Spectroscopic Investigation Research Articles

Molecular dynamics simulations and FTIR Spectroscopy investigations on the hydration, transport, and dielectric properties of the NaF(aq) system at various concentrations

Sodium fluoride has many applications in various fields, such as dentistry, geochemistry, and rechargeable battery technology. Indeed, the determination of the hydration structures, dynamics, and dielectric properties of the NaF electrolyte in aqueous solutions is a crucial element in order to optimize its performance and predict its intervention mechanisms in industrial processes. In this study, we used the molecular dynamics approach to study the NaF(aq) binary system at different concentrations ranging from 0.1 to 1.0 mol.kg−1 using the OPLS-AA force field combined with the extended simple point load water model (SPC/E). Thus, the ions were represented as charged Lennard-Jones particles. The radial distribution functions (RDF) have been calculated to analyze the hydration shell structures of different ion pairs. The microstructures, self-diffusion coefficient, and dielectric constant were determined by molecular dynamics at various concentrations. Moreover, our FTIR spectroscopy data confirm the results obtained from molecular simulations.

Spectroscopic Investigations of Complex Electronic Interactions by Elemental Doping and Material Compositing of Cobalt Oxide for Enhanced Oxygen Evolution Reaction Activity

AbstractDoping and compositing are two universal design strategies used to engineer the electronic state of a material and mitigate its disadvantages. These two strategies are extensively applied to design efficient electrocatalysts for water splitting. Using cobalt oxide (CoO) as a model catalyst, it is proven that the oxygen evolution reaction (OER) performance can be progressively improved, first by Fe‐doping to form Fe‐CoO solid solution, and further by the addition of CeO2 to produce a Fe‐CoO/CeO2 composite. X‐ray absorption spectroscopy (XAS) reveals that distinct electronic interactions are induced by the processes of doping and compositing. Fe‐doping of CoO can break down the structural symmetry, changing the electronic structure of both Co and O species at the surface and decreasing the flat‐band potential (Vfb). In comparison, subsequent compositing of Fe‐CoO with CeO2 induces negligible electronic changes in the Fe‐CoO (as seen in ex situ characterizations), but significantly modifies the oxidative transformations of both Co and Fe under OER conditions. The spectroscopic investigations reveal that Fe‐doping and CeO2 compositing play different roles in modifying the electronic properties of CoO in its pristine state and during OER catalysis, in return, providing useful guidance for the design of more efficient electrocatalysts using these two strategies.

NMR spectroscopic investigations of transition metal complexes in organometallic and bioinorganic chemistry

AbstractThe field of coordination chemistry has evolved to intersect with organic chemistry and biochemistry, giving rise to the disciplines of organometallic and bioinorganic chemistry. Nuclear magnetic resonance (NMR) spectroscopy can be applied for characterizing transition metal complexes, spanning both diamagnetic and paramagnetic complexes prevalent in organometallic compounds and metalloproteins. This review offers a comprehensive overview of a wide variety of characterization techniques, ranging from basic 1H and 13C NMR spectroscopy to advanced methods such as heteronuclear experiments, polarization transfer techniques, relaxometry, and multidimensional NMR spectroscopy. The diverse array of NMR spectroscopic methods outlined here promises to enhance our comprehension of transition metal complexes, facilitating the development of innovative catalysts and therapeutics.

Lattice Oxygen Activation through Deep Oxidation of Co4N by Jahn-Teller-active Dopants for Improved Electrocatalytic Oxygen Evolution.

Triggering the lattice oxygen oxidation mechanism is crucial for improving oxygen evolution reaction (OER) performance, because it could bypass the scaling relation limitation associated with the conventional adsorbate evolution mechanism through the directly formation of oxygen-oxygen bond. High-valence transition metal sites are favorable for activating the lattice oxygen, but the deep oxidation of pre-catalysts suffers from a high thermodynamic barrier. Here, taking advantage of the Jahn-Teller (J-T) distortion induced structural instability, we incorporate high-spin Mn3+ (t2g3eg1) dopant into Co4N. Mn dopants enable a surface structural transformation from Co4N to CoOOH, and finally to CoO2, as observed by various in-situ spectroscopic investigations. Furthermore, the reconstructed surface on Mn doped Co4N triggers the lattice oxygen activation, as evidenced experimentally by pH-dependent OER, tetramethylammonium cation adsorption and on-line electrochemical mass spectrometry measurements of 18O-labelled catalysts. In general, this work not only offers the introducing J-T effect approach to regulate the structural transition, but also provides an understanding about the influence of catalyst's electronic configuration on determining the reaction route, which may inspire the design of more efficient catalysts with activated lattice oxygen.

Excitation-Dependent Emission in Sb3+-Doped All-Inorganic Rare-Earth Double Perovskites for Anticounterfeiting Applications.

Achieving high-efficiency tunable emission in a single phosphor remains a significant challenge. Herein, we report a series of Sb3+-doped all-inorganic double perovskites, Sb3+:Cs2NaScCl6, with efficient excitation-dependent emission. In 0.5%Sb3+:Cs2NaScCl6, strong blue emission with a high photoluminescence quantum yield (PLQY) of 85% is obtained under 265 nm light irradiation, which turns into bright neutral white light with a PLQY of 56% when excited at 303 nm. Spectroscopic and computational investigations were performed to reveal the mechanism of this excitation-dependent emission. Sb3+ doping induces two different excitation channels: the internal transition of Sb3+: 5s2 → 5s5p and the electron transfer transition of Sb3+: 5s → Sc3+ 3d. The former one generates excited Sb3+ ions, which can undergo efficient energy transfer to populate the host self-trapped exciton (STE) state, yielding enhanced blue emission. The latter one leads to the formation of a new STE state with the hole localized on Sb3+ and the electron delocalized on the nearest Sc3+, which accounts for the newly exhibited low-energy emission. The difference in the excitation pathways of the two emitting STE states results in the highly efficient excitation-dependent emission, making the doped systems promising anticounterfeiting materials.

Nanocomposites Derived from Construction and Demolition Waste for Cement: X-ray Diffraction, Spectroscopic and Mechanical Investigations

In the production of cement, raw materials can be partially substituted by regenerable waste provided from glasses, construction and demolition waste in order to reduce the environmental problem and burden of landfills. In this study, limestone–silicate composites were synthesized using starting materials such as glass waste and lime, brick, autoclaved aerated concrete (ACC), mortar or plaster waste. The structure and mechanical properties of the nano-composite materials have been studied. The mean CaCO3 crystallite sizes are higher for composites containing ACC and brick than for doping with lime, mortar and plaster. Cement-based materials are formed by replacing 2.5% of the Portland cement with limestone–silicate composites. The results indicate new possibilities for introducing 2.5%of composites in cement paste because they promote the formation of the C-S-H network, which provides strength and long stability for the cement paste. The influence of varied types of mix composites in the expired cement on the initial cracking strain and stress, tensile strength and compressive strength were investigated. The compressive strength values of composite-expired cement specimens are situated between 11.8 and 15.7 MPa, respectively, which reflect an increase from 22.9 up to 63.54% over the compressive strength of expired cement matrix.

Raman Scattering Enhancement through Pseudo-Cavity Modes.

Raman spectroscopy plays a pivotal role in spectroscopic investigations. The small Raman scattering cross-section of numerous analytes, however, requires enhancement of the signal through specific structuring of the electromagnetic and morphological properties of the underlying surface. This enhancement technique is known as surface-enhanced Raman spectroscopy (SERS). Despite the existence of various proposed alternatives, the approach involving Fabry-Pérot cavities, which constitutes a straightforward method to enhance the electromagnetic field around the analyte, has not been extensively utilized. This is because, for the analyte to experience the maximum electric field, it needs to be embedded within the cavity. Consequently, the top mirror of the cavity will eventually shield it from the external laser source. Recently, an open-cavity configuration has been demonstrated to exhibit properties similar to the classic Fabry-Pérot configuration, with the added advantage of maintaining direct accessibility for the laser source. This paper showcases how such a simple yet innovative configuration can be effectively utilized to achieve remarkable Raman enhancement. The simple structure, coupled with its inexpensive nature and versatility in material selection and scalability, makes it an ideal choice for various analytes and integration into diverse Raman apparatus setups.

MnCo2O4 Spinel Nanorods for Highly Sensitive Electrochemical Detection of Nitrite.

The rational design of nitrite sensors has attracted significant research interest due to their widespread use and the associated risks of methemoglobinemia and carcinogenicity. The undisclosed nitrite-sensing performance of the spinel cobaltite MnCo2O4 (MCO) prepared by an oxalate-assisted coprecipitation method is reported in this study. Spectroscopy and microscopy investigations revealed the formation of uniform MCO nanorods with a high aspect ratio. The electrocatalytic nitrite oxidation at the MCO-coated glassy carbon electrode (MCO/GCE) indicated the promising performance of the synthesized material for nitrite sensing. MCO/GCE detects nitrite in a concentration range of 5 μM to 3 mM and has a limit of detection of 0.95 μM with a higher sensitivity of 857 μA mM-1 cm-2 in a response time of 4 s. In MCO, the mixed-valence states of Co2+/Co3+ confer a high electrical conductivity, and higher valent redox couples of Mn and Co impart remarkable electrocatalytic activity toward nitrite oxidation. MCO spinel undergoes facile and ultrafast faradaic reactions to mediate nitrite oxidation. Additionally, the mesopores of MCO nanorods facilitate the rapid diffusion of electrolyte and nitrite ions. Employing the electrode in sensing nitrite in milk, lake, and tap water samples further validates its potential application in real-life testing. MCO spinel nanorods showcase promising scope for utilization in the electrochemical sensing of nitrite and inspire further exploration of transition-metal oxide-based mixed-spinel materials.

Spectroscopic Investigation of Tomato Seed Germination Stimulated by Trichoderma spp.

Seed germination is a complex process that can be negatively affected by numerous stresses. Trichoderma spp. are known as effective biocontrol agents as well as plant growth and germination stimulators. However, understanding of the early interactions between seeds and Trichoderma spp. remains limited. In the present paper, Fourier-transform infrared spectroscopy (FTIR) and Raman spectroscopy were used to reveal the nature of tomato seed germination as stimulated by Trichoderma. A rapid response of tomato seeds to Trichoderma spp. was observed within 48 h on Murashige and Skoog medium (MS) substrate, preceding any physical contact. Raman analysis indicated that both Trichoderma species stimulated phenolic compound synthesis by triggering plant-specific responses in seed radicles. The impact of T. harzianum and T. brevicompactum on two tomato cultivars resulted in alterations to the middle lamella pectin, cellulose, and xyloglucan in the primary cell wall. The Raman spectra indicated increased xylan content in NA with T9 treatment as well as increased hemicelluloses in GZ with T4 treatment. Moreover, T4 treatment resulted in elevated conjugated aldehydes in lignin in GZ, whereas the trend was reversed in NA. Additionally, FTIR analysis revealed significant changes in total protein levels in Trichoderma spp.-treated tomato seed radicles, with simultaneous decreases in pectin and/or xyloglucan. Our results indicate that two complementary spectroscopic methods, FTIR and Raman spectroscopy, can give valuable information on rapid changes in the plant cell wall structure of tomato radicles during germination stimulated by Trichoderma spp.

Synthesis and Biological Properties of Fluorescent Strigolactone Mimics Derived from 1,8-Naphthalimide.

Strigolactones (SLs) have potential to be used in sustainable agriculture to mitigate various stresses that plants have to deal with. The natural SLs, as well as the synthetic analogs, are difficult to obtain in sufficient amounts for practical applications. At the same time, fluorescent SLs would be useful for the mechanistic understanding of their effects based on bio-imaging or spectroscopic techniques. In this study, new fluorescent SL mimics containing a substituted 1,8-naphthalimide ring system connected through an ether link to a bioactive furan-2-one moiety were prepared. The structural, spectroscopic, and biological activity of the new SL mimics on phytopathogens were investigated and compared with previously synthetized fluorescent SL mimics. The chemical group at the C-6 position of the naphthalimide ring influences the fluorescence parameters. All SL mimics showed effects similar to GR24 on phytopathogens, indicating their suitability for practical applications. The pattern of the biological activity depended on the fungal species, SL mimic and concentration, and hyphal order. This dependence is probably related to the specificity of each fungal receptor-SL mimic interaction, which will have to be analyzed in-depth. Based on the biological properties and spectroscopic particularities, one SL mimic could be a good candidate for microscopic and spectroscopic investigations.

Reaction Mechanism of Hydrogen Generation and Nitrogen Fixation at Carbon Nitride/Double Perovskite Heterojunctions

Photocatalytically active heterojunctions based on metal halide perovskites (MHPs) are drawing significant interest for their chameleon ability to foster several redox reactions. The lack of mechanistic insights into their performance, however, limits the ability of engineering novel and optimized materials. Herein, a report is made on a composite system including a double perovskite, Cs2AgBiCl6/g‐C3N4, used in parallel for solar‐driven hydrogen generation and nitrogen reduction, quantified by a rigorous analytical approach. The composite efficiently promotes the two reactions, but its activity strongly depends on the perovskite/carbon nitride relative amounts. Through advanced spectroscopic investigation and density function theory (DFT) modeling the H2 and NH3 production reaction mechanisms are studied, finding perovskite halide vacancies as the primary reactive sites for hydrogen generation together with a positive contribution of low loaded g‐C3N4 in reducing carrier recombination. For nitrogen reduction, instead, the active sites are g‐C3N4 nitrogen vacancies, and the heterojunction best performs at low perovskites loadings where the composites maximize light absorption and reduce carrier losses. It is believed that these insights are important add‐ons toward universal exploitation of MHPs in contemporary photocatalysis.

Layered double hydroxides matrix as host for curcumin loading: structural and spectroscopic investigations

Layered double hydroxides matrix as host for curcumin loading: structural and spectroscopic investigations

An investigation into the effect of UV irradiation and biofilm colonization on adsorption and desorption behavior of polyurethane (PU) microplastics for bisphenol A (BPA)

Recent studies have demonstrated that microplastics (MPs) can act as a transport vector for pollutants in the environment. However, most studies have focused on carbon-carbon backbone polymers, with little known about heteroatom backbone polymers. In this study, polyurethane (PU) MPs were modified by UV irradiation and microorganism colonization to assess the different aging treatments on the interaction behavior (adsorption/desorption) between PU MPs and bisphenol A (BPA). The results of the adsorption kinetics experiment illustrated that the adsorption process of BPA could be described well by a pseudo-second order kinetic equation on both fresh and aged PU MPs. Although fresh PU MPs revealed the highest saturated adsorption capacity, at low BPA exposure concentrations (≤ 100 μg/L) the adsorption capacities for UV aged and biofilm colonized PU MPs were very similar to fresh MPs or even slightly higher than for fresh MPs, the main adsorption mechanisms including H-bonding interactions and π–π interactions. Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) investigations suggested obvious physicochemical property changes (e.g., generation of new functional groups, erosion, etc.) after UV irradiation and biofilm colonization. This study also showed that different exposure environments (ultrapure water, artificial seawater, simulated gastric fluid) could affect BPA adsorption/desorption via hydrophobic and electrostatic interaction on PU surfaces. These results further clarify the adsorption mechanisms of BPA on PU MPs that have undergone different aging treatments, and provides a theoretical basis for the assessment of environmental behavior and exposure risks when PU MPs and BPA coexist.

Enhancing High Voltage Stability via Fluorination of Functionalized Metal Organic Framework Electrolyte in Lithium Metal Batteries

AbstractThe electrolyte stability under high‐voltage conditions considerably limits the upper cut‐off potential of solid‐state electrolytes (SSEs) and therefore the energy density of all‐solid‐state batteries (ASSBs). In this work, metal‐organic frameworks (MOFs) were fluorinated to lower the energy level of HOMO orbital and allow access to a 4F‐MOF that exhibit enhanced anodic stability. The composited 4F‐MOF/PEO electrolyte could not only transport Li+ ions in the ordered framework channels, but also provide a remarkable high‐voltage stability up to 5.0 V, shielding oxidative decomposition that would otherwise occur at around 3.9 V for conventional PEO electrolytes. In addition, stable lithium deposition was demonstrated for more than 1,300 hours at 0.1 mA ⋅ cm−2, while reversible charge‐discharge cycling performance was delivered in assembled Li||LiNi0.5Mn1.5O4 (LNMO) ASSBs up to 5.0 V. Post‐mortem X‐ray photoelectron spectroscopy (XPS) investigation on cathodes revealed presence of a LiF‐rich cathode electrolyte interface (CEI), supporting promoted stability towards high‐voltage ASSBs.

Photocatalytic degradation of p-aminobenzoic acid on N-biomass charcoal etched with Fe-Al-bilayer hydroxide: New insights through spectroscopic investigation

We investigated the photocatalytic property of etched iron‑aluminum layered double hydroxide (LDH) composites using urea-modified biochar (N-BC) carrier to degrade para-aminobenzoic acid (PABA), a refractory organic pollutant. The prepared FeAl-LDH@FeSx-N-BC composite exhibited excellent photocatalytic performance, attributed to the enhanced photogenerated charge-carrier separation by the etched LDH and the improved comparative surface areas by the doped N-BC. The composite photocatalytically degraded 96 % of PABA. The performance was affected by solute concentration, pH and photocatalyst dose. Adding p-benzoquinone and EDTA-2Na significantly decreased the degradation rate, suggesting that superoxide radicals and holes were co-involved in PABA degradation. The excellent PABA removal efficiency was consistent for three consecutive runs. The samples' reactive oxygen species was confirmed, as electron paramagnetic reverberation explained the photodegradation mechanism. Under xenon lamp irradiation, two PABA photocatalytic degradation pathways were proposed using Liquid Chromatograph Mass Spectrometer (LCMS) and density functional theory. As expected, FeAl-LDH@FeSx-N-BC showed excellent photocatalytic performance, expanding a new direction and possibility for future photocatalytic treatment of water pollutants.

Effects on structure by spectroscopic investigations, valence state and morphology properties of FeCo-containing SnO2 catalysts for glycerol valorization to cyclic acetals

The effects on the structure, valence state and morphological properties of FeCo-containing SnO2 nanostructured solids were investigated. The physicochemical features were tuned by distinct synthesis routes e.g., sol–gel, coprecipitation and nanocasting, to apply them as catalysts in the glycerol valorization to cyclic acetals. Based on Mössbauer and XPS spectroscopy results, all nanosized FeCoSn solids have Fe-based phases, which contain Co and Sn included in the structure, and well-dispersed Fe3+ and Fe2+ surface active sites. Raman, FTIR and EPR spectroscopies measurements of the spent solids demonstrated structural stability for the sol–gel based solid, which is indeed responsible for the highest catalytic performance, among the nanocasted and coprecipitated counterparts. Morphological and elemental analyses illustrated distinct morphologies and composition on solid surface, depending on the synthesis route. The Fe/Co and Fe/Sn surface ratios are closely related to the catalytic performance. The improved glycerol conversion and selectivities of the solid obtained by sol–gel method was ascribed to the leaching resistance and the Sn action as a structural promoter.

Air‐Stable 2D van der Waals MgTeMoO6 Exhibits Strong In‐plane Optical Anisotropy

AbstractExploring 2D van der Waals (vdW) materials is of great importance to the various optoelectronics‐based applications. Herein, mono‐ and few‐layer nanoflakes of a novel 2D vdW MgTeMoO6 are prepared by facile mechanical exfoliation method. These nanoflakes remain highly stable when being exposed in air even for 1 month, which is unique compared to most of 2D materials. Temperature‐dependent Raman spectroscopy reveals that 2D MgTeMoO6 nanosheets exhibit stronger interlayer interaction than that of graphene. In situ, angle‐resolved polarized Raman spectroscopy investigation show evidences for the anisotropic photo–phonon interactions. Notably, strong in‐plane anisotropy for the second harmonic generation (SHG) independent of layer number is observed for 2D MgTeMoO6, making 2D MgTeMoO6 promising in polarization‐sensitive optoelectronic applications.

Spatially Resolved Raman Spectroscopic Investigation of Uranyl Fluoride: A Case Study in the Importance of Instrument Optimization.

Raman spectroscopy is an emerging technique for rapid and nondestructive analysis of nuclear materials for forensic and nonproliferation applications as it is a powerful tool for distinguishing multiple chemical forms of materials with similar stoichiometries. Recent developments in spectroscopic software have enabled rapid data collection with high-speed Raman spectroscopic mapping capabilities. However, some uranium-rich materials are susceptible to degradation in humid air and/or laser-induced phase transformations. To mitigate environmental or measurement-related sample degradation of potential samples of interest, we have taken a systematic approach to define optimized data collection parameters for high-throughput measurements of uranyl fluoride (UO2F2), which is an important intermediate material in the nuclear fuel cycle. First, we systematically describe the influence of optical magnification (5× to 100×), laser power, and exposure time on obtained signal for identical particles of UO2F2 and find that at low laser power and exposure times, comparable signal is obtained regardless of optical magnification. Second, we ensure sample integrity during data collection, and third, collect spectroscopic maps that employ optimized parameters to reduce the time required to obtain spatially resolved spectroscopic information. Reductions of 90% and 99% in measurement times are discussed as they relate to differences in resolving spectroscopic features of particles in identical mapping areas. During this work, we found that additional data processing options were needed and thus developed a customized Python script for importing, processing, analyzing, and visualizing Raman spectroscopic map data.

Hydrogen-bond stabilized π-π stacking in the solvent-induced dimerization of 4-nitro-1-naphthol: A spectroscopic and computational investigation

π-π Stacking is crucial for stabilizing molecular structures and facilitating interactions in biological systems and chemical processes. The presence of electron-withdrawing and electron-donating substituents, particularly the hydroxyl group, significantly influences the energetics and energetically favorable configurations of π-stacked complexes. In this study, we utilized UV–Vis absorption and resonance Raman spectroscopies, alongside density functional theory (DFT) calculations, to investigate the competition between dissociation and self-aggregation of 4-nitro-1-naphthol (NNH) in various polar solvents. Our results demonstrate the self-aggregation of NNH in polar solvents and identify the most likely dimer configuration, which is antiparallel π-stacked and stabilized by hydrogen bonds between hydroxyl and nitro groups. Given its broad applications in mass spectrometry, environmental remediation, and aerosol tracking, a comprehensive understanding of the molecular interactions and structural properties of NNH is essential for its effective use in various scientific fields.

Effect of neem oil biodiesel on the surface and structural integrity of carbon steel alloy: Chromatographic, spectroscopic, and morphological investigations

This study explores the impacts of neem oil biodiesel (BD), which was produced and characterized using GC–MS, FTIR, and UV–Vis spectroscopic techniques to elucidate pure and corrosion-product neem oil BD at room temperature (25 °C) and different immersion durations of 0, 28, 42, and 56 days. The OM and SEM were also employed to study the surface, structural integrity, and interphase interaction between the BD and the carbon steel (C1020) before and after immersion for different durations. The dominant fatty acid (FA) group in both pure and corrosion-product neem oil BD was C18, with a total composition of 72.3 %, hence determining the nature of the BD interaction with the carbon steel. The study revealed that carbon steel (C1020) was susceptible to attacks by neem oil BD, and the duration of immersion had substantial influence on the surface morphology and structural integrity of the steel. It is therefore anticipated that this study will significantly advance the field of alternative fuel research.