Melanin Treatment Effect of Vacuoles-Zinc Oxide Nanoparticles Combined with Ascorbic Acid

Currently, ascorbic acid (AA) is widely used as a skin whitening material, but, AA, an unstable hydrophilic molecule, cannot penetrate the skin easily, due to the hydrophobic character of the stratum corneum. Therefore, we conjugated AA with hydrated zinc oxide-an inorganic matrix with positive surface charge, to improve the stability of AA. The metal-conjugated-ascorbic acid (ZnAA) was then combined with yeast vacuole through the vacuolar membrane proteins that relate to metal transportation to create an enhanced vacuole that contained ZnAA. The characteristics of vacuole with ZnAA (ZnAA_Vac) were next examined by various tests that included X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Field emission scanning electron microscopy (FE-SEM), and energy-dispersive X-ray (EDX) analysis. Furthermore, the ability of ZnAA_Vac to degrade melanin was confirmed in both melanoma cell line B16F10, and the artificial human skin MelanoDerm. The results showed that ZnAA_Vac possessed a higher depigmenting effect than the wild-type vacuole or ascorbic acid by reducing 75% of melanin color. Interestingly, ZnAA_Vac was found to be harmless, and did not cause any cytotoxicity to the cells. Overall, ZnAA_Vac is expected to provide a robust, harmless, and effective whitening agent for the skin.

Crystal-facet and microstructure engineering in ZnO for photocatalytic NO oxidation

Photocatalysis is believed to be an important way of reducing NO pollutant in air and the facet engineering of semiconducting oxides could enhance the efficiency of the photocatalysis. ZnO nanoparticles with different exposed crystalline facets were successfully synthesized using a hydrothermal method and their photocatalytic degradation towards NO was investigated. The crystals from ZnCl₂ precursor were hexagonal mesoporous ones with exposed (0002) facet, while those from zinc acetate were in the form of flakes or wheat ears with enhanced exposure of (101(-)1) facet. Calcination in air imparted an enhanced the textural coefficient of the orientated facets as well as the oxygen defects. The nanocrystals with enhanced (0002) facet and lower flat-band energy did better in photoelectrochemical water-oxidation than those with exposed (101(-)1) facet that showed superior photocatalytic activity (approaching 76.7 ± 0.6% under 365 nm photons) for NO oxidation. According to theoretical calculations, (101(-)1) facet with O termination showed much higher affinity to NO molecules than other configurations, and the oxygen vacancy in ZnO played an minor role in the photocatalytic oxidation of NO. A high quantum efficiency approaching 97.5 ± 1.4% under 275 nm photons was obtained for the ZnO crystals from zinc acetate with mixed (0002) and (101(-)1) facets. This research explores the special characteristics of ZnO with different exposed facets and is important for the future design of highly efficient photocatalyst for hazardous material removal.