Search Results (401)

An acylation reaction was performed on the crystalline surface of cellulose in a composite consisting of microfibrillated cellulose (MFC) and hydroxyapatite (HAP) with an inorganic weight fraction of 68%. The composite was acylated using acetic anhydride, propanoic anhydride, and butanoic anhydride in pyridine in the presence of potassium carbonate at 120 °C for 1 h. The formation of ester linkages was confirmed by infrared spectroscopy, and X-ray diffraction analysis showed that the crystalline structure of cellulose was retained after acylation. From the intensity of the carbonyl stretching vibration in the infrared spectra, the degree of substitution of the acetylated sample was estimated to be approximately 0.2. The acylated MFC–HAP composites were uniaxially hot-pressed at 120 °C and 300 MPa, and the resulting molded specimens were subjected to three-point bending tests. A yield point appeared at a bending strain of 1.1–1.4%, followed by plastic deformation and final fracture, indicating that they exhibited ductile fracture. The elastic moduli were 5.9 GPa (acetyl), 7.6 GPa (propanoyl), 7.4 GPa (butanoyl), 3.6 GPa (hexanoyl), and 7.1 GPa (before acylation), indicating that acyl groups with medium chain lengths did not reduce the rigidity of the composites. When the molded specimens were immersed in water at room temperature for 24 h, the water absorption ratios were 29% (acetyl), 24% (propanoyl), 17% (butanoyl), and 18% (hexanoyl), demonstrating that water resistance improved with increasing acyl chain length. In summary, propanoylation and butanoylation improved the water resistance of the composites without compromising their rigidity in the dry state. Full article

Hydrophilic polymer films containing environment-sensitive chromophores are useful model systems for examining optical responses in polar matrices. In this study, chitosan/poly(vinyl alcohol) (CS–PVA) films containing low nominal loadings of 3-hydroxyflavone (3HF; 0.05–0.20 wt.%) were prepared by solution casting and characterized in terms of macroscopic appearance, thickness, ultraviolet–visible (UV–Vis) response before and after ultraviolet-A (UV-A) exposure, Fourier-transform infrared spectroscopy with attenuated total reflectance (FTIR-ATR), and water-related behavior. All formulations produced continuous and macroscopically translucent films without visible precipitation or phase separation. Film thickness varied substantially among formulations (0.100–0.168 mm), requiring cautious interpretation of raw transmittance data. Before UV-A exposure, the thickness-normalized apparent attenuation coefficient at 365 nm (α_app,365) ranged from 23.84 to 121.74 cm⁻¹ and followed a non-monotonic order: CS–PVA–3HF-0.05 > CS–PVA–3HF-0.20 > CS–PVA–3HF-0.10 > CS–PVA. UV-A exposure for 120 min produced formulation-dependent changes in optical response, with no common concentration-dependent trend. FTIR-ATR spectra showed relatively small variations in the O–H/N–H, carbonyl/amide, and C–O regions; because several band displacements were comparable to the instrumental resolution, these changes were interpreted as variations in the local vibrational environment rather than direct evidence of hydrogen-bond-network restructuring. Water-contact measurements revealed very high apparent water uptake together with post-immersion dry-mass losses above 94%, demonstrating limited aqueous stability. Density functional theory (DFT) calculations combined with Multiwfn wavefunction analysis on isolated 3HF, a three-unit poly(vinyl alcohol) oligomer (PVA3), and a two-unit chitosan oligomer (CS2) described their intrinsic electronic features but did not establish intermolecular complex formation or directly explain the experimental responses. Overall, the results provide a descriptive characterization of the optical and water-related behavior of 3HF-containing CS–PVA films while emphasizing the influence of film geometry and the limitations associated with nominal, rather than analytically verified, chromophore loading and isolated-component computational models. Full article

Economically motivated adulteration of olive oil, coffee and fruit juice is a persistent food-fraud problem for which Fourier-transform infrared (FTIR) spectroscopy with chemometrics offers rapid screening. Linear partial least squares (PLS) is interpretable but cannot capture non-linear mixing; neural networks add flexibility at the cost of becoming black boxes. We evaluated a Kolmogorov–Arnold network (KAN), which places learnable univariate functions on its edges and is therefore intrinsically interpretable, against PLS, support-vector regression, random forests, a multilayer perceptron and a one-dimensional convolutional network on three attenuated total reflectance (ATR)–FTIR datasets (olive oil + sunflower oil, coffee + malt flour, orange juice + apple juice; approximately 350, 400 and 400 spectra). All models were compared under identical, leakage-free validation that splits spectra by physical sample. The compact KAN was consistently competitive (cross-validated coefficients of determination (R²) = 0.86, 0.93 and 0.69) and yielded closed-form equations whose variables map to recognised vibrational bands and whose importance ranking agrees with SHapley Additive exPlanations (SHAP; Spearman ρ = 0.86–0.90); symbolic conversion costs no accuracy. We also report the following limits: PLS was strongest where the chemistry was linear (coffee) and the multilayer perceptron was strongest on fruit juice, whose equation is the weakest (R² = 0.47–0.75 across seeds); a parameter-matched perceptron matched the KAN’s accuracy; and leave-one-brand-out validation degraded every model. The KAN is therefore a promising, compact and genuinely transparent alternative under controlled multi-matrix conditions, not a deployment-ready method. Full article

The ultrafast photochemical reaction dynamics of a cyclic(alkyl)(amino)carbene–carbon disulfide (CAAC–CS₂) dimer containing two adjacent S–S bonds were investigated using femtosecond time-resolved infrared spectroscopy in combination with multireference electronic structure calculations. Time-resolved vibrational spectra and global kinetic analysis reveal that photoexcitation of the S–S n → σ* transition at 375 nm induces subpicosecond (<0.3 ps) homolytic cleavage of one S–S bond, generating a bis-thiyl diradical intermediate. This intermediate undergoes two competing pathways: recombination to regenerate the parent dimer with a time constant of 5.7–8.5 ps, or secondary cleavage of the remaining S–S bond to yield two CAAC–CS₂ monomers with a time constant of 30–35 ps. Wavelength- and temperature-dependent kinetic measurements demonstrate that the branching between these pathways is governed by excess excitation energy and thermally driven radical-pair fluctuations. Multireference electronic structure calculations support a sequential S–S bond cleavage mechanism, in good agreement with the experimental observations. These findings provide direct spectroscopic evidence for a bis-thiyl diradical intermediate and offer new mechanistic insight into the ultrafast photochemistry of adjacent S–S bonds. Full article

This study aimed to synthesize copper(I) iodide nanoparticles (CuI NPs) through a green route using taxo (banana passion fruit) extract as a natural capping and stabilizing agent, and to evaluate their antimicrobial performance against microorganisms isolated from concrete, together with a preliminary cytotoxicity screening. The obtained nanoparticles were characterized by ultraviolet–visible spectroscopy (UV–Vis), Fourier-transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM–EDS), dynamic light scattering (DLS), and X-ray diffraction (XRD). UV–Vis spectra recorded in the 200–704 nm range showed a strong absorption band at 224 nm, consistent with electronic transitions associated with nanostructured CuI. FTIR analysis revealed extract-derived biomolecules adsorbed on the nanoparticle surface, with bands assigned to aliphatic C–H, aromatic moieties, and C–O/C–O–C vibrations, supporting the formation of an organic capping layer. DLS analysis showed a mean hydrodynamic diameter of approximately 32 nm in aqueous suspension, whereas TEM revealed particle sizes ranging from 13 to 42 nm. XRD confirmed a predominantly cubic CuI phase, while SEM–EDS identified Cu and I as the main elements, with minor signals attributed to residual organic coating and/or trace species from the synthesis medium. The CuI NPs exhibited antimicrobial activity against microorganisms isolated from medium-strength concrete, producing inhibitory effects at all tested concentrations (0.014, 0.0087, and 0.0035 mol/L). Preliminary cytotoxicity screening using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay in human foreskin fibroblast (HFF), human breast adenocarcinoma (MCF7), and human glioblastoma (U251) cell lines showed dose- and time-dependent reductions in metabolic viability. The 1.0 mol/L formulations, particularly the precipitated fraction, produced stronger cytotoxic effects, whereas the 0.1 mol/L formulations, especially the residual fraction, preserved comparatively higher metabolic viability. Overall, these findings suggest that taxo-mediated CuI NPs are promising antimicrobial candidates for concrete biodeterioration control, while further colloidal and biological studies are required to better define their behavior under cell-culture conditions and optimize their safe application. Full article

In this work, the structural, optical, vibrational, and stability properties of a series of Al_xAs_x nanostructures are systematically investigated using density functional theory (DFT) and time-dependent density functional theory (TD-DFT). Starting from the fundamental cubic-like Al₄As₄ building block, progressively larger nanostructures were constructed through directional elongation and structural rearrangements, allowing for the exploration of one-dimensional chains, two-dimensional planar structures, and several exotic geometries. The calculated UV–visible absorption spectra reveal that structural dimensionality and topology strongly influence the electronic transitions of the nanostructures, with elongated and distorted configurations exhibiting broader absorption features and richer spectral distribution. Vibrational analysis shows that increasing structural complexity and reducing symmetry lead to a higher density of IR-active modes and more complex infrared spectra. The stability of the nanostructures is evaluated through binding energy calculations, which indicate a clear size-dependent stabilization trend, with the Al₂₄As₂₄-L1 configuration exhibiting the highest stability among the examined systems. In addition, the calculated HOMO-LUMO gaps reveal the semiconducting character of the clusters and demonstrate their sensitivity to geometric topology. The present results establish clear structure–property relationships between dimensional growth and the optical response of AlAs nanoparticles and provide theoretical reference data for future experimental investigations of III-V semiconductor nanostructures. Full article

In this work, the structural, electronic, optical, and vibrational properties of gallium nitride (Ga_xN_x) nanostructures were systematically investigated using density functional theory (DFT) and time-dependent DFT (TD-DFT). A series of nanoparticles was constructed starting from a cubic-like Ga₄N₄ building unit, leading to one-dimensional (1D), two-dimensional (2D), three-dimensional (3D), and hexagonal configurations. Geometry optimizations and vibrational frequency calculations were performed at the B3LYP/def2-TZVP level, while optical properties were investigated using TD-DFT with the CAM-B3LYP functional. Only dynamically stable structures without imaginary vibrational frequencies were considered for spectroscopic analysis. The results reveal a strong dependence of the optical and vibrational behavior on nanoparticle size and geometry. Larger and lower-symmetry systems exhibit broader and red-shifted UV–Vis absorption spectra together with richer IR vibrational features. In contrast, elongated low-dimensional configurations such as Ga₁₂N₁₂–1D and Ga₁₆N₁₆–1D/2D were found to be dynamically unstable. The investigated nanostructures also show a clear tendency toward structural reorganization from cubic-like motifs to compact hexagonal arrangements related to the wurtzite phase of bulk GaN. Benchmark analysis demonstrates that CAM-B3LYP provides reliable excitation energies at moderate computational cost. Overall, the obtained results highlight the strong coupling between structure and optoelectronic properties in Ga_xN_x nanostructures and indicate their potential for nanoscale optoelectronic and photonic applications. Full article

Introduction: Aquatic chemical pollution is among the most worrying threats to ecosystem health. There is an ever-increasing variety of pollutant substances detected across the source-to-sea continuum, causing loss of biodiversity and ecological disequilibrium. Achieving cleaner and healthier systems relies on carrying out sustained, cost-effective, diagnosis and aquatic effects monitoring, within the adaptive management cycle. The available methods are, however, cumbersome, which creates a clear need for innovative expeditious approaches for low-cost surveillance monitoring. In the last decade, Raman Spectroscopy (RS) has gained wide recognition for application to biological questions, for its ability to uncover the complexity of molecules and their interactions. Various fields, from pharmacology to disease diagnosis and prognosis, have suffered an innovation revolution through the application of RS. In this technique inelastic light scattering of a small part of photons of an incident electromagnetic monochromatic light beam (ranging from near-infrared to visible or ultraviolet) is caused by the molecular vibration of chemical bonds. This results in shifts in energy, which indicate discrete vibrational modes of polarisable molecules, providing qualitative and quantitative assessments of the chemical composition and molecular structure of the sample. The technique shows high sensitivity, no need for sample preparation and the possibility of use in non-invasive and label-free analysis. Objective: The aim of this work is to present and discuss evidence about the application of Raman Spectroscopy (RS) to environmental diagnosis and aquatic effect monitoring of pollution. Methodology: The technique was applied to different biological models, i.e., diatoms, zebrafish embryos and larvae and freshwater snails. Quality assessments with diatoms were tested in environmental monitoring, while assessments with other models were done upon exposure to metals and organic contaminants. Results and conclusions: The Raman spectra obtained from the samples analysed comprised bands detected within the 800 to 2000 cm⁻¹ wavenumber range. These were related to bond vibrations of carbohydrates, DNA phosphate groups, proteins or CH, NH and OH stretching in lipids and proteins. Data analysis using chemometric methods clearly distinguished pollutant exposure from control sites or treatments, pointing out the potential for surveyance monitoring. The next steps include the comparison with other sensitive methods (e.g., locomotion and avoidance behaviours, omics methods) to assess efficiency and bring further mechanistic understanding. Full article

Dioxazolones are important precursors for generating nitrenes (highly reactive intermediates widely used for carbon–nitrogen bond formation in organic synthesis) upon exposure to light or heat. The photochemical reaction dynamics of 3-phenyl-1,4,2-dioxazol-5-one in CHCl₃ were investigated using femtosecond time-resolved infrared spectroscopy and electronic structure calculations. Photoexcitation at 267 nm rapidly populates an excited singlet state that serves as the key branching point for subsequent photophysical and photochemical processes. Transient infrared spectra reveal the formation of carbon dioxide, phenyl isocyanate, and singlet benzoyl nitrene through their characteristic vibrational features. Kinetic analysis shows that decarboxylation from the excited singlet state occurs with a time constant of 4.7 ± 1 ns, producing phenyl isocyanate and benzoyl nitrene with time constants of 8.1 ± 2 ns and 11 ± 3 ns, respectively. Competing relaxation pathways include internal conversion to the ground state (7.5 ± 2 ns) and intersystem crossing to the T₁ state (25 ± 5 ns). The T₁ state relaxes to the ground state (350 ± 30 ns) without contributing to product formation. These results demonstrate that both isocyanate and nitrene products originate from the S₁ state and provide detailed mechanistic insight into the competing pathways governing dioxazolone photochemistry in solution. Full article

GaAs_1-xN_x/GaAs (001) (0 < x ≤ 0.037) tensile-strained epilayers are of considerable importance in optoelectronics due to their ability to offer large and resilient band structure engineering. Strain causes valence-band splitting, giant bandgap reduction and phonon frequency shifts. Optimum performance of III-V-Ns in long-wavelength lasers, infrared photodetectors, optical modulators, and multi-junction solar cells is contingent on their distinctive vibrational and optical characteristics. We report results of meticulous simulations of GaAs_1-xN_x alloys to validate Fourier transform infrared (FTIR) reflectivity and spectroscopic ellipsometry (SE) data in the far-infrared and ultraviolet regions. The FTIR spectra showed strong reflectivity peaks and dips in the reststrahlen band region, linked to the transverse optical ${\omega }_{\mathrm{T}\mathrm{O}1}$ and longitudinal optical ${\omega }_{\mathrm{L}\mathrm{O}1}$ modes of the Ga-As bond and a high-frequency ${\omega }_{\mathrm{T}\mathrm{O}2}$ local vibrational mode of GaAs:N. Modified dielectric functions of GaAs_1-xN_x/GaAs epilayers are carefully evaluated using an improved Adachi’s semiemperical method to study the x and E-dependent optical constants. Focusing on the electronic band structures at critical points, this approach provided accurate analytical formulation to evaluate complex dielectric $\tilde{\epsilon }$(E) and refractive indices $\tilde{\mathrm{n}}$(E) for simulating reflectance spectra in a wide energy range with good agreement to the SE data. Full article

The recent motivation for sustainable lubrication has driven the development and advances of bio-based and potentially environmentally favorable alternatives to petroleum-based greases. Yet, their industrial adoption is largely hindered by the thickener weak network or inconsistency leading to grease unacceptable degradation under applied loads and operating temperatures in rotating machinery. This study investigates a novel grease formulated from 80% palm oil and a 20% complex thickener system from carnauba wax (CW) and glycerol monostearate (GMS). The effect of thickener composition on grease performance was investigated by testing their X-ray diffraction (XRD) spectra, Fourier transform infrared (FTIR) spectra, penetration level, oil separation percentage, viscosity, thermal properties, and tribological behavior. GMS-rich blends achieved up to 70% lower friction than lithium grease. However, they showed high wear rates and excessive oil separation ranging from 0.07% at room temperature for the 20% GMS blend to above 9% at 40 °C for softer formulations. The blend of 15% CW + 5% GMS showed only 0.113% and 3.145% oil bleed at room temperature and at 40 °C, respectively, with suitable consistency (NLGI 3) and acceptable dynamic viscosity rates. Regarding thermal behavior, CW-based samples revealed an enhanced melting point compared to GMS. For validation, investigations were conducted on rolling element bearings on a customized test setup operating at 1400 rpm under selected radial loads. The results demonstrate that CW/GMS bio-thickeners achieved lower vibration levels compared to the GMS thickener, approaching the performance of lithium grease. Full article

MgCr₂O₄ nanospinel samples were synthesized using a modified Pechini method, followed by controlled calcination. The resulting materials were evaluated in terms of crystal structure, particle morphology, and optical and electronic properties. Their oxidative activity towards the degradation of organic dyes was investigated via photocatalysis, Fenton-like, and photon-Fenton-like processes. Various analytical techniques were employed to characterize the samples, including X-ray diffraction (XRD) with Rietveld refinements, infrared (IR) spectroscopy, UV–Vis spectroscopy, colorimetry, and transmission and high-resolution transmission electron microscopy (TEM/HRTEM). Structural characterization revealed that MgCr₂O₄ crystallized after calcination at 600 °C, and Rietveld refinements confirmed cubic Fd-3m symmetry. IR spectra confirmed the short-range order through the presence of vibrational modes assigned to CrO₆^2- octahedra. UV–Vis spectroscopy indicated mixed Cr valences (Cr³+/Cr⁶+) for samples calcined at temperatures below 900 °C, with Cr⁶+ eliminated at higher temperatures, confirmed by electron paramagnetic resonance (EPR) spectroscopy. This suggests that an oxidation reaction occurred due to oxygen vacancies in the lattice. Optical bandgap (Eg) increased with temperature. Samples calcined at low temperatures were dark green and became more saturated at temperatures above 900 °C, suggesting photoresponse to visible light, as indicated by the Eg values. The oxidative activity of the nanospinels in degrading the dyes methylene blue (MB) and rhodamine B (RhB) under visible light depended on the nature of the dye, the catalyst concentration, and the use of H₂O₂ in the process to improve the formation of hydroxyl radicals (•OH), as confirmed by photohydroxylation of terephthalic acid (TA). The highest degradation rate was observed in the photo-Fenton-like process, with 96% and 97% degradation of RhB and MB dyes in 60 min, reaching a kinetic rate constant (${\mathit{K}}_{app}$) of 0.055 min⁻¹ and 0.051 min⁻¹, respectively. This study highlights the importance of controlling various parameters to promote the formation of reactive oxygen species (ROS) required for oxidative degradation by nanospinels. Full article

Traditional handmade papers from China, Japan, and Korea, including Xuan paper, Washi, and Hanji, are difficult to distinguish visually because they share cellulose-rich compositions and similar appearances. This study applied near-infrared hyperspectral imaging (NIR-HSI) and machine-learning classifiers to identify selected traditional handmade papers by country and product type. Spectra in the 1250–1700 nm region were analyzed using k-nearest neighbors, support vector machines, and artificial neural networks. The models achieved high classification performance, with F1-scores of up to 1.000, and Y-scrambling confirmed that the results were not attributable to random class assignment. SHAP analysis identified important wavelength regions near 1256, 1360, 1404, 1449, 1537, 1576, 1635, and 1685 nm, which were associated with C–H, O–H, phenolic, hydrogen-bonded polysaccharide, and lignin-related vibrations. These bands varied among paper groups and provided chemically meaningful information for classification, while SAM visualization revealed pixel-level spectral similarity. These results show that NIR-HSI provides a compact, nondestructive, and interpretable approach for classifying selected East Asian handmade papers. Full article

Bent-core liquid crystals are renowned for their remarkable optical and ferro-electrical properties, making them highly sought after for various applications. However, to harness their full potential, a thorough understanding of their structural mechanisms and fluctuations during phase transitions is imperative. In this study, we conducted an in-depth analysis of the structural conformation of a V-shaped liquid crystal, specifically (E) 1,2-phenylene bis[4-((E)-(4-pentyloxy chloro phenyl) diazenyl) benzoate], referred to as V1, utilizing density functional theory (DFT) calculations at the B3LYP/6-311G(d,p) level. Geometry optimization and frequency calculations of the most stable conformers were performed at the same theoretical level. Our investigation into the mesomorphic behavior of V1 unveiled two enantiotropic phase transitions: Isotropic (Iso) → Nematic (N) → Smectic A (SmA) → Crystalline (Cry), with decreasing temperature. To elucidate the molecular alterations of V1 at the microscopic level, Fourier Transform Infrared (FT-IR) and Fourier Transform Raman (FT-Raman) spectra were recorded across various temperature ranges. Remarkably, the simulated vibrational spectra exhibited a striking resemblance to the experimentally observed vibrational spectra at room temperature, validating the accuracy of our computational approach. These findings hold immense promise for advancing further research and facilitating the development of novel applications leveraging the unique properties of bent-core liquid crystals. Full article

Infrared radiation spectra produced by vibration–rotation transitions in multicomponent gases within the vacuum plume of attitude and orbital control engines constitute crucial radiation sources for optical target identification and space maneuver recognition, and rapid prediction of these signatures is essential for real-time forecasting. This study introduces an axisymmetric vacuum plume flow field model based on a simplified point-source approach that accommodates multicomponent combustion gases. Using the Maxwellian velocity distribution and a velocity–position angle algorithm, normalized number density, velocity, and temperature distributions are derived. A plume–freestream interaction model founded on noncentral fully elastic collision theory is incorporated, and overall plume properties are obtained via density-weighted averaging. Neglecting non-equilibrium radiation effects, the high-temperature gas absorption coefficient is calculated using a statistical narrowband model and radiative transfer is solved via the line-of-sight method. The model is validated against direct simulation Monte Carlo results for single-gas and MBB bipropellant plumes and confirmed using infrared spectral data in the 2.0–4.5 μm band. The proposed framework achieves 10²–10³-fold higher computational efficiency than conventional DSMC approaches. Freestream effects on plume diffusion and momentum exchange diminish with increasing altitude, as does the freestream velocity’s enhancement of radiation intensity, whereas greater plume expansion at higher altitudes increases overall radiation intensity. Full article