Particle and surfactant-stabilized emulsion droplets formed in situ serve as templates for hollow silica nanoparticle growth.
We propose a novel analytical method for mercury (Hg) trace determination based on direct Hg preconcentration from aqueous solution onto a gold nanoparticle-decorated silica monolith (AuNP@SiO2). Detection of Hg is performed after thermal desorption by means of atomic fluorescence spectrometry. This new methodology benefits from reagent-free, time- and cost-saving procedure, due to most efficient solid-phase adsorbent and results in high sensitive quantification. The excellent analytical performance of the whole procedure is demonstrated by a limit of detection as low as 1.31 ng L(-1) for only one-min accumulation duration. A good reproducibility with standard deviations ≤5.4% is given. The feasibility of the approach in natural waters was confirmed by a recovery experiment in spiked seawater with a recovery rate of 101%. Moreover, the presented method was validated through reference analysis of a submarine groundwater discharge sample by cold vapor-atomic fluorescence spectrometry resulting in a very good agreement of the found values. Hence the novel method is a very promising new tool for low-level Hg monitoring in natural waters providing easy-handling on-site preconcentration, reagent-free stabilization as well as reagent-free, highly sensitive detection.
Manganese oxides from the compound family of layered birnessites have attracted interest for their use as cathode materials in Li-ion batteries, as supercapacitors, and as water oxidation catalysts. Furthermore, birnessites are also excellent precursors for low-temperature syntheses of manganese oxide-based materials such as LiMnO (spinel and hollandite). Most syntheses leading to highly crystalline birnessites either require hydrothermal conditions for extended periods of time ranging from days to months or a high post-treatment temperature (400-500 °C). Here, we present a novel sol-gel synthesis route leading to the formation of highly crystalline birnessites within one hour without the need for any post-treatment to enhance crystallinity. Small birnessite crystals form virtually immediately upon mixing of the reactants, albeit initially of lower crystallinity. The size of the fully developed monoclinic birnessite platelets is in the micrometer-range with a thickness of about 20-50 nm. Under the studied conditions, the presence of Li, Na, and K is necessary for the formation of well-crystallized birnessites, and the crystal size can be tuned by variation of the synthesis time. This is suggested to be linked to an increase of the Na content in the birnessite with increasing synthesis time.
The nanocasting method is a valuable tool for producing metal oxides with a well-defined nanostructure. However, the precise details on how the metal oxide is developed inside the mesoporous silica template remain unclear. In this study, we clarify how nickel nitrate species are evolving to nickel oxide and how they are redistributed inside mesoporous SBA-15 particles as a function of heating temperature and surrounding gas atmosphere by a combination of in situ small-angle X-ray scattering, X-ray diffraction and thermogravimetric techniques as well as ex situ transmission electron microscopy and nitrogen physisorption measurements. The SBA-15 template was initially impregnated with Ni(NO 3 ) 2 •6H 2 O using the wet infiltration method. The results indicate an initial redistribution of the nickel nitrate salt located outside the pore system into the mesopores due to dissolution, while at temperatures of 110−150 °C (depending on which type of gas flow is used) the mobility of the salt is lost due to drying of the salt. Above 220 °C, the nickel nitrate decomposes, possibly via nickel hydroxynitrate, to NiO, forming nanoparticles inside the pore channels. The results shed light on the events occurring during the nanocasting process and can be used for further optimization of the fidelity of replication.
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