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.     

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.     

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.     

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.     

Crystalline MoVO based complex oxides as selective oxidation catalysts of propane

Three single crystalline MoVO based oxides, MoVO, MoVTeO and MoVTeNbO, all of which have the same orthorhombic layer-type structure with the particular arrangement of MO₆ (M = Mo, V, Nb) octahedra forming slabs with pentagonal, hexagonal, and heptagonal rings in (1 0 0) plane, were synthesized by hydrothermal method and their catalytic performance in the selective oxidation of propane to acrylic acid were compared in order to elucidate the roles of constituent elements and crystal structure in the course of the propane oxidation. It was observed that the rate of propane oxidation was almost the same over all three catalysts, revealing that Mo and V, which were indispensable elements for the structure formation, were responsible for the catalytic activity for propane oxidation. The Te-containing catalysts showed much higher selectivity to acrylic acid than the MoVO catalyst. Since propene was formed as a main product at low conversion levels over every catalyst, it can be concluded that Te located in the central position of the hexagonal ring promoted the conversion of intermediate propene effectively to acrylic acid. The catalyst with Nb occupying the same structural position of V clearly showed the improved selectively to acrylic acid particularly at high conversion region, because the further oxidation of acrylic acid to CO_x was greatly suppressed. These conclusions were further supported by the additional studies of the determination of activation energy and catalytic oxidations of intermediate products of the propane oxidation.     

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.     

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.     

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.     

Thiourea-catalyzed dearomatizing [4+2] cycloadditions of 3-nitroindole

We have developed two efficient thiourea promoted dearomatizing processes involving the cycloadditions of 3-nitroindoles. The C2C3 double bond of the heteroarene can be involved as electron-poor 2π dienophile in [4+2] cycloadditions. While the uncatalyzed process requires harsh conditions, the organocatalyzed reaction takes place at room temperature and atmospheric pressure. The C2C3NO motif of the heteroarene can also react as an electron-poor 4π heterodiene in [4+2] / [3+2] cycloadditions cascades, under high pressure. In contrast to Lewis acid activation, thiourea promotion thus proves efficient even under unconventional activation conditions and in the presence of acid sensitive reactants such as enol ethers.     

Synthesis,pyrolysis of a novel liquid SiBCN ceramic precursor and its application in ceramic matrix composites

SiBCN ceramic precursor, polyborosilazane, was synthesized through a novel method which used sodium borohydride as boron source. Vinyl silazane with SiCl was converted to vinyl silazane with SiH structure, followed by hydroboration reaction and subsequent high-temperature reaction to form soluble polyborosilazane liquid. The process of precursor-to-ceramic conversion was almost completed before 800 °C and the cross-linked polyborosilazane precursor exhibited higher ceramic yield 75.6% at 1200 °C. The SiBCN ceramic annealed at 1400 °C contained BN, SiN and SiC bonds with smooth and dense surface and still retained principally amorphous structure up to 1600 °C. In addition, the viscosity of the polyborosilazane was 65 mPa.s, which can efficiently prepare ceramic matrix composite by means of precursor infiltration and pyrolysis (PIP). The density of as-obtained ceramic matrix composite (CMC) was 1.82 g/cm³, and the average bending strength, bending modulus and tensile strength were 265.2 MPa, 37.5 GPa and 158.6 MPa, respectively.     

In situ synthesis of nano size silicon carbide and fabrication of CSiC composites during the siliconization process of mesocarbon microbeads preforms

CSiC composites with carbon-based mesocarbon microbeads (MCMBs) preforms are a new type of high-performance and high-temperature structural materials for aerospace applications. In the present study, MCMB-SiC composites were fabricated by liquid silicon infiltration (LSI). Physical and mechanical properties such as density, porosity and bending strength were measured before and after siliconization. The results show the CSiC composites have excellent bending strength, density and porosity of 210 MPa, 2.41 g/cm³ and 0.62%, respectively. The chemical analysis shows that the composite is composed of 89% SiC, 2% Si and 9% C. The microstructural results also show the existence of two different areas of SiC, one zone of coarse micron size SiC at SiCSi interface and the other zone consists of fine nano-SiC particles at SiCC interfaces. The formation mechanism governing the siliconization of porous MCMB preform was also investigated.     

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.     

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.     

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.     

Effects of potassium doping on CO hydrogenation over MoS2 catalysts: A first-principles investigation

The effects of potassium (K) doping on the reactivity of CO hydrogenation over MoS₂(100) catalysts are investigated using periodic density functional theory (DFT) calculations. The surface doped K species enhances the CO adsorption by providing both KO and KC bonding. DFT results show that K-doping promotes the CC coupling step forming the H₂CCO precursor that leads to the formation of mixed higher C_2 + oxygenates. Different reaction routes for CO hydrogenation on the Mo and the S edges over MoS₂(100) catalysts are identified.     

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.     

The effect of density functional and dispersion interaction on structure and bonding analysis of uranium(VI) nitride complex [NU{N(CH2CH2NSiMe3)3}]: A theoretical study

Geometry and bonding energy analysis of uranium(VI) nitride complex [NU{N(CH₂CH₂NSiMe₃)₃}] were investigated with the DFT, DFT-D3 and DFT-D3(BJ) methods using density functionals (BLYP, BP86, PW91, PBE, revPBE and TPSS). The BLYP functional yields a UN bond distance of 1.788 Å for the model complex [NU{N(CH₂CH₂NSiMe₃)₃}] which is in close agreement with the experimental value of the UN bond distance of 1.799(7) Å for [NU{N(CH₂CH₂NSiⁱPr₃)₃}]. The calculated Mayer bond order (2.95) and Gopinathan–Jug bond order (3.18) indicate that the UN bond in this complex is essentially UN triple bonds. The electrostatic interaction is significantly smaller than the covalent bonding. The bond dissociation energy (BDE) is largest for the functional PBE and smallest for the functional TPSS. The DFT-D3 dispersion corrections are 5.3 kcal/mol (BLYP) and 5.0 kcal/mol (TPSS).     

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.