Commercial Nanopowder Research Articles

Graphene Supported Silicon Nanocomposites As Anode for Lithium-Ion Batteries

This work indicates Silicon/Grphene (Si/G) nanocomposites anode on the performance in lithium-ion batteries (LIBs).The self-assembled graphene aerogel and silicon (Si/G) anode materials with some surface defects have been successfully prpared by hydrothermal synthesis using chemically modified graphene oxide and commercial Si nanopowder (about 50 nm) as precursor. The morphologies and textural properties of as-obtained Si/G were investigated by scanning electron microscopy, X-ray photoelectron spectroscopy, and other sturucture techniques. The surface defects and electrical conductivities of Si/G can be controlled by adjusting the amount of Si nanopowder. The results indicate that Si/G with Si amount of half exhibits excellent stability and reversible capacity and superior rate capability with excellent cycling stability. It is demonstrated that the 3D porous network with increased defect density, as well as the considerable electrical conductivity, results in the excellent electrochemical performance of the as-made Si/G anodes in LIBs.

Methods of Distributing the IF-WS2 Modifier for Its Introduction into the Structure of the Al2O3 Aluminum Oxide Coating

The microstructures and structures of modified Al2O3/IF-WS2 coatings prepared on aluminum substrates are studied. Amorphous Al2O3 oxide coatings are obtained on EN AW 5251 aluminum alloy using the electrooxidation process. The quality of the IF-WS2 nanopowder is of great importance in the process of its introduction into the nanopores of the Al2O3 oxide coating. Commercial nanopowder tends to agglomerate, and without appropriate pretreatment, it is difficult to introduce it into the nanopores of the coating. To improve the degree of fragmentation of the IF-WS2 nanopowder, an experiment was carried out to distribute the nanopowder in the presence of strong ultrasounds, and new conditions for introducing the powder into the nanopores were used. A two-level design of experiment (DOE) was used. The SEM examination made it possible to conclude that Method A contributed to a more even distribution of nanoparticles in the microstructure of Al2O3 coatings. GIXD analyses showed the presence of WO3 derived from the IF-WS2 modifier next to crystal structures derived from aluminum and WS2. Modification of coatings using Method A resulted in surfaces with lower contact angles measured with polar liquids and higher surface free energy compared to Method B.

Ir metal nanoparticles and IrO2 for acidic oxygen evolution reaction: Insight from Raman spectroscopy

Due to their high activity and stability, Ir-based materials are state-of-the-art electrocatalysts for oxygen evolution reaction (OER) under acidic conditions. However, many factors such as the influence of the activation/conditioning protocol and the resulting oxidation state or the effect of electrolyte adsorption on activity are still debated or overlooked. Herein, Raman spectroscopy was performed on commercial Ir black and IrO2 nanopowders to reveal differences in the samples after activation, as well as adsorption of perchlorates. Specifically, three different activation protocols were performed, 0.05 to 1.45 VRHE (activated), 0.05 to 1.6 VRHE (activated-long range (l.r.)), and 1.1 to 1.6 VRHE (activated-short range (s.r.)), resulting in different OER activity as well as different Raman spectra. However, only Ir(IV) bands remain visible in the ex situ Raman experiments, which was not sufficient to reveal the hydrated phases in the iridium samples. Therefore, mimicked in situ experiments were performed, which allowed the observation of the hydrated phase, particularly for Ir black, but also showed adsorption of perchlorate anions. In addition, the influence of solvation on Raman band shifts is revealed - along with DFT calculations. Overall, this work paves the way for our future in situ Raman spectroscopy experiments with iridium-based electrocatalysts during activation and OER.

Embedding and cross-sectioning as a sample preparation procedure for accurate and representative size and shape measurement of nanopowders

Reliable measurement of the size of polydisperse, complex-shaped commercial nanopowders is a difficult but necessary task, e.g., for regulatory requirements and toxicity risk assessment. Suitable methods exist for the accurate characterization of the size of non-aggregated, stabilized, spherical and monodisperse nanoparticles. In contrast, industrial nanoscale powders usually require dedicated sample preparation procedures developed for the analysis method of choice. These nano-powders tend to agglomerate and/or aggregate, a behavior which in combination with an innate broad particle size distribution and irregular shape often significantly alters the achievable accuracy of the measured size parameters. The present study systematically tests two commercially available nanoscale powders using different sample preparation methods for correlative analysis by scanning electron microscopy, dynamic light scattering, Brunauer–Emmet–Teller method and differential mobility analysis. One focus was set on the sample preparation by embedding nanoparticles in carbon-based hot-mounting resin. Literature on this topic is scarce and the accuracy of the data extracted from cross sections of these particles is unclearly stated. In this paper systematic simulations on the deviation of the size parameters of well-defined series of nanoparticles with different shapes from the nominal value were carried out and the contributing factors are discussed.

Exploring the stability and catalytic activity of monoethanolamine functionalized CuO electrode in electrochemical CO2 reduction.

Electrochemical carbon dioxide reduction reactions (eCO2RR) have emerged as promising strategies for both mitigating CO2 emissions and converting them into valuable products. Despite the promise, challenges such as stability, efficiency, and availability of CO2 on the electrode surface, especially at high current densities, still need to be overcome. Herein, this study explores the precipitation of CuO nanoparticles with monoethanolamine to preserve nitrogen groups on the surface of the material. These groups can act by adsorbing the CO2 and stabilizing its catalytic performance during the electroreduction procedure. The incorporation of monoethanolamine as functionalization on the surface of the CuO catalyst was confirmed by XPS measurements. Electrodes utilizing the S-MEA catalyst demonstrated enhanced electrochemical activity, achieving a current density of -187 mA cm-2 at a half-cell potential of -1.2 V versus RHE. Furthermore, long-term stability tests confirmed consistent activity for at least 100 hours in both flow cell and zero gap cell configurations. These results indicate that electrodes featuring the S-MEA catalyst display notably superior electrochemical activity and stability compared with the non-functionalized CuO (S-KOH) and commercial CuO nanopowder (c-CuO). The S-MEA enhancement is attributed to the introduction of amine functional groups that serve as CO2 adducts, facilitating CO2 adsorption and fostering electrode activation. It was evidenced by higher current densities and improved structural integrity during prolonged tests. The insights gained from the comparative performance of these electrodes provide valuable directions for future research in developing more robust and efficient catalysts for environmental remediation technologies.

Электроимпульсное плазменное спекание прозрачной керамики из алюмомагниевой шпинели с повышенным фактором формы

Magnesium aluminate spinel is a promising material for optical application. It can be used as transparent armor, spacecraft windows, scanners, optical elements in night vision systems, as well as a base (matrix) for scintillation and laser materials. The wide range of practical applications of MgAl2O4 ceramics is due to the complex of its unique properties. The research is aimed to creating transparent ceramic materials with an increased shape factor, relevant and of high practical importance. In the presented work, a comprehensive characterization of the commercial nanopowder of magnesium aluminate spinel is completed. Its main structural features are defined. Rheological properties of nanopowder in the process of its compression and thermal consolidation are investigated on the basis of the provisions of the mechanistic pressing model by approximating experimental data of compaction during spark plasma sintering with a dimensionless logarithmic equation, the graphical representation of which allows us to evaluate the possibility of achieving a non-porous state of the consolidated material and optimize the modes of spark plasma sintering. Shown, that the structure of the sealing surface and the search for the optimal way to increase pressure and temperature during spark pulse plasma sintering on this surface can be used to optimize the consolidation modes of transparent ceramics. Verified discrete element modeling of the processes of packing and consolidation of particles of magnesium aluminate spinel nanopowder has been performed. Model and field experiments have shown that the revealed combination of temperature (1300 °C) and static pressure (100 MPa) is sufficient to obtain a porous ceramic structure and does not lead to excessive recrystallization. It is shown that transparent ceramics based on magnesium aluminate spinel with an increased shape factor can be produced by spark plasma sintering at temperature of 1300 °C and static pressure of 100 MPa. The optical and mechanical properties of the manufactured transparent ceramics are comparable to their analogues. The light transmission of samples reaches 41% of the visible spectrum and 64% in the infrared spectrum, the Vickers microhardness value is 15.6±0.5 GPa, crack resistance is 4.4±0.4 MPa·m1/2, compressive strength is 1.37±0.23 GPa, Poisson's ratio is 0.26±0.01, Young's modulus - 278±6 GPa, shear modulus - 110±2 GPa.

SrTiO3 Based Two Dimensional Nanoplatelets for Low-Cost Solar Hydrogen Generation: Materials Beyond the State-of-the-Art

SrTiO3 is an important multifunctional perovskite, that can possess versatile characteristics such as photocatalytic behaviour, ferroelectricity, high electronic conductivity and others. In the context of solar hydrogen (H2) generation, Domen’s group has investigated SrTiO3 for almost two decades and finally have been able to achieve quantum efficiencies approaching unity [1] and large-scale demonstrations [2]. However, the achieved solar to hydrogen (STH) efficiencies remain well under 1%. One of the key bottlenecks limiting the photocatalytic efficiencies of SrTiO3 is its wide bandgap that limits its visible light absorption capability. Several strategies have been used to reduce the bandgap of SrTiO3 to improve visible light absorption but it can only be improved up to a certain limit. Nevertheless, there are other challenges as well in the form of higher recombination rates and an alternate way to further improve the photocatalytic rates is to employ strategies that can inhibit the recombination of photogenerated charges. Our group has been investigating the effect of Al doping on the morphological as well as chemical properties of SrTiO3 to gain fundamental understanding behind the improvement in photocatalytic rates. Our recent report explains that Al ions in SrTiO3 lattice act as hole trapping sites, which helps in suppressing charge recombination [3].Furthermore, to go beyond the current state-of-the-art, our group has been working on forming 2D SrTiO3 heterostructures. The 2D platelets facilitate efficient charge separation as their low thickness enables fast charge transport to the surface, where they are utilized for redox reactions. 2D area also offers large number of active sites and the possibility to form 2D/2D heterostructure with maximum face contact between two semiconductors. However, SrTiO3 does not have a thermodynamic tendency to grow in 2D morphology. Our group has designed hydrothermal conditions to form 2D SrTiO3-based platelets (Fig. 1) through topochemical transformation reaction at a much lower temperature of 200⁰C [4]. Without any support from noble-metal doping or cocatalysts, the epitaxially grown SrTiO3 heterostructural platelets showed stable and 15 times higher photocatalytic H2 production than the commercial SrTiO3 nanopowders. Our recent study [5] elucidates the role of supersaturation conditions on controlling the morphology of these 2D SrTiO3 nano-platelets and formulates their precise growth mechanism. By optimizing the synthetic procedure, the photocatalytic performance can be tuned to achieve much higher STH efficiencies. The presented synthesis strategy provides guiding principles and ideas for designing other defined 2D semiconductors under hydrothermal conditions, eventually going beyond the current state-of-the-art.

Sulfur impurity removal in magnesium aluminate spinel by acid treatment

MgAl2O4 is a versatile and stable oxide that is useful in various applications. However, the presence of impurities originating as a part of the powder synthesis process can potentially impair desired properties. In this work, we performed acidic treatments with mixtures of HNO3 and H2SO4 on commercial MgAl2O4 nanopowders. The treated powder structure and morphology was found to be largely retained, while changes in specific surface area, adsorbed CO2, and sulfur content were detected. Two sulfur species populations were identified (i.e., S2+ and S6+) and their concentration throughout the surface and bulk of the particles was analyzed. Notably, S2+ was beforehand unknown as a contaminant in MgAl2O4. The S2+ concentration could be diminished below detection limit of XPS by increasing the percentage of H2SO4. The insights gained on sulfur impurities present in commercial nanopowders and their removal possibilities or limitations can help utilize such oxides in applications sensitive to chemical purity.

Sequential deposition of FeNC–Cu tandem CO2 reduction electrocatalysts towards the low overpotential production of C2+ alcohols

Tandem CO2 reduction electrocatalysts that combine a material that selectively produces CO with Cu are capable of producing hydrocarbons at low overpotentials and high selectivity. However, controlling the spatial distribution and the catalytic activity of the CO-making catalyst remains a challenge. In this work, a novel tandem electrocatalyst that overcomes limitations of simple Cu catalysts, namely selectivity and efficiency at low overpotential, is presented. The tandem electrocatalysts are prepared through a sequential spray coating protocol, using a single atom Fe in N-doped C (FeNC) as the selective CO-producing catalyst and commercial Cu nanopowder. The high faradaic efficiency towards CO of FeNC (99% observed at −0.60 V vs. RHE) provides a high CO coverage to the Cu particles, leading to reduced hydrogen evolution and the selective formation of ethanol and n-propanol at a much low overpotential than that of bare Cu.

ZnO tetrapod morphology influence on UV sensing properties.

The aim of this work was to investigate how ZnO tetrapod (ZnO-T) morphology, structure, and surface charge properties (i.e. Debye length) influence their UV sensing properties, shedding light on the underlying photoresponse mechanisms. ZnO-Ts were synthesized and centrifuged to obtain three different fractions with tuned morphology, which were characterized by scanning electron microscopy, transmission electron microscopy, and high-resolution transmission electron microscopy microscopies, x-ray diffraction analysis, Brunauer-Emmett-Teller measurements, FTIR and UV-vis spectroscopies. ZnO-T UV sensors were fabricated and tested comparing among ZnO-T fractions and commercial ZnO nanoparticles. ZnO-T photoresponse was mostly influenced by ZnO-T leg diameter, with the optimal value close to the double Debye length. We also demonstrated how fractionating ZnO-Ts for morphology optimization can increased the responsivity by 2 orders of magnitude. Moreover, ZnO-T showed 3 orders of magnitude higher responsivity compared to commercial ZnO nanopowder. These results are beneficial for the engineering of efficient UV sensors and contribute to a deeper understanding the overall mechanism governing UV photoresponse.

Hierarchical porosity design enables highly recyclable and efficient Au/TiO2 composite fibers for photodegradation of organic pollutants

Titanium dioxide (TiO2) nanomaterials are ideal for photocatalytic degradation of organic pollutants but remain infeasible for industrial and municipal wastewater treatment because they cannot simultaneously satisfy two essential criteria for practical application, i.e., high performance and good recyclability. Here, we design and create hierarchically porous TiO2 fibers by dual-polymer templating sol–gel electrospinning combined with precise control over crystallization. The produced fibers own unique interconnected macropores throughout the fiber body that enable significantly enhanced light absorption and unlimited mass transport, making them ideal hosts for anchoring plasmonic nanoparticles (NPs). The Au NP-coupled TiO2 fibers have photocatalytic efficiencies up to 6.6 times higher than plain TiO2 fibers, showing comparable ability as commercial P25 nanopowder in photodegrading methyl blue (MB) and achieving complete decomposition of methyl orange (MO) in 90 min while P25 degrades only 66% MO. Unlike P25 or anatase TiO2 nanopowders that non-reversibly disperse/aggregate in water, our composite fibers can be recollected through natural sedimentation, and their superior performance remains for at least six cycles. This work offers a practical and feasible design for high-performance recyclable photocatalysts for industrial-scale water treatment.

Enhanced degradation of ciprofloxacin in water using ternary photocatalysts TiO2/SnO2/g-C3N4 under UV, visible, and solar light.

In this study, we report on the synthesis of ternary photocatalysts comprising TiO2/SnO2/g-C3N4 for the degradation of ciprofloxacin (CIP) in water. SnO2 nanoparticles were synthesized via the sol-gel method, while g-C3N4 was obtained through melamine calcination. Commercial TiO2 and SnO2 nanopowders were also used. The heterojunctions were synthesized via the wet impregnation method. The photocatalysts were characterized via various techniques, including XRD, TEM, STEM, FTIR, N2 adsorption, UV-Vis DR, and hole tests. Photocatalytic degradation tests of CIP were carried out under UV, visible, and solar radiation. The P25/npA/g-C3N4 (90/10) material exhibited the best performance, achieving CIP degradation of over 97%. The synthesized materials demonstrated excellent initial adsorption of CIP, around 30%, which facilitated subsequent degradation. Notably, the CIP photocatalytic degradation tests performed under solar radiation showed a synergistic effect between the base materials and carbon nitride in highly energetic environments. These results highlight the effectiveness of ternary photocatalysts TiO2/SnO2/g-C3N4 for CIP degradation, particularly under solar radiation.

Mechanical Behavior of Transparent Spinel Fabricated by Spark Plasma Sintering

In this work, a transparent nanostructured ceramic magnesium aluminate spinel (MgAl2O4) was fabricated by Spark Plasma Sintering (SPS) from commercial spinel nano-powders at different temperatures (1300, 1350 and 1400 °C). The sintered samples were thoroughly examined to assess their microstructural, optical, and mechanical properties. Various techniques such as SEM, AFM, spectrophotometer with an integrating sphere, instrumented Vickers indenter, Pin-on-Disk tribometer, scratch tester, and sandblasting device were employed to characterize the sintered samples. The results indicated the significant impact of the sintering temperature on the properties of the spinel samples. Particularly, the samples sintered at T = 1350 °C exhibited the highest Real In-line Transmission (RIT = 72% at 550 nm and 80% at 1000 nm). These samples demonstrated the highest hardness value (HV = 16.7 GPa) compared to those sintered at 1300 °C (HV = 15.6 GPa) and 1400 °C (HV = 15.1 GPa). The measured fracture toughness of the sintered samples increased substantially with increasing sintering temperature. Similarly, the tribological study revealed that the friction coefficient of the sintered spinel samples increased with the sintering temperature, and the spinel sintered at 1350 °C exhibited the lowest wear rate. Additionally, sandblasting and scratch tests confirmed the significant influence of the sintering temperature on the mechanical properties of the fabricated spinels. Overall, the spinel sintered at 1350 °C presented the best compromise in terms of all the evaluated properties.

P-n heterojunction of nickel oxide on titanium dioxide nanosheets for hydrogen and value-added chemicals coproduction from glycerol photoreforming

Selective photocatalysis to simultaneously produce sustainable hydrogen and value-added chemicals from biomass or biomass derivates is attracting extensive investigations. However, the lack of bifunctional photocatalyst greatly limits the possibility to realize the “one stone kills two birds” scenario. Herein, anatase titanium dioxide (TiO2) nanosheets are rationally designed as the n-type semiconductor, combining with nickel oxide (NiO) nanoparticles, the p-type semiconductor, resulting in the formation of a p-n heterojunction structure. The shorten charge transfer path and the spontaneous formation of p-n heterojunction endow the photocatalyst with efficient spatial separation of photogenerated electrons and holes. As a result, TiO2 accumulates electrons for efficient hydrogen generation while NiO collects holes to selectively oxidize glycerol into value-added chemicals. The results showed that by loading 5% nickel into the heterojunction caused a remarkable rise in the generation of hydrogen (H2). The combination of NiO-TiO2 created 4000 µmolh−1g−1 of H2, which is 50% greater than the H2 production from pure nanosheet TiO2 and 63 times more than the H2 production from commercial nanopowder TiO2. Then, by changing loading amount of Ni, it is found that when 7.5 % of Ni is loaded the highest amount of hydrogen production achieved, 8000 µmolh−1g−1. By employing best sample (S3), 20 % of glycerol converted to value added products, glyceraldehyde and dihydroxyacetone. The feasibility study revealed that glyceraldehyde generates the largest portion of yearly earnings at 89%, while dihydroxyacetone and H2 account for 11% and 0.03% of the annual revenue, respectively. This work provides a good example to simultaneously produce green hydrogen and valuable chemicals with the rational design of dually functional photocatalyst.

Low-temperature and single-step synthesis of fully-dense MgAl2O4 by reaction spark plasma sintering Al2O3 and MgO nano-oxides

The availability of commercial nano-powders and the rapidly maturing powder metallurgy technology have enabled researchers to develop advanced ceramics, with tailored microstructure and improved properties. However, a major challenge in the production of MgAl2O4, from Al2O3 and MgO, is the relatively high-volume expansion (5–8%) accompanying spinellization. This study demonstrates the possibility to prepare fully-dense and single-phase magnesium aluminate spinel, at low temperature and in short time, without the use of a sintering aid. This is achieved by sonication of magnesia and alumina followed by reaction spark plasma sintering. X-ray powder diffraction and scanning electron microscopy methods were used to characterize the starting nano-powders, sonicated powder mixture, spinel formation, and fractured specimens. The values of HV, K1c, and GIC were obtained from indentation measurements. The chemical composition, the SEM images, and the X-ray maps of magnesium and aluminum, confirmed the stoichiometry and homogeneity, at nano scale, of the densified specimens. The fully dense spinel, obtained at 1300 °C and 30 min, had average grain size of 40.92 nm, HV of 17.29 ± 0.185 GPa, K1c of 2.129 ± 0.106 MPa mm1/2, and GIC of 15.488 J/m2.

Photocatalytic degradation of gaseous pollutants on nanostructured TiO2 films of various thickness and surface area

This work deals with the preparation of TiO2 nanoparticulate layers of various mass (0.05 mg/cm2 to 2 mg/cm2) from three commercial nanopowder materials, P90, P25 and CG 300, their characterisation (profilometry, BET and SEM) and evaluation of their photocatalytic activity in the gaseous phase in a flow-through photoreactor according to the ISO standard (ISO 22197-2). Hexane was chosen as a single model pollutant and a mixture of four compounds, namely acetaldehyde, acetone, heptane and toluene was used for the evaluation of the efficiency of simultaneous removal of several pollutants. A linear dependence between the layer mass and the layer thickness for all materials was found. Up to a layer mass 0.5 mg/cm2, the immobilisation P90 and P25 powder did not result in a decrease in BET surface area, whereas with an increase in layer mass to 1 mg/cm2, a decrease of the BET surface was observed, being more significant in the case of P90. The photocatalytic conversion of hexane was comparable for all immobilised powders up to a layer mass of 0.5 mg/cm2. For higher layer mass, the photocatalytic conversion of hexane on P25 and P90 differ; the latter achieved about 30% higher conversion. In the case of the simultaneous degradation of four compounds, acetaldehyde was degraded best, followed by acetone and toluene; the least degraded compound was heptane. The measurement of released CO2 revealed that 90% of degraded hexane was mineralised to CO2 and water while for a mixture of 4 VOCs, the level of mineralisation was 83%.Graphical abstract

Density-Controlled Growth of ZnO Nanowalls for High-Performance Photocatalysts.

ZnO nanowires and nanowalls can be fabricated on the glass substrate with a ZnO seed film and low-cost aluminum (Al) foil by the aqueous solution method (ASM), respectively. The different concentrations of ZnO precursors can use to control the densities of ZnO nanowalls. In addition, FESEM, FETEM, EDS, XRD, XPS, and CL were used to evaluate the characteristics of ZnO nanowalls. The ZnO nanowalls exhibited higher photocatalytic efficiency (99.4%) than that of ZnO nanowires (53.3%) for methylene blue (MB) degradation under UVC light irradiation at the ZnO precursors of 50 mM. This result is attributed to ZnO nanowalls with Al-doped, which can improve the separation of photogenerated electron-hole pairs for enhanced photocatalytic activity. In addition, ZnO nanowalls can also reveal higher photocatalytic activity for the degradation of tetracycline capsules (TC) rather than commercial ZnO nanopowder under UVC light irradiation. The superoxide and hydroxyl radicals play essential roles in the degradation of MB and TC solutions by the radical-trapping experiment. Furthermore, the ZnO nanowalls exhibit excellent recycling and reuse capacity for up to four cycles for the degradation of MB and TC. This study highlights the potential use of ZnO nanowalls directly grown on commercial and low-cost Al foil as noble metal-free photocatalysis.

Influence of Surface Properties and Microbial Growth Media on Antibacterial Action of ZnO

Nano- and microscale ZnO demonstrate robust antibacterial action, although the driving mechanisms remain undetermined. In this study for commercial ZnO nano-powders and home-grown ZnO microparticles of varying morphologies we probe the response to bacterial growth media in isolation and with Staphylococcus aureus bacteria. ZnO microparticles are synthesized via a controllable hydrothermal method and subjected to biological assays with varying microbial environments. Changes in the optoelectronic, structural and chemical properties of these crystals before and after such exposure are characterized utilizing temperature-dependent photoluminescence spectroscopy, scanning electron microscopy and energy-dispersive X-ray spectroscopy. This is done to evaluate the impact of surface-surface interactions in antibacterial assays and the role ZnO surface and morphological properties play in these processes. In our experiments various bacterial environments are employed to elucidate the effects of media interactions on the cytotoxic efficacy of ZnO. In particular, minimum inhibitory concentration assays with Staphylococcus aureus reveal that microscale particles exhibit antibacterial efficacy comparable to that of the nano-powders, indicating that intra-bacterial internalization is not necessary for antimicrobial action. In our studies we determine that the nature of structural and optoelectronic changes in ZnO depends on both the media type and the presence (or absence) of bacteria in these media. Further evidence is provided to support significant cytotoxicity in the absence of particle internalization in bacteria, further highlighting the role of surface and media interactions in this process.

Influence of the textural characteristics and the preparation conditions of the support on coking resistance and performance of Ni/MgAl2O4 catalysts

This study aimed at establishing the influence of the textural properties, interparticle pores in particular, of the support in Ni/MgAl2O4 catalyst on other physicochemical properties and on coke formation during partial oxidation of methane. Ni catalysts were prepared over four different MgAl2O4 supports with different surface area and pore characteristics to establish their impact. Mesoporous MgAl2O4 supports were prepared by modified sol-gel and co-precipitation methods, and were compared with a commercial nano-powder counterpart. The catalysts were characterized by various techniques including powder XRD, XRF, N2 sorption, TEM, CO2-TPD, H2-TPR, DRIFTS, TGA, and Raman spectroscopy. The catalysts over the sol-gel prepared supports showed CH4 conversion around 89%, H2 selectivity close to 100%, H2/CO ratio ∼2.05, and negligible carbon deposits. While the catalyst over the support prepared by coprecipitation showed comparable conversion and products selectivity, it showed a slight decrease in conversion that was referred to the formation of a small amount of carbon deposit. On the other hand, the catalyst based on the commercial MgAl2O4 nano-powder showed conversion ∼84%, H2/CO ratio of 2.2, and large amount of coke deposit that lead to unstable conversion and gradual deactivation. The significantly enhanced coking resistance of the catalysts based on the prepared supports was referred to their larger volume of wider mesopores and their higher density of basic sites. On the other hand, the considerable and rapid coke formation over commercial support-based catalyst was referred to the narrow pores as well as lower pore volume, in addition to the lower density of basic sites, of its support. Narrow pores are expected to get rapidly filled with carbonaceous species blocking some active sites, hindering diffusion of products as well as O2 and CO2 access, and limiting oxidation and removal of these species as they form. The results indicate that the dominance of wide interparticle mesopores (>5 nm) of the support are essential to avoid coke accumulation.

Synthesis, physico-chemical characterizations and antibacterial properties of copper oxide (I) nanopowders elaborated by out-of-phase pulsed sonoelectrochemistry

Nanopowders of copper (I) oxide (Cu2O, cuprite) were synthesized by out-of-phase pulsed sonoelectrochemical method and characterized by several physico-chemical techniques (X-ray diffraction, transmission electronic miscroscopy, energy-dispersive x-ray spectroscopy, centrifugal liquid sedimentation, zeta potentials and specific area measurements). The same analyses were done on commercial cuprite and copper nanopowders for comparison. Once the chemical nature and morphology of the three materials have been determined, bactericidal assays were performed on methicillin-resistant Staphylococcus aureus (MRSA) and Escherichia coli (E. coli) in Trypto-Casein-Soy medium. The results show that sonoelectrochemical Cu2O nanopowders are good antibacterial material as compared to the two commercial nanopowders while using a synthesis method that is inexpensive and adaptable to the industrial scale.