RESUMO
Activated carbon has an excellent porous structure and is considered a promising adsorbent and electrode material. In this study, activated carbon fibers (ACFs) with abundant microporous structures, derived from natural cotton fibers, were successfully synthesized at a certain temperature in an Ar atmosphere and then activated with KOH. The obtained ACFs were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), elemental analysis, nitrogen and carbon dioxide adsorption-desorption analysis, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and N2 adsorption-desorption measurement. The obtained ACFs showed high porous qualities and had a surface area from 673 to 1597 m2/g and a pore volume from 0.33 to 0.79 cm3/g. The CO2 capture capacities of prepared ACFs were measured and the maximum capture capacity for CO2 up to 6.9 mmol/g or 4.6 mmol/g could be achieved at 0 °C or 25 °C and 1 standard atmospheric pressure (1 atm). Furthermore, the electrochemical capacitive properties of as-prepared ACFs in KOH aqueous electrolyte were also studied. It is important to note that the pore volume of the pores below 0.90 nm plays key roles to determine both the CO2 capture ability and the electrochemical capacitance. This study provides guidance for designing porous carbon materials with high CO2 capture capacity or excellent capacitance performance.
RESUMO
A promising phosphors Ca2Al2SiO7:Tm3+,Dy3+ were synthesized by conventional high temperature sintering. Phase identification, crystal structure refinement, luminescence properties, energy transfer mechanism of Tm3+ â Dy3+, and CIE color coordinates were investigated systematically. The phase structure of prepared phosphors were confirmed by XRD analysis and structure refinement. From the results of photoluminescence, the CASO: Tm3+ phosphors showed intense blue light emission peaks at 454 nm (the transition from 1D2 to 3F4), while CASO:Dy3+ phosphors exhibited predominant yellow light emission peaks at 581 nm (the transition from 4F9/2 to 6H13/2), implying that the Dy3+ were located in the non-inverted symmetric site of the CASO host lattice. Meanwhile, the results exhibited that the optimal doping content of Dy3+ was 0.01, and the mechanism of concentration quenching was the nearest-neighbor ions interaction. The overlapped emission (Tm3+)/excitation (Dy3+) spectra, decay curves and the energy level scheme about CASO:Tm3+,Dy3+ confirmed the energy transfer of Tm3+ â Dy3+. Moreover, by adjusting Tm3+/Dy3+ ions concentration, the intensities of yellow emission for Dy3+ and blue emission for Tm3+ could be adjusted to tune the emitting color of CASO:Tm3+, Dy3+. Excited by the most effective excitation wavelength at 355 nm, the CIE coordinates (0.3422, 0.3262) of phosphor CASO:0.01Tm3+, 0.01Dy3+ was closest to the coordinates of white chromaticity (0.33, 0.33). Results indicate that the potential value of phosphors Ca2Al2SiO7:Tm3+,Dy3+ are used as a single-phase color-adjustable phosphors for NUV pumped white-LEDs.
RESUMO
In order to illuminate the effective compounds in Tibetan medicine kandrakari, chemical composition of dry stems of Rubus amabilis were studied by means of various chromatographic techniques, leading to the isolation of 11 compounds. On the basis of spectroscopic data, their structures were elucidated as 1,8-dihydroxy-3,7-dimethoxyxanthone (1), 1-hydroxy-3,7,8-trimethoxyxanthone (2), 1,8-dihydroxy-3,5-dim ethoxyxanthone (3), kaempfero-3-O-(6"-trans-p-coumaroyl) -beta-D-glucopyranoside (4), quercetin (5), kaempferol (6), hyperoside (7), luteolin-7-O-beta-D-glucopy ranoside (8), apigenin-7-O-beta-D-glucopyranoside (9), isovitexin-7-O-glucoside (10), and procyanidin B4 (11). Compounds 1-3 were isolated from the Rubus genus for the first time,and compounds 1-6, 10-11 were isolated from R. amabilis for the first time.
