Pt nanoparticles deposited over carbon nanotubes for selective hydrogenation of cinnamaldehyde

Two kinds of carbon nanotubes (CNTs) with different inner diameter (less than 10 nm: CNTs-1 and between 60 and 100 nm: CNTs-2) were used as catalyst supports. The platinum particles were simply deposited on the outside surface (CNTs-1) and inside (CNTs-2) and were easily reduced to Pt⁰ by refluxing. The catalysts exhibit high activities in the selective hydrogenation of cinnamaldehyde which contains both CC and CO bonds. But the selectivity of these two catalysts was quite different under same reaction conditions. The high selective hydrogenation of CO bond was observed over catalyst 3%Pt/CNTs-2, while the completely hydrogenation of both CC and CO bonds was found over catalyst 3%Pt/CNTs-1.     

Thermally stable pseudo-third-generation Grubbs ruthenium catalysts with pyridine–phosphinimine ligand

The ligand precursors 2-(R₃PN)CH₂Py (R = Ph(1a), Cy(2a)) were prepared from reaction of pyridine azide with various phosphine ligands. Reaction of 1a or 2a with RuCl₂(CHPh)(Py)₂(H₂IMes) (Py = pyridine) afforded the ruthenium alkylidene complex RuCl₂(CHPh)(PyCH₂(NPR₃))(H₂IMes) (R = Ph(1), Cy(2)). Both catalysts showed good thermal stability and latent behavior toward RCM and ROMP reactions.     

Unsymmetrical cyrhetrenyl and ferrocenyl azines derived from 5-nitrofurane: Synthesis,structural characterization and electrochemistry

A new series of unsymmetrical cyrhetrenyl and ferrocenyl azines that were monosubstituted [(η⁵-C₅H₄)–C(R)N–NCH(5-NO₂–2-C₄H₂O)]M {with MRe(CO)₃ and RH (1a) or RMe (1b); MFe(η⁵-C₅H₅) and RH (2a) or RMe (2b)} and disubstituted [Fe{(η⁵-C₅H₄)–C(Me)N–NCH(5-NO₂–2-C₄H₂O)}₂] (3a) were prepared by condensation reactions of the corresponding organometallic hydrazone [(η⁵-C₅H₄)–C(R)N–NH₂)]M with 5-nitro-2-furaldehyde. The ¹H and ¹³C{¹H} NMR spectra indicated that these compounds adopted an (E,E)-configuration about the ˃CN − bond and an s-trans conformation about the N1–N2 bond, and this result was confirmed by X-ray crystallographic analyses of 1a and 2b. The opposite electronic effects of the organometallic fragments correlate with the co-planarity of the [(η⁵-C₅H₄)–C(R)N–NCH(5-NO₂–2-C₄H₂O)] system, the reduction potential of the nitro group (E_1/2) and the chemical shifts of the iminic carbons.     

Origin of the cluster-size effect in the hydrogenation of cinnamaldehyde over supported Au catalysts

Gold nanoclusters supported on γ-Al₂O₃ were more active and selective than platinum nanoclusters in the high-pressure liquid-phase hydrogenation of cinnamaldehyde to cinnamylalcohol, while in the hydrogenation of cyclohexene gold was less active than platinum. The differences in catalytic performance are ascribed to the weaker interaction of gold with the reactants and products compared to platinum. Gold clusters with a diameter below 2 nm are essential to obtain a high activity and selectivity in the hydrogenation of cinnamaldehyde. The size dependence of the selectivity originates from the stronger dependence of the CO hydrogenation rate on cluster size compared to the CC hydrogenation rate. Small clusters exhibit an enhanced π backbonding, which favors CO adsorption over CC adsorption.     

Synthesis,X-ray structure,spectroscopic properties,and theoretical investigations of dinuclear imidazole molybdenum(VI) complex with long MoO bands

One new dinuclear multioxomolybdenum(VI) complex containing long MoO bands with imidazole, [Mo₂O₆(imi)₄] (1) (imi = imidazole), has been prepared and characterized, and the geometric structure, electronic structure and spectroscopic properties, investigated experimentally and theoretically. The rarely observed long MoO bonds in 1 (ca. 0.15 Å longer than documents previously) are analysed by orbital structure analysis. The electronic origins of the optical transitions are also mainly related to the MoO groups with ligand-to-metal charge transfer (LMCT) nature (P_terminal-oxo → d_Mo).     

Ultraviolet,water, and thermal aging studies of a waterborne polyurethane elastomer-based high reflectivity coating

A waterborne aliphatic polyurethane-based coating was studied for accelerated ultra-violet (UV), water (WT), and thermal (TH) aging for a period of 1000 h. To monitor the coating durability, samples were tested every 200 h. ATR-FTIR spectroscopy was used to monitor the chemical changes occurring during the aging process. UV–vis with integrating sphere was used to track the change in diffused reflectance, while the optical microscope and the scanning white light interferometry (SWLI) were used for surface characterization. FTIR studies of coatings subjected to UV exposure indicated a decrease in functional groups such as CONH, CH, CO, and COC. The appearance of functional groups such as NH is attributed to chain scission of the polyurethane binder in the coating. Investigation of the degradation mechanism in water and thermal aging showed physical effects through water penetration and the mismatch in the coefficient of thermal expansion as the primary causes of degradation. In all aging scenarios, the reduction of reflectivity was largely due to physical defects caused by the different aging mechanisms.     

Electrochemical oxidation of methyl orange azo dye at pilot flow plant using BDD technology

Solutions of methyl orange azo dye were degraded by electrochemical oxidation using a 3 L flow plant with a boron-doped diamond (BDD)/stainless steel cell operating at constant current density, ambient temperature and liquid flow rate of 12 L min^?1. A 2³ factorial design considering the applied current density, azo dye concentration and electrolysis time as variable independents was used to analyze the process by response surface methodology. LC–MS analysis revealed the formation of seven oxidation products from the cleavage of the NN group of the dye, followed by deamination, formation of a nitro group and/or desulfonation of the resulting aromatics.     

Towards osseointegration of bioinert ceramics: Can biological agents be immobilized on alumina substrates using self-assembled monolayer technique?

Immobilization of biological agents on inert alumina surfaces could promote bone growth and improve osseointegration. We hypothesize that functional groups on alumina surfaces can be used to link biological agents as a supporting factor e.g. for cell attachment. CH₂, OH, COOH, and NH₂ groups were linked to alumina surfaces using self-assembled monolayer technique (SAM). Subsequently, bovine serum albumin (BSA) was immobilized on each functionalized surface. Contact angle, bicinchoninic acid assay and immunofluorescence were used to detect immobilized BSA. The amount of BSA linked to functionalized surfaces increased in the following order CH₂ < OH < COOH = NH₂. The greatest amount, 26.1 μg/cm² of BSA was found on both, NH₂- and COOH-terminated surfaces. Cell tests confirmed cytocompatibility of all surfaces. The highest proliferation was detected on NH₂-terminated samples. Using the model protein, the results confirmed feasibility for immobilization of biological agents to inert alumina ceramic surfaces using SAM technique.     

Electrically conductive silicon carbide with the addition of TiNbC

The work deals with the preparation of dense SiC based ceramics with high electrical conductivity. SiC samples with different content of conductive TiNbSiCO based phase were hot pressed at 1820 °C for 1 h in Ar atmosphere under mechanical pressure of 30 MPa. The conductive phase is a mixture of 50 wt% TiNbC (molar ratio of Ti/NbC is 1:1.8) and 50 wt% eutectic composition of Y₂O₃SiO₂. Composite with 30% of conductive TiNbSiCO phase showed the highest electrical conductivity 28.4 S mm^?1, while the good mechanical properties of SiC matrix were preserved (fracture toughness K_IC = 5.4 MPa m^1/2 and Vickers hardness 17.8 GPa).The obtained results show that the developed additive system is suitable for the preparation of SiC-based composite with sufficient electrical conductivity for electric discharge machining.     

The effect of Mg(OH)2 on furfural oxidation with H2O2

The oxidation of furfural in H₂O₂ and H₂O₂–Mg(OH)₂ system were systematically investigated and a rational explanation for the reaction mechanism was proposed. 2-formyloxyfuran, from selective oxidation of HCO group in furfural, was a crucial intermediate. The addition of Mg(OH)₂ suppressed the oxidation of furan ring of furfural and enhanced selectivities of 2(5H)-furanone (44.8%) and succinic acid (38.0%). FT-IR, Gaussian calculation and experimental results indicated that the process of furfural oxidation with H₂O₂ is homogeneous, and the synergy between dissolved Mg^2 + cations and OH⁻ ions facilitates the HOO⁻ attacking the carbon atom of HCO other than the CC bound of furan ring.     

Synthesis and reactivity of an 2-azabutadiene-based π-conjugated dithioether: Formation of a N,S-ligated molybdenum chelate complex and C,N,S-pincer complexes of palladium and platinum

Nucleophilic attack of sodium isopropylthiolate on 4,4-dichloro-1,1-diphenyl-2-azabuta-1,3-diene [Cl₂CC(H)–NCPh₂}] (1) affords the 2-azabutadiene derivative [(i-PrS)₂CC(H)–NCPh₂] (2). Upon irradiation of Mo(CO)₆ in THF in the presence of 2, the chelate complex cis-[(OC)₄Mo{(i-PrS)₂CC(H)–NCPh₂}] (3) is obtained. Coordination on Mo occurs through the imine nitrogen and a thioether group. Polydentate dithioether 2 acts as N,C,S-pincer ligand after orthometallation reaction with Pd(II) or Pt(II). The molecular structures of 2 and (C,N,S)-[(i-PrS)₂CC(H)–NC(Ph)C₆H₄)PtCl] (4b) have been determined by X-ray diffraction studies.     

Etherification reactions of propargylic alcohols catalyzed by a cationic ruthenium allenylidene complex

The cationic ruthenium allenylidene complex R_RuR_ax −[Ru(indenyl)L(PPh₃)CCCPh₂]⁺PF₆ catalyzes the etherification of secondary and tertiary propargylic alcohols in a formal nucleophilic substitution reaction utilizing primary and secondary alcohols as the nucleophiles. At a catalyst loading of only 1.1 mol%, the corresponding propargylic ether products were obtained in 9 to 73% isolated yields (18 h reaction time at 100 °C); no further additives are required. The reaction exhibits an induction period; as shown by a control reaction, the high reaction temperature may chemically change the allenylidene complex to be employed as the catalyst but does not lead to catalyst deactivation.     

High efficient adsorption of gold ions onto the novel functional composite silica microspheres encapsulated by organophosphonated polystyrene

The novel functional composite silica microspheres encapsulated by organophosphonated polystyrene (SGPSNP) has been successfully synthesized. SGPSNP was employed to adsorb Au(III) from simulated wastewater, and it exhibited excellent performance, and the maximum adsorption capacity was 980.39 mg/g at 35 °C. The adsorption process optimization was performed using response surface methodology (RSM), and the analysis of variance (ANOVA) of the quadratic model demonstrated that the model was highly significant. Moreover, the regeneration capacities of SGPSNP were investigated, and it has been found that the adsorption capability remains high after several cycles of adsorption–desorption.     

Direct conversion of citrus peel waste into hydroxymethylfurfural in ionic liquid by mediation of fluorinated metal catalysts

A new green technology was developed using citrus peel waste to produce hydroxymethylfurfual (HMF). FT-IR analysis of the waste showed 4 characteristic vibration modes (CH, CO, COH, and CO/COO^?), contributing to sugars. XRD and FESEM elucidated that the waste and its hydrolysate consist of highly amorphous clusters. HCl increased HMF yield by 1.4-fold. CrF₃ increased its yield by 1.7-fold. At 0.2 of the stoichiometric ratio value, HMF yield was highest. The highest HMF yield was achieved in the reaction mixture of 4 g [OMIM]Cl, 1 mL ethyl acetate, 0.1 g CrF₃, 5 mL 0.3 M HCl, and 0.5 g biomass.     

Low energy synthesis of nitrogen functionalized graphene/nanoclay hybrid via submerged liquid plasma approach

This study demonstrates that hard black (HB) (74% carbon, 26% clay; diameter: 0.5 mm) and 4 black (4B) (84% carbon, 16% clay; diameter: 0.5 mm) pencil carbon rods as electrode materials can produce highly dispersive nitrogen-doped few layer graphene/nanoclay hybrids (nanoclay-NFLG). The formation of nanoclay-NFLG was induced by applying high electrical potential across the pencil carbon rod and a platinum sheet electrode submerged in acetonitrile solvent. Electron microscopic analysis shows that in the HB- and 4B-nanoclay-NFLG, the nanoclay (size: >3 nm) was intercalated between the multilayer (>6 layers) of functionalized graphene. Raman spectra of HB- and 4B-nanoclay-NFLG shows a marginal increase in disorder compared to that of pure HB and 4B pencil carbon rods, respectively. X-ray photoelectron spectroscopy studies indicate the presence of pyridinic (NC) and pyrrolic (CHNH) nitrogen in both HB- and 4B-nanoclay-NFLG, which was also confirmed by ultraviolet–visible spectroscopy and infrared spectroscopy studies. The pyridinic and pyrrolic nitrogen present in HB- and 4B-nanoclay-NFLG gives distinct redox peaks in cyclic voltammogram, with high specific capacitances of 40 and 111 F/g, respectively, obtained at the scan rate of 5 mV/s.     

A novel approach for preparation of dense TiC–SiC nanocomposites by sol–gel infiltration and spark plasma sintering

Dense TiC–SiC nanocomposite ceramics were prepared by infiltration of porous TiC scaffolds with a SiOC sol, followed by spark plasma sintering (SPS). The porous nano TiC scaffold was first synthesized by direct carbothermal reduction of a monolithic TiOC precursor obtained from a controlled sol–gel process. The TiC scaffold was infiltrated with a SiOC sol and then the sample was aged in a container for 48 h at 80 °C to convert the sol into gel. After this, the sample was heated at 550 °C to remove the organic components and then 1350 °C to convert the SiOC gel to SiC by carbothermal reduction reaction. The cycle of the infiltration and carbothermal reduction was repeated several times to obtain relatively dense TiC–SiC composite samples. Dense TiC–SiC composite with a uniform nano-sized grain microstructure was obtained by spark plasma sintering at 1800 °C for 5 min under 40 MPa uniaxial pressure. Compared with conventional powder mixing methods, the sol–gel infiltration approach has shown distinct advantages of achieving dense TiC–SiC composites with uniform nano-sized grain structures.     

Deposition of carbon nitride films using an electron cyclotron wave resonance plasma source

Hydrogenated amorphous carbon nitride (a-C:N:H) has been synthesised using a high plasma density electron cyclotron wave resonance (ECWR) technique using N₂ and C₂H₂ as source gases, at different ratios and a fixed ion energy (80 eV). The composition, structure and bonding state of the films were investigated and related to their optical and electrical properties. The nitrogen content in the film rises rapidly until the N₂/C₂H₂ gas ratio reaches 2 and then increases more gradually, while the deposition rate decreases steeply, placing an upper limit for the nitrogen incorporation at 30 at%. For nitrogen contents above 20 at%, the band gap and sp³-bonded carbon fraction decrease from 1.7 to 1.1 eV and ∼65 to 40%, respectively. The transition is due to the formation of polymeric CN, CN and NH groups, not an increase in CH bonds. Films with higher nitrogen content are less dense than the original hydrogenated tetrahedral amorphous carbon (ta-C:H) film but, because they have a relatively high band gap (1.1 eV), high resistivity (10⁹ Ω cm) and moderate sp³-bonded carbon fraction (40%), they should be classed as polymeric in nature.     

Superhard and high-strength yne-diamond semimetals

Two sp + sp³-hybridized yne-diamond (YD) allotropes are designed by employing first-principle calculations. The YDs are constructed by replacing half carbon single bonds (CC) along the <001> direction in 2H-diamond and 4H-diamond with acetylenic linkages (CCCC). Both YDs are energetically more favorable than experimental graphdiyne, theoretical graphynes (e.g., α-, β-, and 6,6,12-graphyne), and T-carbon. The YDs are confirmed to be mechanically and dynamically stable. Different from the recently proposed semiconductive YD based on cubic diamond (i.e. Y-carbon), electronic band structure calculations show that both YDs we proposed are semimetals. Mechanically, two YDs inherit the superhardness and high tensile strength from the parent diamonds. We hope that our present findings can be useful in guiding the design and syntheses of superhard and semimetallic carbon materials.     

Accelerating the crosslinking process of hyperbranched polycarbosilane by UV irradiation

A liquid hyperbranched polycarbosilane (LHBPCS) with stoichiometric C/Si ratio but without unsaturated groups was synthesized. Different from traditional thermal crosslinking, ultraviolet (UV) irradiation crosslinking was taken. The molecular weight, the consumption of SiH group and ceramic yield of LHBPCS showed an increase trend with increasing the UV irradiation time. After 30 min of UV irradiation, 71.8 wt% ceramic yield was obtained. In addition, extra divinyldimethylsilane was added into LHBPCS. Under UV irradiation, both the SiH group and vinyl group of divinyldimethylsilane were consumed. But the reaction extend of vinyl group was much faster than that of SiH group. Compared with pure LHBPCS, the mixture of LHBPCS and 5 wt% divinyldimethylsilane gave a higher ceramic yield of 79 wt% after 30 min of UV irradiation. By heating the crosslinked LHBPCS to 1000 °C, a near stoichiometric SiC ceramic was got. It exhibited excellent thermal stability at 1400 °C in air.     

Efficient reductions of various nitroarenes with scrap automobile catalyst and NaBH4

The effect of scrap automobile catalyst (SAC), a waste material, was investigated as a catalyst for the reduction of nitroarenes to the corresponding amines with sodium borohydride in aqueous ethanol at 5–25 °C. Along with the observed high conversions, the SAC and NaBH₄ combination also exhibits a selectively catalyzed reduction in compounds containing other reducible functionalities, such as CN, Br, Cl and I. Recycling automobile wastes into a catalyst for organic reactions will offer both environmental protection and economic advantages. As a result, an effective, easy to use, low-priced and reliable method has been developed.