Impurity Removal Leading to High-Performance CoSb3-Based Skutterudites with Synergistic Carrier Concentration Optimization and Thermal Conductivity Reduction.

Thermoelectric properties of CoSb3-based skutterudites are greatly determined by the removal of detrimental impurities, such as (Fe/Co)Sb2, (Fe/Co)Sb, and Sb. In this study, we use a facile temperature gradient zone melting (TGZM) method to synthesize high-performance CoSb3-based skutterudites by impurity removal. After removing metallic or semimetallic impurities (Fe/Co)Sb, (Fe/Co)Sb2, and Sb, the carrier concentration of TGZM-Ce0.75Fe3CoSb12 can be reduced to 1.21 × 1020 cm-3 and the electronic thermal conductivity dramatically reduced to 0.7 W m-1 K-1 at 693 K. Additionally, removing these impurities also effectively reduces the lattice thermal conductivity from 7.2 W m-1 K-1 of cast-Ce0.75Fe3CoSb12 to 1.02 W m-1 K-1 of TGZM-Ce0.75Fe3CoSb12 at 693 K. As a consequence, TGZM-Ce0.75Fe3CoSb12 approaches a high power factor of 11.7 µW cm-1 K-2 and low thermal conductivity of 1.72 W m-1 K-1 at 693 K, leading to a peak zT of 0.48 at 693 K, which is 10 times higher than that of cast-Ce0.75Fe3CoSb12. This study indicates that our facile TGZM method can effectively synthesize high-performance CoSb3-based skutterudites by impurity removal and set up a solid foundation for further development.

Ce Filling Limit and Its Influence on Thermoelectric Performance of Fe3CoSb12-Based Skutterudite Grown by a Temperature Gradient Zone Melting Method.

CoSb3-based skutterudite is a promising mid-temperature thermoelectric material. However, the high lattice thermal conductivity limits its further application. Filling is one of the most effective methods to reduce the lattice thermal conductivity. In this study, we investigate the Ce filling limit and its influence on thermoelectric properties of p-type Fe3CoSb12-based skutterudites grown by a temperature gradient zone melting (TGZM) method. Crystal structure and composition characterization suggests that a maximum filling fraction of Ce reaches 0.73 in a composition of Ce0.73Fe2.73Co1.18Sb12 prepared by the TGZM method. The Ce filling reduces the carrier concentration to 1.03 × 1020 cm-3 in the Ce1.25Fe3CoSb12, leading to an increased Seebeck coefficient. Density functional theory (DFT) calculation indicates that the Ce-filling introduces an impurity level near the Fermi level. Moreover, the rattling effect of the Ce fillers strengthens the short-wavelength phonon scattering and reduces the lattice thermal conductivity to 0.91 W m-1 K-1. These effects induce a maximum Seebeck coefficient of 168 µV K-1 and a lowest κ of 1.52 W m-1 K-1 at 693 K in the Ce1.25Fe3CoSb12, leading to a peak zT value of 0.65, which is 9 times higher than that of the unfilled Fe3CoSb12.

Determination of main taxoids in Taxus species by microwave-assisted extraction combined with LC-MS/MS analysis.

A method based on microwave-assisted extraction (MAE) has been developed for the determination of paclitaxel and five related taxoids, namely 10-deacetylbaccatin III (10-DAB III), cephalomannine, 10-deacetylpaclitaxel (10-DAT), 7-xyl-10- deacetylpaclitaxel (7-xyl-10-DAT), and 7-epi-10-deacetylpaclitaxel (7-epi-10-DAT) in Taxus species in this study. The influential parameters of the MAE procedure were optimized, and the optimal conditions were as follows: extraction solvent 80% ethanol solution, solid/liquid ratio 1:10 (g/mL), temperature 50 degrees C, and three extraction cycles, each cycle 10 min. The method validation for LC-MS/MS analysis was performed. The LOD and LOQ were 3.16-9.20 and 12.20-30.45 ng/mL, respectively. Repeatability and reproducibility for the six taxiods with RSD ranged from 2.78 to 3.85% and from 5.26 to 6.60%. The recoveries of the method for the six taxoids were 92.6-105.6%. The developed MAE-LC-MS/MS method was also successfully applied to determine the contents of six taxoids in different Taxus species.

Simultaneous determination of main taxoids in Taxus needles extracts by solid-phase extraction-high-performance liquid chromatography with pentafluorophenyl column.

A simple and accurate RP-HPLC method with pentafluorophenyl (PFP) column was developed for the simultaneous determination of six taxoids, i.e. paclitaxel, 10-deacetylbaccatin III (10-DAB III), 7-xylosyl-10-deacetyltaxol (7-xyl-10-DAT), 10-deacetyltaxol (10-DAT), cephalomannine and 7-epi-10-deacetyltaxol (7-epi-10-DAT), in the extracts from the needles of three Taxus species. The mobile phase consisted of acetonitrile (A) and water (B), and the extracts were separated using gradient elution program: 30% A at the first 7 min, and then ramped to 42% A at 8 min, held until 38 min. The developed method was validated with satisfactory precision (RSD < 2.61%), repeatability (RSD < 2.92%) and recovery (95.19-104.47%). The above taxoids in the extracts of Taxus cuspidata, T. chinensis and T. media were analyzed with the developed RP-HPLC method, and the results showed that the contents of different taxoids in three mentioned species were distinct. Maximal amounts of 10-DAB III, 7-xyl-10-DAT and 7-epi-10-DAT appeared in T. chinensis, while T. media possessed the highest content of 10-DAT, cephalomannine and paclitaxel. The developed method is accurate and efficient. It can be reliably used in the improved determination of taxoids for the quality control of Taxus species.

Enzyme assisted extraction of luteolin and apigenin from pigeonpea [Cajanuscajan (L.) Millsp.] leaves.

Luteolin and apigenin are naturally occurring flavones with a wide spectrum of pharmacological properties. In the present study, enzyme assisted extraction of luteolin and apigenin from pigeonpea leaves using commercial plant cell wall degrading enzyme preparations including cellulase, beta-glucosidase and pectinase were examined. We found that pectinase offered a better performance in enhancement of the extraction yields of luteolin and apigenin than cellulase and beta-glucosidase. The pectinase assisted extraction process was further optimized by varying different parameters such as pectinase concentration, time of incubation, pH of pectinase solution, and incubation temperature. The optimum parameters were obtained as follows: 0.4mg/ml pectinase, incubation for 18h at 30-35°C, pH of pectinase solution 3.5-4. Under the optimum conditions, the extraction yields of luteolin and apigenin achieved 0.268 and 0.132mg/g in pectinase treated sample, which increased 248% and 239%, respectively, compared with the untreated ones.