sensors. MOF derivatization and the construction of heterojunction are potential approaches to obtain high-performance sensors. Here, MOF-derived Co3O4 hollow nanocubes coupled with 2-dimensional g-C3N4 were prepared and further applied to triethylamine sensing. XPS results reveal the significant increase of oxygen defects and chemisorbed oxygen in the composite. Calculations of oxygen escape energy show that the construction of oxygen defects mainly originates from the anoxic environment caused by g-C3N4 coating. And calculation of surface models indicates that oxygen vacancies could enhance the interaction and charge transport at the heterointerface, and simultaneously serves as an adsorption site to improve the adsorption and activity of oxygen molecule. Combined with the energy band adjustment, Co d‐band center regulation and diffusion channel resulted from g-C3N4 coupling, the sensor based on the composite shows higher response, faster response speed and better selectivity to triethylamine. This study could provide a reference for the regulation of oxygen defects, chemisorbed oxygen, and the preparation of high-performance sensors.

Study of Mesoporous Zr-TiO2 Catalyst with Rich Oxygen Vacancies for N-Methylmorpholine Oxidation to N-Methylmorpholine-N-oxide.

A series of Zr-TiO2 catalysts were prepared using a facile sol-gel method and were used for N-methylmorpholine (NMM) oxidation to N-methylmorpholine-N-oxide (NMMO). The structure features of Zr-TiO2 catalysts were studied in detail through a variety of characterization methods, such as XRD, SEM, N2 adsorption-desorption isotherms, XPS, EPR, and O2-TPD. As-obtained 5%Zr-TiO2 catalysts had superior catalytic performance and stability with a 97.6% NMMO yield at 40 °C, which related to Zr doping, a higher surface area, more oxygen vacancies, and oxygen chemisorption on the catalytic surface. This work provides an efficient preparation strategy of TiO2-based catalysts for selective oxidation reactions by a facile method.

Insights into the impact of self-contained sulfur impurity on the superior photocatalytic activity of UV100

The commercial Hombikat UV100 is a TiO2 photocatalyst that is less studied and used than Aeroxide P25, resulting in limited knowledge associated to it. In this study, we used ICP-OES, XPS, and TGA analyses to show that UV100 contains non-negligible traces of sulfur as-received, which can be migrated to the surface of TiO2 through a simple calcination treatment. Ionic chromatography, DRIFTS, and pyridine-TPD analyses confirmed that a portion of the surface sulfate after the thermal induced migration can be removed by distilled water, along with associated sodium cations, without impacting the surface chemistry of the photocatalyst. Calcination of UV100 enhanced the photocatalytic activity in the liquid-phase degradation of phenol, paracetamol, and chloramphenicol, and this activity remained relatively unaffected by the leaching of sulfate. Although EPR indicated that surface-bound sulfate might act as electron trapping centers or oxygen chemisorption centers, the primary reason for the improved photocatalytic activity is likely the increased crystallinity of the anatase phase due to high-temperature calcination, aided by sulfur’s retarding effect on the anatase-to-rutile transition.

Role of morphology in improving the catalytic performance of ZnCo2O4 for soot oxidation

The extent of interaction between carbon and catalyst profoundly shapes soot oxidation results. The catalyst configuration notably influences the frequency of contact points in solid–solid interactions. This investigation studies the impact of three distinct ZnCo2O4 catalyst morphologies and their redox property on soot oxidation. The formation of the cubic phase of ZnCo2O4 via three distinct methods was revealed during XRD analysis. SEM analysis unveiled varying morphologies, including rod-shaped, rose petal-shaped, and bead-like structures. Notably, ZnCo2O4 exhibiting bead-like morphology demonstrated heightened levels of chemisorbed oxygen species which was observed during XPS analysis. The presence of Co2+ and Co3+ occupied at octahedral site ZnCo2O4 acted as the active sites for soot oxidation. With continuous redox property (Co 3+ → Co 2+) leading to the generation of active oxygen species and with an added advantage of surface morphology, the M2 sample (with bead-like morphology) exhibited superior soot oxidation activity, which is evident by its T50% value of 402 °C. This study underscores the essential role of catalyst morphology in influencing soot oxidation activity. Through a comprehensive array of structural, morphological, and catalytic analyses, this work sheds light on the correlation between catalyst architecture and enhanced soot oxidation performance.

Novel β-CdSnO3-SnO2 nanorod-like heterostructure materials for enhancing n-butanol sensing

n-butanol detection is crucial to environmental protection and mankind’s health because of its toxicity and irritation to the respiratory system. Mono-metal oxide semiconductors (such as SnO2) often face disadvantages such as low sensitivity, insufficient selectivity, and a high detection limit. Constructing heterojunctions has been considered an efficient way to enhance the performance of MOS gas sensors. This work presents the synthesis of a series of β-CdSnO3-SnO2 nanorod-like heterostructures with good n-butanol sensitivity using a hydrothermal and post-calcination approach. The optimized CSO/SO-8 shows the highest response value about 90–100 ppm n-butanol at 190 °C, which is 15 times greater than that of SnO2, and 6.5 times more than that of β-CdSnO3. Meanwhile, the CSO/SO-8 also exhibits a short response and recovery time (1–2 s/63 s). More importantly, the detection limit is reduced to ppb level (50 ppb). The improved gas-sensitive properties can be explained by the formation of n-n heterojunctions between β-CdSnO3 and SnO2, which increases the content of chemisorbed oxygen, thus enhancing the performance of the gas-sensitive. Our work not only provides a material with n-n heterostructures but also the strategy for constructing heterojunctions to improve gas-sensitive properties.

3DOM Cu-Ce binary composite oxides for selective catalytic reduction of NO with CO

A series of 3DOM Cu-Ce catalysts for CO-SCR were prepared by a colloidal template method. Among these catalysts, 3DOM Cu1Ce1 catalyst exhibited the best CO-SCR performance (about 100 %) in the widest temperature window (450–700 ℃). Notably, this catalyst still showed excellent stability in the presence of H2O and SO2. It was found that the appropriate molar ratio of Cu and Ce could optimize the pores of Cu-Ce catalysts, and increase their specific surface area. This could contribute to the contact between reaction gas and active sites. The stronger synergistic effect between Cu and Ce could be conducive to the increase of chemisorbed oxygen, and then enhance the redox properties. These might be the key factors for the improvement of 3DOM Cu1Ce1 catalytic activity. In addition, the molar ratio of Cu to Ce had a significant influence on the adsorption of CO, which might cause the difference in the consumption of active oxygen and the formation of oxygen vacancies, thus affecting the CO-SCR performance of 3DOM Cu-Ce catalysts.

Boosting DeNOx performance via magnetic enhancement in synergistically-optimized γ-Fe2O3-CuO composite oxides

Fe or Cu oxides and their composites are cost-effective yet seldom used in DeNOx because they deactivate easily. Doping/supporting enhances activity but increases synthesis complexity and cost. Here, we present a γ-Fe2O3-CuO composite oxide with a high synergy created through co-oxidation, which upon magnetization, exhibits further enhanced DeNOx activity. Detailed quasi in-situ XRD and in-situ DRIFTS analyses indicate that in Fe-Cu composite oxides, iron species inhibit the full reduction of Cu2+ to Cu0, while copper counters the formation of inactive α-Fe2O3, contributing to the γ-Fe2O3-CuO composite’s enhanced stability during reactions. Fascinatingly, pre- and post-magnetization XPS and in-situ DRIFTS analyses demonstrate the magnetic field’s role in promoting the chemisorption of both oxygen and NO, thereby enhancing DeNOx efficiency. This research not only achieves the synergistic coupling of copper and iron oxides and sheds light on the deactivation processes of their pure species but also serves as a pioneering exploration of magnetic manipulation in catalyst design, laying a foundation for future technological advancements.

Cobalt-Doped Ceria Sensitizer Effects on Metal Oxide Nanofibers: Heightened Surface Reactivity for High-Performing Chemiresistive Sensors.

Chemiresistive gas sensors based on semiconducting metal oxides typically rely on noble metal catalysts to enhance their sensitivity and selectivity. However, noble metal catalysts have several drawbacks for practical utilization, including their high cost, their propensity for spontaneous agglomeration, and poisoning effects with certain types of gases. As such, in the interest of commercializing the chemiresistive gas sensor technology, we propose an alternative design for a noble-metal-free sensing material through the case study of Co-doped ceria (Co-CeO2) catalysts embedded in a SnO2 matrix. In this investigation, we utilized electrospinning and subsequent calcination to prepare Co-CeO2 catalyst nanoparticles integrated with SnO2 nanofibers (NFs) with uniform particle distribution and particle size regulation down to the sub-2 nm regime. The resulting Co-CeO2@SnO2 NFs exhibited superior gas sensing characteristics toward isoprene (C5H8) gas, a significant biomarker for monitoring the onset of various diseases through breath diagnostics. In particular, we identified that the Co-CeO2 catalysts, owing to the transition metal doping, facilitated the spillover of chemisorbed oxygen species to the SnO2 sensing body. This resulting in the sensor having a 27.4-fold higher response toward 5 ppm of C5H8 (compared to pristine SnO2), exceptionally high selectivity, and a low detection limit of 100 ppb. The sensor also exhibited high stability for prolonged response-recovery cycles, attesting to the strong anchoring of Co-CeO2 catalysts in the SnO2 matrix. Based on our findings, the transition metal-doped metal oxide catalysts, such as Co-CeO2, demonstrate strong potential to completely replace noble metal catalysts, thereby advancing the development of the commercially viable chemiresistive gas sensors free from noble metals, capable of detecting target gases at sub-ppm levels.

Two-dimensional Mo3-TiS2 monolayer hosting high moisture resistance and abundant surface-chemisorbed oxygen for effective detection of SF6 decomposition gases: Atomic-scale study

Monitoring the SF6 decomposition gas (DPA) by gas sensors can be used to predict the operating status of power equipment, and the sensitivity performance of gas sensors is deeply influenced by the humidity resistance and surface oxygen adsorption performance of their sensing materials. The present research aims to explore a high‐valence transition‐metal ion doped transition metal dichalcogenide (TMD) monolayer that hosts high moisture resistance and abundant surface-chemisorbed oxygen suitable for detecting DPA. Using first-principles methods, the adsorption behavior of three representative types of gases (HF, SO2, and CO2) in DPA, H2O, and O2 on Mo3-TiS2 monolayer are considered. Our results show that SO2 and CO2 molecules are adsorbed above the Mo3 cluster through chemical adsorption, while HF molecule is physically adsorbed. The desorption times for SO2 and CO2 on Mo3-TiS2 adsorbent are 9.89 s at 348 K and 34.96 s at 398 K, respectively. Introducing dopant Mo3 resulted in better anti-humidity performance of TiS2, as the force of Mo3-TiS2 monolayer towards H2O molecule is weakened compared to the intrinsic adsorption system. Additionally, Mo3-TiS2 monolayer exhibits an exceptionally high affinity for O2 molecule, leading to the rupture of chemical bond in O2, and the chemisorbed oxygen ions are acquired through the charge transfer between Mo3 cluster and O2 molecule. The computational findings in this article offer theoretical backing for advancing the development of gas sensors utilizing Mo3-TiS2 and its utilization in the realm of DPA detection.

Surface-Modified Ruthenium Nanorods for an Ampere-Level Bifunctional Hydrogen Evolution Reaction/Oxygen Evolution Reaction Electrocatalyst.

The practical applications of bifunctional ruthenium-based electrocatalysts with two active sites of Ru nanoparticles covered with RuO2 skins are limited. One reason is the presence of multiple equally distributed facets, some of which are inactive. In contrast, ruthenium nanorods with a high aspect ratio have multiple unequally distributed facets containing the dominance of active faces for efficient electrocatalysis. However, the synthesis of ruthenium nanorods has not been achieved due to difficulties in controlling the growth. Additionally, it is known that the adsorption capacity of intermediates can be impacted by the surface of the catalyst. Inspired by these backgrounds, the surface-modified (SM) ruthenium nanorods having a dominant active facet of hcp (100) through chemisorbed oxygen and OH groups (SMRu-NRs@NF) are rationally synthesized through the surfactant coordination method. SMRu-NRs@NF exhibits excellent hydrogen evolution in acid and alkaline solutions with an ultralow overpotential of 215 and 185 mV reaching 1000 mA cm-2, respectively. Moreover, it has also shown brilliant oxygen evolution electrocatalysis in alkaline solution with a low potential of 1.58 V to reach 1000 mA cm-2. It also exhibits high durability over 143 h for the evolution of oxygen and hydrogen at 1000 mA cm-2. Density functional theory studies confirmed that surface modification of a ruthenium nanorod with chemisorbed oxygen and OH groups can optimize the reaction energy barriers of hydrogen and oxygen intermediates. The surface-modified ruthenium nanorod strategy paves a path to develop the practical water splitting electrocatalyst.

Study on Novel SCR Catalysts for Denitration of High Concentrated Nitrogen Oxides and Their Reaction Mechanisms

With the rapid development of industrialization, the emission of nitrogen oxides (NOx) has become a global environmental issue. Uranium is the primary fuel used in nuclear power generation. However, the production of uranium, typically based on the uranyl nitrate method, usually generates large amounts of nitrogen oxides, particularly NO2, with concentrations in the exhaust gas exceeding 10,000 ppm. High concentrations of nitrogen dioxide are also produced during silver electrolysis processing and the treatment of waste electrolyte solutions. Traditional V-W/TiO2 NH3-SCR catalysts typically exhibit high catalytic activity at temperatures ranging from 300 to 400 °C, under conditions of low NOx concentrations and high gas hourly space velocity. However, their performance is not satisfying when reducing high concentrations of NO2. This study aims to optimize the traditional V-W/TiO2 catalysts to enhance their catalytic activity under conditions of high NO2 concentrations (10,000 ppm) and a wide temperature range (200–400 °C). On the basis of 3 wt% Mo/TiO2, various loadings of V2O5 were selected, and their catalytic activities were tested. Subsequently, the optimal ratios of active component vanadium and additive molybdenum were explored. Simultaneously, doping with WO3 for modification was selected in the V-Mo/TiO2 catalyst, followed by activity testing under the same conditions. The results show that: the NOx conversion rates of all five catalysts increase with temperature at range of 200–400 °C. Excessive loading of MoO3 decreased the catalytic performance, with 5 wt% being the optimal loading. The addition of WO3 significantly enhanced the low-temperature activity of the catalysts. When the loadings of WO3 and MoO3 were both 3 wt%, the catalyst exhibited the best denitrification performance, achieving a NOx conversion rate of 98.8% at 250 °C. This catalyst demonstrates excellent catalytic activity in reducing very high concentration (10,000 ppm) NO2, at a wider temperature range, expanding the temperature range by 50% compared to conventional SCR catalysts. Characterization techniques including BET, XRD, XPS, H2-TPR, and NH3-TPD were employed to further study the evolution of the catalyst, and the promotional mechanisms are explored. The results revealed that the proportion of chemisorbed oxygen (Oα) increased in the WO3-modified catalyst, exhibiting lower V reduction temperatures, which are favorable for low-temperature denitrification activity. NH3-TPD experiments showed that compared to MoOx species, surface WOx species could provide more acidic sites, resulting in stronger surface acidity of the catalyst.

Preparation of Ni-B/MgAl2O4 catalysts for hydrogen production via steam reforming of methane

In this paper, a series of B doped Ni/MgAl2O4 catalysts for hydrogen production via steam reforming of methane (SRM) were prepared, and their catalytic activities and stability were evaluated. The characterization of XRD, XPS, TPR, BET, TPO, and TEM revealed that the addition of B could promote Ni dispersion, which lead to the reduce of Ni particle size. 0.5 wt% B was incorporated into Ni/MgAl2O4 would increase Ni particle dispersion rate from 11.2% to 14.8%, which caused Ni particle average size was decreased from 8.78 to 6.96 nm. At the same time, 0.5% B doped would increase the chemisorbed oxygen content of the catalyst, and more oxygen vacancies were formed. Thus, Ni particles sintering and carbon deposition during SRM was suppressed, and the catalytic activity and stability were promoted. Ni-B0.5/MgAl2O4 could achieve 90.2% methane conversion rate and 85% H2 yield under 700 °C with a WHSV of 36,000 mL·(gh)−1 during SRM process, and only a marginal reduction (2%) of methane conversion rate was observed after 48 h reaction. The total carbon content on the used Ni-B0.5/MgAl2O4 catalyst was approximately 0.031 gc∙gcat−1, which was three times lower than that of Ni/MgAl2O4. However, the excess B doping into Ni/MgAl2O4 had a negative effect on the catalytic activity and stability.

Regular perovskite SrTiO3 and monoclinic layered perovskite Nd2Ti2O7 for oxidative coupling of methane: Elucidating the role of chemisorbed oxygen species and lattice oxygen

Herein, regular perovskite SrTiO3 and monoclinic layered perovskite Nd2Ti2O7 have been prepared by the sol-gel method and calcined at different temperatures. As the calcination temperature of SrTiO3 increases, the Ti element on their surface is enriched, and the amount of Sr element that provides basic sites is reduced, resulting in a decrease in the number of basic sites on the catalyst surface. For Nd2Ti2O7, its surface is enriched with Nd elements, but the enrichment amount does not change with the increase in calcination temperature, and it contains less surface basic sites less than SrTiO3. Although the enrichment of Ti on the surface of SrTiO3 is conducive to the formation of oxygen vacancies, the oxygen vacancies on the surface of Nd2Ti2O7 are more abundant than those on SrTiO3. The amount of electron-deficient oxygen species on their surfaces is influenced by the presence of basic sites, which make it more favorable to stabilize electrophilic oxygen species. The C2 selective oxygen species are chemisorbed oxygen (O2-, O2δ-, O22-) for SrTiO3 and surface lattice oxygen for Nd2Ti2O7. This is because the [TiO6] octahedra in the crystal structure of SrTiO3 are tightly stacked, whereas the [TiO6] units in the Nd2Ti2O7 structure are loosely stacked, resulting in a weaker Ti-O bond strength in Nd2Ti2O7 compared with SrTiO3. In addition, the lattice oxygen of SrTiO3 has strong basicity, which is beneficial for activating gas-phase oxygen to generate chemisorbed oxygen species and stabilizing them on the catalyst surface, while the nucleophilic lattice oxygen is more likely to cause deep oxidation of methane and coupling products. However, the and basicity of lattice oxygen in Nd2Ti2O7 are weaker than those in SrTiO3, making it more favorable for C2 selectivity.

Direct Work Function Measurement Using in-situ Ambient Pressure X-ray Photoemission Spectroscopy and Its Application on Copper Oxidation Process.

The work function (WF) measurement plays a critical role in engineering energy materials and energy devices. However, the ultra-high vacuum (UHV) environments of photoemission method limit the practical application for absolute work function measurements of materials, especially under complex working conditions. To understand the energy level of materials under complex chemical environments, the in-situ measurements of work function is necessary in complex metal/semiconductor system for various application. In this paper, we describe the utilization of ambient pressure X-ray photoemission spectroscopy (APXPS) with utilization of low photon energy X-ray for absolute WF measurements at BL02B of the Shanghai Synchrotron Radiation Facility. We herein present the WF measurement during oxygen adsorption on Pt(111) and oxidation of Cu(111) in ambient oxygen environment as demonstration of the APXPS capability for WF measurement. After oxygen chemisorption on Pt and formation of Cu2O, the WF will increase. This is due to charge transfer from metal to chemisorbed oxygen atoms. After the formation of bulk Cu2O and CuO, the WF value almost remain at ~5.5 eV. We believe the direct measurement of absolute work function via APXPS could help bridge the gap between the physical properties and the surface chemical species for metal/semiconductor materials.

Plasma-catalytic synergistic oxidation of NO in the non-thermal plasma system: Insight into the active sites effect

Superoxide radicals-dominated oxidation plays a crucial role in the removal of NOx in gas treatment schemes, especially in the catalytic oxidation of NO at room temperature. However, the specific mechanism underlying radical oxidation processes remains unclear. In this study, a series of transitional metal (Mn, Co, Cr) catalysts anchored on graphitic carbon nitride (g-C3N4) were prepared and then introduced into non-thermal plasma (NTP) system to produce highly reactive superoxide free radicals (•O2-) for deep oxidation of NO. Experimental results revealed that the optimized CrCN catalyst, in combination with the NTP technique, exhibited an impressive oxidation efficiency of up to 100 %, which was 10 % and 30 % higher than that of MnCN and CoCN, respectively. Moreover, it was 1.56 times higher than that of NTP alone, indicating a synergistic effect of the NTP system and catalysis. The characterization results demonstrated that CrCN catalyst, with higher specific surface area and smaller grain sizes, was beneficial to increase the chemisorbed oxygen content and produce superoxide free radicals, which were proved by XPS, ESR technologies. Furthermore, the possible catalytic mechanism was proposed, which provided a basis for further understanding of the catalytic oxidation activity.

P-N Heterojunction formation: Metal Sulfide@Metal Oxide Chemiresistor for ppb H2S Detection from Exhaled Breath and Food Spoilage at Flexible Room Temperature.

The development of a portable, low-cost sensor capable of accurately detecting H2S gas in exhaled human breath at room temperature is highly anticipated in the fields of human health assessment and food spoilage evaluation. However, achieving outstanding gas sensing performance and applicability for flexible room-temperature operation with parts per billion H2S gas sensors still poses technical challenges. To address this issue, this study involves the in situ growth of MoS2 nanosheets on the surface of In2O3 fibers to construct a p-n heterojunction. The In2O3@MoS2-2 sensor exhibits a high response of 460.61 to 50 ppm of H2S gas at room temperature, which is 19.5 times higher than that of the pure In2O3 sensor and 322.1 times higher than that of pure MoS2. The In2O3@MoS2-2 also demonstrates a minimum detection limit of 3 ppb and maintains a stable response to H2S gas even after being bent 50 times at a 60° angle. These exceptional gas sensing properties are attributed to the increase in oxygen vacancies and chemisorbed oxygen on In2O3@MoS2-2 nanofibers as well as the formation of the p-n heterojunction, which modulates the heterojunction barrier. Furthermore, in this study, we successfully applied the In2O3@MoS2-2 sensor for oral disease and detection of food spoilage conditions, thereby providing new design insights for the development of portable exhaled gas sensors and gas sensors for evaluating food spoilage conditions at room temperature.

Enhancement of nitric oxide sensing performance via oxygen vacancy promotion on strontium-doped LaFeO3 perovskites

The potential of Sr-doped LaFeO3 as a nitrogen oxide–sensing material was studied by experimentation and theory calculation. The test results showed a much higher sensitivity and selectivity for a nitric oxide sensor based on Sr-doped LaFeO3 than on pure LaFeO3. The response, which was increased nearly 0.5-fold compared to pure LaFeO3, was attributed to an enhancement of oxygen vacancy and adsorbed oxygen. Further theoretical analysis indicated that Sr doping resulted in the formation of oxygen vacancy defects and altered the adsorption energy of the material, leading to an increase in chemisorbed oxygen species and intermolecular interactions. This work emphasizes the significance of oxygen vacancy defects in gas sensors and provides a feasible approach for enhancing the properties of gas sensors.