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The production of aromatic hydrocarbons from the waste tire pyrolysis attracts more and more attention because of its tremendous potential. Based on styrene-butadiene rubber (SBR), which is the main rubber in the waste passenger car tires, this work studies the temperature influence on primary pyrolysis product distribution by experimental techniques (Py-GC/MS, TG-MS), and then, the formation mechanism of monocyclic aromatic hydrocarbons (MAHs) observed in the experiment was analyzed by first-principles calculations. The experimental results show that the MAHs during the pyrolysis mainly include styrene, toluene, and xylene, and subsequent calculations showed that these compounds were formed through a series of primary and secondary reactions. The formation pathways of these typical MAHs were studied via the reaction energy barrier analysis, respectively. It shows that the MAHs were not only derived from the benzene ring in the SBR chain but also generated from short-chain alkenes through the Diels-Alder reaction. The obtained pyrolysis reaction mechanism provides theoretical guidance for the regulation of the pyrolysis product distribution of MAHs.

Photocatalytic production of hydrogen peroxide (H2O2) has attracted much attentions as a promising method for sustainable solar fuel. Here, we demonstrate that trace water can drastically boost high-efficiency photocatalytic production of H2O2 with a record-high concentration of 113 mmol L−1 using alkali-assisted C3N4 as photocatalyst in water/alcohol mixture solvents. By electron paramagnetic resonance (EPR) measurement, the radical species generated during the photocatalytic process of H2O2 are identified. We propose alcohol is used to provide and stabilize · OOH radicals through hydrogen bond, while trace water could trigger photocatalytic production of H2O2 via providing and transferring indispensable free protons to completely consume · OOH radicals, which breaks the reaction balance of · OOH radical generation from alcohol. Thus · OOH radicals could be supplied by alcohol continuously to serve as a reservoir for high-efficiency production of H2O2. These results pave the way towards photocatalytic method on semiconductor catalysts as an outstanding approach for production of hydrogen peroxide.

A series of high-efficiency CuBx-based bifunctional flexible polyurethane plastic electrodes are fabricated by mild electroless plating for durable electrolysis over 1 A cm−2 in seawater, which also promotes the degradation of polyurethane plastics.

On-site production of hydrogen peroxide (H2O2) using electrochemical methods received considerable attention but limited by the target product selectivity. In this work, an efficient approach was proposed to accelerate high-throughput...

Two–electron ( 2 e - ) oxygen reduction reaction (ORR) shows great promise for on–site electrochemical synthesis of hydrogen peroxide (H2O2). However, it is still a great challenge to design efficient electrocatalysts for H2O2 synthesis. To address this issue, the logical design of the active site by controlling the geometric and electronic structures is urgently desired. Therefore, using density functional theory (DFT) computations, two kinds of hybrid double–atom supported on C2N nanosheet (RuCu@C2N and PdCu@C2N) are screened out and their H2O2 performances are predicted. PdCu@C2N exhibits higher activity for H2O2 synthesis with a lower overpotential of 0.12 V than RuCu@C2N (0.59 V), Ru3Cu(110) facet (0.60 V), and PdCu(110) facet (0.54 V). In aqueous phase, the adsorbed O2 is further stabilized with bulk H2O and the thermodynamic rate–determining step of 2 e - ORR change. The activation barrier on PdCu@C2N is 0.43 eV lower than the one on RuCu@C2N with 0.68 eV. PdCu@C2N is near the top of 2 e - ORR volcano plot, and exhibits high selectivity of H2O2. This work provides guidelines for designing highly effective hybrid double–atom electrocatalysts (HDACs) for H2O2 synthesis.

Thermal stability is the key issue in the industrial application of supported metal nanocatalysts. A combination method of density functional theory calculations, machine learning, and molecular dynamics simulation is adopted to study the sintering behavior of supported platinum (Pt) nanoparticles on graphene or TiO2 nanosheet, and analyze sintering mechanisms under different temperatures, particle sizes, and metal support interactions (MSIs). The results show that the agglomeration of supported nanoparticles is mainly based on the mechanism of small particle migration and growth. Small-sized particles with high surface energy determine the sintering rate. In addition, the increase of temperature is conducive to the agglomeration of particles, especially for systems with strong MSI. Based on the analysis of the sintering process, a sintering kinetic model of supported Pt nanoparticles related to particle size, temperature, and MSI is established, which provides theoretical guidance for the design of supported metal catalysts with high thermal stability.

Two-dimensional (2D) materials have been developed into various catalysts with high performance, but employing them for developing highly stable and active nonprecious hydrogen evolution reaction (HER) catalysts still encounters many challenges. To this end, the machine learning (ML) screening of HER catalysts is accelerated by using genetic programming (GP) of symbolic transformers for various typical 2D MA2Z4 materials. The values of the Gibbs free energy of hydrogen adsorption (ΔGH*) are accurately and rapidly predicted via extreme gradient boosting regression by using only simple GP-processed elemental features, with a low predictive root-mean-square error of 0.14 eV. With the analysis of ML and density functional theory (DFT) methods, it is found that various electronic structural properties of metal atoms and the p-band center of surface atoms play a crucial role in regulating the HER performance. Based on these findings, NbSi2N4 and VSi2N4 are discovered to be active catalysts with thermodynamical and dynamical stability as ΔGH* approaches to zero (-0.041 and 0.024 eV). In addition, DFT calculations reveal that these catalysts also exhibit good deuterium evolution reaction (DER) performance. Overall, a multistep workflow is developed through ML models combined with DFT calculations for efficiently screening the potential HER and DER catalysts from 2D materials with the same crystal prototype, which is believed to have significant contribution to catalyst design and fabrication.

The electrochemical synthesis of hydrogen peroxide (H2O2) provides a greener and more efficient method compared with classic catalysts containing toxic metals. Herein, we used first-principles density functional theory (DFT) calculations to investigate 174 different single-atom catalysts with graphyne substrates, and conducted a three-step screening strategy to identify the optimal noble metal-free single atom catalyst. It is found that a single Ni atom loaded on γ-graphyne with carbon vacancies (Ni@V-γ-GY) displayed remarkable thermodynamic stability, excellent selectivity, and high activity with an ultralow overpotential of 0.03 V. Furthermore, based on ab-initio molecular dynamic and DFT calculations under the H2O solvent, it was revealed that the catalytic performance for H2O2 synthesis in aqueous phase was much better than that in gas phase condition, shedding light on the hydrogen bond network being beneficial to accelerate the transfer of protons for H2O2 synthesis.

Revealing the effect of external applied potential on the reaction mechanism and product selectivity is of great significance in electrochemical studies. In this work, the grand canonical density functional theory method was applied to simulate the explicit electrocatalytic process of oxygen evolution reaction and electrochemical ozone production due to the O3 product sensitivity toward the applied potential. Over the Pt/Pd single atom embedded on B/N co-doped graphene (Pt/Pd-BNC) surface, crossover points of O2/O3 selectivity inversion were predicted to be 1.33 and 0.89 V vs standard hydrogen electrode, which were also consistent with the previous experimental results. An in-depth analysis of the energetic terms in the reaction free energies also found the considerable impact of the applied potential on the Helmholtz free energy term, with optimal potential predicted for the key elementary steps, and linear correlations between electrode potential (U) and reaction free energy were found for each elementary step. This study offers extensive knowledge on the potential effect on the O2/O3 selective formation on two-dimensional anode surfaces and provides new insights for investigating the reactivity/selectivity on electrode surfaces in real reaction conditions.

BackgroundHighly Active Anti-Retroviral Therapy (HAART) can successfully suppress HIV-1 viral replication and reconstruct immune function reconstruction in HIV infected patients. However, about 15-30 % of HIV infected patients still fail to recover their CD4+T cell counts after HAART treatment, which means immune reconstruction failure. Pyroptosis plays an important role in the death of CD4+T cells in HIV infected patients. The study aims to explore the association between the expression of pyroptosis in peripheral blood and immune function reconstruction in HIV infected patients.MethodsOne hundred fifty-three HIV-infected patients including immunological nonresponders group (INR), immunological responders group (IR) and normal immune function control group (NC) were analyzed. The expression of GSDMD and Caspase-1 in peripheral blood of HIV infected patients were measured by qPCR. The concentrations of IL-1β and IL-18 in the peripheral serum were quantified by ELISA. The associations between the expression of pyroptosis in peripheral blood and immune function reconstruction were analyzed using multivariate logistic models.ResultsThe relative expression of GSDMD mRNA and caspase-1 mRNA in peripheral blood, as well as the expression of IL-18 cytokine in the INR, were significantly higher than those in the IR and NC(PP>0.05). Multivariate logistic analysis showed that the patients with baseline CD4+T cell counts less than 100 cells/μL (aOR=5.913, 95%CI=1.061-32.958, P=0.043), high level of expression of Caspase-1mRNA (aOR=2.833,95%CI=1.127-7.126, P=0.027) and IL-18 cytokine (aOR=8.569, 95%CI=1.661-44.195, P=0.010) had significant poor CD4+T cell recovery. ConclusionsThe pyroptosis was overactivated in peripheral blood in HIV infected patients with immune reconstitution failure. The baseline CD4+T cell count less than 100 cells/μL, high relative expression of Caspase-1 mRNA, and high expression of IL-18 cytokine are independent risk factors that affect the reconstruction of immune function.

The choice of support is one of the most significant components in the direct synthesis of H2O2. Aiming to improvement of activity and selectivity of H2O2 on Pd/TiO2 surface, we systematically investigated the important elementary steps on Pd/TiO2-Vo@C, Pd/TiO2-Vo, Pd/TiO2-2Vo, Pd/TiO2, and Pd/C using the first-principles calculations. The Bader charge analysis and charge density difference of O2 adsorption elucidate the relationship between the electronic distribution and chemisorption energy. The effective barrier analysis further enables to quantitatively estimate the reactivity of H2O2 and H2O. We demonstrate unambiguously that the selectivity of H2O formation is boosted as the oxygen vacancy concentration raised. Moreover, the introduction of C into a TiO2 with appropriate oxygen vacancies can slightly reduce the effective barrier for H2O2 formation and increase the effective barrier for H2O formation leading to a higher activity and selectivity of H2O2 formation. Our finding suggests that carbon-doped oxygen vacancy TiO2 supported Pd is potential alternative catalyst compared with the Pd/TiO2.

Styrene-butadiene rubber (SBR) is widely used in tires in the automotive segment and vulcanization using sulfur is a common process to enhance its mechanical properties. However, the addition of sulfur as the cross-linking agent usually results in impurities in pyrolysis products during rubber recycling, and thus the desulfurization during tire pyrolysis attracts much attention. In this work, the pyrolysis of vulcanized SBR is studied in detail with the help of ReaxFF molecular dynamics simulation. A series of cross-linked SBR models were built with different sulfur contents and densities. The following ReaxFF MD simulations were performed to show products distributions at different pyrolysis conditions. The simulation results show that sulfur products distribution is mainly controlled by sulfur contents and temperatures. The reaction mechanism is proposed based on the analysis of sulfur products conversion pathway, where most sulfur atoms are bonded with hydrocarbon radicals and the rest transfer to H2S. High sulfur contents tend to the formation of elemental sulfur intermediate, and temperature increase facilitates the release of H2S.

Understanding the microscopic structure and thermodynamic properties of electrode/electrolyte interfaces is central to the rational design of electric-double-layer capacitors (EDLCs). Whereas practical applications often entail electrodes with complicated pore structures, theoretical studies are mostly restricted to EDLCs of simple geometry such as planar or slit pores ignoring the curvature effects of the electrode surface. Significant gaps exist regarding the EDLC performance and the interfacial structure. Herein the classical density functional theory (CDFT) is used to study the capacitance and interfacial behavior of spherical electric double layers within a coarse-grained model. The capacitive performance is associated with electrode curvature, surface potential, and electrolyte concentration and can be correlated with a regression-tree (RT) model. The combination of CDFT with machine-learning methods provides a promising quantitative framework useful for the computational screening of porous electrodes and novel electrolytes.

Electrolyzing water technology to prepare high-purity hydrogen is currently an important field in energy development. However, the preparation of efficient, stable, and inexpensive hydrogen production technology from electrolyzed water is a major problem in hydrogen energy production. The key technology for hydrogen production from water electrolysis is to prepare highly efficient catalytic, stable and durable electrodes, which are used to reduce the overpotential of the hydrogen evolution reaction and the oxygen evolution reaction of electrolyzed water. The main strategies for preparing catalytic electrodes include: (i) choosing cheap, large specific surface area and stable base materials, (ii) modulating the intrinsic activity of the catalytic material through elemental doping and lattice changes, and (iii) adjusting the morphology and structure to increase the catalytic activity. Based on these findings, herein, we review the recent work in the field of hydrogen production by water electrolysis, introduce the preparation of catalytic electrodes based on nickel foam, carbon cloth and new flexible materials, and summarize the catalytic performance of metal oxides, phosphides, sulfides and nitrides in the hydrogen evolution and oxygen evolution reactions. Secondly, parameters such as the overpotential, Tafel slope, active site, turnover frequency, and stability are used as indicators to measure the performance of catalytic electrode materials. Finally, taking the material cost of the catalytic electrode as a reference, the successful preparations are comprehensively compared. The overall aim is to shed some light on the exploration of high-efficiency and economical electrodes in energy chemistry and also demonstrate that there is still room for discovering new combinations of electrodes including base materials, composition lattice changes and morphologies.

Developing economical, efficient and stable bifunctional catalysts for hydrogen production from seawater is of great significance for hydrogen utilization. Herein, sulfur doped iron oxide nanosheet arrays supported on nickel foam (FeOx-Ni3S2@NF) are prepared by a one-pot solvothermal reaction. Owing to the high intrinsic activity of FeOx-Ni3S2, the large catalytic specific surface area of nanosheet arrays and the fast charge transportation capability achieved by the self-supporting configuration, the FeOx-Ni3S2@NF electrode delivers excellent catalytic performance in alkaline simulated seawater (1 M KOH + 0.5 M NaCl). Impressively, a low overpotential of 120 mV at 50 mA cm-2 with a Tafel slope of 57 mV dec-1 for the hydrogen evolution reaction and an overpotential of 470 mV at 200 mA cm-2 with a Tafel slope of 62 mV dec-1 for the oxygen evolution reaction are achieved. More importantly, the voltage is only 1.5 V at 50 mA cm-2 for continuous overall water splitting for 100 h at 200 mA cm-2 with negligible decay in alkaline simulated seawater with almost 100% Faraday efficiency. This work provides a simple and universal strategy to prepare highly efficient bifunctional catalytic materials, promoting the development of Earth-abundant materials to catalyse seawater splitting to produce high-purity hydrogen.

Telemedicine provides an attractive vision for tele-monitoring human health conditions and, thus, offers the opportunity for timely preventing chronic disease. A key limitation of promoting telemedicine in clinic application is the lack of a noninvasive med-tech and effective monitoring platform, which should be wearable and capable of high-performance tele-monitoring of health risk. Here we proposed a volatolomics-based telemedicine for continuously and noninvasively assessing human health status through continuously tracking the variation of volatile markers derived from human breath or skin. Particularly, a nanosensor-based flexible electronic was specifically designed to serve as a powerful platform for implementing the proposed cost-effective healthcare. An all-flexible and highly packed makeup (all functional units were integrated in a 2*2*0.19 cm3 plate) enables an electronic, compact configuration and the capability of resisting negative impact derived from customers' daily movement. Notably, the nanosensor-based electronic demonstrates high specificity, quick response rate (t90% = 4.5 s), and desirable low detection limit (down to 0.117 ppm) in continuous tele-monitoring chronic-disease-related volatile marker (e.g., acetone). Assisted by the power saved light fidelity (Li-Fi) communicating technology, a clinic proof on the specifically designed electronic for noninvasively and uninterrupted assessing potential health risk (e.g., diabetics) is successfully implemented, with the accuracy of around 81%. A further increase in the accuracy of prewarning is predicted by excluding the impact of individual differences such as the gender, age, and smoking status of the customer. These promising pilot results indicate a bright future for the tailor-made nanosensing-device-supported volatolomics-based telemedicine in preventing chronic diseases and increasing patients' survival rate.

Research on water-splitting electrocatalysts is crucial to establishing a solution to the energy crisis. Herein, we report a facile bottom-up strategy for the preparation of high performance supported electrocatalysts for overall water-splitting reaction via a rationally designed defect covalent triazine frameworks (CTFs) support. Specifically, defect CTFs are obtained via binary-precursor polymerization, followed by loading Ru nanoparticles (Ru/D-CTFs-900) with high HER performance at a current density of 10 mA cm−2. The overpotential is only 17 mV. Calcination of the resultant Ru–RuO2/D-CTFs-300 in air, produces excellent OER performance with 190 mV overpotential (at 10 mA cm−2). Furthermore, overall water splitting measurements reveal the potential of 1.47 V, which is better than the majority of the reported Ru-based catalysts. Moreover, density functional theory calculation results show that excellent electrocatalytic properties are attributed to the synergistic effect of Ru nanoparticles and carbon support.

Yttria-stabilized zirconia (YSZ)-based potentiometric gas sensor has been widely utilized for detecting non-methane hydrocarbons (NMHCs) that derived from exhaust gases. Nevertheless, poor selectivity and sensitivity still remained a challenging issue. Herein, we reported an efficient strategy to sense NMHCs (e.g., C3H6) at high temperature through the gas phase reaction combined light-regulated sensing technique. When the YSZ-based sensor that was attached with ZnO sensing electrode and Mn-based reference electrode was operated without illumination, significant mutual interference that derived from CO was witnessed for sensing C3H6. On the contrary, enhanced sensitivity and selectivity are observed by simply illuminating the sensor. The low detection limit of the sensor to C3H6 extends to 0.768 ppm with the response/recovery rate of 27 s/30 s. These pilot results clearly indicate the validity of employing gas phase reaction combined light-regulated sensing technique in tailoring the response selectivity and sensitivity for future exhaust gas sensing.

Catalytic performance of supported metal catalysts not only depends on the reactivity of metal, but also the adsorption and diffusion properties of gas molecules which are usually affected by many factors, such as temperature, pressure, properties of metal clusters and substrates, etc. To explore the impact of each of these macroscopic factors, we simulated the movement of CO molecules confined in graphene nanoslits with or without supported Pt nanoparticles. The results of molecular dynamics simulations show that the diffusion of gas molecules is accelerated with high temperature, low pressure or low surface-atom number of supported metals. Notably, the supported metal nanoparticles greatly affect the gas diffusion due to the adsorption of gas molecules. Furthermore, to bridge a quantitative relationship between microscopic simulation and macroscopic properties, a generalized formula is derived from the simulation data to calculate the diffusion coefficient. This work helps to advise the diffusion modulation of gas molecules via structural design of catalysts and regulation of reaction conditions.

In this study, machine learning (ML) models combined with density functional theory (DFT) calculations and Gibbs free energy of hydrogen adsorption (ΔGH*) were employed to facilitate the high-throu...

The electrochemical oxygen reduction reaction (ORR) to afford hydrogen peroxide (H2O2) provides an alternative to the traditional anthraquinone oxidation process. A major obstacle for this reaction is designing two-electron (2e−) ORR catalysts with high activity and selectivity. Combining the advantages of alloy catalysts and single-atom catalysts, hybrid double-atom catalysts (HDACs) are bringing new opportunities as highly efficient 2e− ORR catalysts. Herein, we developed a novel thermodynamic screening strategy based on oxygen and hydrogen proton adsorptions by density functional theory calculation. In accordance with theoretical predictions, Pd and Cu were screened out from 25 specimens as active centers. And a catalyst of N vacancy g-C3N4 doped with Pd–Cu hybrid double atoms (PdCu@V_C3N4) was designed. The Sabatier method illustrates that PdCu@V_C3N4 is located at the top of the 2e− ORR volcano plot with an extremely low overpotential of 0.02 V. Furthermore, the dynamic rate-determining step is OOH* intermediate formation with a dynamic activation barrier of 0.64 eV. The high selectivity and activity of PdCu@V_C3N4 are attributed to end-on O2 adsorption configuration by “slope” geometric construction and electronic regulation of neighboring hybrid atoms. Our work predicts potential HDACs for future experiments, and also provides a general method for the quick screening and design of highly efficient H2O2 catalysts.

Electrocatalytic ammonia synthesis provides an energy-efficient alternative to the Haber−Bosch process. The aim is to find promising electrocatalysts which are able to change the reaction pathway and reduce the overpotential. Here, based on density functional theory, a comprehensive mechanism study of the N2 activation and NH3 synthesis on the Mo2TiC2 MXenes is presented. For catalytic reaction mechanism, nineteen different possible pathways are screened for the lowest overpotential, where the corresponding potential-determining step are compared by Gibbs free energy calculation. The result reveals Mo2TiC2 MXenes exhibit both valid N2-philicity and high catalytic activity for electrocatalytic ammonia synthesis through a dissociation mechanism with a low overpotential of 0.26 V. Further, the competing reaction of H2 evolution is simultaneously suppressed which shows a relatively high potentials of 0.74 V. This study shows a brand new material for catalyzing NH3 synthesis under ambient conditions and provides the theory background to reduce the overpotential by changing the reaction pathway.

Using water as a hydrogen source is a promising strategy for alternative hydrogen peroxide (H2O2) synthesis. By a series of ab initio molecular dynamics (AIMD) simulations and reactive molecular dynamics (RxMD) calculations, fundamental details have been revealed regarding how liquid water interacts with oxygen on a metal-free carbon nitride catalyst, and the two-step reaction mechanism of H2O2 synthesis. Metal-free porous graphitic carbon nitride (g-C5N2) catalysts are also systematically screened by using a thermodynamics approach through the ab initio density functional theory (DFT) method. Key results include: (a) pristine g-C5N2 is most active to catalyze the H2O/O2 reaction and produce H2O2; (b) the adsorption and activation of water at unsaturated carbon sites of g-C5N2 are critical to initiate the H2O/O2 reaction, producing HOO* intermediates; (c) interfacial free water and adsorbed water at g-C5N2 form a synergetic proton transfer cluster to promote HOO* intermediates to form H2O2. To the best of our knowledge, this work presents long-needed theoretical details of direct H2O2 synthesis via the water/oxygen system, which can guide further optimization of carbon-based catalysts for oxygen reduction reactions.

To search the new effective nitrogen reduction reaction (NRR) electrocatalyst is very important for the ammonia-based industry. Herein, we reported the design of a novel NRR electrocatalyst with Ru NPs loaded on oxygen-vacancy TiO2 (Ru/TiO2-Vo). Structural characterizations revealed that oxygen vacancy was loaded in the matrix of Ru/TiO2-Vo. Electrocatalytic results indicated that Ru/TiO2-Vo showed good NRR performance (2.11 µg h−1 cm−2). Contrast tests showed that NRR property of Ru/TiO2-Vo was much better than those of Ru/TiO2(B) (0.53 µg h−1 cm−2) and Ru/P25 (0.42 µg h−1 cm−2). Furthermore, density functional theory calculation results indicated catalytic mechanism of NRR and rate-determining step (*N2 + 1/2H2 → *N+*NH) was the potential-determining step with the overpotential requirement of 0.21 V. A combination of electronic structure analysis and catalytic measurement shed light on the synergistic effect of Ru and oxygen vacancy on the NRR performance.

Two-dimensional (2D) materials have been developed into various catalysts with high performance, but employing them for developing highly stable and active nonprecious hydrogen evolution reaction (HER) catalysts still encounters many challenges. To this end, the machine learning (ML) screening of HER catalysts is accelerated by using genetic programming (GP) of symbolic transformers for various typical 2D MA

Developing economical, efficient and stable bifunctional catalysts for hydrogen production from seawater is of great significance for hydrogen utilization. Herein, sulfur doped iron oxide nanosheet arrays supported on nickel foam (FeO

Selective conversion of methane (CH4) into value-added chemicals represents a grand challenge for the efficient utilization of rising hydrocarbon sources. We report here dimeric copper centers supported on graphitic carbon nitride (denoted as Cu2@C3N4) as advanced catalysts for CH4 partial oxidation. The copper-dimer catalysts demonstrate high selectivity for partial oxidation of methane under both thermo- and photocatalytic reaction conditions, with hydrogen peroxide (H2O2) and oxygen (O2) being used as the oxidizer, respectively. In particular, the photocatalytic oxidation of CH4 with O2 achieves >10% conversion, and >98% selectivity toward methyl oxygenates and a mass-specific activity of 1399.3 mmol g Cu−1h−1. Mechanistic studies reveal that the high reactivity of Cu2@C3N4 can be ascribed to symphonic mechanisms among the bridging oxygen, the two copper sites and the semiconducting C3N4 substrate, which do not only facilitate the heterolytic scission of C-H bond, but also promotes H2O2 and O2 activation in thermo- and photocatalysis, respectively.

High-performance tracking trace amounts of NO2 with gas sensors could be helpful in protecting human health since high levels of NO2 may increase the risk of developing acute exacerbation of chronic obstructive pulmonary disease. Among various gas sensors, Graphene-based sensors have attracted broad attention due to their sensitivity, particularly with the addition of noble metals (e.g., Ag). Nevertheless, the internal mechanism of improving the gas sensing behavior through doping Ag is still unclear. Herein, the impact of Ag doping on the sensing properties of Graphene-based sensors is systematically analyzed via first principles. Based on the density-functional theory (DFT), the adsorption behavior of specific gases (NO2, NH3, H2O, CO2, CH4, and C2H6) on Ag-doped Graphene (Ag–Gr) is calculated and compared. It is found that NO2 shows the strongest interaction and largest Mulliken charge transfer to Ag–Gr among these studied gases, which may directly result in the highest sensitivity toward NO2 for the Ag–Gr-based gas sensor.

The reaction/diffusion kinetics are fundamentally determined by the electronic properties of supported Pd catalysts and further govern the catalytic activity and selectivity in the partial hydrogen...

SnO2-based materials are helpful to detect low concentration of volatile organic compounds (VOCs), whereas high operating temperatures (≥ 350 °C), poor selectivity and inadequate detection limit of the pristine SnO2 hinder their broader applications. An alternative strategy to address these challenge issues is to adopt porous SnO2 nanotubes (NTs) constructed with ultrathin walls to monitor VOCs. However, inconvenient synthetic routes and low-yield rate of NTs with satisfactory wall thickness restrained the application of SnO2 NTs. Herein, we directly turned SnS2 nanosheets to the porous SnO2 NTs by thermal oxidizing the SnS2 precursor in air. After thermal treatment, high crystallinity and porous hierarchical SnO2 NTs with ultrathin walls were successfully synthesized without any impurities. After decorated with Au nanoparticles (NPs), a strong interaction between the Au NPs and hierarchical SnO2 NTs was witnessed. Compared with those reported SnO2-based materials, hierarchical SnO2 NTs indeed improved the gas sensing properties; particularly, the sensor using Au-SnO2 NTs composite gave the largest sensing magnitude, satisfactory detection limit and high selectivity to acetone at operating temperature of 200 °C. Conclusively, the innovation of transforming SnS2 to the hierarchical SnO2 NTs paves the way to building SnO2 NTs from 2 dimensions ultrathin bricks, and for high performance sensing VOCs.

Yttria-stabilized zirconia (YSZ) based potentiometric gas sensors have been widely utilized for detecting NOx (NO and NO2). Nevertheless, it is still remains challenging issue for YSZ-based sensors to sense total NOx due to the opposite response signals to NO and NO2. Herein, we report an efficient strategy to sense total NOx at high temperature (above 300 °C) by designing a dual functional sensing electrode (SE); namely, the SE will simultaneously convert NO (in NOx mixture) to NO2 and electrocatalyze all of the obtained NO2 to generate the response signal of total NOx. In comparison with those previously reported total NOx sensors, the proposed total NOx sensor will be featured with a simplified sensor configuration and desirable long-term stability. To confirm the practicability of the proposed strategy, the NO conversion rate of several metal oxides and their composites have been measured and it turns out that the Co3O4/NiO shows relatively high NO conversion rate. Further study indicates a YSZ-based sensor consisting of (Co3O4 + 20 wt % NiO)-SE and Mn-based RE demonstrates satisfactory performance in detecting total NOx. For instance, analogous response magnitude to NO and NO2 as well as the mixture of NO/NO2 (within 35 ppm) is witnessed for the sensor; particularly, the sensor gives acceptable stability and response/recovery rate at the operating temperature of 500 °C within the examined period. In summary, the use of dual functional SE (e.g., Co3O4/NiO composite SE) indeed addressed those issues of concern in monitoring the level of total NOx and has provided a promising alternative way for designing future high-performance total NOx sensor.

Supported noble metal nanoparticles (NPs) are widely applied as heterogeneous catalysts in numerous reactions, in which the morphology of metal clusters is of crucial to the catalytic performance. In this study, the multiscale simulations concerned with the adsorption and morphological behavior of Pd, Au clusters and NPs on Mo2C, Mo2CO2 and Mo2CF2 have been performed systematically by density functional theory (DFT) and molecular dynamics (MD). There is an obvious morphological tendency of two-dimension (2D) to three-dimension (3D) for supported Pdn/Aun (n = 4–6) clusters from bare to O, F-terminated Mo2C. The electronic properties analysis shows that more charge transfer occurred on clusters leads to the stronger interaction between clusters and Mo2C MXene. The plots of projected density of states (PDOS) describe that the O, F groups weaken the strong interaction between clusters and bare Mo2C, showing that the nature of the change of morphology is the modification of d states of Pd, Au NPs by the introduction of O, F groups. The MD simulations of large supported Pdn/Aun NPs on bare and functionalized Mo2C are corresponded to the 2D-3D growth of DFT result, which shows that for metal NPs, the average coordination number as well as the interaction of Pd/Au NPs and support varies with the order of bare-O-F. Based on the multiscale simulations, the morphology ranges from Pd/Au clusters to NPs have been governed efficiently by surface groups, which may enlighten the design of metal-supported catalysts.