Showing papers on "Thermogravimetric analysis published in 2018"

Application of yolk–shell Fe 3 O 4 @N-doped carbon nanochains as highly effective microwave-absorption material

Abstract: Yolk–shell Fe3O4@N-doped carbon nanochains, intended for application as a novel microwave-absorption material, have been constructed by a three-step method. Magnetic-field-induced distillation-precipitation polymerization was used to synthesize nanochains with a one-dimensional (1D) structure. Then, a polypyrrole shell was uniformly applied to the surface of the nanochains through oxidant-directed vapor-phase polymerization, and finally the pyrolysis process was completed. The obtained products were characterized by X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), and thermogravimetric analyses (TGA) to confirm the compositions. The morphology and microstructure were observed using an optical microscope, scanning electron microscope (SEM), and transmission electron microscope (TEM). The N2 absorption–desorption isotherms indicate a Brunauer–Emmett–Teller (BET) specific surface area of 74 m2/g and a pore width of 5–30 nm. Investigations of the microwave absorption performance indicate that paraffin-based composites loaded with 20 wt.% yolk–shell Fe3O4@N-doped carbon nanochains possess a minimum reflection loss of −63.09 dB (11.91 GHz) and an effective absorption bandwidth of 5.34 GHz at a matching layer thickness of 3.1 mm. In addition, by tailoring the layer thicknesses, the effective absorption frequency bands can be made to cover most of the C, X, and Ku bands. By offering the advantages of stronger absorption, broad absorption bandwidth, low loading, thin layers, and intrinsic light weight, yolk–shell Fe3O4@N-doped carbon nanochains will be excellent candidates for practical application to microwave absorption. An analysis of the microwave absorption mechanism reveals that the excellent microwave absorption performance can be explained by the quarter-wavelength cancellation theory, good impedance matching, intense conductive loss, multiple reflections and scatterings, dielectric loss, magnetic loss, and microwave plasma loss.

Covalent organic frameworks: efficient, metal-free, heterogeneous organocatalysts for chemical fixation of CO2 under mild conditions

Abstract: The cycloaddition of CO2 to epoxides to form cyclic carbonates is very promising and does not generate any side products. Metal-free, heterogeneous organocatalysts offer an environmentally friendly alternative to traditional metal-based catalysts. Herein two triazine-based covalent organic frameworks (COF-JLU6 and COF-JLU7) were successfully synthesized under solvothermal conditions. The structural and chemical properties of COFs were fully characterized by using powder X-ray diffraction analysis, structural simulation, Fourier transform infrared spectroscopy, 13C solid-state NMR spectroscopy, electron microscopy, thermogravimetric analysis and nitrogen adsorption. The two COF materials combine mesopores, high crystallinity and good stability, as well as a large number of hydroxy groups in the pore walls. They possess a high Brunauer–Emmett–Teller (BET) specific surface area up to 1390 m2 g−1 and a large pore volume of 1.78 cm3 g−1. The COF-JLU7 displays a high CO2 uptake of 151 mg g−1 at 273 K and 1 bar. Importantly, COF-JLU7 was found to be a highly effective catalyst to convert CO2 into cyclic carbonate through the cycloaddition reaction with epoxides under mild conditions. The effect of reaction parameters, such as reaction temperature, reaction time and CO2 pressure, on the catalytic performance was also investigated in detail. Moreover, the new framework-based catalyst can be recovered and reused five times without a significant loss of catalytic efficiency.

Valorization of acid isolated high yield lignin nanoparticles as innovative antioxidant/antimicrobial organic materials

Abstract: In this study, dissolution of pristine alkali lignin into ethylene glycol, followed by addition of different acidic conditions (HCl, H2SO4, and H3PO4 at different pH) has been considered as a simple method to prepare high yield lignin nanoparticles (LNP). Field emission scanning electron microscopy (FESEM), Zeta potential, gel permeation chromatography (GPC), and thermogravimetric analysis (TGA) have been utilized to determine the influence of the precipitation procedures on particle size, Zeta potential, molecular weight, and thermal stability of final obtained LNP. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and nuclear magnetic resonance (NMR) were also considered to investigate the influence of lignin chemical structures and composition on its antioxidative and antimicrobial behaviors. Results from DPPH (1,1-diphenyl-2-picryl-hydrazyl) activity revealed the antioxidant response of LNP aqueous solutions, whereas results from antimicrobial tests confirmed LNP ...

A Crystalline Polyimide Porous Organic Framework for Selective Adsorption of Acetylene over Ethylene.

Abstract: The separation of acetylene from ethylene is a crucial process in the petrochemical industry, as even small acetylene impurities can lead to premature termination of ethylene polymerization. Herein, we present the synthesis of a robust, crystalline naphthalene diimide porous aromatic framework via imidization of linear naphthalene-1,4,5,8-tetracarboxylic dianhydride and triangular tris(4-aminophenyl)amine. The resulting material, PAF-110, exhibits impressive thermal and long-term structural stability, as indicated by thermogravimetric analysis and powder X-ray diffraction characterization. Gas adsorption characterization reveals that PAF-110 has a capacity for acetylene that is more than twice its ethylene capacity at 273 K and 1 bar, and it exhibits a moderate acetylene selectivity of 3.9 at 298 K and 1 bar. Complementary computational investigation of each guest binding in PAF-110 suggests that this affinity and selectivity for acetylene arises from its stronger electrostatic interaction with the carbonyl oxygen atoms of the framework. To the best of our knowledge, PAF-110 is the first crystalline porous organic material to exhibit selective adsorption of acetylene over ethylene, and its properties may provide insight into the further optimized design of porous organic materials for this key gas separation.

Constructing bio-templated 3D porous microtubular C-doped g-C3N4 with tunable band structure and enhanced charge carrier separation

Abstract: For the first time, the bio-templated porous microtubular C-doped (BTPMC) g-C3N4 with tunable band structure was successfully prepared by simple thermal condensation approach using urea as precursors and kapok fibre which provides a dual function as a bio-templates and in-situ carbon dopant. Prior to the thermal condensation process, the impregnation strategies (i.e. direct wet and hydrothermal impregnation) of urea on the treated kapok fibre (t-KF) were compared to obtained well-constructed bio-templated porous microtubular C-doped g-C3N4. The details on a physicochemical characteristic of the fabricated samples were comprehensively analyze using X-ray diffraction (XRD), Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), Field-emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM), N2 adsorption-desorption, Thermogravimetric (TGA), and UV–vis spectroscopy. Our finding indicated that the hydrothermal impregnation strategy resulted in well-constructed microtubular structure and more carbon substitution in sp2-hybridized nitrogen atoms of g-C3N4 as compared to the direct wet impregnation. Also, compared to pure g-C3N4, the fabricated BTPMC g-C3N4 exhibited extended photoresponse from the ultraviolet (UV) to visible and near-infrared regions and narrower bandgap. The bandgap easily tuned with the increased t-KF loading in urea precursor which responsible for in-situ carbon doping. Moreover, as compared to pristine g-C3N4, dramatic suppression of charge recombination of the BTPMC g-C3N4 was confirmed through photoluminescence, photocurrent response, and electrochemical impedance spectroscopy. The resultants BTPMC g-C3N4 possesses more stable structure, promoted charge separation, and suitable energy levels of conduction and valence bands for photocatalysis application.

Effect of alkali activator concentration and curing condition on strength and microstructure of waste clay brick powder-based geopolymer

Abstract: The effect of alkali activator concentration and curing conditions on consistency and strength of waste clay brick powder-based geopolymer composites was investigated. For this purpose, geopolymer mortars with twenty different activator concentrations were produced and those mixtures having optimum alkali activator concentration were subjected to different curing conditions. Test results indicated that the optimum alkali activator concentration corresponded to M s (SiO 2 /Na 2 O) ratio of 1.6 and Na 2 O content of 10% by weight of the binder. A maximum compressive strength of 36.2 MPa was achieved by curing at 90 °C, 40% RH for 5 days. In order to characterise the morphology and the structure of the resultant composites, x-ray powder diffraction analysis, thermogravimetric analysis, fourier transform infrared spectroscopy analysis, scanning electron microscopy analysis and micro computed tomography analysis were performed. It was determined that the microstructure analysis results were consistent with the compressive strength results. Denser structure was observed by microstructure analysis in the mixtures having high compressive strength.

An in-situ IR study on the adsorption of CO2 and H2O on hydrotalcites

Abstract: In-situ IR technique was used to study the reversible adsorption of CO2 and H2O at elevated temperatures on a potassium-promoted hydrotalcite for its use in sorption-enhanced water-gas shift (SEWGS). It was found that mainly bidentate carbonate species are responsible for the reversible (cyclic) adsorption capacity of the sorbent. The presence of H2O can enhance the decomposition of bidentate carbonates bond to the stronger basic surface-sites. The basic strength of the involved adsorption sites for bidentate formation appears to be highly heterogeneous. At higher operating temperatures, reversible formation of bulk carbonates seem to participate in the reversible adsorption for CO2. The presence of H2O on the sorbent can lead to the formation of bi-carbonate, especially at lower operating temperatures of 300 °C. The transient absorbance of the main absorption bands for carbonate species identified during this study can be used in the development of a detailed description of the reversible adsorption/desorption kinetics reported before using thermogravimetric analyses.

Synthesis of hydrophobic carbon nanotubes/reduced graphene oxide composite films by flash light irradiation

Abstract: Carbon nanotubes/graphene composites have superior mechanical, electrical and electrochemistry properties with carbon nanotubes as a hydrophobicity boosting agent. Their extraordinary hydrophobic performance is highly suitable for electrode applications in lithium ion batteries and supercapacitors which often employ organic electrolytes. Also the hydrophobic features enable the oil enrichment for the crude oil separation from seawater. The ever reported synthesis routes towards such a composite either involve complicated multi-step reactions, e.g., chemical vapor depositions, or lead to insufficient extrusion of carbon nanotubes in the chemical reductions of graphene oxide, e.g., fully embedding between the compact graphene oxide sheets. As a consequence, the formation of standalone carbon nanotubes over graphene sheets remains of high interests. Herein we use the facile flash light irradiation method to induce the reduction of graphene oxides in the presence of carbon nanotubes. Photographs, micrographs, X-ray diffraction, infrared spectroscopy and thermogravimetric analysis all indicate that graphene oxides has been reduced. And the contact angle tests confirm the excellent hydrophobic performances of the synthesized carbon nanotube/reduced graphene oxide composite films. This one-step treatment represents a straightforward and high efficiency way for the reduction of carbon nanotubes/graphene oxides composites.

Synthesis of polyamide grafted carbon microspheres for removal of rhodamine B dye and heavy metals

Abstract: Polyamide branches grafted onto carbon microspheres (CMS) was successfully synthesized by interfacial polymerization of 1,3,5-trimesoyl chloride and 1,3-phenylene diamine in situ with CMS. The obtained CMS-polyamide was characterized by Fourier transform infrared spectroscopy, thermogravimetric analyzer, scanning electron microscopy and Energy-dispersive X-ray spectroscopy. The sorption efficiency of the CMS-polyamide was evaluated by using rhodamine B (RhB) dye-polluted solutions. It exhibited excellent adsorption performance for the removal of RhB with adsorption capacity of 19.9 mg/g. The pseudo-second-order equation and the Langmuir model exhibited a good correlation with the adsorption kinetics and isotherm data with R2 of >0.99. Tests of adsorption/desorption were performed, and the results showed that dye loaded CMS-polyamide could be regenerated (97%) using acetone. Possible adsorption mechanisms have been proposed, where electrostatic attraction, π-π stacking interactions and complexation interaction with metal dominate the adsorption of RhB. The excellent removal rate (≈100%) of RhB, even in the presence of heavy metals (Pb, Cd, Hg, Cr, Ni, and Cu) in single and binary systems, endowed the CMS-polyamide with the potential for applications in water treatment.

Production of Nanocellulose from Pineapple Leaf Fibers via High-Shear Homogenization and Ultrasonication

Abstract: In this study, the isolation and characterization of nanocellulose from pineapple leaf fibers (PLF) were carried out. Chemical pretreatment included pulping, bleaching, and acid hydrolysis to remove lignin, hemicellulose, and extractive substances were conducted. This was followed by high-shear homogenization and ultrasonication to produce nanocellulose. Morphological changes to the PLF due to treatment were investigated using scanning electron microscopy (SEM). This showed that the PLF had a diameter of 1–10 µm after high-shear homogenizing. Transmission electron microscopy (TEM) indicated that the nanofibers after ultrasonication for 60 min showed 40–70 nm diameters. Particle size analysis (PSA) indicates that the fibers had an average diameter of 68 nm. Crystallinity index was determined by X-ray diffraction (XRD) and had the highest value after acid hydrolysis at 83% but after 60 min ultrasonication, this decreased to 62%. Meanwhile, Fourier transform infrared (FTIR) spectroscopy showed there was no chemical structure change after acid hydrolysis. The most significant finding from thermal gravimetric analysis (TGA) is that the higher degradation temperature of nanofibers indicates superior thermal stability over untreated fiber. These results indicate that PLF waste could become a viable source of commercially valuable nanocellulose.

Synthesis of polyacrylamide immobilized molybdenum disulfide (MoS2@PDA@PAM) composites via mussel-inspired chemistry and surface-initiated atom transfer radical polymerization for removal of copper (II) ions

Abstract: In present work, novel polyacrylamide immobilized molybdenum disulfide (MoS2@PDA@PAM) composites were synthesized via the mussel-inspired chemistry and surface initiated atom transfer radical polymerization (SI-ATRP). The as-prepared MoS2@PDA@PAM composites were characterized by energy dispersive X-ray spectroscopy (EDX), transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). Characterization results provide sufficient evidences for the successful functionalization of MoS2 with PAM. The products were used as adsorbents for removing of copper (II) ions. Results show the introduction of PAM onto MoS2 could enhance the adsorption capacity of MoS2@PDA@PAM towards copper (II) ions. The amount of adsorbed copper (II) ions by MoS2@PDA@PAM composites is 2.5 times that of pristine MoS2. The effects of various experimental factors on the adsorption process, including contact time, initial copper (II) ion concentrations, solution pH and temperature, were also studied in this work. The batch experiments show that the adsorption of copper (II) ions onto MoS2@PDA@PAM is dependent on time, pH and temperature. The optimum solution pH is observed at pH 7 and the increase of temperature is favorable for the adsorption of MoS2@PDA@PAM towards copper (II). Based on the experiment data, the adsorption kinetics, isotherms and thermodynamics were also investigated. The kinetics and isotherm studies show that pseudo-second-order kinetic and Freundlich isotherm models could well fit with the adsorption data. The thermodynamic results show that the adsorption of copper (II) ions on MoS2@PDA@PAM is a spontaneous and endothermic process. The adsorption process is mainly governed by the chemisorption involving the electrostatic interaction and/or chemical chelation between copper (II) ions and amino groups on the surface of MoS2@PDA@PAM. Taken together, it is proven that the PAM can be immobilized onto the MoS2 nanosheets via the mussel-inspired chemistry and SI-ATRP, and it can enhance the adsorption performance of MoS2@PDA@PAM composites, which might be used as adsorbents to remove heavy metal ions in real environment treatment.

Thermal reduction of graphene oxide: How temperature influences purity

Abstract: Among various methods used for the reduction of graphene oxide (GO) into a purer form of graphene, the thermal reduction method provides a simpler, safer, and economic alternative, compared to other techniques. Thermal reduction of GO causes significant weight loss and volume expansion of the material. Current work investigates the onset temperature where reduction in terms of exfoliation takes place, which is determined to be 325 °C at standard atmospheric pressure. Reduction temperature plays the most crucial role as it controls the quality of reduced graphene oxide in terms of weight percentage of carbon and lattice defect. The study leads to achieving highest content with a minimum defect in the graphene lattice at the optimum temperature, which is found to be 350 °C at standard atmospheric pressure. The thermal reduction process has been analyzed with the help of Fourier transform infrared spectroscopy, thermogravimetric analysis, and thermal degradation kinetics. From thermal degradation kinetics of GO, the rate of reaction has been found to be independent of concentration and is a sole function of temperature.

Conductive Polymers Encapsulation To Enhance Electrochemical Performance of Ni-Rich Cathode Materials for Li-Ion Batteries

Abstract: Ni-rich cathode materials have drawn lots of attention owing to its high discharge specific capacity and low cost. Nevertheless, there are still some inherent problems that desiderate to be settled, such as cycling stability and rate properties as well as thermal stability. In this article, the conductive polymers that integrate the excellent electronic conductivity of polyaniline (PANI) and the high ionic conductivity of poly(ethylene glycol) (PEG) are designed for the surface modification of LiNi0.8Co0.1Mn0.1O2 cathode materials. Besides, the PANI–PEG polymers with elasticity and flexibility play a significant role in alleviating the volume contraction or expansion of the host materials during cycling. A diversity of characterization methods including scanning electron microscopy, energy-dispersive X-ray spectrometer, transmission electron microscopy, thermogravimetric analysis, Fourier transform infrared have demonstrated that LiNi0.8Co0.1Mn0.1O2 cathode materials is covered with a homogeneous and thor...