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.     

Nonlinear optical properties in tetrametallic Fe3Mn complexes with pseudo-C3 symmetry

New type of 3D chromophores [{CpFeC₅H₄CRCH4-py}₃Mn(CO)₃]BF₄ (1) with weakly interaction subchromophore were synthesized and found to display improved nonlinearity compared with their 1D reference systems [(CpFeC₅H₄CRCH4-py)Mn(CO)₅]BF₄ (2).     

Preparation of high-temperature stable SiBCN fibers from tailored single source polyborosilazanes

Bulk SiBCN ceramics derived from polyborosilazanes of the type [B(C₂H₄SiRNH)₃]_n (1a, R = CH₃; 2a, R = H; C₂H₄ = CHCH₃, CH₂CH₂) exhibit an exceptional structural stability at high temperature. Therefore, such quaternary systems are of great scientific and technical interest as fibrous reinforcements intended for high-temperature applications. In this context, the design of novel polyborosilazanes, which display properties tailored for the preparation of SiBCN fibers, is studied. Boron-modified polysilazanes of the type [B(C₂H₄SiRNCH₃)₃]_n (1b, R = CH₃; 2b, R = H) are prepared via aminolysis of the tris(dichlorosilylethyl)boranes B(C₂H₄SiRCl₂)₃ (1, R = CH₃; 2, R = H). It is shown that the functionalisation of the precursors with NCH₃ units improves their processability (i.e. solubility) compared to that of their ammonolysed analogs [B(C₂H₄SiRNH)₃]_n (1a, R = CH₃; 2a, R = H). In addition to the influence of the NCH₃ units, the presence of the SiCH₃ functions in such polymers offers the best potential for the preparation of fibers by melt-spinning. As-spun fibers are then converted under controlled atmosphere into high-temperature stable SiBCN fibers according to the polymer-derived ceramic route.     

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.     

Periodic,vdW-corrected density functional theory investigation of the effect of Al siting in H-ZSM-5 on chemisorption properties and site-specific acidity

Twelve crystallographically distinct Al substitution sites of H-ZSM-5 are modeled by periodic density functional theory using the vdW-DF functional. While the stability of Al substitution and Brønsted acid OH bond length at different active site positions are similar, the OH stretch frequency, SiOAl bond angle, and adsorption energies of various probe molecules differ notably without observable correlations between these properties. Comparison of adsorption energy values with and without van der Waals corrections demonstrates the significance of the inclusion of dispersion interactions. Our data indicate that theoretical investigations of H-ZSM-5 require a careful selection of the location of the active site.     

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.     

Growth of junctions in 3D carbon nanotube-graphene nanostructures: A quantum mechanical molecular dynamic study

Junctions are the key component for 3D CNT-graphene seamless hybrid nanostructures attractive for numerous innovative applications. Growth mechanism of junctions of vertical carbon nanotubes (CNTs) growing from graphene in the presence of iron nanoparticles as catalysts was simulated using quantum mechanical molecular dynamics methods. When nanotube grew on graphene via a “base-growth” mechanism, it was found that the junctions were a mixture of CC and FeC covalent bonds. We further explored the formation mechanisms of pure CC bonded junctions by moving the catalyst during CNT growth or etching and annealing after growth. Our simulations provided possible avenues to produce pure CC bonded junctions that seamlessly connect graphene and nanotubes in the 3D nanostructures.     

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.     

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.     

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.     

Hydrodenitrogenation of Simple Aromatic Amines on Molybdena Catalysts

The hydrotreatment of some aromatic amines was studied at temperatures ranging from 400 to 450°C and P_H2=1 atm under flow conditions. Hydrogenolysis of aromatic amines involves direct cleavage of the C(sp²)N bond without saturation of the aromatic ring. The presence of hydrogen sulphide in the reaction stream has a promotional effect on the hydrogenolysis of C(sp³)N bond and an inhibitive effect on the hydrogenolysis of C(sp²)N bond. The use of a saturated hydrocarbon as diluent facilitates CN bond hydrogenolysis in the presence of hydrogen, irrespective of the carbon being sp² or sp³ hybridized.     

Catalytic reactions of dioxygen with ethane and methane on platinum clusters: Mechanistic connections,site requirements,and consequences of chemisorbed oxygen

C₂H₆ reactions with O₂ only form CO₂ and H₂O on dispersed Pt clusters at 0.2–28 O₂/C₂H₆ reactant ratios and 723–913 K without detectable formation of partial oxidation products. Kinetic and isotopic data, measured under conditions of strict kinetic control, show that CH₄ and C₂H₆ reactions involve similar elementary steps and kinetic regimes. These kinetic regimes exhibit different rate equations, kinetic isotope effects and structure sensitivity, and transitions among regimes are dictated by the prevalent coverages of chemisorbed oxygen (O^*). At O₂/C₂H₆ ratios that lead to O^*-saturated surfaces, kinetically-relevant CH bond activation steps involve O^*O^* pairs and transition states with radical-like alkyls. As oxygen vacancies (¹) emerge with decreasing O₂/alkane ratios, alkyl groups at transition states are effectively stabilized by vacancy sites and CH bond activation occurs preferentially at O^** site pairs. Measured kinetic isotope effects and the catalytic consequences of Pt cluster size are consistent with a monotonic transition in the kinetically-relevant step from CH bond activation on O^*O^* site pairs, to CH bond activation on O^** site pairs, to O₂ dissociation on ^** site pairs as O^* coverage decrease for both C₂H₆ and CH₄ reactants. When CH bond activation limits rates, turnover rates increase with increasing Pt cluster size for both alkanes because coordinatively unsaturated corner and edge atoms prevalent in small clusters lead to more strongly-bound and less-reactive O^* species and lower densities of vacancy sites at nearly saturated cluster surfaces. In contrast, the highly exothermic and barrierless nature of O₂ activation steps on uncovered clusters leads to similar turnover rates on Pt clusters with 1.8–8.5 nm diameter when this step becomes kinetically-relevant at low O₂/alkane ratios. Turnover rates and the O₂/alkane ratios required for transitions among kinetic regimes differ significantly between CH₄ and C₂H₆ reactants, because of the different CH bond energies, strength of alkylO^* interactions, and O₂ consumption stoichiometries for these two molecules. Vacancies emerge at higher O₂/alkane ratios for C₂H₆ than for CH₄ reactants, because their weaker CH bonds lead to faster scavenging of O^* and to lower O^* coverages, which are set by the kinetic coupling between CH and OO activation steps. The elementary steps, kinetic regimes, and mechanistic analogies reported here for C₂H₆ and CH₄ reactions with O₂ are consistent with all rate and isotopic data, with their differences in CH bond energies and in alkyl binding, and with the catalytic consequences of surface coordination and cluster size. The rigorous mechanistic interpretation of these seemingly complex kinetic data and cluster size effects provides useful kinetic guidance for larger alkanes and other catalytic surfaces based on the thermodynamic properties of these molecules and on the effects of metal identity and surface coordination on oxygen binding and reactivity.     

Benzyne-functionalized graphene and graphite characterized by Raman spectroscopy and energy dispersive X-ray analysis

The benzyne functionalization of chemical vapor deposition grown large area graphene and graphite was performed using a mixture of o-trimethylsilylphenyl triflate and cesium fluoride that react with the carbon surface. The reaction requires at least 2 days of treatment before the appearance of Raman and energy-dispersive X-ray spectral signatures that verify modification. Raman spectra of modified graphene and graphite show a rich structure of lines corresponding to CCC, CH, and low frequency modes of surface-attached benzyne rings.     

Degradation of mechanical and electrical properties after long-term oxidation and corrosion of non-oxide structural ceramic composites

This work summarizes the results related to the influence of the starting composition and of microstructure on properties degradation, due to oxidation and corrosion, relatively to the following structural ceramics: Si₃N₄TiN, Si₃N₄MoSi₂, AlNSiCMoSi₂, AlNSiC.The effects of: (i) long-term oxidation in air (100 h), in the temperature range 600–1500 °C and (ii) of long-term corrosion (400 h) in acid or basic aqueous solution at RT, 40 and 70 °C, on the electrical resistivity and mechanical strength of the composites are analysed and compared. The degradation of the properties are related to the characteristics of the surface and sub-surface damage after oxidation and corrosion treatments.     

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.     

Property influence and poisoning mechanism of HgCl2 on V2O5-WO3/TiO2 SCR-DeNOx catalysts

In this paper, HgCl₂ was loaded by impregnation method to study its property influence and poisoning mechanism on V₂O₅-WO₃/TiO₂ SCR-DeNO_x catalyst. For HgCl₂-containing catalysts, deactivation was observed in simulated gas stream, and its catalytic activity declined with the increase of HgCl₂ loadings. Brønsted acid sites (VOH) and VO bond were affected evidently by HgCl₂, new NH₃ adsorption site ClVOH was generated after HgCl₂ addition. Interactions between HgCl₂ and V₂O₅ resulted in the loss of SCR active sites, and –HgCl existed as the stable form on the bridge site. Finally, the probable schematic diagram of HgCl₂ poisoning mechanism was also proposed.     

Clean borrowing hydrogen methodology using hydrotalcite supported copper catalyst

The catalytic activity of Mg–Al hydrotalcite supported copper catalyst was investigated for clean CC and CN bond forming reactions using alcohols as alkylating agent via borrowing hydrogen methodology. The catalyst showed excellent conversion of ketone and amine substrates (71–99%) to alkylated products with high selectivity in alkylation reactions.     

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.     

Infrared spectroscopy of some carbon-based materials relevant in combustion: Qualitative and quantitative analysis of hydrogen

A detailed procedure for the quantitative analysis of aromatic and aliphatic hydrogen based on infrared spectroscopy was set up and implemented on some carbon-based materials produced from organic precursors (naphthalene pitch) and/or relevant in combustion field (asphaltenes, carbon particulate matter, carbon black), spanning in the H/C atomic ratio range from 0.1 to 1. The quantitative FT-IR analysis involved the spectral deconvolution in the CH vibrations regions and the calibration factors of diverse standard species having spectral characteristics suitable for the detailed peak-to-peak analysis of the CH stretching (3100–2800 cm⁻¹) and aromatic CH bending (900–700 cm⁻¹) regions. The good agreement between the H/C atomic ratio obtained by quantitative FT-IR analysis and elemental analysis showed a reasonable reliability of the procedure. The major value of the developed FT-IR quantitative technique relies also on the capacity of discriminating between the different kinds of aliphatic and aromatic hydrogen. The quantitative and detailed analysis of hydrogen in form of CH₃, CH₂ and CH groups and in form of solo, duo and trio/quatro aromatic hydrogens showed to be useful also for inferring the structure of the aromatic moieties constituting the CC backbone of carbon materials.