Showing papers on "Thermogravimetric analysis published in 2010"

Effect of fiber surface-treatments on the properties of poly(lactic acid)/ramie composites

Abstract: Ramie fiber reinforced poly(lactic acid) (PLA) composites were prepared by a two-roll mill. Ramie was treated by alkali and silane (3-aminopropyltriethoxy silane and γ-glycidoxypropyltrimethoxy silane). Effect of surface treatment on the properties of the composites was studied. The tensile, flexural and impact strength of the composites have a significant improvement. Dynamic mechanical analysis (DMA) results show that the storage moduli of the composites with treated ramie increase with respect to the plain PLA and the composites with untreated fiber whereas tangent delta decreases. The Vicat softening temperature of the composites with treated fiber is greatly higher than that of the composites with untreated fiber. The results of thermogravimetric analysis (TGA) show that fiber treatment can improve the degradation temperature of the composites. Moreover, the morphology of fracture surface evaluated by scanning electron microscopy (SEM) indicates that surface treatment can get better adhesion between the fiber and the matrix.

Characterization of polyurethane resins by FTIR, TGA, and XRD

Abstract: Fourier Transformed Infrared Spectroscopy, Thermogravimetric Analysis, and X-ray Diffractometry have been used to investigate the rigid, semi rigid, and soft polyurethane (PU) forms, which were developed by the Group of Analytic Chemistry and Technology of Polymers - USP - Sao Carlos. The -NCO/-OH ratios were 0.6, 0.5, and 0.3% for rigid, semi rigid, and soft PUs, respectively, showing that different ratios cause differences in thermal behaviors and crystalline structures of the synthesized PU resins.

Cellulose nanofibers from white and naturally colored cotton fibers

Abstract: Suspensions of white and colored nanofibers were obtained by the acid hydrolysis of white and naturally colored cotton fibers. Possible differences among them in morphology and other characteristics were investigated. The original fibers were subjected to chemical analysis (cellulose, lignin and hemicellulose content), X-ray diffraction (XRD) analysis, and scanning electron microscopy (SEM). The nanofibers were analyzed with respect to yield, elemental composition (to assess the presence of sulfur), zeta potential, morphology (by scanning transmission electron microscopy (STEM)) and atomic force microscopy (AFM), crystallinity (XRD) and thermal stability by thermogravimetric analysis in air under dynamic and isothermal temperature conditions. Morphological study of several cotton nanofibers showed a length of 85–225 nm and diameter of 6–18 nm. The micrographs also indicated that there were no significant morphological differences among the nanostructures from different cotton fibers. The main differences found were the slightly higher yield, sulfonation effectiveness and thermal stability under dynamic temperature conditions of the white nanofiber. On the other hand, in isothermal conditions at 180 °C, the colored nanofibers showed a better thermal stability than the white.

Magnetic dendritic materials for highly efficient adsorption of dyes and drugs.

Abstract: A versatile and robust adsorbent with both magnetic property and very high adsorption capacity is presented on the basis of functionalization of iron oxide-silica magnetic particles with carboxylic hyperbranched polyglycerol (Fe3O4/SiO2/HPG-COOH). The structure of the resulting product was confirmed by Fourier transform infrared (FTIR) spectra, thermo gravimetric analysis (TGA), zeta-potential, and transmission electron microscopy (TEM). According to the TGA results, the density of the carboxylic groups on the surface of Fe3O4/SiO2/HPG-COOH is calculated to be as high as 3.0 mmol/g, posing a powerful base for adsorbing dyes and drugs. Five kinds of dyes and one representative anticancer drug were chosen to investigate the adsorption capacity of the as-prepared magnetic adsorbent. The adsorbent shows highly efficient adsorption performance for all of the adsorbates especially for the cationic dyes and drug. For example, the saturated adsorption capacity of the Fe3O4/SiO2/HPG-COOH for methyl violet (MV) can...

Plasma-Induced Grafting of Cyclodextrin onto Multiwall Carbon Nanotube/Iron Oxides for Adsorbent Application

Abstract: The magnetic composite of β-cyclodextrin grafted onto multiwalled carbon nanotubes/iron oxides (denoted as MWCNTs/iron oxides/CD) was synthesized using the plasma-induced grafting technique and was developed for the removal of inorganic and organic pollutants from aqueous solutions. The characteristic results of Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (XRD), and thermogravimetric analysis (TGA) showed that β-CD was grafted onto the MWCNTs/iron oxides. The grafted β-CD on the MWCNTs/iron oxides contributed to an enhancement of the adsorption capacity because of the strong abilities of the multiple hydroxyl groups and the inner cores of the hydrophobic cavity in β-CD to form complexes with metal ions and organic pollutants. MWCNTs/iron oxides/CD can be separated and recovered from solution by magnetic separation. The adsorption of Pb(II) on MWCNTs/iron oxides/CD was found to be dependent on pH, and the adsorption of 1-naphthol was fou...

Efficient and large-scale synthesis of few-layered graphene using an arc-discharge method and conductivity studies of the resulting films

Abstract: An arc-discharge method using a buffer gas containing carbon dioxide has been developed for the efficient and large-scale synthesis of few-layered graphene. The resulting samples of few-layered graphene, well-dispersed in organic solvents such as N,N-dimethylformamide (DMF) and 1,2-dichlorobenzene (o-DCB), were examined by transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, atomic force microscopy (AFM), and thermal gravimetric analysis (TGA). The electrical conductivity and transparency of flexible films prepared using a direct solution process have also been studied.

Solvent-Assisted Thermal Reduction of Graphite Oxide

Abstract: The thermal behavior of graphite oxide (GO) is essential to study and design GO reduction and functionalizion reaction. We provide a detailed description of the thermal reduction of GO dispersed in solvent (H2O and dimethylformamide (DMF)) at temperatures of 100 and 150 °C, respectively. The thermal stability and structure change of GO during the thermal treatment were characterized using UV−vis spectroscopy, Raman spectroscopy, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA). It was found that at temperatures of 100 and 150 °C the carboxylic and carbonyl groups decomposed. GO dispersed in H2O and DMF at temperatures of 100 and 150 °C exhibited increased rates of reduction than in dry condition. Moreover, the reduction rate was found to be highly dependent on the solvent used. At 150 °C, DMF accelerates the GO reduction rate significantly, while dimethyl sulfoxide (DMSO) has less acceleration effect. Howe...

Lithium-doped conjugated microporous polymers for reversible hydrogen storage.

Abstract: Hydrogen storage is of great interest as environmentally clean and efficient fuels are required for future energy applications. Several pioneering strategies have been developed and significant performances have been achieved for hydrogen storage, including chemisorption of dihydrogen in the form of light metal hydrides, metal nitrides and imides, physisorption of dihydrogen onto carbon, clathrate hydrates, and porous network materials such as carbon nanotubes (CNTs), zeolites, and metal–organic framework (MOF) materials. However, hydrogen storage in these systems requires either high pressure or very low temperature, or both, thus severely limiting the applicability for mobile applications, which require working conditions of 1– 20 bar and ambient temperature. The synthesis of functional materials with high hydrogen uptake and delivery under safe and ambient conditions remains a key challenge for establishing hydrogen economy. It has been reported that atomically dispersed alkalimetal ions (e.g., Li andNa) are capable of clustering several H2 molecules bound through electrostatic charge–quadrupole and charge-induced dipole interactions. Thus ab initio simulations showed that Li-doped pillared graphene can bind reversibly up to 6.5 mass% of H2 at 20 bar at room temperature. In addition, ab initio simulations showed that doping of MOFs with atomically dispersed alkali-metal cations can reversibly achieve up to 5.5 mass% of H2 at 100 bar at room temperature. These results suggest that the high electron affinity of the sp carbon framework can essentially separate the charge from the Li center, thus providing strong stabilization of the molecular H2 and dramatically improving the hydrogen uptake value compared to that of undoped systems. Recently, experimental investigations also showed that H2 uptake of the MOFs can be remarkably improved by introduction of Li ions into MOF systems. For instance, an Li-doped MOF, which was prepared by reaction of lithium diisopropylamide (LDA) with theMOF MIL-53(Al), was reported to exhibit nearly double the hydrogen uptake compared with an undoped MOF. The doping of Li into the MOF has also been reported to remarkably enhance the isosteric heats of H2 adsorption compared to those of the undoped MOF. To date, no material that consists of an active Li dopant and has ultrahigh hydrogen storage capacity has been reported. The difficulty in demonstrating this concept relates to whether agglomeration of the Li atoms occurs during synthesis. Recently, conjugated microporous polymers (CMPs) have received considerable research interest for hydrogen storage because of their finely tunable microporosity, large surface areas, and high stability. Herein, we report the first experimental evidence that Li ion dopants dramatically enhance hydrogen storage in a CMP matrix. The hydrogen storage amount can reach up to 6.1 wt% at 1 bar and 77 K, which is among the best reported to date for physisorption hydrogen storage materials including MOFs and CNTs. The CMP we selected was produced from 1,3,5-triethynylbenzene, which has active sites (C C bonds) for binding of metallic ions, large BET surface areas with microporous character, and good chemical (totally insoluble in all organic solvents), and thermal stability (thermogravimetric analysis (TGA) shows that the thermal decomposition temperature of the CMP is greater than 300 8C). These physicochemical properties suggest that the selected CMP is appropriate as a host for Li doping. Also, this material contains only three kinds of light elements (C, H, and Li), which is a great advantage for gravimetric adsorption. We synthesized the CMP by Pd/Cu-catalyzed homocoupling polymerization. To dope the CMP with Li, we immersed the CMP in a solution of the naphthalene anion radical salt (LiC10H8C ) in THF. The mixture was stirred for several hours under an inert atmosphere to allow thorough penetration of Li ions into the CMP network. The mixture was filtered and the solid product was washed with dry THF several times followed by removal of the solvent at room temperature and subsequent removal of the naphthalene under vacuum at 120 8C. The field emission scanning electron microscopy (FE-SEM) images (Figure 1a,b) show that the CMP and Li-CMP consist of agglomerated microgel particles and have porous features. TGA shows that the CMP have good thermal stability (Figure 1c, thermal decomposition temperature> 300 8C). In the case of the CMP treated with LiC10H8C (0.5 wt% Li), an obvious weight loss (ca. 10%) was observed in the temperature range 100–150 8C. This feature suggests the removal of the residual naphthalene absorbed in the CMP matrix, and is consistent with a previous report. Figure 1d shows the high-resolution [*] K.-L. Han, Prof. W.-Q. Deng State Key Lab of Molecular Reaction Dynamics Dalian Institute of Chemical Physics, Chinese Academy of Sciences Dalian 116023 (China) E-mail: dengwq@dicp.ac.cn Homepage: http://www.nmce.dicp.ac.cn/

Doped nanosized ceria solid solutions for low temperature soot oxidation: Zirconium versus lanthanum promoters

Abstract: The relative efficacies of zirconium and lanthanum promoters in ceria solid solutions were investigated systematically for low temperature soot oxidation. Thus nanosized CeO 2 –ZrO 2 (CZ, 1:1) and CeO 2 –La 2 O 3 (CL, 8:2) solid solutions, and a reference CeO 2 (C) were synthesized and investigated by means of various characterization techniques namely, XRD, TEM, BET surface area, XPS, UV–vis DRS, Raman and TPR. The catalytic efficiency for oxygen storage/release capacity (OSC) and soot oxidation were evaluated by a thermogravimetric (TG) method. The XRD results suggested formation of solid solutions and TEM studies confirmed nanosized nature of the particles. Raman and XPS measurements disclosed the presence of oxygen vacancies and lattice defects in both CZ and CL samples and these were more prominent in the case of CL sample. XPS studies revealed existence of both Ce 3+ and Ce 4+ (confirming redox nature), and the concentration of former is relatively higher in CL sample. The CL solid solution exhibited high intense and more resolved O 2− → Ce 3+ charge transfer transition band compared to CZ in the UV–vis DRS study. TPR measurements indicated a facile reduction of ceria after La 3+ incorporation. Activity studies revealed that La 3+ doped ceria accelerates the oxidation rate of soot compared to pure ceria and Zr 4+ doped ceria. An attempt has been made to explain the enhanced activity of CL sample in terms of active oxygen formation provoked by defective structure of ceria due to the presence of La 3+ .

Calorimetric and thermogravimetric study on the influence of calcium sulfate on the hydration of ye’elimite

Abstract: Calcium sulfoaluminate (CSA) cements, which represent a CO2-friendly alternative to conventional Portland cements, are produced by blending CSA clinker with gypsum and/or anhydrite. The hydration kinetics and the hydrated phase assemblages of the main hydraulic phase ye’elimite (calcium sulfoaluminate) with calcium sulfate were studied by isothermal conduction calorimetry, thermogravimetric analysis, X-ray diffraction analysis and thermodynamic modelling. Two calcium sulfates with different reactivities (gypsum and anhydrite) were applied. It was found that the pure phase without any calcium sulfate addition exhibits very slow hydration kinetics during the first 10 h. The hydration can be accelerated by the addition of calcium sulfate or (less effective) by increasing the pH of the aqueous phase. The amount of the calcium sulfate determines the ratio between the hydration products ettringite, monosulfate and amorphous aluminium hydroxide. The reactivity of the added calcium sulfate determines the early hydration kinetics. It was found that the more reactive gypsum was better suited to control the hydration behaviour of ye’elimite.

Investigation of reactive cerium-based oxides for H2 production by thermochemical two-step water-splitting

Abstract: This study focuses on the use of cerium-based mixed oxides for hydrogen production by solar-driven thermochemical two-step water-splitting. Mixed cerium oxides are proposed in order to decrease the reduction temperature of ceria and to avoid material sublimation occurring above 2,000 °C during the high-temperature solar step. Ceria-based nanopowders were synthesized by soft chemistry methods including the modified Pechini method. The influence of the synthesis method, the type of cationic element mixed with cerium, and the content of this added element was investigated by comparing the reduction temperatures of the derived materials. The synthesized powders were characterized by X-ray diffraction, thermogravimetric analysis, SEM, and Raman spectroscopy. Results showed that the synthesized pure cerium oxide is more reactive toward reduction than a commercial powder. Among the different elements added to ceria that were screened, the addition of zirconium significantly improved the reduction of ceria at temperatures below 1,500 °C. Increasing zirconium content further favored cerium reduction yield up to 70%. Water-splitting tests were performed to demonstrate the reactivity of the developed materials for H2 production. The amount of H2 evolved was enhanced with a temperature increase, the maximum H2 production from Ce0.75Zr0.25O2−δ was 0.24 mmol/g at 1,045 °C, and the powder reactivity upon cycling was demonstrated via thermogravimetry through two successive reduction–hydrolysis reactions.

TiO2 Immobilized in Cellulose Matrix for Photocatalytic Degradation of Phenol under Weak UV Light Irradiation

Abstract: TiO2/cellulose composite films have been prepared via a sol−gel method from the hydrolysis of a precursor TiO2 sol solution in the regenerated cellulose films prepared on the basis of cellulose dissolution at low temperature. The structure and properties of the composite films were characterized by using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, thermal gravimetric analysis, FT-IR, UV−visible spectroscopy, and photocatalytic degradation tests. The micronanoporous structure and hydroxyl groups in the regenerated cellulose films at the wet state provided cavities and affinity for the creation and the immobilization of TiO2 nanoparticles in the cellulose matrix through electrostatic and hydrogen bonding interactions. The TiO2/cellulose composite films exhibited a good photocatalytic activity for photodegradation of phenol under weak UV light irradiation, leading to an important application in photodegradation of organic pollutant. This was a portable photocatalyst, wh...

Chitosan filler effects on the experimental characterization, spectroscopic investigation and thermal studies of PVA/PVP blend films

Abstract: Structural, optical, thermal and morphological studies were performed for pure PVA/PVP (50/50) blend and PVA/PVP blend filled with different concentrations of chitosan upto 40 wt% using casting method. The prepared films were investigated by different techniques. All techniques demonstrate the complexation between chitosan and the polymers blend. There were some changes in the IR absorption bands position and its intensities. UV–vis analysis revealed intensity of the shoulder around 273–280 nm increase with increasing chitosan content. Differential scanning calorimetry (DSC) showed thermal stability of the product samples and that has improved after filling chitosan increases. Scanning electron microscope (SEM) images of different concentrations of films revealed that large crystals characteristic of chitosan were also frequently present, when chitosan content increase upto 20 wt%, rough surfaces and crystalline structures are the dominant features. The X-ray diffraction (XRD) showed that the incorporation of chitosan into the polymeric matrix causes decreasing in the crystallinity degree of the samples and this indicates the complexation between the filler and the polymers blend. Thermogravimetric analysis (TGA) is used to study the samples in the temperature range of 30–500 °C. Figures show typical TGA thermograms of weight loss as a function of temperature for the present system.