Synthesis and Characterization of Metallic, Core-shell and Composite nanoparticles

ABSTRACT Silver nanoparticles exhibit size, shape and the surrounding dielectric medium dependent optical properties (scattering and absorption) in the visible spectral region. These optical properties can be explained in terms of the collective oscillation of the \u27free conduction band electrons\u27 or \u27surface plasmons\u27 induced by an external electromagnetic field. Dipole and Quadrupole Plasmon resonances have been observed for silver particles less than 100nm in diameter prepared using various synthetic techniques. However higher order resonances have been elusive due to lack of experimental techniques to prepare colloidal solutions of large silver nanoparticles in the size range above 100nm. Controlled hydrogen reduction of silver (I) oxide at 70˚C resulted in the formation of a colloidal solution of submicron silver particles. These particles exhibit the ability to optically excite higher order multipoles of the plasmon resonances, i.e. octupole and hexadecapole in its extinction spectra and the features match well with the Mie extinction calculations. Core-shell particles represent a distinct class of nanomaterial with collective physicochemical properties that are unique and different from the individual components. Metal silver cores coated with amorphous semiconductor titania shell hybrid nanoparticles were prepared using controlled hydrolysis and condensation of titanium(IV) butoxide (sol-gel technique). Hydrothermal treatment at 350˚C resulted in the conversion of the amorphous titania shell into its crystalline anatase form. Progressive red shifts in the plasmon resonance peaks in the extinction spectra were observed for amorphous and crystalline anatase titania coated silver nanoparticles. The anatase form of titania is one of the most effective semiconductor photocatalyst when excited with UV light (λ≤ 380nm). Metal ion doping into anatase titania is one means to shift its band gap transition to the visible spectral region for its practical application in the solar spectral region. A modified sol-gel technique using titanium (IV) butoxide and iron(III) nitrate nonahydrate precursor followed by heat treatment in air was employed to prepare iron (III) ion doped anatase titania nanocomposites with the onset of band gap transition red-shifted (~λ= 475nm) to the visible spectral region. The direct photocatalytic effect was observed in the degradation of dye pollutant sulforhodamine-B in the presence of iron(III) ion doped titania nanocomposites upon visible light irradiation. Hydrogen reduction of silver(I) oxide in the presence of ~200nm polystyrene microspheres (Polysciences Inc.) at 70˚C led to the formation of silver nanoparticles attached to polystyrene microspheres. Extinction spectra of the resulting colloidal solution revealed a suppressed quadrupolar plasmon resonance peak when compared to the resonance observed for colloidal silver nanoparticles in the same size range without the presence of polystyrene beads. Electron microscopy images support the above observation with the polystyrene microspheres attached to one of the crystalline surface of the particle. Further acetone treatment lead to the encapsulation of the silver nanoparticles within the polystyrene microspheres as observed in the electron microscopy images and red shifts in the plasmon resonance peaks with the evolution of a prominent quadrupolar resonance peak in the extinction spectra. These silver-polystyrene particles represent a unique metal-polymer core shell nanostructure

Immobilization of active human carboxylesterase 1 in biomimetic silica nanoparticles

The encapsulation of proteins in biomimetic silica has recently been shown to successfully maintain enzymes in their active state. Organophosphate (OP) compounds are employed as pesticides as well as potent chemical warfare nerve agents. Because these toxicants are life threatening, we sought to generate biomimetic silicas capable of responding to OPs. Here, we present the silica encapsulation of human drug metabolism enzyme carboxylesterase 1 (hCE1) in the presence of a range of catalysts. hCE1 was successfully encapsulated into silica particles when lysozyme or the peptide R5 were used as catalysts; in contrast, polyethyleneimine (PEI), a catalyst employed to encapuslate other enzymes, did not facilitate hCE1 entrapment. hCE1 silica particles in a column chromatography format respond to the presence of the organophosphate (OP) pesticides paraoxon and dimethyl-p-nitrophenyl phosphate in solution. These results may lead to novel approaches to detect OP pesticides or other weaponized agents that bind hCE1

Investigating the Control by Quantum Confinement and Surface Ligand Coating of Photocatalytic Efficiency in Chalcopyrite Copper Indium Diselenide Nanocrystals

In the past few years, there has been immense interest in the preparation of sustainable photocatalysts composed of semiconductor nanocrystals (NCs) as one of their components. We report here, for the first time, the effects of structural parameters of copper indium diselenide (CuInSe2) NCs on visible light-driven photocatalytic degradation of pollutants under homogeneous conditions. Ligand exchange reactions were performed replacing insulating, oleylamine capping with poly(ethylene glycol) thiols to prepare PEG-thiolate-capped, 1.8–5.3 nm diameter CuInSe2 NCs to enhance their solubility in water. This unique solubility property caused inner-sphere electron transfer reactions (O2 to O2•−) to occur at the NC surface, allowing for sustainable photocatalytic reactions. Electrochemical characterization of our dissolved CuInSe2 NCs showed that the thermodynamic driving force (−ΔG) for oxygen reduction, which increased with decreased NC size, was the dominant contributor to the overall process when compared to ..

DESIGNING EFFICIENT LOCALIZED SURFACE PLASMON RESONANCE-BASED SENSING PLATFORMS: OPTIMIZATION OF SENSOR RESPONSE BY CON-TROLLING THE EDGE LENGTH OF GOLD NANOPRISMS

poster abstractOver the last few years, the unique localized surface plasmon resonance (LSPR) properties of plasmonic nanostructures have been used to design la-bel-free biosensors. In this research, we demonstrate that it is the difference in edge length of gold nanoprisms that significantly influences their bulk re-fractive index sensitivity and local sensing efficiency. Nanoprisms with edge lengths in the range of 28-51 nm were synthesized by the chemical-reduction method and sensing platforms were fabricated by chemisorptions of these nanoprisms onto silanized glass substrates. The plasmonic nanosensors prepared from 28 nm edge length nanoprisms exhibited the largest sensitivity to change in bulk refractive index with a value of 647 nm/RIU. The refractive index sensitivity decreased with increasing edge length, with nanoprisms of 51 nm edge lengths displaying a sensitivity of 384 nm/RIU. In contrast, we found that the biosensing efficiency of sensing platforms modified with biotin increased with increasing edge length, and the sensing platforms fabricated from 51 nm edge length nanoprisms displaying the highest local sensing efficiency. The lowest concentration of streptavidin that could be measured reliably was 1.0 pM and the limit of detection for the sensing platforms fabricated from 51 nm edge length nanoprisms was 0.5 pM, which is much lower than found with gold bipyramids, nanostars, and nanorods

Solvent-like ligand-coated ultrasmall cadmium selenide nanocrystals: Strong electronic coupling in a self-organized assembly

Strong inter-nanocrystal electronic coupling is a prerequisite for delocalization of exciton wave functions and high conductivity. We report 170 meV electronic coupling energy of short chain poly(ethylene glycol) thiolate-coated ultrasmall (<2.5 nm in diameter) CdSe semiconductor nanocrystals (SNCs) in solution. Cryo-transmission electron microscopy analysis showed the formation of a pearl-necklace assembly of nanocrystals in solution with regular inter-nanocrystal spacing. The electronic coupling was studied as a function of CdSe nanocrystal size where the smallest nanocrystals exhibited the largest coupling energy. The electronic coupling in spin-cast thin-film (<200 nm in thickness) of poly(ethylene glycol) thiolate-coated CdSe SNCs was studied as a function of annealing temperature, where an unprecedentedly large, ∼400 meV coupling energy was observed for 1.6 nm diameter SNCs, which were coated with a thin layer of poly(ethylene glycol) thiolates. Small-angle X-ray scattering measurements showed that CdSe SNCs maintained an order array inside the films. The strong electronic coupling of SNCs in a self-organized film could facilitate the large-scale production of highly efficient electronic materials for advanced optoelectronic device application

How to reprogram the excitonic properties and solid-state morphologies of π-conjugated supramolecular polymers

The development of supramolecular tools to modulate the excitonic properties of non-covalent assemblies paves the way to engineer new classes of semicondcuting materials relevant to flexible electronics. While controlling the assembly pathways of organic chromophores enables the formation of J-like and H-like aggregates, strategies to tailor the excitonic properties of pre-assembled aggregates through post-modification are scarce. In the present contribution, we combine supramolecular chemistry with redox chemistry to modulate the excitonic properties and solid-state morphologies of aggregates built from stacks of water-soluble perylene diimide building blocks. The n-doping of initially formed aggregates in an aqueous medium is shown to produce π-anion stacks for which spectroscopic properties unveil a non-negligible degree of electron-electron interactions. Oxidation of the n-doped intermediates produces metastable aggregates where free exciton bandwidths (ExBW) increase as a function of time. Kinetic data analysis reveals that the dynamic increase of free exciton bandwidth is associated with the formation of superstructures constructed by means of a nucleation-growth mechanism. By designing different redox-assisted assembly pathways, we highlight that the sacrificial electron donor plays a non-innocent role in regulating the structure-function properties of the final superstructures. Furthermore, supramolecular architectures formed via a nucleation-growth mechanism evolve into ribbon-like and fiber-like materials in the solid-state, as characterized by SEM and HRTEM. Through a combination of ground-state electronic absorption spectroscopy, electrochemistry, spectroelectrochemistry, microscopy, and modeling, we show that redox-assisted assembly provides a means to reprogram the structure-function properties of pre-assembled aggregates

Photoluminescent Nanostructures from Graphite Oxidation

The graphite intercalation compound (GIC) of 3:1 sulfuric to nitric acid mixture was used to produce photoluminescent (PL) nanostructures by oxidizing micrographite, nanographite, nanographite platelets, onion-like-carbon, and highly oriented pyrolytic graphite. The GIC used in this work is a Stage I intercalation compound that expands the graphitic planes to a maximum degree; this expansion was visible as a blue color for these graphitic materials in suspension with the GIC solution. The GIC intercalates into the graphitic layers to facilitate oxidation, resulting in graphite oxide, which may be fully exfoliated to graphene oxide. This treatment produced carbon nanostructures that were colloidally stable and photoluminesced across the visible wavelength range. It was possible to control the PL color of the reaction suspension by tuning the reaction temperature or reaction time; higher temperatures or longer reaction times caused a blue shift in the PL wavelength. Various graphitic oxide nanostructures were observed in the reaction suspension with increasing reaction time, including nanoribbons, graphene-like nanoplatelets, and round single-digit nanoparticles. Using separation methods for a PL orange reaction supernatant solution, it was possible to isolate individual PL colors spanning the visible wavelength region. These PL colors exhibit a blue shift in emission wavelength with filters that decreased in molecular weight or as the migration distanced increased in a denaturing polyacrylamide gel. Chemical functionalization of the PL blue carbon product from the oxidation of nanographite platelet allowed for the fluorescent coating of silica beads

Mesoporous Carbon/Zirconia Composites: A Potential Route to Chemically Functionalized Electrically-Conductive Mesoporous Materials

Mesoporous nanocomposite materials in which nanoscale zirconia (ZrO₂) particles are embedded in the carbon skeleton of a templated mesoporous carbon matrix were prepared, and the embedded zirconia sites were used to accomplish chemical functionalization of the interior surfaces of mesopores. These nanocomposite materials offer a unique combination of high porosity (e.g., ∼84% void space), electrical conductivity, and surface tailorability. The ZrO₂/carbon nanocomposites were characterized by thermogravimetric analysis, nitrogen-adsorption porosimetry, helium pychnometry, powder X-ray diffraction, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. Comparison was made with templated mesoporous carbon samples prepared without addition of ZrO₂. Treatment of the nanocomposites with phenylphosphonic acid was undertaken and shown to result in robust binding of the phosphonic acid to the surface of ZrO₂ particles. Incorporation of nanoscale ZrO₂ surfaces in the mesoporous composite skeleton offers unique promise as a means for anchoring organophosphonates inside of pores through formation of robust covalent Zr–O–P bonds

Sustainable Mesoporous Carbons as Storage and Controlled-Delivery Media for Functional Molecules

Here, we report the synthesis of surfactant-templated mesoporous carbons from lignin, which is a biomass-derived polymeric precursor, and their potential use as a controlled-release medium for functional molecules such as pharmaceuticals. To the best of our knowledge, this is the first report on the use of lignin for chemical-activation-free synthesis of functional mesoporous carbon. The synthesized carbons possess the pore widths within the range of 2.5–12.0 nm. In this series of mesoporous carbons, our best result demonstrates a Brunauer–Emmett–Teller (BET) surface area of 418 m²/g and a mesopore volume of 0.34 cm³/g, which is twice the micropore volume in this carbon. Because of the dominant mesoporosity, this engineered carbon demonstrates adsorption and controlled release of a representative pharmaceutical drug, captopril, in simulated gastric fluid. Large-scale utilization of these sustainable mesoporous carbons in applications involving adsorption, transport, and controlled release of functional molecules is desired for industrial processes that yield lignin as a coproduct