Colloidal semiconductor nanocrystals are among the best candidates for realizing a nano-structured single photon source at room temperature. In this paper we present a new and efficient optical method to assess the quality of a sample of nanocrystals as single-photon emitters, by an ensemble measurement of photoluminescence. We relate the ensemble photoluminescence measurements to the photon statistics of single emitters by a simple theoretical model. As an example we compare two different kinds of CdSe/CdS dot-in-rods, showing a similar degree of single photon emission when observed on a selection of single nanocrystals. The results are compared with anti-bunching measurements realized on single nanocrystals of the two kinds.

A colloidal nonaqueous approach to semiconductor−magnetic hybrid nanocrystals (HNCs) with selectable heterodimer topologies and tunable geometric parameters is demonstrated. Brookite TiO2 nanorods, distinguished by a curved shape-tapered profile with richly faceted terminations, are exploited as substrate seeds onto which a single spherical domain of inverse spinel iron oxide can be epitaxially grown at either one apex or any location along their longitudinal sidewalls in a hot surfactant environment. The topologically controlled arrangement of the component material lattices, the crystallographic relationships holding between them, and strain distribution across individual heterostructures have been studied by combining X-ray diffraction and absorption techniques with high-resolution transmission electron microscopy investigations. Supported by such structural knowledge, the synthetic achievements are interpreted within the frame of various mechanistic models offering complementary views of HNC formation. The different HNC architectures are concluded to be almost equivalent in terms of surface−interface energy balance associated with their formation. HNC topology selection is rationalized on the basis of a diffusion-limited mechanism allowing iron oxide heterogeneous nucleation and growth on the TiO2 nanorods to switch from a thermodynamically controlled to a kinetically overdriven deposition regime, in which the anisotropic reactivity offered by the uniquely structured seeds is accentuated under high spatially inhomogeneous monomer fluxes. Finally, the multifunctional capabilities of the heterostructures are highlighted through illustration of their magnetic and photocatalytic properties, which have been found to diverge from those otherwise exhibited by their individual material components and physical mixture counterparts.

In this work we report on the self-assembly of monodisperse iron oxide nanocrystals on silica-coated Au surfaces achieved by magnetic field-assisted solution deposition techniques and discuss the effects of the interactions that contribute to promote their ordered arrangement into small clusters, chain-like structures or high-density particle multilayer superlattices. The results highlight the roles of inter-particle and nanocrystal-substrate interactions in controlling the nucleation and growth of self-assembled clusters and superstructures made of spherical magnetic nanocrystals.

Colloidal inorganic nanocrystals (NCs) constitute an important class of advanced nanomaterials owing to the flexibility with which their dimensionality-dependent physical–chemical properties can be controlled by engineering their compositional, structural, and geometric features in the synthesis stage and the versatility with which they can be exploited in disparate technological fields, spanning from optoelectronics, energy conversion/production to catalysis, and biomedicine. In recent years, building upon knowledge acquired on the thermodynamic and kinetic processes that underlie NC evolution in liquid media, synthetic nanochemistry research has made tremendous advances, opening new possibilities for designing, creating, and mastering increasingly complex NC-based assemblies, in which sections of different materials are grouped together into free-standing, easily processable multifunctional nanocomposite systems. This chapter will provide an overview of this fast-growing research field by illustrating progress achieved in the wet-chemical development of last-generation breeds of so-called hybrid or heterostructured nanocrystals (HNCs) in asymmetric non-core/shell geometries, in which distinct material modules are interconnected in heterodimer, heterooligomer, and anisotropic multidomain architectures via heteroepitaxial bonding interfaces of limited extension. The focus will be on HNCs that incorporate at least one magnetic material component combined with semiconductors and/or plasmonic metals, which hold potential for generating enhanced, unconventional magnetic behavior, on one side, and diversified or even new properties and capabilities, on the other side. Various synthetic strategies, all based on the manipulation of seeded-growth techniques, will be described and rationally interpreted within the framework of the currently understood mechanisms of colloidal heteroepitaxy.

Inorganic nanomaterials represent unique solid-state platforms on which unusual optoelectronic, magnetic chemical, and catalytic properties can be manipulated, tuned, and even allowed to coexist and exchange-couple, holding considerable potential for both fundamental studies and practical applications in optoelectronics, energy technologies, catalysis, and biomedicine. Among the available synthetic approaches, colloidal techniques stand out as powerful routes to nanocrystals with programmable composition, crystal structure, geometry, and surface functionalities. Knowledge of thermodynamic and kinetic growth conditions and processes underlying monophasic nanocrystal evolution in liquid media has triggered significant advances in these fabrication tools, paving the way to increasingly sophisticate multifunctional hybrid nanoarchitectures, in which sections of different materials are assembled together as free-standing, easily processable all-inorganic nanoheterostructures. In this chapter we will illustrate recent progress made in the wet-chemical development and characterization of last-generation breeds of colloidal heterostructured nanocrystals (HNCs), in which distinct material modules are interconnected via direct bonding (heteroepitaxial) interfaces in elaborate onion-like or oligomer-type topologies. Emphasis will be put on HNCs that entail at least one magnetic material component, combined with semiconductors and/or plasmonic metals as a means of generating enhanced, unconventional magnetic behavior as well as diversified properties and capabilities. Diverse synthetic strategies, all based on manipulation of seeded-growth techniques, will be described and interpreted within the framework of the relevant heteroepitaxial deposition mechanisms that enable topological selection of HNCs with selected spatial configurations.

Hybrid nanocrystals (HNCs), based on ZnO nanorods (NRs) decorated with magnetic Fe-based domains, were synthesized via a colloidal seeded-growth method. The approach involved heterogeneous nucleation of Fe nanocrystals on size-tailored ZnO nanorod seeds in a noncoordinating solvent, followed by partial surface oxidation of the former to the corresponding Fe@FexOy core@shell domains. HNCs with variable population and size of the Fe-based nanodomains could be synthesized depending on the surface reactivity of the ZnO seeds. The structure–property relationships in these HNCs were carefully studied. In HNCs characterized by a large number of small Fe@FexOy core@shell nanodomains on the ZnO seed surface, the interfacial communication across the Fe-core and FexOy-shell generated a sizable exchange-bias effect mediated by frozen interfacial spins. On the other hand, in HNCs carrying a lower density of comparatively larger Fe@FexOy domains, partial removal of the Fe-core created an inner void in between that led to suppressed exchange coupling anisotropy. As a further proof of functionality, the HNCs exhibited pronounced band-edge ultraviolet fluorescence. The latter was blue-shifted compared to the parent ZnO NRs, inferring coupling of the semiconductor and magnet sections.

Suitable postsynthesis surface modification of lead-chalcogenide quantum dots (QDs) is crucial to enable their integration in photovoltaic devices. Here we exploit arenethiolate anions to completely replace pristine oleate ligands on PbS QDs in the solution phase, thus preserving the colloidal stability of QDs and allowing their solution-based processability into photoconductive thin films. Complete QD surface modification relies on the stronger acidic character of arenethiols compared to that of alkanethiols and is demonstrated by FTIR and UVvisNIR absorption spectroscopy analyses, which provide quantitative evaluation of stoichiometry and thermodynamic stability of the resulting system. Arenethiolate ligands induce a noticeable reduction of the optical band gap of PbS QDs, which is described and explained by charge transfer interactions occurring at the organic/inorganic interface that relax exciton confinement, and a large increase of QD molar absorption coefficient, achieved through the conjugated moiety of the replacing ligands. In addition, surface modification in the solution phase promotes switching of the symmetry of PbS QD self-assembled superlattices from hexagonal to cubic close packing, which is accompanied by further reduction of the optical band gap, ascribed to inter-QD exciton delocalization and dielectric effects, together with a drastic improvement of the charge transport properties in PbS QD solids. As a result, smooth dense-packed thin films of arenethiolate-capped PbS QDs can be integrated in heterojunction solar cells via a single solution-processing step. Such single PbS QD layers exhibit abated cracking upon thermal or chemical postdeposition treatment, and the corresponding devices generate remarkable photocurrent densities and overall efficiencies, thus representing an effective strategy toward low-cost processing for QD-based photovoltaics.

One frontier approach of colloidal chemistry to nanoscale entities capable to exhibit enhanced or even unconventional physical–chemical properties as well as diversified capabilities for multitask applications envisages fabrication of breed-new hybrid nanocrystals (HNCs) with a spatially controlled distribution of their chemical composition. These are all-inorganic multicomponent nanoheterostructures in which domains of distinct materials are arranged via permanent bonding interfaces in elaborate concentric/eccentric onion-like or oligomer-type architectures. This review covers recent progress achieved in the wet-chemical development of HNCs based on functional associations of semiconductors, metals and magnetic compounds. Within the frame of seeded-growth techniques to heteroepitaxial deposition in solution media, relevant synthetic strategies are illustrated, along with systematic examination of the mechanisms by which heterostructures can be selectively accessed in nonequivalent topological configurations. The peculiar properties and technological perspectives offered by such novel generations of complex nanomaterials are also succinctly highlighted.

Colloidal inorganic nanocrystals, free-standing crystalline nanostructures generated and processed in solution phase, represent an important class of advanced nanoscale materials owing to the flexibility with which their physical–chemical properties can be controlled through synthetic tailoring of their compositional, structural and geometric features and the versatility with which they can be integrated in technological fields as diverse as optoelectronics, energy storage/ conversion/production, catalysis and biomedicine. In recent years, building upon mechanistic knowledge acquired on the thermodynamic and kinetic processes that underlie nanocrystal evolution in liquid media, synthetic nanochemistry research has made impressive advances, opening new possibilities for the design, creation and mastering of increasingly complex “colloidal molecules”, in which nanocrystal modules of different materials are clustered together via solid-state bonding interfaces into free-standing, easily processable multifunctional nanocomposite systems. This Review will provide a glimpse into this fast-growing research field by illustrating progress achieved in the wet-chemical development of last-generation breeds of all-inorganic heterostructured nanocrystals (HNCs) in asymmetric non-onionlike geometries, inorganic analogues of polyfunctional organic molecules, in which distinct nanoscale crystalline modules are interconnected in hetero-dimer, hetero-oligomer and anisotropic multidomain architectures via epitaxial heterointerfaces of limited extension. The focus will be on modular HNCs entailing at least one magnetic material component combined with semiconductors and/or metals, which hold potential for generating enhanced or unconventional magnetic properties, while offering diversified or even new chemical-physical properties and functional capabilities. The available toolkit of synthetic strategies, all based on the manipulation of seeded-growth techniques, will be described, revisited and critically interpreted within the framework of the currently understood mechanisms of colloidal heteroepitaxy.

Excitation of lattice vibrations in nanostructured anatase TiO2 frequently occurs at energy values differing from that found for the corresponding bulk phase. Particularly, investigations have long aimed at establishing a correlation between the low-frequency E-g(1) mode and the mean crystallite size on the basis of phonon-confinement models. Here, we report a detailed Raman study, supported by X-ray diffraction analyses, on anatase TiO2 nanocrystals with rod-shaped morphology and variable geometric parameters, prepared by colloidal wet-chemical routes. By examining the anomalous shifts of the E-g(1) mode in the spectra of surfactant-capped nanorods and in those of corresponding organic-free derivatives (obtained by a suitable thermal oxidative treatment), an insight into the impact of exposed facets and of the coherent crystalline domain size on Raman-active lattice vibrational modes has been gained. Our investigation offers a ground for clarifying the current lack of consensus as to the applicability of phonon-confinement models for drawing information on the size of surface-functionalized TiO2 nanocrystals upon analysis of their Raman features.

We present an alternative approach for controlling the water adhesion on solid superhydrophobic surfaces by varying their coverage with a spray coating technique. In particular, micro-, submicro-, and nanorough surfaces were developed starting from photolithographically tailored SU-8 micropillars that were used as substrates for spraying first poly(tetrafluoroethylene) submicrometer particles and subsequently iron oxide nanoparticles. The sprayed particles serve to induce surface submicrometer and nanoscale roughness, rendering the SU-8 patterns superhydrophobic (apparent contact angle values of more than 150°), and also to tune the water adhesion between extreme states, turning the surfaces from “non-sticky” to “sticky” while preserving their superhydrophobicity. The influence of the chemical properties and of the geometrical characteristics of the functionalized surfaces on the wetting properties is discussed within the frame of the theory. This simple method can find various applications in the fabrication of microfluidic devices, smart surfaces, and biotechnological and antifouling materials.

Single-layered photopolymerized nanocomposite films of polystyrene and TiO2 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 TiO2 nanorods and the underlying layer lead to different amounts of nanorods exposed on the nanocomposites surface. Moreover, due to the unique property of TiO2 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.

Monodisperse cubic spinel iron oxide magnetic nanoparticles with variable sizes were prepared following a multi-injection seeded-growth approach. As expected from such a well-known synthetic route, all samples were characterized by narrow size distributions, and showed excellent stability in both organic and aqueous media without the presence of aggregates, thus becoming ideal candidates for the study of their hyperthermia performance. Specific Loss Power measurements indicated low heating powers for all samples without a maximum for any specific size, contrary to what theory predicts. The magnetic study showed the formation of size-dependent nonsaturated magnetic regions, which enlarged with the particle size, evidencing a clear discrepancy between the crystal size and the effective magnetic volume. Strain map analysis of high resolution transmission electron micrographs indicated the presence of highly strained crystal areas even if nanoparticles were monocrystalline. The origin of the crystal strain was found to be strictly correlated with the seeded-growth synthetic procedure used for the preparation of the nanoparticles, which turned out to alter their magnetic structure by creating antiphase boundaries. Considering the calculated effective magnetic volumes and their magnetic dispersions in each sample, a reasonable agreement between hyperthermia experiments and theory was obtained.

We demonstrate the fabrication of nanocomposite coatings, of organic-capped colloidal TiO2 nanorods dispersed into a poly(methyl methacrylate) matrix, with rising value of refractive index from the bottom to the top layers, and UV-induced surface wettability alteration, in a reversible manner. This behaviour is attributable to preferential dispersion of the TiO2 nanoparticles towards the superficial layers of the coatings. Above a critical TiO2 loading, the nanorods at the surface form aggregates deteriorating the optical and the surface properties of the nanocomposites. The optimal conditions for nanocomposite films preparation in terms of optimized nanorods dispersion, optical clarity, and surface smoothness are determined.

We present a simple technique for magnetic-field-induced formation, assembling, and positioning of magnetic nanowires in a polymer film. Starting from a polymer/iron oxide nanoparticle casted solution that is allowed to dry along with the application of a weak magnetic field, nanocomposite films incorporating aligned nanocrystal-built nanowire arrays are obtained. The control of the dimensions of the nanowires and of their localization across the polymer matrix is achieved by varying the duration of the applied magnetic field, in combination with the evaporation dynamics. These multifunctional anisotropic free-standing nanocomposite films, which demonstrate high magnetic anisotropy, can be used in a wide field of technological applications, ranging from sensors to microfluidics and magnetic devices.

Three families of linear shaped TiO2 anatase nanocrystals with variable aspect ratio (4, 8, 16) and two sets of branched TiO2 anatase nanocrystals (in the form of open-framework sheaf-like nanorods and compact braid-like nanorod bundles, respectively) were employed to fabricate high-quality mesoporous photoelectrodes and then implemented into dye-sensitized solar cells to elucidate the intrinsic correlation holding between the photovoltaic performances and the structure of the nanocrystal building blocks. To this aim, the chemical capacitance and the charge-transfer resistance of the photoelectrodes were extrapolated from electrochemical impedance spectroscopy measurements and used to draw a quantitative energy diagram of the dye-sensitized solar cells realized, on the basis of which their photovoltaic performances have been discussed. It has thus been revealed that photoanodes made from braid-like branched-nanorod bundles exhibited the most favorable conditions to minimize recombination at the interface with the electrolyte due to their deep distribution of trap states, whereas linear-shaped nanorods with higher aspect-ratios result in more remarkable downshift of the conduction band edge.

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 TiO2 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 TiO2 is subtly different to that in the corresponding bulk.

Brookite titanium dioxide (TiO2) nanorods, synthesized by a surfactant-assisted aminolysis route, were used as precursors for the fabrication of thin films by using the matrix-assisted pulsed-laser deposition (MAPLE) technique. Thin films with controllable thickness were grown on a variety of substrates for different characterizations. High-resolution scanning and transmission electron microscopy investigations evidenced the formation of rough TiO2 films incorporating individually distinguishable nanocrystals with different shapes. Suitable alumina substrates equipped with interdigitated electrical contacts (IDC) and heating elements were used to fabricate gas-sensing devices based on resistive transduction mechanism. Electrical characterization measurements in controlled environment were carried out. Typical gas sensor parameters (such as gas response, sensitivity, stability and detection limit) towards selected oxidizing and reducing gases, namely NO2 and CO, respectively, were extracted in dark condition. Very interesting optically activated enhancement of the response towards NO2 oxidizing gas was achieved in controlled atmosphere upon irradiating the sensing layer with UV light with low energy close to the TiO2 sensing layer band-gap width.

A three-dimensional (3D) ordered superlattice of colloidal iron oxide nanocrystals obtained by magnetic-field-assisted self-assembly has been studied by grazing incidence small-angle X-ray scattering (GISAXS). A new model to simulate and interpret GISAXS patterns is presented, which returns the structural and morphological details of 3D nanocrystal-built supercrystals. The model is applied to a sample with a suitable surface morphology, allowing the observation of “volume diffraction” even at extremely low grazing incidence angle. In this particular case, the average fcc-like stacking of the nanocrystals (building blocks), their spherical shape, and statistical information on their size distribution and positions within the superlattice have been safely deduced. The proposed model is expected to be amendable for the analysis of more complex structures and applicable to a large variety of nanocrystal-based assemblies.

We demonstrate the fabrication of all-inorganic heterostructured n–p junction devices made of colloidal PbS quantum dots (QDs) and TiO2 nanorods (NRs). The entire device fabrication procedure relies on room-temperature processing, which is compatible with flexible plastic substrates and low-cost production. Through Kelvin Probe Force Microscopy and femtosecond pump and probe spectroscopy we decipher the electron transfer process occurring at the interface between the colloidal PbS QDs and TiO2 anatase NRs. Overall we demonstrate a high power conversion efficiency of [similar]3.6% on glass and [similar]1.8% on flexible substrates, which is among the highest reported for entirely inorganic-nanocrystal based solar cells on plastic supports.

Titanium dioxide (TiO2) nanorods in the brookite phase, with average dimensions of 3–4 nm × 20–50 nm, were synthesized by a wet-chemical aminolysis route and used as precursors for thin films that were deposited by the matrix-assisted pulsed laser evaporation (MAPLE) technique. A nanorod solution in toluene (0.016 wt% TiO2) was frozen at the liquid-nitrogen temperature and irradiated with a KrF excimer laser at a fluence of 350 mJ/cm2 and repetition rate of 10 Hz. Single-crystal Si wafers, silica slides, carbon-coated Cu grids and alumina interdigitated slabs were used as substrates to allow performing different characterizations. Films fabricated with 6000 laser pulses had an average thickness of ∼150 nm, and a complete coverage of the selected substrate as achieved. High-resolution scanning and transmission electron microscopy investigations evidenced the formation of quite rough films incorporating individually distinguishable TiO2 nanorods and crystalline spherical nanoparticles with an average diameter of ∼13 nm. Spectrophotometric analysis showed high transparency through the UV-Vis spectral range. Promising resistive sensing responses to 1 ppm of NO2 mixed in dry air were obtained.

We demonstrate the fabrication of polymeric membranes that incorporate a few layers of periodically aligned magnetic microchains formed upon the application of variable magnetic fields. A homogeneous solution containing an elastomeric polymer and a small amount of colloidal magnetic nanoparticles is spin coated on glass slides, thereby forming thin magnetic membranes of ca. 10 μm thickness. Subsequent application of a homogeneous magnetic field results in the orientation of the magnetic clusters and their further motion into the matrix along the field lines forming layers of aligned chains. The study of the kinetics of alignment demonstrates that the chains are formed in the first hour of exposure to the magnetic field. Above all, a detailed microscopy study reveals that the dimensions and the periodicity of the microchains are effectively controlled by the intensity of the magnetic field, in good agreement with the theoretical simulations. This ability to form and manipulate the size and the distribution of chains into the polymeric matrix gives the opportunity to develop multifunctional composite materials ready to be used in various applications such as electromagnetic shielding, or multifunctional magnetic membranes etc.

We demonstrate a general approach by which colloidal anatase TiO2 nanocrystals with anisotropically tailored linear and branched shapes can safely be processed into high-quality mesoporous photoelectrodes for dye-sensitized solar cells (DSSCs). A detailed study has been carried out to elucidate how the nanoscale architecture underlying the photoelectrodes impacts their ultimate performances. From the analysis of the most relevant electrochemical parameters,an intrinsic correlation between the photovoltaic performances and the structure of the nanocrystal building blocks has been deduced and explained on the basis of relative contributions of the electron transport and light-harvesting properties of the photoelectrodes. Depending on the nanocrystals incorporated,these devices can exhibit an energy conversion efficiency of 5.2% to 7.8%,which ranks 38% to 53% higher than that achievable with corresponding cells based on reference spherical nanoparticles. It has been ascertained that DSSCs based on high aspect-ratio linear nanorods allow for a remarkable improvement in the charge-collection efficiency due to minimization of detrimental charge-recombination processes at the photoelectrode/electrolyte interface. On the other hand,DSSCs fabricated from branched nanocrystals with a peculiar bundle-like configuration are characterized by a drastic reduction of undesired charge-trapping phenomena. These findings can be useful in the design and fabrication of future generations of high-performing DSSCs based on colloidal nanocrystals with properly engineered size and shape parameters.

A colloidal crystal-splitting growth regime has been accessed, in which TiO2 nanocrystals, selectively trapped in the metastable anatase phase, can evolve to anisotropic shapes with tunable hyperbranched topologies over a broad size interval. The synthetic strategy relies on a nonaqueous sol–gel route involving programmed activation of aminolysis and pyrolysis of titanium carboxylate complexes in hot surfactant media via a simple multi-injection reactant delivery technique. Detailed investigations indicate that the branched objects initially formed upon the aminolysis reaction possess a strained monocrystalline skeleton, while their corresponding larger derivatives grown in the subsequent pyrolysis stage accommodate additional arms crystallographically decoupled from the lattice underneath. The complex evolution of the nanoarchitectures is rationalized within the frame of complementary mechanistic arguments. Thermodynamic pathways, determined by the shape-directing effect of the anatase structure and free-energy changes accompanying branching and anisotropic development, are considered to interplay with kinetic processes, related to diffusion-limited, spatially inhomogeneous monomer fluxes, lattice symmetry breaking at transient Ti5O5 domains, and surfactant-induced stabilization. Finally, as a proof of functionality, the fabrication of dye-sensitized solar cells based on thin-film photoelectrodes that incorporate networked branched nanocrystals with intact crystal structure and geometric features is demonstrated. An energy conversion efficiency of 6.2% has been achieved with standard device configuration, which significantly overcomes the best performance ever approached with previously documented prototypes of split TiO2 nanostructures. Analysis of the relevant photovoltaic parameters reveals that the utilized branched building blocks indeed offer light-harvesting and charge-collecting properties that can overwhelm detrimental electron losses due to recombination and trapping events.

The thermal degradation behaviour of oleic acid-capped colloidal anatase TiO2 nanorods, poly(methyl methacrylate), and their nanocomposites has been studied. Thermogravimetric and differential thermal analysis have been carried out in nitrogen atmosphere for both nanorods, and nanocomposites with nanorod loading from 5 to 30 wt% relative to the polymer. Our study shows that the degradation of the oleic acid-capped nanorods in nitrogen is mainly endothermic and occurs in two steps. The thermal stability of the nanocomposites is improved on increasing the filler loading in the considered range, as the nanorods prevent rapid heat diffusion and limit further degradation. This effect seems to be favoured by the nanorods increased mobility, leading to enhanced dispersion in the matrix upon heating the samples during the thermal analysis.

The aim of the present work is to study the influence of the precipitation temperature in the synthesis of nanohydroxyapatite (n-HAp) on the properties of the resulting n-HAp powder for the fabrication of highly porous scaffolds for bone tissue engineering. The n-HAp powder was obtained by a wet precipitation technique starting from calcium nitrate tetrahydrate (Ca(NO3)(2)*4H(2)O) and phosphoric acid (H3PO4) at different temperatures: 10 degrees C, 37 degrees C and 50 degrees C. Highly porous scaffolds were fabricated using the three different powders by the sponge replica method and sintering at 1300 degrees C. Combined X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses on powders indicated that on increasing the precipitation temperature the formation of pure n-HAp is accelerated, without significant changes in particles morphology and size. Scaffolds characterized by high porosity (89%) and good compressive strength (0.53 MPa for n-HAp prepared at 37 degrees C) were obtained. XRD analyses on sintered n-HAp confirmed the thermal stability of the material. Therefore, the as-synthesized n-HAp powder can be successfully used for the fabrication of highly porous scaffolds as bone substitutes.

Exploiting the intrinsic photosensitivity of TiO2 nanoparticles, we demonstrated how ultraviolet (UV) pulsed laser irradiation of acrylate polymer nanocomposite solutions can separate the initial clusters of these colloidal semiconductor nanorods into clearly distinct units. From the irradiated solutions, optically clear nanocomposite films are obtained which exhibit enhanced optical properties with respect to the nanocomposites obtained without previous UV treatment.

Photopolymerized nanocomposite films of polystyrene and TiO2 nanorods are found to change their surface wettability characteristics in a controlled manner, depending on both the substrate used and on the number of film layers realized. The constituents of the nanocomposite solutions, namely styrene monomers and TiO2 nanorods, interact differently with the surface on which they are deposited, depending on its wettability. This interaction influences their dispersion along the depth and on the surface of the photopolymerized film, impacting on its wetting properties. We demonstrate that that the diverse amount of TiO2 nanorods exposed each time on the surface of the final film, which depends on the wettability of the surface lying underneath, is responsible for the layer-by-layer alternated surface characteristics. Moreover, due to the presence of TiO2 nanorods on the sample's surface, the wettability characteristics can be tuned in a reversible manner upon UV irradiation and vacuum storage cycles.

Patterned polymeric coatings enriched with colloidal TiO2 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.

In this study, we present a novel composite material based on commercially available polyurethane foams functionalized with colloidal superparamagnetic iron oxide nanoparticles and submicrometer polytetrafluoroethylene particles, which can efficiently separate oil from water. Untreated foam surfaces are inherently hydrophobic and oleophobic, but they can be rendered water-repellent and oil-absorbing by a solvent-free, electrostatic polytetrafluoroethylene particle deposition technique. It was found that combined functionalization of the polytetrafluoroethylene-treated foam surfaces with colloidal iron oxide nanoparticles significantly increases the speed of oil absorption. Detailed microscopic and wettability studies reveal that the combined effects of the surface morphology and of the chemistry of the functionalized foams greatly affect the oil-absorption dynamics. In particular, nanoparticle capping molecules are found to play a major role in this mechanism. In addition to the water-repellent and oil-absorbing capabilities, the functionalized foams exhibit also magnetic responsivity. Finally, due to their light weight, they float easily on water. Hence, by simply moving them around oil-polluted waters using a magnet, they can absorb the floating oil from the polluted regions, thereby purifying the water underneath. This low-cost process can easily be scaled up to clean large-area oil spills in water

The matrix-assisted pulsed laser evaporation (MAPLE) has been recently exploited for depositing films of nanomaterials by combining the advantages of colloidal inorganic nanoparticles and laser-based techniques. MAPLE-deposition of nanomaterials meeting applicative purposes demands their peculiar properties to be taken into account while planning depositions to guarantee a congruent transfer (in terms of crystal structure and geometric features) and explain the deposition outcome. In particular, since nanofluids can enhance thermal conductivity with respect to conventional fluids, laser-induced heating can induce different ablation thermal regimes as compared to the MAPLE-treatment of soft materials. Moreover, nanoparticles exhibit lower melting temperatures and can experience pre-melting phenomena as compared to their bulk counterparts, which could easily induce shape and or crystal phase modification of the material to be deposited even at very low fluences. In this complex scenario, this review paper focuses on examples of MAPLE-depositions of size and shape controlled nanoparticles for different applications highlights advantages and challenges of the MAPLE-technique. The influence of the deposition parameters on the physical mechanisms which govern the deposition process is discussed.

TiO2 nanorods in the brookite phase, having a mean size of 5 nm×50 nm, were prepared through a chemical route. The nanorods were dissolved in pure to luene (0,016 wt % TiO2). The solution was frozen at the liquid-nitrogen temperature and used as a target for the matrix-assisted pulsed laser evaporation (MAPLE) process. Target irradiation was accomplished with a KrF excimer laser (λ=248 nm,τ=20 ns), operated at fluences from F=25 to 350 mJ/cm2. Films were deposited at the repetition rate of 10 Hz using 6000 laser pulses. Film thickness resulted to be ∼ 100 nm at the highest fluence. It was not possible to use a higher number of laser pulses due to the melting of the target (~ 5 mm thick with a diameter of ~ 2.5 mm), even if continuously refrigerated at the LN temperature. Several substrates were used to fully characterize the deposited layers: <100> single-crystal Si wafers, silica slides, Cu carbon-coated grids and alumina interdigital slabs. High-resolution scanning and transmission electron microscopy investigations evidenced the formation of quite rough films incorporating individually distinguishable TiO2 single nanorods. Crystalline spheres were also detected in films, starting from the threshold fluence of 50 mJ/cm2 . Surface density and dimension of the spheres increase with increasing laser fluence. The sphere formation process and the target melting are discussed and attributed to nanosize effects. Films were positively tested as resistive sensors towards very low NO2 concentrations (≅ 1 ppm).

The formation of Pd nanoparticles (NPs) by matrix-assisted pulsed laser evaporation (MAPLE) of a palladium acetate solution has been studied as a function of the carrier solvent, laser-pulse number, metal precursor concentration and post-deposition thermal heating. Structural and compositional analyses demonstrate that: (i) the conventional MAPLE process can induce self-reduction of the metal salt precursor, thereby leading to the formation of metallic Pd(0) NPs; (ii) the solvent critically determines the size, morphology, and size distribution of the resulting NPs; and (iii) the cumulative effects of laser-pulse number and solute concentration are less influential than the type of solvent used. For diethyl ether-derived samples, a bimodal distribution of NP sizes spanning from ∼1 nm up to 20 nm was obtained. Conversely, by using acetone, a mono-modal distribution of sizes in the ∼1 nm–6 nm range (mean diameter of 1.5±0.7 nm) and a more uniform and densepacked surface coverage (NP coverage was twice as dense as the one obtained with diethyl ether) resulted in. These observations point out that solvents with low dynamical viscosity coefficients and high volatility favor the formation of larger and more broadly dispersed NPs. A general theoretical picture has been proposed to describe the NP formation pathways on account of the solvent properties and the mechanisms underlying the MAPLE process enabled by the technique.

In the realm of semiconductor nanomaterials, a crystal lattice heavily doped with cation/anion vacancies or ionized atomic impurities is considered to be a general prerequisite to accommodating excess free carriers that can support localized surface plasmon resonance (LSPR). Here, we demonstrate a surfactant-assisted nonaqueous route to anisotropic copper sulfide nanocrystals, selectively trapped in the covellite phase, which can exhibit intense, size-tunable LSPR at near-infrared wavelengths despite their stoichiometric, undoped structure. Experimental extinction spectra are satisfactorily reproduced by theoretical calculations performed by the discrete dipole approximation method within the framework of the Drude–Sommerfeld model. The LSPR response of the nanocrystals and its geometry dependence are interpreted as arising from the inherent metallic-like character of covellite, allowed by a significant density of lattice-constitutional valence-band free holes. As a consequence of the unique electronic properties of the nanocrystals and of their monodispersity, coherent excitation of symmetric radial breathing modes is observed for the first time in transient absorption experiments at LSPR wavelengths.

Colloidal inorganic nanocrystals stand out as an important class of advanced nanomaterials owing to the flexibility with which their physical–chemical properties can be controlled through size, shape, and compositional engineering in the synthesis stage and the versatility with which they can be implemented into technological applications in fields as diverse as optoelectronics, energy conversion/production, catalysis, and biomedicine. The use of microwave irradiation as a non-classical energy source has become increasingly popular in the preparation of nanocrystals (which generally involves complex and time-consuming processing of molecular precursors in the presence of solvents, ligands and/or surfactants at elevated temperatures). Similar to its now widespread use in organic chemistry, the efficiency of “microwave flash heating” in dramatically reducing overall processing times is one of the main advantages associated with this technique. This Review illustrates microwave-assisted methods that have been developed to synthesize colloidal inorganic nanocrystals and critically evaluates the specific roles that microwave irradiation may play in the formation of these nanomaterials.

Recent developments in the exploitation of transparent conductive oxide nanocrystals paved the way to the realization of a new class of electrochemical systems capable of selectively shielding the infrared heat loads carried by sunlight and prospected the blooming of a key enabling technology to be implemented in the next generation of "zero-energy" building envelopes. Here we report the fabrication of a set of electrochromic devices embodying an engineered nanostructured electrode made by high aspect-ratio tungsten oxide nanorods, which allow for selectively and dynamically controlling sunlight transmission over the near-infrared to visible range. Varying the intensity of applied voltage makes the spectral response of the device change across three different optical regimes, namely fully transparent, near-infrared only blocking and both visible and near-infrared blocking. It is demonstrated that the degree of reversible modulation of the thermal radiation entering the glazing element can approach a remarkable 85%, accompanied by only a modest reduction in the luminous transmittance.

Blinking and single-photon emission can be tailored in CdSe/CdS core/shell colloidal dot-in-rods. By increasing the shell thickness it is possible to obtain almost non-blinking nanocrystals, while the shell length can be used to control single-photon emission probability.

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 UV laser irradiation. This wettability change is reversible, with the hydrophobic character of the nanocomposites being fully recovered after a couple of days storage of the samples 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.

We report on a novel approach to integrate colloidal anatase TiO2 nanorods as key functional components into polymer bulk heterojunction (BHJ) photovoltaic devices by means of mild, all-solution-based processing techniques. The successful integration of colloidal nanoparticles in organic solar cells relies on the ability to remove the long chain insulating ligands, which indeed severely reduces the charge transport. To this aim we have exploited the concomitant mechanisms of UV-light-driven photocatalytic removal of adsorbed capping ligands and hydrophilicization of TiO2 surfaces in both solid-state and liquid-phase conditions. We have demonstrated the successful integration of the UV-irradiated films and colloidal solutions of TiO2 nanorods in inverted and conventional solar cell geometries, respectively. The inverted devices show a power conversion efficiency of 2.3% that is a ca. three times improvement over their corresponding cell counterparts incorporating untreated TiO2, demonstrating the excellent electron-collecting property of the UV-irradiated TiO2 films. The integration of UV-treated TiO2 solutions in conventional devices results in doubled power conversion efficiency for the thinner active layer and in maximum power conversion efficiency of 2.8% for 110 nm thick devices. In addition, we have demonstrated, with the support of device characterizations and optical simulations, that the TiO2 nanocrystal buffer layer acts both as electron-transporting/hole-blocking material and optical spacer.

We have developed a room-temperature solution processing approach to integrate colloidal anatase titanium dioxide nanorods (TiO2 NRs) and lead sulfide quantum dots (PbS QDs) into a heterostructured p-n junction device. To this aim we have exploited a post-deposition treatment to remove surface-adsorbed ligands by means of UV-light-irradiation of TiO2 NRs and a dilute acid treatment of PbS QDs. Here we report a systematic study on the optimization of the post-deposition treatments and device fabrication. Our approach is fully compatible with plastic device technology and is potentially useful for the integration of crystalline TiO2 as active component into disparate solar cell architectures and organic optoelectronic devices.

Thanks to their high stability, good optoelectronic and extraordinary electrochromic properties, tungsten oxides are among the most valuable yet underexploited materials for energy conversion applications. Herein, colloidal one-dimensional carved nanocrystals of reduced tungsten trioxide (WO3-x) are successfully integrated, for the first time, as a hole-transporting layer (HTL) into CH3NH3PbI3 perovskite solar cells with a planar inverted device architecture. Importantly, the use of such preformed nanocrystals guarantees the facile solution-cast-only deposition of a homogeneous WO3-x thin film at room temperature, allowing achievement of the highest power conversion efficiency ever reported for perovskite solar cells incorporating raw and un-doped tungsten oxide based HTL.

Editorial article to the themed collection: "Colloidal Self- Assembled Supracrystals and Heterostructures"

An engineered photoelectrode for dye solar cells has been developed through the combination of three mesoporous stacks made of shape-tailored TiO2 anatase nanocrystals, which have been ad hoc synthesized by suitable colloidal routes. Optimization of light harvesting and charge collection efficiency allowed us to obtain a high power conversion efficiency of 10.26%.

Water wetting and adhesion control on polymeric patterns are achieved by tuning the configuration of their surface's structural characteristics from single to dual and triple length-scale. In particular, surfaces with combined micro-, submicrometer-,and nanoroughness are developed, using photolithographically structured SU-8 micro-pillars as substrates for the consecutive spray deposition of polytetrafluoroethylene (PTFE) submicrometer particles and hydrophobically capped iron oxide colloidal nanoparticles. The PTFE particles alone or in combination with the nanoparticles render the SU-8 micropillars superhydrophobic. The water adhesion behaviour of the sprayed pillars is more complex since they can be tuned gradually from totally adhesive to completely non adhesive. The influence of the hierarchical geometrical features of the functionalized surfaces on this behaviour is discussed within the frame of the theory. Specially designed surfaces using the described technique are presented for selective drop deposition and evaporation. This simple method for liquid adhesion control on superhydrophobic surfaces can find various applications in the field of microfluidics, sensors, biotechnology, antifouling materials, etc.

Integrating nanocrystals (NCs) into magnetic tunnel structures is of considerable interest due to expectation of novel properties from their spin selective transport and single electron features. Superstructures by cplloidal NCs having translational and orientational order and interesting collective magnetic properties can be prepared by solution casting through sensitive interparticle and particle-substrate interactions. In this work, we discuss the study on magnetic field induced assembly of mono-dispersed iron oxide NCs to obtain spin filter effect across (he superlattice array, when sandwiched between gold electrodes. The deposition of mixed phase Fe3O4@gamma-Fe2O3 NCs on SiO2/Au surface proceeds through slow solvent evaporation and are studied for controlled interparticle spacing. For specific NC concentration, the ordering depends on the substrate chemistry and the ligands passivating NC surface, which affects the concentration of cluster nuclei formed. In presence of a magnetic field, the tunnel structure exhibits enhanced positive tunnel magnetoresistance at low temperatures, which could be related to their ferromagnetism and the attempts by electrons to percolate NC superlattice with preserved spin. A sign reversal for magnetoresistance is exhibited by the vertical tunnel junctions on raising the temperature.

We report on the unprecedented direct observation of spin-polarization transfer across colloidal magneto-plasmonic Au@Fe-oxide core@shell nanocrystal heterostructures. A magnetic moment is induced into the Au domain when the magnetic shell contains a reduced Fe-oxide phase in direct contact with the noble metal. An increased hole density in the Au states suggested occurrence of a charge-transfer process concomitant to the magnetization transfer. The angular to spin magnetic moment ratio, morb/mspin, for the Au 5d states, which was found to be equal to 0.38, appeared to be unusually large when compared to previous findings. A mechanism relying on direct hybridization between the Au and Fe states at the core/shell interface is proposed to account for the observed transfer of the magnetic moment.

A method for enhancing the surface wettability of PDMS microchannels used in microfluidic devices, is presented. Colloidal TiO2 nanorods are mixed in a PDMS solution that was used subsequently to realize parallel microchannels, through a replica molding procedure. TiO2 has the intrinsic capability of increasing dramatically its hydrophilicity upon UV irradiation. Due to this property, incorporating TiO2 nanofillers into the PDMS microchannels we manage to induce their hydrophobic-to-hydrophilic conversion upon UV irradiation. This conversion is essential for water to fill the microfluidic channels, in contrast to what happens for the non-irradiated nanocomposite or pure PDMS channels, which are characterized by high hydrophobicity and do not allow water to penetrate. The reversibility of the wettability changes permits to the microchannels to recover their original hydrophobicity.

We have developed a general X-ray powder diffraction (XPD) methodology for the simultaneous structural and compositional characterization of inorganic nanomaterials. The approach is validated on colloidal tungsten oxide nanocrystals (WO3−x NCs), as a model polymorphic nanoscale material system. Rod-shaped WO3-x NCs with different crystal structure and stoichiometry are comparatively investigated under an inert atmosphere and after prolonged air exposure. An initial structural model for the as-synthesized NCs is preliminarily identified by means of Rietveld analysis against several reference crystal phases, followed by atomic pair distribution function (PDF) refinement of the best-matching candidates (static analysis). Subtle stoichiometry deviations from the corresponding bulk standards are revealed. NCs exposed to air at room temperature are monitored by XPD measurements at scheduled time intervals. The static PDF analysis is complemented with an investigation into the evolution of the WO3−x NC structure, performed by applying the modulation enhanced diffraction technique to the whole time series of XPD profiles (dynamical analysis). Prolonged contact with ambient air is found to cause an appreciable increase in the static disorder of the O atoms in the WO3−x NC lattice, rather than a variation in stoichiometry. The time behavior of such structural change is identified on the basis of multivariate analysis.

Chemically synthesized brookite titanium dioxide (TiO2) nanorods with average diameter and length dimensions of 3–4 nm and 35–50 nm, respectively, were deposited by the matrix-assisted pulsed laser evaporation technique. A toluene nanorod solution was frozen at the liquid-nitrogen temperature and irradiated with a KrF excimer laser (λ=248 nm, τ=20 ns) at the repetition rate of 10 Hz, at different fluences (25 to 350 mJ/cm2). The deposited films were structurally characterized by high-resolution scanning and transmission electron microscopy. 〈100〉 single-crystal Si wafers and carbon-coated Cu grids were used as substrates. Structural analyses evidenced the occurrence of brookite-phase crystalline nanospheres coexisting with individually distinguishable TiO2 nanorods in the films deposited at fluences varying from 50 to 350 mJ/cm2. Nanostructured TiO2 films comprising only nanorods were deposited by lowering the laser fluence to 25 mJ/cm2. The observed shape and phase transitions of the nanorods are discussed taking into account the laser-induced heating effects, reduced melting temperature and size-dependent thermodynamic stability of nanoscale TiO2.

Suitable post-synthesis surface modification of lead-chalcogenide quantum dots (QDs) is crucial to enable their integration in photovoltaic devices. We have developed a solution-phase ligand exchange strategy that exploits arenethiolate anions to replace the pristine oleate ligands on PbS QDs, while preserving the long-term colloidal stability of QDs and allowing their solution-based processability into photoconductive thin-films. Complete QD surface modification is demonstrated by IR spectroscopy analysis, whereas UV-Vis-NIR Absorption Spectroscopy provides quantitative evaluation of stoichiometry and thermodynamic stability of the resulting system. Arenethiolate ligands permit to reduce the inter-particle distance in PbS QD solids, leading to a drastic improvement of the photoinduced charge transport properties. Therefore, smooth dense-packed thin-films of arenethiolate-capped PbS QDs obtained via a single solution-processing step are integrated in heterojunction solar cells: such devices generate remarkable photocurrent densities (14 mA cm(-2)) and overall efficiencies (1.85%), which are outstanding for a single PbS QD layer. Solution-phase surface modification of QDs thus represents an effective intermediate step towards low-cost processing for all-inorganic and hybrid organic/inorganic QD-based photovoltaics. (c) 2013 Elsevier B.V. All rights reserved.

Nanocomposites of polystyrene and TiO2 colloidal nanorods with different loadings have been prepared by mixing pre-synthesized oleic acid capped colloidal TiO2 nanorods into commercial polystyrene via solvent blending using chloroform. The microstructure and morphology of the nanocomposites was evaluated by wide angle X-ray diffraction and transmission electron microscopy. The observations revealed that the surfactant plays an important role for interactions between the polymer and the filler. Differential scanning calorimetry showed that the glass transition temperature of the nanocomposites decreased which is consistent with the surfactant acting as a plasticizer in the polystyrene matrix. Thermogravimetric analysis revealed that the nanocomposites show no significant improvement in thermal stability as compared to the bare PS up to a temperature of 400 degrees C. However, after 400 degrees C, the TGA curve shifts a little to higher temperature as compared to the bare PS. The dynamic mechanical properties of the nanocomposites indicate that the storage modulus, loss modulus, and glass transition temperature do not change with increasing nanorods content of 2 and 4 wt% but decrease afterward for 8 wt%. Transmission electron microscopy images clearly show debonding characteristics in polystyrene matrix.

We have developed a novel and straightforward approach for the green synthesis of reduced graphite oxide (rGO). First, graphite oxide (GO) was prepared by the Hummers' oxidation method, starting from high-surface-area graphite. Then, rGO was generated from GO in aqueous suspension through a UV-irradiation treatment. The influence of different process parameters (including type of UV source, irradiation time and atmosphere) on the GO reduction efficiency was explored and evaluated on the basis of the data acquired by several experimental techniques, such as infrared spectroscopy in attenuated total reflectance mode, X-ray diffraction, UV-vis absorption spectrophotometry, X-ray photoelectron spectroscopy and thermogravimetry. The acquired results allowed identifying appropriate sets of reaction conditions under which GO reduction yield could be maximized. In particular, the highest reduction degree was obtained by exposing GO to UV light in a UV oven for 48 h under inert atmosphere. The reduction strategy developed by us represents an innovative low-cost and easy route to graphene-based nanomaterials, which does not require any stabilizer, photocatalyst or reducing agent. For this reason, our method represents an attractive environmentally friendly alternative approach for the preparation of stable rGO dispersions in large-scale amounts, to be utilizable in disparate engineering applications.

Novel nanostructured films employing hyperbranched and all-linear TiO2 nanorods have been developed with the aim to overcome the impediments to the diffusion of bulky redox shuttles in photo-electrochemical devices. The porosity of the working electrodes has been tailored by appropriately selecting the nanocrystal building blocks to study how the electrode features affect the electrochemical parameters underlying the charge-transport phenomena and the photovoltaic properties of dye-sensitized solar cells. An optimized combination of porosity, light-harvesting capability, and enhanced electron-transport properties leads to a remarkable improvement of the device efficiency from 1.3% to 8.6%. These results suggest that it is indeed possible to properly design photoanodes based on shape-engineered nanocrystals, which can be suitable for different electrochemical devices such as fuel cells or storage devices employing viscous or quasi-solid electrolytes.

Thick films of nanocomposites made of poly(methyl methacrylate) matrix and colloidal anatase TiO2 nanorods fillers were prepared by solvent mixing and solution drop casting. Different concentrations of nanorods were tested in order to examine the influence of the nanoscale fillers on the composites material properties and structure. The thermal properties of the samples were investigated through thermogravimetric analysis, which showed an increase in thermal stability of the nanocomposites on increasing nanorods concentration, for the range of concentrations used. The viscoelastic properties were investigated through dynamic mechanical analysis, which showed an increase in both the storage and loss modulus on increasing nanorods concentration. The in-depth distribution of the TiO2 nanorods in the matrix was evaluated through cross-sectional transmission electron microscopy, which pointed out a uniform dispersion of mesoscale nanorods agglomerates with increasing diameter of 100–200 nm range on increasing nanorods concentration.

In this work, we report on 4% power conversion efficiency (PCE) depleted bulk heterojunction (DBH) solar cells based on a high-quality electrode with a three-dimensional nanoscale architecture purposely designed so as to maximize light absorption and charge collection. The newly conceived architecture comprises a mesoporous electron-collecting film made of networked anisotropic metal-oxide nanostructures, which accommodates visible-to-infrared light harvesting quantum dots within the recessed regions of its volume. The three-dimensional electrodes were self-assembled by spin-coating a solution of colloidal branched anatase TiO2 NCs (BNC), followed by photocatalytic removal of the native organic capping from their surface by a mild UV-light treatment and filling with small PbS NCs via infiltration. The PCE = 4% of our TiO2 BNC/PbS QD DBH solar cell features an enhancement of 84% over the performance obtained for a planar device fabricated under the same conditions. Overall, the DBH device fabrication procedure is entirely carried out under mild processing conditions at room temperature, thus holding promise for low-cost and large-scale manufacturing.

The sensing performance comparisons presented in this work were carried out by exploiting a suitable magneto-plasmonic sensor in both the traditional surface plasmon resonance configuration and the innovative magneto-optic surface plasmon resonance one. The particular multilayer transducer was functionalized with TiO2 Brookite nanorods layers deposited by matrix assisted pulsed laser evaporation, and its sensing capabilities were monitored in a controlled atmosphere towards different concentrations of volatile organic compounds mixed in dry air.

The ability to create photoanodes in which the structural and morphological features of the underlying TiO2 nanocrystalline constituents provide a tailored nanotexture with a higher degree of functionality still represents an indispensible step toward boosting the ultimate light-to electricity conversion of photoelectrochemical devices. This is especially evident for dye solar cells. In this paper we have systematically analyzed the impact of several different TiO2 nanorod morphologies on the most meaningful electrochemical features of the mesoporous photoelectrode of a dye solar cell. The most relevant findings have been then adopted as design criteria to realize an optimized multilayered photoelectrode with a properly engineered architecture which embodies three different breeds of nanocrystal with synergistic peculiarities. It exhibited superior power conversion efficiencies with respect to conventional nanoparticle-based reference film.

Magnetic tunnel junctions sandwiching a superlattice thin film of iron oxide nanocrystals (NCs) have been investigated. The transport was found to be controlled by Coulomb blockade and single-electron tunneling, already at room temperature. A good correlation was identified to hold between the tunnel magnetoresistance (TMR), the expected magnetic properties of the NC arrays, the charging energies evaluated from current−voltage curves, and the temperature dependence of the junction resistance. Notably, for the first time, a switching from negative to positive TMR was observed across the Verwey transition, with a strong enhancement of TMR at low temperatures.

The peculiar architecture of a novel class of anisotropic TiO 2(B) nanocrystals, which were synthesized by an surfactant-assisted nonaqueous sol-gel route, was profitably exploited to fabricate highly efficient mesoporous electrodes for Li storage. These electrodes are composed of a continuous spongy network of interconnected nanoscale units with a rod-shaped profile that terminates into one or two bulgelike or branch-shaped apexes spanning areas of about 5 × 10 nm2. This architecture transcribes into a superior cycling performance (a charge capacitance of 222 mAh g-1 was achieved by a carbon-free TiO2(B)-nanorods-based electrode vs 110 mAh g-1 exhibited by a comparable TiO 2-anatase electrode) and good chemical stability (more than 90% of the initial capacity remains after 100 charging/discharging cycles). Their outstanding lithiation/delithiation capabilities were also exploited to fabricate electrochromic devices that revealed an excellent coloration efficiency (130 cm2 C-1 at 800 nm) upon the application of 1.5 V as well as an extremely fast electrochromic switching (coloration time ∼5 s)

Method for preparing a colloid solution of titanium dioxide nanoparticles in a solution of acrylic resin in organic solvent, comprising: mixing titanium dioxide nanoparticles with a solution of acrylic resin in organic solvent, so as to obtain the aforementioned colloid solution. The colloid solution is subjected to a stabilization treatment suitable for preventing or reducing nanoparticle aggregation, the treatment comprising: irradiating the colloid solution with pulsed coherent light having a wavelength substantially comprised in the ultraviolet absorption band of the titanium dioxide nanoparticles.