Publications - Treetop

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Recent and selected publications
Stefania Porcu*, Enrica Tuveri, Marco Palanca, Claudia Melis, Ignazio Macellaro La Franca, Jessica Satta, Daniele Chiriu, Carlo Maria Carbonaro, Pierluigi Cortis, Antonio De Agostini, and Pier Carlo Ricci*

The need to find a rapid and worthwhile technique for the in situ detection of the content of delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD) in Cannabis sativa L. is an ever-increasing problem in the forensic field. Among all the techniques for the detection of cannabinoids, Raman spectroscopy can be identified as the most cost-effective, fast, noninvasive, and nondestructive. In this study, 42 different samples were analyzed using Raman spectroscopy with 1064 nm excitation wavelength. The use of an IR wavelength laser showed the possibility to clearly identify THC and CBD in fresh samples, without any further processing, knocking out the contribution of the fluorescence generated by visible and near-IR sources. The results allow assigning all the Raman features in THC- and CBD-rich natural samples. The multivariate analysis underlines the high reproducibility of the spectra and the possibility to distinguish immediately the Raman spectra of the two cannabinoid species. Furthermore, the ratio between the Raman bands at 1295/1440 and 1623/1663 cm–1 is identified as an immediate test parameter to evaluate the THC content in the samples.

Analytical Chemistry;

Jessica Satta, Andrea Pinna, Giorgio Pia , Luca Pilia, Carlo Maria Carbonaro, Daniele Chiriu, Luigi Stagi, Qader Abdulqader Abdullah  and Pier Carlo Ricci

Halide perovskite colloidal nanocrystals have recently gained much attention thanks to their superior stability compared with their bulk counterpart and to their unique optical properties. In this paper, two systems combining nanocrystals and nanoporous gold are studied to create an optimal metal semiconductor heterojunction that can be used in photocatalysis and photovoltaic devices. The perovskite degradation phenomenon is observed when the nanoporous gold powder is mixed into the hexane suspension of nanocrystals, while the charge separation efficiency is increased by synthesizing the nanocrystals directly onto the gold porous structure. The analysis of the structural and optical properties evidences an energy transfer efficiency of 47%, along with the high structural stability of the hybrid system..

Crystals 2022, 12(6), 863;
Chiara Olla, Stefania Porcu, Francesco Secci, Pier Carlo Ricci  and Carlo Maria Carbonaro

The introduction of N doping atoms in the carbon network of Carbon Dots is known to increase their quantum yield and broaden the emission spectrum, depending on the kind of N bonding introduced. N doping is usually achieved by exploiting amine molecules in the synthesis. In this work, we studied the possibility of introducing a N–N bonding in the carbon network by means of hydrothermal synthesis of citric acid and hydrazine molecules, including hydrated hydrazine, di-methylhydrazine and phenylhydrazine. The experimental optical features show the typical fingerprints of Carbon Dots formation, such as nanometric size, excitation dependent emission, non-single exponential decay of photoluminescence and G and D vibrational bands in the Raman spectra. To explain the reported data, we performed a detailed computational investigation of the possible products of the synthesis, comparing the simulated absorbance spectra with the experimental optical excitation pattern. The computed Raman spectra corroborate the hypothesis of the formation of pyridinone derivatives, among which the formation of small polymeric chains allowed the broad excitation spectra to be experimentally observed.

Materials 2022, 15(4), 1468;
Jessica Satta, Alberto Casu, Daniele Chiriu, Carlo Maria Carbonaro, Luigi Stagi, Pier Carlo Ricci*

CsPbI 3 inorganic perovskite is synthesized by a solvent-free, solid-state reaction, and its structural and optical properties can be deeply investigated using a multi-technique approach. X-ray Diffraction (XRD) and Raman measurements, optical absorption, steady-time and time-resolved luminescence, as well as High-Resolution Transmission Electron Microscopy (HRTEM) imaging, were exploited to understand phase evolution as a function of synthesis time length. Nanoparticles with multiple, well-defined crystalline domains of different crystalline phases were observed, usually surrounded by a thin, amorphous/out-of-axis shell. By increasing the synthesis time length, in addition to the pure α phase, which was rapidly converted into the δ phase at room temperature, a secondary phase, Cs 4 PbI 6, was observed, together with the 715 nm-emitting γ phase..

Nanomaterials 11 (7), 1823
Riccardo Corpino, Damiano Angioni, Jessica Satta, Franca Chika Ugbo, Daniele Chiriu, Carlo M Carbonaro, Claudio Melis, Luigi Stagi, Pier Carlo Ricci*

The study of new phosphors requires in-depth knowledge of the mechanisms and radiative emission paths and, with this aim, the study here reported focuses on the emission properties of CaZnOS crystals single doped with Terbium and co-doped with Terbium and Europium. By studying the optical properties and, in particular, the kinetics of recombination with time-resolved luminescence, the de-excitation mechanisms and the charge transfer processes have been established. A fundamental role is played by the defective centers and their efficient energy transfer process to the excited levels of Terbium, the mechanism being also active among co-doping rare earths (from Tb3+ to Eu3+), allowing further tuning of the emission properties. Beside photoluminescence, the study shows that in case of mechanical stimulus as well, the mechano-luminescence follows the same path, where the defective states of the matrix efficiently excite the levels of dopants, producing a green emission at 545 nm from Tb3+ and a red emission above 600 nm from Eu3+. Therefore, studying the relative ratio of dopants, it is shown how precisely tune across the visible part of the spectrum the mechano-luminescence emission.

Journal of Alloys and Compounds 868, 159007
Spencer D Golze, Stefania Porcu, Chen Zhu, Eli Sutter, Pier Carlo Ricci, Edward C Kinzel, Robert A Hughes, Svetlana Neretina

Symmetry-breaking synthetic controls allow for nanostructure geometries that are counter to the underlying crystal symmetry of a material. If suitably applied, such controls provide the means to drive an isotropic metal along a growth pathway yielding a three-dimensional chiral geometry. Herein, we present a light-driven solution-based synthesis yielding helical gold spirals from substrate-bound seeds. The devised growth mode relies on three separate symmetry-breaking events ushered in by seeds lined with planar defects, a capping agent that severely frustrates early stage growth, and the Coulombic repulsion that occurs when identically charged growth fronts collide. Together they combine to advance a growth pathway in which planar growth emanates from one side of the seed, advances to encircle the seed from both clockwise and counterclockwise directions, and then, upon collision of the two growth fronts, sees one front rise above the other to realize a self-perpetuating three-dimensional spiral structure..

Nano Letters 21 (7), 2919-2925
Francesca Assunta Pisu, Carlo Maria Carbonaro, Riccardo Corpino, Pier Carlo Ricci, Daniele Chiriu

In this study, we proposed a preliminary kinetic model applied to the carbonation process of fresh lime with the intention to realize a diagnostic tool for aged fresco paintings. The model can be useful, in particular, in the fields of conservation and restoration of ancient lime wall paintings. The dating procedure was achieved through the analysis of 1064 nm excited Raman spectra collected on artificially aged lime samples in addition to ancient samples taken from literature and covering a period of two thousand years. The kinetic model was developed monitoring the concentration of emitting defective centers related to the intensity of 780 cm− 1 calcium hydroxide band as a function of the time and depth. This preliminary model shows how Raman spectroscopy, especially NIR micro-Raman, is advantageous for diagnostics and conservation in the cultural heritage field.

Crystals 11 (3), 257
Antonio Cappai, Claudio Melis, Luigi Stagi, Pier C Ricci, Francesca Mocci, Carlo M Carbonaro

The molecular emission model is the most accredited one to explain the emission properties of carbon dots (CDs) in a low-temperature bottom-up synthesis approach. In the case of citric acid and urea, the formation of a citrazinic acid (CZA) single monomer and oligomers is expected to affect the optical properties of the CDs. It is therefore mandatory to elucidate the possible role of weak bonding interactions in determining the UV absorption spectrum of some molecular aggregates of CZA. Although this carboxylic acid is largely exploited in the synthesis of luminescent CDs, a full understanding of its role in determining the final emission spectra of the produced CDs is still very far to be achieved. To this aim, by relying on purely first-principles density functional theory calculations combined with experimental optical characterization, we built and checked the stability of some molecular aggregates, which could possibly arise from the formation of oligomers of CZA, mainly dimers, trimers, and some selected tetramers. The computed vibrational fingerprint of the formation of aggregates is confirmed by surface-enhanced Raman spectroscopy. The comparison of experimental data with calculated UV absorption spectra showed a clear impact of the final morphology of the aggregates on the position of the main peaks in the UV spectra, with particular regard to the 340 nm peak associated with n-π* transition.

The Journal of Physical Chemistry C 125 (8), 4836-4845
Jessica Satta, Claudio Melis, Carlo Maria Carbonaro, Andrea Pinna, Manuel Salado, Daniel Salazar, Pier Carlo Ricci

A major issue in the development of Lead halide perovskites is the assessment of the crystal structure of the samples, due to their typically limited time-stability, and the understanding of the role of external factors that can induce a crystal phase transformation (such as humidity, intense light flux, temperature, etc.). In this perspective, it is of utmost importance to have at disposal a fast and reliable experimental tool able to give an immediate indication of the polymorph of the sample with the possibility to integrate in-situ measurements for constant monitoring. In this paper we propose Raman spectroscopy as the ideal technique to solve this problem. The vibrational analysis of CsPbI3 in the α-phase and δ-phase and of the Cs4PbI6 secondary phase is reported and all the vibrational modes are assigned by comparing experimental spectra of the phases to Raman modes calculated within the DFT framework. Finally, the mechanism of laser induced phase degradation was studied using in-situ Raman measurements providing new insights on the secondary phase generated during the process.

Journal of Materiomics 7 (1), 127-135
Stefania Porcu, Micaela Castellino, Ignazio Roppolo, Carlo Maria Carbonaro, Simonetta Palmas, Laura Mais, Maria Francesca Casula, Svetlana Neretina, Robert A Hughes, Francesco Secci, Pier Carlo Ricci

Eco-sustainable solutions for the neutralization of air and water pollutants have increasingly gravitated toward the use of heterogeneous photocatalysts. This approach, which transforms pollutants into harmless substances through a light-driven chemical reaction on a catalytic surface, must comply with eco-sustainability requirements and be easily applicable. Semiconductor-based photocatalysis is a promising pathway for the degradation of environmental pollutants and, among all the various semiconductors used, titanium dioxide has proved itself to be the foremost material for environmental remediation due to its highly desirable photocatalytic properties. Titanium dioxide, however, poorly exploits the visible part of the electromagnetic spectrum due to the relatively large band-gap of its anatase phase, and as such, the UV portion of the solar spectrum is largely responsible for its photocatalytic activity. Herein, we demonstrate a highly efficient visible light hybrid catalyst based on titanium dioxide and phenyl carbon nitride (PhCN). With the organic component providing a broad absorption up to 600 nm and fast charge exchange to the conduction band of TiO2, the combination allows for the highly efficient photocatalytic degradation of Rhodamine B under visible excitation.

Applied Surface Science 531, 147394
Dipartimento di Fisica - Cittadella Universitaria sp.8 Km 0-700 09042 Monserrato /CA) - Italy
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