Raman Shift Spectroscopy Research Articles

Magnetically Separable Mixed-Phase α/γ-Fe2O3 Catalyst for Photo-Fenton-like Oxidation of Rhodamine B

Iron oxides are widely used as catalysts for photo-Fenton-like processes for dye oxidation. In this study, we report on the synthesis of an α/γ-Fe2O3 mixed-phase catalyst with magnetic properties for efficient separation. The catalyst was synthesized using glycine–nitrate precursors. The synthesized α/γ-Fe2O3 samples were characterized using scanning electron microscopy, X-ray diffraction spectroscopy (XRD), Raman shift spectroscopy, X-ray photoelectron spectroscopy (XPS), and vibrating sample magnetometer (VSM). The diffraction peaks were indexed with two phases, α-Fe2O3 as the main phase (79.6 wt.%) and γ-Fe2O3 as the secondary phase (20.4 wt.%), determined using the Rietveld refinement method. The presence of Fe2+ was attributed to oxygen vacancies. The mixed-phase α/γ-Fe2O3 catalyst exhibited remarkable photo-Fenton-like degradation performance for Rhodamine B (RhB) in neutral pH. The effects of operating parameters, including H2O2 concentration, catalyst concentration, and RhB concentration, on the degradation efficiency were investigated. The removal rates of color were 99.2% after 12 min at optimal conditions of photo-Fenton-like oxidation of RhB. The sample exhibited a high saturation magnetization of 28.6 emu/g. Additionally, the α/γ-Fe2O3 mixed-phase catalyst showed long-term stability during recycle experiments, with only a 5% decrease in activity.

Photoluminescence from carbon structures grown by inductively coupled plasma chemical vapor deposition

Carbon micro/nanostructures were grown by inductively coupled plasma chemical vapor deposition (ICP-CVD) at low pressure into a tubular reactor under pure methane and using substrates of SAE 304 stainless steel. The samples show diverse structures and properties depending on the position inside the quartz tube, due to the different temperatures and environmental conditions. In this experiment, the authors have obtained structures with different scales (micro and nano), depending on the growing temperature and the position inside the reactor. Carbon microstructures were obtained on the extreme parts of the tubular reactor at low temperatures. In contrast, carbon nanostructures appeared after the plasma resonator at temperatures higher than 700 °C. X-ray photoelectron spectroscopy and Fourier transform infrared spectrometry evidenced functional groups with hydrogen and oxygen atoms except for nanostructures at 750 °C showing vertical carbon nanowalls with more than ten crystalline layers, such as it was verified by field emission SEM, TEM, and Raman shift spectroscopy. An intense photoluminescence in the visible range was revealed from the samples excited by laser (325 nm), except the nanowall samples, which exhibited a poor photoluminescence. The purpose of this work is to study the photoluminescence of carbon structures produced by ICP-CVD and to evidence the role of hydrogen and oxygen functional groups with hydrogen and oxygen atoms. The understanding of these processes provides additional criteria for designing new materials based on carbon, which is environmentally friendly, for application to luminescent devices.

Modification of magnetron sputter deposition of nc-WC/a-C(:H) coatings with an additional RF discharge

It is known that the degree of ionization of the coating precursors is one of the key factors in a control of the structure and properties of sputter deposited carbon-based coatings. Numerous modifications of a conventional magnetron sputtering technique were elaborated in order to increase the degree of plasma ionization. The most effective of them were based on an application of an additional source of plasma excitation, independent of magnetron discharge. This paper presents results of the investigations of nc-WC/a-C(:H) coatings, deposited by means of magnetron sputtering of graphite and tungsten targets, enhanced by an additional radio-frequency discharge of a maximum power of 150 W, limited to a volume directly adjacent to the specimens. In order to assess thickness, surface morphology and chemical composition of the coatings, scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) techniques were used, while Raman Shift Spectroscopy (RSS) together with XPS was applied to determine the types of bonds between carbon atoms. Tribological properties of the coatings were investigated using a ‘pin-on-disc’ method, with the friction couple comprising bearing steel counterbody. It has been found that additional RF discharge has a significant effect on the type of bonds of carbon atoms in the coating. In the case of non‑hydrogenated nc-WC/a-C coatings, an introduction of additional RF discharge caused an increase of a contribution of sp3 hybridized carbon atoms by 32%, as well as an increase of friction coefficient. The highest share of sp3 hybridization was obtained in the case of hydrogenated nc-WC/a-C:H coatings deposited in Ar + CH4 atmosphere with an enhancement of additional RF discharge maintained at 150 W of power. These conditions brought about a decreased friction coefficient (to a value of 0.05) and a decreased wear rate (to an approximate value of 10−17 m3 N−1 m−1).

The synthesis of C, N-codoped TiO2 hollow spheres by a dual-frequency atmospheric pressure cold plasma jet

Titanium dioxide has been widely applied in many fields, but the photon utilization efficiency of it was low because of the wide band gap, amounting to 3.2 eV. Many studies have shown that doping TiO2 with nonmetals (N, S, C and so on) could narrow the TiO2 band gap. In the paper, the titanium tetraisopropoxide (TTIP) used as the precursor in the argon/oxygen which was driven by dual-frequency (100 kHz/100 MHz) atmospheric pressure plasma jet via tuning the nitrogen flow ratio was investigated. The structures of the synthetic C, N-codoped TiO2 hollow sphere were investigated by X-ray diffraction and Raman shift spectroscopy. The results indicated that the synthetic crystals consist of anatase and rutile. The scanning electron microscopy and transmission electron microscopy demonstrated that the synthetic crystals were hollow spheres. The elements of the C, N-codoped TiO2 were characterized by energy-disperse spectroscopy. The patterns reveal that carbon and nitrogen are incorporated in the deposited TiO2 crystal. The C element increased but N element decreased with the increase in nitrogen gas flow. The chemical bond and composition of TiO2 were characterized by X-ray photoelectron spectroscopy, which indicates that C is derived from the dissociation of tetraisopropoxide and N element is originated from the electron ionization of N2 molecules. The optical absorption of these samples was detected by UV–Vis absorbance spectra. The results indicated that the band gap of S1 and S2 is 2.91 and 3.10 eV, respectively. Excited species of the plasma discharge were diagnosed by optical emission spectroscopy.

Properties of graphene/Au nanocomposite prepared by laser irradiation of the mixture of individual colloids

Production and characterization of Au/graphene nanocomposite using laser ablation method are investigated experimentally. First, graphene nanosheets and Au nanoparticles were synthesized by irradiating their bulk in deionized water with the fundamental harmonic of Nd:YAG-pulsed laser separately. Then, composition of four different volumetric ratios of the Au/graphene nanostructures was irradiated by the second harmonic wavelength of pulsed Nd:YAG laser to form Au/graphene nanocomposite. Productions were studied employing UV–Vis–NIR absorption spectroscopy, X-ray diffraction, FTIR spectroscopy, photoluminescence spectroscopy, Raman shift spectroscopy, and TEM images. Results show that Au nanoparticles were melted by absorption of second harmonic photons of Nd:YAG laser and composed by graphene nanosheets, but the values of sp2 domains were decreased noticeably in the graphene structure after green laser irradiation.

Edge decoration of MoS2 monolayer with ferromagnetic CoFe nanoparticles

Molybdenum disulfide (MoS2) monolayers decorated with ferromagnetic CoFe nanoparticles on the edges were synthesized through a one-step pyrolysis of precursor molecules in an argon atmosphere. The CoFe precursor was spin coated on the MoS2 monolayer grown on Si/SiO2 substrates. Highly-ordered, body-centered cubic (bcc) CoFe nanoparticles were revealed under optimized pyrolysis conditions, possessing coercivity up to 1000 Oe at room temperature. The CoFe nanoparticles were well-positioned along the edge sites of MoS2 monolayers. The vibration modes of Mo and S atoms were confined after the decoration by CoFe nanoparticles, as characterized by Raman shift spectroscopy. The sizes of nanoparticles growing on the MoS2 monolayers are more uniform than those from other preparation routines. Finally, the optimized pyrolysis temperature and conditions provide recipes for decorating related noble metal catalytic materials.

Facile preparation and adsorption performance of graphene oxide-manganese oxide composite for uranium

To overcome the limits of low adsorption capacity and the separation difficulty of solid from liquid phase for graphene oxide (GO), a novel nanocomposite graphene oxide-manganese oxide (GOMO) was facilely fabricated under ultrasonic radiation. The structures and micro-morphology of the products were characterized by fourier transform infrared (FT-IR) spectroscopy, raman shift spectroscopy, X-ray diffraction (XRD) pattern and scanning electron microscopy (SEM). The effect of solution pH, adsorbent dose, contact time, initial uranium concentration, ionic strength and temperature on uranium removal efficiency was studied by batch adsorption experiments. The product GOMO was used to examine the feasibility of the removal of high salt content in uranium-containing wastewater. The adsorption results were fitted using the Langmuir and Freundlich isotherm models. The kinetic parameters in the adsorption process were measured and fitted. Five adsorption/desorption cycles were performed using 3 M HNO3 as the regenerant in order to evaluate the reuse of GOMO.

A new method for deposition nitrogen-doped TiO2 nanofibers with mixed phases of anatase and rutile

A new method for deposition nitrogen-doped TiO2 nanofibers films was proposed. By using atmospheric pressure plasma jet generated by dual-frequency power sources, the morphologies of these TiO2 films were investigated by scanning electron microscopy. The structures of these films were characterized by X-ray diffraction and Raman Shift Spectroscopy. The elemental composition of these films [Colour figure can be viewed at wileyonlinelibrary.com] were characterized by means of X-ray photoelectron spectroscopy. The optical absorption of these films were studied by UV-vis absorbance spectra. These results indicated that the nitrogen-doped nanofibers TiO2 films have mixed phases of anatase and rutile. They also display narrow band gap. The I-V characteristics curves exhibited good conductivity ability. Optical emission spectroscopy (OES) was measured to analyze the active group.

Synthesis of Mixed-Phase TiO2 Nanopowders Using Atmospheric Pressure Plasma Jet Driven by Dual-Frequency Power Sources

Mixed-phase TiO2 nanopowders with different ratios of anatase and rutile have been successfully synthesized using atmospheric pressure plasma jet driven by dual-frequency power sources. The crystal structures of the TiO2 nanopowders were characterized by X-ray diffraction, SAED, HRTEM, and Raman shift spectroscopy. These results indicated that samples possessed anatase and rutile structure, in addition, the crystallinity of the TiO2 nanopowders increased and the chlorine contamination decreased with discharge RF power increasing. The photocatalytic activity of the TiO2 nanopowders was evaluated by decomposition methylene blue solution. The TiO2 nanopowders which were produced at the discharge RF power of 110 W had the highest photocatalytic activity. Optical emission spectroscopy (OES) was used to detect various excited species in the plasma jet. The results indicate that the various RF power significantly changes the intensities of emission lines (Ar, Ar+, Ti, Ti+, Ti2+, Ti3+ and O), which results in the TiO2 nanopowders a mixture of anatase and rutile phases. The nonequilibrium chemical composition could be formed in one step without anneal. It may have potential applications for synthesizing nanosized particles of high crystallinity by reactive nonthermal plasma processing.

Hydrogen content influence on tribological properties of nc-WC/a-C:H coatings

Hydrogen content has high influence on low-friction properties of an amorphous carbon coating a-C with or without transition metal additions. In the paper the nanocrystalline nc-WC/a-C:H coatings deposited by means of magnetron sputtering were investigated. Hydrogen content up to 37% was obtained by the use of different flows of pure hydrogen or methane mixed with pure argon. The coatings were investigated by means of SEM, EDS, and SAED HR TEM in order to obtain thickness, sufrace morphology, chemical composition as well as nanostructure. Moreover, these were investigated: type of bonds between carbon atoms by means of Raman Shift Spectroscopy and hydrogen content by means of SIMS and inert gas fusion crucible method. Tribological properties were elaborated by means of ‘pin-on-disc’ method. It was stated that coefficient of friction, microstructure and type of bonds between carbon atoms are highly dependent from the hydrogen content. It is the main parameter for achieving of low friction coefficient (below 0.1) as well as very low wear rate (in a range of 10−17m3·N−1·m−1. Obtained results confirmed that proposed nc-WC/a-C:H coatings can be used for improving tribological properties of hard steels and hardened titanium alloys.

Tuning The Crystallographic Structure And Morphology Of Nanocrystalline CaB6 Films Deposited By DC Magnetron Sputtering

Abstract Through changing the argon pressure, CaB6 films with different crystallographic orientation and morphology on glass substrates were prepared by direct current (DC) magnetron sputtering method. The film textures, crystallite sizes, composition and morphology were investigated by a spectrum of characterizing techniques in terms of X-ray diffraction (XRD), field emission scanning electron microscopy with energy dispersive spectrometer (FESEM-EDS), atomic force microscopy (AFM), Raman shift spectroscopy. The influence of argon pressure on microstructure was studied. The average grain size increased with the argon pressure increasing from 0.8 Pa to 1.5 Pa. Meanwhile, the dominant crystal face changed from (110) to (100). Then the grain size decreased when the argon pressure increased to 2.0 Pa. The surface morphology evolved from typical cauliflower-like nanocrystalline clusters to faceted rectangular pyramids. It was found that considerable amount of argon atoms were trapped in the films. The formation process of CaB6 films was also analyzed in this paper.

Nb-doped TiO2 nanoparticles for organic dye-sensitized solar cells

Nb-doped anatase TiO2 nanoparticles were prepared by the sol–gel process followed by a hydrothermal treatment and successfully used as the photoanodes in organic dye-sensitized solar cells (DSSCs). Phase identification of the TiO2 samples was confirmed by X-ray diffraction and Raman shift spectroscopy. The electronic structure and Nb doping in the TiO2 lattice were confirmed by X-ray photoelectron spectroscopy and energy-disperse X-ray spectroscopy, respectively. Also, the conduction band edge (CB) shift due to the Nb-doping in the TiO2 lattice by UV-vis diffuse reflectance spectroscopy and the effect of Nb doping on the charge transporting and recombination behaviors of the DSSCs by electrochemical impedance spectroscopy (EIS) analysis were investigated. The Nb-doped TiO2 exhibited a positive shift of the conduction band edge (CB) compared to the undoped TiO2. Consequently, the increased driving force for electron injection, that is, the difference between the CB of TiO2 and the lowest unoccupied molecular orbital (LUMO) energy level of the dye, could correspondingly contribute to the enhancement of the electron injection efficiency, but the Voc has the opposite behavior. The Voc drop in the DSSCs based on the Nb-doped TiO2 could be prevented using a multi-functional HC-A as a coadsorbent instead of DCA. As expected, a PCE of 7.41% was obtained for the NKX2677/HC-A-sensitized DSSC based on the 2.5 mol% Nb-doped TiO2, which was an improvement of 11% relative to that of the DSSC based on the undoped TiO2.

Spectral optical properties of Cu_2ZnSnS_4 thin film between 073 and 65 eV

A polycrystalline Cu2ZnSnS4 thin film was deposited on fused quartz by co-evaporation. The selected thickness was ~100 nm to avoid artifacts in its optical properties caused by thicker as-grown films. The composition and phase of the film were checked with x-ray fluorescence, Raman shift spectroscopy, scanning transmission electron microscopy, and energy dispersive x-ray spectroscopy. An improved spectroscopic ellipsometry methodology with two-side measurement geometries was applied to extract the complex dielectric function ε = ε1 + iε2 of the Cu2ZnSnS4 thin film between 0.73 and 6.5 eV. Five critical points were observed, at 1.32 (fundamental band gap), 2.92, 3.92, 4.96, and 5.62 eV, respectively. The ε spectra are in reasonable agreement with those from theoretical calculations.

Characterization of thin TiO 2 films prepared by plasma enhanced chemical vapour deposition for optical and photocatalytic applications

Thin titanium oxide films were deposited using a radio frequency (RF) plasma enhanced chemical vapour deposition method. Their optical properties and thickness were determined by means of ultraviolet–visible absorption spectrophotometry. Films of the optical parameters very close to those of titanium dioxide have been obtained at the high RF power input. Their optical quality is high enough to allow for their use in a construction of stack interference optical filters. At the same time, these materials exhibit strong photocatalytic effects. The results of structural analysis, carried out by Raman Shift Spectroscopy, show that the coatings posses amorphous structure. However, Raman spectra of the same films subjected to thermal annealing at 450 °C disclose an appearance of a crystalline form, namely that of anatase. Surface morphology of the films has also been characterized by Atomic Force Microscopy revealing granular, broccoli-like topography of the films.