Metallothermic Reduction of Silica Nanoparticles to Porous Silicon for Drug Delivery Using New and Existing Reductants

In this study, the influence of metals (Mg, Al, and Ca) and reaction conditions (time, temperature, and metal grain size) on the metallothermic reduction of Stöber silica nanoparticles (NPs) to form porous Si has been explored. Mg metal was found to be an effective reducing agent even at temperatures below its melting point; however, it also induced a high degree of structural damage and morphology change. Al was effective in reducing silica NPs only at its melting point or above, but the resulting particles retained a higher degree of structural morphology as compared to those reduced using Mg. Ca was found to be ineffective in reducing silica. A new reductant, a mixture of 70 % Mg and 30 % Al, was found to induce the least amount of morphology change, and the reactions proceeded at a temperature (450 °C) lower than those required with Mg or Al individually. Furthermore, porous Si NPs obtained using Mg, Al, and the mixture of 70 % Mg and 30 % Al as reductants have been investigated as carriers for ibuprofen loading and release. Porous Si obtained from reductions with Mg and the Mg/Al mixture showed higher drug loading and a sustained drug release profile, whereas porous Si obtained from Al reduction had lower loading and showed a conventional release profile over 24 h

Oxidant-Activated Reactions of Nucleophiles with Silicon Nanocrystals

The oxidant-activated reactivity of Si toward nucleophiles was evaluated for Si nanocrystals (Si-NCs) of differing diameters, d. In the presence of ferrocenium as a one-electron, outer-sphere oxidant, d ≥ 8 nm Si-NCs readily reacted with nucleophiles, including methanol, butanol, butylamine, butanoic acid, butylthiol, and diethylphosphine. However, d < 8 nm Si-NCs did not undergo such reactions, and stronger oxidants such as acetylferrocenium or 1,1′-diacetylferrocenium were required. Butylamine-, butylthiol-, and butanol-functionalized d ≥ 8 nm Si-NCs were partially oxidized and exhibited photoluminescence originating from defect states. In contrast, butanoic acid-functionalized Si-NCs were minimally oxidized and displayed core emission resulting from the excitation and relaxation of electrons across the Si-NC bandgap. Diethylphosphine-functionalized Si-NCs were stable only under inert conditions and showed core emission, with the Si–P bonds being highly susceptible to oxidation and rapidly decomposing upon exposure to ambient conditions. The general reactivity is consistent with the redox potential of the one-electron oxidant and the valence band edge position of the Si-NCs. The trends in reactivity thus provide an example of differential chemical reactions of nanoparticles relative to bulk materials, reflecting the differences in electronic structure and the continuum of electronic properties between variously sized Si nanoparticles and bulk Si samples

Influence of Halides on the Optical Properties of Silicon Quantum Dots

Silicon quantum dots (Si-QDs) have received substantial attention over the last two decades owing to their abundance, biocompatibility, and optical properties. Similar to their group II−VI and III−V quantum dot counterparts, hydride-terminated Si-QDs with diameters smaller than 5 nm can exhibit size-dependent photoluminescence (PL) in the visible spectral region. However, the hydride surface is highly susceptible to oxidation and requires further modification to passivate it and render the QDs soluble in common solvents

Do jeito que você gosta (As you like it)

Shakespeare conta com cerca de duas dúzias de obras-primas dentre as trinta e nove peças que escreveu, e ninguém negaria a As You Like It uma posição de destaque, ainda que alguns (erroneamente) a considerem a menor das obras-primas. A quem Rosalinda não for capaz de agradar, nenhum outro personagem shakesperiano, ou em toda a literatura, poderá fazê-lo. Harold Bloo

Charge transfer state emission dynamics in blue-emitting functionalized silicon nanocrystals

We explore the dynamics of blue emission from dodecylamine and ammonia functionalized silicon nanocrystals (Si NCs) with average diameters of ∼3 and ∼6 nm using time-resolved photoluminescence (TRPL) spectroscopy. The Si NCs exhibit nanosecond PL decay dynamics that is independent of NC size and uniform across the emission spectrum. The TRPL measurements reveal complete quenching of core state emission by a charge transfer state that is responsible for the blue PL with a radiative recombination rate of ∼5 × 10^7 s^(−1). A detailed picture of the charge transfer state emission dynamics in these functionalized Si NCs is proposed

Silicon 1s Near Edge X-ray Absorption Fine Structure Spectroscopy of Functionalized Silicon Nanocrystals

NSERCPeer ReviewedSilicon 1s Near Edge X-ray Absorption Fine Structure (NEXAFS) spectra of silicon nanocrystals have been examined as a function of nanocrystal size (3 – 100 nm), varying surface functionalization (hydrogen or 1-pentyl termination), or embedded in oxide. The NEXAFS spectra are characterized as a function of nanocrystal size and surface functionalization. Clear spectroscopic evidence for long range order is observed Si-NCs that are 5-8 nm in diameter or larger. Energy shifts in the silicon 1s NEXAFS spectra of covalently functionalized silicon nanocrystals with changing size are attributed to surface chemical shifts and not to quantum confinement effects