Metallic Nickel Nanoparticles Research Articles

Furfural Hydrogenation Over Reduced Pure (LaBO3) and Substituted (LaB0.5B'0.5O3) (B, B': Fe, Co, Ni) Perovskites

AbstractA series of pure and 50 % substituted Fe‐containing (LaFeO3, LaFe0.5Ni0.5O3 and LaFe0.5Co0.5O3) and Co/Ni‐containing (LaCoO3, LaNiO3, and LaCo0.5Ni0.5O3) perovskites were used as precursors to synthesize metallic reduced catalysts to be tested for the liquid hydrogenation of furfural. The catalytic reaction was carried out in a batch reactor at 200 °C and 3.0 MPa of H2 pressure. The calcined perovskites and reduced catalysts were characterized by X‐ray diffraction (XRD), N2 physisorption at 77 K, temperature programmed reduction (H2‐TPR), temperature programmed CO2 and NH3 desorption (CO2‐TPD and NH3‐TPD), Atomic Absorption Spectroscopy (AAS) and X‐ray photoelectron spectroscopy (XPS) techniques. The LaCo0.5Ni0.5O3 reduced catalyst display the highest activity in furfural conversion, which was attributed to a cooperative effect between highly dispersed nickel and cobalt metal nanoparticles after reduction process. The effect of the nature of B‐cation have a high impact on the products selectivity in the hydrogenation of furfural, suggesting that enriched‐Ni metal surface was selectivity to tetrahydrofurfuryl alcohol, meanwhile enriched‐Co metal surface was selective to furfuryl alcohol formation, which was also supported with adsorption mode of furfural over the active sites obtained by quantum calculation.

Bioaccessibility of Metallic Nickel and Nickel Oxide Nanoparticles in Four Simulated Biological Fluids

Bioaccessibility of metals from substances and alloys is increasingly used as part of the assessment to predict potential toxicity. However, data are sparse on the metal bioaccessibility from nanoparticle (NP) size metal substances. This study examines nickel ion release from metallic nickel and nickel oxide micron particles (MPs) and NPs in simulated biological fluids at various timepoints including those relevant for specific routes of exposure. The results suggest that MPs of both metallic nickel and nickel oxide generally released more nickel ions in acidic simulated biological fluids (gastric and lysosomal) than NPs of the same substance, with the largest differences being for nickel oxide. In more neutral pH fluids (interstitial and perspiration), nickel metal NPs released more nickel ions than MPs, with nickel oxide results showing a higher release for MPs in interstitial fluid yet a lower release in perspiration fluid. Various experimental factors related to the particle, fluid, and extraction duration were identified that can have an impact on the particle dissolution and release of nickel ions. Overall, the results suggest that based on nickel release alone, nickel NPs are not inherently more hazardous than nickel MPs. Moreover, analyses should be performed on a case-by-case basis with consideration of various experimental factors and correlation with in vivo data.

Nanoarchitectonics of bimodal porous carbon nanosheet with NiO/Ni nanoparticles derived from nitrile-functionalized benzoxazine for a supercapacitor electrode material

Nitrile-functionalized benzoxazine was successfully synthesized as a precursor for porous carbon. NH4Cl was used as a template to generate the nanosheet morphology and mesopore structure, while nickel(II) chloride in the hydrate form was used as a nickel source. The results showed that carbon samples based on pristine nitrile-functionalized benzoxazine revealed the standard isotherm of type I, representing a microporous nature. This isotherm was altered to type IV, indicating a mesoporous nature after adding the NH4Cl template, and the morphology of the carbon sample was also transformed into a more nanosheet-like structure with increasing NH4Cl loading. The specific surface area, mesoporosity and pore volume of the as-prepared samples tended to increase when increasing NH4Cl template loading, with Ni-PCN5 (5 g of NH4Cl template) having the maximum mesoporosity of 88.7%. The maximum specific surface area and pore volume are 556 m2 g−1 for Ni-PCN5–350 and 0.71 cm3 g−1 for Ni-PCN5, respectively. In addition, the metallic nickel nanoparticles were successfully embedded in the carbon structure, which were further transformed into nickel oxide nanoparticles after an annealing process. This annealing process also resulted in carbon samples with the standard isotherm of type I. For electrochemical performance, Ni-PCN-300 also showed the highest value of the specific capacitance, as high as 181 F g−1 measured at a current density of 0.1 A g−1 in a 1 mol L−1 KOH aqueous electrolyte solution, with an excellent cycling stability of 96.5% over 2000 testing cycles. In short, this work demonstrates a facile, inexpensive and eco-friendly approach to rationally design and synthesize nickel/nickel oxide nanoparticles-embedded porous carbon nanosheets with a micro- and mesoporous structure, as a promising candidate for a supercapacitor electrode material.

Hydrazine metal complexes as a single source in the mechanochemical preparation of metallic magnetic nanoparticles and investigation of their magnetic hyperthermia properties

Ferromagnetic metallic cobalt and nickel nanoparticles were synthesized by intramolecular metal-hydrazine ligand oxidation reduction reaction in basic media and the solid state. Nickel nanoparticles Ni1 and Ni2 are obtained from two complexes, Ni(N2H4)2(C2O4) and Ni(N2H4)2(HCO2)2, respectively. X-ray powder diffraction (XRD) and energy-dispersive X-ray (EDX) data show pure fcc crystal structures of nanoparticles. Scanning electron microscopy (SEM) images revealed both Ni1 and Ni2 nanoparticles have agglomerated sphere morphologies. The crystallite size estimated by using the Scherer method for Ni1 and Ni2 were 18.7 and 6.2 nm. Vibrating sample magnetometer (VSM) data show the coercivity of metallic nickel samples Ni1 and Ni2 are 50 and 153 Oe, respectively. Both nanoparticles cause an increase in the temperature of water under applied alternative magnetic field and showed specific loss power (SLP) of 70 W/g and 104.8 W/g, respectively. The same method is used in preparation of cobalt nanoparticles from two complexes, Co(N2H4)2(C2O4) and Co(N2H4)2(HCO2)2. XRD analysis data show both nanoparticles have hcp crystal structure. SEM images show nanosheet structure with sheet thickness of 10 to 30 nm. Coercivity of Co1 and Co2 nanoparticles obtained by VSM and Hc are 182 and 171 Oe, respectively. In spite of high coercivity in both Co1 and Co2 nanoparticles, the magnetic hyperthermia heating effects are not observed in practice and specific loss power (SLP) is zero.

Insights into interfacial catalysis for aqueous reduction of 4-Nitrophenol catalyzed by Ni metal nanoparticles encapsulated within biomass-derived N-doped carbon matrix

As we strive towards a sustainable future in the field of catalysis, it is imperative to draw inspiration from Mother Nature. In this study, we present a straightforward and environmentally friendly approach for the in situ synthesis of nickel metal nanoparticles encapsulated within nitrogen-doped carbon (NNC), derived from daikon biomass. Among the various examined NNC catalysts, NNC-2 characterized by its substantial surface area and high doping content, emerges as the most promising candidate for catalyzing the reduction of 4-nitrophenol. Ab initio molecular dynamics simulations unveil that NNC-2 facilitates a robust Ni-NC interfacial interaction, which stabilizes Ni nanoparticles and supports the exceptional durability and recyclability. Theoretical calculations further elucidate the structure–activity relationship of the catalyst and the mechanistic aspects of the surface reduction of 4-nitrophenol. This insight enhances our understanding of the catalytic processes over carbon-based catalysts, providing a foundation for optimizing catalytic performance and guiding future developments in the field.

Co-assisted strategy of sacrificial salt-template and nitrogen-doping to promote lithium storage performance of NiO-Ni/N-C frameworks

Tailoring the omnidirectional conductivity networks in nickel oxide-based electrodes is important for ensuring their long lifespan, stability, high capacity, and high-rate capability. In this study, nickel metal nanoparticles and a three-dimensional nitrogen-doped carbon matrix were used to embellish the nickel oxide composite NiO–Ni/N–C via simplified hard templating. When a porous nitrogen-doped carbon matrix is present, a rapid pathway would be established for charging and discharging the electrons and lithium ions in a lithium-ion battery, thereby alleviating the volumetric expansion of the NiO nanoparticles during the operation of the battery. Moreover, the Ni0 ions added to serve as active sites to improve the capacity of the NiO-based electrodes and strengthen their conductivities. The multielement-effects of the optimal NiO–Ni/N–C electrode leads it to exhibit a capacity of 1310.8 mAh g-1 at 0.1 A g-1 for 120 loops and a rate capability of 441.5 mAh g-1 at 20.0 A g-1. Kinetic analysis of the prepared electrodes proved their ultrafast ionic and electronic conductivities. This strategy of hard templating reduces the number of routes required for preparing different types of electrodes, including NiO-based electrodes, and improves their electrochemical performance to enable their use in energy storage applications.

Ultra-small Ni@NiFe2O4/TiO2 magnetic nanocomposites activated peroxymonosulphate for solar light-driven photocatalytic mineralization of Simazine

In the heterogeneous photocatalytic degradation of environmental contaminants the recovery, reuse of employed nanocatalyst was crucial and it is essentially required for the scale up applications. Besides, designing a magnetic material with heterojunction that can effectively oxidize the toxic organic contaminants to non-toxic substance under different reaction conditions including direct solar light irradiation remains a challenge. Considering the above facts, herein, we tailored heterojunction between the magnetic materials and non-magnetic materials with ultra-small Ni nanoparticles modified NiFe2O4/TiO2 nanostructures (Ni@NiFe2O4/TiO2 magnetic nanocomposites) through a simple sonochemical route. The Raman phonons at ∼ 540 cm−1 consistent to nickel metal nanoparticles and the spinel ferrites crystal structure confirmed the formation of Ni@NiFe2O4/TiO2 magnetic nanocomposites. The reduced optical bandgap of the resulting nanocomposites indicated the effective absorption of direct solar light irradiation when compared to the bare TiO2. Thus in-turn, enhanced the photocatalytic efficiency of simazine degradation in the presence of Ni@NiFe2O4/TiO2 magnetic nanocomposites (k´= 11.0 × 10–4 s−1) and augmented the activation of peroxymonosulphate (PMS) in the presence of Ni@NiFe2O4/TiO2 magnetic nanocomposites (k´= 32.5 × 10–4 s−1). Ni@NiFe2O4/TiO2 +PMS exhibited 3 folds enhanced efficiency in the presence of sunlight. The as-prepared NiFe2O4/TiO2 magnetic nanocatalysts were more stable and the efficiency of simazine oxidation was approximately same for the continuous five cycles at the optimized experimental conditions. The Ni@NiFe2O4/TiO2 magnetic nanocomposites preparation and the activation of PMS may promise the applications in an efficient wastewater treatment.

The role of metallic nickel nanoparticles to remove dispersed oil from produced water in Sudan oil field plant

Abstract In this study, nickel nanoparticles (NiNPs) were synthesized and utilized for removing dispersed oil from oilfield-produced water in Sudan. The synthesis process involved using two concentration of hydrazine as a reducing agent and sodium hydroxide as solvent. Physiochemical characterizations, such as X-ray diffraction (XRD) and transmission electron microscopy (TEM), confirmed the successful preparation of NiNPs. The TEM analysis revealed an average particle size ranging from 70 to 90 nm, with a change in morphology from star-shaped to monodispersed spherical particles. The crystal structure analysis confirmed the face-centered-cubic (FCC) configuration of the NiNPs, validating their structural properties. Significantly, the NiNPs demonstrated an impressive capability to remove oil form produced water, achieving a remarkable efficiency of 98% in eliminating dispersed oil from produced water. The oil removal process followed Freundlich isotherms, as evidenced by the high value of the linear regression coefficient. Additionally, the kinetics of the oil removal process conformed well to the pseudo-second-order model, indicating a rapid reaction. This study successfully demonstrated the efficient removal of dispersed oil from produced water using nickel nanoparticles, which interacted physically with the oil particles. These findings highlight the potential of NiNPs as an effective adsorbent for treating oilfield-produced water and mitigating environmental contamination.

Cobalt hydroxide supported nickel nanoparticles for an efficient electrocatalytic urea oxidation reaction

An efficient electrochemical urea oxidation reaction (UOR) could be used in energy production technology. Metallic nickel nano-particles (Ni NPs) are incorporated in cobalt hydroxide layered material to form Ni/Co(OH)2. The synthesized material is utilized as an electrocatalyst in UOR. It has been revealed that the incorporation of Ni NPs into cobalt hydroxide significantly enhances their electrocatalytic activity toward UOR. Ni/Co(OH)2 catalyzes UOR at a very low anodic potential of 1.15 V vs RHE with a peak current density of 14.2 mAcm−2 and Tafel slope of 75 mVdec−1. The current work is a step ahead towards use of transition metal hydroxide (TMH) as support in the electrocatalytic oxidation applications especially UOR.

Carbonized Nickel Complex of Sodium Pectate as Catalyst for Proton-Exchange Membrane Fuel Cells.

Sodium pectate derivatives with 25% replacement of sodium ions with nickel ions were obtained by carbonization to temperatures of 280, 550, and 800 °C, under special protocols in an inert atmosphere by carbonization to temperatures of 280, 550, and 800 °C. The 25% substitution is the upper limit of substitution of sodium for nickel ions, above which the complexes are no longer soluble in water. It was established that the sample carburized to 550 °C is the most effective active element in the hydrogen-oxidation reaction, while the sample carbonized up to 800 °C was the most effective in the oxygen-reduction reaction. The poor performance of the catalytic system involving the pectin coordination biopolymer carbonized up to 280 °C was due to loss of proton conductivity caused by water removal and mainly by two-electron transfer in one catalytic cycle of the oxygen-reduction reaction. The improved performance of the system with coordination biopolymer carbonized up to 550 °C was due to the better access of gases to the catalytic sites and four-electron transfer in one catalytic cycle. The (Ni-NaPG)800C sample contains metallic nickel nanoparticles and loose carbon, which enhances the electrical conductivity and gas capacity of the catalytic system. In addition, almost four-electron transfer is observed in one catalytic cycle of the oxygen-reduction reaction.

Biofabrication of nickel oxide nanoparticles from Pedalium Murex leaf extract: A promising approach for biomedical and environmental applications

Nanotechnology has become a rapidly progressing field in materials science due to the biosynthesis of nanoparticles (NPs) that has found numerous biomedical applications. The goal of this study was to use the methanolic leaf extract of Pedalium murex (MEPM) as a capping and bio-fabrication agent at room-temperature for the green biosynthesis of nickel metal nanoparticles (NiONPs). Pedalium murex has been widely used in complementary medicine. Characterization of the MEPM stabilized NiONPs was analyzed by UV–Vis, X-ray diffraction spectroscopy (XRD), Fourier-transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM). Furthermore, the antioxidant and antibacterial properties of MEPM and NiONPs were studied. Biosynthesized NiONPs showed a lower total flavonoid and phenolic content than MEPM. Compared to MEPM, NiONPs (68%) showed superior antioxidant activity. The antimicrobial activity of the green synthesized NiONPs against Bacillus cereus, Streptococcus pyogenes, Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae and S. typhi was significantly higher than that of MEPM. Congo red (CR) and Rhodamine-B (Rh-B) dye degradation were used to evaluate the catalytic activity of the biosynthesized NPs. Maximum degradation efficiencies of 83% and 85% were observed for the CR and RhB dyes, respectively, both of which followed first-order reaction kinetics. Generally, the biosynthesized NiONPs fabricated by MEPM showed excellent antioxidant and antibacterial efficacy. Therefore, the NiONPs is an eco-friendly, cost-effective, simple, and a promising approach for many biological applications.

Recycled and Nickel- or Cobalt-Doped Lead Materials from Lead Acid Battery: Voltammetric and Spectroscopic Studies.

The active mass of the plates of aspent car battery with higher wear after an efficient desulfatization can be used as sources of a new electrode. This paper proposes the recycling of spent electrodes from a lead acid battery and the incorporation of NiO or Co3O4 contents by the melt-quenching method in order to enrich the electrochemical properties. The analysis of X-ray diffractograms indicates the gradual decrease in the sulfated crystalline phases, respectively, 4PbO·PbSO4 and PbO·PbSO4 phases, until their disappearance for higher dopant concentrations. Infrared (IR) spectra show a decreasing trend in the intensity of the bands corresponding to the sulfate ions and a conversion of [PbO3] pyramidal units into [PbO4] tetrahedral units by doping with high dopant levels, yielding to the apparition of the PbO2 crystalline phase. The observed electron paramagnetic resonance (EPR) spectra confirm three signals located on the gyromagnetic factor, g~2, 2.2 and 8 assigned to the nickel ions in higher oxidation states as well as the metallic nickel nanoparticles. This compositional evolution can be explained by considering a process of the drastic reduction in nickel ions from the superior oxidation states to metallic nickel. The linewidth and the intensity of the resonance lines situated at about g~2, 2.17, 4.22 and 7.8 are attributed to the Co+2 ions from the EPR data. The best reversibility of the cyclic voltammograms was highlighted for the samples with x = 10 mol% of NiO and 15 mol% of Co3O4, which are recommended as suitable in applications as new electrodes for the lead acid battery.

Achieving super dispersed metallic nickel nanoparticles over MCM-41 for highly active and stable hydrogenation of olefins and aromatics

Hydrogenation of olefins and aromatics is of significance for fuel processing and hydrogen storage, and developing nickel (Ni) catalyst highly active at low reaction temperature is the key to low the process cost. Herein we developed an ammonium citrate assisted impregnation method to fabricate loaded Ni catalyst (NiM-2) for hydrogenation. The Ni2+ species are anchored on the support MCM-41 strongly and evenly in form of Ni-citrate complex via the H-bonding between Si-OH group of MCM-41 and –COO- of citrate. During reduction, the carbon layerstemporarily formed by carbonization of citrate species inhibit the transfer and sintering of Ni species, and finally induces ultra-small metallic Ni nanoparticles after carbon layers slow decomposition by Ni species. Low coordination numbers and strong electron interaction between small metallic Ni nanoparticles and MCM-41 support upshift the d-band center of metallic Ni atoms. In hydrogenation, the small particle size and easier reduction for oxidized Ni species provide abundant active sites for reaction, and the upshifted d-band center induces strongly adsorption and activation of C = C bonds, which is confirmed for the first time in our work. As a result, the catalyst exhibits superior activity compared with reported and commercial Ni-based catalysts for hydrogenation of olefins and aromatics. Specifically, the catalyst with higher Ni loading (18%) exhibits good activity under room temperature and 0.1 MPa for hydrogenation of dicyclopentadiene and are comparable to Pd catalysts, making it as one of the best non-precious metal catalysts for hydrogenation reaction. And also, NiM-2 shows extremely high stability.

Application of nanoparticles to increase biological hydrogen production: the difference in metabolic pathways in batch and continuous reactors

An alternative to improve the production of biorefinery products, such as biohydrogen (H2) and volatile fatty acids (VFA), is the combination of nanotechnology and biological processes. In order to compare the use of both processes in two different reactor configurations, batch reactors and continuous anaerobic fluidized bed reactors (AFBR) were studied under the same conditions (37 °C, pH 6.8, Clostridium butyricum as inoculum and glucose as substrate) to evaluate the influence of zero valence iron and nickel nanoparticles (NPs) on H2 and VFA production. There was a shift in the production of acetic and butyric acids to produce mainly valeric acid when NPs were added in batch reactors. Meanwhile, in AFBR the change was from lactic acid to butyric and acetic acids with the addition of NPs. It showed that the effect of NPs on the fermentation process was different when the configuration of batch and continuous reactors was compared. The H2 yield in both reactor configurations increased with the addition of NPs. In batch reactors from 6.6 to 8.0 mmol H2 g-1 of COD, and in AFBR from 4.9 to 6.2 mmol of H2 g-1 of COD. Therefore, given the simplicity and low cost of the synthesis of metallic NPs, it is a promising additive to optimize the fermentation process in different reactor configurations.

Carbon Surface-Influenced Heterogeneity of Ni and Co Catalytic Sites as a Factor Affecting the Efficiency of Oxygen Reduction Reaction.

Highly porous carbon black and micro/mesoporous activated carbon were impregnated with cobalt and nickel nitrates, followed by heat treatment at 850 °C in nitrogen. Detailed information about chemistry and porosity was obtained using XPS, XRD, TEM/EDX, and nitrogen adsorption. The samples were used as ORR catalysts. Marked differences in the performance were found depending on the type of carbon. Differences in surface chemistry and porosity affected the chemistry of the deposited metal species that governed the O2 reduction efficiency along with other features of the carbon supports, including electrical conductivity and porosity. While dissociating surface acidic groups promoted the high dispersion of small metal species, carbon reactivity with oxygen and acidity limited the formation of the most catalytically active Co3O4. Formation of Co3O4 on the highly conductive carbon black resulted in an excellent performance with four electrons transferred and a current density higher than that on Pt/C. When Co3O4 was not formed in a sufficient quantity, nickel metal nanoparticles promoted ORR on the Ni/Co-containing samples. The activity was also significantly enhanced by small pores that increased the ORR efficiency by strongly adsorbing oxygen, which led to its bond splitting, followed by the acceptance of four electrons.

A Nickel-decorated porous graphitized carbon/sulfur cathode enabling excellent cycling stability of all-solid-state lithium-sulfur batteries

• A high electrical conductivity of Nickel-decorated porous graphitized carbon (Ni-PGC) host materials are prepared by a simple and effective calcination. • Ni-PGC-sulfur cathode realizes the fast redox kinetics of all-solid-state lithium-sulfur batteries. • Applying Ni-PGC-S material to all-solid-state Li-S battery can significantly improve the utilization of active materials. All-solid-state lithium-sulfur batteries (ASSLSBs) with high theoretical specific capacity and low cost are considered a promising electrochemical energy storage system. However, it suffers from large polarization, low sulfur utilization, and severe capacity decay, owing to the sluggish solid-solid reactions between sulfur and its discharging products (such as lithium sulfide, etc.). Herein, a Nickel-decorated porous graphitized carbon (Ni-PGC) is prepared using a one-step calcination method for the sulfur host in ASSLSBs with PEO-based solid electrolytes. The high specific surface area (638.2 m 2 g -1 ) of porous carbon structure with sufficient pore volume (0.69 cm 3 g -1 ) could uniformly disperse the active material (Sulfur). The metallic Nickel nanoparticles embedding in the porous network could significantly improve the electronic conductivity of composite cathode in ASSLSBs. As a result, the higher electrical conductivity of 8.22 S cm -1 is achieved from the Ni-PGC-S cathode, compared to 0.33 S cm -1 for the amorphous carbon-sulfur cathode. Furthermore, Li + diffusion coefficients (4.19×10 -11 cm 2 s -1 at the cathodic peak of 2.40 V, 7.54×10 -11 cm 2 s -1 at the cathodic peak of 2.05 V, and 2.69×10 -10 cm 2 s -1 at the anodic peak of 2.35 V) of the Ni-PGC-S cathode at 60 o C, are 11.11 times, 3.17 times and 2.17 times of the amorphous carbon-sulfur cathode without Ni doping. Therefore, the all-solid-state lithium-sulfur batteries assembled with the Ni-PGC-S cathode exhibit an extraordinary initial discharge capacity of 1311.3 mAh g -1 and a low cycling degradation (0.30 % per cycle) at 60 o C and 0.1 C. Even at 1 C, the battery delivers 375.8 mAh g -1 after 300 cycles.

NiO-Based Aerogels-Unexpected Formation of Metallic Nickel Nanoparticles during Supercritical Drying Process.

The aim of the study is to investigate the influence of the solvents applied both in sol-gel process and for supercritical drying (SCD) on NiO aerogels' properties. NiO aerogels were synthesized using methanol and 2-methoxy-ethanol (MeGl) as sol solvents. SCD was performed using iso-propanol, methanol and tert-butyl-methyl ether as supercritical fluids. The obtained samples were characterized using low-temperature nitrogen adsorption, X-ray diffraction analysis, mass-spectra analysis and STEM and TEM methods. It was found that specific surface area and the phase and chemical composition strongly depend on the synthesis conditions. We revealed that Ni2+ cations were reduced into Ni0 when 2-methoxy-ethanol was applied as a sol solvent. The mechanism of the Ni2+ cations reduction is proposed. We consider that at the stage of sol preparation, the Ni2+-MeGl chelate was formed. This chelate decomposes at the SCD stage with the release of MeGl, which, in turn, eliminates methanol and leads to the formation of aldehyde. The latter is responsible for the nickel reduction. The proposed mechanism was confirmed experimentally.

Structure Sensitivity of CO2 Conversion over Nickel Metal Nanoparticles Explained by Micro-Kinetics Simulations.

Nickel metal nanoparticles are intensively researched for the catalytic conversion of carbon dioxide. They are commercially explored in the so-called power-to-methane application in which renewably resourced H2 reacts with CO2 to produce CH4, which is better known as the Sabatier reaction. Previous work has shown that this reaction is structure-sensitive. For instance, Ni/SiO2 catalysts reveal a maximum performance when nickel metal nanoparticles of ∼2-3 nm are used. Particularly important to a better understanding of the structure sensitivity of the Sabatier reaction over nickel-based catalysts is to understand all relevant elementary reaction steps over various nickel metal facets because this will tell as to which type of nickel facets and which elementary reaction steps are crucial for designing an efficient nickel-based methanation catalyst. In this work, we have determined by density functional theory (DFT) calculations and micro-kinetics modeling (MKM) simulations that the two terrace facets Ni(111) and Ni(100) and the stepped facet Ni(211) barely show any activity in CO2 methanation. The stepped facet Ni(110) turned out to be the most effective in CO2 methanation. Herein, it was found that the dominant kinetic route corresponds to a combination of the carbide and formate reaction pathways. It was found that the dissociation of H2CO* toward CH2* and O* is the most critical elementary reaction step on this Ni(110) facet. The calculated activity of a range of Wulff-constructed nickel metal nanoparticles, accounting for varying ratios of the different facets and undercoordinated atoms exposed, reveals the same trend of activity-versus-nanoparticle size, as was observed in previous experimental work from our research group, thereby providing an explanation for the structure-sensitive nature of the Sabatier reaction.

Molecular dynamics study of the mechanical properties and deformation behavior of graphene/metal composites

Graphene-metals composites are novel structures with improved properties intensively studied in the last decades. In this work, the results of molecular dynamics simulation of the fabrication, deformation behavior, and mechanical properties of composites based on crumpled graphene filled with metal (nickel and copper) nanoparticles are presented. It is found that exposure followed by hydrostatic compression at 1000 K is an efficient way to obtain composite materials. Composite based on crumpled graphene and Cu nanoparticles shows better mechanical properties than composite with Ni nanoparticles. This can be explained by the fact that copper nanoparticles at elevated temperatures melt earlier than Ni nanoparticles, which contributes to easier deformation of graphene flakes and the formation of new chemical bonds in the graphene matrix. However, it is important to note that both composites withstand considerable deformation under uniaxial tension. The results obtained contribute to a better understanding of the processes of formation, deformation behavior, and mechanical properties of composites based on crumpled graphene and metal nanoparticles.

Effects of Nickel Nanoparticles on Rhodococcus Cell Surface Morphology and Nanomechanical Properties

Nickel nanoparticles (NPs) are used for soil remediation and wastewater treatment due to their high adsorption capacity against complex organic pollutants. However, despite the growing use of nickel NPs, their toxicological towards environmental bacteria have not been sufficiently studied. Actinobacteria of the genus Rhodococcus are valuable bioremediation agents degrading a range of harmful and recalcitrant chemicals. Both positive and negative effects of metal ions and NPs on the biodegradation of organic pollutants by Rhodococcus were revealed, however, the mechanisms of such interactions, in addition to direct toxic effects, remain unclear. In the present work, the influence of nickel NPs on the viability, surface topology and nanomechanical properties of Rhodococcus cells have been studied. Bacterial adaptations to high (up to 1.0 g/L) concentrations of nickel NPs during prolonged (24 and 48 h) exposure were detected using combined confocal laser scanning and atomic force microscopy. Incubation with nickel NPs resulted in a 1.25–1.5-fold increase in the relative surface area and roughness, changes in cellular charge and adhesion characteristics, as well as a 2–8-fold decrease in the Young’s modulus of Rhodococcus ruber IEGM 231 cells. Presumably, the treatment of rhodococcal cells with sublethal concentrations (0.01–0.1 g/L) of nickel NPs facilitates the colonization of surfaces, which is important in the production of immobilized biocatalysts based on whole bacterial cells adsorbed on solid carriers. Based on the data obtained, cell surface functionalizing with NPs is possible to enhance adhesive and catalytic properties of bacteria suitable for environmental applications.