Roberto Comparelli

Colloidal oxide nanoparticles for the photocatalytic degradation of organic dye

Abstract In this work, easily processable and highly crystalline ZnO and TiO2 nanoparticles, with a narrow size distribution, obtained by using novel non-hydrolytic synthetic approaches were both tested for the photocatalyzed degradation of an organic dye, methyl red (2-(4-Dimethylamino-phenylazo)-benzoic acid)—C.I. 13020) and their behaviour comparatively examined with respect to TiO2 and ZnO commercial powders. The experiments were carried out using semiconducting oxides under UV and visible light illumination. Preliminary studies on the influence of various experimental factors as pH and dye concentration were performed. The obtained results demonstrated a high photocatalytic efficiency of nanosized semiconducting particles.

Optical properties of hybrid composites based on highly luminescent CdS nanocrystals in polymer

High quality luminescent CdS nanocrystals (NCs), with band edge emission tunable in the blue region of the visible spectrum, were synthesized by means of thermal decomposition of precursors with oleic acid as the surfactant and incorporated in optically transparent polystyrene (PS) and poly(methyl methacrylate) (PMMA). The optical properties of the obtained nanocomposite films were investigated by absorption and emission spectroscopies. Enhancement of the band edge luminescence of CdS quantum dots was observed in both polymer matrices and the fluorescence of the composites retained narrow emission profiles. Capping exchange at the NC surface with octylamine, demonstrated to improve the luminescence properties in solution, was performed in order to investigate the role played by surface ligands in the nanocomposite. Octylamine capped NCs immobilized in the polymers showed high defect state emission and visible quenching of band edge luminescence, indicating an effective interaction between oleic acid and PMMA and PS polymeric chains.

Ion-directed assembly of gold nanorods: a strategy for mercury detection.

Water-soluble gold nanorods (Au NRs) have been functionalized with an N-alkylaminopyrazole ligand, 1-[2-(octylamino)ethyl]-3,5-diphenylpyrazole (PyL), that has been demonstrated able to coordinate heavy metal ions. The N-alkylaminopyrazole functionalized Au NRs have been characterized by electron microscopy and spectroscopic investigation and tested in optical detection experiments of different ions, namely, Zn(2+), Cd(2+), Hg(2+), Cu(2+), Pb(2+), and As(3+). In particular, the exposure of the functionalized NRs to increasing amounts of Hg(2+) ions has resulted in a gradual red-shift and broadening of the longitudinal plasmon band, up to 900 nm. Interestingly, a significantly different response has been recorded for the other tested ions. In fact, no significant shift in the longitudinal plasmon band has been observed for any of them, while a nearly linear reduction in the plasmon band intensity versus ion concentration in solution has been detected. The very high sensitivity for Hg(2+) with respect to other investigated ions, with a limit of detection of 3 ppt, demonstrates that the functionalization of Au NRs with PyL is a very effective method to be implemented in a reliable colorimetric sensing device, able to push further down the detection limit achieved by applying similar strategies to spherical Au NPs.

High quality CdS nanocrystals: surface effects

Stable and highly luminescent CdS nanocrystals (NCs) have been synthesized by means of decomposition of suitable precursors (CdO and elemental sulphur) in octadecene (ODE) and oleic acid at high temperature. Absorption and steady state photoluminescence (PL) measurements have been carried out to study the intrinsic properties of nanocrystals and the effect of ligand and solvent on emission properties. Ageing of nanocrystals has been investigated, and an efficient mechanism of emission recovery has been identified, showing the active role of non coordinating solvent and oleic acid in modifying the surface states.

Colloidal Inorganic Nanocrystal Based Nanocomposites: Functional Materials for Micro and Nanofabrication

The unique size- and shape-dependent electronic properties of nanocrystals (NCs) make them extremely attractive as novel structural building blocks for constructing a new generation of innovative materials and solid-state devices. Recent advances in material chemistry has allowed the synthesis of colloidal NCs with a wide range of compositions, with a precise control on size, shape and uniformity as well as specific surface chemistry. By incorporating such nanostructures in polymers, mesoscopic materials can be achieved and their properties engineered by choosing NCs differing in size and/or composition, properly tuning the interaction between NCs and surrounding environment. In this contribution, different approaches will be presented as effective opportunities for conveying colloidal NC properties to nanocomposite materials for micro and nanofabrication. Patterning of such nanocomposites either by conventional lithographic techniques and emerging patterning tools, such as ink jet printing and nanoimprint lithography, will be illustrated, pointing out their technological impact on developing new optoelectronic and sensing devices.

Photodegradation of nalidixic acid assisted by TiO2 nanorods/Ag nanoparticles based catalyst

Two different nanosized TiO2-based catalysts supported onto glass with tailored photocatalytic properties upon irradiation by UV light were successfully employed for the degradation of nalidixid acid, a widely diffused antibacterial agent of environmental relevance known to be non-biodegradable. Anatase rod-like TiO2 nanocrystals (TiO2NRs) and a semiconductor oxide-noble metal nanocomposite TiO2 NRs/Ag nanoparticles (NPs), synthesized by colloidal chemistry routes, were cast onto glass slide and employed as photocatalysts. A commercially available catalyst (TiO2 P25), also immobilized onto a glass slide, was used as a reference material. It was found that both TiO2 NRs/Ag NPs composite and TiO2 NRs demonstrated a photocatalytic efficiency significantly higher than the reference TiO2 P25. Specifically, TiO2 NRs/Ag NPs showed a photoactivity in nalidixic acid degradation 14 times higher than TiO2 P25 and 4 times higher than bare TiO2 NRs in the first 60min of reaction. Several by-products were identified by HPLC-MS along the nalidixic acid degradation, thus getting useful insight on the degradation pathway. All the identified by-products resulted completely removed after 6h of reaction.

Biofunctionalization of anisotropic nanocrystalline semiconductor-magnetic heterostructures.

Asymmetric binary nanocrystals (BNCs) formed by a spherical γ-Fe(2)O(3) magnetic domain epitaxially grown onto a lateral facet of a rodlike anatase TiO(2) nanorod have been functionalized with PEG-terminated phospholipids, resulting in a micellar system that enables the BNC dispersion in aqueous solution. The further processability of the obtained water-soluble BNC including PEG lipid micelles and their use in bioconjugation experiments has been successfully demonstrated by covalently binding to bovine serum albumin (BSA). The whole process has also been preliminarily performed on spherical iron oxide nanocrystals (NCs) and TiO(2) nanorods (NRs), which form single structural units in the heterostructures. Each step has been thoroughly monitored by using optical, structural, and electrophoretic techniques. In addition, an investigation of the magnetic behavior of the iron oxide NCs and BNCs, before and after incorporation into PEG lipid micelles and subsequently bioconjugation, has been carried out, revealing that the magnetic characteristics are mostly retained. The proposed approach to achieving water-soluble anisotropic BNCs and their bioconjugates has a large potential in catalysis and biomedicine and offers key functional building blocks for biosensor applications.

Luminescent nanocrystals in phospholipid micelles for bioconjugation : An optical and structural investigation

Organic capped luminescent CdSe@ZnS nanocrystals (NCs) have been incorporated in block copolymer micelles, formed by polyethylene glycol modified phospholipids (PEG lipids). The obtained water soluble NC including PEG lipid micelles have been conjugated with bovine serum albumine (BSA). The entire process has been investigated by using optical, structural and electrophoretic complementary techniques. Such an integrated approach has allowed to elucidate critical issues, such as the time and temperature effects on the phase behavior of the PEG lipid/NC aggregate structures, the emitting properties of the NCs before and after micelle formation and bio-conjugation and the effect of conjugation on the biological moiety. The overall results provide relevant insight on the fabrication of the bio-conjugates, on their stability and on preparative procedure reproducibility, in view of the use of the resulting protein decorated NCs as multifunctional hybrid building blocks for the fabrication of a variety of supramolecular assemblies to exploit in biological sensing and diagnostic applications.

Photoactive Hybrid Material Based on Pyrene Functionalized PbS Nanocrystals Decorating CVD Monolayer Graphene

A simple and facile solution-based procedure is implemented for decorating a large area, monolayer graphene film, grown by chemical vapor deposition, with size-tunable light absorbing colloidal PbS nanocrystals (NCs). The hybrid is obtained by exposing a large area graphene film to a solution of 1-pyrene butyric acid surface coated PbS NCs, obtained by a capping exchange procedure onto presynthesized organic-capped NCs. The results demonstrate that at the interface, multiple and cooperative π-π stacking interactions promoted by the pyrene ligand coordinating the NC surface lead to a successful anchoring of the nano-objects on the graphene platform which concomitantly preserves its aromatic structure. Interligand interactions provide organization of the nano-objects in highly interconnected nanostructured multilayer coatings, where the NCs retain geometry and composition. The resulting hybrid exhibits a sheet resistance lower than that of bare graphene, which is explained in terms of electronic communication in the hybrid, due to the interconnection of the NC film and to a hole transfer from photoexcited PbS NCs to graphene, channelled at the interface by pyrene. Such a direct electron coupling makes the manufactured hybrid material an interesting component for optoelectronics, sensors and for optical communication and information technology.

Electroactive layer-by-layer plasmonic architectures based on Au nanorods.

Nanostructured films based on Au nanorods (NRs) have been obtained by layer-by-layer (LbL) assembly driven by electrostatic interaction between metal nanoparticles and polyelectrolytes. Multilayer films have been fabricated by using LbL assembly of poly(sodium styrenesulfonate) (PSS) and positively charged Au NRs on a polyelectrolyte-modified substrate. The effect of fabrication parameters, including the nature of the substrate, the polyelectrolyte initial anchoring layer, and the number of layers has been investigated by means of UV-vis absorbance spectroscopy and atomic force microscopy (AFM). The results demonstrated the dependence of morphology and plasmonic features in the multilayered nanostructured architectures from the nature of the anchoring polyelectrolyte on the substrate, the number of layers, and the kind of NR mutual assembly. In addition, a study of the electrochemical activity at the solid/liquid interface has been carried out in order to assess charge transport through the NR multilayer by using two molecular probes in solution, namely, potassium ferricyanide, a common and well-established redox mediator with reversible behavior, and cytochrome C, a robust model redox protein. The presented systematic study of the immobilization of Au NRs opens the venue to several application areas, such as (bio)chemical sensing.