Visible Raman Spectroscopy Research Articles

Comparative Analysis of Structural, Optical, and Electronic Properties of Nickel Oxide and Potassium‐Doped Nickel Oxide Nanocrystals

ABSTRACTMetal oxide semiconductors, known for their exceptional optical transparency, high carrier mobility, and stability, have found extensive use in emerging technologies such as optoelectronics and energy storage devices. Among all metal oxide semiconductors, nickel oxide (NiO) stands out as a highly favorable candidate due to its p‐type conductivity along with its substantial band gap (3.5–4 eV) for the broad range of applications, including gas sensors, high‐rate Lithium‐ion batteries, high‐performance supercapacitors, and photovoltaic devices. In light of these versatile applications, our current study presents a comprehensive comparative analysis of the structural and optoelectronic properties of NiO and potassium (K)‐doped NiO nanocrystals. The nanocrystals were synthesized using the co‐precipitation route and subsequently annealed at 500°C under ambient conditions. The effect of K doping on the structural and optoelectronic characteristics was systematically examined using various techniques, including x‐ray diffraction, UV–visible spectroscopy, Raman spectroscopy, and Hall effect measurements. To explore the structural characteristics, XRD measurements were performed, which confirm the FCC structure of nanocrystals. The optical property analysis suggested that the formation of the energy level can contribute to reduction of the band gap. A sharp peak at 397 cm−1 is associated with NiO bond in FTIR spectra which verifies the formation of nanocrystals. Moreover, the incorporation of K increases the intensity of the Raman peaks, which provides evidence for the higher degree of crystallinity in doped samples. These results of Raman scattering are in good agreement with XRD outcomes. In addition, the resistivity of NiO nanocrystals decreases monotonically with the increasing K concentration. The results of temperature‐dependent resistivity further demonstrate that electrons required more energy to jump from one polaron state to another in the case of x = 0.01 M and 0.03 M doped Ni0.5‐xKxO samples. The combination of a diminished band gap and enhanced conductivity makes these materials exceptionally promising for applications in optoelectronics and energy storage.

Selective passivation of 2D MoS2 nanosheets surface defects by spontaneous growth of Au nanoparticles for full response-recovery NO2 detection at room temperature

Full recovery at room temperature (RT) is quite challengng for two dimensional transition metal dichalcogenides chemiresistive gas sensors. The main reason for the incomplete recovery is the strong bonding of gas molecules onto sensing layer defects. Here, we show that the recovery rate of MoS2 chemiresistive NO2 sensors can be improved by selective passivation of MoS2 nanosheets (NSs) defects with Au nanoparticles (NPs) via a simple spontaneous reduction method. MoS2 NSs were produced by liquid shear exfoliation. Pristine and Au NPs functionalized MoS2 were characterized using ς-potential, UV–Visible spectroscopy, TEM, SEM, AFM, EDS, XRD, XPS and Raman spectroscopy. The analyses confirm the presence of Au NPs on the edges of MoS2 NSs at defective sites with NP sizes of 1–4 nm and 5–30 nm. Both pristine MoS2 and Au-decorated MoS2 NSs were employed to fabricate NO2 chemiresistive devices. Au-decorated MoS2 sensors showed an improved performance (for 1 ppm NO2, Au-MoS2 sensor exhibited a response of 5.6 % instead of 2.2 % for MoS2 sensor), and gave faster response and better recovery time. Concurrently, the functionalization is independent of the adsorption and desorption of NO2. Most importantly, the functionalization of MoS2 NSs helps to full response-recovery within one hour, without either thermal or UV irradiation treatment.

A paradigm for natural eutectic solvents based on fatty acids: Molecular interactions and toxicological considerations

In this work, we present experimental and molecular modeling results on archetypal hydrophobic natural deep eutectic solvents (NADES) based on fatty acids (octanoic and dodecanoic acid) and menthol, a representative monoterpenoid. Our goal is to provide a multiscale characterization to enhance the understanding of this field by studying these selected archetypical mixtures. We examine their liquid state properties, intermolecular forces, nanoscopic arrangements, toxicity, and environmental impact.The computational study integrates quantum chemistry, molecular dynamics (both all-atom and coarse-grained approaches), and thermodynamic modeling (COSMO-RS approach) to analyze the fluids and their interactions with biological entities, such as proteins and plasma membranes. The experimental characterization focuses on elucidating intermolecular interactions and liquid phase dynamics using NMR spectroscopy, visible and UV Resonance Raman spectroscopy (UVRR). Notably, this is the first report of UVRR data on NADES.Additionally, we simulate the effect of the molecular moieties forming the solvents on biological targets—specifically, protein and cell membrane models –. This in silico analysis aims to rationalize and predict their potential toxicity.Overall, our experimental findings and in silico simulations contribute to a deeper understanding of these novel solvents in terms of their network of interactions. Additionally, they highlight the potential impact on biological targets, providing new data to accurately define the eco-friendliness of type V DES and their suitability as sustainable alternatives to traditional molecular solvents.

Structural and biophysical insights into the interactions of anisotropic gold nanoparticles with human telomeric G-quadruplex DNA: Spectroscopic and calorimetric approach

We are reporting curcumin-induced synthesis of anisotropic citrate capped Gold nanoparticles (ctGNPs). The techniques such as UV–visible spectroscopy, Raman spectroscopy, FT-IR, X-ray diffraction (XRD), and Transmission Electron Microscopy (TEM) were used to characterize the nanoparticles. The synthetic route shows the formation of an anisotropic gold nanostructure consisting of spherical, triangles, hexagonals, and a low-yield rod with an aspect ratio ranging from 4.2 to 8.5. Curcumin-derived ctGNPs shows stability at different physiological conditions and better biocompatibility. Synthesized nanoparticles are found non-toxic towards eukaryotic cells but more effective against the cancer cell lines HeLa and MCF-7. The interaction of these synthesized nanoparticles with human telomeric G-quadruplex (GQ) DNA was studied using different physiochemical methods. The spectroscopic studies show that synthesized nanoparticles have stronger binding affinity towards telomeric GQ as compared to ds DNA through Van der Waals and H-bonding interactions. Thermodynamic interpretation reveals that the formation of the complex between the telomeric GQ and ctGNPs are enthalpy driven and entropy unfavourable process, resulting in motion freezing and, eventually, AuNP aggregation. Thus, our study shows a new approach to understand the interaction of telomeric G-quadruplexes with gold nanoparticles generated via the green route.

Resonance Raman spectral analysis of the heme site structure of cytochrome c oxidase with its positive regulator CHCHD2

Cytochrome c oxidase (CcO) reduces O2, pumps protons in the mitochondrial respiratory chain, and is essential for oxygen consumption in the cell. The coiled-coil-helix-coiled-coil-helix domain-containing 2 (CHCHD2; also known as mitochondrial nuclear retrograde regulator 1 [MNRR1], Parkinson's disease 22 [PARK22] and aging-associated gene 10 protein [AAG10]) is a protein that binds to CcO from the intermembrane space and positively regulates the activity of CcO. Despite the importance of CHCHD2 in mitochondrial function, the mechanism of action of CHCHD2 and structural information regarding its binding to CcO remain unknown. Here, we utilized visible resonance Raman spectroscopy to investigate the structural changes around the hemes in CcO in the reduced and CO-bound states upon CHCHD2 binding. We found that CHCHD2 has a significant impact on the structure of CcO in the reduced state. Mapping of the heme peripheries that result in Raman spectral changes in the structure of CcO highlighted helices IX and X near the hemes as sites where CHCHD2 takes action. Part of helix IX is exposed in the intermembrane space, whereas helix X, located between both hemes, may play a key role in proton uptake to a proton-loading site in the reduced state for proton pumping. Taken together, our results suggested that CHCHD2 binds near helix IX and induces a structural change in helix X, accelerating proton uptake.

Synthesis of graphene-based nanocomposites with superior doxycycline removal efficiency and antimicrobial studies

Herein, we report the successful preparation of high-quality graphene (G) nanosheets up to the kg scale using an electrochemical technique using graphite rods from scrap dry cell batteries. The as-prepared graphene was then decorated in-stiu with niobium oxide (Nb2O5) and silver (Ag) nanoparticles to prepare Nb2O5@G and Ag@G nanocomposites. Powdered X-ray diffraction (p-XRD), Fourier-transform (FT-IR) infrared spectroscopy, UV–visible (UV–vis) spectroscopy, Raman spectroscopy, and scanning electron microscopy (SEM) were used to characterize the as-prepared nanocomposite material. This binary Nb2O5@G nanocomposite was subsequently used to degrade doxycycline antibiotic with an efficiency of 98.5 % in 120 min under visible light conditions. To determine the optimal scope of the as-prepared composite catalyst, degradation studies were performed at different pH values, photocatalyst doses and temperatures. Kinetics studies revealed that the processes followed pseudo-first-order kinetics. In addition, the as-synthesized graphene, Nb2O5@G and Ag@G nanocomposites were used for selective application against E. coli bacterial strains. Overall, Ag@G has shown good potential application prospects in the development of antibacterial materials in comparison with Nb2O5@G and pristine graphene. This study highlights the potential of as-prepared graphene-based nanocomposites for use in waste treatment and environmental bioremediation.

Fabrication of magnetite/GO/potassium copper hexacyanoferrate nanocomposite for removal of radioactive cesium ions

Metal hexacyanoferrates (MHCF) are a class of inorganic adsorbents used for wastewater management due to the presence of interstitial sites for capturing heavy metal ions. In present work, we are reporting the synthesis of magnetic nanocomposite of Fe3O4/graphene oxide/potassium copper hexacyanoferrate via wet chemical and coprecipitation approach. Potassium copper hexacyanoferrate (KCuHCF) and Graphene oxide (GO) both are marvelous adsorbents but their nano-size becomes a major obstacle in their separation process after the adsorption of the radionuclides. Thus, our synthesized nanocomposite Fe3O4/GO/KCuHCF enhances the recovery of KCuHCF even after radioactive Cs+ adsorption with adsorption capacity of 18 mg g−1 coinciding well with the Langmuir adsorption isotherm mechanism. The synthesized adsorbent is characterized thoroughly using UV–Visible spectroscopy, FT-IR, TGA, XPS, Raman spectroscopy, TEM-EDAX and XRD. This synthesized nanocomposite is used for the batch extraction of radioactive Cs+ from low level radioactive waste (LLW). The extraction kinetics followed pseudo-second-order kinetics mechanism.

Altering the physical properties of NiO thin films grown through the ultrasonic spray pyrolysis method by incorporating impurity lead dopants

The technology of p-type transparent semiconductors is utilized in various fields, and enhancing their performance holds industrial significance. Thus, improving the versatility and efficiency of the p-type transparent conducting oxides (TCO) has become critical for the semiconductor industries and technologies. To be used as hole carrier layes in optoelectronic devices, this study aimed to modify the physical features of nickel oxide (NiO) through a doping approach which may broaden and strengthen the usage of NiO. A cost-effective ultrasonic pyrolysis spray technique was employed for pure and lead (Pb) doped nickel oxide thin film production. The influence of the lead concentration on optical, structural, and morphological traits of the NiO nanostructures was examined via various analyses, including energy-dispersive X-ray spectroscopy (EDAX), scanning electron microscopy (SEM), Photoluminescence, UV–visible spectroscopy, X-Ray Diffraction, and Raman spectroscopy, were utilized to investigate the optical and structural characteristics of these films. In correlation, the X-Ray Diffraction results indicated that the Pb doping induced strain and altered lattice parameters of the grown nanostructures while the cubic phase of NiO maintained. The crystallite size of NiO samples ranged from 31.49 nm to 18.75 nm based on Pb doping concentration which was notably influenced by species and doping content. The UV–vis measurements demonstrated that optical parameters, such as optical band gap, were sensitive to Pb doping ratios. The Raman spectrum analysis confirmed the successful incorporation of Pb ions into NiO. Additionally, the intensity of the PL spectra decreased with increasing Pb content, offering potential applications as window layers in solar cells, smart windows, and other optoelectronic devices.

Spectroscopic characterization of fluorite of Amba Dongar, Gujarat, India: Linking chemical composition with color

This work addresses the long-standing debate surrounding the origin of color variation in fluorite (CaF2) through a novel quantitative approach. By examining eight carefully selected fluorite samples having different hue of colors from the Amba Dongar mine in Gujarat, India, a rigorous quantitative analysis was conducted. This approach combined chemical compositional data and optical spectroscopic features to elucidate the relationship between elemental composition, concentration, and color variation in fluorite. Precise elemental concentration data for trace transition metals, alkali metals, and rare earth elements (REEs) were obtained through inductively coupled plasma mass spectroscopy (ICP-MS) analysis of powdered fluorite samples. Optical spectroscopic techniques, including UV–visible absorption, emission (photoluminescence and fluorescence), and Raman spectroscopy, were employed to capture characteristic spectral signatures for specific color of the study sample. The work unveils a strong correlation between specific elemental concentrations and observed spectral features, particularly influenced by alkaline metals, transition group elements, and REEs. Fluorite’s optical absorption behavior lacks a clear pattern in UV and infrared wavelength ranges but correlates well with transition metal, alkaline element, and REE concentrations in visible wavelength regions, influencing coloration. Luminescent centers in the study fluorite samples correspond to specific REE concentrations, indicating a strong linkage between emission wavelengths with the presence of specific REE. UV–visible and fluorescence in fluorite result from trivalent REE or Eu2+ ions, with emission intensity affected by REE concentration and specific REE or combinations thereof. Raman spectroscopy identifies characteristic modes related to F-substitution and REE impurities, providing insights into fluorite’s structural composition. This quantitative correlation between elemental composition and spectroscopic characteristics represents a novel contribution for understanding color variation mechanisms in fluorite. The comprehensive analysis of this present work underscores the intricate interplay of mineral composition, and element concentration particularly alkaline metals, transition group elements, and REEs, for variation in spectral signatures with variation in fluorite’s visual attributes.

Synthesis and characterization of graphene oxide, tin oxide, and reduced graphene oxide-tin oxide nanocomposites

The present study reports the synthesis and characterization of graphene oxide (GO), tin oxide nanostructures, and reduced GO (rGO)-tin oxide nanocomposites. The modified Hummer's method was used for the synthesis of GO. Tin oxide nanoparticles were synthesized by co-precipitation method using SnCl2 as tin source. The rGO-tin oxide nanocomposites were synthesized by hydrothermal method using GO and SnCl2 as tin source. The synthesized nanostructures were characterized using powder XRD, FESEM, EDX spectroscopy, TEM, SAED, FTIR spectroscopy, UV–visible spectroscopy, Raman spectroscopy, and TGA. The XRD pattern of the graphite powder shows intense (002) plane peak at 2θ = 26.78° along with the other graphitic XRD peaks. In addition, XRD peaks at 2θ ∼ 14°, 16.8°, 21.18°, and 24.18° were also observed. The characteristic GO (001) plane peak in the XRD pattern could be not be observed in the oxidative exfoliation GO. The Raman spectrum of the graphite powder shows intense crystalline G band, low-intensity defect related D, multi-layered graphitic flake related 2D-band with intensity ratio ID/IG=0.08 and I2D/IG=0.46. The oxidative exfoliated GO shows the degradation of the graphite XRD peaks, but the characteristic GO (001) plane XRD peak could not be observed. The TEM image shows the formation of GO sheets on the oxidative exfoliation of graphite. The d-spacing obtained from the observed hexagonal SAED pattern of the oxidative exfoliated GO was found to be much lower than graphite d-spacing. Raman, UV–visible, FTIR, and TGA studies indicate the formation of GO under oxidative exfoliation of graphite under Hummer’s method. The band gap values of around 1.70 eV from the UV–visible optical absorption also indicates the formation of graphene in the oxidative exfoliated GO. The observed results indicate the formation of graphene embedded amorphous GO.

Modification induced by 120 MeV Ag ion irradiation in ZnS

We report the structural, morphological, and optical properties of ZnS thin films before and after swift heavy ion (SHI) irradiation of 120 MeV Ag ions. These films were deposited by the spin coating method on the glass substrate and irradiated at various ion fluencies from 1 × 1011 to 1 × 1013 ions/cm2. The Grazing Incidence X-ray diffraction (GIXRD), Scanning electron microscopy (SEM), UV–visible transmittance, Photoluminescence (PL), and Raman Spectroscopy were used to characterize these ZnS thin films. The GIXRD patterns show a mixed phase of cubic and hexagonal structure after the ion irradiation. The crystallite sizes of pure and irradiated films are significantly modified. Raman spectroscopy shows a slight increase in the intensity of the 3LO mode of ZnS on irradiation. The SEM image shows nanoflake-like structures in pristine, and the irradiated thin films depict various morphologies (rod, platy, and sphere-like). UV–visible shows a cut-off wavelength at 339 nm and the spectra are blue-shifted with the increase in ion fluence. The Tauc plots reveal the increase in the band gap. The intensity of PL decreases with ion irradiation. Hence the analytical results show that the structural and optical properties of ZnS thin films are altered on swift heavy ion irradiation which may have potential applications in optoelectronic applications.

Investigation on Structural, Optical, and Thermal Properties of Graphene Oxide (GO) Nanoparticles

The aim of the study , A nanoparticles of graphene oxide (GO) was synthesized by modified Hummer’s method. A new approach to synthesis graphene is oxidizing graphite powder with mixture with concentrated Sulphuric acid (H2SO4), Sodium Nitrate (Na NO3) and Potassium permanganate (KMnO4), Currently,an improved method for the preparation of graphene Oxide was most common one. The Graphene Oxide (GO) was characterized by X-Ray diffractration, FT-IR Spectroscopy, UV Visible Spectroscopy , Raman Spectroscopy and TGA analysis. The X-ray diffractration (XRD) results of Graphene oxide nanoparticles was found to be 12.9 nm with a hexagonal crystal structure. Key Words: Graphene oxide, Hummer’s method,Graphite, X-ray diffratcration, FI-IR analysis,UV-Visible spectroscopy ,Raman spectroscopy and TGA-DTA analysis

Maximizing visible Raman resolution of nanodiamond grains fabricated by coaxial arc plasma deposition through oxygen plasma etching optimization

Among the nondestructive carbon material characterization tools, the prominence of visible Raman spectroscopy has surged remarkably for many years due to its ability to explore a diverse array of carbon bonding configurations. However, to fully unlock the distinctive features concealed within carbon composite materials, additional specimen treatments or precise spectroscope calibrations are necessary. In the same regard, the tiny diamond grain size (5–10 nm) and the pronounced amount of sp2 carbon in the ultrananocrystalline diamond film represent major challenges in visible light excitation. In this work, we employ calibrated oxygen plasma reactive ion etching conditions to manifest the nanodiamond visible Raman signature from ultrananocrystalline diamond/amorphous carbon composite (UNCD/a‐C) films fabricated by coaxial arc plasma deposition. Upon plasma etching, the broad defect band in the visible Raman spectra converged toward the diamond characteristic Raman peak at 1332 cm−1. A detailed explanation of band components of the Raman spectra is extracted through peak fitting procedures. The results of Raman spectroscopy are further correlated with the electrical characteristics of the nitrogen‐doped UNCD/a‐C films due to the optimized oxygen plasma etching processes.

Effects of inorganic seed promoters on MoS2 few-layers grown via chemical vapor deposition

In the last years, transition metal dichalcogenides (TMDs), especially at the two-dimensional (2D) limit, gained a large interest due to their unique optical and electronic properties. Among them, MoS2 received great attention from the scientific community due to its versatility, workability, and applicability in a large number of fields such as electronics, optoelectronics and electrocatalysis. To open the possibility of 2D-MoS2 exploitation, its synthesis over large macroscopic areas using cost-effective methods is fundamental. In this study, we report a method for the synthesis of large-area (∼cm2) few-layers MoS2 via liquid precursor CVD (L-CVD), where the Mo precursor (i.e. ammonium heptamolybdate AHM) is provided via a solution that is spin-coated over the substrate. Given the capability of organic and inorganic molecules, such as alkaline salts, to enhance MoS2 growth, we investigated the action of different inorganic salts as seed promoters. In particular, by using visible Raman spectroscopy, we focused on the effect of Na(OH), KCl, KI, and Li(OH) on the thickness, morphology, uniformity and degree of coverage of the grown MoS2. We optimized the process tuning parameters such as the volume of spin-coated solution, the growth temperature, and the seed promoter concentration, to synthesise the lowest possible thickness which resulted to be 2 layers (2L) of the highest quality. We witnessed that the addition of an inorganic seed promoter in the solution improves the extension of the grown MoS2 promoting lateral growth front, and therefore the degree of coverage. From this study, we conclude that, amongst the investigated seed promoters, K-based salts proved to grant the growth of high-quality two-layer MoS2 with optimal and uniform coverage of the SiO2/Si substrate surface.

Direct synthesis of V2O5 from metals and study the adsorption properties with organic dyes

Scientists from all around the world are currently interested in vanadium oxide (V2O5) due to its applications in fuel cells, display components, poisonous gas sensors,... The ability to absorb dyes for environmental treatment is the most remarkable among them. In this paper, the authors have presented a direct synthesis of V2O5. The sample were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), UV–visible spectrophotometry (UV-Vis) and Raman spectroscopy. The authors also investigated the adsorption properties of prepared V2O5 with Methylene Blue (MB) - a colorant widely used in the dyeing industry that causes great harm to the environment and health. The results show that the material can absorb MB up to 90% in the absence of light after 3 minutes. Finally, a few other organic dyes were investigated in order to evaluate the materials' selectivity.

Synthesis, characterization and multi-spectroscopic DNA/HSA interaction studies of synthetic human Follicle-Stimulating Hormone Beta 33–53 peptide conjugated PEGylated graphene oxide nanoparticles

The objective of the current study was to synthesize, characterize and explore the interaction of PEGylated graphene oxide (pGO) and synthetic human Follicular stimulating hormone β 33–53 peptide conjugated PEGylated graphene oxide nanoparticles (pGO-FSH) with human serum albumin (HSA) and calf thymus DNA (CT-DNA). The pGO/ pGO-FSH nanoparticles were synthesized using a modified Hummer’s method, and the FSH peptide was conjugated through a maleimide crosslinking reaction. Synthesized nanoparticles were then characterized using techniques like FT-IR, UV–Visible absorbance, CD and Raman spectroscopy, and XRD and TGA. Morphological and particle size analysis was studied using SEM, TEM, DLS, and zeta potential measurements. The presence of FSH β 33–53 peptide was confirmed qualitatively and quantitatively using CD spectroscopy and Bradford’s assay. Binding studies of pGO/pGO-FSH nanoparticles with HSA and DNA were carried out using biophysical techniques. The complex formation between pGO/pGO-FSH nanoparticles and HSA was revealed by UV absorbance spectroscopy, and the observed fluorescence quenching was confirmed by steady-state fluorescence spectroscopy. Time-resolved fluorescence quenching studies have shown that dynamic quenching plays an important role in binding HSA with pGO/pGO-FSH nanoparticles. However, structurally no significant changes were observed in the native structure of HSA upon binding with pGO/pGO-FSH nanoparticles suggesting that the latter did not induce any structural distortions together, confirmed by DSC, FT-IR, and CD spectroscopy experimental findings. Binding constants and thermodynamic parameters calculated using double logarithmic and Van’t Hoff plots suggested weak and moderate binding affinity along with the involvement of hydrophobic and hydrogen bonding interactions between HSA and pGO/pGO-FSH nanoparticles, respectively. UV absorbance and fluorescence spectroscopy have revealed that pGO/pGO-FSH nanoparticles interact with DNA by binding at the minor groove region. These findings were further confirmed by DNA melting and viscosity studies. CD and FT-IR spectroscopy studies have shown no changes in the helical structure of B-form of DNA, thereby emphasizing the groove-binding nature of pGO/pGO-FSH nanoparticles. The obtained results are useful in further considering the potentiality of pGO-FSH nanoparticles as drug-delivery systems for in vivo applications, especially to target ovarian cancer.

Quantifying the levels and oxidative potential of submicron carbon black in plant leaves

Large amounts of the submicron carbon black are emitted in urban areas. Here, we developed a quantitative method using dual-wavelength ultraviolet–visible spectroscopy and Raman spectroscopy (respectively) for carbon black with amorphous structures and with ordering in a graphene sheet. Further, the dithiothreitol (DTT) assay and the ascorbic acid (AA) assay, were used to assess the oxidative potential (OP) of water extracts of leaf samples. Humic acids were adopted as a reference for the OP comparisons with carbon black in both assays. Using dual-wavelength ultraviolet–visible spectroscopy to determine carbon black with amorphous structures, our results achieved coefficients of determination greater than 0.99 in the linear range between 0.5 and 200 μg mL−1. Determination of carbon black with ordering in a graphene sheet using dual-wavelength Raman spectroscopy showed a linear in the range from 2 to 200 μg mL−1. The contents of carbon black with amorphous structures in tree leaves of passive bio-monitoring samplers were found to be in the range of 0.27–0.32 mg m−2, while the carbonaceous particles ordered with a graphene sheet were undetected. The OP of water extracts of leaves varied from 29 to 38 nmol min−1 mg−1 determined by DTT assay, and 16–30 nmol min−1 mg−1 by AA assay, respectively. The water-soluble ions enhanced the OP of submicron carbon black due to the presence of sp2-hybridized carbon atoms. These findings can help frame measures to mitigate health risks from nano-carbon black emitted from varied sources.

Synthesis and characterization of Pt/CuBi2O4. Application to photocatalytic H2 evolution under visible light

The platinized spinel Pt/CuBi2O4 (Pt/CBO) is successfully employed as catalyst for the H2 formation under visible irradiation for the first time. CBO is synthetized by sol gel route from nitrates precursors and calcined at 800 °C. The X-Ray Diffractometry (XRD), X-Ray photoelectron spectroscopy (XPS), UV–Visible diffuse reflectance, Raman spectroscopy and Scanning Electron Microscopy (SEM/EDX) were used for the physical characterization. CBO crystallizes in a tetragonal symmetry (Space Group: P4/ncc). The spinel is p-type semiconductor with a narrow optical gap (1.51 eV) with a transition directly permitted. The reduction of adsorbed H2O molecules to gaseous H2 at ∼ -0.5 VAg/Agcl is evidenced by cyclic voltammetry. The latter is determined from the capacitance measurement in KOH (0.1 M) solution where the spinel exhibits a chemical stability with an exchange current of 50 µA cm−2. The conduction band deriving from the Bi3+: 6p, (3.59 eV/Vacuum / −1.15 VAg/Agcl) is energetically localized above the H2O level (∼-0.7 VAg/Agcl), leading to the feasibility of CBO for the H2 release. The photo-electrochemical activity shows an optimal H2 formation of 270 µmol with a release rate of 8.1 µmol h−1 (mg catalyst)−1 under visible illumination (LED lamp: 3 × 13 W, 1.65 × 1019 photons s−1) in KOH electrolyte (0.1 M) using I− as reducing agent. Pt-islands deposited under UV light improves significantly the photocatalysis (61 %) due to its low overvoltage (∼70 mV) with a quantum yield of 0.91 %, compared to CBO alone.

Optical and acoustic phonons in turbostratic and cubic boron nitride thin films on diamond substrates

We report an investigation of the bulk optical, bulk acoustic, and surface acoustic phonons in thin films of turbostratic boron nitride (t-BN) and cubic boron nitride (c-BN) grown on B-doped polycrystalline and single-crystalline diamond (001) and (111) substrates. The characteristics of different types of phonons were studied using Raman and Brillouin-Mandelstam light scattering spectroscopies. The atomic structure of the films was determined using high-resolution transmission electron microscopy (HRTEM) and correlated with the Raman and Brillouin-Mandelstam spectroscopy data. The HRTEM analysis revealed that the cubic boron nitride thin films consisted of a mixture of c-BN and t-BN phases, with c-BN being the dominant phase. It was found that while visible Raman spectroscopy provided information for characterizing the t-BN phase, it faced challenges in differentiating the c-BN phase either due to the presence of high-density defects or the overlapping of the Raman features with those from the B-doped diamond substrates. In contrast, Brillouin-Mandelstam spectroscopy clearly distinguishes the bulk longitudinal and surface acoustic phonons of the c-BN thin films grown on diamond substrates. Additionally, the angle-dependent surface Brillouin-Mandelstam scattering data show the peaks associated with the Rayleigh surface acoustic waves, which have higher phase velocities in c-BN films on diamond (111) substrates. These findings provide valuable insights into the phonon characteristics of the c-BN and diamond interfaces and have important implications for the thermal management of electronic devices based on ultra-wide-band-gap materials.

Protonation of Asp116 and distortion of the all-trans retinal chromophore in Krokinobacter eikastus rhodopsin 2 causes a redshift in absorption maximum upon dehydration.

Water is usually indispensable for protein function. For ion-pumping rhodopsins, water molecules inside the proteins play an important role in ion transportation. In addition to amino acid residues, water molecules regulate the colors of retinal proteins. It was reported that a sodium-pumping rhodopsin, Krokinobacter eikastus rhodopsin 2 (KR2), showed a color change from red to purple upon dehydration under crystalline conditions. Here, we applied comprehensive visible and IR absorption spectroscopy and resonance Raman spectroscopy to KR2 in liposomes under hydration-controlled conditions. A large increase in the hydrogen-out-of-plane (HOOP) vibration at 947 (H-C11=C12-H Au mode) and moderate increases at 893 (C7-H and C10-H) and 808 (C14-H) cm-1 were observed under dehydrated conditions, which were assigned by using systematically deuterated retinal. Moreover, the Asn variant at Asp116, which functions as a counter ion for the protonated retinal Schiff base (PRSB), caused a large redshift in the absorption maximum and constitutive increase in the HOOP modes under hydrated and dehydrated conditions. The protonation of a counter ion at Asp116 clearly causes a redshift in the absorption maximum as the all-trans retinal chromophore twists upon dehydration. Namely, the results strongly suggested that water molecules are important for maintaining the hydrogen-bonding network at the PRSB and deprotonation state of Asp116 in KR2.