Showing papers on "Thermogravimetry published in 2008"

Functionalization of Halloysite Clay Nanotubes by Grafting with γ-Aminopropyltriethoxysilane

Abstract: Surface modification of natural halloysite clay nanotubes with γ-aminopropyltriethoxysilane (APTES) was investigated. Untreated and modified samples were characterized by nitrogen adsorption, X-ray diffraction, elemental analysis, thermogravimetry, transmission electron microscopy, atomic force microscopy, MAS nuclear magnetic resonance (29Si, 13C, 29Al), and Fourier transform infrared spectroscopy. The modification mechanism was found to include not only the direct grafting of APTES onto the hydroxyl groups of the internal walls, edges and external surfaces of the nanotubes but other processes in which oligomerized APTES condensed with the directly grafted APTES to form a cross-linked structure. The thermal and evacuation pretreatment conditions were found to play an important role in controlling the extent and mechanism of the modification. The extent of modification is also strongly affected by the morphological parameters of the original clay samples. This study demonstrates that the surface chemistry...

Thermal activation of CaO-based sorbent and self-reactivation during CO2 capture looping cycles.

Abstract: In this study, the thermal activation of different types of CaO-based sorbents was examined. Pretreatments were performed at different temperatures (800−1300 °C) and different durations (6−48 h) us...

Base‐Induced Formation of Two Magnesium Metal‐Organic Framework Compounds with a Bifunctional Tetratopic Ligand

Abstract: Two coordination polymers constructed from magnesium and the tetratopic organic linker 2,5-dihydroxyterephthalic acid are reported, denominated CPO-26-Mg and CPO-27-Mg. The organic component carries two different types of protic functional groups. The degree of deprotonation of the organic component can be regulated by the amount of sodium hydroxide employed in the synthesis, thus determining which of the compounds forms. In CPO-26-Mg, only the carboxylic acid groups of the linker are deprotonated and take part in the construction of the three-dimensional framework. The structure is non-porous, and its topology is based on the PtS net. In CPO-27-Mg, both the carboxylic acid and the hydroxy groups are deprotonated and involved in the construction of a microporous three-dimensional framework which is based on a honeycomb motif containing large solvent-filled channels. The metal atoms are arranged in chiral chains along the intersection of the honeycomb and contain one water molecule in their coordination sphere, which allows for the creation of coordinatively unsaturated metal sites upon dehydration. CPO-27-Mg is a potentially useful lightweight adsorbent with a pore volume of 60 % of the total volume of the structure and an apparent Langmuir surface area of up to 1030 m2 g–1. Its thermal stability was investigated by thermogravimetry and variable-temperature powder X-ray diffraction, which shows framework degradation to commence at 160 °C in air, at 235 °C under nitrogen, and at 430 °C in a dynamic vacuum. Thermogravimetric dehydration and re-hydration experiments at miscellaneous temperatures indicate that it is possible to obtain open metal sites in CPO-27-Mg, but the water is more tightly bound in this material than in the previously reported isostructural nickel compound.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Synthesis, crystallization mechanism, and catalytic properties of titanium-rich TS-1 free of extraframework titanium species.

Abstract: A new route to the synthesis of TS-1 has been developed using (NH4)2CO3 as a crystallization-mediating agent. In this way, the framework Ti content can be significantly increased without forming extraframework Ti species. The prepared catalyst had a Si/Ti ratio as low as 34 in contrast to the ratio of 58 achieved with the methods A and B established by the Enichem group (Clerici, M. G.; Bellussi, G.; Romano, U. J. Catal. 1991, 129, 159) and Thangaraj and Sivasanker (Thangaraj, A.; Sivasanker, S. J. Chem. Soc., Chem. Commun. 1992, 123), respectively. The material contained less defect sites than the samples synthesized by the other two methods. As a result, it showed much higher activity for the oxidation of various organic substrates, such as linear alkanes/alkenes and alcohols, styrene, and benzene. The crystallization mechanism of TS-1 in the presence of (NH4)2CO3 was studied by following the whole crystallization process with X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), thermogravimetry/differential thermal analysis (TG/DTA), inductively coupled plasma atomic emission spectrometry (ICP), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), diffuse reflectance UV-vis spectroscopy, and (29)Si MAS (magic-angle spinning) NMR spectroscopy techniques. It was shown that the presence of (NH4)2CO3 not only drastically lowered down pH, slowing down the crystallization process and making the incorporation of Ti into the framework match well with nucleation and crystal growth, but also modified the crystallization mechanism. It seems that the solid-phase transformation mechanism predominated in the crystallization process initiated by dissociation, reorganization, and recoalescence of the solidified gel although a small amount of nongelatinated Ti shifted to the solid during the crystal growth period. In contrast, a typical homogeneous nucleation mechanism occurred in the method A system. Thus, although in the method A system most of Ti cations was inserted into the lattice after the crystallization was nearly completed, the inclusion of Ti started at the earlier nucleation period in the presence of (NH4)2CO3. This is favorable for the incorporation of Ti into the framework, resulting in a more homogeneous distribution of Ti in the framework. Oxidation of 1-hexene and 2-hexanol over the samples collected during the whole crystallization process indicated that condensation of Ti-OH and Si-OH proceeded even after the crystallization was completed. This resulted in an increase in hydrophobicity and an overall improvement in microscopic character of Ti species and consequently a great increase in the catalytic activity with further progress of crystallization.

Fabrication of Superhydrophobic Cellulose-Based Materials through a Solution-Immersion Process

Abstract: An industrial waterproof reagent [(potassium methyl siliconate) (PMS)] was used for fabricating a superhydrophobic surface on a cellulose-based material (cotton fabric or paper) through a solution-immersion method. This method involves a hydrogen bond assembly and a polycondensation process. The silanol, which was formed by a reaction of PMS aqueous solution with CO2, Was assembled on the cellulose molecule surface via hydrogen bond interactions. The polymethylsilsesquioxane coatings were prepared by a polycondensation reaction of the hydroxyl between cellulose and silatiol. The superhydrophobic cellulose materials were characterized by FTIR spectroscopy, thermogravimetry, and surface analysis (XPS, FESEM, AFM, and contact angle measurements).

Synthetic Routes and Formation Mechanisms of Spherical Boron Nitride Nanoparticles

Abstract: A new concept is proposed to explain the formation of spherical boron nitride (BN) nanoparticles synthesized by the chemical vapor deposition (CVD) reaction of trimethoxyborane (B(OMe)(3)) with ammonia. The intermediate phases formed during the CVD under different reaction conditions are analyzed by X-ray diffraction, electron microscopy, thermogravimetry, and spectroscopy techniques. The transition mechanism from in intermediate B(OMe)(3-x)H3-xN (x < 2) phase having single B-N bonds to the BN nanoparticles is elucidated. This particularly emphasizes the CVD temperature effect governing the conversion of the N-H...O-B hydrogen bonds in (OMe)(3)B center dot NH3 into the N-B bonds in B(OMe)(3-x)H3-xN. The spherical morphology strongly depends on the remnant impurity oxygen formed upon Me2O group elimination in the intermediate. Two types of spherical BN nanoparticles primarily attractive for immediate commercialization (with C and H impurities at a level less than 1 wt %) are synthesized by the adjustment of experimental parameters: high oxygen-containing (similar to 6.3 wt %) BN spheres with a diameter of similar to 90 nm and a specific surface area of 26.8 m(2) g(-1);and low oxygen-containing (< 1 wt 0%) BN spheres with a diameter of similar to 30 nm and a surface area of 52.7 m(2) g(-1). Finally, the regarded synthetic techniques are fully optimized in the present work.

Flame retardancy mechanisms of metal phosphinates and metal phosphinates in combination with melamine cyanurate in glass‐fiber reinforced poly(1,4‐butylene terephthalate): the influence of metal cation

Abstract: The pyrolysis and fire behavior of glass-fiber reinforced poly(butylene terephthalate) (PBT/GF) with two different metal phosphinates as flame retardants in combination with and without melamine cyanurate (MC) were analyzed by means of thermogravimetry, thermogravimetry coupled with infrared spectroscopy, flammability, and cone calorimeter tests as well as scanning electron microscopy/energy dispersive X-ray spectroscopy and X-ray fluorescence spectroscopy. In PBT/GF, dosages of 13–20% of the halogen-free flame retardant aluminum phosphinate or aluminum phosphinate in combination with MC fulfill the requirements for electrical engineering and electronics applications (UL 94 = V-0; LOI > 42%), whereas the use of the same amount of zinc phosphinate or zinc phosphinate in combination with MC does not improve the fire behavior satisfactorily (UL 94 = HB; LOI = 27–28%). The performance under forced flaming conditions (cone calorimeter) is quite similar for both of the metal phosphinates. The use of aluminum and zinc salts results in similar flame inhibition predominantly due to the release of the phosphinate compounds in the gas phase. Both metal phosphinates and MC interact with the polymer changing the decomposition characteristics. However, part of the zinc phosphinate vaporizes as a complete molecule. Because of the different decomposition behavior of the metal salts, only the aluminum phosphinate results in a small amount of thermally stable carbonaceous char. In particular, the aluminum phosphinate-terephthalate formed is more stable than the zinc phosphinate-terephthalate. The small amount of char has a crucial effect on the thermal properties and mechanical stability of the residue and thus the flammability. Copyright © 2008 John Wiley & Sons, Ltd.

Pyrolysis Characteristics and Kinetics of Sewage Sludge by Thermogravimetry Fourier Transform Infrared Analysis

Abstract: The characteristics and gas product properties of pyrolyzing sewage sludge were determined, aiming to utilize efficiently the waste for energy recovery. The pyrolysis of two predried sludge materials (S1 and S2) was conducted in a thermogravimetry analyzer (TGA). It was found that the pyrolysis mainly occurred at about 150–550 °C, with two and one reaction stages found respectively for S1 and S2. Using the global reaction kinetic model, the activation energy was calculated at ∼30 kJ mol−1 in the first reaction stage for all the selected heating rates, and the pre-exponential factors increased with the increasing heating rate. The kinetic parameters calculated explained well the pyrolysis characteristics observed. In the meantime, the gas products released under different pyrolysis conditions were analyzed online using Fourier transform infrared (FTIR) spectroscopy; the results showed that the gas composition was highly dependent on temperature, and the releasing of the gas species was consistent with the ...

A kinetic study on the thermal behaviour of chitosan

Abstract: The thermal behaviour of chitosan was studied by means of thermogravimetry, mass spectrometry and infrared spectrometry. Kinetic parameters were obtained by advanced kinetic evaluation (differential isoconversional analysis) from DSC curves, in non-isothermal conditions, at several heating rates, between 5 and 30°C min−1. The results showed that the decomposition of chitosan does not follow a single mechanism because both the activation energy and the pre-exponential factor are not constant during the course of the reaction. A comparison with the results obtained by applying different conventional calculating methods is also shown.

Polyaniline-carbon nanotube composites

Abstract: The key developments in polyaniline-carbon nanotube (PANI-CNT) composites are reviewed. Apart from in situ chemical polymerization and electrochemical deposition, a number of interesting approaches including the use of aniline functionalized CNTs and ultra- sound/microwave/γ-radiation initiated polymerization have been used in the preparation of composites. The structure and properties of these composites have been investigated by a va- riety of techniques including absorption, infrared (IR), Raman, X-ray photoelectron spec- troscopy methods, scanning electron and scanning probe microscopy techniques, cyclic voltammetry, and thermogravimetry. The experimental results indicate favorable interaction between PANI and CNTs. The CNT content in these composites controls their conductive, mechanical, and thermal properties. The most interesting characteristic is their easy dis- persibility in aqueous solution. The performance evaluation studies of PANI-CNT compos- ites in a number of applications including supercapacitors, fuel cells, sensors, and actuators are highlighted.

A Novel Coordination Polymer as Positive Electrode Material for Lithium Ion Battery

Abstract: A new coordination polymer based on an aromatic carbonyl ligand is prepared and investigated as a positive active material for lithium ion batteries, namely, [Li2(C6H2O4)] (1). It is synthesized by the dehydration of [Li2(C6H2O4)·2H2O] (2). These compounds are characterized by Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), elemental analysis (EA), single crystal X-ray diffraction methods and powder X-ray diffraction (XRD). As positive material, compound 1 has an initial discharge capacity of 176 mAh·g−1 and a columbic efficiency of 93.18% in the first cycle. It might provide a new method for finding new positive-electrode materials in lithium ion batteries.

Application of thermal analysis methods for characterization of polymer/montmorillonite nanocomposites

Abstract: Thermal analysis is a useful tool for investigating the properties of polymer/clay nanocomposites and mechanisms of improvement of thermal properties. This review work presents examples of applications of differential scanning calorimetry (DSC), modulated temperature differential scanning calorimetry (MT-DSC), dynamic mechanical thermal analysis (DMA), thermal mechanical analysis (TMA), thermogravimeric analysis (TG) and thermoanalytical methods i.e. TG coupled with Fourier transformation infrared spectroscopy (TG-FTIR) and mass spectroscopy (TG-MS) in characterization of nanocomposite materials. Complex behavior of different polymeric matrices upon modification with montmorillonite is briefly discussed.

Surface modification of Au/TiO2 catalysts by SiO2 via atomic layer deposition

Abstract: Atomic layer deposition (ALD) was utilized for the surface engineering of metallic nanoparticles to tame their sintering problems and catalytic activities. We chose the surface modification of gold nanocatalysts as an example to demonstrate the concept of this ALD-based approach. Herein, an active Au/TiO2 catalyst was modified by amorphous SiO2 via ALD, and the samples were characterized by inductively coupled plasma-optical emission spectrometry (ICP-OES), scanning (SEM-EDX) and transmission electron microscope−energy-dispersive X-ray spectrometry (TEM-EDX), X-ray diffraction (XRD), and thermogravimetry/differential thermogravimetry (TG/DTG), and the catalytic activities in CO oxidation and H2 oxidation were tested with respect to the pretreatment temperature and SiO2 content. A significant sintering resistance and changes in catalytic activities were observed. The difference between the SiO2/Au/TiO2 samples prepared by gas-phase ALD and solution-phase chemical grafting was discussed.

Contribution to the study of hydroxymetylation reaction of alkali lignin

Abstract: The hydroxymethylation of alkali lignin with formaldehyde in alkaline solution was studied. The influence of reaction conditions of the hydroxymethylation of alkali lignin was followed by modifying the temperature, time, and the ratios of NaOH to lignin and CH2O to lignin. Three different types of alkali lignin were utilized. The reaction was followed by total consumption of formaldehyde, and the resulting products were characterized through FTIR-spectra, thermogravimetry analysis, ash and moisture contents, as well as by the amounts of OH groups.

Titania–phosphonate hybrid porous materials: preparation, photocatalytic activity and heavy metal ion adsorption

Abstract: Organic–inorganic hybrid materials of porous titania–phosphonate were synthesized using organically bridged tetra- or penta-phosphonates. Claw molecules of ethylene diamine tetra(methylene phosphonic acid) and diethylene triamine penta(methylene phosphonic acid) were anchored to the titania network homogeneously. The synthesized titania–phosphonate hybrids possess irregular mesoporosity formed by the assembly of nanoparticles in a crystalline anatase phase, revealed by the measuement of X-ray diffraction, nitrogen adsorption, scanning and transmission electron microscopy. The structure and chemical states of the materials were characterized by chemical analysis, FT-IR, MAS NMR, XPS and thermogravimetric analysis, revealing the integrity of organic groups inside the framework. The optical properties, catalysis and adsorption performances were also investigated. These porous titania–phosphonate materials exhibited high photocatalytic activity in photodecomposition of Rhodamine B dye molecules whether under UV or visible-light irradiation, and a large capacity for selective adsorption of Cd(II) ions, making them promising adsorbents and photocatalysts for practical applications including wastewater cleanup.

Oxidation investigation of nickel nanoparticles

Abstract: This work reported an experimental investigation of complete oxidation of nickel nanoparticles using simultaneous thermogravimetry analysis (TGA) and differential scanning calorimetry (DSC). Nickel nanoparticles and their elemental compositions were characterized by Brunauer–Emmett–Teller (BET) analysis, transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). The oxidation experiments were performed under isoconversion conditions for seven heating rates, varying from 2 to 20 K min−1, with temperatures up to 1000 °C. The experiments revealed unique oxidation behaviour of nickel at the nanometre scale, such as early oxidation and melting phenomena, variable activation energies and different oxidation kinetics between low and high conversion ratios. Unlike its bulk counterpart where the activation energy is a constant, the activation energy of nickel nanoparticles depended on the conversion ratio, ranging between 1.4 and 1.8 eV. The oxidation kinetics of nickel nanoparticles changed from the classical diffusion controlled mechanism to a pseudo-homogeneous reaction as conversion ratios were over 50%. The oxidation mechanisms of nickel nanoparticles were further discussed and future studies to enhance understanding were identified.