Search Results (219)

In this work, a glassy carbon electrode (GCE) modified with reduced graphene oxide and β-cyclodextrin (rGO/β-CD) nanocomposite was developed for the electrochemical detection of nitrofurantoin (NFT). The structural and morphological characteristics of the synthesized nanocomposite were determined using scanning electron microscopy (SEM), Raman spectroscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Moreover, the electrochemical behavior of the modified electrodes was thoroughly examined using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), with the rGO/β-CD-modified glassy carbon electrode (GCE) demonstrating superior electron transfer capability. Key experimental parameters, including scan rate, material loading, and solution pH, were systematically optimized. After optimizing the experimental conditions, the modified sensor showed excellent electrocatalytic performance and selectivity toward NFT, achieving a broad linear detection range from 0.5 to 120 μM, a low limit of detection (LOD) of 0.048 μM, and a high sensitivity of 12.1 µA µM^–1 cm^–2 using differential pulse voltammetry (DPV). Furthermore, the fabricated electrode exhibited good anti-interference ability, stability, precision, and real-time applicability for NFT detection in a wastewater sample. These results highlight the potential of the rGO/β-CD nanocomposite as a high-performance platform for electrochemical sensing applications. Full article

Ultrafine fibers from poly(3-hydroxybutyrate) (PHB) and polyvinylpyrrolidone (PVP) and their blends with different component ratios in the range of 0/100 to 100/0 wt.% were obtained, and their structure and dynamic properties were studied. The polymers were obtained via electrospinning in solution mode. The structure, morphology, and segmental dynamic behavior of the fibers were determined using optical microscopy, SEM, EPR, DSC, and IR spectroscopy. The low-temperature maximum on the DSC endotherms provided information on the state of the PVP hydrogen bond network, which made it possible to determine the enthalpies of thermal destruction of these bonds. The PHB/PVP fiber blend ratio significantly affected the structural and dynamic parameters of the system. Thus, at low concentrations of PVP (up to 9%) in the structure of ultra-fine fibers, the distribution of this polymer occurs in the form of tiny particles, which are crystallization centers, which causes a significant increase in the degree of crystallinity (χ) activation energy (E_act) and slowing down of molecular dynamics (τ). At higher concentrations of PVP, loose interphase layers were formed in the system, which caused a decrease in these parameters. The strongest changes in the concentration of hydrogen bonds occurred when PVP was added to the composition from 17 to 50%, which was due to the formation of intermolecular hydrogen bonds both in PVP and during the interaction of PVP and PHB. The diffusion coefficient of water vapor in the studied systems (D) decreased as the concentration of glassy PVP in the composition increased. The concentration of the radical decreased with an increase in the proportion of PVP, which can be explained by the glassy state of this polymer at room temperature. A characteristic point of the 50/50% mixture component ratio was found in the region where an inversion transition of PHB from a dispersion material to a dispersed medium was assumed. The conducted studies made it possible for the first time to conduct a comprehensive analysis of the effect of the component ratio on the structural and dynamic characteristics of the PHB/PVP fibrous material at the molecular scale. Full article

This study investigates the mechanical properties of double hydrophilic block copolymers (DHBCs) based on poly[oligo(ethylene glycol) methacrylate] (POEGMA) and poly(vinyl benzyl trimethylammonium chloride) (PVBTMAC) blocks by employing small amplitude oscillatory shear (SAOS) rheological measurements. We report that the mechanical properties of DHBCs are governed by the interfacial glass transition temperature (T_g^inter), verifying the disordered state of these copolymers. An increase in zero shear viscosity can be observed by increasing the VBTMAC content, yielding a transition from liquid-like to gel-like and finally to an elastic-like response for the PVBTMAC homopolymer. By changing the block arrangement along the backbone from statistical to sequential, a distinct change in the viscoelastic response is obvious, indicating the presence/absence of bulk-like regions. The tunable viscosity values and shear-thinning behavior achieved through alteration of the copolymer composition and block arrangement along the backbone render the studied DHBCs promising candidates for drug delivery applications. In the second part, the rheological data are analyzed within the framework of the classical free volume theories of glass formation. Specifically, the copolymers exhibit reduced fractional free volume and similar fragility values compared to the PVBTMAC homopolymer. On the contrary, the activation energy increases by increasing the VBTMAC content, reflecting the required higher energy for the relaxation of the glassy VBTMAC segments. Overall, this study provides information about the viscoelastic properties of DHBCs with densely grafted macromolecular architecture and shows how the mechanical and dynamical properties can be tailored for different drug delivery applications by simply altering the ratio between the two homopolymers. Full article

The electrochemical behavior of copper (II) on glassy carbon from an eutectic mixture of choline chloride (ChCl) and ethylene glycol (EG) was investigated using cyclic voltammetry (CV). The redox and deposition processes were studied for electrolyte concentrations of 0.01 M and 0.5 M Cu(II), with particular attention paid to the effects of different Cu(II) concentrations on the copper deposition potential and morphology of the copper deposits. The CV results showed that the Cu(II) species are reduced to Cu(0) via two separate steps. Higher Cu(II) concentrations in the electrolyte triggered the formation of differently coordinated Cuⁿ⁺ complexes next to the electrode, which shifted the electrodeposition potential of Cu(I)/Cu(0) couples towards more positive values. The Cu deposits were obtained potentiostatically from 0.01 M and 0.5 M Cu(II)-ChCl:EG electrolyte and analyzed using scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction. The different copper concentrations in electrolytes induced different morphologies of electrodeposited copper, where the mixture of irregular grains and carrot or needle-like dendrites was obtained from 0.01 M, and rose-like forms were obtained from 0.5 M electrolytes. This study is the first to identify these rose-like forms and the mechanism of their formation, which is discussed in detail. Full article

The mechanical properties of materials are fundamentally determined by the behavior of atomic bonds under stress. Probing bond behavior during deformation, however, is highly challenging, particularly for materials with complex chemical compositions and/or atomic structures, such as metallic glasses (MGs). As a result, a significant gap exists in the current understanding of the mechanical properties of MGs in relation to the atomic bond behavior and how this relationship is influenced by metallurgical factors (e.g., alloy composition, processing conditions). Here, we present our study of the compositional effects on the tensile behavior of atomic bonds in Cu_93−xZr_xAl₇ (x = 40, 50, 60 at.%) MGs using large-scale molecular dynamics (MD) simulations and statistical analysis. Specifically, we examine the populations (fractions), mean bond lengths, mean bond z-lengths, and mean bond z-strains of the different bond types before and during tensile loading (in the z-direction), and we compare these quantities across the different alloy compositions. Among our key findings, we show that increasing the Zr content in the alloy composition leads to shortened Zr-Zr, Al-Cu, Al-Zr, and Cu-Zr bonds and elongated Cu-Cu bonds, as evidenced by their mean bond lengths. During deformation, the shorter Zr-Zr bonds and longer Cu-Cu bonds in the higher-Zr-content alloys, compared with those in the x = 40 alloy, appear stronger (more elastic stretching in the z-direction) and weaker (less z-stretching), respectively, consistent with general expectations. In contrast, the Al-Cu, Al-Zr, and Cu-Zr bonds in the higher-Zr-content alloys appear weaker in the elastic regime, despite their shortened mean bond lengths. This apparent paradox can be reconciled by considering the fractions of these bonds associated with icosahedral clusters, which are known to be more resistant to deformation than the rest of the glassy structure. We also discuss how the compositional effects on the bond behavior relate to variations in the overall stress–strain behavior of the different alloys. Full article

This paper aims to investigate the mechanical behavior of a polycarbonate through cyclic tensile, compression, and torsiontests atstrain rates that reduce viscous effects for this material. Measurements included axial and transverse strains for uniaxial tests and shear strains for torsion. Tensile tests exhibited nonlinear elasticity, ratcheting, and plasticity, accompanied by an increase in volumetric strain. Compression tests revealed nonlinear elasticity, with the surprising result of positive plastic axial and volumetric strains, accompanied by marginal transverse strains. Torsional tests showed an elastic but nonlinear relationship between shear stress and strain. In these latter tests, positive plastic volumetric strains were observed, which suggests that deviatoric stress can also induce volumetric plastic strains. These findings are of great importance for developing mathematical models of glassy amorphous polymers, and the observations contribute to understanding the complex behavior of such materials. Full article

The mechanical response of monolithic CuZr metallic glass (MG) and MG/Cu composite substrates under high-velocity impact was investigated using molecular dynamics simulations, with variations in impact velocity and initial temperature. Higher impact velocities resulted in deeper penetration and increased plastic deformation, with the monolithic MG exhibiting greater energy absorption and slightly more extensive projectile fragmentation. The MG/Cu composite displayed enhanced plastic deformation, attributed to the higher stiffness of the crystalline Cu phase, which promoted plasticity in the amorphous matrix. Temperature effects were more pronounced in the composite, where elevated temperatures enhanced strain localization and atomic mobility in the glassy phase. This was supported by a decrease in dislocation density and the population of hexagonal close-packed (HCP) atoms with increasing temperature, indicating a shift in plastic activity toward the amorphous matrix. These findings provide insights into the interplay between impact velocity, temperature, and material composition, contributing to a deeper understanding of MG-based composite behavior under extreme loading conditions. Full article

Understanding the dynamics of sorption and desorption is essential for assessing the persistence and mobility of pesticides. These processes continue to influence ecological outcomes even after pesticide use has ended, as demonstrated by our study on dimethoate behavior in distinct soil samples from Croatia, including coastal, lowland, and mountainous regions. This study focuses on the sorption/desorption behavior of dimethoate in soil, explores the relationship between its molecular structure and the properties of soil organic and inorganic matter, and evaluates the mechanisms of the sorption/desorption process. The behavior of dimethoate was analyzed using a batch method, and the results were modeled using nonlinear equilibrium models: Freundlich, Langmuir, and Temkin models. Soils with a higher organic matter content, especially total organic carbon (TOC), showed a better sorption capacity compared to soils with a lower TOC. This is probably due to the less flexible structures in the glassy phase, which, unlike the rubbery phase in high TOC soils, do not allow dynamic and flexible binding of dimethoate within the organic matter. The differences between the H/C and O/C ratios indicate that in high TOC soils, flexible aliphatic compounds, typical of a rubbery phase, retain dimethoate more effectively, whereas a higher content of oxygen-containing functional groups in low TOC soils provides strong association. The lettered soils showed stronger retention of dimethoate through interactions with clay minerals and metal cations such as Mg²⁺, suggesting that clay plays a significantly more important role in enhancing dimethoate sorption than organic matter. These results highlight the importance of organic matter, clay, and metal ions in the retention of dimethoate in soil, indicating the need for remediation methods for those pesticides that, although banned, have had a long history of use. Full article

Aceclofenac (ACF), a non-steroidal anti-inflammatory drug, was obtained in its amorphous state by cooling from melt. The glass transition was investigated using dielectric and calorimetric techniques, namely, dielectric relaxation spectroscopy (DRS), thermally stimulated depolarization currents (TSDC), and conventional and temperature-modulated differential scanning calorimetry (DSC and TM-DSC). The dynamic behavior in both the glassy and supercooled liquid states revealed multiple relaxation processes. Well below the glass transition, DRS was able to resolve two secondary relaxations, γ and β, the latter of which was also detectable by TSDC. The kinetic parameters indicated that both processes are associated with localized motions within the molecule. The main (α) relaxation was clearly observed by DRS and TSDC, and results from both techniques confirmed a non-Arrhenian temperature dependence of the relaxation times. However, the glass transition temperature (T_g) extrapolated from DRS data significantly differed from that obtained via TSDC, which in turn showed reasonable agreement with the calorimetric T_g (T_g-DSC = 9.2 °C). The values of the fragility index calculated by the three experimental techniques converged in attributing the character of a moderately fragile glass former to ACF. Above the α relaxation, TSDC showed a well-defined peak. In DRS, after “removing” the high-conductivity contribution using ε’ derivative analysis, a peak with shape parameters α_HN = β_HN = 1 was also detected. The origin of these peaks, found in the full supercooled liquid state, has been discussed in the context of structural and dynamic heterogeneity. This is supported by significant differences observed between the FTIR spectra of the amorphous and crystalline samples, which are likely related to aggregation differences resulting from variations in the hydrogen bonds between the two phases. Additionally, the pronounced decoupling between translational and relaxational motions, as deduced from the low value of the fractional exponent x = 0.72, derived from the fractional Debye–Stokes–Einstein (FDSE) relationship, further supports this interpretation. Full article

Batch cells are pivotal in advancing the foundational research of CO₂ reduction by providing precise control over reaction conditions to study catalyst behavior and reaction mechanisms, generating insights that drive the development of scalable systems like flow reactors and ultimately supporting sustainability through the industrial adoption of carbon-neutral technologies. Therefore, a one-dimensional numerical model is developed to study electrochemical CO₂ reduction reactions in a batch cell with three different working electrode configurations: solid electrode, glassy carbon electrode, and gas-diffusion-layer electrode. The experimental results of two Cu-based catalysts are used to obtain electrochemical kinetic parameters and to validate the numerical model. The simulation results demonstrate that both gas-diffusion-layer electrodes and glassy carbon electrodes with porous catalyst layers have superior performance over solid electrodes in terms of total current density. Furthermore, we studied the impact of the key parameters of batch cells with glassy carbon electrodes, such as boundary-layer thickness, catalyst-layer thickness, catalyst-layer porosity, electrolyte nature, and the strength of an electrolyte relative to the total current density at a fixed applied cathodic potential of −1.0 V vs. RHE. Full article

This article presents the synthesis, electrophysical, and catalytic properties of a La_0.9MnO₃–LaFeO₃ nanocomposite material. The nanocomposite was synthesized via the sol–gel (Pechini) method. X-ray diffraction (XRD) analysis revealed a polycrystalline, biphasic perovskite structure combining both hexagonal and cubic symmetry. The microstructure and elemental composition, examined using field emission scanning electron microscopy (FESEM), indicated an average particle size of approximately 186.9 nm. The composite exhibits semiconducting behavior within the temperature ranges of 293–323 K and 343–393 K. Developing electrocatalysts free of precious metals for the hydrogen evolution reaction (HER) is increasingly important to facilitate the production of hydrogen from renewable sources. In this study, the conductive La_0.9MnO₃–LaFeO₃ composite was deposited on graphite and, for the first time, evaluated as an electrocatalyst for HER in acidic media. The resulting composite films were tested using linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) in a glassy carbon electrode (GCE) setup, providing insights into their potential as effective, cost-efficient electrocatalysts. Full article

The development of innovative, cost effective, and biocompatible sensor materials for rapid and efficient practical applications is a key area of focus in electroanalytical chemistry. In this research, we report on a novel biocompatible sensor, made using a unique polybenzoxazine-based carbon combined with amino cellulose and hyaluronic acid to produce a bio-polymer complex (PBC-ACH) (polybenzoxazine-based carbon with amino cellulose and hyaluronic acid). This sensor material is fabricated for the first time to enable the electroreduction of the herbicide, metribuzin (MTZ). The PBC-ACH sensor presents multiple advantages, including ease of fabrication, excellent biocompatibility, and low-cost production, making it suitable for various applications. In optimized experimental conditions, the sensor was fabricated by modifying a glassy carbon electrode (GCE) with the PBC-ACH complex, resulting in the creation of a GCE/PBC-ACH electrode. This modified electrode demonstrated the ability to detect MTZ at nanomolar levels, with an LoD of 13.04 nM, showcasing a high sensitivity of 1.40 µA µM⁻¹ cm⁻². Moreover, the GCE/PBC-ACH sensor exhibited remarkable selectivity, stability, and reproducibility in terms of its electrochemical performance, which are essential features for reliable sensing applications. The potential mechanism behind the detection of MTZ using the GCE/PBC-ACH sensor was investigated thoroughly, providing insights into its sensing behavior. Additionally, tests on real samples validated the sensor’s practicality and efficiency in detecting specific analytes. These findings emphasize the potential of the GCE/PBC-ACH sensor as a highly effective electrochemical sensor, with promising applications in environmental monitoring and other fields requiring precise analyte detection. Full article

In this paper, a novel molecularly imprinted polymer membrane modified glassy carbon electrode for electrochemical sensors (MIP-OH-MWCNTs-GCE) for epinephrine (EP) was successfully prepared by a gel-sol method using an optimized functional monomer oligosilsesquioxane-Al₂O₃ sol-ITO composite sol (ITO-POSS-Al₂O₃). Hydroxylated multi-walled carbon nanotubes (OH-MWCNTs) were introduced during the modification of the electrodes, and the electrochemical behavior of EP on the molecularly imprinted electrochemical sensors was probed by the differential pulse velocity (DPV) method. The experimental conditions were optimized. Under the optimized conditions, the response peak current values showed a good linear relationship with the epinephrine concentration in the range of 0.0014–2.12 μM, and the detection limit was 4.656 × 10⁻¹¹ M. The prepared molecularly imprinted electrochemical sensor was successfully applied to the detection of actual samples of horse serum with recoveries of 94.97–101.36% (RSD), which indicated that the constructed molecularly imprinted membrane electrochemical sensor has a high detection accuracy for epinephrine in horse blood, and that it has a better value for practical application. Full article

Carbon fiber reinforced epoxy resin composites (CFRP) demonstrate superior wear resistance and fatigue durability, which are anticipated to markedly enhance the service life of structures under complex conditions. In the present paper, the friction behaviors and wear mechanisms of CFRP under different applied loads, sliding speeds, service temperatures, and water lubrication were studied and analyzed in detail. The results indicated that the tribological properties of CFRP were predominantly influenced by the applied loads, as the tangential displacement generated significant shear stress at the interface of the friction pair. Serviced temperature was the next most impactful factor, while the influence of water lubrication remained minimal. Moreover, when subjected to a load of 2000 g, the wear rate and scratch width of the samples exhibited increases of 158% and 113%, respectively, compared to those loaded with 500 g. This observed escalation in wear characteristics can be attributed to irreversible debonding damage at the fiber/resin interface, leading to severe delamination wear. At elevated temperatures of 100 °C and 120 °C, the wear rate of CFRP increased by 75% and 112% compared to that at room temperature. This augmentation in wear was attributed to the transition of the epoxy resin from a glassy to an elastic state, which facilitated enhanced fatigue wear. Furthermore, both sliding speed and water lubrication displayed a negligible influence on the friction coefficient of CFRP, particularly under water lubrication conditions at 60 °C, where the friction coefficient was only 15%. This was because the lubricant properties and thermal management provided by the water molecules, which mitigated the frictional interactions, led to only minor abrasive wear. In contrast, the wear rate of CFRP at a sliding speed of 120 mm/s was found to be 74% greater than that observed at 60 mm/s. This significant increase can be attributed to the disparity in sliding rates, which induced uncoordinated deformation in the surface and subsurface of the CFRP, resulting in adhesive wear. Full article

Active fillers such as carbon black and silica are added to rubber to improve its mechanical and viscoelastic properties. These fillers cause reinforcement in rubber compounds through physical and/or chemical interactions. Consequently, the compounds’ rheological, mechanical, and viscoelastic behavior are affected. Changing the filler loading influences these properties due to the different interactions (filler-filler and filler-polymer) taking place in the compounds. In addition, rubbers with varying microstructures can interact differently with fillers, and the presence of polymer functionalization to enhance interactions with fillers can further add to the complexity of the network. In this work, the effects of different loadings (0–108 phr/0–25 vol. %) of a highly dispersible grade of silica with three types of solution styrene-butadiene rubbers (SSBR) and one butadiene rubber (BR) on their rheological, mechanical, and viscoelastic properties were investigated. It was observed that the Mooney viscosity and hardness of the compounds increased with an increasing filler loading due to the increasing stiffness of the compounds. Payne effect measurements on uncured compounds provided information about the breakdown of the filler-filler network and the extent of the percolation threshold (15–17.5 vol. %) in all the compounds. At high filler loadings, the properties for BR compounds worsened as compared to SSBR compounds due to weak polymer-filler interaction (strong filler-filler interaction and the lower compatibility of BR with silica). The quasi-static mechanical properties increased with the filler loading and then decreased, thus indicating an optimum filler loading. In strain sweeps on cured rubber compounds by dynamic shear measurements, it was observed that the type of rubber, the filler loading, and the temperature had significant influences on the number of glassy rubber bridges in the filler network and, thus, a consequential effect on the load-bearing capacity and energy dissipation of the rubber compounds. Full article