Showing papers on "Thermogravimetric analysis published in 2012"

Synthesis of Surface-Functionalized WS2 Nanosheets and Performance as Li-Ion Battery Anodes

Abstract: Separation of bulk tungsten disulfide (or WS2) into few-layer two-dimensional (2-D) crystals is of interest because of their high surface area for certain chemical processes and size-dependent optical and electronic characteristics. Herein, we demonstrate a process that involves the physical separation of weakly bonded WS2 layers by use of a strong acid treatment (chlorosulfonic acid) at 2 mg/mL, followed by quenching in deionized (DI) water. X-ray photoelectron spectroscopy of the superacid-treated WS2 suggests the formation of W–O type bonds, signifying oxidation of tungsten and reduction of the sulfur phase. Thermogravimetric analysis showed a three-phase weight-loss pattern, suggesting acid functionalization of WS2 surfaces. We also studied the electrochemical behavior of an acid-treated WS2 anode in a lithium half-cell configuration that showed a three-step charge–discharge behavior, characteristic of a conversion reaction. The electrochemical capacity was 118 mAh/g after 50 cycles.

Effect of fiber surface treatments on mechanical and abrasive wear performance of polylactide/jute composites

Abstract: The main focus of this work is to improve the adhesion of jute fiber with polylactide (PLA). For this purpose, surface of the jute fiber was modified by alkali, permanganate, peroxide and silane treatments. The surface modified fibers were characterized by FTIR spectroscopy. Unidirectional composites were prepared with treated jute fibers and PLA matrix by hot pressing of solvent impregnated prepregs. Surface treatments resulted in enhancement of tensile and flexural properties and reduction in Izod impact strength. Dynamic mechanical analysis (DMA) results showed that, treated composites have higher storage modulus and lower tangent delta with respect to untreated composite. The degree of interfacial adhesion between the jute fiber and PLA was estimated using adhesion parameter obtained through DMA data. The results of thermogravimetric analysis (TGA) showed a higher thermal stability for silane treated composites. Experimental results on abrasive wear tests revealed that the wear resistance of composite is sensitive to fiber/matrix adhesion.

A series of furan-aromatic polyesters synthesized via direct esterification method based on renewable resources

Abstract: A series of furan-aromatic polyesters were successfully synthesized via direct esterification method starting from 2,5-furandicarboxylic acid, ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, and 1,8-octanediol and characterized by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (1H NMR), X-ray diffraction (XRD), differential scanning calorimeter (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), tensile tests, and so on. The preliminary evidence clearly showed that direct esterification method was rewarding and worthy to synthesize these furan-aromatic polyesters. The densities of furan-aromatic polyesters were ranging from 1.19 to 1.38 kg/m3. The FTIR and 1H NMR confirmed their expected structures in detail. The results of XRD showed that these furan-aromatic polyesters were crystalline polyesters. The results of DSC, TGA, DMA, and tensile tests showed that they behaved as thermoplastic polyester, had satisfactory thermal and mechanical properties, and their thermal stabilities were quite similar to that of corresponding benzene-aromatic polyesters. The results of contact angle measurement showed that they were hydrophilic. The properties above showed that furan-aromatic polyesters based on renewable resources could be a viable alternative to their successful petrochemical benzene-aromatic counterpart. Furthermore, they could be used as biopolymer materials according their satisfactory thermal and mechanical properties and hydrophilicity in the future. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Thermal and structural studies of poly (vinyl alcohol) and hydroxypropyl cellulose blends

Abstract: Polymers and polymeric composites have steadily reflected their importance in our daily life. Blending poly(vinyl alcohol) (PVA) with a potentially useful natural biopolymers such as hydroxypropyl cellulose (HPC) seems to be an interesting way of preparing a polymeric blends. In the present work, blends of PVA/HPC of compositions (100/0, 90/10, 75/25, 50/50, 25/75, and 0/100 wt/wt%) were prepared to be used as bioequivalent materials. Thermal analyses [differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA)], and X-ray diffraction (XRD) were employed to characterize and reveal the miscibility map and the structural properties of such blend system. The obtained results of the thermal analyses showed variations in the glass transition temperature (Tg) indicating the miscibility of the blend systems. Moreover, the changes in the melting temperature (Tm), shape and area were attributed to the different degrees of crystallinity and the existence of polymer-polymer interactions between PVA and HPC molecules. The X-ray diffraction (XRD) analysis showed broadening and sharpening of peaks at different HPC concentrations with PVA. This indicated changes in the crystallinity/amorphosity ratio, and also suggested that the miscibility between the amorphous components of homo-polymers PVA and HPC is possible. The results showed that HPC doped in PVA film can improve the thermal stability of the film under investigation, leading to interesting technological applications.

Carboxyl-functionalized graphene oxide–polyaniline composite as a promising supercapacitor material

Abstract: We report a novel and facile synthesis of a high-quality graphene oxide (GO)–polyaniline (PANI) composite by in situ polymerization suitable for supercapacitor application. Unlike the use of the edged carboxyl groups of graphene sheets as linkers, the current work makes the most of the ample oxygenated groups on the basal plane of graphene sheets to combine with the amine nitrogens of the PANI chain. This is tactically realized by a carboxyl-functionalized process of GO with oxalic acid treatment prior to the combination. The as-constructed carboxyl-functionalized graphene oxide–polyaniline (CFGO–PANI) composite was roundly characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier-transformed infrared spectrometry (FTIR), Raman spectrometry, and thermogravimetric analysis (TGA), and a stable, highly efficient charge-transfer configuration was disclosed and confirmed. The fabricated electrode composed of this CFGO–PANI material showed an excellent electrochemical capacitance performance with aqueous H2SO4 electrolytes.

Carbohydrate-Derived Hydrothermal Carbons: A Thorough Characterization Study

Abstract: Hydrothermal carbonization (HTC) is an aqueous-phase route to produce carbon materials using biomass or biomass-derived precursors. In this paper, a comprehensive physicochemical and textural characterization of HTC materials obtained using four different precursors, namely, xylose, glucose, sucrose, and starch, is presented. The development of porosity in the prepared HTC materials as a function of thermal treatment (under an inert atmosphere) was specifically monitored using N2 and CO2 sorption analysis. The events taking place during the thermal treatment process were studied by a combined thermogravimetric/infrared (TGA-IR) measurement. Interestingly, these inexpensive biomass-derived carbon materials show good selectivity for CO2 adsorption over N2 (CO2/N2 selectivity of 20 at 273 K, 1 bar and 1:1 gas composition). Furthermore, the elemental composition, morphologies, degree of structural order, surface charge, and functional groups are also investigated.

Hydrothermal Synthesis of Co3O4-Graphene for Heterogeneous Activation of Peroxymonosulfate for Decomposition of Phenol

Abstract: This paper reports the synthesis of Co3O4–reduced graphene oxide (rGO) hybrids and the catalytic performance in heterogeneous activation of peroxymonosulfate (PMS) for the decomposition of phenol. The surface morphologies and structures of the Co3O4–rGO hybrids were investigated by field emission scanning electron microscopy (SEM), energy-dispersive X-ray spectrometer (EDS), transmission electron microscopy (TEM), powder X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). Through an in situ chemical deposition and reduction, Co3O4–rGO hybrids with Co3O4 nanoparticles at an average size of 33 nm were produced. Catalytic testing showed that 20 mg/L of phenol could be completely oxidized in 20 min at 25 °C on Co3O4–rGO hybrids, which is mostly attributed to the generation of sulfate radicals through Co3O4-mediated activation of PMS. Phenol oxidation was fitted by a pseudo-zero-order kinetic model. The rate constant was found to in...

Chemical reduction of an aqueous suspension of graphene oxide by nascent hydrogen

Abstract: One of the major challenges in the chemical reduction of graphene oxide is increasing the C/O atomic ratio of the chemically converted graphene. In this paper, we report a simple and effective method to reduce aqueous suspensions of graphene oxide using nascent hydrogen generated in situ by the reaction between Al foil and HCl, Al foil and NaOH and Zn powder and NaOH. The nascent hydrogen-reduced graphene oxides (nHRGOs) were characterized by elemental analysis, UV-vis spectra, Raman spectra, X-ray photoelectron spectroscopy, thermogravimetric analysis and electrical conductivity measurements. The reduction efficiency of graphene oxide strongly depended on the reaction medium and the rate of nascent hydrogen generation. The best nHRGO achieved a C/O atomic ratio greater than 21 and a bulk electrical conductivity as high as 12 500 S m−1, corresponding to the nascent hydrogen generated from the reaction between Al foil and HCl. Since nascent hydrogen could be produced on a metal surface upon oxidation in solution, other metals with low standard reduction potentials, such as Mg, Mn, and Fe, can be applied to reduce graphene oxide.

On the origin of the electroactive poly(vinylidene fluoride) β-phase nucleation by ferrite nanoparticles via surface electrostatic interactions

Abstract: Flexible multiferroic 0–3 composite films, comprising NiFe2O4 and CoFe2O4 ferrite nanoparticles in a polyvinylidene fluoride (PVDF) matrix, have been prepared by solvent casting and melt crystallization to investigate the polymer β-phase nucleation mechanism. Infrared spectroscopy confirms the nucleation of the polymeric electroactive β-phase with the addition of both ferrites, although the loading of ferrite nanoparticles needed to obtain the highest amount of β-phase was found to be one order of magnitude higher in the NiFe2O4/PVDF nanocomposites. Transmission electron microscopy imaging and thermogravimetric analyses indicate the formation of an interface in the nanocomposites with the β-phase nucleation. It is shown that the essential factor for the nucleation of the β-phase in the ferrites/PVDF nanocomposites is the static electric interaction between the magnetic particles with a negative zeta potential and the CH2 groups having a positive charge density.

Surface area and pore size characteristics of nanoporous gold subjected to thermal, mechanical, or surface modification studied using gas adsorption isotherms, cyclic voltammetry, thermogravimetric analysis, and scanning electron microscopy

Abstract: Nitrogen adsorption/desorption isotherms are used to investigate the Brunauer, Emmett, and Teller (BET) surface area and Barrett-Joyner-Halenda (BJH) pore size distribution of physically modified, thermally annealed, and octadecanethiol functionalized np-Au monoliths. We present the full adsorption-desorption isotherms for N2 gas on np-Au, and observe type IV isotherms and type H1 hysteresis loops. The evolution of the np-Au under various thermal annealing treatments was examined using scanning electron microscopy (SEM). The images of both the exterior and interior of the thermally annealed np-Au show that the porosity of all free standing np-Au structures decreases as the heat treatment temperature increases. The modification of the np-Au surface with a self-assembled monolayer (SAM) of C18-SH (coverage of 2.94 × 1014 molecules cm−2 based from the decomposition of the C18-SH using thermogravimetric analysis (TGA)), was found to reduce the strength of the interaction of nitrogen gas with the np-Au surface, as reflected by a decrease in the ‘C’ parameter of the BET equation. From cyclic voltammetry studies, we found that the surface area of the np-Au monoliths annealed at elevated temperatures followed the same trend with annealing temperature as found in the BET surface area study and SEM morphology characterization. The study highlights the ability to control free-standing nanoporous gold monoliths with high surface area, and well-defined, tunable pore morphology.

1D hollow α-Fe2O3 electrospun nanofibers as high performance anode material for lithium ion batteries

Abstract: Hollow-structured α-Fe2O3 nanofibers were successfully synthesized by a simple electrospinning technique using iron acetylacetonate (Fe(acac3)) and polyvinylpyrrolidone (PVP) precursor. Fe (acac)3–PVP composite fibers were calcined at high temperature to form an interconnected 1D hollow-structure of α-Fe2O3 nanofibers. Thermogravimetric analysis (TGA), X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET) were employed to characterize α-Fe2O3 hollow fibers. Based on the characterization results, a formation mechanism for electrospun α-Fe2O3 hollow fibers is proposed. Electrochemical measurements showed that the hollow-structure of α-Fe2O3 nanofibers played an important role in improving the electrode cycle stability and rate capability in lithium ion batteries. The α-Fe2O3 hollow fiber anodes exhibit a high reversible capacity of 1293 mA h g−1 at a current density of 60 mA g−1 (0.06 C) with excellent cycle stability and rate capability. Based on our study this high performance is attributed to the interconnected hollow-structure of large aspect ratio α-Fe2O3 nanofibers, which makes them a potential candidate for lithium ion batteries.

Synthesis of network reduced graphene oxide in polystyrene matrix by a two-step reduction method for superior conductivity of the composite

Abstract: Polymer/graphene composites have attracted much attention due to their unique organic–inorganic hybrid structure and exceptional properties. In this paper, we report the synthesis of polystyrene/reduced graphene oxide (PS/r-GO) composites by a two-step in situ reduction technique, which consists of a hydrazine hydrate reduction and a subsequent thermal reduction at 200 °C for 12 h. The structure and micromorphology of PS/r-GO composites were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and thermogravimetric analysis. The results show that the GO can be efficiently reduced by the two-step in situ reduction method, and the r-GO sheets are well dispersed and ultimately form a continuous network structure in the polymer matrix. PS/r-GO composite films (5 wt% GO) are prepared by the hot press molding method, possessing a conductivity as high as 22.68 S m−1. The superior conductivity arises from the high reduction degree of GO and its high dispersion and the formation of a network structure in the polymer matrix. These polymer/r-GO composites are expected to be applied in multiple electric devices. The techniques for preparing polymer/r-GO composite films could be further extended to other similar systems.