RESUMO
The organic compound niacin or nicotinic acid, also known as vitamin B3 (VitB3), is essential for human nutrition and metabolic regulation. However, in high doses, it can provoke side effects, such as hyperglycemia, liver damage, and flushing. Development of a controlled release system that slowly releases VitB3 into the organism would avoid high dosing peaks, thus contributing to decrease the occurrence of side effects in nutritional supplementation. Here, we show that the slow and controlled release of VitB3 in an acid environment can be achieved via its intercalation in layered double hydroxides (LDHs). The synthesis of a ZnAl-VitB3 system is shown, in which VitB3 is intercalated in a ZnAl LDH. The presence of VitB3 in the ZnAl-VitB3 system was confirmed by elemental analysis, infrared (FTIR) and NMR spectroscopy, while successful intercalation in the LDHs was revealed by powder X-ray diffraction (PXRD). In vitro release tests were carried out in a concentrated HCl solution of pH 1.5, a pH similar to the human stomach environment. The results showed a steady release of VitB3 from the LDH host, with 90% of the vitamin liberated in the first 60 min after the suspension of the LDH in the acidic solution.
RESUMO
The photoluminescence properties (PL) of Eu3+ hosted in the hydroxide layers of layered double hydroxides (LDHs) enables calibrationless quantification of anions in the interlayers. The concept is demonstrated during the nitrate-to-carbonate ion exchange in Zn2+/Al3+/Eu3+ LDHs and can be implemented as a remote optical sensor to detect intrusion of anions such as Cl- or CO32-.
RESUMO
Synthesis of layered materials exhibiting hierarchical porosity remains challenging, but nevertheless worthwhile because it turns such solids into functional materials with high specific surface area. Using a soft-templating strategy in combination with the incorporation of 8-fold coordinated Eu3+, self-assembly of self-supported layered double hydroxide (LDH) nanotubes has been achieved. Heteromorphic equimolar substitution of Al3+ by Eu3+ in Zn2+/Al3+ LDH solids intercalated with 1,3,5-benzenetricarboxylate anions (BTC) assists precipitation of the double hydroxide layers onto the convex surface of Pluronic® P-123 worm-like micelles, yielding multilayer cylinders of BTC-intercalated LDHs. Removal of the micellar template is easily achieved by liquid extraction with methanol, yielding a network of interconnected, well-defined, self-supported, multi-walled, hollow cylindrical nanotubes. Removal of Eu3+ from the synthesis disables formation of the nanotubular morphology, but still yields LDHs containing a network of embedded mesopores, resulting in a specific surface area that is 5-fold higher as compared to standard LDHs.
RESUMO
Luminescent layered double hydroxides (LDH) intercalated by isophthalate (ISO) and nitrilotriacetate (NTA) have been synthesized and characterized by powder X-ray diffraction (PXRD), extended X-ray absorption fine structure (EXAFS), elemental analysis (ICP-OES and CHN), and photoluminescence spectroscopy. While PXRD shows the successful formation of ZnAlEu LDHs, EXAFS reveals that the Eu activators are hosted in the hydroxide layers with an eightfold, oxygen-rich coordination, distinct from the sixfold coordination expected for the octahedral sites of metal cations in LDHs. This kind of coordination should locally distort the brucite-like layers. Additionally, the intercalation of ISO and NTA in the LDHs is shown to change the coordination environment around Eu compared to nitrate-intercalated ZnAlEu LDHs, which suggests that these anions directly interact with the Eu centers and/or strongly affect their coordination geometry. Finally, from the photoluminescence results, analyzed based on the Judd-Ofelt theory, it is determined that Eu is most likely in an environment with no inversion symmetry.
RESUMO
Self-supported oligo-layered ZnAlEu LDH nanotubes (∅ 20 nm) self-assemble upon controlled hydrolysis of the metal ions (Zn2+, Al3+, Eu3+) in the presence of 1,3,5-benzenetricarboxylate anions and non-ionic worm-like micelles. Their high surface area and easily accessible cylindrical mesopores (175 m2 g-1; 0.75 cm3 g-1) facilitate interaction with 5 nm CdTe quantum dots, enhancing the overall luminescence behavior.