Visible Raman Spectroscopy Research Articles

Glassy carbon electrodes modified with gelatin functionalized reduced graphene oxide nanosheet for determination of gallic acid

A simple approach for the preparation of gelatin functionalized reduced graphene oxide nanosheet (Gel-RGONS) by chemical reduction of graphene oxide (GO) using gelatin as both reducing agent and stabilizing agent in an aqueous solution was developed. The morphology and structure of the Gel-RGONS were examined by X-ray diffraction, transmission electron microscopy, ultraviolet–visible spectroscopy and Raman spectroscopy. Gelatin acted as a functionalizing reagent to guarantee good dispersibility and stability of the r in distilled water. Moreover, a new electrochemical sensor was developed based on Gel-RGONS modified glassy carbon electrode (Gel-RGONS/GCE). Gel-r exhibits excellent electrocatalytic activity to gallic acid (GA) oxidation. The experimental conditions such as pH, adsorption time and scan rate were optimized for the determination of GA. Under optimum conditions, the sensor responded linearly to GA in the concentration of 1.0 × 10−6 to 1.1 × 10−4 M with detection limit of 4.7 × 10−7 M at 3σ using linear sweep voltammetry (LSV). The method has been successfully applied to the determination of GA in sample of black tea.

Ion track diameter in fullerene C70 thin film using Raman active vibrational modes of C70 molecule

The effect of energy deposition in fullerene C70 (∼150 nm) thin film deposited by resistive heating method on glass, quartz and silicon substrates was investigated. The samples were irradiated with 90 MeV Ni ion beam at the fluences ranging from 1 × 1012 to 3 × 1013 ions/cm2. The pristine and Ni ion irradiated samples were examined for morphological and optical changes by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), UV–visible absorption spectroscopy and Raman spectroscopy. After ion irradiation, bigger grains are shown on surface as revealed by SEM analysis indicating the agglomeration of the smaller particles into bigger particles at the surface. UV–visible absorption studies reflect that the direct band gap of the film decreases with increase in ion fluence. At higher fluence, fullerene C70 is transformed into amorphous carbon (a-C) which is confirmed by Raman spectroscopy. The damage cross-section (σ) and radius of the damaged cylindrical zone (r) are approximated to be ∼1.72 × 10−13 cm2 and ∼2.3 nm, respectively using Raman active vibrational modes.

Glutamine and Asparagine Side Chain Hyperconjugation-Induced Structurally Sensitive Vibrations.

We identified vibrational spectral marker bands that sensitively report on the side chain structures of glutamine (Gln) and asparagine (Asn). Density functional theory (DFT) calculations indicate that the Amide III(P) (AmIII(P)) vibrations of Gln and Asn depend cosinusoidally on their side chain OCCC dihedral angles (the χ3 and χ2 angles of Gln and Asn, respectively). We use UV resonance Raman (UVRR) and visible Raman spectroscopy to experimentally correlate the AmIII(P) Raman band frequency to the primary amide OCCC dihedral angle. The AmIII(P) structural sensitivity derives from the Gln (Asn) Cβ-Cγ (Cα-Cβ) stretching component of the vibration. The Cβ-Cγ (Cα-Cβ) bond length inversely correlates with the AmIII(P) band frequency. As the Cβ-Cγ (Cα-Cβ) bond length decreases, its stretching force constant increases, which results in an upshift in the AmIII(P) frequency. The Cβ-Cγ (Cα-Cβ) bond length dependence on the χ3 (χ2) dihedral angle results from hyperconjugation between the Cδ═Oϵ (Cγ═Oδ) π* and Cβ-Cγ (Cα-Cβ) σ orbitals. Using a Protein Data Bank library, we show that the χ3 and χ2 dihedral angles of Gln and Asn depend on the peptide backbone Ramachandran angles. We demonstrate that the inhomogeneously broadened AmIII(P) band line shapes can be used to calculate the χ3 and χ2 angle distributions of peptides. The spectral correlations determined in this study enable important new insights into protein structure in solution, and in Gln- and Asn-rich amyloid-like fibrils and prions.

Enhancement of adhesion and corrosion resistance of diamond-like carbon thin films on Ti–6Al–4V alloy by nitrogen doping and incorporation of nanodiamond particles

Abstract Pure diamond-like-carbon (DLC) and nitrogenated diamond-like-carbon (N-DLC) were deposited by Ion Beam Deposition using a low energy End-Hall Source on titanium and silicon substrates. The beam energy used during the deposition had a mean value of 65 eV. The structure and composition of the films were investigated by visible Raman Spectroscopy and X-ray Absorption Spectroscopy (XAS). Hardness and Young's modulus of the coatings were measured by nanoindentation. Adhesion of the coatings to the substrates was measured by Rockwell C indentation tests. To investigate the corrosion property of the coatings, Tafel polarization tests were performed from − 1.5 V to 1.5 V in 0.89% NaCl solution using the Standard Calomel Electrode as a reference. In our studies, DLC deposited directly on bare titanium alloy (Ti–6Al–4 V) shows poor adhesion and premature delamination. Pre-deposited nanodiamonds on titanium substrate greatly enhance the adhesion. The films produced on nano-diamond pretreated substrates are dense, smooth, and uniform, and DLC films show an average hardness value of 11 GPa, slightly higher than N-DLC (with an average hardness of 9 GPa). Despite its relatively lower hardness, nitrogen doping increases both adhesion and corrosion resistance of DLC coating.

Charge separation promoted by phase junctions in photocatalysts

Since the 1980s, photocatalysis research has expanded at an unexpected rate. Fabrication of phase junctions has proved to be an effective method to enhance photocatalytic performance. As a model photocatalyst, titanium dioxide (TiO2) has been extensively studied. This feature article mainly reviews the study on TiO2 surface phase junctions, including the characterization of the surface phases of TiO2, the use of anatase: rutile TiO2 phase junctions in photocatalytic hydrogen production, and the current understanding of how TiO2 phase junctions work in photocatalysis. The surface structure of TiO2 can be well characterized by ultraviolet (UV) Raman spectroscopy, unlike X-ray diffraction and visible Raman spectroscopy. Based on these results, the mechanism of phase transformation processes of TiO2 was clearly identified. The infrared (IR) spectra of probe molecules CO and CO2 on TiO2 further characterized the surface structure of TiO2, strongly supporting the UV Raman results. Furthermore, the typical visible emission of anatase and near-infrared emission of the rutile phase of TiO2 make photoluminescence (PL) a suitable technique to characterize the surface phase structure of TiO2. PL can also provide information about the carrier dynamics of TiO2 in photocatalysis. Because of the surface phase junction formed between anatase and rutile, the mixed-phase structure of TiO2 exhibits a superior H2 production activity to those of pure anatase or rutile phase. The activity of Degussa P25 TiO2 can be further increased by three to five times by tuning the phase structure through thermal treatment. Moreover, the phase transformation of TiO2 from anatase to rutile can be controlled by surface modification with Na2SO4, resulting in catalysts with activity six times higher than that of P25. High-resolution transmission electron microscopy provided a clear phase-junction image of TiO2, which showed atomic contact at the interface of the phase junction. The mechanism of phase junctions improving photocatalytic performance was investigated by time-resolved spectroscopic techniques. The charge transfer process across the anatase: rutile phase junction was confirmed by the results of time-resolved IR measurements, and electron transfer from anatase to rutile phases is proposed to occur in mixed-phase TiO2. These studies on the phase junctions of TiO2 improve our understanding of photocatalysis and may inspire new ideas for the design of promising photocatalytic systems.

Deep ultra violet and visible Raman spectroscopy studies of ion implanted 6H-SiC: Recrytallisation behaviour and thermal decomposition/thermal etching of the near surface region

The recystallisation behaviour and thermal decomposition of the near surface amorphised region of 6H-SiC have been investigated by Raman spectroscopy. 360keV ions of iodine and silver were implanted at room temperature into wafers of 6H-SiC resulting in the amorphisation of the near surface region. Vacuum annealing of the samples was performed at 1200°C for 5h and then sequentially from 1200 to 1600°C in steps of 100°C for 30h at each annealing temperature. Raman spectroscopy was performed using two laser wavelength excitation regimes, the 514nm laser (visible region) and the 244nm laser (deep ultraviolet region, DUV). Measurements in the visible region for samples annealed at 1200°C for 5h showed that the characteristic 6H-SiC peaks, namely, the Transverse Optical (TO) and Longitudinal Optical (LO) are similar to the virgin samples, albeit with lower intensity due to some retained defects upon recystallisation of the SiC surface region. The similarities between the virgin spectra and the annealed sample were due to the deep penetration of the 514nm laser into 6H-SiC resulting in the signal from the bulk undamaged 6H-SiC contributing to the overall spectra. However, DUV laser excitation, which only probes the near surface region, shows that after annealing the peaks are broader and asymmetrical compared to the virgin samples. DUV Raman spectra of samples annealed at 1600°C indicate that SiC has completely decomposed and the top surface layer is now covered by a carbon layer. However the deeper penetrating laser in the visible region showed that the extent of decomposition at 1600°C was greater for the silver implanted samples than for the iodine implanted samples.

Graphene oxide wrapped Fe3O4@Au nanohybrid as SERS substrate for aromatic dye detection

An active surface-enhanced Raman scattering (SERS) substrate composed of graphene oxide (GO) wrapped gold nanoparticles (AuNPs) decorated-magnetic sphere Fe3O4 (GO wrapped Fe3O4@Au hybrid) was prepared and used for aromatic dye detection. The hybrid was characterized by SEM, EDX, XRD, UV–visible spectroscopy and Raman spectroscopy. This hybrid showed high activity for SERS detection of aromatic dye due to the synergistic interaction among GO nanosheet, AuNPs and Fe3O4 sphere. The dosages of AuNPs and GO were optimized to achieve a high sensitivity. The unique GO wrapped Fe3O4@Au hybrid has several advantages (such as high adsorption to target dye molecules, low noise response and high SERS enhancement ability) as SERS substrate over previously reported Fe3O4 and AuNPs co-decorated GO sheet. Finally, the hybrid was successfully used for SERS detection of aromatic dye pollutant malachite green (MG) and nile blue A (NBA) even at concentration down to 1nM and 0.1nM, respectively. Potential of this substrate for multiplex detection of dye mixture (MG and NBA), and practical detection of MG in real sample were also evaluated. Our results suggested that the hybrid of GO wrapped Fe3O4@Au can be used as an efficient SERS platform for aromatic dye detection.

Effect of cerium doping on the textural, structural and optical properties of zinc oxide: Role of cerium and hydrogen peroxide to enhance the photocatalytic degradation of endocrine disrupting compounds

ZnO and Ce-doped ZnO photocatalysts with different Ce molar content (0.5–1–2–4%) have been successfully synthesized by a hydrothermal method. The synthesized samples were characterized by X-ray diffraction (XRD), Nitrogen physisorption at 77K; Fourier transformed infrared spectroscopy (FTIR), UV–visible spectroscopy, Photoluminescence spectra (PL), and Raman spectroscopy. The XRD demonstrates that the products have the same crystal structure, and loading of Ce4+ ions does not change the structure of ZnO. BET surface area analysis revealed that all the samples can be described as type IV. The FTIR proves the formation of ZnO. It was also observed that the cerium doping increased the visible light absorption ability of Ce-doped ZnO and a red shift appeared for Ce-doped ZnO when compared to pure ZnO. The photocatalytic activity of the synthesized catalysts was evaluated by the degradation and the mineralization of bisphenol A (BPA) and nonylphenol (NP) pollutants in aqueous solutions in the presence of hydrogen peroxide (H2O2) under UV irradiation. The small crystallite size, the high specific surface area and the low band gap by allowing to the high charge separation efficiency were attributed to the increase of the catalytic activity.

Synthesis and Characterization of YVO4-Based Phosphor Doped with Eu3+ Ions for Display Devices

YVO4:Eu nanophosphor has been synthesized by the sol–gel method. Samples were characterized by x-ray diffraction (XRD), energy-dispersive x-ray spectroscopy, Fourier-transform infrared spectroscopy, ultraviolet–visible (UV–Vis) spectroscopy, photoluminescence, and Raman spectroscopy. The XRD profile confirms the tetragonal phase of the Eu3+-doped YVO4 nanophosphor. The efficiency of the prepared phosphor was analyzed by means of its emission spectral profile. We also observed rich red emission from the prepared phosphor on excitation by an ultraviolet source. The calculated Commission International de l’Eclairage coordinates reveal excellent color purity efficiency. Such luminescent powder is useful as red phosphor in display device applications.

Enhanced activity and stability of binuclear iron (III) phthalocyanine on graphene nanosheets for electrocatalytic oxygen reduction in acid

Binuclear iron (III) phthalocyanine (bi-FePc) and iron (III) phthalocyanine (FePc) are synthesized in situ on graphene nanosheets (GNS) by a microwave-assisted method. TEM, ultraviolet–visible spectroscopy and Raman spectroscopy confirm that bi-FePc is supported on GNS through π–π interactions. The catalytic activity of the bi-FePc/GNS and FePc/GNS composites in the oxygen reduction reaction (ORR) is investigated by CV and RDE measurements. The bi-FePc/GNS composite shows a more positive onset potential (0.12 V vs. Hg/Hg2SO4) for the ORR than FePc/GNS (−0.02 V vs. Hg/Hg2SO4), and a four-electron mechanism similar to commercial Pt/C (0.22 V vs. Hg/Hg2SO4). Moreover, bi-FePc/GNS exhibits good stability with 100% retention after 36,000 s, while Pt/C has a retention of only 50% after the same period. Additionally, bi-FePc/GNS shows higher tolerance toward methanol than the Pt/C catalyst. XPS and X-ray absorption fine structure spectroscopy demonstrate that compared with FePc/GNS, bi-FePc/GNS possesses a higher concentration of Fe3+ and smaller skeleton radius of the phthalocyanine ring, which has a square-planar structure that evidently favors the ORR. Thus, bi-FePc/GNS is a promising candidate as a cathode catalyst in direct methanol fuel cells.

Doping inhomogeneity and staging of ultra-thin graphite intercalation compound flakes probed by visible and near-infrared Raman spectroscopy**Project supported by the National Natural Science Foundation of China (Grant Nos. 11225421, 11474277, and 11434010).

When ultra-thin graphite intercalation compounds (GICs) are deposited on the SiO2/Si substrate, it is found that their colors are dependent on the thickness of GIC flakes. The sample colors of ultrathin GIC flakes can no longer provide qualitative information on the stage index. Here, multi-wavelength Raman spectroscopy is thus applied to study the doping inhomogeneity and staging of ultra-thin GICs by FeCl3 intercalation. The G band intensity of stage-1 GIC flakes is strongly enhanced by 532-nm laser excitation, while that of stage-2 and stage-3 flakes exhibits strong intensity enhancement for 785-nm laser excitation. The near-infrared lasers are suggested to probe the doping inhomogeneity and staging of ultra-thin GIC flakes.

Probing the influence of the center atom coordination structure in iron phthalocyanine multi-walled carbon nanotube-based oxygen reduction reaction catalysts by X-ray absorption fine structure spectroscopy

Three different pentacoordinate iron phthalocyanine (FePc) electrocatalysts with an axial ligand (pyridyl group, Py) anchored to multi-walled carbon nanotubes (MWCNTs) are prepared by a microwave method as high performance composite electrocatalysts (FePc–Py/MWCNTs) for the oxygen reduction reaction (ORR). For comparison, tetracoordinate FePc electrocatalysts without an axial ligand anchored to MWCNTs (FePc/MWCNTs) are assembled in the same way. Ultraviolet–visible spectrophotometry (UV–Vis), Raman spectroscopy (RS), and high-resolution transmission electron microscopy (HRTEM) are used to characterize the obtained electrocatalysts. The electrocatalytic activity of the samples is measured by linear sweep voltammetry (LSV), and the onset potential of all of the FePc–Py/MWCNTs electrocatalysts is found to be more positive than that of their FePc/MWCNTs counterparts. X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS) spectroscopy are employed to elucidate the relationship between molecular structure and electrocatalytic activity. XPS indicates that higher concentrations of Fe3+ and pyridine-type nitrogen play critical roles in determining the electrocatalytic ORR activity of the samples. XAFS spectroscopy reveals that the FePc–Py/MWCNTs electrocatalysts have a coordination geometry around Fe that is closer to the square pyramidal structure, a higher concentration of Fe3+, and a smaller phthalocyanine ring radius compared with those of FePc/MWCNTs.

Photocatalytic activity of ZnO doped with Ag on the degradation of endocrine disrupting under UV irradiation and the investigation of its antibacterial activity

Ag-doped ZnO photocatalysts with different Ag molar content (0.0, 0.5, 1.0, 2.0 and 4.0%) were prepared via hydrothermal method. The X-ray diffraction (XRD), Nitrogen physisorption at 77K, Fourier transformed infrared spectroscopy (FTIR), UV–-Visible spectroscopy, Photoluminescence spectra (PL) and Raman spectroscopy were used to characterize the structural, textural and optical properties of the samples. The results showed that Ag-doping does not change the average crystallite size with the Ag low content (≤1.0%) but slightly decreases with Ag high content (>1.0%). The specific surface area (SBET) increases with the increase of the Ag content. The band gap values of ZnO are decreased with the increase of the Ag doping level. The results of the photocatalytic degradation of bisphenol A (BPA) and nonylphenol (NP) in aqueous solutions under UV irradiation and in the presence of hydrogen peroxide (H2O2) showed that silver ions doping greatly improved the photocatalytic efficiency of ZnO. The TOC conversion BPA and NP are 72.1% and 81.08% respectively obtained using 1% Ag-doped ZnO. The enhancement of photocatalytic activity is ascribed to the fact that the modification of ZnO with an appropriate amount of Ag can increase the separation efficiency of the photogenerated electrons-holes in ZnO. The antibacterial activity of the catalysts which uses Escherichia coli as a model for Gram-negative bacteria confirmed that Ag-doped ZnO possessed more antibacterial activity than the pure ZnO.

Effects of swift heavy ion irradiation on structural, optical and photocatalytic properties of ZnO-CuO nanocomposites prepared by carbothermal evaporation method.

ZnO–CuO nanocomposite thin films were prepared by carbothermal evaporation of ZnO and Cu, combined with annealing. The effects of 90 MeV Ni7+ ion irradiation on the structural and optical properties of ZnO–CuO nanocomposites were studied by using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), UV–visible absorption spectroscopy and Raman spectroscopy. XRD studies showed the presence of ZnO and CuO nanostructures in the nanocomposites. FESEM images revealed the presence of nanosheets and nanorods in the nanocomposites. The photocatalytic activity of ZnO–CuO nanocomposites was evaluated on the basis of degradation of methylene blue (MB) and methyl orange (MO) dyes under sun light irradiation and it was observed that swift heavy ion irradiation results in significant enhancement in the photocatalytic efficiency of ZnO–CuO nanocomposites towards degradation of MB and MO dyes. The possible mechanism for the enhanced photocatalytic activity of ZnO–CuO nanocomposites is proposed. We attribute the observed enhanced photocatalytic activity of ZnO–CuO nanocomposites to the combined effects of improved sun light utilization and suppression of the recombination of photogenerated charge carriers in ZnO–CuO nanocomposites.

ChemInform Abstract: UV Raman Spectroscopic Characterization of Catalysts and Catalytic Active Sites

AbstractReview: 131 refs.

Conversion of polypropylene to two‐dimensional graphene, one‐dimensional carbon nano tubes and zero‐dimensional C‐dots, all exhibiting typical sp 2 ‐hexagonal carbon rings

For the first time single precursor, polypropylene (PP) has been used to synthesise two-dimensional (2D) graphene, 1D carbon nanotubes (CNT) and 0D carbon dots (C-dots). The carbon chains of PP polymer contain tertiary carbon atoms that have considerably lower resistance against degradation and cracking which is easy at low activation energy. Thermal cracking of PP was used for the synthesis of 2D graphene, 1D CNT and 0D C-dots materials. Although the basic structure of all three materials is same, that is, having hexagonal lattice of carbon, they show different properties. Morphology of these carbon materials was characterised by scanning electron microscopy, transmission electron microscopy and properties along with sp2 and sp3 content were analysed by ultra-violet–visible spectroscopy, X-ray diffraction (XRD) and Raman spectroscopy. It was observed with the help of Raman and XRD that as the dimensionalities of hexagonal carbon decreases there is an increase in defects, for example, graphene synthesised from PP showed negligible defects, CNT had considerable disorderness, whereas 0D C-dots showed maximum disorderness. This could be the reason for scientists turning from CNT to graphene as future material for its application in electrical and electronic fields, nevertheless, only time will tell whether graphene can be the answer as currently being thought of.

Nitric oxide activation by caa3 oxidoreductase from Thermus thermophilus.

Visible and UV-resonance Raman spectroscopy was employed to investigate the reaction of NO with cytochrome caa3 from Thermus thermophilus. We show the formation of the hyponitrite (HO-N=N-O)(-) bound to the heme a3 species (νN=N = 1330 cm(-1)) forming a high spin complex in the oxidized heme a3 Fe/CuB binuclear center of caa3-oxidoreductase. In the absence of heme a3 Fe(2+)-NO formation, the electron required for the formation of the N=N bond originates from the autoreduction of CuB by NO, producing nitrite. With the identification of the hyponitrite intermediate the hypothesis of a common phylogeny of aerobic respiration and bacterial denitrification is fully supported and the mechanism for the 2e(-)/2H(+) reduction of NO to N2O can be described with more certainty.

The structure and optical properties of regio-regular poly(3-hexylthiophene) and carboxylic multi-walled carbon nanotubes composite films

The introduction of small amounts of carboxylic multi-walled carbon nanotubes into regio-regular poly(3-hexylthiophene) (P3HT) can vary the structure and optical properties of the polymer. The microstructure of the composite film was analysed by various techniques including x-ray diffraction, ultraviolet–visible optical absorption, Raman spectroscopy, and Fourier-transform infrared spectroscopy. It is shown that the presence of carbon nanotubes can improve the crystallinity and increase the conjugation length of P3HT in the films. Furthermore, an obvious photoluminescence quenching is observed in the P3HT/CNTs composite films, suggesting the possibility of photoinduced electron transfer between P3HT and carbon nanotubes due to the π–π interaction of these two components. These results are important for applications in bulk heterojunction solar cells and organic photo-detectors.

UV Raman Spectroscopic Characterization of Catalysts and Catalytic Active Sites

UV Raman spectroscopy has been demonstrated to be a powerful technique in catalysis because it can avoid the fluorescence interference occurring in visible Raman spectroscopy and concurrently enhance the Raman scattering intensity owing to the short wavelength of the excitation laser and resonance Raman effect. This article briefly reviews the recent advances in the study on heterogeneous catalysis by UV Raman spectroscopy, including the identification of isolated transition metal ions in molecular sieves, in situ study of zeolite assembly mechanisms and catalytic reaction mechanisms, and the monitoring of the surface phase transformation of metal oxide photocatalysts. UV (resonance) Raman spectroscopy, with the power of resonance enhancement for Raman signal and the advantage of high sensitivity for surface structure, coupling with in situ methodology, can provide the information about the active sites/phase and their assembling mechanisms, which are helpful for the understanding of heterogeneous catalysis and the rational design of highly active and selective catalysts.

Wafer Scale Synthesis and High Resolution Structural Characterization of Atomically Thin MoS2 Layers

Synthesis of atomically thin MoS2 layers and its derivatives with large‐area uniformity is an essential step to exploit the advanced properties of MoS2 for their possible applications in electronic and optoelectronic devices. In this work, a facile method is reported for the continuous synthesis of atomically thin MoS2 layers at wafer scale through thermolysis of a spin coated‐ammonium tetrathiomolybdate film. The thickness and surface morphology of the sheets are characterized by atomic force microscopy. The optical properties are studied by UV–Visible absorption, Raman and photoluminescence spectroscopies. The compositional analysis of the layers is done by X‐ray photo­emission spectroscopy. The atomic structure and morphology of the grains in the polycrystalline MoS2 atomic layers are examined by high‐angle annular dark‐field scanning transmission electron microscopy. The electron mobilities of the sheets are evaluated using back‐gate field‐effect transistor configuration. The results indicate that this facile method is a promising approach to synthesize MoS2 thin films at the wafer scale and can also be applied to synthesis of WS2 and hybrid MoS2‐WS2 thin layers.