Dr. Anca Gabriela Mirea

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.

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.

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.

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.

There has been increased interest in the synthesis of benfotiamine during the past few years, most likely as a direct consequence of growing market demand. It has much higher bioavailability than thiamine (vitamin B1) and therefore is more suitable for therapeutic purposes, especially in oral form. We report herein our research in an academic-private R&D project in which we investigate all aspects of the process on small and large scales. The procedure involves two labor-intensive steps, starting from thiami3ne chloride hydrochloride with the key intermediate thiamine monophosphate phosphate (TMP-the phosphate ester of thiamine monophosphate). We obtained the crystalline form of benfotiamine directly from the synthesis in the crystalline form required on the market, as proven by XRD powder spectroscopy, IR, and RAMAN.

In this study, molybdenum doped iron cobaltite and cobalt ferrite catalysts were prepared by coprecipitation, and their structural, morphological, and optical, properties were evaluated by XRD, BET, SEM, FTIR, Raman, XPS and UV-VIS techniques. Their catalytic behavior evaluated in the malic acid oxidative decarboxylation reaction underlined the importance of the incorporation of Mo into the structure of iron cobaltite and cobalt ferrite catalysts. The catalysts with the highest molybdenum content forming cobaltite and iron molybdate phases showed better activity, with cobaltite-based catalysts being more active than ferrite-based ones.

This work reports the design and synthesis of novel oxadiazole-decorated azobenzenes, structural analysis of the resulting compounds and behavior under light irradiation. The synthetic strategy involved constructing amino functionalized heterocyclic key intermediates which were used either to yield electrophilic diazonium salts able to react with phenol moieties or as nucleophilic partners in Bayer-Mills reaction with nitroso-substituted derivatives. The amino-derived oxadiazole intermediates were investigated by absorption and emission spectroscopy providing blue and green emitted light. The target oxadiazole-decorated azobenzenes were structurally characterized, including solid-state structures, and subsequently used in irradiation experiments in order to take advantage of the azo group known to provide photoswitching abilities. We noticed quenching of the emissive properties in presence of the azo group; however, all compounds were very stable to repeated cycles of light irradiation. In addition, according to structural diversification we could obtain half-lives of the meta stable isomers within hours to hundreds of hours range. The experimental results were very well correlated with DFT calculations. The synthesis of novel oxadiazole-decorated azobenzenes using amino functionalised heterocyclic intermediates used either to provide electrophilic diazonium salts able to react with phenols or as nucleophilic partners in Bayer-Mills reaction is reported in this work. The oxadiazole-decorated azobenzenes were used in irradiation experiments to determine the parameters that characterize a photoswitch, yielding appealing results. The experimental results were very well correlated with DFT calculations.+image

Plastics are indispensable materials for packaging and many products from our daily life, and their recycling is essential to ensure a circular economy. In this study, -SO3H-modified, Ti3C2-MXene was used as a recoverable solid acid catalyst for upcycling of polyethylene terephthalate (PET) to terephthalic acid (TPA) and ethylene glycol by hydrolysis. For the grafting of -SO3H groups to the Ti3C2Tx surface (where T-x represents the surface moieties, such as -OH or -O), sulfonation with an aryl diazonium salt obtained from sulfanilic acid was employed. X-ray photoelectron and Fourier transform infrared spectroscopy analyses provided a direct indication that sulfonation of the Ti3C2Tx was successfully performed, while X-ray diffraction and transmission electron microscopy analyses evidence the presence of -SO3H groups between the Ti3C2Tx layers due to the increases of the interlayer spacing through the intercalation of functional groups. The higher the concentration of acid groups, the higher the interlayer spacing. The depolymerization of PET in water occurred with a very good isolated yield in TPA (99%) for the MXene with the highest amount of sulfonic acid groups. We conclude that the acidity is mandatory to perform the hydrolysis reaction, in agreement with the acidity measurements, which show that the MXenes modified with the highest amount of derived sulfonic acids are the most active. Nevertheless, the accessibility to the acidic sites is a key factor that promotes the 2D acid-modified MXene materials as important catalysts for PET upcycling to TPA.

Electronic and stability properties of quasi-2D alkylammonium perovskites are investigated using density functional theory (DFT) calculations and validated experimentally on selected classes of compounds. Our analysis is focused on perovskite structures of formula (A)(2)(A ')(n-1)PbnX3n+1, with large cations A = butyl-, pentyl-, hexylammonium (BA, PA, HXA), small cations A ' = methylammonium, formamidinium, ethylammonium, guanidinium (MA, FA, EA, GA) and halogens X = I, Br, Cl. The role of the halogen ions is outlined for the band structure, stability and defect formation energies. Two opposing trends are found for the absorption efficiency versus stability, the latter being assessed with respect to possible degradation mechanisms. Experimental validation is performed on quasi-2D perovskites based on pentylammonium cations, namely: (PA)(2)PbX4 and (PA)(2)(MA)Pb2X7, synthesized by antisolvent-assisted vapor crystallization. Structural and optical analysis are inline with the DFT based calculations. In addition, the thermogravimetric analysis shows an enhanced stability of bromide and chloride based compounds, in agreement with the theoretical predictions.

Iron-doped Co3O4 oxides prepared by a surfactant-assisted method exhibited good catalytic activity in malic acid conversion, and the oxygen defects associated with the presence of Co2+ played a key role in catalyst activation for pyruvic acid production. The most active catalyst, for which the malic acid conversion was 70% and the pyruvic acid yield was 24%, has an inverse spinel type structure (Fe3+ replaces Co2+ from tetrahedral sites, while Fe2+ replaces Co3+ from octahedral sites) as well as a small energy difference between the highest occupied orbital and the lowest unoccupied orbital (low band-gap, E-g). The catalyst with the highest Co2+ loading showed the highest yield of pyruvic acid.

Light-emissive compounds able to transfer protons, either intra-or intermolecularly in the excited state, have increasingly attracted attention, especially by structural diversification of recognized fluorophores. We report herein synthesis and structural characterization of novel 1,3,4-oxadiazole-based compounds functionalised by salicylaldehyde or o-vanillin moieties. Solution absorption and emission spectroscopy performed on the resulted compounds indicated the essential influence of the established (intra and/or intermolecular) hydrogen bonds onto the optical properties. Theoretical calculations positively contributed to the effort of understanding the emissive behaviour of the compounds and the calculated data correlated very well to experiments. Occurrence of hydrogen bond interactions has been also observed in solid state and we discuss their molecular structures and the effects on the luminescent behaviour. The phenol groups in close proximity of the oxadiazole core were further exploited in cocrystallization experiments with pyridine-based co-partners. Hydrogen bonding were also found responsible for the supramolecular recognition between the two components. One type of the resulted co -crystals preserved the luminescence of the starting compound.

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.

TiO2-based mixed oxide-carbon composite supports have been suggested to provide enhanced stability for platinum (Pt) electrocatalysts in polymer electrolyte membrane (PEM) fuel cells. The addition of molybdenum (Mo) to the mixed oxide is known to increase the CO tolerance of the electrocatalyst. In this work Pt catalysts, supported on Ti1-xMoxO2-C composites with a 25/75 oxide/carbon mass ratio and prepared from different carbon materials (C: Vulcan XC-72, unmodified and functionalized Black Pearls 2000), were compared in the hydrogen oxidation reaction (HOR) and in the oxygen reduction reaction (ORR) with a commercial Pt/C reference catalyst in order to assess the influence of the support on the electrocatalytic behavior. Our aim was to perform electrochemical studies in preparation for fuel cell tests. The ORR kinetic parameters from the Koutecky-Levich plot suggested a four-electron transfer per oxygen molecule, resulting in H2O. The similarity between the Tafel slopes suggested the same reaction mechanism for electrocatalysts supported by these composites. The HOR activity of the composite-supported electrocatalysts was independent of the type of carbonaceous material. A noticeable difference in the stability of the catalysts appeared only after 5000 polarization cycles; the Black Pearl-containing sample showed the highest stability.

MAX phases and MXenes are important materials that have recently gained great popularity due to their special properties, which render them particularly useful in many applications, including catalytic ones. This can be seen in the large number of publications that appear annually on these materials and their applications. This review aims to evaluate MAX phases and MXenes as materials for heterogeneous, non-electrocatalytic, catalytic applications. The review begins with a brief introduction to the MAX phase and MXene properties that recommend them as potential materials for heterogeneous catalytic applications, followed by four sections grouped according to the processes in which they have already proven effective. These include supports to activate the C-H or C-O bonds in applications such as dehydrogenation of light or aromatic alkanes, methanol formation from CH4, dry reforming, and CO oxidation or the water gas shift reaction (Section 2), and their use in fine chemical reactions (Section 3) and in chemical degradation (Section 4). The last section deals with photocatalytic applications (Section 5). The review ends by highlighting the huge potential of these materials for a wide range of heterogeneous catalytic applications as well as the challenges ahead.