Gianvito Caputo

Electron diffractive imaging of oxygen atoms in nanocrystals at sub-ångström resolution

High-resolution imaging of low-atomic-number chemical elements using electron microscopy is challenging and may require the use of high doses of electrons. Electron diffractive imaging, which creates real-space images using diffraction intensities and phase retrieval methods, could overcome such issues, although it is also subject to limitations. Here, we show that a combination of electron diffractive imaging and high-resolution transmission electron microscopy can image individual TiO(2) nanocrystals with a resolution of 70 pm while exposing the specimen to a low dose of electrons. Our approach, which does not require spherical and chromatic aberration correction, can reveal the location of light atoms (oxygen) in the crystal lattice. We find that the unit cell in nanoscale TiO(2) is subtly different to that in the corresponding bulk.

Light-controlled directional liquid drop movement on TiO2 nanorods-based nanocomposite photopatterns.

Patterned polymeric coatings enriched with colloidal TiO(2) nanorods and prepared by photopolymerization are found to exhibit a remarkable increase in their water wettability when irradiated with UV laser light. The effect can be completely reversed using successive storage in vacuum and dark ambient environment. By exploiting the enhancement of the nanocomposites hydrophilicity upon UV irradiation, we prepare wettability gradients along the surfaces by irradiating adjacent surface areas with increasing time. The gradients are carefully designed to achieve directional movement of water drops along them, taking into account the hysteresis effect that opposes the movement as well as the change in the shape of the drop during its motion. The accomplishment of surface paths for liquid flow, along which the hydrophilicity gradually increases, opens the way to a vast number of potential applications in microfluidics.

Determination of surface properties of various substrates using TiO2 nanorod coatings with tunable characteristics

We present a novel approach to cover different substrates with thin light-sensitive layers that consist of organic-capped TiO2 nanorods (NRs). Such NR-based coatings exhibit an increasing initial hydrophobicity with increasing NR length, and they demonstrate a surface transition from this highly hydrophobic state to a highly hydrophilic one under selective UV–laser irradiation. This behaviour is reversed under long dark storage. Infrared spectroscopy measurements reveal that light-driven wettability changes are accompanied by a progressive hydroxylation of the TiO2 surface. The surfactant molecules that cover the NRs do not appear to suffer for any significant photocatalytic degradation.

Optically controlled liquid flow in initially prohibited elastomeric nanocomposite micro-paths

The significant increment of TiO2 surface wettability upon UV irradiation makes it a promising component of materials or systems with tunable surface wetting characteristics. This remarkable property of TiO2 is retained in the nanocomposite materials developed for this work, which consist of the elastomer PDMS enriched with organic-capped nanorods of TiO2. In particular, the nanocomposites demonstrate a surface transition from a hydrophobic state to a hydrophilic one under selective pulsed UV laser irradiation. This wettability change is reversible, with the hydrophobic character of the nanocomposites being fully recovered after a couple of days of samples storage in moderate vacuum. The hydrophobic-to-hydrophilic transition and recovery can be repeated tens of times on the same sample without any apparent fatigue. As verified by XPS and AFM analysis, the wettability enhancement is exclusively attributed to the TiO2 nanorods exposed on the nanocomposite surface. The tuning of the surface wettability properties of the PDMS/TiO2 materials, together with the easy processability of this elastomer, opens the way to the realization of microfluidic devices with controlled liquid flow. We demonstrate the potentiality of such systems by fabricating microfluidic channels with walls of PDMS and PDMS/TiO2 nanorods composite materials. The combination of the used geometry with the hydrophobic character of both the pure and nanocomposite PDMS prohibits the penetration of water in their developed microchannels. After UV irradiation, water penetration is allowed inside the irradiated nanocomposite microfluidic channels, whereas it is still forbidden after the irradiation of the bare PDMS microchannels, revealing the essential role of the TiO2 nanofillers.

Advances in the Chemical Fabrication of Complex Multimaterial Nanocrystals

In this work, recent achievements of nanochemistry research in the fabrication of colloidal nanoheterostructures are reviewed through revisiting relevant papers and related patents. Attention is focused on newly conceived generations of hybrid nanocrystals (HNCs) with a topologically controlled composition, in which size and shape tailored domains of different inorganic materials are permanently assembled together in a single multifunctional particle. Strategies for accessing HNCs in various configurations, such as core/shell systems, hetero-oligomers based on nearly spherical portions, and highly asymmetric nanostructures comprising joint sections with different shapes, are discussed. The chemical-physical properties and technological advantages offered by such complex nanocrystals are also highlighted.

Thermal and Mechanical Characterization of PMMA TiO2 Nanocomposites

Hybrid composite films made of an organic polymeric matrix and an inorganic nanosized filler, namely titania prolate nanoparticles, have been prepared and characterized both thermally and mechanically. The filler content has been varied, while still being kept in the regime of unsaturated, homogeneous nanocomposites. On increasing, the filler content there is an abrupt increase in hardness at an intermediate load, while the elastic modulus increases almost linearly. The glass transition temperature is also increased, with a tendency to saturation. The morphological characterization of the films confirms a lack of phase separation, with only a continuous, slight increase in surface roughness, and no major effects on the top film features.

Controlled Swapping of Nanocomposite Surface Wettability by Multilayer Photopolymerization

Single-layered photopolymerized nanocomposite films of polystyrene and TiO(2) nanorods change their wetting characteristics from hydrophobic to hydrophilic when deposited on substrates with decreasing hydrophilicity. Interestingly, the addition of a second photopolymerized layer causes a swapping in the wettability, so that the final samples result converted from hydrophobic to hydrophilic or vice versa. The wettability characteristics continue to be swapped as the number of photopolymerized layers increases. In fact, odd-layered samples show the same wetting behavior as single-layered ones, while even-layered samples have the same surface characteristics as double-layered ones. Analytical surface studies demonstrate that all samples, independently of the number of layers, have similar low roughness, and that the wettability swap is due to the different concentration of the nanocomposites constituents on the samples surface. Particularly, the different interactions between the hydrophilic TiO(2) nanorods and the underlying layer lead to different amounts of nanorods exposed on the nanocomposites surface. Moreover, due to the unique property of TiO(2) to reversibly increase its wettability upon UV irradiation and subsequent storage, the wetting characteristics of the multilayered nanocomposites can be tuned in a reversible manner. In this way, a combination of substrate, number of photopolymerized layers, and external UV light stimulus can be used in order to precisely control the surface wettability properties of nanocomposite films, opening the way to a vast number of potential applications in microfluidics, protein assays, and cell growth.

Titanate Fibroin Nanocomposites: A Novel Approach for the Removal of Heavy-Metal Ions from water

In this study, we report the fabrication of nanocomposites made of titanate nanosheets immobilized in a solid matrix of regenerated silk fibroin as novel heavy-metal-ion removal systems. The capacity of these nanocomposite films to remove lead, mercury, and copper cations from water was investigated, and as shown by the elemental quantitative analysis performed, their removal capacity is 73 mmol/g for all of the ions tested. We demonstrate that the nanocomposites can efficiently retain the adsorbed ions, with no release of titanate nanosheets occurring even after several exposure cycles to ionic solutions, eliminating the risk of release of potentially hazardous nanosubstances to the environment. We also prove that the introduction of sodium ions in the nanocomposite formulation makes the materials highly selective toward the lead ions. The developed biopolymer nanocomposites can be potentially used for the efficient removal of heavy-metal-ion pollutants from water and, thanks to their physical and optical characteristics, offer the possibility to be used in sensor applications.

Light Responsive Silk Nanofibers: An Optochemical Platform for Environmental Applications

Photochromic spiropyran-doped silk fibroin poly(ethylene oxide) nanofibers which combine the attractive properties and biocompatibility of silk with the photocontrollable and reversible optical, mechanical, and chemical response of the spiropyran dopants are herein presented. As proved, the reversible variation of the absorption and emission signals of the mats and of their Youngs modulus upon alternate UV and visible light irradiation is ascribed to the reversible photoconversion of the spiropyran form to its polar merocyanine counterpart. Most importantly, the interactions of the merocyanine molecules with acidic vapors as well as with heavy metal ions dispersed in solution produce analyte-specific spectral changes in the emission profile of the composite, accompanied by a characteristic chromic variation. Because of the high surface-to-volume ratio of the nanofibrous network, such interactions are fast, thus enabling both an optical and a visual detection in a 30-60 s time scale. The sensing platform can be easily regenerated for more than 20 and 3 cycles upon acid or ion depletion, respectively. Overall, the photocontrolled properties of the silk composites combined with a straightforward preparation method render them suitable as porous materials and scaffolds with tunable compliance and reusable nanoprobes for real time optical detection in biomedical, environmental, and industrial applications.

Reversible wettability of hybrid organic/inorganic surfaces of systems upon light irradiation/storage cycles

In this work we present hybrid organic/inorganic structures that can exhibit reversible surface wettability, altered in a controllable manner. In particular, we use the method of photo-patterning to produce polymeric SU-8 pillars of specific geometries, onto which we subsequently deposit colloidal TiO2 nanorods. In this way, we combine the microroughness of the polymeric pillars with the nanoroughness of the nanorod-coating to create highly hydrophobic surfaces. The hydrophobicity of these systems can be changed reversibly into hydrophilicity upon irradiation of the hybrid structures with pulsed UV laser light. This behaviour is due to the well-known property of TiO2, that becomes superhydrophilic upon UV light irradiation. This