Showing papers by "Alice Scarpellini published in 2015"

Tuning the Optical Properties of Cesium Lead Halide Perovskite Nanocrystals by Anion Exchange Reactions

Abstract: We demonstrate that, via controlled anion exchange reactions using a range of different halide precursors, we can finely tune the chemical composition and the optical properties of presynthesized colloidal cesium lead halide perovskite nanocrystals (NCs), from green emitting CsPbBr3 to bright emitters in any other region of the visible spectrum, and back, by displacement of Cl– or I– ions and reinsertion of Br– ions. This approach gives access to perovskite semiconductor NCs with both structural and optical qualities comparable to those of directly synthesized NCs. We also show that anion exchange is a dynamic process that takes place in solution between NCs. Therefore, by mixing solutions containing perovskite NCs emitting in different spectral ranges (due to different halide compositions) their mutual fast exchange dynamics leads to homogenization in their composition, resulting in NCs emitting in a narrow spectral region that is intermediate between those of the parent nanoparticles.

From Binary Cu2S to Ternary Cu–In–S and Quaternary Cu–In–Zn–S Nanocrystals with Tunable Composition via Partial Cation Exchange

Abstract: We present an approach for the synthesis of ternary copper indium sulfide (CIS) and quaternary copper indium zinc sulfide (CIZS) nanocrystals (NCs) by means of partial cation exchange with In3+ and Zn2+. The approach consists of a sequential three-step synthesis: first, binary Cu2S NCs were synthesized, followed by the homogeneous incorporation of In3+ by an in situ partial cation-exchange reaction, leading to CIS NCs. In the last step, a second partial exchange was performed where Zn2+ partially replaced the Cu+ and In3+ cations at the surface, creating a ZnS-rich shell with the preservation of the size and shape. By careful tuning reaction parameters (growth and exchange times as well as the initial Cu+:In3+:Zn2+ ratios), control over both the size and composition was achieved. This led to a broad tuning of photoluminescence of the final CIZS NCs, ranging from 880 to 1030 nm without altering the NCs size. Cytotoxicity tests confirmed the biocompatibility of the synthesized CIZS NCs, which opens up oppor...

Surface-structured bacterial cellulose with guided assembly-based biolithography (GAB).

Abstract: A powerful replica molding methodology to transfer on-demand functional topographies to the surface of bacterial cellulose nanofiber textures is presented. With this method, termed guided assembly-based biolithography (GAB), a surface-structured polydimethylsiloxane (PDMS) mold is introduced at the gas-liquid interface of an Acetobacter xylinum culture. Upon bacterial fermentation, the generated bacterial cellulose nanofibers are assembled in a three-dimensional network reproducing the geometric shape imposed by the mold. Additionally, GAB yields directional alignment of individual nanofibers and memory of the transferred geometrical features upon dehydration and rehydration of the substrates. Scanning electron and atomic force microscopy are used to establish the good fidelity of this facile and affordable method. Interaction of surface-structured bacterial cellulose substrates with human fibroblasts and keratinocytes illustrates the efficient control of cellular activities which are fundamental in skin wound healing and tissue regeneration. The deployment of surface-structured bacterial cellulose substrates in model animals as skin wound dressing or body implant further proves the high durability and low inflammatory response to the material over a period of 21 days, demonstrating beneficial effects of surface structure on skin regeneration.

Elastomeric Nanocomposite Foams for the Removal of Heavy Metal Ions from Water

Abstract: We report the fabrication and utilization of elastomeric polymer nanocomposite foams for the efficient removal of Pb2+ and Hg2+ heavy metal ions from polluted water. The polydimethylsiloxane (PDMS) foams are properly modified in order to become hydrophilic and allow the polluted water to penetrate in their volume. The ZnSe colloidal nanocrystals (NCs) that decorate the surface of the foams, act as active components able to entrap the metal ions. In this way, after the dipping of the nanocomposite foams in water polluted with Pb2+ or Hg2+, a cation exchange reaction takes place, and the heavy metal ions are successfully removed. The removal capacity for the Pb2+ ions exceeds 98% and the removal of Hg2+ ions approaches almost 100% in the studied concentrations region of 20–40 ppm. The reaction is concluded after 24 h, but it should be noticed that after the first hour, more than 95% of both the metal ions is removed. The color of the foams changes upon heavy metal ions entrapment, providing thus the opportu...

Direct Synthesis of Carbon-Doped TiO2–Bronze Nanowires as Anode Materials for High Performance Lithium-Ion Batteries

Abstract: Carbon-doped TiO2–bronze nanowires were synthesized via a facile doping mechanism and were exploited as active material for Li-ion batteries. We demonstrate that both the wire geometry and the presence of carbon doping contribute to the high electrochemical performance of these materials. Direct carbon doping for example reduces the Li-ion diffusion length and improves the electrical conductivity of the wires, as demonstrated by cycling experiments, which evidenced remarkably higher capacities and superior rate capability over the undoped nanowires. The as-prepared carbon-doped nanowires, evaluated in lithium half-cells, exhibited lithium storage capacity of ∼306 mA h g–1 (91% of the theoretical capacity) at the current rate of 0.1C as well as excellent discharge capacity of ∼160 mAh g–1 even at the current rate of 10 C after 1000 charge/discharge cycles.

Synthesis of Highly Fluorescent Copper Clusters Using Living Polymer Chains as Combined Reducing Agents and Ligands.

Abstract: We present the synthesis of colloidally stable ultrasmall (diameter of 1.5 ± 0.6 nm) and fluorescent copper clusters (Cu-clusters) exhibiting outstanding quantum efficiencies (up to 67% in THF and approximately 30% in water). For this purpose, an amphiphilic block copolymer poly(ethylene glycol)-block-poly(propylene sulfide) (MPEG-b-PPS) was synthesized by living anionic ring-opening polymerization. When CuBr is mixed with the living polymer chains in THF, the formation of Cu-clusters is detected by the appearance of the fluorescence. The cluster growth is quenched by the addition of water, followed by THF removal. The structural features of the MPEG-b-PPS copolymer control the cluster formation and the stabilization: the poly(propylene sulfide) segment acts as coordinating and reducing agent for the copper ions in THF, and imparts a hydrophobic character. This hydrophobic block protects the Cu-clusters from water exposure, thus allowing to obtain a stable emission in water. The PEG segment instead provid...

Morphology‐Dependent Electrochemical Properties of CuS Hierarchical Superstructures

Abstract: © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Hierarchical superstructures formed by self-assembled nanoparticles exhibit interesting electrochemical properties that can potentially be exploited in Li-ion batteries (LIBs) as possible electrode materials. In this work, we tested two different morphologies of CuS superstructures for electrodes, namely, tubular dandelion-like and ball-like assemblies, both of which are composed of similar small covellite nanoparticles. These two CuS morphologies are characterized by their markedly different electrochemical performances, suggesting that their complex structures/morphologies influence the electrochemical properties. At 1.12Ag-1, the cells made with CuS tubular structures delivered about 420mAhg-1, and at 0.56Ag-1, the capacity was as high as about 500mAhg-1 with good capacity retention. Their ease of preparation and processing, together with good electrochemical performance, make CuS tubular dandelion-like clusters attractive for developing low-cost LIBs based on conversion reactions.

Induced growth of dendrite gold nanostructure by controlling self-assembly aggregation dynamics

Abstract: Self-assembly of gold nanoparticles (AuNPs) is an important growth mode for fabricating functional materials In this work we report a dendrite structure formed by slowing down the aggregation dynamics of AuNPs self-assembly The obtained results show that the aggregation dynamics is dominated by the Reaction Limited Aggregation Model (RLA) more than the Diffusion Limited Aggregation Model (DLA) In which the repulsion due to electrostatic forces is dominant by the Van Der Walls attraction forces, and low sticking probability of nanoparticles The aggregation dynamics of AuNPs can be slowed down if the water evaporation of the drop casted colloidal AuNPs on a quartz substrate is slowed Slowing down the evaporation allows electrostatic repulsion forces to decrease gradually At certain point, the attraction forces become higher than the electrostatic repulsion and hence cluster aggregation take place slowly The slow aggregation dynamics allows the nanoparticles to sample all possible orientation in the sticking site, searching for the lowest energy configuration The size distribution of the nanoparticles in liquid is confirmed using dynamic light scattering based on Stokes–Einstein equation for diffusion coefficient in water X-ray and photoluminescence (PL) spectra of the sample after aggregation showed a shift which is related to the aggregation compared with non-aggregated colloidal nanoparticles in the solution The study shows that dendrite self similar structure can be formed by slowing down the aggregation dynamics of nanoparticles as a result of minimizing the Helmholtz free surface energy of the system

Laser-induced localized formation of silver nanoparticles on chitosan films: study on particles size and density variation

Abstract: We present the in situ localized formation of silver nanoparticles in chitosan films by pulsed UV laser irradiation, as a result of the photoreduction of the silver nitrate precursor loaded throughout the volume of the polymer. The UV pulsed irradiation is also found to be responsible for the photofragmentation of the previously formed nanoparticles, leading to their average size reduction as the number of pulses increases. In fact, their diameter changes from ~150 to ~30 nm for irradiation with 5 to 200 pulses, respectively. After irradiation the formation of nanoparticles continues for several days, since the already formed nanoparticles act as seeds for the reduction of the unreacted precursor. Indeed, few weeks after irradiation, the chitosan films present a metallic mirror-like appearance on the previously irradiated areas, as they are fully covered by silver. Taking advantage of all these simultaneous mechanisms, and controlling the number of pulses and elapsed time after irradiation, Ag nanoparticles of specific size can be formed in situ on desired areas of the film. Through this process is envisioned the fabrication of nanocomposites with functional properties.

Nanocomposite fabrication via direct ultra-fast laser ablation of titanium in aqueous monomer solution

Abstract: A novel approach to fabricating nanocomposites comprising inorganic nanoparticles embedded in an organic matrix is presented. Ultra-fast laser ablation of a titanium metal target in aqueous e-caprolactam monomer solution is used to produce ultra-small TiO2 nanoparticles and to simultaneously initiate the polymerization of the monomer without the use of chemicals. The spectroscopic analysis and TEM studies reveal the formation of an organic matrix and its conjugation to the nanoparticles' surface. The laser beam induces the formation of TiO2 nanoparticles, which subsequently act as photoinitiators of the polymerization of e-caprolactam upon absorbing the photon energy provided by the unfocused part of the beam. This work can open new pathways for cost-effective and environmentally friendly nanocomposite production, in one step.

Synergistic Action of Alginate Chemical Reduction and Laser Irradiation for the Formation of Au Nanoparticles with Controlled Dimensions

Abstract: Freestanding natural polymeric films with homogeneous dispersion of gold nanoparticles (Au NPs) are obtained via in situ reduction of gold(III) chloride trihydrate by sodium alginate (SA) biopolymer matrix, during water evaporation without the use of additional reducing agents. The size and size distribution of the prepared Au NPs can be tuned by changing the concentration of the precursor and/or the procedure of the films’ preparation. The nanocomposite films after preparation are stable in ambient conditions and can be used without the need of further processing, or can be redissolved in water. In the case of water dissolution, the aqueous solutions are irradiated with UV laser pulses turning the previously formed Au NPs into smaller ones with narrow size distributions through photofragmentation. This technique is proposed as a green way of synthesizing Au NPs of tunable size in aqueous solution of alginate, or incorporated in alginate freestanding polymeric films, that due to their biocompatibility can be used as passive labels or active sensors in biomedical applications.