Preparation,characterization and catalytic activity of a nano-Co(II)-catalyst as a high efficient heterogeneous catalyst for the selective oxidation of ethylbenzene,cyclohexene, and benzyl alcohol

This paper reports the preparation of a nano-Co(II)-catalyst (NCC) by anchoring of Co ions on immobilized bipyridylketone over the nano-sized SiO₂/Al₂O₃ mixed oxides. The nano-Co(II)-catalyst has been characterized by elemental analysis, BET, FT-IR, DR UV–vis and SEM. The catalytic activity of the catalyst towards the oxidation of ethylbenzene, cyclohexene, and benzylalcohol to different chemically and pharmaceutically important products were evaluated with tert-butyl hydroperoxide (TBHP) in the absence of solvent. Under optimized conditions, the nano-catalyst proved highly selective towards the acetophenone, 2-cyclohexene-1-one and benzaldehyde as reaction products, with excellent conversion rates.     

Preparation and properties of enhanced nanocomposites based on PLA/PC blends reinforced with silica nanoparticles

In order to lower brittleness of biobased polylactic acid (PLA), its blending with polycarbonate and nanosilica is aimed. In this line, to increase compatibility of the ingredients, dicumyl peroxide (DCP) and Cobalt (II) acetylacetonate (Co) were used as grafting and transesterification catalysts, respectively. The X‐ray diffraction (XRD) spectra demonstrated high compatibility of the ingredients by broadening of the PLA characteristic peaks and, also, good dispersion of nanosilica particles, especially in PLA/PC/Silica/Co sample. The EDX maps confirmed good nanosilica dispersion, too. The silica nanoparticle size was ranged from 20 to 100 nm in transmission electron microscopy (TEM) pictures. All nanocomposites showed improved thermal stability in thermogravimetric analysis (TGA). Differential scanning calorimetry (DSC) results demonstrated lower T_g, T_m, and crystallinity values for the fabricated nanocomposites. Notably, the dynamic mechanical thermal analysis (DMTA) curves confirmed the T_g, T_m, and T_cc trend obtained in DSC; moreover, much higher surface under tan δ peak for PLA/PC/Silica/Co sample was obtained, which implies its higher toughness. The precise tensile study of the samples confirmed significantly higher elongation at break of the nanocomposites, more considerably in PLA/PC/Silica/Co sample, with nearly negligible defect on tensile strength and modulus. In a concise, the obtained results confirmed the higher efficiency of Co catalyst, which leads to the sample with improved characteristics compared with DCP.     

Investigation of Asphaltene Aggregate Size Distribution Under Aggregation and Breakage Phenomena Using Monte Carlo Simulation

In this article, the aggregation and breakage processes are simulated through Monte Carlo method for asphaltene aggregates under shear-induced petroleum mixtures. The simulation results are verified by the aggregate size distributions of two types of asphaltenes having different fractal dimensions extracted from Iranian crude oil types. The obtained aggregate size distributions are affected by shear rate, toluene to heptane ratios and the oil type. The dynamic evolution of asphaltene aggregates shows an ascendant trend with time until they reach a maximum average diameter and then descent to a steady-state size. The asphaltene fractal dimension affects the aggregation process.     

Investigation of polypropylene degradation during melt processing using a profluorescent nitroxide probe: A laboratory-scale study

Degradation of polypropylene (PP) during melt processing was studied using a novel profluorescence technique. The profluorescent nitroxide probe, 1,1,3,3-tetramethyldibenzo[e,g]isoindolin-2-yloxyl (TMDBIO) was added to PP during melt processing to act as a sensor for carbon-centred radicals. Trapping of carbon-centred radicals, formed during degradation of PP, led to an increase in fluorescence emission from TMDBIO adducts. Through analysis of viscosity changes during processing cumulative chain scission degradation was estimated. At processing temperatures of 210 °C or below, fluorescence emission from TMDBIO adducts could be correlated with cumulative chain scissions when the number of chain scissions was small. At higher temperatures, a correlation was not observed most probably due to radical-trap instability rather than decomposition of the TMDBIO. Thus, TMDBIO may be used as a profluorescent sensor for degradation of PP during melt processing when the processing temperature is 210 °C or below.     

β-cyclodextrin-bonded silica particles as novel sorbent for stir bar sorptive extraction of phenolic compounds

A stir bar coated with β-cyclodextrin-bonded-silica (CDS) as novel sorbent has been developed and used to analyze seven phenolic compounds in aqueous samples, followed by thermal desorption and gas chromatography-mass spectrometric detection. Significant parameters affecting sorption process such as the time and temperature of sorption and desorption, ionic strength, pH and stirring rate have been optimized and discussed. The coating has a high thermal stability up to 300°C and long application lifetime (80 times). The porous structure of CDS coating provides high surface area and allows high extraction efficiency. Under the selected conditions, linearity range of 0.1-400 μg/L, limit of quantifications of 0.08-3.3 μg/L and method detection limits of 0.02-1.00 μg/L have been obtained. A satisfactory repeatability (RSD ≤ 6.5, n = 7) with good linearity (0.9975 ≤ r(2) ≤ 0.9996) of results illustrated a good performance of the present method. The recovery of different natural water samples was higher than 81.5%.     

Fabrication of Au‐Nanoparticle/TiO2‐Nanotubes Electrodes Using Electrochemical Methods and Their Application for Electrocatalytic Oxidation of Hydroquinone

Gold nanoparticle (Au‐NPs)‐Titanium oxide nanotube (TiO₂‐NTs) electrodes are prepared by using galvanic deposition of gold nanoparticles on TiO₂‐NTs electrodes as support. Scanning electron microscopy and energy‐dispersive X‐ray spectroscopy results indicate that nanotubular TiO₂ layers consist of individual tubes of about 60–90 nm diameters and gold nanoparticles are well‐dispersed on the surface of TiO₂‐NTs support. The electrooxidation of hydroquinone of Au‐NPs/TiO₂‐NTs electrodes is investigated by different electrochemical methods. Au‐NPs/TiO₂‐NTs electrode can be used repeatedly and exhibits stable electrocatalytic activity for the hydroquinone oxidation. Also, determination of hydroquinone in skin cream using this electrode was evaluated. Results were found to be satisfactory and no matrix effects are observed during the determination of hydroquinone content of the “skin cream” samples.     

Modeling of the rough spherical nanoparticles manipulation on a substrate based on the AFM nanorobot

In this paper, dynamic behavior of the rough spherical micro/nanoparticles during pulling/pushing on the flat substrate has been investigated and analyzed. For this purpose, at first, two hexagonal roughness models (George and Cooper) were studied and then evaluations for adhesion force were determined for rough particle manipulation on flat substrate. These two models were then changed by using of the Rabinovich theory. Evaluations were determined for contact adhesion force between rough particle and flat substrate; depth of penetration evaluations were determined by the Johnson–Kendall–Roberts contact mechanic theory and the Schwartz method and according to Cooper and George roughness models. Then, the novel contact theory was used to determine a dynamic model for rough micro/nanoparticle manipulation on flat substrate. Finally, simulation of particle dynamic behavior was implemented during pushing of rough spherical gold particles with radii of 50, 150, 400, 600, and 1,000 nm. Results derived from simulations of particles with several rates of roughness on flat substrate indicated that compared to results for flat particles, inherent roughness on particles might reduce the rate of critical force needed for sliding and rolling given particles. Given a fixed radius for roughness value and increased roughness height, evaluations for sliding and rolling critical forces showed greater reduction. Alternately, the rate of critical force was shown to reduce relative to an increased roughness radius. With respect to both models, based on the George roughness model, the predicted rate of adhesion force was greater than that determined in the Cooper roughness model, and as a result, the predicted rate of critical force based on the George roughness model was closer to the critical force value of flat particle.     

Synthesis and characterization of Ni(II) complexes bearing of 2‐(1H–benzimidazol‐2‐yl)‐phenol derivatives as highly active catalysts for ethylene oligomerization

Novel Ni(II) complexes of 2‐(1H–benzimidazol‐2‐yl)‐phenol derivatives (HL_x: x  =  1–5; C1–C5 ) have been synthesized and characterized. In the mononuclear complexes, the ligands were coordinated as bidentate, via one imine nitrogen and the phenolate oxygen atoms. The structures of the compounds were confirmed on the basis of FT‐IR, UV–Vis, ¹H‐, ¹³C–NMR, inductively coupled plasma and elemental analyses (C, H and N). The purity of these compounds was ascertained by melting point (m.p.) and thin‐layer chromatography. The geometry optimization and vibrational frequency calculations of the compounds were performed using Gaussian 09 program with B3LYP/TZVP level of theory. All Ni(II) complexes were activated with diethylaluminum chloride (Et₂AlCl), so that C2 showed the highest activity [6600 kg mol^?1 (Ni) h^?1], where the ligand contains a chlorine substituent. Oligomers obtained from the complexes consist mainly of dimer and trimer, and also exhibit high selectivity for linear 1‐butene and 1‐hexene. Both the steric and electronic effects of coordinative ligands affect the catalytic activity and the properties of the catalytic products.     

Synthesis,characterization and crystal structure of a dioxomolybdenum(VI) complex with a N,O type bidentate Schiff base ligand as a catalyst for homogeneous oxidation of olefins

The synthesis of a Mo(VI) Schiff base complex, cis-[MoO₂{(4,6-bis(tert-butyl)-2-{(benzyl)iminomethyl}phenolate)₂}], cis-[MoO₂(L)₂] where L = 4,6-bis(tert-butyl)-2-{(benzyl)iminomethyl}phenol, derived from benzylamine and 3,5-di-tert-butylsalycilaldehyde is reported. Full characterization of this complex was accomplished with elemental analyses, spectroscopic studies (NMR, IR and electronic) and X-ray structure analysis. This complex was tested as a catalyst for the homogeneous oxidation of olefins. The Mo(VI) complex is catalytically active for the epoxidation of aliphatic substrates at 80 °C, yielding the epoxide as the sole product in yields up to 100% and turnover numbers up to 5000. Under the optimized conditions styrene was oxidized in an 81% conversion to produce styrene oxide, benzaldehyde, and acetophenone.