RESUMO

Methane is an abundant resource and the main constituent of natural gas. It can be converted into higher value-added products and as a subproduct of electricity co-generation. The application of polymer electrolyte reactors for the partial oxidation of methane to methanol to co-generate power and chemical products is a topic of great interest for gas and petroleum industries, especially with the use of materials with a lower amount of metals, such as palladium complex. In this study, we investigate the ideal relationship between cis-[6-(pyridin-2-yl)-1,3,5-triazine-2,4-diamine(dichloride)palladium(II)] (Pd-complex) nanostructure and carbon to obtain a stable, conductive, and functional reagent diffusion electrode. The physical and structural properties of the material were analyzed by Fourier transform infrared (FT-IR) and Raman spectroscopies, transmission electron microscopy (TEM), and X-ray powder diffraction (XRD) techniques. The electrocatalytic activity studies revealed that the most active proportion was 20% of Pd-complex supported on carbon (m/m), which was measured with lower values of open-circuit and power density but with higher efficiency in methanol production with reaction rates of r = 4.2 mol L-1·h-1 at 0.05 V.

RESUMO

Cobalt-Prussian blue analogues are remarkable catalysts for the oxygen evolution reaction (water oxidation) under mild conditions such as neutral pH. Although there are extensive reports in the literature about the application of these catalysts in water oxidation (the limiting step for hydrogen evolution), some limitations must be overcome in terms of improving the turnover frequency, oxygen production, long term stability, and elucidation of the mechanism. Another important feature to consider is the industrial processability of electrolytic cells for water splitting. For these reasons, we have reported herein a comparison of the electrochemical and chemical properties of three catalysts produced from cobalt-Prussian blue. Co-Co PBA 60 refers to cobalt-Prussian blue heated up to 60 °C with a high content of water. Co-Co PBA 200 is the same starting material but heated up to 200 °C with a low water content. Finally, Co3O4 is a thermal decomposition product obtained from heating cobalt-Prussian blue up to 400 °C. Although Co-Co PBA 60 has a higher overpotential for water oxidation than Co-Co PBA 200, this catalyst is kinetically faster than Co PBA 200. It is suggested that the water coordinated to Co2+ in Co-Co PBA 60 can accelerate the reaction and that there is a balance between the thermodynamic and kinetic characteristics for determining the final properties of the catalyst at pH = 7. Another important observation is that the Co3O4 catalyst has the best performance among the considered catalysts with the highest TON and TOF. This suggests that the different mechanisms and surface effects demonstrated by the Co3O4 catalyst are more conducive to efficient water oxidation than those of Prussian blue. Further studies concerning the effect of water and surface on these catalysts under mild conditions are essential to gain a better understanding of the mechanism of water oxidation and to advance the development of new catalysts.

RESUMO

Three-dimensional printing techniques have been widely used in the fabrication of new materials applied to energy, sensing and electronics due to unique advantages, such as fast prototyping, reduced waste generation, and multiple fabrication designs. In this paper, the production of a conductive 3D-printing filament composed of Ni(OH)2 microparticles and graphene within a polylactic acid matrix (Ni-G-PLA) is reported. The nanocomposite was characterized by thermogravimetric, energy-dispersive X-ray spectroscopic, scanning electronic microscopic, Raman spectroscopic and electrochemical techniques. Characteristics such as printability (using fused deposition modelling), electrical conductivity and mechanical stability of the polymer nanocomposite were evaluated before and after 3D printing. The novel 3D-printed disposable electrode was applied for selective detection of glucose (enzyme-less sensor) with a detection limit of 2.4 µmol L-1, free from the interference of ascorbic acid, urea and uric acid, compounds typically found in biological samples. The sensor was assembled in a portable electrochemical system that enables fast (160 injection h-1), precise (RSD < 5%) and selective determination of glucose without the need of enzymes (electrocatalytic properties of the Ni-G-PLA nanocomposite). The obtained results showed that Ni-G-PLA is a promising material for the production of disposable sensors for selective detection of glucose using a simple and low-cost 3D-printer.

Assuntos

RESUMO

This communication shows the electrochemical synthesis of Prussian blue (PB) films on additive manufactured (3D-printed) electrodes from iron impurities found at the graphene-polylactic acid (G/PLA) substrate and its application as a highly selective sensor for H2O2. The 3D-printed G/PLA electrode was immersed in dimethylformamide for 30 min to exposure the iron impurities within the PLA matrix. Next, cyclic voltammograms (200 cycles) in the presence of potassium ferricyanide in 0.1 mol L-1 KCl + 0.01 mol L-1 HCl were performed to grow the PB films. The sensing properties of this novel PB/G/PLA platform were evaluated for the amperometric detection of H2O2 using batch-injection analysis, with a limit of detection of 0.56 µmol L-1 under the application of 0.0 V (vs Ag/AgCl/KClsat.). The applicability of the sensor was demonstrated for the analysis of milk samples (10-fold diluted in the supporting electrolyte), resulting in proper recovery values (94-101%).

Assuntos

RESUMO

Abstract The treatment of infections caused by resistant microorganisms represents a big challenge in healthcare due to limited treatment options. For this reason, the discovery of new active substances which are able to perform innovative and selective actions is of great impact nowadays. Statins and triazenes (TZC) have consolidated as a promising class of compounds, characterized by the expressive biological activity, especially antimicrobial activities. The aim of this study was to assess the in vitro synergistic antibacterial effect of the association of statins and a new TZC complex {[1-(4-bromophenyl)-3-phenyltriazene N 3-oxide-κ 2 N 1,O 4](dimethylbenzylamine-κ 2 C 1,N 4)palladium(II)} (Pd(DMBA)LBr) against American Type Culture Collection (ATCC) strains and clinical isolates. The complex and the statins showed bacterial activity of all tested strains and clinical isolates, evidencing that TZC complexion with metals can be promising. Simvastatin showed synergy when associated to the complex (FICI≤0.5), being the minimum inhibitory concentration (MIC) of 16 µg mL-1 found in 6 samples. Thus, it is possible to infer that the association between Pd(DMBA)LBr and simvastatin consists of an alternative to increase the pontential of these compounds, since statins have low toxicity.

Assuntos

RESUMO

In the title compound, C13H13ClO4, the dihedral angle between the chloro-benezene ring and the least-squares plane through the 4-meth-oxy-2-oxobut-3-enoate ethyl ester residue (r.m.s. deviation = 0.0975 Å) is 54.10 (5)°. In the crystal, mol-ecules are connected by meth-oxy-ketone and benzene-carboxyl-ate carbonyl C-H⋯O inter-actions, generating a supra-molecular layer in the ac plane.

RESUMO

The mol-ecule of the title compound, C9H7IN4OS, is almost planar (r.m.s. deviation = 0.0373 Å). In the mol-ecule, N-H⋯N and N-H⋯O hydrogen bonds generate, respectively, S(5) and S(6) ring motifs. In the crystal, mol-ecules are linked via N-H⋯O hydrogen bonds, forming chains propagating along [010]. These chains are linked via S⋯I contacts [3.4915 (16) Å], forming sheets lying parallel to (100). A region of disordered electron density, probably a disordered tetra-hydro-furan solvent mol-ecule, was treated using the SQUEEZE routine in PLATON [Spek (2009). Acta Cryst. D65, 148-155]. The formula mass and unit-cell characteristics were not taken into account during refinement.

RESUMO

In the title compound, C14H13ClN4S, obtained from a reaction of 2-benzoyl-4-chloro-aniline with thio-semicarbazide in ethanol, the dihedral angle between the aromatic rings is 81.31 (13)°. In the crystal, the mol-ecules are linked by three N-H⋯S hydrogen bonds, forming centrosymmetric rings with set-graph motif R 2 (2)(8) and R 2 (2)(18), and resulting in the formation of a two-dimensional network lying parallel to (010).

RESUMO

The title mol-ecule, C9H7ClN4OS, is almost planar, with an r.m.s. deviation of 0.034 (2) Šfor the mean plane through all the non-H atoms. Intra-molecular N-H⋯O and N-H⋯N hydrogen bonds form S(6) and S(5) ring motifs, respectively. In the crystal, mol-ecules are assembled into inversion dimers through pairs of co-operative N-H⋯Cl inter-actions. These dimers are connected along the b axis by N-H⋯O and N-H⋯S hydrogen bonds, generating layers parallel to (103). The layers are further connected along the a axis into a three-dimensional network, through weak π-π stacking inter-actions [centroid-centroid distance = 3.849 (2) Å].