An interface-controlled reaction in normal microemulsions (water/ethanol/sodium oleate/oleic acid/n-hexane) was designed to prepare NaYF4:Yb3+, Er3+ upconversion nanoparticles. The phase diagram of the system was first studied to obtain the appropriate oil-in-water microemulsions. Transmission electron microscopy and X-ray powder diffractometer measurements revealed that the as-prepared nanoparticles were spherical, monodisperse with a uniform size of 20 nm, and of cubic phase with good crystallinity. Furthermore, these nanoparticles have good dispersibility in nonpolar organic solvents and exhibit visible upconversion luminescence of orange color under continuous excitation at 980 nm. Then, a thermal treatment for the products was found to enhance the luminescence intensity. In addition, because of its inherent merit in high yielding and being economical, this synthetic method could be utilized for preparation of the UCNPs on a large scale.
The single crystal structure of sodium yttrium fluoride (NaYF4) nanoparticles formed mainly by aggregation in aqueous phase was first confirmed by high resolution transmission electron microscope (HRTEM). Then, effects of reactant concentrations and pH on the formation of NaYF4 nanocrystals were investigated and described in the presence of sodium citrate (Na-citrate). The results showed that the non-aggregation formation of NaYF4 was dominant under a low concentration range of reactants, and the aggregation formation was dominant under a high concentration range of reactants. For comparison, NaYF4 nanocrystals were also synthesized by co-precipitation in the presence of various other chelators, not only amino-carboxyl (H2N-C) types involving (Na-EDTA) and sodium nitrilotriacetate (Na-NTA) but also hydroxyl-carboxyl (HO-C) types including sodium citrate (Na-citrate), sodium malate (Na-malate), and potassium sodium tartrate (K, Na-tartate). All the chelators showed a similar influence on the particle formation. However, the size of the final product was different corresponding to the different chelators. An upconversion fluorescent material, cubic NaYF4 nanocrystal co-doped with ytterbium and erbium with diameter about 10 nm was successfully achieved at room temperature. Under 980 nm laser excitation, the red emissions at 652 and 679 nm were much stronger than green emissions at 520 and 541 nm. Additionally, effects of concentrations of the different chelators on the fluorescent properties of the formed NaYF4:Yb, Er nanocrystals were also investigated. Different chelators affected the fluorescent properties differently, according to their respective physical and chemical properties.
Indole is a recalcitrant compound whose aerobic biodegradation is triggered by a mono-oxygenation process. Generally, the mono-oxygenation process involves intracellular electron carriers and molecular oxygen as co-substrates; the increase of concentrations for either one can accelerate the biotransformation of refractory substances. In this study, the initial biotransformation of indole proved to be a special mono-oxygenation reaction, neither endogenous nor exogenous electron donors have influences on indole biodegradation. However, oxygen plays a significant role in indole mono-oxygenation. Higher dissolved oxygen led to a faster rate of indole biodegradation. As the product of indole mono-oxygenation, unstable indoxyl indirectly turned out to exist by its tautomer 2-oxindole. Intermediates like isatin, N-formylanthranilic acid, and anthranilic acid were confirmed. In addition, coupling biodegradation with UV photolysis accelerated indole mineralization, and longer photolysis time gave faster TOC removal. This is because the supplement of endogenous electron donors by photolysis could enhance the catabolism of isatin and anthranilic acid, thus promoting indole mineralization. The biodegradation of these two intermediates was further verified to be initiated by donor-requiring steps, so the photolytic products which generated labile electron donors could accelerate their oxygenations. This study provides valuable information on further controlling the process of aerobic biodegradation for indole.
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