Simple synthesis of mesoporous carbon with magnetic nanoparticles embedded in carbon rods

Magnetically separable ordered mesoporous carbon containing magnetic nanoparticles embedded in the carbon walls was synthesized using a simple synthetic procedure. The resulting magnetically separable mesoporous carbon was denoted as M-OMC (magnetically separable ordered mesoporous carbon) poly(pyrrole) with residual Fe²⁺ ions in the mesoporous channel was converted to carbon material containing superparamagnetic nanoparticles. The size of the magnetic nanoparticles obtained was restricted by the channel size of the SBA-15 silica template, which resulted in the generation of superparamagnetic nanoparticles embedded in the carbon rods. The blocking temperature of M-OMC is 110 K. Pore size and textural property of M-OMC is similar to that of hexagonally ordered mesoporous carbon fabricated using SBA-15 silica as a template. The saturation magnetization of M-OMC is ca. 30.0 emu/g at 300 K, high enough for magnetic separation.     

Methane sorption on ordered mesoporous carbon in the presence of water

An ordered mesoporous carbon was synthesized using SBA-15 as the template. The sorption isotherms of methane on the synthesized carbon material were collected. Its ordered structure was confirmed by the XRD, SEM and TEM examinations. The BET surface area is 1100-1200 m²/g, the total pore volume is 1.24-1.30 cm³/g, and the pore size distribution is very narrow and centered at 2-5 nm. As high as 41.2 wt.% of methane was stored per unit mass of carbon at 275 K and pressures less than 7 MPa in the presence of 3.86 times more water. This sorption amount is 31% higher than the largest sorption capacity reached by activated carbon in the presence of water, which was equal to or higher than the storage capacity of compression till 20 MPa. The enthalpy change corresponding to the sudden change of isotherms was equal to the enthalpy change of methane hydrate formation; therefore, the mechanism of the enhanced methane storage was considered due to the formation of methane hydrate in the porous carbon material.     

Diffusion coefficients of l-menthone and l-carvone in mixtures of carbon dioxide and ethanol

The molecular diffusion coefficients of l-menthone and l-carvone in supercritical carbon dioxide (SCCO₂) and carbon dioxide containing 5 and 10 mol% ethanol as a modifier were measured by the Taylor-Aris chromatographic peak broadening (CPB) method over the ranges of temperature from 308.15 to 338.15 K and pressure from 15 to 30 MPa. It was found that the correlation relationships between diffusion coefficients and the temperature, pressure, viscosity, and density, such as the linear correlation between the D₁₂ and ρ, and between the D₁₂ and T/η, which were valid in binary systems, were also suitable for ternary systems of carbon dioxide containing modifier. The diffusion coefficients in modified SCCO₂ decreased with increasing the ethanol mole fraction due to the chemical association between the two solutes and ethanol. Of several models used to predict experimental data in pure carbon dioxide, the two models of Funazukuri-Ishiwata-Wakao and He-Yu-1998 were the best with the AAD less than 3.2%. Furthermore, the models of modified Wilke-Chang, Scheibel, Reddy-Doraiswamy, Lusis-Ratcliff, Hayduck-Minhas, Tyn-Calus, and Lai-Tan overestimated the diffusion coefficient in ethanol modified SCCO₂ with the AAD values increaseing with the percentage of ethanol, which were probably due to the increase of the volume of solvaton sphere as a true diffusion unit with the percentage of ethanol. Moreover, the free volume model of Dymond is good for predicting the experimental data in pure carbon dioxide and ethanol modified SCCO₂ with the AAD values range from 3.21 to 1.90%.     

Electrochemical detection of l-cysteine using a boron-doped carbon nanotube-modified electrode

A boron-doped carbon nanotube (BCNT)-modified glassy carbon (GC) electrode was constructed for the detection of l-cysteine (L-CySH). The electrochemical behavior of BCNTs in response to l-cysteine oxidation was investigated. The response current of L-CySH oxidation at the BCNT/GC electrode was obviously higher than that at the bare GC electrode or the CNT/GC electrode. This finding may be ascribed to the excellent electrochemical properties of the BCNT/GC electrode. Moreover, on the basis of this finding, a determination of L-CySH at the BCNT/GC electrode was carried out. The effects of pH, scan rate and interferents on the response of L-CySH oxidation were investigated. Under the optimum experimental conditions, the detection response for L-CySH on the BCNT/GC electrode was fast (within 7 s). It was found to be linear from 7.8 × 10⁻⁷ to 2 × 10⁻⁴ M (r = 0.998), with a high sensitivity of 25.3 ± 1.2 nA mM⁻¹ and a low detection limit of 0.26 ± 0.01 μM. The BCNT/GC electrode exhibited high stability and good resistance against interference by other oxidizable amino acids (tryptophan and tyrosine).     

Templated synthesis of mesoporous carbon from sucrose—the way from the silica pore filling to the carbon material

Mesoporous carbon materials were synthesized using sucrose as carbon precursor and commercial silica as template. Every step of the synthesis such as pore filling, loss of carbon precursor during carbonization and development of the carbon pore system during silica removal have been investigated in detail. As a criterion for the quality of the obtained carbon materials, the pore size distribution estimated by applying density functional theory was used.     

Thermal degradation of poly(l-lactide): effect of alkali earth metal oxides for selective l,l-lactide formation

To achieve the feed stock recycling of poly(l-lactide) (PLLA) to l,l-lactide, PLLA composites including alkali earth metal oxides, such as calcium oxide (CaO) and magnesium oxide (MgO), were prepared and the effect of such metal oxides on the thermal degradation was investigated from the viewpoint of selective l,l-lactide formation. Metal oxides both lowered the degradation temperature range of PLLA and completely suppressed the production of oligomers other than lactides. CaO markedly lowered the degradation temperature, but caused some racemization of lactide, especially in a temperature range lower than 250 °C. Interestingly, with MgO racemization was avoided even in the lower temperature range. It is considered that the effect of MgO on the racemization is due to the lower basicity of Mg compared to Ca. At temperatures lower than 270 °C, the pyrolysis of PLLA/MgO (5 wt%) composite occurred smoothly causing unzipping depolymerization, resulting in selective l,l-lactide production. A degradation mechanism was discussed based on the results of kinetic analysis. A practical approach for the selective production of l,l-lactide from PLLA is proposed by using the PLLA/MgO composite.     

Amorphous cell studies of polyglycolic, poly(l-lactic), poly(l,d-lactic) and poly(glycolic/l-lactic) acids

In this paper static amorphous state properties (solubility parameter, free volume (using the Voorintholt method and the Voronoi tessellations) and pair correlation functions, the last ones also by including water molecules in the cells), which can be related to the probability for water uptake, have been studied for polyglycolic (PGA), poly(l-lactic) (PLLA), poly(l,d-lactic) (PLLA/PDLA) and poly(glycolic/l-lactic) (PGA/PLLA) acids, known to be biodegradable polymers. The polymer consistent force field, as modified by the authors, has been used in the calculations. The main purpose of this paper is to investigate, which of the amorphous state properties would be relevant for water uptake. We also discuss the validity of th6e methods used for these kinds of studies, and the related reliability of the computed results. Chain flexibilities of the studied polyesters in the amorphous phase have been analyzed, and the intermolecular interactions are found to cause the most significant variations in the distributions of the adjacent chain dihedral angle pairs and in the related populations of the low-energy regions of the comonomers. The solubility parameters, as calculated from the cohesion energy densities of the constructed models, suggest PGA being most compatible with water, in agreement with experiments. On the other hand, the quantitative structure-property relationships method ‘Synthia’ suggests a very similar solubility in water for all particular polyesters. In the PLAs and PGA/PLLA, however, a larger number of hydrogen bonds is formed between the water molecules and the carbonyl oxygen atoms of the chains showing a better possibility of PLLA and its copolymers to break into shorter chains. As an explanation, the hydrophobic methyl groups of the lactide units are suggested to push the water molecules closer to the carbonyl groups than in homo-PGA.     

Carbon-coated anatase: the role of the carbon layer for photocatalytic performance

Carbon-coated anatase-type TiO₂ was prepared by the heat treatment of powder mixtures of photocatalyst TiO₂ (ST-01) with different carbon precursors, poly(vinyl alcohol), hydroxyl propyl cellulose and poly(ethylene terephthalate), at a temperature between 700 and 900 °C for 1 h in an Ar gas flow. Since the carbon layers formed on the TiO₂ particles were porous, the samples prepared showed a high adsorptivity, in addition to the photoactivity of TiO₂. The carbon coating was shown to suppress the phase transition from photoactive anatase to much less active rutile, but seemed to reduce the amount of UV radiation reaching the surface of the TiO₂ particles. A balance among different factors controlled by the carbon layer on the TiO₂ particles was required to get high photocatalytic performance, i.e., high rate constant for the photodecomposition of methylene blue. On the sample prepared at 850 °C with a carbon content of about 3.5 wt%, the highest rate constant in the present work was obtained, in which the transition from anatase to rutile was suppressed and carbon layer was thin enough to transmit UV rays.     

The effect of silica template structure on the pore structure of mesoporous carbons

We have synthesized two kinds of mesoporous carbons using a spherical silica sol (SMC1 carbon) and an elongated silica sol (SMC3 carbon) as templates. Nitrogen isotherms and electrochemical experiments were performed to investigate the effect of the silica template structure on the pore structure of the resulting mesoporous carbons. When carbons produced using the same silica to resorcinol molar ratio were compared, both nitrogen isotherms and electrochemical studies revealed that the SMC3 carbons exhibit simpler pore connectivity than SMC1 carbons.     

Adsorption of lipopolysaccharide on carbon sieves

Adsorption of lipopolysaccharide, LPS, on carbon sieves Carboxen 1003 and Carboxen 1010 has been studied. LPS adsorption kinetics is initially faster on smaller size (1-10 μm) particles of predominantly microporous Carboxen 1010 compared to Carboxen 1003 (150-200 μm) particles. However, the adsorption capacity of micro/meso/macroporous Carboxen 1003 by LPS is higher than that of Carboxen 1010 since the former carbon has wider pores that can accommodate large lipopolysaccharide molecules or their agglomerates. Carboxen 1010 probably adsorbs LPS mainly on the external (macropore) surface.     

Catalytic graphitization of templated mesoporous carbons

Graphitic porous carbons with a wide variety of textural properties were obtained by using a silica xerogel as template and a phenolic resin as carbon precursor. The synthetic procedure used to prepare them was as follows: (a) infiltration of the porosity of silica by a solution containing phenolic resin, (b) carbonization of the silica-resin composite, (c) removal of the silica skeleton, (d) impregnation of the templated porous carbon with a metallic salt and (e) catalytic graphitization of the impregnated carbon by heat treatment at 900 °C. The graphitization of the carbons thus prepared varies as a function of the carbonization temperature used and the type of metal employed as catalyst (Fe, Ni or Mn). The porous characteristics of these materials change greatly with the temperatures used during the carbonization step. These graphitized carbons exhibit high electrical conductivities up to two orders larger than those obtained for the non-graphitized samples.     

Titanium complexes based on aminodiol ligands for the ring opening polymerization of l- and d,l-lactide

A series of new titanium isopropoxide complexes (1-4-Ti(OⁱPr)₂ based on enantiopure (1-H₂), racemic (2-H₂), meso (3-H₂) and diastereomeric (4-H₂) aminodiol ligands have been prepared and tested as initiators for the ring opening polymerization (ROP) of l/rac-lactide in solution and in bulk conditions. All complexes were shown to have significant activity in solution at 70 °C and higher activity in bulk at 130 °C with a good control over the molar mass distribution and molecular weights. The complex derived from the racemic-aminodiol ligand gave partially heterotactic polylactide in ROP of rac-lactide and afforded atactic polylactide in the bulk, whereas all other complexes yielded atactic polylactides both in solution and in bulk. Ligand variation (chirality) in the complexes has little effect on either the activity or selectivity of the initiators. The polymerization kinetics using (1-Ti(OⁱPr)₂) as an initiator indicated a first order reaction with respect to the monomer concentration.     

Synthesis and characterization of poly(l-glutamic acid)-block-poly(l-phenylalanine)

Poly(γ-benzyl l-glutamate)-block-poly(l-phenylalanine) was prepared via the ring opening polymerization of γ-benzyl l-glutamate N-carboxyanhydride and l-phenylalanine N-carboxyanhydride using n-butylamine·HCl as an initiator for the living polymerization. Polymerization was confirmed by ¹H-nuclear magnetic resonance spectroscopy and matrix assisted laser desorption ionization time of flight mass spectroscopy. After deprotection, the vesicular nanostructure of poly(l-glutamic acid)-block-poly(l-phenylalanine) particles was examined by transmission electron microscopy and dynamic light scattering. The pH-dependent properties of the nanoparticles were evaluated by means of ζ-potential and transmittance measurements. The results showed that the block copolypeptide could be prepared using simple techniques. Moreover, the easily prepared PGA-PPA block copolypeptide showed pH-dependent properties due to changes in the PGA ionization state as a function of pH; this characteristic could potentially be exploited for drug delivery applications.     

Controlled crystal nucleation in the melt-crystallization of poly(l-lactide) and poly(l-lactide)/poly(d-lactide) stereocomplex

Among the various inorganic nucleators examined, Talc and an aluminum complex of a phosphoric ester combined with hydrotalcite (NA) were found to be effective for the melt-crystallization of poly(l-lactide) (PLLA) and PLLA/poly(d-lactide) (PDLA) stereo mixture, respectively. NA (1.0 phr (per one hundred resin)) can exclusively nucleate the stereocomplex crystals, while Talc cannot suppress the homo crystallization of PLLA and PDLA in the stereo mixture. Double use of Talc and NA (in 1.0 phr each) is highly effective for enhancing the crystallization temperature of the stereo complex without forming the homo crystals. The stereocomplex crystals nucleated by NA show a significantly lower melting temperature (207 °C) than the single crystal of the stereocomplex (230 °C) in spite of recording a large heat of crystallization ΔH_c (54 J/g). Photomicrographic study suggests that the spherulites with a symmetric morphology are formed in the stereo mixture added with NA while the spherulites do not grow in size in the mixture added with Talc. The exclusive growth of the stereocomplex crystals by the melt-crystallization process will open a processing window for the PLLA/PDLA.     

Direct fabrication of mesoporous carbons using in-situ polymerized silica gel networks as a template

Mesoporous carbons were synthesized by in-situ polymerized silica gel networks as a template. The co-condensation of carbon precursor (sucrose) and silica precursor (sodium silicate) followed by heat treatment generated a carbon/silica nanocomposite. After etching the silica template, mesoporous carbons were obtained. Under optimum synthesis conditions a mesoporous carbon with a high surface area of >800 m²/g and a narrow pore size distribution centered at 3 nm was produced. The three-dimensionally interconnected silica structures effectively functioned as the template for the porous carbon materials.     

Titanium carbide derived nanoporous carbon for energy-related applications

High surface area nanoporous carbon has been prepared by thermo-chemical etching of titanium carbide TiC in chlorine in the temperature range 200-1200 °C. Structural analysis showed that this carbide-derived carbon (CDC) was highly disordered at all synthesis temperatures. Higher temperature resulted in increasing ordering and formation of bent graphene sheets or thin graphitic ribbons. Soft X-ray absorption near-edge structure spectroscopy demonstrated that CDC consisted mostly of sp² bonded carbon. Small-angle X-ray scattering and argon sorption measurements showed that the uniform carbon-carbon distance in cubic TiC resulted in the formation of small pores with a narrow size distribution at low synthesis temperatures; synthesis temperatures above 800 °C resulted in larger pores. CDC produced at 600-800 °C show great potential for energy-related applications. Hydrogen sorption experiments at −195.8 °C and atmospheric pressure showed a maximum gravimetric capacity of ∼330 cm³/g (3.0 wt.%). Methane sorption at 25 °C demonstrated a maximum capacity above 46 cm³/g (45 vol/vol or 3.1 wt.%) at atmospheric pressure. When tested as electrodes for supercapacitors with an organic electrolyte, the hydrogen-treated CDC showed specific capacitance up to 130 F/g with no degradation after 10 000 cycles.     

Synthesis and characterization of tailorable biodegradable thermoresponsive methacryloylamide polymers based on l-serine and l-threonine alkyl esters

A series of monomers based on the methyl, ethyl, and isopropyl esters of N^α-(methacryloyl)-serine and -threonine were synthesized, and used in an AIBN-initiated radical polymerization reaction to yield polymers with an M_n ranging between 6.6 and 23.8 kDa. The newly synthesized polymers showed LCST behavior in aqueous solution that could be tailored by subtle variations of the hydrophobicity of the monomers to obtain a broad range of cloud points between 1.5 and >100°C. According to HPLC, the hydrolytic t_1/2-values (pH 7.4 at 37°C) of the monomers were found to be 5, 12, and 40 days of the methyl, ethyl, and isopropyl esters, respectively, while the hydrolysis rate of poly[N^α-(methacryloyl)-Ser-OMe] and poly[N^α-(methacryloyl)-Thr-OMe] was found to be significantly lower compared to the corresponding monomers. In order to obtain thermoresponsive nanoparticles, N^α-(methacryloyl)-Thr-OEt was polymerized with (PEG monomethyl ether 5000)₂-ABCPA as macroinitiator to yield an amphiphilic block co-polymer, poly[N^α-(methacryloyl)-Thr-OEt]-b-(PEG monomethyl ether 5000), which forms particles of 300 nm at a temperature higher than its cloud point of 24°C. Incubation at physiological conditions induced ester hydrolysis resulting in a destabilization of the particles making these particles suitable for drug delivery purposes.