Showing papers on "Thermogravimetric analysis published in 2015"

Synthesis and applications of novel graphitic carbon nitride/metal-organic frameworks mesoporous photocatalyst for dyes removal

Abstract: Metal-organic frameworks (MOFs) have been attracted considerable attention for their applications in gas storage/separation, adsorption as well as catalysis. In this study, a facile solvothermal method was employed to prepare MOFs and graphitic carbon nitride (g-C3N4) hybrids, and a g-C3N4/Ti-benzenedicarboxylate (MIL-125(Ti)) heterostructures photocatalyst was successfully synthesized. The as-obtained materials were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), N2 adsorption–desorption isotherm, thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflection spectroscopy (UV–vis DRS), and photoluminescence (PL) spectroscopy. It is indicated that the hybrids have large surface area, mesoporous structure, thermal stability, and enhanced visible-light absorption. Compared with pure MIL-125(Ti) and g-C3N4, the composites exhibited more efficient photocatalytic performance for Rhodamine B degradation from aqueous solution under visible-light irradiation. The optimal g-C3N4 content in g-C3N4/MIL-125(Ti) composite was determined to be 7.0 wt%, and the corresponding photodegradation rate for RhB was 0.0624 min−1, about 2.1 and 24 times higher than that of pure g-C3N4 and MIL-125(Ti), respectively. The indirect dye photosensitization, the Ti3+–Ti4+ intervalence electron transfer, and the synergistic effect between MIL-125(Ti) and g-C3N4 were the three reasons for improved photo-degradation performance. Therefore, it is reasonable to believe that metal-free semiconductor/MOFs photocatalysts have great potentiality in environmental remediation.

Mercury sorption by silica/carbon nanotubes and silica/activated carbon: a comparison study

Abstract: Nanocomposites of silica incorporated with carbon nanotubes (silica/CNT) and activated carbon (silica/AC) were synthesized and characterized by scanning electron microscopy (SEM), element mapping, energy dispersive X-ray spectroscopy (EDX), thermogravimetric analyzer (TGA) and Fourier transform infrared spectroscopy (FTIR). Silica/CNT and silica/AC were investigated for efficient removal of mercury ions from aqueous solutions. The adsorbents have been analyzed on the basis of adsorption capacity, reusability, and their application in packed columns. The effects of experimental parameters, like pH, contact time and initial concentrations on the adsorption of mercury ions, were optimized. The kinetic data for the adsorption process obeyed a pseudo-second-order kinetic model with R2 of 0.999. Fitting the data to an intraparticle diffusion model indicated that surface adsorption and intraparticle diffusion were concurrently operating. In addition, this study used the Langmuir, Freundlich and Temkin isotherms to describe the behaviour of equilibrium adsorption. The equilibrium adsorption of the studied mercury ions is best fitted using the Freundlich isotherm, with silica/CNT of higher capacity than silica/AC. The silica/CNT showed better performance than silica/AC indicating silica/CNT has better efficiency.

Investigation of the electromagnetic absorption properties of Ni@TiO2 and Ni@SiO2 composite microspheres with core-shell structure.

Abstract: In this work, amorphous TiO2 and SiO2-coated Ni composite microspheres were successfully prepared by a two-step method. The phase purity, morphology, and structure of composite microspheres are characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM). Due to the presence of the insulator SiO2 shell, the core–shell Ni–SiO2 composite microspheres exhibit better antioxidation capability than that of pure Ni microspheres. The core–shell Ni–SiO2 composite microspheres show the best microwave absorption properties than those of pure Ni microspheres and Ni–TiO2 composites. For Ni–SiO2 composite microspheres, an optimal reflection loss (RL) as low as −40.0 dB (99.99% absorption) was observed at 12.6 GHz with an absorber thickness of only 1.5 mm. The effective absorption (below −10 dB, 90% microwave absorption) bandwidth can be adjusted between 3.1 GHz and 14.4 GHz by tuning the absorber thickness in the range of 1.5–4.5 mm. The excellent microwave absorption abilities of Ni–SiO2 composite microspheres are attributed to a higher attenuation constant, Debye relaxation, interface polarization of the core–shell structure and synergistic effects between high dielectric loss and high magnetic loss.

High-yield synthesis and optical properties of g-C3N4

Abstract: Graphitic carbon nitride (g-C3N4), a metal-free semiconductor with a band gap of 2.7 eV, has received considerable attention owing to its fascinating photocatalytic performances under visible-light. g-C3N4 exhibits high thermal and chemical stability and non-toxicity such that it has been considered as the most promising photocatalyst for environmental improvement and energy conservation. Hence, it is of great importance to obtain high-quality g-C3N4 and gain a clear understanding of its optical properties. Herein, we report a high-yield synthesis of g-C3N4 products via heating of high vacuum-sealed melamine powder in an ampoule at temperatures between 450 and 650 °C. Using transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), electron energy loss spectroscopy (EELS), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), the chemical composition and crystallization of the as-produced g-C3N4 are demonstrated. A systematic optical study of g-C3N4 is carried out with several approaches. The optical phonon behavior of g-C3N4 is revealed by infrared and Raman spectroscopy, and the emission properties of g-C3N4 are investigated using photoluminescence (PL) spectroscopy, while the photocatalytic properties are explored by the photodegradation experiment.

A new magnetic nano zero-valent iron encapsulated in carbon spheres for oxidative degradation of phenol

Abstract: In this study, magnetic carbon encapsulated nano iron hybrids (nano Fe0/Fe3C@CS) were synthesized via a novel one-pot hydrothermal method followed by self-reduction in N2 atmosphere. The structural, morphological, and physicochemical properties of the samples were thoroughly investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), N2 sorption isotherms and thermogravimetric analysis–differential scanning calorimetry (TGA–DSC). Catalytic performance of the as-synthesized nanoparticles was tested in activation of oxone® for phenol degradation in aqueous solutions. Superior catalytic performance was observed by complete removal of 20 ppm phenol within 10 min. The formation of Fe3C was found to contribute to a better stability and magnetic separation of Fe0/Fe3C@CS in its repeated uses. Both electron paramagnetic resonance (EPR) and classic quenching tests were carried out to investigate the mechanism of radical generation and evolution in phenol oxidation. Different from Co- and Mn-based catalysts in generation of sulfate radicals, Fe0/Fe3C@CS selectively induced hydroxyl radicals for phenol degradation.

Development of ion conducting polymer gel electrolyte membranes based on polymer PVdF-HFP, BMIMTFSI ionic liquid and the Li-salt with improved electrical, thermal and structural properties

Abstract: Ion conducting polymer gel electrolyte membranes based on polymer poly(vinylidene fluoride-co-hexafluoropropylene) PVdF-HFP, ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide BMIMTFSI with and without the Li-salt (having the same anion i.e. the TFSI− anion) have been synthesized. Prepared membranes have been characterized by scanning electron microscopy, X-ray diffraction, Fourier transform infrared (FTIR), differential scanning calorimetry, thermogravimetric analysis (TGA) and complex impedance spectroscopic techniques. Incorporation of IL in the polymer PVdF-HFP/polymer electrolyte (i.e. PVdF-HFP + 20 wt% LiTFSI) changes different physicochemical properties such as melting temperature (Tm), glass transition temperature (Tg), thermal stability, degree of crystallinity (Xc), and ionic transport behaviour of these materials. The ionic conductivity of polymeric gel electrolyte membranes has been found to increase with increasing concentration of IL and attains a maximum value of 2 × 10−3 S cm−1 at 30 °C and ∼3 × 10−2 S cm−1 at 130 °C. A high total ionic transference number >0.99 and the cationic transference number (tLi+) ∼ 0.22 with a wider electrochemical window (ECW) ∼ 4.0–5.0 V for the polymer gel electrolyte membrane containing higher loading of IL (∼70 wt% of IL) have been obtained. Temperature dependent ionic conductivity obeys Arrhenius type thermally activated behaviour.

Propane Dehydrogenation over Pt/TiO2-Al2O3 Catalysts

Abstract: This paper describes an investigation on understanding catalytic consequences of Pt nanoparticles supported on a TiO2–Al2O3 binary oxide for propane dehydrogenation (PDH). The TiO2–Al2O3 supports were synthesized by a sol–gel method, and the Pt/TiO2–Al2O3 catalysts were prepared by an incipient wetness impregnation method. Both as-prepared and post-experiment catalysts were characterized employing N2 adsorption–desorption, X-ray diffraction, Raman spectra, H2–O2 titration, temperature-programmed desorption, thermogravimetric analysis, temperature-programmed oxidation, transmission electron microscopy, and Fourier-transform infrared spectra of chemisorbed CO. We have shown that TiO2 is highly dispersed on Al2O3, and the addition of appropriate amount of TiO2 improves propylene selectivity and catalytic stability, which is ascribed to the electron transfer from partially reduced TiOx (x < 2) to Pt atoms. The increased electron density of Pt could reduce the adsorption of propylene and facilitate the migrati...

Strength and hydration properties of reactive MgO-activated ground granulated blastfurnace slag paste

Abstract: Ground granulated blastfurnace slag (GGBS) is widely used as a partial replacement for Portland cement or as the major component in the alkali-activated cement to give a clinker-free binder. In this study, reactive MgO is investigated as a potentially more practical and greener alternative as a GGBS activator. This paper focuses on of the hydration of GGBS, activated by two commercial reactive MgOs, with contents ranging from 2.5% to 20% up to 90 days. The hydration kinetics and products of MgO–GGBS blends were investigated by selective dissolution, thermogravimetric analysis, X-ray diffraction and scanning electron microscopy techniques. It was found that reactive MgO was more effective than hydrated lime in activating the GGBS based on unconfined compressive strength and the efficiency increased with the reactivity and the content of the MgO. It is hence proposed that reactive MgO has the potential to serve as an effective and economical activator for GGBS.

The role of ceria on the activity and SO2 resistance of catalysts for the selective catalytic reduction of NOx by NH3

Abstract: We investigated the influence of Ce on the catalytic activity of V/Sb/Ce/Ti and its deactivation due to SO2. We studied the properties of the catalyst using physio-chemical techniques, including transmission infrared spectroscopy (IR), NH3 and SO2 temperature programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), H2 temperature programmed reduction (H2-TPR), and thermal gravimetric analysis (TGA). The catalysts V/Sb/Ti and V/Sb/Ce/Ti showed an excellent NOx conversion and N2 selectivity in the temperature range of 200–400 °C. Increasing Bronsted acid sites and the NH3 adsorption positively affected the efficiency of the catalyst. The Ce4+ ratio increased upon the addition of Sb and V to Ce/Ti. The catalyst V/Sb/Ce/Ti was prepared by controlling the Ce4+ ratio and exhibited an excellent activity upon increasing the Ce4+ ratio. The V/Sb/Ti (or V/W/Ti) showed one route in which NH4HSO4 formed by converting SO2 into SO3 upon the injection of SO2 in the selective catalytic reduction (SCR) reaction. In addition to this route, the reaction in the presence of V/Sb/Ce/Ti can proceed via a second route, in which Ce2(SO4)3 is formed in the reaction of Ce with SO2 and O2. Thus, V/Sb/Ce/Ti can inhibit the formation of NH4HSO4 due to the consumption of SO2 in the formation of Ce2(SO4)3. Therefore, V/Sb/Ce/Ti was found to have excellent SO2 resistance compared to V/Sb/Ti (or V/W/Ti).

Synthesis of Fe3O4 nanoparticles and its antibacterial application

Abstract: The Present work outlines the antibacterial activity of Fe3O4 nanoparticles synthesized through chemical combustion method where ferric nitrate is used as precursor material and urea as fuel with the assistant of Tween 80, a non-ionic surfactant. The obtained Fe3O4 nanoparticles were characterized by X-ray diffraction, differential thermal analysis/thermo gravimetric analysis (DTA/TGA), particle size analyzer, SEM with EDAX and TEM. Various parameters such as dislocation density, micro strain, analysis of weight loss and surface morphological studies were calculated. The particle size was calculated from XRD and it was found to be 33–40 nm. Using well diffusion method antibacterial activity of Fe3O4 nanoparticles was tested against gram-positive and gram-negative Staphylococus aureus, Xanthomonas, Escherichia coli and Proteus vulgaris. Fe3O4 nanoparticles exhibited strong antibacterial activity against bacterial species.

Electrospun polyamide 6/poly(allylamine hydrochloride) nanofibers functionalized with carbon nanotubes for electrochemical detection of dopamine.

Abstract: The use of nanomaterials as an electroactive medium has improved the performance of bio/chemical sensors, particularly when synergy is reached upon combining distinct materials In this paper, we report on a novel architecture comprising electrospun polyamide 6/poly(allylamine hydrochloride) (PA6/PAH) nanofibers functionalized with multiwalled carbon nanotubes, used to detect the neurotransmitter dopamine (DA) Miscibility of PA6 and PAH was sufficient to form a single phase material, as indicated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), leading to nanofibers with no beads onto which the nanotubes could adsorb strongly Differential pulse voltammetry was employed with indium tin oxide (ITO) electrodes coated with the functionalized nanofibers for the selective electrochemical detection of dopamine (DA), with no interference from uric acid (UA) and ascorbic acid (AA) that are normally present in biological fluids The response was linear for a DA concentration range

Zeolitic imidazolate metal organic framework ZIF-8 with ultra-high adsorption capacity bound tetracycline in aqueous solution

Abstract: ZIF-8 nanoparticles were prepared with a convenient method at room temperature. The morphology and components of the ZIF-8 were characterized by scanning electron microscopy (SEM), powder X-ray diffraction spectroscopy (PXRD), thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FT-IR) and zeta potential analysis. The ZIF-8 nanoparticles were relatively stable under neutral and alkaline solutions, while their structure easily collapsed partially in the strong acidic aqueous solution. The adsorption kinetics and isotherms of ZIF-8 for tetracycline were evaluated in detail. The effects of key parameters such as pH, contact time, temperature and ionic strength on the adsorption of tetracycline were studied. The data on the adsorption of tetracycline on the ZIF-8 nanoparticles fitted well to the pseudo-second-order kinetics model, while the adsorption isotherm data can be explained respectively by the Langmuir isothermal model and the Freundlich isotherm model to varying degrees. The equilibrium quantity of tetracycline on ZIF-8 obtained in adsorption kinetic studies was 124.6 mg g−1 at 25 °C, while the value calculated by the Langmuir isotherm model was above 1000 mg g−1 at the same temperature. This implied that the adsorption capacity of ZIF-8 to tetracycline can be improved to a large extent. The analysis of the adsorption mechanism showed that electrostatic attraction and π–π stacking interaction both played crucial roles in the adsorption process. Regeneration experiments indicated that the used adsorbent still showed excellent applicability after four rounds of recycling.

A designable magnetic MOF composite and facile coordination-based post-synthetic strategy for the enhanced removal of Hg2+ from water

Abstract: A magnetic MOF composite was successfully prepared by a novel and green strategy through reasonable design. The nano Fe3O4@SiO2 core was first coated by a shell of Cu(OH)2 as the self-template, followed by a conversion of Cu(OH)2 into HKUST-1 at room temperature in a water–ethanol mixture solvent, and Fe3O4@SiO2@HKUST-1 core–shell nanostructures were obtained successfully. Based on this, a Bi-I-functionalized-magnetic HKUST-1 composite was prepared through a flexible coordination-based post-synthetic strategy. Powder X-ray diffraction spectrometry, N2 sorption–desorption isotherms and Fourier transform infrared spectroscopy were used for the characterization of the magnetic MOF composites. The core–shell morphology was confirmed by transmission electron microscope images and the result of thermogravimetric analysis showed that the magnetic composites had excellent thermal stability. Besides, the adsorption of Hg2+ on Fe3O4@SiO2, Fe3O4@SiO2@HKUST-1 and Bi-I-functionalized magnetic MOF composites was investigated, and a good adsorption selectivity of Bi-I-functionalized magnetic MOF composites towards Hg2+ was demonstrated, with high adsorption capacity (264 mg g−1) and fast adsorption dynamics. The Bi-I-functionalized magnetic HKUST-1 composite was then successfully employed for the selective removal of Hg2+ from water, demonstrating great potential application of the prepared magnetic MOF composite as a fascinating adsorbent in environmental monitoring.

Facile synthesis of morphology and size-controlled zirconium metal–organic framework UiO-66: the role of hydrofluoric acid in crystallization

Abstract: UiO-66 with crystal size ranging from hundreds of nanometers to a few micrometers and with cubic and cuboctahedral morphologies were synthesized. Crystal size and morphology varied with the additive amount of hydrofluoric acid and the concentration of reactants (ZrCl4 and H2BDC) during solvothermal synthesis. According to energy dispersive spectrometry (EDS) and 19F MAS NMR measurements, the fluorine ions directly bonded to Zr in the SBUs (secondary building units) in the MOF framework due to their strongest electronegativity. The bonding of the fluorine ions and Zr not only compensated for the charge imbalance of the framework caused by missing linkers but also competed with the linkers to coordinate with the Zr metal centers, thereby controlling the processes of nucleation and growth of the UiO-66 crystals. The samples were further characterized by scanning electron microscopy (SEM), powder X-ray diffraction (XRD), Fourier transform-infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA) and Ar sorption isotherms, showing that the introduction of fluorine enhanced the thermostability and porosity of UiO-66.