Distribution Of Active Sites Research Articles

Molecular weight-dependent adsorption heterogeneities of humic acid on microplastics in aquatic environments: Further insights from fluorescence spectra combined with two-dimensional correlation spectroscopy and site energy distribution analysis

Microplastics as emerging environmental contaminants have attracted global attention. Ubiquitous dissolved organic matter (DOM), a heterogeneous mixture with various organic components and continuous molecular weight (MW) distribution, can significantly influence the fate, bioavailability and toxicity of microplastics in aquatic environments. However, to date, understanding of the MW-dependent adsorption heterogeneities of DOM on microplastics in aquatic environments has remained unknown. In this study, the soil humic acid (HA), a representative DOM, was fractionated into > 100 kDa HA, 30–100 kDa HA, 10–30 kDa HA, 3–10 kDa HA and < 3 kDa HA, whose adsorption behaviors on polystyrene microplastics (PSMPs) under different electrolytes at pH6.0 investigated by multispectral techniques, as well as two-dimensional correlation spectroscopy and site energy distribution analysis. High molecular weight MW-fractionated HAs dominated the soil HA. Compared to the lower molecular weight MW-fractionated HAs, the higher molecular weight counterparts exhibited higher aromaticity, showing higher adsorption affinities onto PSMPs in aquatic environments. Adsorption isotherms and kinetics of the MW-fractionated HAs onto PSMPS can be reasonably explained by Langmuir models and the linear driving force (LDF) model, respectively. Enhanced aromaticity in residual solutions was observed, suggesting that the preferable adsorption of the higher aromatic moieties in the pristine and MW-fractionated HAs on PSMPs could be subsequently replaced by the lower aromatic moieties for the limited binding sites. Combined, the humic-like materials in MW-fractionated HAs could be significantly impacted the complexation of PSMPs in aquatic environments. The heterogeneous/complicated distributions of active adsorption sites in the humic-like materials of the MW-fractionated HAs, and the subsequent subtle changes of these sites to PSMPs were characterized by synchronous fluorescence spectroscopy coupled with two-dimensional correlation spectroscopy. High molecular weight MW-fractionated HAs provided more active adsorption sites than those in the low molecular weight counterparts, which also possessed stronger adsorption affinities and higher complexation capacities to PSMPs. The site energy distributions for the adsorption of the MW-fractionated HAs on PSMPs were calculated based on Langmuir model. The adsorption heterogeneities of PSMPs at the experimental conditions were close. This study provides deep insights into the MW-dependent adsorption heterogeneities of HA on PSMPs, and the results are of significance to understand the biogeochemical behaviors of DOM and MPs in aquatic environments.

Porous Fe, N co-doped carbon with high electrocatalytic oxygen reduction reaction performance in Zn-air battery

Non-Pt electrocatalysts for oxygen reduction reactions (ORR) have been developed using metal and nitrogen co-doped carbon electrocatalysts. However, challenges remain regarding the porosity of the catalyst, distribution of active sites, and the easy aggregation of the metal components. Herein, we report a bottom-up preparation strategy to obtain a porous ethynyl-linked conjugated microporous polymer (CMP) precursor containing triazine units and bipyridine, ensuring high N content and coordination with Fe 3+ . The Fe doped CMP is then carbonization into a Fe, N co-doped nanoporous carbon material (BPCMP-Fe-800), which can be taken as the electrocatalyst in ORR. BPCMP-Fe-800 catalyst exhibits electrocatalytic performance dominated by 4e − transfer mechanism with the onset potential of 0.97 V, half-wave potential of 0.85 V, and higher kinetic current density of 11.3 mA cm −2 (0.8 V). In addition, when applied as cathode electrocatalyst in zinc-air batteries, BPCMP-Fe-800 displays more competitive power density (179.5 mW cm −2 ) and specific capacity (790.5 mAh g −1 ) compared with Pt/C. Our study demonstrates a general and facile approach for porous Fe, N co-doped carbon with the potential as alternatives to Pt catalysts for efficient ORR catalytic performances and provides new insights of multi-atom catalysts for other energy conversion related catalytic reactions.

Effect of the Rare Earth Metals (Tb, Nd, Dy) addition for the modification of nickel catalysts supported on alumina in CO2 Methanation

In the current research, a group of rare-earth metals functionalized mesoporous Ni-M/Al2O3 (M = Tb, Dy, Nd) composite oxides were prepared by the one-pot sonochemical pathway and applied in the CO2 methanation procedure. Promoters can partially influence the textural and catalytic characteristics of Ni–Al2O3 catalysts. Physicochemical characteristics of the as-fabricated catalysts were identified utilizing X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Energy-dispersive X-ray spectroscopy (EDS), Temperature Programmed Reduction (H2-TPR), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), and Brunauer-Emmett-Teller (BET) analyses. Among the specimens, the catalyst modified by Terbium (Tb) manifested better catalytic performance and CH4 selectivity, particularly at low temperatures (350–400 °C). The influence of reaction temperature (200–500 °C) was scrutinized below space velocity (GHSV) of 25,000 ml/gcath, atmospheric pressure, and stoichiometric ratio of CO2 to H2 (1: 4). The impact of the desired content of nickel and terbium was examined. The 25Ni–5Tb–Al2O3 operates the best function for CO2 methanation, which can attain the highest CO2 conversion of 66.93% at 400 °C at atmospheric pressure. The superior catalytic performance of 25Ni–5Tb–Al2O3 could be assigned to the appropriate fabrication method and the promotion effect of Terbium. The synthesis effect could be assigned to its large surface area, obtaining by the hot spot mechanism. The addition of Terbium promotes the Ni distribution on the supports as well as accelerates the positive reaction due to the oxygen vacancies of Terbium. Besides, these outcomes could be defined with the maximum distribution of active nickel sites on the catalyst and improvement in the catalyst reduction ability at low temperatures.

Rotation induced by non-uniform gas–solid phase reactions of a non-spherical particle

• The particle rotation induced by gas–solid phase reactions is revealed; • The non-uniform gas–solid phase reaction directly results to the rotation of non-spherical particle; • The rotation characteristics of coal particle during combustion are discussed. Particle rotation plays an important role in gas–solid flow. The particle rotation induced by gas–solid phase reaction is investigated in this work. The non-uniform gas–solid phase reaction direct results to the rotation of a non-spherical particle. Based on the random distribution of active sites, the combustion of non-spherical particles is numerical investigated. According to the numerical results of chemical reaction rate on the particle surface, the net force and the rotation frequency of non-spherical particle were obtained by post-processing. The bearing force and rotation of cubic particles caused by gas–solid chemical reactions are systematically numerically studied. The rotational frequency is basically consistent with the experimental results in the reference. For coal char particles with an active area ratio of 0.8, the rotational frequency can reach 1000 Hz at side length of 60 μm. The effects of active area ratio, ambient gas temperature and particle size on the induced thrust and the rotational frequency of coal char particles are analyzed. The unbalanced force on the particle surface increase with the reaction rates. The rotation velocity increases with the decrease of particle size. And it increases with the increase of ambient temperature..

Anchoring Cu Species over SiO2 for Hydrogenation of Dimethyl Oxalate to Ethylene Glycol

Recently, the Cu-based catalyst has attracted wide attention for the hydrogenation of dimethyl oxalate (DMO) to ethylene glycol (EG) due to its high catalytic activity and it is low cost. However, its poor stability, ease of agglomeration, and the short life of the catalyst restrict its further development in industrial applications. Here, we constructed a novel MOF-derived Cu/SiO2 catalyst (MOF-CmS for short) with a controllable distribution of Cu active sites for the hydrogenation of the DMO to EG reaction. The catalyst was prepared by a hydrothermal method with the HKUST-1 uniformly coated on the surface of the silica microspheres. After the calcination, the highly dispersed and uniform Cu species were loaded on the surface of the silica. The resulted MOF-CmS catalyst showed a 100% conversion of DMO and over 98% selectivity of EG at 200 °C and 2 MPa while a traditional Cu/SiO2 catalyst exhibited serious agglomeration of Cu active sites and low catalytic activity (DMO conversion of 86.9% and EG selectivity of 46.6%). It is believed that the highly dispersed active metal center and the interaction between the active metal and carrier were the main reasons for higher catalytic activity of the MOF-CmS catalyst. Therefore, the developed method opened another avenue to synthesize highly dispersed and stable Cu-based catalysts.

Influence of Metal Cation and Temperature on Localized Corrosion Behavior of Steels in Aqueous Environments

Steels are abundantly used in many areas because of their good formability and low price. Steels suffer from corrosion in aqueous environments with chloride ions. Corrosion of steels is also a serious problem for long-term usage of steel structures such as bridges and buildings. There are many studies focused on chloride ions. There are reports that metal cations have a tendency to inhibit the corrosion of steels in a chloride aqueous environment by forming a layer on the steel.The other important factor for corrosion of steels in an aqueous environment is temperature. The corrosion rate of metal in cold regions is expected to slow because of low temperature. A recent study on atmospheric exposure tests carried out in different places in Hokkaido, it has elucidated that the corrosion rate in the cold region is the same as in the warm region.However, it is not fully elucidated that temperature, especially below freezing point, and metal cations on corrosion behavior and distribution of active dissolution site. The purpose of this study is to investigate the influence of temperature and metal cations on thecorrosion behavior of steels.Steel sheets of 15 x 20 mm and 20 x 20 mm were used as specimens. Three solutions of 0.1 mM ZnCl2, 0.5 mM ZnCl2 and 1.0 mM ZnCl2 were used for examination of the effect of metal cations, and 20 mass % NaCl solution was used for examination of effect of temperature. After the tests, the morphology of specimens was examined by optical microscope and scanning electron microscope.After the wet/dry corrosion tests used 10 mL solutions droplets, corrosion products were formed on the specimens. The corrosion processes under NaCl and MgCl2 were similar. Yellow corrosion products were firstly observed in the solution during the wet period. In the case of under ZnCl2, after the formation of oxide layer on the specimens the corrosion proceeded in localized areas. The color of almost half area of the exposed surface was light, which might indicate less corrosion occurred in the area. The initial corrosion stage of steel preferred to form a brown area in the center of the droplet. There are no similar corrosion products thatcan be observed in comparison to the samples under MgCl2 and NaCl solutions.A lot of corrosion products and localized corroded areas were formed on specimens after being immersed at 273 K, while less corrosion products and homogenously corroded surface were observed on specimens after being immersed at 293K.The results indicated that corrosion morphology and preferentially corroded area were changed with the kind of metal cation and temperature.

Differentiating supported platinum single atoms, clusters and nanoparticles by styrene hydrogenation

Supported metal catalysts often consist of metal sites ranging from nanoparticles to subnanometer clusters and single atoms. It remains a necessity to differentiate these sites to guide design of optimal catalysts. Here we report a simple method to assess the distribution of metal active sites in catalyst samples. The method takes the advantage of the structure sensitivity of styrene hydrogenation over titania supported platinum (Pt) catalysts with Pt aggregates varied from single atom to ∼1.40 nm nanoparticles. The physicochemical properties were characterized by STEM, XPS, XANES, H2-TPR and CO-chemisorption measurements. The reactivity of Pt sites was quantified by styrene hydrogenation at ambient conditions. The nanometer-sized Pt clusters have significantly higher activity than Pt nanoparticles, sub-nanometer clusters or isolated single atoms. The relationship between activity and structural/electronic properties of Pt sites influenced by particle sizes was discussed. Similar relationship was found in the carbon supported Pt catalysts.

Low supported nickel-cobalt catalyst for hydrogenation of maleic anhydride

In order to prepare supported catalysts with low-metal loading, a series of NiCo/Clay catalysts were prepared and used in the hydrogenation of maleic anhydride. The hydrogenation reaction was carried out in a fixed-bed for 8 h with reaction pressure = 1 MPa, reaction temperature = 180 °C, molar ratio of H2: maleic anhydride = 50, WHSV = 2 h−1. Ni4Co1/Clay (loaded 3 wt%Ni and 0.75 wt%Co) can maintain no obvious catalyst deactivation within 8 h. The overall conversion of maleic anhydride is not less than 95 %, and the selectivity of succinic anhydride is up to 100 %. N2 adsorption–desorption characterization, X-ray diffraction, temperature-programmed reduction, temperature-programmed desorption, X-ray photoelectron spectroscopy and transmission electron microscopy were performed to verify the changes in catalyst morphology, active species, reduction performance and hydrogenation activity after adding Co as a promoter. With the addition of Co additive, the distribution of active sites on the carrier is more uniform, the grain size of active metal becomes smaller and the reduction temperature decreases. The addition of Co not only increased the active center of the catalyst but also effectively avoided the catalyst's deactivation.

17O Labeling Reveals Paired Active Sites in Zeolite Catalysts

Current needs for extending zeolite catalysts beyond traditional gas-phase hydrocarbon chemistry demand detailed characterization of active site structures, distributions, and hydrothermal impacts. A broad suite of homonuclear and heteronuclear NMR correlation experiments on dehydrated H-ZSM-5 catalysts with isotopically enriched 17O frameworks reveals that at least two types of paired active sites exist, the amount of which depends on the population of fully framework-coordinated tetrahedral Al (Al(IV)-1) and partially framework-coordinated tetrahedral Al (Al(IV)-2) sites, both of which can be denoted as (SiO)4-n-Al(OH)n. The relative amounts of Al(IV)-1 and Al(IV)-2 sites, and subsequent pairing, cannot be inferred from the catalyst Si/Al ratio, but depend on synthetic and postsynthetic modifications. Correlation experiments demonstrate that, on average, acidic hydroxyl groups from Al(IV)-1/Al(IV)-2 pairs are closer to one another than those from Al(IV)-1/Al(IV)-1 pairs, as supported by computational DFT calculations. Through-bond and through-space polarization transfer experiments exploiting 17O nuclei reveal a number of different acidic hydroxyl groups in varying Si/Al catalysts, the relative amounts of which change following postsynthetic modifications. Using room-temperature isotopic exchange methods, it was determined that 17O was homogeneously incorporated into the zeolite framework, while 17O → 27Al polarization transfer experiments demonstrated that 17O incorporation does not occur for extra-framework AlnOm species. Data from samples exposed to controlled hydrolysis indicates that nearest neighbor Al pairs in the framework are more susceptible to hydrolytic attack. The data reported here suggest that Al(IV)-1/Al(IV)-2 paired sites are synergistic sites leading to increased reactivity in both low- and high-temperature reactions. No evidence was found for paired framework/nonframework sites.

Advances in cutting‐edge electrode engineering toward CO2 electrolysis at high current density and selectivity: A mini‐review

AbstractElectrochemical CO2 conversion has been raised as a promising solution for building a carbon‐neutral economy under today's circumstances of increasing energy shortages and air pollution from human activities. Research on electrochemical CO2 reduction reaction (CO2RR) is gradually entering a pilot‐scale stage. The use of device‐level CO2 electrolysis in the production of value‐added chemicals and fuels at a high production rate and selectivity is highly required to make the technology economical and sustainable. With more exploration toward device‐level performance optimization, it gradually becomes clear that electrode engineering on structures, surface properties, active site distribution, and density, as well as the electrode–electrolyte interface, is more critical than the intrinsic activity of catalytic sites. Taking this into account, this review focuses on interpreting the design principles in aspects with the aim of enhancing the CO2RR toward a specific product yield and production rate. This mini‐review summarizes the advances in this dynamic field in the most recent 5 years, including the fabrication of porous gas diffusion electrodes, and self‐supporting electrodes, establishment of tandem or cascade electrode function, as well as tuning of interfacial cation buffering and wettability, and analyze the trends in the future scientific and technological development of device‐level CO2 electrolysis. Hopefully, this mini‐review could provide some insights into the opportunities in the next‐generation electrode design for the industrial carbon cycle.

Enhanced photocatalytic organic pollutant degradation and H2 evolution reaction over carbon nitride nanosheets: N defects abundant materials

Post thermal treatment of bulk graphitic carbon nitride (g-C3N4) by ammonia gas acts as a significant structure regulation approach, while pure ammonia-assisted g-C3N4 synthesis from precursors like melamine is rarely investigated. Here we prove the synthesis of N-defects abundant carbon nitride nanosheets (ACN) through a one-pot thermal polymerization of melamine in pure ammonia gas, for photocatalytic organic pollutant removal in water and H2 evolution applications. Compared to bulk g-C3N4 (BCN), ACN-550 (ACN prepared at 550 °C) exhibited thin-layered porous morphology with higher surface area and abundant N defects, resulting in wider distribution of active sites. Moreover, the abundant N defects in the heptazine heterocycle structure could change the electronic structure of g-C3N4, leading to more efficient transport of photogenerated charge carriers and enhanced photoreduction potential, which gives rise to notable improvement activities in photocatalytic reaction. With superoxide ion radical and photoinduced holes as the predominant reactive species, ACN-550 realized efficient photocatalytic bisphenol A (BPA) degradation, which is 1.6- and 4.7-fold high over commercial TiO2 (P25) and BCN, respectively. ACN-550 exhibited excellent reusability and stability in five consecutive photocatalytic BPA degradation tests. In photo-reductive H2 production system by ACN-550, 761.8 ± 4.3 μmol/h/g H2 was produced, which was 11.6-fold as high as that by BCN.

锂硫电池非均相电催化剂

<p indent="0mm">With the rapid development of electronic transportation and portable electronics, commercial lithium-ion batteries would be unsatisfactory to meet the needs of future markets owing to the relatively low energy density. Seeking a reliable substitution system is becoming imperative. Lithium-sulfur (Li-S) battery has been recognized as a cutting-edge energy storage system because of its high theoretical capacity (1672 mAh g^–1) and cost-effectiveness of sulfur resources. Nevertheless, the severe shuttle effect and sluggish reaction kinetics significantly restrict its further commercialization. In the developing history of Li-S batteries, physical confinement and chemical adsorption have often been employed to achieve the anchoring of polysulfides. However, these strategies are still difficult to fully solve the problems of slow reaction kinetics and poor cycle performance. Recent years have witnessed the introduction of heterogeneous electrocatalysts into the Li-S system, which readily meets with great success in suppressing the shuttle effect and elevating the reaction kinetics. In this review, we introduce the basic reaction of Li-S battery and point out the main challenges in its current development stage, followed by summarizing the effects of electrocatalysts. Firstly, the polar electrocatalyst is able to effectively adsorb polysulfide and inhibit its diffusion in the electrolyte. Secondly, the electrocatalyst can effectively promote the conversion of polysulfide and improve the utilization rate of sulfur species. Thirdly, the uniform distribution of active sites in the electrocatalyst also contributes to the uniform deposition of short-chain polysulfides. In addition, the concepts and comparisons of homogeneous and heterogeneous electrocatalysts are presented, manifesting the essential significance of heterogeneous electrocatalysts in Li-S system. Homogeneous electrocatalysts usually refer to small soluble organic molecules with the same phase state as soluble polysulfides in the reaction system. Homogeneous electrocatalysts have more specific catalytic sites, whilst heterogeneous electrocatalysts have more diverse morphologies and higher possibility of multi-site synergistic catalysis. Then the common regulation strategies for heterogeneous electrocatalysts are classified, including vacancy regulation, doping regulation, heterostructure modulation, size control, and phase modulation. In further contexts, the underlying mechanisms of different regulation strategies for promoting polysulfide conversion are discussed. The introduction of heterogeneous electrocatalysts can effectively promote the reaction kinetics and improve their electrochemical performance. However, there are still many obstacles waiting to be solved in the practicability of Li-S batteries. For instance, there is a lack of highly selective and stable electrocatalysts. The identification of real catalytic sites in the electrocatalysts still remains unclear. Moreover, Li-S batteries have poor performance under lean electrolyte and low lithium consumption. In view of these issues, future development strategy is put forward from four aspects, encompassing material exploration, precise synthesis, characterization methods and practical application, aiming to bridge the gap between the reality and ideal in working Li-S batteries.

Cation‐Vacancy Ordered Superstructure Enhanced Cycling Stability in Tungsten Bronze Anode

AbstractNiobium‐based tungsten bronze oxides have recently emerged as attractive fast‐charging anodes for lithium‐ion batteries (LIBs), owing to their structural openings and adjustability. However, electrodes with tungsten bronze structures usually suffer from structural variability induced by Li+ intercalation/de‐intercalation, leading to unsatisfactory cycling performance. To circumvent this limitation, a novel tetragonal tungsten bronze (TTB) structure, Ba3.4Nb10O28.4 (BNO), is developed as an anode material for LIBs with prominent cycling performance. An unprecedented cation‐vacancy ordered superstructure with a periodic distribution of active and inactive sites is revealed inside the BNO. Through multiple characterizations and theoretical studies, it is demonstrated that this superstructure can improve the lithium‐ion diffusion and disperse the structural strain induced by Li+‐intercalation to enable stable Li+‐storage. Benefiting from the superstructure‐induced local structural stability, both the BNO bulk and Ba3.4Nb10O28.4@C (BNO@C) microspheres can deliver &gt;90% capacity retention after 250 cycles at 2 C and close to 90% capacity retention after 2000 cycles at 10 C. These results are of significant importance for establishing the structure–property relationship between the cation‐vacancy ordered superstructure and Li+‐storage performance, facilitating the rational design of stable tungsten bronze anodes.

Unveiling Secondary-Ion-Promoted Catalytic Properties of Cu-SSZ-13 Zeolites for Selective Catalytic Reduction of NOx.

The incorporation of secondary metal ions into Cu-exchanged SSZ-13 zeolites could improve their catalytic properties in selective catalytic reduction of NOx with ammonia (NH3-SCR), but their essential roles remain unclear at the molecular level. Herein, a series of Cu-Sm-SSZ-13 zeolites have been prepared by ion-exchanging Sm ions followed by Cu ions, which exhibit superior NH3-SCR performance. The NO conversion of Cu-Sm-SSZ-13 is nearly 10% higher than that of conventional Cu-SSZ-13 (175-250 °C) after hydrothermal ageing, showing an enhanced low-temperature activity. The Sm ions are found to occupy the six-membered rings (6MRs) of SSZ-13 by X-ray diffraction Rietveld refinement and aberration-corrected scanning transmission electron microscopy. The Sm ions at 6MRs can facilitate the formation of more active [ZCu2+(OH)]+ ions at 8MRs, as revealed by temperature-programmed reduction of hydrogen. X-ray photoelectron spectroscopy and density functional theory (DFT) calculations indicate that there exists electron transfer from Sm3+ to [ZCu2+(OH)]+ ions, which promotes the activity of [ZCu2+(OH)]+ ions by decreasing the activation energy of the formation of intermediates (NH4NO2 and H2NNO). Meanwhile, the electrostatic interaction between Sm3+ and [ZCu2+(OH)]+ results in a high-reaction energy barrier for transforming [ZCu2+(OH)]+ ions into inactive CuOx species, thus enhancing the stability of [ZCu2+(OH)]+ ions. The influence of the ion-exchanging sequence of Sm and Cu ions into SSZ-13 is further investigated by combining both experiments and theoretical calculations. This work provides a mechanistic insight of secondary ions in regulating the distribution, activity, and stability of Cu active sites, which is helpful for the design of high-performance Cu-SSZ-13 catalysts for the NH3-SCR reaction.

Efficient Catalysis for Low-Temperature CO Selective Catalytic Reduction over an Fe-Cu Bimetal Oxide Catalyst Supported on Amorphous SiO2

Efforts have been devoted to exploring the effective composite catalysts for low-temperature selective catalytic reduction of NOx by CO (CO-SCR) using Fe-Cu bimetal oxide (Fe2Cu1) as the active component and rice husk ash (RHA), amorphous SiO2, and activated carbon (AC) as supports. The results showed that the beneficial role of RHA as a catalyst support for CO-SCR was primarily reliant on amorphous SiO2 in RHA and not on AC. Both Fe2Cu1/RHA and Fe2Cu1/amorphous SiO2 catalysts exhibited the best catalytic performance of CO-SCR, which had good stability, wide active temperature range, high conversion ratio, 100% N2 selectivity, and superior resistance to O2, SO2, and H2O (g). The CO and NOx conversion ratios of Fe2Cu1/amorphous SiO2 could reach up to approximately 100% from 100 to 500 °C. The excellent SCR performance was associated with the large specific surface area and good structural stability of amorphous SiO2, the uniform distribution of active sites, dual redox cycle of Fe2O3 and CuO species, and many surface-adsorbed oxygen species, which made amorphous SiO2-based catalysts highly competitive for application in the SCR process. This research provides the underlying insights for the improvement of industrial application to realize ″non-ammonia SCR″ technology with near-zero NOx/CO emissions synergistically at low temperatures.

Engineering hollow mesoporous silica supported cobalt molybdate catalyst by dissolution-regrowth strategy for efficiently aerobic oxidative desulfurization

Heterogeneous catalysts show superior separable and recyclable property in comparison with homogeneous catalysts. However, the conventional synthetic method faces the problem of uneven distribution of active sites. Here, a facile dissolution-regrowth strategy was developed to prepare hollow mesoporous silica nanospheres supported cobalt molybdate (CoMoO4/HMS) under mild conditions, simultaneously, CoMoO4 was obtained in situ. The homogenous dispersion of the active species made the catalyst manifest an outstanding desulfurization efficiency in aerobic oxidative desulfurization compared with the supported single-metal oxides catalysts or supported CoMoO4 catalyst prepared by wet impregnation. The removal efficiency of three sulfur-containing substances, such as dibenzothiophene, 4-methyldibenzothiophene and 4,6-dimethyldibenzothiophene, could reach 100% by 5 h with molecular oxygen as an oxidant. Besides, the sulfur removal of DBT almost did not reduce after at least 8 cycles under the optimal reaction conditions. Through electron spin resonance spectroscopy and radical quenching experiments, O2− was determined as the main active oxygen species for sulfur oxidation. This dissolution-regrowth strategy can be used to prepare a series of supported multi-metal oxides for various applications.

Quantitative analysis of framework Al at channel intersections of HZSM-5 zeolite by toluene adsorption–desorption

Precise analysis of the framework Al (AlF) at channel intersections of HZSM-5 zeolite is the basis of fine tuning of the spatial distribution of active sites within different pores which is critical to promote the catalytic performance in various applications. However, existing technologies cannot provide reliable quantitative results either in theory or practice due to the co-existence of Al pair and single Al. Here we report a new method based on toluene adsorption–desorption. As a promising probe, toluene can be preferentially adsorbed on AlF at channel intersection under low loading (≤4 molecules/unit cell) due to spatial matching and energetic heterogeneity. After strengthening the toluene/AlF affinity through replacing H+ by Na+ and designing a new stepwise TPD technique (toluene-STPD), the contents of AlF atoms at channel intersections of HZSM-5 samples were successfully calculated by counting the desorbed toluene molecules based on the 1:1 stoichiometric relationship between adsorbed toluene and AlF.

Controlled Growth Interface of Charge Transfer Salts of Nickel-7,7,8,8-Tetracyanoquinodimethane on Surface of Graphdiyne

Controlled Growth Interface of Charge Transfer Salts of Nickel-7,7,8,8-Tetracyanoquinodimethane on Surface of Graphdiyne

Nanoarchitectured superparamagnetic iron oxide-doped mesoporous carbon nanozymes for glucose sensing

The incorporation of nanoarchitectonics into the development of nanozymes to achieve target-specific geometry, dense active sites, and cascade catalysis is highly demanded for developing ultrasensitive bioassays. The improved dispersion and uniform distribution of metal active sites onto a three-dimensional (3D) mesoporous carbon support (MC) with a high surface area can lead to enhanced substrate binding, mobility, and collision probability and therefore, increased peroxidase mimetic activity. Herein, we report the fabrication of well-dispersed superparamagnetic iron oxide (IO) nanoparticles (NPs) on mesoporous carbon (IO-MC) support with high Fe3+ active sites, high surface area, and ordered mesoporous pore channels that show promising catalytic activity at room temperature. The as-prepared IO-MC shows good nanozyme activity at room temperature with highly favorable Michaelis-Menten constant, Km (0.242 mM) and fast reaction rate (0.193 × 10−7 MS−1). Finally, we demonstrate the functionality and pre-eminence of IO-MC nanozyme for bioassay. As a proof-of-concept, we develop a superior glucose assay that provides a LOD (limit of detection) of 2 µM in the spiked sample. These findings suggest that homogeneously dispersed iron oxide NPs on MC show promising potential as next-generation nanozyme for developing sensitive bioassays.

Dual-template induced multi-scale porous Fe@FeNC oxygen reduction catalyst for high-performance electrochemical devices

The oxygen reduction reaction (ORR), as a key semi-reaction in various electrochemical conversions, was widely studied. The FeNC catalyst showed great potential to replace precious Pt as the ORR catalyst. The multi-scale porous structure was crucial for the catalytic activity of the FeNC catalyst due to the discrete distribution of active sites. Therefore, a dual-template strategy was developed using solid NaCl as the hard template and self-polymerized resin as the soft template to construct a smooth multi-scale porous FeNC (FeNC-DT) catalyst with embedded metallic Fe. The as-prepared catalyst exhibited a half-wave potential of 0.954 V vs. a reversible hydrogen electrode under alkaline conditions. The corresponding zinc-air battery and direct methanol fuel cell (DMFC) using FeNC-DT as the catalyst performed superior to the precious-metal-based catalysts in power density. Especially, the self-breathing DMFC achieved a maximum power of 23 mW/cm2, indicating a great application prospect of the FeNC-DT catalyst in actual electrochemical devices.