Growth of multiwalled carbon nanotubes from acetylene over in situ formed Co nanoparticles on MgO support

The performance of Co catalysts supported on MgO at different Co loading (10%-75%) for the formation of carbon nanotubes through acetylene decomposition at 600 ^°C with H₂/C₂H₂ mixture for 1 h is investigated. The yield of MWNTs increases with an increase in Co loading (up to 50%). Starting from 1 g of catalyst precursor, about 8 g of MWNTs was obtained. The XRD patterns of catalyst precursor indicate the presence of cobalt in oxidic phase that eventually transformed into the catalytically active Co nanoparticles (12-18 nm) under the influence of acetylene and was responsible for the growth of coiled-like multi-walled CNTs as revealed by SEM and HRTEM images. It is suggested that bending in coil shaped MWNTs has the potential for functionalization for its biomedical applications.     

Carbon nanotubes growth from C2H2 and C2H4/NH3 by catalytic LCVD on supported iron–carbon nanocomposites

We report about the synthesis of carbon nanotubes by catalytic LCVD (C-LCVD), using a CW CO₂ laser and alternatively, C₂H₂/C₂H₄/NH₃ and C₂H₂/C₂H₄-containing gas mixtures. Different core–shell Fe–C nanocomposites (as synthesized and toluene extracted) were used employed as catalysts. The nanotubes grown from Fe–C residue demonstrate the lowest mean diameters. Prevalent curled and coiled morphologies are obtained for the CNTs grown in the presence of ammonia.     

Co on thin Al2O3 films grown on Ni3Al(1 0 0)

The growth of Co on thin Al₂O₃ layers on Ni₃Al(1 0 0) was investigated by Auger electron spectroscopy, high resolution electron energy loss spectroscopy (EELS), and scanning tunneling microscopy. At 300 K, Co grows in three-dimensional clusters on top of the Al₂O₃ layer. A defect structure of the alumina layer plays a crucial role during the early stage of Co growth. After deposition of 10 Å of Co, a complete screening of the dipoles of the Al₂O₃ layer due to the Co film is found in the EELS measurements. Annealing the Co film reveals a process of coalescence of Co clusters and, above 700 K, diffusion of the Co atoms through the oxide film into the substrate takes place.     

Alumina contribution to CO oxidation: A TPR and IR study

The alumina contribution to CO oxidation in the absence of O₂ on metal oxide supported catalysts was investigated by CO TPR and in-situ FTIR and DRIFT studies up to 800 °C. These tests were performed on two Al₂O₃ supported catalysts (1 wt.% Pt/La/γ-Al₂O₃ and 8 wt.% Cu/γ-Al₂O₃) and on two corresponding alumina supports (5 wt.% La₂O₃ stabilised γ-Al₂O₃ and high mechanical resistant spherical γ-Al₂O₃ particles). The quantitative determination of CO consumption and CO₂ and H₂ formation on the alumina supports was in agreement with a WGS reaction occurring between surface OH and CO with a predominantly 2:1 stoichiometry. In the CO TPR of metal oxide supported catalysts, in addition to the reduction of the metal, a WGS reaction took place with enhanced kinetics. This enhancement was the result of a CO spillover phenomenon from the metal to alumina hydroxyls. This phenomenon significantly affected the evaluation of the reduction degree of the supported metal and could not be neglected in the subsequent calculations.     

Study of the interaction of Na9[SbW9O33]·19.5H2O with bovine serum albumin: Spectroscopic and voltammetric methods

The interaction of Na₉[SbW₉O₃₃]·19.5H₂O (SbW) with bovine serum albumin (BSA) is studied by spectroscopic and voltammetric methods. Absorption spectroscopy of BSA and the linear sweep voltammetry of SbW proved the formation of ground-state SbW–BSA complex. Fluorescence quenching of serum albumin by SbW is also found to be a static quenching process. The binding constant K_a is 4.13×10⁴ L mol⁻¹ for SbW–BSA at pH 7.40 Tris–HCl buffer at 295 K. The number of binding sites and the apparent binding constants at different temperatures are obtained from the analysis of the fluorescence quenching data. The thermodynamic parameters determined by the Van’t Hoff analysis of the binding constants (ΔH=−80.01 kJ mol⁻¹ and ΔS=−182.85 J mol⁻¹ K⁻¹) clearly show that the binding is absolutely entropy driven. Hydrogen bonding and van der Waals interaction force play major role in stabilizing the complex. The effect of SbW on the conformation of BSA is analyzed using synchronous fluorescence spectroscopy.     

Surface modification of HMS material with silica sol leading to a remarkable enhanced catalytic performance of Cu/SiO2

Cu/SiO₂ catalysts with different bimodal pore structures adjusted by the ratio of HMS and silica sol were prepared via modified impregnation method. Structure evolutions of the catalyst were systematically characterized by N₂-physisorption, X-ray diffraction, H₂ temperature-programmed reduction, N₂O titration and X-ray photoelectron spectroscopy. The results show that the composite silica supported copper catalysts showed remarkably enhanced catalytic performance in the selective hydrogenation of dimethyl oxalate to ethylene glycol compared to the individual silica supported ones obtained by the same method. The dimethyl oxalate conversion and the ethylene glycol selectivity can reach 100% and 98% at 473 K with 2.5 MPa H₂ pressure and 1.5 h⁻¹ liquid hour space velocity of dimethyl oxalate over the optimized Cu/SiO₂ catalyst. The remarkably enhanced catalytic performance of Cu/SiO₂ catalysts might be attributed to the homogeneous dispersion and uniformity of the active copper species and to the larger copper surface areas attained on the HMS supports with large pore diameters and surface areas.     

Mesoporous (ZrO2-TiO2)/Al2O3 ternary carriers as hydrodesulfurization catalysts support

Ternary systems at various compositions were synthesized by coprecipitating Zr and Ti (to get a ZrO₂-TiO₂ 40-60 mol%) chlorides in aqueous basic media (provided by urea thermal decomposition) over an alumina substrate. Materials characterization included N₂ physisorption, X-ray diffraction, thermal analysis, high-resolution electron microscopy and Raman and UV-vis spectroscopies. High interaction among components was clearly evidenced by various techniques. Textural properties of ternary oxides could be tuned depending on composition of formulations. Mixed oxides with 10 or 20 mol% of ZrO₂-TiO₂ (at 40-60% mol, in turn) had the most suitable combination of textural properties (surface area, average pore diameter and pore volume) for the intended application (support of catalyst for hydrodesulfurization de oil-derived middle distillates). The suitability of those ternary supports was demonstrated in the dibenzothiophene hydrodesulfurization where the corresponding supported MoS₂ catalysts (at 2.8 atom Mo nm⁻²) were much more active (on a per mass of catalyst basis) than when impregnated over either alumina or zirconia-titania oxides.     

Genesis of supported carbon-coated Co nanoparticles with controlled magnetic properties,prepared by decomposition of chelate complexes

Following procedures formerly developed for the preparation of supported heterogeneous catalysts, carbon-coated cobalt nanoparticles dispersed on porous alumina have been prepared by impregnation of γ-Al₂O₃ with (NH₄)₂[Co(EDTA)] and thermal decomposition in inert atmosphere. Below 350 °C, Co(II) ions are complexed in a hexa-coordinated way by the EDTA ligand. The thermal treatment at 400–900 °C leads to the EDTA ligand decomposition and recovering of the support porosity, initially clogged by the impregnated salt. According to X-ray absorption spectroscopy, and due to in situ redox reactions between the organic ligand and Co(II), both oxidic and metallic cobalt phases are formed. Characterisation by transmission electron microscopy, X-ray diffraction and magnetic measurements reveals that an increase in the treatment temperature leads to an increase of the degree of cobalt reduction as well as to a growth of the cobalt metal particles. As a consequence, the samples prepared at 400–700 °C exhibit superparamagnetism and a saturation magnetisation of 1.7–6.5 emu g⁻¹ at room temperature, whilst the sample prepared at 900 °C has a weak coercivity (0.1 kOe) and a saturation magnetisation of 12 emu g⁻¹. Metal particles are homogeneously dispersed on the support and appear to be protected by carbon; its elimination by a heating in H₂ at 400 °C is demonstrated to cause sintering of the metal particles. The route investigated here can be of interest for obtaining porous magnetic adsorbents or carriers with high magnetic moments and low coercivities, in which the magnetic nanoparticles are protected from chemical aggression and sintering by their coating.     

Surface morphology and composition of c-, a- and m-sapphire surfaces in O2 and H2 environments

This paper reports that monitoring the composition of the c(0 0 0 1), a(11–20) and m(10–10) sapphire surfaces is essential for a proper interpretation of the surface morphologies obtained after annealing at 1253 and 1473 K in ArH₂ or ArO₂ atmospheres. Our experimental investigations, which have used Auger electron spectroscopy (AES) and atomic force microscopy (AFM) on the surfaces of 99.99% pure sapphire wafers, have led to the following original conclusions: (i) Calcium segregates at the c-surface of sapphire both under ArO₂ and ArH₂. (ii) Potassium adsorption enhances the kinetics of step-bunching on the c-surface under ArO₂. (iii) The step edges on the a-surface may develop a comb-like morphology made of parallel strips along the [10–10] direction. (iv) At 1253 K, clean m-surfaces may be stable. (v) Under ArH₂, alumina surface diffusion is much slower than under ArO₂ for all surface orientations, the surface concentration of impurities is low, and the Al–O ratio of the AES signals at the surface is significantly larger.     

XPS and XRD investigation of Co/Pd/TiO2 catalysts by different preparation methods

In the article, the Co/Pd/TiO₂, Co/TiO₂ and Pd/TiO₂ catalysts prepared by the impregnation and sol–gel method are studied by using X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The result shows that Co²⁺ and metal Pd may act as the active center for the direct synthesis of acetic acid from CH₄ and CO₂ by a two-step reaction sequence. When the catalysts are prepared by the sol–gel, Co²⁺ can enter the crystal lattice of the TiO₂, causing the phase transition from anatase to rutile at lower temperature, but existence of Pd²⁺ can prevent from the phase transition. When the catalysts are prepared by the impregnation, the phase transition is inhibited not only Co²⁺ but also Pd²⁺.     

Exploring the mechanism of NO–C2H4 reactions on the surface of stepped Pt(3 3 2)

Fourier transform infra red reflection–absorption spectroscopy (FTIR-RAS), thermal desorption spectroscopy (TDS), and auger electron spectroscopy (AES), were employed to explore the mechanism of NO reduction in the presence of C₂H₄ on the surface of stepped Pt(3 3 2). Both NO–Pt and C₂H₄–Pt interactions are enhanced when NO and C₂H₄ are co-adsorbed on Pt(3 3 2). As a result, C₂H₄ is dissociated at surface temperatures as low as 150 K, and the N–O stretch band is weakened. The presence of post-exposed C₂H₄ leads NO desorption from steps to decrease significantly, but the same effect on NO desorption from terraces becomes appreciable only at higher post-exposures of C₂H₄, e.g., 0.6 L and 1.2 L, and proceeds to a much slighter extent. Auger spectra indicate that as a result of the reaction with O from NO dissociation, the amount of surface C species is greatly reduced when NO is post-exposed to a C₂H₄ adlayer. It is concluded that reduction of NO in the presence of C₂H₄ proceeds very effectively on the surface of the Pt(3 3 2), through a mechanism of NO dissociation and subsequent O removal. Following this mechanism, the significant dissociation of adsorbed NO molecules on steps at surface temperatures below 400 K, and subsequent rapid reaction between the resultant O and C-related species, accounts for the considerable amount of N₂ desorption at temperatures below 400 K.     

Effect of H2 dilution on a-CN:H films deposited by hot-wire chemical vapor deposition

Hydrogenated amorphous carbon nitride (a-CN:H) thin films were deposited by hot-wire chemical vapor deposition (HWCVD) using the gas mixture of CH₄, NH₃ and H₂ precursor gases. The structural and electronic environments studies of H₂ diluted a-CN:H films were carried out by Raman spectroscopy and X-ray photoelectron spectroscopy. The nitrogen content increases while the total carbon contents decreases with increase in H₂ flow rate from 0 sccm to 20 sccm in the a-CN:H films. Moreover, the detail analysis of the carbon core orbital, valence band and hole states of a-CN:H were discussed with different H₂ flow rate.     

碳纳米管负载Cu-Co复合氧化物的富氢气氛中CO催化消除

采用超声处理辅助浸渍法制备了多壁碳纳米管负载的Cu-Co复合氧化物催化剂. 利用XRD、TEM、H₂-TPR、XPS和Raman光谱等表征了催化剂的结构性质. 在Cu和Co氧化物以及金属氧化物与碳纳米管载体间存在强相互作用. 催化剂在富氢气氛中CO催化消除反应中,与单一Cu或Co催化剂相比,Cu-Co复合氧化物催化剂表现出独特的反应特性,特别是在较高反应温度下可同时结合CO优先氧化和CO甲烷化的反应途径来实现高效CO消除. 当Cu/Co比为1/8时活性最优,可以实现在150～250 o和高反应空速 (120 L/(h·g))富氢气氛中CO的完全消除.     

Sono-enhanced degradation of dye pollutants with the use of H2O2 activated by Fe3O4 magnetic nanoparticles as peroxidase mimetic

Sono-enhanced degradation of a dye pollutant Rhodamine B (RhB) was investigated by using H₂O₂ as a green oxidant and Fe₃O₄ magnetic nanoparticles (MNPs) as a peroxidase mimetic. It was found that Fe₃O₄ MNPs could catalyze the break of H₂O₂ to remove RhB in a wide pH range from 3.0 to 9.0 and its peroxidase-like activity was significantly enhanced by the ultrasound irradiation. At pH 5.0 and temperature 55 °C, the ultrasound-assisted H₂O₂–Fe₃O₄ catalysis removed about 95% of RhB (0.02 mmol L⁻¹) in 15 min with a apparent rate constant of 0.15 min⁻¹ for the degradation of RhB, being 6.5 and 37.6 folds of that in the simple catalytic H₂O₂–Fe₃O₄ system, and the simple ultrasonic US-H₂O₂ systems, respectively. The beneficial synergistic behavior between Fe₃O₄ catalysis and ultrasonic was demonstrated to be dependent on Fe₃O₄ dosage, H₂O₂ concentration, pH value and temperature. As a tentative explanation, the observed significant synergistic effects was attributed to the positive interaction between cavitation effect accelerating the catalytic breakdown of H₂O₂ over Fe₃O₄ nanoparticles, and the function of Fe₃O₄ MNPs providing more nucleation sites for the cavitation inception.     

Ultrahigh Electron Emissive Carbon Nanotubes with Nano-sized RuO2 Particles Deposition

Multi-wall carbon nanotubes (MWNTs) have a great commercial potential as electron field emitters, but suffer from fundamental problems such as stability and brightness. By depositing the MWNTs with nano-sized ruthenium dioxide (RuO₂) particles, a new high performance emitter has been developed. When compared to MWNTs, the MWNTs impregnated with 1–2 nm sized RuO₂ have superior and more efficient electrical characteristics. MWNTs supported by a silicon substrate showed a reduction in the onset voltage from 5.4 to 4 V/μm after RuO₂ impregnation. The long-term stability of the impregnated MWNTs is also demonstrated with only a 20% increase in applied voltage required after 700 h operation at 40 mA/cm².     

Combined spectroscopy and microscopy of supported MoS2 nanoparticles

Supported molybdenum-sulfide nanoparticles are known catalysts for petroleum hydrodesulfurization as well as for electrochemical hydrogen evolution. In this study, we investigate molybdenum-sulfide nanoparticles supported on Au(1 1 1) using X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM), aiming to correlate spectroscopically determined chemical states with atomically resolved nanostructure. The results of this study allow us to conclude the following: (1) the XPS results from our model system are in good agreement with previously published results on supported MoS₂ for industrial applications, validating in part the fidelity of the model system; (2) STM reveals that catalytically active, crystalline MoS₂ nanoparticles exhibiting the well-known metallic edge state are only present after a post-deposition annealing step in the synthesis procedure, without which the particles exhibit amorphous shapes and incomplete sulfidation; and (3) the sulfided nanoparticles are found to be stable in air at room temperature.     

Deposition and characterization of binary Al2O3/SiO2 coating layers on the surfaces of rutile TiO2 and the pigmentary properties

Binary Al₂O₃/SiO₂-coated rutile TiO₂ composites were prepared by a liquid-phase deposition method starting from Na₂SiO₃·9H₂O and NaAlO₂. The chemical structure and morphology of binary Al₂O₃/SiO₂ coating layers were investigated by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, TG-DSC, Zeta potential, powder X-ray diffraction, and transmission electron microscopy techniques. Binary Al₂O₃/SiO₂ coating layers both in amorphous phase were formed at TiO₂ surfaces. The silica coating layers were anchored at TiO₂ surfaces via Si-O-Ti bonds and the alumina coating layers were probably anchored at the SiO₂-coated TiO₂ surfaces via Al-O-Si bonds. The formation of continuous and dense binary Al₂O₃/SiO₂ coating layers depended on the pH value of reaction solution and the alumina loading. The binary Al₂O₃/SiO₂-coated TiO₂ composites had a high dispersibility in water. The whiteness and brightness of the binary Al₂O₃/SiO₂-coated TiO₂ composites were higher than those of the naked rutile TiO₂ and the SiO₂-coated TiO₂ samples. The relative light scattering index was found to depend on the composition of coating layers.     

Surface modification of Ni and Co metal nanowires through MeV high energy ion irradiation

Nickel (Ni) and cobalt (Co) metal nanowires were fabricated by using an electrochemical deposition method based on an anodic alumina oxide (Al₂O₃) nanoporous template. The electrolyte consisted of NiSO₄ · 6H₂O and H₃BO₃ in distilled water for the fabrication of Ni nanowires, and of CoSO₄ · 7H₂O with H₃BO₃ in distilled water for the fabrication of the Co ones. From SEM and TEM images, the diameter and length of both the Ni and Co nanowires were measured to be ∼ 200 nm and 5–10 μm, respectively. We observed the oxidation layers in nanometer scale on the surface of the Ni and Co nanowires through HR–TEM images. The 3 MeV Cl²⁺ ions were irradiated onto the Ni and Co nanowires with a dose of 1 × 10¹⁵ ions/cm². The surface morphologies of the pristine and the 3 MeV Cl²⁺ ion-irradiated Ni and Co nanowires were compared by means of SEM, AFM, and HR–TEM experiments. The atomic concentrations of the pristine and the 3 MeV Cl²⁺ ion-irradiated Ni and Co nanowires were investigated through XPS experiments. From the results of the HR–TEM and XPS experiments, we observed that the oxidation layers on the surface of the Ni and Co nanowires were reduced through 3 MeV Cl²⁺ ion irradiation.     

Characterization of the metallic phase in nanocrystalline ZnAl2O4-supported Pt catalysts

In this study several complementary methods as XRD, HRTEM, O₂ and H₂ adsorption, as well as H₂-O₂ titration were used for characterization of the metallic phase in 0.5-3.0 wt.% Pt/ZnAl₂O₄ catalysts. Three nanocrystalline ZnAl₂O₄ spinels used as a supports were prepared by the solvothermal and co-precipitation method. It was found that irrespective of the preparation method they form very good support materials with a high capacity to achieve high platinum dispersion. O₂ and H₂ chemisorption data showed metal dispersion up to 90% and good correspondence with HRTEM results was observed. The H₂-O₂ titration method may be applied for determination of Pt dispersion only in the high-loaded Pt/ZnAl₂O₄ catalysts. The catalytic performances of Pt supported on the prepared spinels were evaluated in the propane total oxidation reaction.     

Lamp-assisted CVD of carbon micro/nano-structures using metal catalysts and CH2I2 precursor

Carbon micro/nanofibers and nanotubes were deposited via chemical vapor deposition (CVD) using CH₂I₂ precursor and different metal catalysts (Pd, Ni, Fe, Co and Mn) on Si (1 0 0) substrates. A versatile and low-cost IR lamp technique is employed to induce the deposition process. With this method carbon features could be obtained already at temperatures much lower than with common techniques. Palladium metal was deposited by laser-assisted CVD from a liquid solution of the ammine complex and the 3d metals by thermal evaporation. Large-scale periodicity of nano-sized metal catalysts, and subsequently of carbon deposits was obtained by using monolayers of polystyrene microspheres as mask. The carbon structures were analyzed by SEM and micro-Raman spectroscopy.