National Institute Of Materials Physics - Romania

This study aimed to develop and characterise novel hydrogels based on natural bioactive compounds for topical antimicrobial applications. Four gel systems were formulated using different polymers, namely polyacrylic acid (Carbopol 940, CBP-G), chitosan with high and medium molecular weights (CTH-G and CTM-G), and sodium alginate (ALG-G), incorporating tinctures of Verbena officinalis and Aloysia triphylla, Laurus nobilis essential oil, and a beta-cyclodextrin-clove essential oil complex. All gels displayed a homogeneous macroscopic appearance and maintained stability for over 90 days. Rheological studies demonstrated gel-like behaviour for CBP-G and ALG-G, with well-defined linear viscoelastic regions and distinct yield points, while CTM-G exhibited viscoelastic liquid-like properties. SEM imaging confirmed uniform and continuous matrices, supporting controlled active compound distribution. Thermogravimetric analysis (TG-DTA) revealed a two-step degradation profile for all gels, characterised by high thermal stability up to 230 degrees C and near-total decomposition by 500 degrees C. FTIR spectra confirmed the incorporation of bioactive compounds and products and highlighted varying interaction strengths with polymer matrices, which were stronger in CBP-G and CTH-G. Antimicrobial evaluation demonstrated that chitosan-based gels exhibited the most potent inhibitory and antibiofilm effects (MIC = 2.34 mg/mL) and a cytocompatibility assessment on HaCaT keratinocytes showed enhanced cell viability for chitosan gels and dose-dependent cytotoxicity for alginate formulations at high concentrations. Overall, chitosan-based gels displayed the most favourable combination of stability, antimicrobial activity, and biocompatibility, suggesting their potential for topical pharmaceutical use.

Synchrotron-based small- and wide-angle X-ray scattering is used to elucidate the structure of low-dimensional lepidocrocite-titanate-based nanofilaments. In the colloidal state, they consist of quantum-confined 1D NFs, loosely associated into nanoribbons, one lepidocrocite sheet thick (about 4 & Aring;), 30-40 & Aring; wide (5-8 NFs), and more than 300 & Aring; long. In the dry state, they reach a final state of extended sheets, stacked three to about twenty high, whose crystallinity increases with stack height, in parallel with a decrease in photocatalytic activity. These findings suggest a kinetic pathway for the self-assembly of initially 1D titanate nanoribbons into 2D and ultimately 3D structures, providing context for a recent body of work on these low-dimensional materials.

In this study, we expand the processing space of new, quantum-confined one-dimensional lepidocrocite (1DL) titania-based nanofilaments (NFs). Our previous work to date entailed reacting Ti-precursors (e.g., TiB2, TiOSO4, TiN, TiC, etc.) with the quaternary ammonium compound (quat) tetramethylammonium hydroxide (TMAH) for tens of hours under ambient pressures at temperatures ranging from 50 degrees C to 80 degrees C. Herein, we expand the list of quats that result in 1DL NFs to tetraethylammonium hydroxide (TEAH), tetrapropylammonium hydroxide (TPAH), tetrabutylammonium hydroxide (TBAH), and choline hydroxide (ChoH). We also show that tetrabutylphosphonium hydroxide (TBPH) can be used to the same end result. These quats and TBPH are less toxic than TMAH, especially Cho+, which is fully biocompatible. And, while all the quats and TBPH result in the same 1D product, their de-flocculation in various organic solvents is different. Reacting with less polar quats (e.g., TBA) and washing with less polar solvents (e.g., dichloromethane) favors the formation of porous mesostructured particles. 2D structures are favored if the opposite is chosen. Said otherwise, by the judicious choice of a quat (e.g., TPAH) and solvent (e.g., tert-butanol) combination, we produced stable 1DL colloidal suspensions in dimethyl sulfoxide, methanol, ethanol, acetonitrile, isopropyl alcohol, butanol, and acetone. This enhanced colloidal stability is critical in applications in coatings, inks, and catalytic systems where non-aqueous stable dispersions are paramount. The high band-gap energies, Eg, measured (3.8-3.9 eV) confirm quantum confinement. The Eg are also quite insensitive to d spacings between the 2D sheets. These 1DLs exhibit significant adsorption and dye (rhodamine 6G) degradation capabilities. For example, TEA-1DL colloidal suspensions adsorb 64% of the dye in the dark in about 5 min and decolorize 99% of the remaining dye within 30 min under the irradiance of one sun.

We present herein the synthesis of novel [2 + 2] and [3 + 3] N-acylhydrazone-based macrocycles using a pool of dialdehydes and dihydrazides, under thermodynamic control. The resulting macrocycles, which were assigned triangular and rectangular shapes, were characterised in the solid state. The rectangular macrocycle was further investigated in solution by absorption and emission spectroscopy. Additionally, the rectangular macrocycle was used in various assays to investigate the hosting capacity towards various guests using NMR, HRMS, UV-visible and fluorescence spectroscopy. Theoretical calculations regarding structure and properties of the novel compounds were in agreement with the experimental details. The experimental data showed intriguing results toward tetra-n-butylammonium fluoride.

Synchrotron-based small- and wide-angle X-ray scattering is used to elucidate the structure of low-dimensional lepidocrocite-titanate-based nanofilaments. In the colloidal state, they consist of quantum-confined 1D NFs, loosely associated into nanoribbons, one lepidocrocite sheet thick (about 4 & Aring;), 30-40 & Aring; wide (5-8 NFs), and more than 300 & Aring; long. In the dry state, they reach a final state of extended sheets, stacked three to about twenty high, whose crystallinity increases with stack height, in parallel with a decrease in photocatalytic activity. These findings suggest a kinetic pathway for the self-assembly of initially 1D titanate nanoribbons into 2D and ultimately 3D structures, providing context for a recent body of work on these low-dimensional materials.

Most photocatalytic processes involve physicochemical phenomena occurring at the semiconductor-water interface. The interfacial charge transfer strongly depends on the charge carrier self-trapping or defect-based trapping mechanisms active in the crystal lattice of the photocatalyst. Thus, the crystal lattice distortion is expected to influence the photocatalytic efficiency during polymorphic phase transformations (PPT). A simple synthesis method involving the ultrasound-assisted excess hydrolysis of titanium tetra-isopropoxide (TTIP) (hydrolysis ratio (number of moles of water/number of moles of TTIP) r = 245) was used to obtain multiphase titanium dioxide (TiO2) nanomaterials with complex defect structures. Electron paramagnetic resonance (EPR) spectroscopy was employed to characterize the paramagnetic centers in the synthesized TiO2 and their behavior during incipient PPT. The calcined samples showed a complex defect structure comprising three types of paramagnetic centers: F+-centers (an electron trapped in an oxygen vacancy (Ov)), V-centers (oxygen ions with trapped holes) and paramagnetic centers involving Ti3+ such as Ti3+- Ov. The sample obtained at 600 degrees C, temperature marking the onset of a massive mixed transformation of anatase into rutile and brookite, composed of approximately 81 % anatase, 10 % brookite, and 9 % rutile, exhibited an intense and broadened EPR signal and enhanced photocatalytic activity for hydroxyl radical generation and hydrogen production by water splitting, despite its rather low specific surface area of 34 m2/g. The results revealed the synergistic effects of charge carrier trapping mechanisms in the early stages of PPT, boosting the photocatalytic performance of TiO2. The present study supports the design of facile synthesis methods for better TiO2 photocatalysts and promotes the development of further studies regarding lattice defect engineering during phase transformations in nanomaterials.

Herein we present a comparative study among different spray-coated nanometric mesoporous electron transporting layers (ETLs) in perovskite solar cells (PSC), namely m-TiO2, 2 , m-SnO2 2 and m-SnO2 2 quantum dots (mSnO2QDs). 2 QDs). The solutions used for deposition were prepared from commercial pastes and colloidal suspensions for m-TiO2 2 and m-SnO2. 2 . For m-SnO2QDs 2 QDs in-house QDs solutions were prepared. The formamidiniummethylamonium-potassium (FAMA@10 K) has been used as light absorber material in the fabricated PSCs. The structural, compositional and morphological studies, correlated with the photovoltaic performance of PSCs, indicate that the m-SnO2 2 QDs layer is the best candidate among the three investigated mesoporous ETLs. Compared with the suspensions used for the other two ETLs, the in-house prepared SnO2 2 QDs solution presents smaller agglomerates of nanoparticles and results in the formation of a thinner, more uniform and compact mesoporous ETL. The FAMA@10 K perovskite deposited on m-SnO2 2 QDs ETL presents a lower roughness, better uniformity and a higher amount of PbI2. 2 . Our work unveils that the SnO2 2 QDs solution can be easily produced in laboratory and when is deposited as mesoporous scaffold in a PSC with FAMA@10 K perovskite, the power conversion efficiency increases up to 14.90 %, being with up to 27 % larger than in the PSCs with m-TiO2 2 and mSnO2 2 ETLs prepared from commercial solutions. By modeling the J-V dynamic hysteresis with more than 90 % match between the calculated and experimental J-V data, for all three types of mesoporous ETLs, the relevant parameters that explain the hysteresis magnitude and account for ionic-induced recombination processes in PSCs were determined.

Herein we show that the Ti3SiC2 MAX phase can be used as a support for deposition of different amounts of metal oxides (MOx, M = Cu or V) (5, 10 and 20 wt%) for the direct oxidation of methane to formaldehyde using molecular oxygen, at relatively low temperatures and atmospheric pressure. The oxides were deposited using a hydrothermal method at 180 degrees C without affecting the bulk MAX phase structure. However, during the hydrothermal treatment (HT) a thin oxide layer - found to play an important role in the reaction's selectivity- was evidenced by X-ray photoelectron spectroscopy. We thus conclude that the MOx species are responsible for the CH4 activation, while the Ti3SiC2 surface is responsible for the high selectivity to formaldehyde indicating that, Ti3SiC2 has great potential for designing innovative catalysts for direct oxidation of methane using molecular oxygen and at atmospheric pressure.

The increasing demand for greener technologies in environmental remediation makes carbon materials from biomass and its derivatives some of the most attractive resources for a sustainable future. However, integrating these materials with stable free radicals remains challenging. This study presents a straightforward one-pot hydrothermal route using raw honey as the carbon source and 4-amino 2,2,6,6-tetramethylpiperidine-1-oxyl (4-amino-TEMPO) as the free radical. The addition of TEMPO derivative initiates Maillard reactions between its amino group and the carbonyl groups of the carbohydrates in honey, resulting in the formation of a functionalized hydrochar with a spherical morphology (similar to 8 mu m). The presence of free radicals within the carbonaceous matrix was confirmed by electron spin resonance spectroscopy, supported by infrared spectroscopy, elemental analysis, thermal analysis, scanning electron microscopy, and X-ray photoelectron spectroscopy. The free radical content was estimated at 0.4 mmol center dot g(-1). The material effectively removed methylene blue, fluorescein, and doxorubicin from water in the presence of green oxidants like hydrogen peroxide and sodium hypochlorite. After 24 h, removal efficiencies reached 92% for doxorubicin, 73% for methylene blue, and 23% for fluorescein. Moreover, the hydrochar demonstrated good regeneration capability, maintaining its dye removal efficiency over several cycles.

TiO2-C (carbon) hybrid materials are promising electrocatalyst supports because the presence of TiO2 results in enhanced stability. Use of new types of carbonaceous materials such as reduced graphene oxide instead of traditional active carbon provides certain benefits. Although the rutile polymorph of TiO2 seems to have the most beneficial properties in these hybrid materials, the anatase type is more frequent in TiO2-rGO composites, especially in graphite oxide (GO) derived ones, as GO has several properties which may interfere with rutile formation. To explore and evaluate these peculiarities and their influence on the composite formation, we compared TiO2-C systems formulated with GO and Black Pearls (BP) carbon. Various physicochemical methods, such as attenuated total reflection infrared (ATR-IR)-, solid state NMR-, Raman- and X-ray photoelectron spectroscopy, X-ray powder diffraction (XRD), electron microscopy, etc. were used to characterize the samples from the different stages of our multistep sol-gel synthesis. Our experiments demonstrated that utilization of GO is indeed feasible for composite preparation, although its sodium contamination has to be removed during the synthesis. On the other hand, high temperature treatment and/or solvothermal treatment during composite synthesis resulted in decomposition of the functional groups of the GO and the functional properties of the final product were similar in case of both composites. However, Pt/TiO2-GO derived sample showed higher oxygen reduction reaction activity than Pt/TiO2-BP derived one. Based on the decrease of electrochemical surface area, the stability order was the following: Pt/C (commercial) < Pt/TiO2-BP derived C < Pt/TiO2-GO derived C.