Effects of five extraction methods on total content, composition, and stability of flavonoids in jujube.

The present study investigated the effects of different extraction methods including water-water bath (W-WB), ethanol-water bath (E-WB), deep eutectic solvent (DES) combined with ultrasound-assisted extraction (DES-UAE), microwave-assisted extraction (DES-MAE), and enzyme-assisted extraction (DES-EAE) on flavonoids (total flavonoid content, flavonoid composition, and stability) in jujube. The highest total flavonoid content of 8.03 mg/g was obtained by the DES-MAE extraction. Fifteen types of flavonoids were identified from jujube. The amount of rutin produced by the E-WB and DES-UAE methods was 66.88 ± 1.58 µg/g and 45.23 ± 3.22 µg/g, respectively. The retention of flavonoids in DES-UAE extracts were 98.15 ± 0.51%, 64.25 ± 2.21% after 2 h of high temperature treatment at 90 °C and 21 days of dark storage, respectively. The flavonoids extracted by different methods were suitable for dark storage under different light contrasts, where the retention of flavonoids extracted by DES-UAE method was 86.44 ± 2.45%. In conclusion, DES-UAE would be an efficient method for flavonoid extraction from jujube.

Co-sensitization promoted light harvesting with a new mixed-addenda polyoxometalate [Cu(C12H8N2)2]2[V2W4O19]·4H2O in dye-sensitized solar cells.

A di-vanadium-substituted Lindqvist-type polyoxometalate [Cu(C12H8N2)2]2[V2W4O19]·4H2O (1) was hydrothermally synthesized and characterized structurally by single crystal X-ray diffraction analysis. X-ray photoelectron spectroscopy and energy disperse spectroscopy tests further prove the existence of vanadium. Ultraviolet photoelectron spectroscopy and density functional theoretical studies indicate that the energy level of 1 matches well with the conduction band of the TiO2. Furthermore, considering the semiconductor-like nature of 1 and the introduction of transition metal element Cu synchronously extends the absorption to the visible region, which should also be beneficial to the photovoltaic device performance. 1-Doped TiO2 composites (denoted as 1@TiO2) have been successfully fabricated by a simple sol-gel method, and introduced into the dye-sensitized solar cells (DSSCs) as co-sensitizers in N719-sensitized photoanodes by mixing 1@TiO2 with P25 nanoparticles with different weight ratios to enhance the photoelectric conversion efficiency. The investigations show that the DSSC assembled with 1@TiO2/19P25 photoanode has the best performance and the overall improvement of the efficiency is 21.6% compared with pure P25. Furthermore, the electrochemical impedance spectroscopy and open-circuit voltage decay investigations show that the cosensitization of 1 and N719 can promote electron transfer and restrain charge recombinations in the DSSCs, resulting in a longer electron lifetime.