Zero-valent trigonal selenium nanoparticles (SeNPs) were potentiostatically formed at room temperature (298 K) on the surface of a glassy carbon electrode (GCE) from SeO₂ dissolved in ethaline, a deep eutectic solvent composed of choline chloride and ethylene glycol. The mechanisms and kinetics of SeNP electrochemical nucleation and growth on GCE were investigated using both potentiodynamic and potentiostatic techniques. From cyclic voltammetry, the equilibrium potential (Eeq) of the Se(IV)/Se(0) redox couple, the exchange current density (j0), and the charge transfer coefficient (α) for the faradaic reaction Se(IV)ethaline + 4e−GCE/Se(0) $$\rightleftarrows$$ Se(s) were determined to be Eeq = 96 mV vs. Ag QRE, j0 = (1.2 ± 0.1) µA·cm⁻², and α = 0.4 ± 0.1. Analysis of the experimental potentiostatic current density transients (j–t plots) recorded at various overpotentials revealed that the SeNP electrodeposition mechanism involves three consecutive processes: (i) Adsorption and double-layer charging, (ii) Multiple 3D nucleation and diffusion-controlled growth of SeNPs, and (iii) Residual water reduction on the growing SeNP surfaces (2H2ODES + 2e− (Se) $$\rightleftarrows$$ H2(g) + 2OH− (DES)). The applied theoretical model enabled deconvolution of the total j–t response into these individual contributions, allowing for extraction of key kinetic parameters, including the SeNP nucleation frequency (A), the number density of active nucleation sites (N0), and the diffusion coefficient of Se(IV) in ethaline, DSe(IV) (298 K) = (4.91 ± 0.04) x 10− 9 cm2s− 1. Furthermore, from the dependence of A on overpotential, beside j0 and α, additional thermodynamic parameters were determined: the surface energy (σ), the critical nucleus size (nc), and the Gibbs free energy for the formation of the critical nucleus (ΔG(nc)) across the range of applied overpotentials. SEM analysis revealed the formation of smooth, quasi-spherical SeNPs with an average diameter of (118 ± 26) nm, uniformly distributed across the GCE surface. High-resolution XPS spectra recorded in the Se 3d region confirmed the presence of selenium in its zero-valent state. The Raman spectrum displays characteristic signals at 236 and 141 cm⁻¹, indicating that the predominant allotropic form of selenium in the nanoparticles is trigonal Se. Additionally, the optical band gap of the electrodeposited film was estimated using UV–Vis spectroscopy and the Kubelka–Munk method. A band gap of 1.7 eV was obtained, which is consistent with previously reported values for trigonal Se nanoparticles.

Abstract Natural deep eutectic solvents (NADES) have emerged as promising alternatives to conventional organic solvents, offering advantages such as low melting points and biodegradability, aligned with green chemistry principles. In this work, a hydrophobic NADES (hNADES) composed of menthol and decanoic acid (1:1 molar ratio) was combined with soy wax to formulate a biodegradable binder for carbon paste electrodes (CPE), serving as a substitute for mineral oil. The binder and its precursors were characterized by thermal analyses (TGA/DTG and DSC) and FTIR spectroscopy, which evidenced chemical interactions between soy wax and hNADES through marked shifts in functional groups associated with hydrogen-bond formation. A hydrophilic ternary NADES based on glucose, tartaric acid, and glycerol (tNADES (gly) ) was also incorporated to enhance conductivity by improving paste cohesion and promoting proton-coupled electron transfer (PCET) mechanisms, attributed to the presence of free carboxylic acid groups. Electrochemical performance was assessed via cyclic voltammetry, enabling optimization of composition and identification of CPE (50) /hNADES:wax(3:1)/20%tNADES (gly) as the most suitable formulation. Electrochemical impedance spectroscopy further confirmed a pronounced decrease in charge-transfer resistance for the sustainable composite when compared with mineral-oil-based CPE (bare CPE). The resulting electrode, composed exclusively of non-toxic and biodegradable components, was evaluated to detect ascorbic acid, paracetamol, and sulfamethoxazole using differential pulse voltammetry, demonstrating its potential as an environmentally friendly electrochemical sensor which application could be further investigated to detect pollutants in hydric resources, for instance. The most significant analytical response was observed for paracetamol oxidation, presenting higher peak current values and better concentration-current correlation than the bare CPE (mineral oil composition).

Abstract We report on the translational diffusion behavior of the chromophore Rhodamine B (RB) in a series of alkylimidazolium room temperature ionic liquids (RTILs), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (EMIM TFSI), 1- n -butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (BMIM TFSI), 1-methyl-3- n -octylimidazolium bis(trifluoromethylsulfonyl) imide (OMIM TFSI), and 1- n -butyl-3-methylimidazolium tetrafluoroborate (BMIM BF 4 ). We compare these results to published data on the electrical conductivity of the same RTILs. This comparison underscores the inability of conductivity in RTILs to be accounted for solely on the basis of constituent ion translational diffusion as described in the Nernst-Einstein model. The dependence of the “excess” conductivity on RTIL cation structure and system temperature points to the important role of exchange-mediated ion transport in RTILs, and from the temperature-dependence of the excess conductivity, we determine the activation energy for the exchange process. The activation energy for the exchange process is less than a typical hydrogen bond, suggesting a facile process, and the cation structure dependence of the activation energy is consistent with the intrinsically heterogeneous nature of RTILs.