•A new FIA–DEMS configuration has been developed to characterize screen-printed electrodes (SPEs).•HER on a SPE modified with carbon-supported platinum catalyst was studied.•In-situ ...spectroelectrochemical identification/quantification of H2 was accomplished.•A vast diversity of electrochemical reactions can be studied by the novel FIA–DEMS.
In situ detection and quantification of reaction intermediates and products is of paramount importance in applied and fundamental research. In the present work, differential electrochemical mass spectrometry (DEMS) is coupled with flow injection analysis (FIA) to study the hydrogen evolution reaction (HER) on a carbon screen-printed electrode (SPE) modified with a carbon-supported platinum (Pt/C) catalyst. Using this approach, the gaseous and volatile species produced during an electrochemical reaction of interest can be detected and quantified. The reported results support the viability of the novel setup, which can be employed not only for the HER, but also for a vast diversity of electrochemical reactions occurring at various modified SPEs.
The antifungal effect of three furyl compounds closely related to resveratrol, (E)-3,4,5-trimethoxy-β-(2-furyl)-styrene (1), (E)-4-methoxy-β-(2-furyl)-styrene (2) and ...(E)-3,5-dimethoxy-β-(2-furyl)-styrene (3) against Botrytis cinerea was analyzed. The inhibitory effect, at 100 µg ml(-1) of compounds 1, 2, 3 and resveratrol on conidia germination, was determined to be about 70%, while at the same concentration pterostilbene (a dimethoxyl derivative of resveratrol) produced complete inhibition. The title compounds were more fungitoxic towards in vitro mycelial growth than resveratrol and pterostilbene. Compound 3 was the most active and a potential explanation of this feature is given using density functional theory (DFT) calculations on the demethoxylation/demethylation process. Compound 3 was further evaluated for its effects on laccase production, oxygen consumption and membrane integrity of B. cinerea. An increase of the laccase activity was observed in the presence of compound 3 and, using Sytox Green nucleic acid stain, it was demonstrated that this compound altered B. cinerea membrane. Finally, compound 3 partially affected conidia respiration.
The photoelectrocatalytic reduction of CO2 on ITO-modified electrodes, with electrostatic assemblies (polycations/quantum dots) (polycations = poly diallyldimethylammonium, PDDA, and ...poly(2-trimethylammonium)ethyl methacrylate, PMAEMA)), is described in the present work. Nanoparticles of CdTe (5.6 nm) were incorporated through an electric field directed layer-by-layer assembly method on ITO electrodes. Modified surfaces were active toward the reduction of CO2 at −400 mV vs Ag/AgCl; the activity of ITO-(PMAEMA/QDs)6 electrodes was enhanced by 300 mV under irradiation conditions. The photoelectrocatalytic effect was associated with the structure of the polycation and its influence in the assembly. Reaction products at −450 mV were H2, CO, CH3OH, and HCOH.
Deep eutectic solvents (DES) formed using choline chloride (ChCl),
p
-toluenesulfonic acid (
p
TSA) of stoichiometry ChCl: pTSA (1:1) and (1:2), and its ternary eutectic mixtures with phosphoric acid ...(PA) 85% as an additive (ChCl:
p
TSA: PA) were evaluated for cellulose nanocrystal (CNC) isolation. Initially, the hydrolytic efficiency to produce CNC of each DES was compared before and after adding phosphoric acid by Hammett acidity parameters and the Gutmann acceptor number. Moreover, different DES molar ratios and reaction time were studied at 80°C for CNC optimization. The nanomaterial characteristics were analyzed by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). The ternary eutectic mixture ChCl:
p
TSA: PA molar ratio (1:1:1.35) was chosen as a suitable recyclable ternary system at the laboratory scale. A CNC yield of about 80% was obtained from the hydrolysis of commercial cellulose in five cycles of recovery, but it dropped to 35% in pre-pilot scaling. However, no variation in the average size of the resulting CNC was observed (132 ± 50 nm x 23 ± 4 nm), which presented high thermal stability (Tmax 362°C) and high crystallinity of about 80% after 3 h of reaction time.
In the search for new materials to fight against antibiotic-resistant bacteria, a hybrid composite from metallic copper nanoparticles (CuNPs) and a novel cationic π-conjugated polyelectrolyte (CPE) ...were designed, synthesized, and characterized. The CuNPs were prepared by chemical reduction in the presence of CPE, which acts as a stabilizing agent. Spectroscopic analysis and electron microscopy showed the distinctive band of the metallic CuNP surface plasmon and their random distribution on the CPE laminar surface, respectively. Theoretical calculations on CuNP/CPE deposits suggest that the interaction between both materials occurs through polyelectrolyte side chains, with a small contribution of its backbone electron density. The CuNP/CPE composite showed antibacterial activity against Gram-positive (
and
) and Gram-negative (
and
) bacteria, mainly attributed to the CuNPs' effect and, to a lesser extent, to the cationic CPE.
A one-pot green method for aqueous synthesis of fluorescent copper sulphide nanoparticles (NPs) was developed. The reaction was carried out in borax–citrate buffer at physiological pH, 37 °C, aerobic ...conditions and using Cu (II) and the biological thiol cysteine. NPs exhibit green fluorescence with a peak at 520 nm when excited at 410 nm and an absorbance peak at 410 nm. A size between 8–12 nm was determined by dynamic light scattering and transmission electron microscopy. An interplanar atomic distance of (3.5 ± 0.1) Å and a hexagonal chalcocite crystalline structure (βCh) of Cu2S NPs were also determined (HR-TEM). Furthermore, FTIR analyses revealed a Cu-S bond and the presence of organic molecules on NPs. Regarding toxicity, fluorescent Cu2S NPs display high biocompatibility when tested in cell lines and bacterial strains. Electrocatalytic activity of Cu2S NPs as counter electrodes was evaluated, and the best value of charge transfer resistance (Rct) was obtained with FTO/Cu2S (four layers). Consequently, the performance of biomimetic Cu2S NPs as counter electrodes in photovoltaic devices constructed using different sensitizers (ruthenium dye or CdTe NPs) and electrolytes (S2−/Sn2− or I−/I3−) was successfully checked. Altogether, novel characteristics of copper sulfide NPs such as green, simple, and inexpensive production, spectroscopic properties, high biocompatibility, and particularly their electrochemical performance, validate its use in different biotechnological applications.
This work describes the formation of modified electrodes layer-by-layer assembly of a μ-{meso-5,10,15,20-tetra(pyridyl)porphyrin}tetrakis{bis(bipyridine)chloride ruthenium(II)} coordinated with ...Zn(II) and Mn(III) in its central cavity and an anionic polyoxotungstate SiW12O404−. The bilayer formation was monitored using electrochemical and UV–vis techniques, following the oxidation process of the RuIII/II couple and the absorbance of the Soret band of porphyrin complexes respectively. It was possible to form 10 stable bilayers onto ITO surface. SEM studies were carried out finding that the morphology of the film depends on the metal center in the porphyrin. The thickness of these films was estimated as 0.603μm for Zn(II)TRP4+/SiW12O404− and 2.18μm for Mn(III)TRP5+/SiW12O404− modified electrodes respectively. Raman spectroscopy showed that new bands appeared for Mn(III)TRP5+/SiW12O404− assembly confirming stronger interactions than only electrostatic forces.
Kinetics parameters such as charge transfer coefficient, α, and heterogeneous electron transfer rate constant, ks were obtained for both electrodes.
Using electrochemical and UV–vis data it was possible to estimate the energy levels involved in the charge transfer process through the films formed.
Sensor properties of Zn(II)TRP4+/SiW12O404− modified electrode toward chlorite oxidation was tested. The results show electrocatalytic activity, amperometric determination demonstrate a detection limit of 13.8μM.
Fourth generation polyamidoamine dendrimer (PAMAM, G4) modified with fluorescein units (F) at the periphery and Pt nanoparticles stabilized by L-ascorbate were prepared. These dendrimers modified ...with hydrophobic fluorescein were used to achieve self-assembling structures, giving rise to the formation of nanoaggregates in water. The photoactive fluorescein units were mainly used as photosensitizer units in the process of the catalytic photoreduction of water propitiated by light. Complementarily, Pt-ascorbate nanoparticles acted as the active sites to generate H2. Importantly, the study of the functional, optical, surface potential and morphological properties of the photosensitized dendrimer aggregates at different irradiation times allowed for insights to be gained into the behavior of these systems. Thus, the resultant photosensitized PAMAM-fluorescein (G4-F) nanoaggregates (NG) were conveniently applied to light-driven water photoreduction along with sodium L-ascorbate and methyl viologen as the sacrificial reagent and electron relay agent, respectively. Notably, these aggregates exhibited appropriate stability and catalytic activity over time for hydrogen production. Additionally, in order to propose a potential use of these types of systems, the in situ generated H2 was able to reduce a certain amount of methylene blue (MB). Finally, theoretical electronic analyses provided insights into the possible excited states of the fluorescein molecules that could intervene in the global mechanism of H2 generation.
This work describes the preparation of a new tetraruthenated porphyrin and the corresponding polymeric film. This macromolecule consists of a Ni(II) tetrapyridylporphyrin coordinated to four Ru(5-NO
...2-phen)
2Cl
+ moieties. The 5-NO
2-phen ligands are reduced at −0.90
V, generating a radical anion that is able to generate polymeric coatings onto glassy carbon (GC) electrodes. These polymeric films are very stable in aqueous solutions. The polymeric films are characterized by electrochemistry, infrared spectroelectrochemistry (IR-SEC) and atomic force microscopy (AFM).
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