National Institute Of Materials Physics - Romania

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.

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 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.

This work examines the effect of incorporating a third cation M (M = Mg, Al, Mn, or Fe) into Nb-promoted NiO catalysts (Ni0.85Nb0.15O) on their physicochemical properties and catalytic performance in the oxidative dehydrogenation (ODH) of ethane into ethylene. Therefore, a series of mixed oxides with the composition Ni0.765Nb0.135M0.1O was synthesized, characterized, and analyzed for catalytic behavior. The addition of the third cation markedly modified the redox and semiconductive properties of the catalysts, thus affecting their ODH performance. The selectivity toward ethylene was strongly dependent on the cation modifier, as it modulated the density of nonselective sites on the catalyst surface. In the low-temperature region, Mn-NiNbO demonstrated the highest conversion rates but with the lowest ethylene selectivity, whereas Fe-NiNbO, despite being less active than the undoped NiNbO, exhibited the highest ethylene selectivity. Overall, undoped NiNbO emerged as the best catalyst in terms of both activity and selectivity at isoconversion. All catalysts underwent partial reduction under reaction conditions, with the degree of reduction inversely correlated with the specific reaction rates. Although none of the catalysts remained stable at 400 degrees C, Al-NiNbO showed the least deactivation over time. The deactivation was linked to a reduction in p-type conductivity and a loss of redox functionality during operation.

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.

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.

Design of composite support materials based on Sn-doped TiO2 and carbon is one of the strategies to develop corrosion-resistant and CO-tolerant Pt electrocatalysts for polymer electrolyte membrane (PEM) fuel cells. As the synthesis methodology may have crucial influence on the structural and functional properties of the composites, different preparation routes for the novel support materials are explored and compared. Ti(1-x)SnxO2-C (x: 0.1-0.3) composites with different mixed oxide/carbon ratios were prepared by two sol-gel-based synthesis routes, namely (i) the introduction of a Sn precursor after the formation of the TiO2-rutile nuclei on the carbon backbone (route A), and (ii) simultaneous introduction of Ti and Sn precursors, resulting in good mixing of the Sn- and Ti-sol before the addition of the carbon (route B). The bulk and surface microstructure of the composites and the electrocatalysts obtained by their Pt-loading were investigated in detail. The incorporation of tin into the TiO2-rutile unit cell was confirmed by X-ray powder diffraction and Raman spectroscopy; the results indicated doping levels in good accordance with the amount of tin precursor. The advantages of composites and Pt electrocatalysts obtained via synthesis route B were that they do not contain segregated Sn-0 or SnO2 phases, have a more homogeneous/uniform mixed oxide distribution over the carbon backbone, and the electrochemically active surface area values (similar to 60-80 m(2)/g(Pt)) are twice as high as those of catalysts with similar compositions synthesized by method A. A common feature of the composites prepared by routes A and B was the presence of a tin oxide-rich overlayer identified by X-ray photoelectron spectroscopy. As a consequence, the electrocatalytic behavior of the catalysts was not influenced by the Ti/Sn ratio and was mainly dependent on the synthesis method used in the preparation of composite support materials. Elemental maps confirmed the formation of areas where Pt and the Sn doping element were in atomic proximity to each other, which means a favorable interaction either for the bifunctional mechanism or the electronic ligand effect. An increase in carbon content in composite materials led to an increase in both catalytic activity and long-term stability. The results of electrochemical studies showed that Sn-containing Pt catalysts with a high carbon content (75 wt%) are the most promising for potential use both as an anode and a cathode for PEM fuel cells.

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.

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.