Superhydrophobic Silicon Nanocrystal-Silica Aerogel Hybrid Materials: Synthesis, Properties, and Sensing Application.

Silicon nanocrystals (SiNCs) are abundant and exhibit exquisitely tailorable optoelectronic properties. The incorporation of SiNCs into highly porous and lightweight substrates such as aerogels leads to hybrid materials possessing the attractive features of both materials. This study describes the covalent deposition of SiNCs on and intercalation into silica aerogels, explores the properties, and demonstrates a prototype sensing application of the composite material.

Cellulose nanocrystal-derived hollow mesoporous carbon spheres and their application as a metal-free catalyst.

In this contribution, we demonstrate the fabrication of hollow mesoporous carbon spheres (HCSs) derived from cellulose nanocrystals (CNCs). The HCSs were prepared by templating CNCs onto sacrificial silica spheres followed by heat treatment. Mesoporous carbon spheres result from the removal of the silica spheres by etching.

Cooperative Noncovalent Interactions Induce Ion Pair Separation in Diphenylsilanides.

This crystallographic and computational study describes an unusual potassium silanide structure. A contact ion pair is expected in the solid state between potassium and silicon, yet the potassium cation binds an aromatic ring and the anionic silanide interacts with CH bonds on neighboring crown ether molecules. These structure-bonding phenomena are attributed to strong soft-soft interactions.

In situ IR-spectroscopy as a tool for monitoring the radical hydrosilylation process on silicon nanocrystal surfaces.

Among a variety of SiNC functionalization methods, radical initiated grafting is very promising due to its straightforward nature and low propensity to form surface oligomers. In the present study, we employed in situ IR spectroscopy in combination with visible light transmittance measurements to investigate the radical induced grafting process on the well-defined SiNCs. Our findings support the proposed model: unfunctionalized hydride-terminated SiNCs form agglomerates in organic solvents, which break up during the grafting process.

Phosphorus Pentachloride Initiated Functionalization of Silicon Nanocrystals.

Phosphorus pentachloride (PCl) has long been used to chlorinate hydrocarbons. It has also been applied in silicon surface chemistry to facilitate alkylation via a two-step halogenation/Grignard route. Here we report a study of the reaction of PCl with hydride-terminated silicon nanocrystals (H-SiNCs).

Instantaneous Functionalization of Chemically Etched Silicon Nanocrystal Surfaces.

Remarkable advances in surface hydrosilylation reactions of C=C and C=O bonds on hydride-terminated silicon have revolutionized silicon surface functionalization. However, existing methods for functionalizing hydride-terminated Si nanocrystals (H-SiNCs) require long reaction times and elevated temperatures. Herein, we report a room-temperature method for functionalizing H-SiNC surfaces within seconds by stripping outermost atoms on H-SiNC surfaces with xenon difluoride (XeF ).

Alkoxy-Terminated Si Surfaces: A New Reactive Platform for the Functionalization and Derivatization of Silicon Quantum Dots.

Alkoxy-terminated silicon quantum dots (SiQDs) were synthesized via hydrosilylation of aliphatic ketones on hydride-terminated SiQD (H-SiQD) surfaces under microwave-irradiation. Aromatic ketones undergo hydrosilylation on H-SiQD surfaces at room temperature without requiring any catalyst. The alkoxy-terminated SiQDs are soluble in organic solvents, colloidally stable, and show bright and size dependent photoluminescence (PL).

Grafting Poly(3-hexylthiophene) from Silicon Nanocrystal Surfaces: Synthesis and Properties of a Functional Hybrid Material with Direct Interfacial Contact.

Hybrid functional materials (HFMs) comprised of semiconductor nanoparticles and conjugated polymers offer the potential of synergetic photophysical properties. We have developed HFMs based upon silicon nanocrystals (SiNCs) and the conductive polymer poly(3-hexylthiophene) (SiNC@P3HT) by applying surface-initiated Kumada catalyst transfer polycondensation (SI-KCTP). One unique characteristic of the developed SiNC@P3HT is the formation of a direct covalent bonding between SiNCs and P3HT.

Application of Engineered Si Nanoparticles in Light-Induced Advanced Oxidation Remediation of a Water-Borne Model Contaminant.

Surface-engineered amphiphilic polymer-coated silicon nanoparticles (SiNPs) were employed as photocatalysts to capture and degrade a model organic contaminant (methanol) in water. This study represents the first time SiNPs have been employed in the initiation of advanced oxidation processes that are commonly used to degrade organic constituents in industrial wastewaters. The quantum yield of photocatalytic methanol oxidation and the corresponding yield factor for the generation of active OH radicals are reported.

Spherical nitrogen-doped hollow mesoporous carbon as an efficient bifunctional electrocatalyst for Zn-air batteries.

Materials based upon porous carbon have gained considerable attention due to their high surface area, electric conductivity, thermal and chemical stability, low density, and availability. These superior properties make them ideal for diverse applications. Doping these carbon nanostructures holds promise of designing the properties of these structures and opening the door to practical applications.

Radical Initiated Hydrosilylation on Silicon Nanocrystal Surfaces: An Evaluation of Functional Group Tolerance and Mechanistic Study.

Hydrosilylation is among the most common methods used for modifying silicon surface chemistry. It provides a wide range of surface functionalities and effective passivation of surface sites. Herein, we report a systematic study of radical initiated hydrosilylation of silicon nanocrystal (SiNC) surfaces using two common radical initiators (i.

Direct Evaluation of the Quantum Confinement Effect in Single Isolated Ge Nanocrystals.

To address the yet open question regarding the nature of quantum confinement in Ge nanocrystals (Ge NCs) we employed scanning tunneling spectroscopy to monitor the electronic structure of individual isolated Ge NCs as a function of their size. The (single-particle) band gaps extracted from the tunneling spectra increase monotonically with decreasing nanocrystal size, irrespective of the capping ligands, manifesting the effect of quantum confinement. Band-gap widening of ∼1 eV with respect to the bulk value was observed for Ge-NCs 3 nm in diameter.

One-pot synthesis of functionalized germanium nanocrystals from a single source precursor.

One-pot syntheses of surface functionalized germanium nanocrystals (GeNCs) based upon traditional hot injection and microwave-assisted heating of a Ge(II) dihydride single source precursor have been developed. The reported procedures offer in situ hydrogermylation-based covalent attachment of alkene/alkyne derived surface moieties that give access to hydrophobic or hydrophilic GeNCs.

Water-soluble photoluminescent d-mannose and l-alanine functionalized silicon nanocrystals and their application to cancer cell imaging.

Herein, we report the straightforward synthesis, photoluminescent properties, and cell imaging studies of d-mannose and l-alanine functionalized silicon nanocrystals (SiNCs). Tailoring nanocrystal surface functionalization is essential to interfacing SiNCs with their environment and rendering them stable - surface modification also offers the opportunity to target specific cell types for imaging. A simple and versatile surface modification procedure was developed to tether biomolecules onto the SiNC surfaces and render them water-soluble.

Borane-catalyzed room-temperature hydrosilylation of alkenes/alkynes on silicon nanocrystal surfaces.

Room-temperature borane-catalyzed functionalization of hydride-terminated silicon nanocrystals (H-SiNCs) with alkenes/alkynes is reported. This new methodology affords formation of alkyl and alkynyl surface monolayers of varied chain lengths (i.e.

Photoluminescent silicon nanocrystals with chlorosilane surfaces--synthesis and reactivity.

We present a new efficient two-step method to covalently functionalize hydride terminated silicon nanocrystals with nucleophiles. First a reactive chlorosilane layer was formed via diazonium salt initiated hydrosilylation of chlorodimethyl(vinyl)silane which was then reacted with alcohols, silanols and organolithium reagents. With organolithium compounds a side reaction is observed in which a direct functionalization of the silicon surface takes place.

Chloride surface terminated silicon nanocrystal mediated synthesis of poly(3-hexylthiophene).

Abundant and environmentally benign metal-free silicon-based reagents, including chloride surface-terminated silicon nanocrystals (Cl-SiNCs) and silicon wafers as well as molecular chlorosilanes, were explored as catalysts for the synthesis of poly-3-hexylthiophene (P3HT) at room temperature. Cl-SiNC catalysts exhibit the highest activity of those investigated, and systems based upon single-crystal silicon wafers provide convenient, straightforward purification. The as-prepared P3HT exhibits moderate molecular weights and bears H/Br or Br/Br end groups; these properties will allow direct application and also facilitate their use as macroinitiators in the syntheses of block and/or telechelic polymers.

Low temperature synthesis of silicon carbide nanomaterials using a solid-state method.

Silicon carbide (SiC) nanomaterials have been prepared via the solid-state metathesis reaction of various silica sources, magnesium and carbon. This approach enables synthesis of crystalline β-SiC nanomaterials of varied morphologies at 600 °C - the lowest temperature reported to date. The resulting materials were characterized using XRD, FTIR, XPS, TEM and SEM techniques.

Cytotoxicity of surface-functionalized silicon and germanium nanoparticles: the dominant role of surface charges.

Although it is frequently hypothesized that surface (like surface charge) and physical characteristics (like particle size) play important roles in cellular interactions of nanoparticles (NPs), a systematic study probing this issue is missing. Hence, a comparative cytotoxicity study, quantifying nine different cellular endpoints, was performed with a broad series of monodisperse, well characterized silicon (Si) and germanium (Ge) NPs with various surface functionalizations. Human colonic adenocarcinoma Caco-2 and rat alveolar macrophage NR8383 cells were used to clarify the toxicity of this series of NPs.