Search Results (110)

Background/Objectives: Arthrospira platensis (A. platensis) is a cyanobacterium rich in bioactive compounds with proven antioxidant, antimicrobial, and stabilizing properties, making it an ideal candidate for the green synthesis of zinc oxide nanoparticles (ZnO NPs). This study aimed to synthesize ZnO NPs using A. platensis extract and to evaluate the influence of post-synthesis temperature on their physicochemical and antimicrobial properties. Methods: ZnO NPs were synthesized via a co-precipitation method using A. platensis extract, followed by post-synthesis treatments at 80 °C and 400 °C. Comprehensive characterization was performed using Ultraviolet–Visible Spectroscopy (UV–Vis), Fourier Transform Infrared Spectroscopy (FT–IR), Field Emission Scanning Electron Microscopy (FE–SEM), and Energy Dispersive X-ray Spectroscopy (EDX) to assess optical, structural, and compositional features. Antioxidant activity (DPPH assay) and antimicrobial properties against Staphylococcus aureus, Escherichia coli, and Candida albicans were also evaluated. Results: FE–SEM analysis confirmed a temperature-dependent effect, with ZnO NPs synthesized at 80 °C appearing as polydispersed, irregular aggregates (45.2 ± 8.6 nm), while calcination at 400 °C yielded compact, angular nanoparticles (37.1 ± 6.3 nm). In contrast, pure ZnO NPs were smaller (26.4 ± 4.1 nm), and A. platensis extract alone showed amorphous, irregular structures. FTIR spectra demonstrated the involvement of biomolecules in nanoparticle capping and stabilization, whereas EDX analysis revealed that higher calcination reduced organic residues and increased zinc purity. Antioxidant assays indicated a decrease in phenolic and flavonoid content with increasing temperature, leading to reduced DPPH radical scavenging activity. Antimicrobial evaluation showed superior inhibition zones (17.8–26.0 mm) for A. platensis-ZnO NPs compared to the crude extract, with S. aureus being most susceptible, particularly to the 400 °C nanoparticles. Conclusions: The study demonstrates that A. platensis extract provides a sustainable and efficient route for ZnO NP biosynthesis. Calcination temperature significantly affects nanoparticle morphology, biochemical composition, and antimicrobial performance. These findings highlight the potential of A. platensis-ZnO NPs as eco-friendly antimicrobial agents for biomedical, pharmaceutical, and food preservation applications. Full article

This study presents the electrical and optical properties of 35P₂O₅–xV₂O₅–(65–x) Sb₂O₃ glasses for 0 ≤ x ≤ 65 mol%. The direct current (DC) resistivity was measured by the Van der Pauw method and optical absorption spectra were taken in the Ultraviolet–Visible-Near-Infrared (UV–VIS–NIR) range. Electrical transport is attributed to simultaneous hopping of small polarons (SPs) between V⁴⁺ and V⁵⁺ (vanadium ion) sites and small bipolarons (SBPs) between the Sb³⁺ and Sb⁵⁺ (antimony ion) sites. The resistivity exhibits a non-linear dependence on the ionic fraction of vanadium (n_v), whereas the resistivity exhibits a minimum in the composition range 0 ≤ n_V ≤ 0.3, and a resistivity maximum was observed in the range 0.3 ≤ n_V ≤ 0.5. On further increasing n_v, the resistivity exhibits a monotonic decline. In the composition range 0 ≤ n_V ≤ 0.3, where the hopping distance between V ions decreases, while that between the Sb ions increases, the resistivity minimum has been shown to be the consequence of decreasing tunneling distance of SPs between the V⁴⁺ and V⁵⁺ ion sites. In the composition range 0.3 ≤ n_V ≤ 0.5, the resistivity, activation energy for DC conduction, glass transition temperature, and density exhibit their respective maxima even though the separation between the V⁴⁺ and V⁵⁺ sites continues to decrease. This feature is explained by enhanced localization of electrons on account of increased disorder (entropy) among the SPs and SBPs, like that of Anderson localization. This argument is further supported by a shift in the polaronic optical absorption bands associated with the SPs and SBPs toward higher energies. The transport behavior of all the glasses except the x = 0 composition has been explained by adiabatic transport, principally, by the SPs on V ions while the Sb ions contribute little to the total transport process. The results provide a clear relation between composition, polaron/bipolaron contributions, and conduction in these glasses. Full article

Background/Objectives: Magnetic nanoparticles, particularly iron oxide-based materials, such as magnetite (Fe₃O₄), have gained significant attention as contrast agents in medical imaging This study aimsto syntheze and characterize Fe₃O₄-based core–shell nanostructures, including Fe₃O₄@TiO₂ and Fe₃O₄@SiO₂, and to evaluate their potential as tunable contrast agents for diagnostic imaging. Methods: Fe₃O₄, Fe₃O₄@TiO₂, and Fe₃O₄@SiO₂ nanoparticles were synthesized via co-precipitation at varying temperatures from iron salt precursors. Fourier transform infrared spectroscopy (FTIR) was used to confirm the presence of Fe–O bonds, while X-ray diffraction (XRD) was employed to determine the crystalline phases and estimate average crystallite sizes. Morphological analysis and particle size distribution were assessed by scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX) and transmission electron microscopy (TEM). Magnetic properties were investigated using vibrating sample magnetometry (VSM). Results: FTIR spectra exhibited characteristic Fe–O vibrations at 543 cm⁻¹ and 555 cm⁻¹, indicating the formation of magnetite. XRD patterns confirmed a dominant cubic magnetite phase, with the presence of rutile TiO₂ and stishovite SiO₂ in the coated samples. The average crystallite sizes ranged from 24 to 95 nm. SEM and TEM analyses revealed particle sizes between 5 and 150 nm with well-defined core–shell morphologies. VSM measurements showed saturation magnetization (Ms) values ranging from 40 to 70 emu/g, depending on the synthesis temperature and shell composition. The highest Ms value was obtained for uncoated Fe₃O₄ synthesized at 94 °C. Conclusions: The synthesized Fe₃O₄-based core–shell nanomaterials exhibit desirable structural, morphological, and magnetic properties for use as contrast agents. Their tunable magnetic response and nanoscale dimensions make them promising candidates for advanced diagnostic imaging applications. Full article

This paper presents a modern spectroscopic characterization of the synthetic oil from oil sands of Beke, Munaily-Mola, and Dongeleksor. The pyrolysis process was carried out at temperatures up to 580 °C with a controlled heating rate, and the products obtained were analyzed using Fourier transform infrared spectroscopy (FTIR), gas chromatography–mass spectrometry (GC–MSD), and nuclear magnetic resonance (NMR) spectroscopy. The FTIR spectra showed a predominance of aliphatic hydrocarbons in the sample from Munaily-Mola synthetic oil, while the content of aromatic compounds was higher in the sample from Beke. GC–MSD analysis revealed significant differences in the distribution of hydrocarbons between the samples, with the Munaily-Mola sample containing a higher proportion of heavy hydrocarbons. NMR spectroscopy provided additional information about the structural composition of the extracted oil. The results indicate the potential of pyrolysis as an effective method for processing oil sands, while the composition of the product varies depending on the geological origin of the raw materials. These findings provide valuable information for optimizing oil sands processing technologies and improving the efficiency of synthetic oil production. Full article

Understanding spatial variations in land surface temperature (LST) is critical for analyzing urban climate dynamics, especially within the framework of two-dimensional (2D) turbulence theory. This study assesses the spatial sampling behavior of urban thermal fields across eight metropolitan areas, encompassing diverse morphologies, surface materials, and Köppen–Geiger climate zones. We analyzed thermal infrared (TIR) imagery from two remote sensing platforms—MODIS (1 km) and Landsat (30 m)—to evaluate resolution-dependent turbulence indicators such as spectral slopes and breakpoints. Power spectral analysis revealed systematic divergences across spatial scales. Landsat exhibited more negative breakpoint values, indicating a greater ability to capture fine-scale thermal heterogeneity tied to vegetation, buildings, and surface cover. MODIS, in contrast, emphasized broader thermal gradients, suitable for regional-scale assessments. Seasonal differences reinforced the turbulence framework: summer spectra displayed steeper, more variable slopes, reflecting increased thermal activity and surface–atmosphere decoupling. Despite occasional agreement between sensors, spectral metrics remain inherently resolution-dependent. MODIS is better suited for macro-scale thermal structures, while Landsat provides detailed insights into intra-urban processes. Our findings confirm that 2D turbulence indicators are not fully scale-invariant and vary with sensor resolution, season, and urban form. This multi-sensor comparison offers a framework for interpreting LST data in support of climate adaptation, urban design, and remote sensing integration. Full article

The thermal resistance of carbon fiber–reinforced poly(phenylene sulfide) to harsh oxidative conditions is investigated through thermogravimetric experiments performed in an oxygen atmosphere. While these materials usually show great resistance against thermal decomposition in a nitrogen atmosphere, the experiments in oxygen reveal the total decomposition of both the matrix and the carbon fibers. The Gram–Schmidt signal, obtained by coupling thermogravimetric analysis in standard conditions with Fourier-transform infrared spectroscopy, exhibits multiple events, evidencing that the decomposition proceeds through distinct stages. The first step characterizes the char formation, while the second relates to its oxidative decomposition. A third step, only observed for composites, is interpreted as the signature of the oxidative decomposition of carbon fibers. To mimic the sudden elevation of temperature encountered during a fire, the analyses are performed at rates of up to 500 K min⁻¹. These specific experimental conditions reveal a complex dependence of the thermogravimetric signature on the heating rate. Independent of the atmosphere, nitrogen or oxygen, the characteristic temperature of decomposition follows a bell-shape trend, resulting from the combination of lag effects and thermal-conductivity limitations. Additionally, the increase of the heating rate causes the Gram–Schmidt signal to evolve toward a broad peak with indistinct events. To investigate whether these changes affect the decomposition products, the infrared spectra, continuously recorded to probe the whole decomposition, are compared with those from the database. The char formation is characterized by the production of sulfur dioxide, while carbon dioxide is the main product emitted during both char and fiber oxidative decomposition. Owing to the merging of the decomposition stages, sulfur-dioxide detection is partly supplanted by that of carbon dioxide under fast elevations of temperature. Full article

Chrysomya nigripes Aubertin, 1932, is a species of Calliphoridae widely distributed in Southeast Asia, with studies and case reports confirming the value of this species in estimating the minimum postmortem interval (PMI_min). However, data on the growth and development of this species’ intra-puparial age are not yet complete. Here, we investigated the intra-puparial morphological changes of C. nigripes at seven temperatures, ranging from 16 °C to 34 °C. We also investigated the potential value of Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) coupled with chemometric methods for the intra-puparial age estimation of C. nigripes at 19 °C, 25 °C, and 31 °C. The spectral data within the wavenumber range of 1800–900 cm⁻¹, collected from the second thoracic segment of all puparia, were processed. Through this procedure, the mean values of ATR-FTIR spectra of C. nigripes of puparia at each intra-puparial age under various constant temperature conditions were obtained. The results showed that at 16 °C, C. nigripes could not complete its developmental process, while it could do so at the remaining six constant temperatures. With an increase in temperature, the average duration of the intra-puparial period was reduced from the longest at 19 °C of 192 ± 0 h to 77.3 ± 4.6 h at 34 °C. The intra-puparial morphological changes were divided into 12 sub-stages, and the development of the compound eyes, mouthparts, antennae, thorax, legs, wings, and abdomen were divided into 6–8 sub-stages. The Partial Least Squares Discriminant Analysis (PLS-DA) classification model predicted better results compared to the Random Forest (RF) classification model, with an accuracy of 58.3%, 77.8%, and 100% at 19 °C, 25 °C, and 31 °C, respectively. In this study, each sub-stage of the C. nigripes pupa and the time range of structure emergence were recorded, and it was concluded that the spectral trends were time-dependent. Thus, ATR-FTIR combined with chemometrics could also be used as a tool to assist in estimating the intra-puparial stage of C. nigripes and provide a reference value for PMI_min. Full article

This experimental study analyses the extent of chemo-mineralogical changes that occur when a building stone encounters a cycling isothermal treatment at 600 °C. Four carbonate and two silicate European building stones were analysed in their fresh quarried and thermally treated conditions by means of colour measurements, in situ X-ray diffraction (XRD), and optical microscopy. Furthermore, powdered samples were characterised by Fourier-transform infrared spectroscopy, simultaneous thermal analysis, and cycling thermogravimetry (TG). The in situ XRD spectra revealed a surface-limited phase transformation of solid calcite and dolomite under isothermal conditions during the first 10 min at 600 °C and 500 °C, respectively. The onset of thermal decomposition and extent of phase transformation were governed by the microstructure of the solid samples. Inter- and intragranular microcracks are induced to varying degrees, and their incidence depended on the stone’s microstructure. Discolouration indicated a transformation of minor elements across the entire analysed sample volumes. Kaolinite was preserved even after three hours of thermal treatment at its dehydroxylation temperature due to its sheltering in confined pore spaces. Mass loss was more pronounced when cyclic treatment was employed compared to a non-periodic treatment, as determined by a TG analysis performed at same time intervals. Examining the chemo-mineralogical and microstructural changes caused by heat treatment allows us to study how and if regaining mechanical strength and restoring physical properties are possible for purposes of heritage restoration after fire damage. Full article

Experimental protocols based on Electron Paramagnetic Resonance (EPR) and Raman spectroscopy are presented for the investigation of the Fe(II) spin transition in Cu(II)-doped 1-D spin-crossover (SCO) nanoparticles of the type [Fe_1−xCu_x(NH₂trz)₃]Br₂ where x = 0.03 and 0.06 and NH₂trz = 4-amino-1, 2, 4-triazole. The resulting nanoparticles were characterized using Transmission Electron Microscopy (TEM), Infrared (IR) spectroscopy, and powder X-ray diffraction (p-XRD). Magnetic susceptibility measurements revealed a dependence on the scan rate, with critical temperatures and hysteresis widths varying accordingly. EPR spectroscopy provided insights into the doped nanoparticles’ structural changes and spin-state transitions. The Cu(II) dopants exhibited significant g-factor anisotropy and hyperfine structure, indicative of a distorted octahedral coordination. The EPR spectra indicated that the spin transition occurs in domains populated by ions of the same spin state. Cu(II) ions show different spectral characteristics depending on whether they are in high-spin or low-spin domains of Fe(II). Changes in Raman bands induced by laser power reveal structural and electronic rearrangements during the LS to HS transition. The findings provide insights into metal–ligand interactions and the molecular mechanisms underlying the SCO process. Full article

The non-isothermal melt crystallization process of poly[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyhexanoateate] (PHBHx) was monitored using attenuated total reflection infrared (ATR IR) measurement. The resulting time- and temperature-dependent spectra were subjected to the two-dimensional correlation spectroscopy (2D-COS) analysis. The C=O stretching region of the PHBHx sample consisted of several distinct IR contributions attributable to the population of amorphous component, well-ordered type I lamellar crystal, and less ordered inter-lamellar type II crystal. The spectral intensity change in type I crystal occurs in the earlier stage of the crystallization at a higher temperature range compared to the overall intensity decrease in the amorphous component occurring throughout the crystallization process. The growth of the type II crystal started in a later stage at a lower temperature than the creation of the type I crystal. An early decrease in a small but distinct portion of the amorphous component may be related to a crystallization precursor species with some level of molecular order. Hetero-mode correlation analyses revealed that the crystalline band intensity changes in the C-H stretching and fingerprint regions all occur later than the population changes in crystalline species reflected by the carbonyl stretching bands. This observation suggests that the spectral intensity changes in the C-H stretching and fingerprint regions do not directly represent the population dynamics of the crystalline and amorphous species but probe instead the molecular state of the crystalline entities still undergoing the evolutionary changes. Full article

We studied specially designed InAs/GaSb/AlSb/GaSb M-structures, a type-II superlattice (T2SL), that can serve as active materials for short-wavelength infrared (SWIR) applications. To obtain the dispersion relation of the investigated M-structures, k·p perturbation theory based on the eight-band model implemented in the nextnano++ v1.18.1 (nextnano GmbH, Munich, Germany) software was used. Numerical band-gap engineering and dispersion calculations for the investigated M-structures (composed of 6/1/5/1 monolayers, with InSb interfaces included) revealed the presence of an additional energy level within the energy gap. This energy level originates from the InSb-like interfaces and does not appear in structures with different layer or interface thicknesses. Its properties strongly depend on interface thickness, temperature, and strain. Numerical calculations of the probability density function ${|\Psi |}^2$, absorption coefficients, and optical absorption spectra at varying temperatures demonstrate that, under specific conditions, such as an optimised interface thickness and temperature, optical absorption increases significantly. These theoretical results are based on structures fabricated using molecular-beam epitaxy (MBE) technology. High-resolution X-ray diffraction (HRXRD) measurements confirm the high crystallographic quality of these M-structures. Full article

The narrow bandgap InN material, with exceptional physical properties, has recently gained considerable attention, encouraging many scientists/engineers to design infrared photodetectors, light-emitting diodes, laser diodes, solar cells, and high-power electronic devices. The InN/Sapphire samples of different film thicknesses that we have used in our methodical experimental and theoretical studies are grown by plasma-assisted molecular-beam epitaxy. Hall effect measurements on these samples have revealed high-electron-charge carrier concentration, η. The preparation of InN epifilms is quite sensitive to the growth temperature T, plasma power, N/In ratio, and pressure, P. Due to the reduced distance between N atoms at a higher P, one expects the N-flow kinetics, diffusion, surface components, and scattering rates to change in the growth chamber which might impact the quality of InN films. We believe that the ionized N, rather than molecular, or neutral species are responsible for controlling the growth of InN/Sapphire epifilms. Temperature- and power-dependent photoluminescence measurements are performed, validating the bandgap variation (~0.60–0.80 eV) of all the samples. High-resolution X-ray diffraction studies have indicated that the increase in growth temperature caused the perceived narrow peaks in the X-ray-rocking curves, leading to better-quality films with well-ordered crystalline structures. Careful simulations of the infrared reflectivity spectra provided values of η and mobility μ, in good accordance with the Hall measurements. Our first-order Raman scattering spectroscopy study has not only identified the accurate phonon values of InN samples but also revealed the low-frequency longitudinal optical phonon plasmon-coupled mode in excellent agreement with theoretical calculations. Full article

We report on the dynamic interactions between β-cyclodextrin (β-CD) and each one of the two enantiomers of asparagine (d-Asp, l-Asp). Molecular docking methodologies were applied to elucidate the formation of the β-CD—d-Asp and β-CD—l-Asp inclusion complexes. Ultrasonic relaxation spectra revealed a single relaxation process in the frequency range studied that is attributed to the complexation between β-CD and asparagine enantiomers. Kinetic parameters and thermodynamic properties for each system were determined directly from the concentration- and temperature-dependent acoustic measurements, respectively. Both β-CD—d-Asp and β-CD—l-Asp systems revealed subtle differences in their thermodynamic and kinetic properties. The infrared absorption spectra of the host molecule, the guest enantiomers, and both inclusion complexes were recorded to verify and further elucidate the complexation mechanism. DFT methodologies were performed to calculate the theoretical IR spectra of the inclusion complexes and compared with the corresponding experimental spectra. The close resemblance between the experimental and theoretically predicted IR spectra is supportive of the formation of inclusion complexes. The encapsulation of asparagine enantiomers in β-cyclodextrin enables not only applications in drug delivery but also the detection and separation of chimeric molecules. Full article

Biosorbents have demonstrated considerable potential for the remediation of metals in aqueous environments. An aqueous extract of Enteromorpha intestinalis L. (EiE) and its extract-coated silver nanoparticles have been prepared and employed for the removal of iron. Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), UV-visible spectroscopy, transmission electron microscopy (TEM), gas chromatography-mass spectroscopy (GC-MS), and zeta potential were employed to characterize the prepared biosorbents. The adsorption properties of the biosorbents were investigated in batch experiments, with a range of factors taken into account, including pH, contact time, initial ion concentrations, biosorbent dosage, and temperature. A minimum-run resolution IV design (MRR-IV) was developed with the objective of optimizing the removal efficiency. The mechanisms of adsorption were investigated using both the Langmuir and Freundlich isotherms. Kinetic studies were conducted using the pseudo-first-order and pseudo-second-order models. A variety of active constituents, including organic acids, lipids, alcohols, and terpenes, were identified through the use of GC-MS, with the findings supported by FTIR spectra. Transmission electron microscopy (TEM) revealed that the nanoparticle size ranged from 5 to 44 nm, while X-ray diffraction (XRD) demonstrated a high degree of crystallinity. A screening study employing the MRR-IV methodology, facilitated by the Design-Experiment, Ver 13., indicates that three factors exert a considerable influence on the biosorption process. The study demonstrated that the biosorption mechanism is pH-dependent, with an optimal pH of 5. The adsorption performance was found to follow Freundlich isothermal models and pseudo-first-order kinetics. Full article

Ethylene and sulfur dioxide molecules were co-deposited on a CsI window at cryogenic temperature, and the photoproducts upon UV irradiation were observed using Fourier transform infrared (FTIR) spectroscopy. The products were found to be UV wavelength-dependent; at shorter wavelengths (λ = 266 nm) one strong peak was observed while more than three peaks were identified at longer UV wavelengths (λ = 300 nm). Spectral features changed seamlessly along with UV wavelength. Density functional theory (DFT) calculations were carried out for potential products, and spectral matches between observations and calculations seemed satisfactory, assuming a cyclic molecule (oxathietane 2-oxide) as the main photoproduct at longer UV wavelengths. On the other hand, the spectra of photoproducts at shorter UV wavelengths were reproduced by assuming the decomposition products of an intermediate, from the supplementary experiments using deuterated samples. Plausible photoreaction schemes were presented to account for the observed photoproducts. Full article