Publications

Catalytic activity of TiO2, 2%Re-TiO2 and 10%Re-TiO2 in the conversion of carbohydrates into levulinic acid under autoclave conditions was evaluated. These materials were prepared by aerogel method, for the first time to the best of our knowledge, and characterized by XPS, SEM-EDX, DRIFTS, DR UV-vis, Raman, N-2 adsorption/desorption isotherms, TGA and XRD. Further, the surface acidity was probed by NH3-TPD and pyridine-FT-IR where it was observed that increasing the amount of rhenium doped into TiO2 led to an increase in the total number of acid sites (Lewis + Bronsted) but with an overall lower strength. The presence of both Bronsted and Lewis acid sites led to the hypothesis that these materials may be well suited for conversion of carbohydrates into levulinic acid. Indeed a levulinic acid yield of 57% was reached over 10%Re-TiO2 for a low mass ratio catalyst to glucose (1 : 5). Moreover, the 10%Re-TiO2 catalyst was reused in the conversion of glucose for four catalytic cycles without a significant loss of the catalytic activity.

The reactions between [CuX(PPh3)](4) or [CuX(PPh3)(3)], X = Cl or Br, and N-benzoyl-N'-(4-methoxyphenyl)thio-urea (BTU-OMe), N-benzoyl-N'-(4-methylphenyl)thiourea (BTU-Me) in toluene gave new four-coordinated tetrahedral copper(I) complexes of two types: [CuX(BTU)(PPh3)(2)] (1, 2) and [CuX(BTU)(2)(PPh3)] (3,4) [BTU = N-benzoyl-N'-(4-methoxy/methyl phenyl)thiourea derivatives, X = Cl (a) and Br (b)]. These complexes were fully characterized by several analytical and spectroscopic (IR, UV/VIS, H-1, C-13 and P-31 NMR) techniques. The molecular structure of a representative complex, [Cu(BTU-OMe)(PPh3)(2)Cl] (3a), was determined by the single crystal X-ray diffraction method which reveals a distorted tetrahedral geometry where the Cu(I) ion is surrounded by one BTU ligand molecule, two PPh3 groups and one chloride anion. These eight heteroleptic complexes were found to emit in solid state with lifetimes in the 12-99 mu s range and with the highest quantum yield of 4.0% for 3b. The reaction between [CuBr(PPh3)](4) and N-benzoyl-N',N'-(di-n-butyl)thiourea (BTU-Bu-2) ligand gave the simple [CuBr(BTU-Bu-2)(3)] complex (5), when the PPh3 molecules were completely removed by the BTU derivative. The spectroscopic data indicated a distorted tetrahedral geometry produced by three BTU ligand molecules and one bromide anion. Complex 5 has the highest quantum yield (11%) with the lifetime of 29 mu s in solid-state.

The green macroalga Ulva rigida represents a promising feedstock for biorefinary due to its fast growth and cosmopolitan distribution. The main component of the cell walls of U. rigida is a sulfated glucuronorhamnan polysaccharide known as ulvan. Herein it was found that due to the high (hydrogen)sulfate group content of ulvan, hydrothermal autohydrolysis at 130 degrees C renders a high percentage of rhamnose (78-79 % recovery from the initial content in the raw material), a rare sugar of high added value. In addition, acid catalysis by a triflate-based graphene oxide under oxygen-free conditions at 180 degrees C affords moderate amounts of tartaric acid (24-26 %). The same triflate-based graphene oxide catalyst under oxygen pressure yields remarkably high percentages of succinic acid (65 %). The catalyst preserves its activity for at least five consecutive reuses.

Microporous graphitic carbons obtained by pyrolysis of a-cyclodextrin have been conveniently doped with N and P elements by performing the thermal graphitization adding urea or phosphoric acid as source of these elements. Electron microscopy shows that doping does not influence the structure and dimensions of the micropores, while XPS reveals the distribution of these dopant elements in two main families corresponding to pyridinic and pryrrolic N atoms and to triphenylphosphine and triphenylphosphine oxide for P doping. Thermo-programmed desorption of H2, CO2 and NH3 indicates that the presence of dopant element is responsible for chemisorption of these gases and introduces basic and acid sites. These desorption measurements agree with the catalytic performance of the series of carbons for the chemo and stereo selective hydrogenation of internal aliphatic and aromatic alkynes to cis configured alkenes. N/P doped microporous carbons were found to be stable under the reaction conditions, according to the constant TOF values and XRD and XPS characterization of the materials after their use as catalysts. In addition microporosity appears to play a positive effect by comparing the activity of microporous carbons with the performance of analogous N/P-doped graphenes. (c) 2021 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

The performances of 3.5 at.% Nd:LGSB bifunctional laser and nonlinear optical (NLO) crystal were investigated. A high-quality single crystal with incongruent melting, having dimensions of about 12 mm in diameter and 35 mm in length, was grown along the c-axis by the Czochralski technique. The phase-matching curve for type I second harmonic generation (SHG) was determined. Efficient laser emission at 1062 nm, along the phase-matching direction for SHG of 1062 nm radiation, was obtained under the pump at 807 nm with a fiber-coupled laser diode. The Nd:LGSB laser operated with a high slope efficiency of eta(sa) = 0.56 (with respect to the absorbed pump power), delivering the highest output power of 2.1 W for 4.04 W of absorbed pump power. Preliminary SFD experiments resulted in achieving a maximum green output power of 48 mW at 3.94 W absorbed pump power.

The influence of the severe plastic deformation via high-speed high-pressure torsion (HSHPT) on the structural and magnetic properties of the Zr13Co87 alloys is investigated. Moderate applied deformation promotes the growth of the rhombohedral hard magnetic phase leading to the increase of the sample's hardness and magnetic coercivity. A higher degree of deformation affects the samples morphology leading to a critical value of the grain size under which the exchange coupling of the soft phase is less effective. Additionally, it produces a random alignment of the anisotropy axes, which are both detrimental to the hard magnetic properties.

The species cis-[Cu(tbg)(2)](ClO4)(2) (CuTP) (tbg: 1-(o-tolyl)biguanide) was designed as a novel antimicrobial and biocompatible agent. The single-crystal X-ray diffraction revealed a mononuclear species with a very interesting structure consisting of two tautomeric forms of tbg arranged in a cis-configuration. A complex hydrogen bond network with perchlorate anions involved in different interactions leads to a supramolecular structure. The EPR data indicated the formation of a stable cis-trans mixture in dimethylsulfoxide. Moreover, the EPR experiments evidenced no activity against the superoxide radical (O-2 center dot(-)) but scavenging ability of the hydroxyl radical (HO center dot). This complex exhibited excellent antibacterial properties against planktonic and biofilm embedded gram-negative (Klebsiella pneumoniae, Enterobacter cloacae) and gram-positive (Bacillus subtilis, Lysteria monocytogenes) bacteria. The best efficiency was noticed against E. cloacae and L. monocytogenes with minimal inhibitory concentration and minimal biofilm eradication for a concentration value of 1.95 mu g/ml. One of the possible mechanisms of antimicrobial activity is represented by reactive oxygen species (ROS) generation. The complex was not cytotoxic on L929 fibroblasts. The in silico analysis confirmed the drug-likeness and safety profile of the tested compound and its potential for developing novel antimicrobial and therapeutic tools, targeting other clinical conditions besides infectious diseases.

We describe herein synthesis of novel hydroxy-bis-2,5-disubstituted-1,3,4-oxadiazoles and their ability to emit green light, through ESIPT mechanism. Unlike previous reports, our compounds exhibit very good quantum yields, most likely avoiding the presumed intramolecular fluorescence quenching in presence of the second oxadiazole moiety. Studies regarding behaviour of the compounds in polar and non-polar solvents are also described, indicating the possibility to modulate the emission according to the environment. The solid-state structural analysis, corroborated with fluorescence data, suggest the importance of the tert-butyl group in preservation of the luminescent properties. The corresponding benzyl-protected compounds, precursors to the target hydroxy-bis-2,5-disubstituted-1,3,4-oxadiazoles were also investigated for their optical properties and found to display very intense blue emission, with quantum yields values in dichloromethane (between 0.423 and 0.499) almost equal to the standard quinine sulfate.

We present an array of 225 field-effect transistors (FETs), where each of them has a graphene monolayer channel grown on a 3-layer deposited stack of 22 nm control HfO2/5 nm Ge-HfO2 intermediate layer/8 nm tunnel HfO2/p-Si substrate. The intermediate layer is ferroelectric and acts as a floating gate. All transistors have two top gates, while the p-Si substrate is acting as a back gate. We show that these FETs are acting memtransistors, working as two-input reconfigurable logic gates with memory, the type of the logic gate depending only on the values of the applied gate voltages and the choice of a threshold current.

In this work, polyvinylidene fluoride was obtained in the form of one-dimensional structures with the help of electrospinning technique. Several types of precursor solutions were tested to find the optimal experimental conditions to produce smooth, continuous and beadless fibres, morphologically suitable for the development of piezoelectric scaffolds dedicated to tissue engineering applications. Thus, the influence of solvent type, polymer concentration, as well as electrospinning parameters (feeding rate, spinneret-collector distance, and applied voltage) was assessed and the best situation was the one with a 2:3 ratio between dimethylformamide and acetone, 20 % polymer concentration, 1 mL/h flow, 20 cm distance and 18 kV voltage. In the end, the fibres were loaded with barium titanate commercial particles, as first attempt to produce a piezoelectric composite with potential in the medical field.