Thermal Gravimetric Differential Scanning Calorimeter Research Articles

Thermal stabilization of extraframework Cs+ in zeolite 13X

Given the reversible nature of ion exchange, Cs+-exchanged zeolite 13X was thermally treated to safely retain extraframework Cs+. By thermal gravimetric-differential scanning calorimeter (TG-DSC) analysis, both endothermic and exothermic peaks, indicative of phase transitions, gradually shifted to higher temperatures at the higher surface loading of Cs+ (i.e., [Cs+]0/[NaX]0), indicating that extraframework Cs+ stabilized the zeolite framework. By thermal treatment at ≤ 800 °C, X-ray diffraction (XRD) showed that the samples with [Cs+]0/[NaX]0 = 0.5 and 5 mmol/g maintained the faujasite framework. Nonetheless, as indicated by Cs LIII-edge X-ray absorption spectroscopy (XAS) analysis, the Cs-Si(Al) interaction at ∼4.37 Å became stronger relative to the Cs-O interaction at ∼2.98 Å with the increasing treatment temperature, indicating that thermally induced dehydration caused extraframework Cs+ to migrate from spacious sites to confined (less exchangeable) sites. Thus, the redistribution of extraframework Cs+ among exchange sites was responsible for the lower leaching with the increasing treatment temperature. On the other hand, by thermal treatment at ≥ 900 °C, bulk-phase analyses such as XRD, scanning electron microscopy, and surface area measurement showed that the zeolite framework completely broke down to form non-porous phases. The XAS analysis further indicated that Cs+ was mainly incorporated into amorphous phases at 900 °C and pollucite at ≥ 1,000 °C. This was consistent with the markedly low Cs+ leaching for the ≥ 900 °C-treated samples. Since pollucite can provide the greatest retainability of Cs+, the thermal treatment leading to its formation is recommended before storing Cs+-exchanged zeolite 13X at nuclear waste repositories.

Improvement of the catalytic activity of MCM-48 synthesized from metakaolinite in the alkylation of phenol with tert-butyl alcohol

M/MCM-48 (M and MCM-48 represent metakaolinite and Mobile composite of matter) mesoporous molecular sieves with good thermal and hydrothermal stabilities were synthesized by a hydrothermal method using metakaolinite as partial Si and Al sources. The samples were characterized by X-ray diffraction (XRD), NH3 temperature-programmed desorption (NH3-TPD), thermal gravimetric-differential scanning calorimeter (TG-DSC), transmission electron microscopy (TEM), Fourier transform-infrared (FT-IR) and N2 physical adsorption. The effect of crystallization time and temperature on the synthesis of M/MCM-48 was investigated. The catalytic activity of M/MCM-48 was evaluated by the alkylation of phenol with tert-butyl alcohol (TBA). M/MCM-48 with long-range ordering was synthesized at the crystallization temperature of 120°C for 36h. The H-M/MCM-48, H-Al/MCM-48 and H-MCM-48 catalysts (H represents the protonated sample) were prepared via an ion-exchanged method. Under comparable conditions, H-M/MCM-48 exhibited a higher catalytic activity than H-MCM-48. A maximum phenol conversion of 73.4% with a 4-tert-butylphenol selectivity of 70.0% was achieved over the H-M/MCM-48 catalyst at the reaction temperature of 140°C.

Microwave synthesis and textural property of europium substituted mesoporous molecular sieves

Using cetyltrimethyl ammonium bromide (CTAB) as the template and sodium silicate as the silicon source, the MCM-41 mesoporous molecular sieves with Eu incorporated in the framework were synthesized under microwave irradiation condition and the influence of the Si/Eu molar ratio on the crystalline structure, textural properties and the long-range ordering of the resulting sample was investigated by various physicochemical techniques such as X-ray diffraction (XRD), transmission electron microscope (TEM), diffuse reflectance ultraviolet–visible spectroscopy (UV–vis), thermal gravimetric–differential scanning calorimeter (TG–DSC) and N 2 physical adsorption. The results of N 2 adsorption and XRD reveal that the synthesized sample has the ordered hexagonal mesoporous structure. UV–vis spectra provide the strong evidences that most of europium ions were incorporated into the framework of the MCM-41 sample. The crystalline structure, textural properties and mesoporous ordering of the resultant mesoporous materials are related to the amount of europium incorporation. Small amount europium incorporated into the silica-based MCM-41 does not strongly modify the structure of mesoporous molecular sieve. An increase of the Eu content in sample led to reduction of the specific surface area and the deterioration of the long-range ordering.

Effect of the thermal and hydrothermal treatment on textural properties of Zr-MCM-41 mesoporous molecular sieve

Zr-containing mesoporous molecular sieves were synthesized by hydrothermal method using cetyltrimethyl ammonium bromide as a template and sodium silicate and zirconium sulfate as raw materials. The structure and morphology of the synthesized samples were characterized via various physicochemical methods, including X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, solid state nuclear magnetic resonance ( 29Si MAS-NMR) techniques, thermal gravimetric–differential scanning calorimeter (TG–DSC) and N 2 physical adsorption, respectively. The effect of the different initial ZrO 2:SiO 2 molar ratio, the different thermal treatment temperature and the different hydrothermal treatment time on textural property was investigated. The experimental results reveal that the as synthesized samples possess a typical mesoporous structure of MCM-41. On the other hand, the specific surface area and pore volume of the synthesized Zr-MCM-41 mesoporous molecular sieve decrease with the increase of the amount of zirconium incorporated in the starting material, the rise of thermal treatment temperature and the prolonging of hydrothermal treatment time, the mesoporous ordering becomes poor. Also, when the molar ratio of ZrO 2:SiO 2 in the starting material is 0.1, the mesoporous structure of the Zr-MCM-41 mesoporous molecular sieve still retains after calcination at 750 °C for 3 h or hydrothermal treatment at 100 °C for 6 d, and have specific surface areas of 423.9 and 563.9 m 2/g, respectively.

Temperature Effects on ZnO Film Electrodeposition

A thermodynamic study of temperature effects on the 0.1 mol·L-1 Zn(NO3)2 system by means of potential-pH diagram, species repartition diagram, and solubility of ZnO/Zn(OH)2 was presented with the aim of guiding future electrodeposition conditions and for the prediction of the ultimate product. These thermodynamic calculations were testified by analyzing curves of the cathodic current density as a function of time and cyclic voltammetry (CV), X-ray diffraction (XRD), scanning electron microscopy (SEM), thermal gravimetric-differential scanning calorimeter (TG-DSC), and ultraviolet-visible (UV-Vis) spectroscopy. Optical studies revealed that the ZnO films exhibited a high transmittance in the visible region (80%) and a steep absorption edge. A reaction mechanism was proposed for ZnO electrodeposition in zinc nitrate aqueous solutions.