Georgiana Stoica

The influence of the mesoporous TiO2 scaffold on the performance of methyl ammonium lead iodide (MAPI) perovskite solar cells: charge injection, charge recombination and solar cell efficiency relationship

Methyl Ammonium Lead Iodide (MAPI) perovskite solar cells have achieved over 20% light-to-energy conversion efficiency with the use of a thin mesoporous layer of TiO2 as a scaffold for the MAPI. Although other solar cell configurations have also been reported, so far only those containing mesoporous TiO2 (mpTiO2) have achieved such performance. Herein we describe an exhaustive study of the effects, on the MAPI solar cell performance, of different synthetic routes to achieve nanocrystalline TiO2 nanoparticles that are used to fabricate the mpTiO2 layer. Furthermore, we also measured the interfacial charge transfer dynamics to elucidate the device function–charge recombination kinetics relationship in the different types of synthesised mpTiO2. Our results show that the choice of the chemical properties of the mpTiO2 layer is of utmost importance to achieve high solar-to-energy conversion efficiencies with remarkable effects on the measured charge carrier recombination kinetics.

Perturbing the properties of layered double hydroxides by continuous coprecipitation with short residence time

A previous work (S. Abello and J. Perez-Ramirez, Adv. Mater., 2006, 18, 2436) revealed an unanticipated variation in the textural properties of Mg–Al hydrotalcite, prepared by continuous coprecipitation with short residence time, τ = 1 s which, at that time, was not fully understood. Herein, we report the generalisation of such variation in physical properties to layered double hydroxides (LDHs) of different composition (Ni–Al, Mg–Al, and Mg–Fe hydrotalcite-like compounds). In particular stable colloidal suspensions and, on drying, impervious LDH particles have been prepared using the in-line dispersion precipitation (ILDP) method with τ = 1 s. This is thought to be a consequence of variation in the mechanism of inter-crystallite interactions with decreasing crystallite size. The resulting materials are characterised using multiple techniques and are compared to analogous materials attained at longer residence times (τ = 12 s). We show that despite the apparent compositional similarity and structural isomorphicity of the precipitates, their textural and morphological properties and their thermal stability differ strongly. Thermal activation of the LDHs, however, resulted in the development of comparable textural properties in the corresponding oxides, independent of the residence time.

The effect of the silica thickness on the enhanced emission in single particle quantum dots coated with gold nanoparticles

The fabrication of highly luminescent, chemically stable and biocompatible small optical probes is of key interest in bioimaging. Herein we develop a multistep synthesis of hybrid superstructures that comprise quantum dot cores and dense layers of gold nanoparticles separated by a silica shell. This architecture allows for the versatile control of the QD–metal interactions by controlling the thickness of the dielectric spacer. The shell thickness is optimized at the nanometer scale in order to increase the enhanced photoluminescence. Further characterization of the emission in the single particle regime shows that our brighter particles require smaller acquisition times to yield better imaging results.

Reevaluation of the Structure and Fundamental Physical Properties of Dawsonites by DFT Studies

Dawsonite-type compounds, with the general formula MAlCO(3)(OH)(2), where M = Na(+), K(+), or NH(4)(+), recently have become attractive materials because of their potential interest in geochemical CO(2) sequestration, CO(2) capture in power plants, and heterogeneous catalysis. However, the number of studies assessing the properties of these materials is limited. In the present paper, we report a theoretical reevaluation of the structural and essential physicochemical properties of Na-, K-, and NH(4)-dawsonites as determined by density functional theory (DFT) investigations. The calculated structure of Na- and K-dawsonites is in good agreement with previous data, while for NH(4)AlCO(3)(OH)(2), the calculations suggest orientation disorder of the ammonium ions in the structure. The normal-mode analysis, electronic and bonding properties, and elastic properties are reported for the three analogue dawsonites. The calculated formation enthalpy is -1714, -1699, and -1655 kJ/mol for K-, Na-, and NH(4)-dawsonite, respectively. This study comprises a first step toward a better understanding of the diversity of dawsonite intrinsic properties, which is required to tune their practical applications.

Photoluminescent CdSe@CdS/2D as potential biocompatible materials

We have successfully fabricated herein a complex hybrid nanostructure composed of 1D CdSe@CdS nanorods and 2D Mg-Al brucite-like nanosheets. The novel material exhibits enhanced photoluminescence when compared to as-prepared CdSe@CdS rods. The results show that the two different starting materials can be heterogeneously integrated as functional components, the nanorods being aligned in parallel to the hydrotalcite crystals. Of particular interest are the changes in the fluorescence emission lifetime of the nanorods depending on the starting form of the host hydrotalcite (as-such or delaminated). The material enhanced photoluminescence reduces the need for a higher concentration of CdSe@CdS nanorods, a requisite for their biological use as markers.

Increasing cell viability using Cd-free – InP/ZnS@silica@layered double hydroxide – materials for biological labeling

In this work we describe the synthesis and characterization of InP/ZnS@silica@LDH nanoparticles and, moreover, their use as biomarkers. The use of dual systems combining silica shells and hydrotalcite nanocoatings favors the cell viability in clear contrast with the system with only silica shells. Furthermore, the use of Cd-free luminophores extends the cells lifetime and illustrates the potential of the InP/ZnS@silica@LDH material as a biomarker.

Lanthanide-doped nanoparticles for specific recognition of toll-like receptor (TLR) in human neutrophils

KYF4:Yb,Er nanoparticles were fabricated and functionalized with streptavidin for the recognition of toll-like receptors (TLRs) on human neutrophil through biotinylated lipopolysaccharide (biotin–LPS). X-Ray diffraction, Infrared spectroscopy, Transmission Electron Microscopy and Agarose Gel Electrophoresis were used to characterize the as-prepared and functionalized nanoparticles. Confocal Scanning Laser Microscopy was applied to study the TLR specific recognition using KYF4:Yb,Er and the uptake of the nanoparticles functionalized with BSA/Dextran–streptavidin in the presence of biotin–LPS by human neutrophils under normal (37 °C) and cell stressing conditions (4 °C). Confocal microscopy studies showed that the uptake of the functionalized KYF4:Yb,Er nanoparticles occurs faster and with a higher rate at 37 °C compared to the uptake at 4 °C, indicating that the uptake mechanism is an energy dependent process. Research reported in this work provides relevant guidance for the development of lanthanide doped KYF4:Yb,Er nanoparticles as specific intracellular probes, allowing control of the nanoparticle–cell interactions by tuning the surface properties. Furthermore, our results would pave the way to the use of lanthanide-doped materials for imaging cellular processes such as uptake of nanoparticles and recognition of receptors involved in immune responses.

Layered double hydroxides as carriers for quantum dots@silica nanospheres

Quantum dot-hydrotalcite layered nanoplatforms were successfully prepared following a one-pot synthesis. The process is very fast and a priori delamination of hydrotalcite is not a prerequisite for the intercalation of quantum dots. The novel materials were extensively characterized by X-ray diffraction, thermogravimetry, infrared spectroscopy, transmission electron microscopy, true color fluorescence microscopy, photoluminescence, and nitrogen adsorption. The quantum dot-hydrotalcite nanomaterials display extremely high stability in mimicking physiological media such as saline serum (pH 5.5) and PBS (pH 7.2). Yet, quantum dot release from the solid structure is noted. In order to prevent the leaking of quantum dots we have developed a novel strategy which consists on using tailor made double layered hydrotalcites as protecting shells for quantum dots embedded into silica nanospheres without changing either the materials or the optical properties.