Core-shell structured hydroxyapatite (HA)/meso-silica was prepared and used as absorbance of methylene blue (MB). HA/meso-silica was synthesized in three steps: preparation of nano-sized HA by wet precipitation method, coating of dense silica and deposition of meso-silica shell on HA. As-received samples were characterized by Fourier transformed infare spectra, small angle X-ray diffraction, nitrogen adsorption-desorption isotherm and transmission electron microscopy. A wormhole framework mesostructure was found for HA/meso-silica. The specific surface area and pore volume were 128 m2•g-1 and 0.36 cm3•g-1, respectively. From the adsorption isotherm, HA/meso-silica with the great specific surface area exhibited a prominent adsorption capacity of MB (134.0 mg/g) in comparison with bare HA (0 mg/g). This study might shed light on surface modification of conventional low-cost adsorbents for removal of organic pollutants from aqueous solutions.
A pulse laser-diode-array (LDA)-pumped, intracavity frequency-doubled Nd: YVO4 laser has been demonstrated. An birefringent filter consisting of a KTP crystal and two Brewster plates(BP) has been used in the system to realize single-frequency output. Up to 72.4 mW average output power is obtained for 800 mW pumping power with an optical-to-optical conversion efficiency of 9.1%. The maximum peak power of the single-frequency green laser is 22.3 W with the pulse width 162μs.
Large-sized hydroxyapatite (HA) crystals with different morphologies, such as whisker-like, tubular and plate-form shape were prepared at different hydrothermal temperatures. Reaction solutions with small concentration of Ca2+, PO43- and OH- ions were used for HA synthesis. Phase identifications and morphological characterizations indicated that HA crystal grew along c axis under the modulation of glutamic acid adsorbent. The formation mechanism was explained according to the interfacial structures between glutamic acid and HA, as well as thermodynamic and kinetic considerations of crystal nucleation and growth. Understanding the evolution of crystal morphology in a specified reaction solution might favor to control the shape of crystals by the hydrothermal method.
The influence of citric acid on phase evolution of calcium phosphate is studied by the electrical conductivity of reaction solutions. The conductance curves are divided into three distinct regions and assigned to the formation of amorphous calcium phosphate (ACP), hydroxyapatite (HA) and the solubility of HA, respectively. When more citric acid is added, the width of region I decreases because more Ca2+ ions would prefer to foster the nucleation of HA from ACP. Decreasing rate of conductivity in region II becomes smaller with more addition of citric acid because the supersaturation of HA decreases in solutions. And thus, HA powders with larger grain size are synthesized with more citric acid addition.
A high dispersed nanofiber cryptomelane-type manganese dioxide was synthesized by a facile hydrothermal reduction route. The morphological characterization was examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The structure and electrochemical properties of the synthesized manganese dioxide were characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) surface area analyses, and an electrochemical workstation (EW). A glassy carbon electrode (GCE) modified with the nanostructured cryptomelane-type manganese dioxide was investigated for amperometric detection of hydrogen peroxide (H2O2) in phosphate buffer solution with a pH 7.4 at an open circuit potential of 0.2 V. The oxidation peak current was found to increase by 1.3 μA with the addition of 0.1 mmol•L-1 H2O2 based on a MnO2 nanofiber-gelatin/GCE electrode. The amperometric signals are linearly proportional to the H2O2 concentration in the range 0.1-1.5 mmol •L-1 with a correlation coefficient of 0.996 using the GCE modified with 0.1% (w, mass fraction) cryptomelane-type manganese oxides. The sensor is sensitive and its significant electrocatalytic activity results from the nanostructure of the cryptomelane-type manganese oxides. In addition, the sensor has a good reproducibility, a low detection limit, simplicity, and a low cost of construction. These results demonstrate that this material with high electrocatalytic activity offers great promise as a new class of nanostructured electrodes for biosensors.
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