Surface Atomic Ratio Research Articles

Unveiling the Dynamic Electrocatalytic Activity of Online Synthesized Bimetallic Nanocatalysts via Electrochemiluminescence Microscopy.

Effective bimetallic nanoelectrocatalysis demands precise control of composition, structure, and understanding catalytic mechanisms. To address these challenges, we employ a two-in-one approach, integrating online synthesis with real-time imaging of bimetallic Au@Metal core-shell nanoparticles (Au@M NPs) via electrochemiluminescence microscopy (ECLM). Within 120 s, online electrodeposition and in situ catalytic activity screening alternate. ECLM captures transient faradaic processes during potential switches, visualizes electrochemical processes in real-time, and tracks catalytic activity dynamics at the single-particle level. Analysis using ECL photon flux density eliminates size effects and yields quantitative electrocatalytic activity results. Notably, a nonlinear activity trend corresponding to the shell metal to Au surface atomic ratio is discerned, quantifying the optimal surface component ratio of Au@M NPs. This approach offers a comprehensive understanding of catalytic behavior during the deposition process with high spatiotemporal resolution, which is crucial for tailoring efficient bimetallic nanocatalysts for diverse applications.

Insight into the role of metal support interface through the synergistic effect between Ag and α-Bi2Mo3O12 support for the selective oxidation of propylene to acrolein

Pre-synthesized morphologically tailored size and shape selective silver nanoparticles (AgNPs) decorated on bismuth molybdate support (AgNPs/α–Bi2Mo3O12) using simple wet impregnation method was employed. The prepared AgNPs/α-Bi2Mo3O12 nanocatalysts were tested in the selective partial oxidation of propylene to acrolein reaction. The introduction of well-defined size and shape of AgNPs on α–Bi2Mo3O12 is greatly promoted the strong metal support interactions (SMSI), creation of oxygen vacancies (Ov) and high propylene adsorption binding energy (calculated by DFT). The strong metal support interactions between Ag and α-Bi2Mo3O12 is clearly elucidated by the high quality HRTEM and STEM–HAADF microscopic images. In addition, surface atomic molar ratio measured by XPS analysis determined the key redox properties of AgNPs/α–Bi2Mo3O12 system and their influence on the overall catalytic efficiency in the oxidation of propylene via reduction of Mo6+ to Mo5+ initiated at low temperatures in Ag/α–Bi2Mo3O12 system. The Mo reduction is further confirmed by the activated oxygen removal from the MoO42– moieties after Ag incorporation on α–Bi2Mo3O12. Thus, confirmed the oxidation reaction pathway follows a Mars–van–Krevelen process. Further, DFT calculations supported the propylene adsorption is more favorable over Ag/α–Bi2Mo3O12 than bare α–Bi2Mo3O12 support. The propylene oxidation performance over Ag/α–Bi2Mo3O12 system was 5.5 times higher than bare α–Bi2Mo3O12 support, probably due to an enabled strong metal support interaction and increased oxygen vacancies.

A comparative theoretical study of the mechanism of ammonia decomposition on various Co/Ni catalysts using density functional theory

Bimetallic Co/Ni catalysts have emerged as promising candidates for efficient H2 production via ammonia decomposition. However, due to the diverse range of surface configurations and atomic ratios observed in various Co/Ni catalysts, it is necessary to systematically understand their heightened activity. In this study, a comparative theoretical investigation employing density functional theory was presented to explore the mechanisms of ammonia decomposition on the Co-Ni(1 1 1), Ni-Co(1 1 1), Co2Ni(1 1 1), and CoNi2(1 1 1) surfaces. Our findings highlighted the outstanding catalytic activity presented by Co/Ni catalysts can be attributed to the simplified NN recombination process, with Ni-Co(1 1 1) displaying the lowest energy barrier. We verified that the exceptional performance of Co/Ni surfaces is due to the exclusive synergistic and alloying effects that arise from combining Co and Ni metals. Electronic structure analysis had proved the combined effect of electron transfer from Cobalt to Nickel, resulting in moderate N binding energy, aid in the desorption and transfer of Nitrogen atoms. In addition, we showed that the appropriate Co/Ni catalyst ratio and catalyst surface configuration can improve the catalytic activity of hydrogen production, which provided another strategy for catalyst design.

Highly sensitive resistive humidity sensor based on strontium-doped lanthanum ferrite nanofibers

Humidity sensors are the most widely applied sensors. Although some highly sensitive humidity sensors have been explored, devices that can accurately detect low humidity are still required. Improving the adsorption of water molecules by surface regulation is an effective way to enhance humidity sensitivity. In this study, electrospinning prepared a series of lanthanum ferrite samples doped with different concentrations of strontium. For the sample with a surface atomic ratio between strontium and lanthanum was approximately 0.2, there was a 6×104 times change in the resistance of the sensor to 90% relative humidity, and the response was 6.76 for 4% relative humidity. Negligible hysteresis, and excellent stability demonstrate the advantages of the strontium-doped lanthanum ferrite nanofibers. The sensing mechanism was discussed by measuring the change of band gap and work function of samples with different concentrations of strontium doping. Furthermore, suitable doping also decreased the adsorption energy and increased the charge transfer during the adsorption of water molecules on the surface of lanthanum ferrite based on the calculations. This study provides a new perspective for enhancing the sensitivity of humidity sensors via surface regulation.

Temperature-mediated in-situ formation of antimony nanoclusters inside carbon nanofibers for chloride-driven capacitive deionization

Slow desalination kinetics and poor durability constrain the practical application of faradic electrode-directed capacitive deionization (FDI) systems. In view of this, we developed a temperature-mediated in-situ synthesis strategy for fabricating Sb nanoclusters inside carbon nanofibers (Sb NCs@CNF) as Cl− capturing electrodes for high-efficiency FDI. The synthetic strategy allows “temperature-controlled evaporation” of Sb species from the nanofibers, which not only makes the formation of ultrasmall Sb NCs possible but also provides CNF shells to enhance the structural stability and electrical conductivity of Sb NCs. Benefiting from the specific interaction between Sb species and Cl− ions, ultrasmall size, high surface atom ratio of Sb NCs, as well as the protective CNFs shell, the as-fabricated Sb NCs@CNF-based Cl−-driven FDI achieved fast desalination rate (up to 0.24 mg g−1 s−1, through expanding the contribution of surface-controlled capacitance) and excellent cycling stability (only 12.4 % desalination capacity reduction after 30 cycles). In addition to the unprecedented design of Sb NCs-based Cl− capturing electrode materials, this study also provides a paradigm in the temperature-mediated in-situ synthesis of non-coinage MNCs, which may stimulate more research activities in the design and application of carbon-protected MNCs.

Multicationic LDH-derived Co(x)CeMgAlO mixed oxide catalysts for the total oxidation of methane

Several Co(x)CeMgAlO mixed oxides with different cobalt contents x between 7 and 50 at% with respect to cations, but with fixed 10 at% Ce and Mg/Al atomic ratio of 3, were obtained by the calcination of layered double hydroxide (LDH) precursors at 750 °C. The mixed oxide catalysts were characterized by XRD, nitrogen adsorption, DRIFT, DR-UV-Vis, SEM-EDX, including elemental mapping, XPS, H2-TPR and O2-TPO techniques. XRD analysis indicated the coexistence of Co3O4 crystallites with periclase-like and ceria phases, distributed homogeneously as shown by EDX measurements. The surface composition determined by XPS and the redox properties studied by H2-TPR and O2-TPO were shown to be key factors controlling the catalytic behavior of the investigated materials. Their catalytic performance was evaluated in the total oxidation of methane, used as a volatile organic compound (VOC) model molecule. Co(40)CeMgAlO mixed oxide showed the highest catalytic activity for methane combustion with a T50 of 528 °C, associated with its greatest Co/Ce surface atomic ratio and the best redox properties in the Co(x)CeMgAlO series. In addition, the influence of the contact time on the catalytic activity of the Co(40)CeMgAlO mixed oxide has been examined and its good stability was evidenced from combustion tests with prolonged time on stream. Nevertheless, the addition of water vapors to the reaction mixture induces textural and structural changes of the mixed oxide with negative consequences on its performance.

Sub-1 nm: A Critical Feature Size in Materials Science

ConspectusSize is one of the most important issues in materials science. Sizes of conventional nanomaterials are usually one to one hundred nanometers and, according to size effect, nanomaterials usually exhibit different optical, electrical, magnetic, thermal, and catalytic properties compared with bulk materials. As the important transition from atomic scale to nanoscale, subnanometer scale is a critical feature size in materials science. With the size of nanomaterials decreasing to subnanometer scale, they further show some distinctive properties. First, subnanometer materials (SNMs) show ultrahigh specific surface area and nearly 100% surface atomic ratio, greatly enhancing their interaction with external fields. Second, the intermolecular interaction between SNMs can dominate their self-assembly process, similar to the self-assembly process of some biomacromolecules. Third, due to the dimensional similarity, one-dimensional (1D) SNMs exhibit polymer-analogue properties, endowing them easy processability. And thus, SNMs not only show excellent optical, catalytic, adhesive properties, etc. but also can be processed into functional fabrics, films, gels, and so on. In order to construct functional SNMs, a good/poor solvent system and cluster–nuclei coassembly strategy are developed, which are facile and widely applicable. Until now, various SNMs with different compositions, morphologies, and structures have been prepared successfully through these two methods, and temperature-scale and large-scale preparation are realized for some SNMs, laying a solid foundation for practical applications of SNMs. Based on the cluster–nuclei strategy, multiple effective components can be combined into the block copolymer-analogue structures, and the performance can be improved due to the synergistic effect. And through assembling polyoxometalate (POM) clusters into clusterphene structures, electron delocalization may be realized to greatly enhance the catalytic performance. This Account summarizes some work of our group on SNMs, including structures, polymer-analogue properties, assembly, processing, and catalytic performance. In the structure part, the intrinsic chirality, block copolymer-analogue structure, and metal cation-bridging-POM anion structure are mainly introduced. Then the polymer-analogue properties of 1D SNMs are briefly discussed, including the dispersion, gelation, and adhesion properties. Subsequently, the self-assembly, electrospinning, and wet-spinning of SNMs and surfactant-assisted assembly of POM clusters etc. are introduced. Finally, tailoring catalytic properties in subnanometer scale through synergetic effects and possible electronic delocalization is discussed, which is based on the cluster–nuclei coassembly strategy and surfactant-assisted assembly of POM clusters. The SNMs show great potential in catalysis, optics, adhesion, gelation, and so on, paving a new path for the applications of nanomaterials. This Account briefly introduces the current progress and future challenges in the field of SNMs and we hope this Account will be informative for researchers interested in SNMs and give new inspiration to them.

Transition Metal Dichalcogenides for Photo/Electrochemical Energy‐Based Applications

The increasingly depleted fossil fuels have brought unprecedented energy crises and environmental hazards, so the developments of novel renewable clean energy resources have become an urgent need for social development. In recent years, the rise in 2D nanomaterials has brought new hope for energy conversion and storage. These unique 2D nanomaterials have a large specific surface area and a high surface atomic ratio. Among many energy solutions, the photo‐/electrocatalytic process of hydrogen production is widely studied as practical applications of energy conversion. Hydrogen evolution reaction is the conversion of solar energy into hydrogen energy. The design and synthesis of high‐efficiency hydrogen production photo‐/electrocatalysts are particularly important for improving energy conversion performance that has become a hotspot for scientists to study in pursuit of this goal. The stabilization of metal‐phase 1T‐MS2 (M = molybdenum/tungsten), its heterojunction liquid‐phase synthesis, photocatalytic properties, and the supercapacitor properties of the synthesized structure is studied. For use in supercapacitors, transition metal dichalcogenides‐based materials including metallic and semiconducting phases have gained great scientific interest. The large specific area and sheet‐like morphology allow layered transition metal dichalcogenides (TMDs) nanomaterials to store charges by intrasheet and intersheet double layers over individual layers of TMD.

Coordination Engineering of Ultra‐Uniform Ruthenium Nanoclusters as Efficient Multifunctional Catalysts for Zinc–Air Batteries

The lack of highly efficient, inexpensive catalysts severely hinders the large‐scale application of electrochemical energy conversion technologies (e.g., electrochemical hydrogen evolution reaction (HER) for hydrogen production, metal–air batteries (Cathode: oxygen reduction reaction (ORR))). As a new class of nanomaterials with a high ratio of surface atoms and tunable composition and electronic structure, metal nanocluster (NCs) are promising candidates as catalysts. Herein, a novel catalyst using S,N‐doped carbon matrix (NSCSs) is synthesized to efficiently stabilize high density and ultra‐uniform ruthenium (Ru) nanoclusters (Ru@NSCSs) by small‐molecule self‐assembly pyrolysis approach. The obtained Ru@NSCSs catalyst exhibits outstanding HER activity in all pH conditions (especially with a low overpotential of 5 mV at a current density of 10 mA cm−2 in 1 m KOH) and excellent ORR performance (half‐wave potential (E 1/2) of 0.854 V in 0.1 m KOH). Based on the experimental investigations and theoretical calculations, it is discovered that the S‐atom can modulate the electronic structure and optimization of redox states on the surficial sites of Ru NCs during the ORR process. This work provides a feasible strategy for understanding and regulating the metal–support interface of ultra‐uniform nanoclusters catalysts.

Boosting the activity of PdAg2/Al2O3 supported catalysts towards the selective acetylene hydrogenation by means of CO-induced segregation: A combined NAP XPS and mass-spectrometry study

Selective hydrogenation (or semi-hydrogenation) of acetylene into ethylene is an important industrial process. The aim of the present work is thus to learn regularities governing the CO-induced segregation and elaborate practical procedures for tuning the surface structure of Pd-Ag nanoparticles to improve their catalytic performance towards the selective hydrogenation of acetylene to ethylene. Utilizing NAP XPS the CO adsorption-induced Pd atoms segregation in supported PdAg2/Al2O3 catalysts already at room temperature has been shown. The surface enrichment with Pd further increases if the treatment temperature is increased up to 250 °C. This specific configuration with a redistributed Pd/Ag surface atomic ratio is appreciably stable and self-sustained even at the absence of CO at moderately elevated temperatures. Nevertheless, a reductive treatment in hydrogen at 450 °C reverts the nanoparticle surface structure to the pristine state. Catalytic properties of this peculiar CO-induced configuration of PdAg2/Al2O3 towards the selective acetylene hydrogenation was investigated using a combination of NAP XPS and MS techniques. The PdAg2/Al2O3 catalyst with the surface enriched with Pd due to the CO-induced segregation manifests improved activity with 100 % selectivity under the conditions used. The results obtained clearly demonstrate that CO adsorption-induced segregation is a powerful tool that can be used to optimize the surface composition and catalytic performance of bimetallic nanoparticles.

LDHs-based bifunctional electrocatalyst for effective tunable syngas generation via CO2 reduction

Electrocatalytic reduction of CO2 into syngas (CO and H2) has been recognized to be a promising approach to achieve carbon neutrality. However, producing syngas with tunable H2/CO ratios in a wide range is still challenging. Herein, nitrogen doped graphene aerogel (GA) supported both single-atomic Ni and Ni nanoparticles (NPs) with a surface atomic ratio of 1.11 were constructed by using layered double hydroxide (LDHs) and g-C3N4 as Ni and N precursors, respectively. H2 and CO are the only products of CO2 electroreduction and the ratio of H2/CO can be tuned from 0.4 to 2.5 by changing applied potentials. In addition, the catalyst exhibits a large CO Faradaic efficiency (74%) and good long-term stability (12 h) at a relatively small potential (−0.67 V vs. RHE). This study will shed a new light on the construction of bifunctional catalysts for efficient tunable syngas generation via electroreduction of CO2.

Structural features and thermal stability of hollow-core Si nanowires: A molecular dynamics study

A molecular dynamics simulation with a Tersoff modified potential was used to investigate the structural features of hollow-core Si nanowires with outer radii of 1.6–3.8 nm at different temperatures. By utilizing the identifying diamond structure method and with analysis of the radial distribution function, we found that an increase in the cavity volume causes amorphization of the nanowires and may be associated with the large ratio of surface atoms to the total number of atoms in the nanowires. Typically, complete amorphization of hollow nanowires occurs when the wall thickness is comparable to the lattice constant of silicon. The simulation also showed that, for a given temperature, there is some threshold volume of the cavity, exceeding which leads to the complete amorphization of the nanowire. In addition, systematic work on the melting behavior of hollow-core Si nanowires was carried out. It was found that the melting of the Si hollow-core nanowires starts from the surface and rapidly extends to the inner regions of the nanowires as the temperature increases. The melting temperature of the Si nanowires was reduced by 200–500 K when the cavity volume fraction increased. It was observed that melting points decrease drastically in hollow-core nanowires with percentages of surface atoms above 50%. The present results provide a deep understanding of the different physical properties of hollow-core nanowires.

Glycerol Valorization over ZrO2-Supported Copper Nanoparticles Catalysts Prepared by Chemical Reduction Method

Copper nanoparticles (NPs) and ZrO2-supported copper NPs (Cu NPs/ZrO2) were synthesized via a chemical reduction method applying different pH (4, 7 and 9) and evaluated in a glycerol dehydration reaction. Copper NPs were characterized with transmission electron microscopy (TEM) and UV–vis spectroscopy. Transmission electron microcopy (TEM) results revealed a homogeneous distribution of copper NPs. A hypsochromic shift was identified with UV–vis spectroscopy as the pH of the synthesis increased from pH = 4 to pH = 9. Zirconia-supported copper NPs catalysts were characterized using N2 physisorption, X-ray diffraction (XRD), TEM, X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), temperature-programmed desorption of ammonia (NH3-TPD) and N2O chemisorption. The presence of ZrO2 in the chemical reduction method confirmed the dispersion of the copper nanoparticles. X-ray diffraction indicated only the presence of tetragonal zirconia patterns in the catalysts. XPS identified the Cu/Zr surface atomic ratio of the catalysts. TPR patterns showed two main peaks for the Cu NPS/ZrO2 pH = 9 catalyst; the first peak between 125 and 180 °C (region I) was ascribed to more dispersed copper species, and the second one between 180 and 250 °C (region II) was assigned to bulk CuO. The catalysts prepared at pH = 4 and pH = 7 only revealed reduction at lower temperatures (region I). Copper dispersion was determined by N2O chemisorption. With NH3-TPD it was found that Cu NPs/ZrO2 pH = 9 exhibited the highest total quantity of acidic sites and the highest apparent kinetic constant, with a value of 0.004 min−1. The different pH applied to the synthesis media of the copper nanoparticles determined the resultant copper dispersion on the ZrO2 support, providing active domains for glycerol conversion.

Effects of Nano Aluminum Powder on the Mechanical Sensitivity of RDX-Based Explosives.

As nano-aluminum powder (NAP) can improve the detonation performance of aluminum-containing explosives, more and more explosives with NAP as the metal ingredient have been studied. It is believed that the mechanical sensitivity of explosives can be significantly enhanced by the added nano-sized aluminum powder. However, the mechanism for the enhancement has not been clarified. In order to illuminate the effects of NAP on the mechanical sensitivity of explosives, two RDX-based aluminum-containing explosives with the same weight ratio and preparation process were investigated despite the aluminum powders with different nano-size and micron-size. The morphology and surface atomic ratio of the two explosives were examined by scanning electron microscopy with energy dispersive spectroscopy tests. The contact angle and other microstructures properties of the explosives were calculated by Material Studio software. Results revealed that the impact and friction activity was determined by the aluminum particle sizes and explosive components. This paper clarified the mechanism for the increase in explosives sensitivity by the addition of NAP, which provide reference for the scientific and technical design of novel explosives.

A novel model for predicting the effective specific heat capacity of molten salt doped with nanomaterial for solar energy application

In order to establish instructions for high-performance molten salt preparation, this paper focuses on accurate prediction method on the effective heat capacity of nanomaterial-enhanced molten salt (NMS). With carbon nanotube (CNT) enhanced carbonate eutectic (Li2CO3-K2CO3) taken as the study subject, the microscopic mechanism of nanomaterial on the effective specific heat capacity enhancement of molten salt is revealed. The nanolayer content is calculated, and the specific heat capacity of CNT and nanolayer is quantified. Accordingly, the effective heat capacity prediction model is completed. In addition, the CNT-enhanced carbonate eutectic is experimentally prepared with a high-energy ball milling method. Its effective specific heat capacity is measured and used to validate the prediction model. The results show that, firstly, the thickness of nanolayer is 0.65 nm and 0.98 nm in the single-walled CNT case and multi-walled CNT case, respectively. Secondly, the specific heat capacity of CNT is 1.613 J·g−1·K−1 at 800 K, and the specific heat capacity of nanolayer increases with increasing the surface atom ratio. Finally, the effective specific heat capacity of CNT-enhanced carbonate salt is predicted and validated with experimental results. It is revealed that, in the cases of well-dispersed nanomaterial-enhanced molten salt, the prediction method presented in this research has considerable accuracy (error < 2.90%). Furthermore, the effective specific heat capacity of NMS doped with CNT of various diameter is given.

Bioglass Ti coatings: Influence of thermal annealing on the evolution of calcium phosphate formation, phase and morphology

Bioglass films were prepared on Ti disks used for dental implants using very simple sol-gel synthesis and dip-coating process. The influence of annealing temperatures, 37 °C and 600 °C, on the surface morphology and chemical composition was investigated using SEM, AFM, DRIFT and XPS techniques. Biocompatible calcium phosphate phases were successfully formed when the disks were kept in contact with simulated biological fluid at three different immersion times: 7, 24 and 160 h. For the films annealed at 37 °C calcium phosphate was formed which was confirmed through the analysis of the intensity ratios of P-O, Ti-O-Ti and Si-O absorption bands in the DRIFT spectra. Ca/P and O/Ca surface atomic ratios obtained by XPS data indicated the formation of dibasic calcium phosphate dehydrate and dibasic calcium phosphate, revealing a coated material at low temperatures, 37 °C, promising for medical applications.

Activity and sulfur resistance of co-impregnated bimetallic PdNi/γ-Al2O3 catalysts during hydrogenation of styrene

Pyrolysis gasoline (PyGas) is an unstable byproduct of the pyrolysis of naphtha and other hydrocarbons for the production of olefins. PyGas is stabilized by hydrogenation at mild conditions. The hydrogenation of styrene to ethylbenzene is considered a model test reaction for studying the selectivity of the catalysts because it has the slowest rate of conversion. The catalytic activity and selectivity of two bimetallic co-impregnated Pd–Ni catalysts supported on γ-alumina were assessed and compared to those of a commercial monometallic Pd catalyst (AXENS LD265). The laboratory-prepared catalysts had different metal content and Pd:Ni atomic ratios (1:1 and 1:7). Catalytic tests of selective hydrogenation of styrene to ethylbenzene were made in a batch stirred tank reactor and in a continuous fixed bed trickle bed reactor. The sulfur resistance of the bimetallic catalysts in semicontinuous condition, was assessed by means of the same operational conditions using thiophene as a model poison compound. The support, Pd–Ni co-impregnated catalysts and LD265 commercial catalysts were further characterized by N2 chemisorption, EPMA, OM, ICP elemental analysis, temperature programmed reduction, XPS and X-Ray diffraction. The results indicated the presence of different metal species: Pd0, Pdδ+, Ni0 and NiO. The lab-prepared bimetallic catalysts were found to be active for the selective hydrogenation of styrene (both in the batch and continuous system). During the continuous evaluations, the commercial LD265 catalyst had an intermediate activity level that lied between the values corresponding to the Pd–Ni bimetallic catalysts: PdNi(1:1) $$ \gg $$ LD265 > PdNi(1:7). During the poison free semicontinuous evaluations, the pattern of conversion as a function of contact time of co-impregnated Pd–Ni catalysts are quite similar to that of commercial LD265 catalyst, though the catalytic activity is slightly better for PdNi(1:1). After 90 min of contact time the order of conversion was: PdNi(1:1) > LD265 > PdNi(1:7). On the other hand, during the poison semicontinuous tests (with 300 pp of thiophene), the initial reaction rates of the co-impregnated catalysts decreased, pointing a poisoning of the active sites by thiophene. PdNi(1:1) had higher initial reaction rate than PdNi(1:7) during poison free or poisoned in both conditions. PdNi(1:7) was more sulfur resistant than PdNi(1:1). The higher activity of the PdNi(1:1) catalyst was attributed to the presence of Pd0 and Pdn+/Nim+ species that favored respectively, the homolytic cleavage of the H–H bond and the adsorption of styrene. The higher sulfur resistance of the PdNi(1:7) catalyst would be associated with the higher Cl/Al surface atomic ratio in this catalyst (electronic effect) and the presence of electrodeficient species of Pd (Pdxδ+OyClz) that prevented the adsorption of thiophene by steric hindrance (geometrical effect of the large species) or by electronic effects.

Fragmenting C60 toward enhanced electrochemical CO2 reduction

Carbon-based metal-free catalysts exhibit great applications in electrochemical CO2 reduction (ECR), while most studies merely focus on large-sized carbons with limited ratio of surface atoms for engineering to create surface active centers. Here, we report a joint treatment of C60 by heating and plasma to induce a dramatic performance promotion during ECR. The electrochemical measurements indicate the Faraday efficiency for ECR toward CO production kept at high level over 80% in a wide potential region from − 0.4 to − 0.7 V versus RHE, with the highest value reaching 96.8%. The physical characterization reveals that fragmentation of C60 occurs together with N/O doping, both of which could induce change in electron structure, causing the formation of *COOH intermediate and ultimately leading to the optimized activity and selectivity for CO production. This treatment route was further revealed to be applicative for other carbon materials, e.g., single-walled carbon nanotube, to promote its ECR activity and selectivity.

Molten salt synthesis and characterization of 1D sodium hexatitanate nanowires

The synthesis of Na2Ti6O13 nanowires (NTNW) was performed at chemical interaction between rutile nanopowder with sodium chloride flux on the surface of molten aluminum under air. Synthesis of NTNW proceeds at two stages reaction at the three-phase boundary “gaseous medium (air)/molten salt/molten metal (Al)” under the quasi-autocatalytic mechanism.SEM, micro-Raman spectroscopy, X-Rays photoelectron spectroscopy, electron dispersive spectroscopy, and XRD are used to characterise NTNWs.The composition and morphology of NTNW can be controlled by experiment parameters. The increasing of synthesis temperature up to 850 °C allows getting single-phase product. Further increase in temperature up to 950 °C leads to increase in sodium concentration in NTNW. The ratio between the length and diameter of NTNW reaches 50.During high-temperature MS synthesis at 850–950 °C NTNW with some reduced Ti3+ were obtained. When the temperature of sodium hexatitanate nanorods and nanowires synthesis in molten salt media elevated to 950 °C, the amount of reduced Ti3+ atoms increased, giving a Ti3+/Ti4+ surface atomic ratio of 0.112.The sodium hexatitanate nanorods mainly formed by TiO6 octahedrons connected with corner-shared OO bridge bands wherein Na ions stay between layers. This position of Na+ ions is prospective for possible application of sodium hexatitanates in sodium-ion batteries.

Surface structure tuning of BiOCl nanosheets by the sequential introduction of oxygen vacancies, PO43− and Ag+ for boosting photodegradation of tetracycline hydrochloride

The surface structure significantly impacts the physicochemical properties of semiconductors. Constructing heterojunction is a universal approach to tune surface structure, which can effectively accelerate the charge transfer at the interface. Here, BiOCl nanosheets which occupy high ratio of surface atoms to entire atoms were used as a model photocatalyst, and a strategy was proposed to tune its surface structure by sequential introduction of oxygen vacancies, PO43− and Ag+ on surface of BiOCl nanosheets. In order to inhibit the overgrowth of heterogeneous component, the excess PO43− was timely removed by centrifugation before adding Ag+. As a result, the as-obtained optimal sample which was confirmed to be a composite composed of BiOCl, BiPO4 and AgCl showed superior photocatalytic activity for tetracycline hydrochloride degradation with the rate of 38 times higher than that of pristine BiOCl, which was mainly attributed to the quick migration of photongenerated carrier. The active species h+ and •O2− played a vital role in this degradation process. Our strategy not only greatly saved investment of noble metal Ag, but also provide superior stability. On the basis of experimental results and density functional theory calculation, the visible-light driven catalytic mechanism was revealed.