Thermogravimetry analysis,compressive strength and thermal conductivity tests of non-autoclaved aerated Portland cement–fly ash–silica fume concrete

Journal of Thermal Analysis and Calorimetry - This paper reports the investigated thermogravimetry analysis, compressive strength and thermal conductivity tests of non-autoclaved aerated Portland...     

Preparation of silica–alumina composite membranes for hydrogen separation by multi-step pore modifications

In the present paper, a silica–alumina composite membrane for hydrogen separation was prepared within an α-alumina support by the multi-step pore modification. The α-alumina support has an asymmetric structure composed of a thin dense skin layer and a thick coarse layer and the average pore size of its skin layer is 80 nm. The composite membrane layer was formed in the vicinity of the interphase between the two layers of the support by two consecutive steps; namely, in situ silica sol–gel reaction and soaking and vapor deposition. In order to enhance the hydrogen selectivity, palladium (Pd) particles were impregnated in the final step utilizing Pd-acetate as a Pd precursor. Although both silica and Pd induced the surface diffusion, Pd was more effective for selective hydrogen adsorption than silica. This multi-step method produced a porous membrane with moderate hydrogen selectivity and satisfactory hydrogen permeance at high temperature and at high transmembrane pressure. The separation factor of hydrogen relative to nitrogen was maintained at about 10 even when the transmembrane pressure was as high as 110 kPa, and the hydrogen permeance was still much higher than that of non-porous polymeric membranes. In addition, the microstructural distributions of Si and Pd within the intermediate membrane layer were examined by a scanning electron microscopy (SEM) and an energy dispersive X-ray analysis (EDX)     

Carbon–silica composite bio-sorbents with a high density of oxygen-containing sites for efficient methylene blue adsorption

Research on Chemical Intermediates - There is a growing trend to employ agricultural waste/by-products (AWBs) as substrates for the development of dye bio-sorbents, and surface modification plays a...     

High-temperature oxidation of FeCrAl alloy with alumina–silica–ceria coatings deposited by sol–gel method

One-layer protective coatings made up of SiO₂–Al₂O₃ or SiO₂–Al₂O₃–CeO₂ oxides were synthesized on a FeCrAl alloy substrate by the sol–gel method from sols containing tetraethyl orthosilicate, aluminum tri-sec-butoxide and cerium(III) 2,4-pentanedionate as the precursors. Coating solutions with the Si:Al:Ce molar ratio of 3:1:0, 3:1:0.1; 3:1:0.01, and 3:1:0.001 were used. The composition and morphology of the obtained gels were examined by TG/DSC, XRD, and SEM techniques. It was found that a small addition of cerium affected the morphology of the forming coatings and improved the FeCrAl alloy resistance to high-temperature oxidation (in air at T = 900 °C for t = 100 h). The oxidation of all the investigated samples conformed to the parabolic rate. The protection effectiveness of the one-layer coatings after 100 h of high-temperature oxidation was as high as 70 %.     

Compressive strength development and hydration of cement–fly ash composite treated with microwave irradiation

Journal of Thermal Analysis and Calorimetry - In recent times, the use of multi-walled carbon nanotubes (MWCNTs)/water nanofluids as a coolant has garnered immense interest due to their high...     

Performances of NaCS–WSC protein drug microcapsules with different degree of substitution of NaCS using sodium polyphosphate as cross-linking agent

Sodium cellulose sulfate–water soluble chitosan (NaCS–WSC) microcapsules loaded with lactoferrin were fabricated with special performances using different degree of substitution (DS) of NaCS and WSC as potential micro-drug-carriers for colon. Effect of using cross-linking agent (sodium polyphosphate) and DS of NaCS on the structures and performances of microcapsules was studied. The results of laser scanning confocal microscope showed that fluorescein isothiocyanate-labeled lactoferrin distributed evenly in the drug-loaded microcapsules with cross-linker. NaCSs (DS: 0.51 and DS: 0.66, respectively) were chosen to prepare lactoferrin loaded microcapsules with WSC and cross-linker for comparison studies. DS of NaCS had some effects on erosion properties in which the erosion ratios of microcapsules with DS of 0.51 were higher than that with DS of 0.66, but showed no effect on swelling behaviors. Drug loading and encapsulation efficiencies of microcapsules (DS: 0.66) were 51.05 ± 0.97 and 75.88 ± 1.44 %, respectively, which were higher than that of microcapsules with DS of 0.51. In vitro release studies showed that the percentage of drug release of microcapsules (DS: 0.51) were higher than that of microcapsules with DS of 0.66 in simulated colonic fluid (pH 6.4) under mechanism of Anomalous (non-Fickian) transport, indicating that they are promising candidates as sustained protein drug delivery carriers with special performances.     

Formation of AlOOH and silica composite hierarchical nanostructures thin film by sol–gel dip-coating for superhydrophobic surface with high adhesion force

Nanosheet AlOOH and silica spheres composite thin film was deposited onto glass by sol–gel dip-coating method through hydrolysis of boiling water immersion. A silica sol and an alumina sol are employed in dipping process for the preparation of hierarchical nanostructures thin film. The morphology and structure of the films were characterized using field emission scanning electron microscopy and X-ray diffraction. The super-hydrophobicity with high adhesion forces can be attributed to both the rough multi-scale structural coating and surface enrichment of low surface energy with the chemical vapor deposition of 1H,1H,2H,2H-perfluorodecyltriethoxysilane.     

Dynamics of the surface layer in cyanobiphenyl–aerosil nanocomposites with a high silica density

Composites were prepared from an aerosil and 4-n-alkyl-4′cyanobiphenyls with five to eight carbon atoms in the alkyl chain. Their high silica density of ～7?g aerosil in 1?cm³ of liquid crystal (LC) allows the observation of the behaviour of a thin cyanobiphenyl layer (having nearly a monolayer structure) on the silica particles. The systems are investigated by dielectric spectroscopy (10^?2–10⁹?Hz) in a large temperature range (220–370?K). All the composites show a (main) relaxation process at frequencies much lower than the processes observed for the bulk LC that was assigned to the dynamics of the molecules in the surface layer. The temperature dependence of its characteristic frequencies obeys the Vogel–Fulcher–Tammann law, which is found to be typical for glass-forming liquids. The quasi two-dimensional character of the glass transition in the surface layer is discussed for the first time. At the nematic-to-isotropic transition temperature of the bulk, the composites show a continuous decrease of the characteristic frequencies as a function of the alkyl chain length, while the bulk LCs show the well known odd–even behaviour. The magnitude and temperature dependence of the slow relaxation process in the composites (molecules on an outer surface) agree with those of the same molecules confined to the nanopores of molecular sieves (internal surface).     

Quiescent hydrothermal synthesis of reduced graphene oxide–periodic mesoporous silica sandwich nanocomposites with perpendicular mesochannel alignments

Quiescent hydrothermal conditions were applied to synthesis of the sandwich nanocomposites of reduced graphite oxide (rGO) and periodic mesoporous silica (PMS) with vertically aligned mesochannels. It was found that the formation of the PMS–rGO–PMS sandwich structure is very sensitive to the surface and synthesis conditions. Although a higher temperature hydrothermal condition promotes reduction of GO and formation of bulky mesoporous nanoparticles, quiescent hydrothermal condition can serve as an alternative approach to obtain the unusual nanocomposites and slightly promote the structural stability of PMS on the surface of rGO.     

Development of polybenzoxazine–silica–titania (PBZ–SiO2–TiO2) hybrid nanomaterials with high surface free energy

In the present work, silica and titania reinforced polybenzoxazine (PBZ–SiO₂–TiO₂) hybrid nanomaterial possessing high surface free energy have been developed using dimethylol-functional benzoxazine monomer (4HBA-BZ), tetraethoxysilane (TEOS), 3-(isocyanatopropyl)triethoxysilane (ICPTS), titaniumisopropoxide (TIPO) through an in situ sol–gel process. Data obtained from the contact angle measurement indicate that the hybrid materials are hydrophilic in nature and possess a high surface free energy. For example, hybrid PBZ obtained from 1:1:0.6:0.4 (m:m:w:w) ratio of 4HBA-BZ:ICPTS:TEOS:TIPO (PBST₄) exhibit a high surface free energy of 38.2 mJm^?2 which is higher than that of neat polybenzoxazine (29.5 mJm^?2). Further data resulted from thermal studies indicate that the hybrid PBZ possess higher values of T_g, thermal stability and char yield than those of neat PBZ.     

Experimental and Nitta–Chao model prediction of high pressure density of p-xylene with dialkyl carbonates or n-alkanes

New data of high pressure density have been reported for p-xylene pure component and its binary mixtures with dimethyl carbonate, diethyl carbonate, n-octane and n-decane at (288.15, 298.15 and 308.15) K and (0.1, 5, 10, 20, 30 and 40) MPa and they have been compared with those available in the literature. The high pressure density has been correlated and predicted using a modified Tait equation and Nitta Chao group contribution model respectively. The derived thermophysical properties such as isothermal compressibility (κ_T), isobaric thermal expansivity (α_P) and internal pressure (π) have been also calculated.     

Deprotection of dithioacetals with 30% hydrogen peroxide catalyzed by tantalum(V) chloride–sodium iodide or niobium(V) chloride–sodium iodide

The reaction of dithioacetals with 30% hydrogen peroxide in the presence of catalytic amounts of tantalum(V) and iodide ion effectively produced carbonyl compounds in high yields. Dithioacetals also can be deprotected using the niobium(V) catalyzed oxidation of iodide ion by hydrogen peroxide under mild conditions.     

Involvement of cyan and ester groups in surface interactions of aerosil–cyanophenyl alkyl benzoate systems with high silica density: Infrared investigations

Composites prepared from aerosil A380 and liquid crystals (LCs) of 4-n-alkyl-4′-cyanophenyl benzoate type, with four to six carbon atoms in the alkyl chain were investigated by infrared spectroscopy. Their high silica content (of 2–7 g aerosil/1 g of LC) was given by thermogravimetric investigations and allows the observation of a rather thin LC layer on the silica particles. Several surface species onto the external surface of the grains were demonstrated. Arguments are given that monomer and dimer species are present in the bulk cyanophenyl benzoate materials while bulk-like species along with hydrogen-bonded ones coexist in the so-called surface layer of the composites. The main interaction of LC molecules with the aerosil surface is by hydrogen bonding taking place with the involvement of the cyan group. There is a contribution of ester carbonyl group to these surface interactions but this cannot be well quantified.     

Adsorption equilibrium,kinetics and mechanism of Pb(II) over carbon–silica composite biosorbent with designed surface oxygen groups

Research on Chemical Intermediates - Heavy metal contamination, especially contamination involving Pb(II), is a major environmental problem faced by modern society; hence, research on...     

Characterization of graphite–polyurethane composite electrodes modified with organofunctionalized SBA-15 nanostructured silica in the presence of heavy metal ions. Application to anodic stripping voltammetry

A graphite–polyurethane composite electrode with Santa Barbara Amorphous 15, SBA-15, mesoporous silica organofunctionalized with 2-benzothiazolethiol (BTSBA) as bulk modifier has been characterized electrochemically by voltammetry and electrochemical impedance spectroscopy (EIS) in the presence of cadmium ions, as an example of a toxic trace heavy metal, as well as by solid-state ¹³C-NMR and by scanning electron microscopy. EIS measurements performed on the modified composite electrodes to investigate the influence of BTSBA on the deposition of cadmium during square wave anodic stripping voltammetry showed that organofunctionalization of the SBA-15 bulk modifier in the composite electrode facilitates heavy metal deposition. Experiments were also carried out with a mixture of submicromolar cadmium, lead, copper and mercury ions and led to similar conclusions.     

Selective synthesis of α-trifluoromethyl-β-aryl enamines or vinylogous guanidinium salts by treatment of β-halo-β-trifluoromethylstyrenes with secondary amines under different conditions

Unprecedented selective reactions of β-halo-β-trifluoromethylstyrenes with secondary amines under different conditions were discovered. Depending on the electronic properties of the starting styrenes and the reaction parameters, two pathways were found. With neat secondary amines a series of α-trifluoromethyl-β-aryl enamines were prepared in high yields. In contrast, the reactions of the mentioned styrenes with the same amines in polar solvents by substitution of all halogen atoms gave vinylogous guanidinium salts. Possible reaction mechanisms are discussed.     

A needle trap device packed with a sol–gel derived,multi-walled carbon nanotubes/silica composite for sampling and analysis of volatile organohalogen compounds in air

A needle trap device (NTD) packed with silica composite of multi-walled carbon nanotubes (MWCNTs) prepared based on sol–gel technique was utilized for sampling and analysis of volatile organohalogen compounds (HVOCs) in air. The performance of the NTD packed with MWCNTs/silica composite as sorbent was examined in a variety of sampling conditions and was compared with NTDs packed with PDMS as well as SPME with Carboxen/PDMS-coated fibers. The limit of detection of NTDs for the GC/MS detection system was 0.01–0.05 ng mL⁻¹ and the limit of quantitation was 0.04–0.18 ng mL⁻¹. The RSD were 1.1–7.8% for intra-NTD comparison intended for repeatability of technique. The NTD-MWCNTs/silica composite showed better analytical performances compared to the NTD-PDMS composite and had the same analytical performances when compared to the SPME-Carboxen/PDMS fibers. The results show that NTD-MWCNTs-GC/MS is a powerful technique for active sampling of occupational/environmental pollutants in air.