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The dehydration behavior and non-isothermal dehydration kinetics of donepezil hydrochloride monohydrate (Form I)
Tiantian LIU, Yuanyuan RAN, Bochao WANG, Weibing DONG, Songgu WU, Junbo GONG
Front Chem Sci Eng. 2014, 8 (1): 55-63.
https://doi.org/10.1007/s11705-013-1352-3
Powders of donepezil hydrochloride monohydrate (Form I) underwent isomorphic dehydration, losing 3% w/w water between 90% and 10% relative humidity (RH) without changing its powder X-ray pattern. Below 10% RH, additional dehydration occurred in conjunction with a reversible phase transition between the monohydrate state and a dehydrated state, with a 4.0% w/w loss to 0% RH. A combination of methods was used to understand the structural changes occurring during the desolvation process, including dynamic vapor sorption measurements, thermal analysis and powder X-ray diffraction. Form I showed the characteristics of the channel hydrate, whose non-isothermal dehydration behavior proceeds in two steps: (1) the loss of non-crystalline water adsorbed on the surface, and (2) the loss of one crystalline water in the channel. Dehydrated Form I is structurally similar to the monohydrate Form I. According to the heat of fusion and the crystal density criteria, the two crystal forms belonged to the univariant system, and the anhydrate (Form III) is stable. The dehydration kinetics was achieved from the TG-DTG curves by both the Achar method and the Coats-Redfern method with 15 frequently cited basic kinetic models. The dynamic dehydration processes for steps 1 and 2 were best expressed by the Zhuralev-Lesokin-Tempelman equation, suggesting a three-dimensional diffusion-controlled mechanism.
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Mayenite supported perovskite monoliths for catalytic combustion of methyl methacrylate
Zekai ZHANG, Zhijian KONG, Huayan LIU, Yinfei CHEN
Front Chem Sci Eng. 2014, 8 (1): 87-94.
https://doi.org/10.1007/s11705-014-1410-5
To improve their thermal stability, La0.8Sr0.2MnO3 cordierite monoliths are washcoated with mayenite, which is a novel Al-based material with the crystal structure of 12MO·7Al2O3 (M= Ca, Sr). The monoliths are characterized by means of nitrogen adsorption/desorption, scanning electron microscopy, and X-ray diffraction. Catalytic performances of the monoliths are tested for methyl methacrylate combustion. The results show that mayenite obviously improves both the physic-chemical properties and the catalytic performance of the monoliths. Because mayenite improves the dispersity of La0.8Sr0.2MnO3 and also prevents the interaction between La0.8Sr0.2MnO3 and cordierite or γ-Al2O3, both crystal structure and surface morphology of La0.8Sr0.2MnO3 phase can thereby be stable on the mayenite surface even at high temperature up to 1050 oC. Under the given reaction conditions, La0.8Sr0.2MnO3 monolith washcoated with 12SrO·7Al2O3 shows the best catalytic activity for methyl methacrylate combustion among all the tested monoliths.
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Particle formation of hydroxyapatite precursor containing two components in a spray pyrolysis process
W. Widiyastuti, Adhi Setiawan, Sugeng Winardi, Tantular Nurtono, Heru Setyawan
Front Chem Sci Eng. 2014, 8 (1): 104-113.
https://doi.org/10.1007/s11705-014-1406-1
The particle formation mechanism of hydroxyapatite precursor containing two components, Ca(OOCCH3)2 and (NH4)2HPO4 with a ratio of Ca/P= 1.67, in a spray pyrolysis process has been studied by computational fluid dynamics (CFD) simulation on the transfer of heat and mass from droplets to the surrounding media. The focus included the evaporation of the solvent in the droplets, a second evaporation due to crust formation, the decomposition reaction of each component of the precursor, and a solid-state reaction that included the kinetic parameters of the precursor regarding its two components that formed the hydroxyapatite product. The rate of evaporation and the reacted fraction of the precursor both increased with temperature. The predicted average size of the hydroxyapatite particles agreed well with the experimental results. Therefore, the selected models were also suitable for predicting the average size of particles that contain two components in the precursor solution.
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Fe3O4 encapsulated mesoporous silica nanospheres with tunable size and large void pore
Tingting LIU, Lihong LIU, Jian LIU, Shaomin LIU, Shi Zhang QIAO
Front Chem Sci Eng. 2014, 8 (1): 114-122.
https://doi.org/10.1007/s11705-014-1413-2
Magnetic Fe3O4 and mesoporous silica core-shell nanospheres with tunable size from 110–800 nm were synthesized via a one step self-assembly method. The morphological, structural, textural, and magnetic properties were well-characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, N2 adsorption-desorption and magnetometer. These nanocomposites, which possess high surface area, large pore volume and well-defined pore size, exhibit two dimensional hexagonal (P6mm) mesostructures. Interestingly, magnetic core and mesoporous silica shell nanocomposites with large void pore (20 nm) on the shell were generated by increasing the ratio of ethanol/water. Additionally, the obtained nanocomposites combined magnetization response and large void pore, implying the possibility of applications in drug/gene targeting delivery. The cell internalization capacity of NH2-functionalized nanocomposites in the case of cancer cells (HeLa cells) was exemplified to demonstrate their nano-medicine application.
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