Showing papers on "Fourier transform infrared spectroscopy published in 2012"

Photo-catalyzed degradation of hazardous dye methyl orange by use of a composite catalyst consisting of multi-walled carbon nanotubes and titanium dioxide.

Abstract: The high rate of electron/hole pair recombination reduces the quantum yield of the processes with TiO2 and represents its major drawback. Adding a co-adsorbent increases the photocatalytic efficiency of TiO2. In order to hybridize the photocatalytic activity of TiO2 with the adsorptivity of carbon nanotube, a composite of multi-walled carbon nanotubes and titanium dioxide (MWCNT/TiO2) has been synthesized. The composite was characterized by means of X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier transform infrared absorption spectroscopy (FTIR), and diffuse reflectance UV–vis spectroscopy. The catalytic activity of this composite material was investigated by application of the composite for the degradation of methyl orange. It was observed that the composite exhibits enhanced photocatalytic activity compared with TiO2. The enhancement in photocatalytic performance of the MWCNT/TiO2 composite is explained in terms of recombination of photogenerated electron–hole pairs. In addition, MWCNT acts as a dispersing agent preventing TiO2 from agglomerating activity during the catalytic process, providing a high catalytically active surface area. This work adds to the global discussion of how CNTs can enhance the efficiency of catalysts.

Effects of hydrolysis conditions on the morphology, crystallinity, and thermal stability of cellulose nanocrystals extracted from kenaf bast fibers

Abstract: Cellulose nanocrystals (CNC) were first isolated from kenaf bast fibers and then characterized. The raw fibers were subjected to alkali treatment and bleaching treatment and subsequent hydrolysis with sulfuric acid. The influence of the reaction time on the morphology, crystallinity, and thermal stability of CNC was investigated. Fourier transform infrared spectroscopy showed that lignin and hemicellulose were almost entirely removed during the alkali and bleaching treatments. The morphology and dimensions of the fibers and acid-released CNC were characterized by field emission scanning electron microscopy and transmission electron microscopy. X-Ray diffraction analysis revealed that the crystallinity first increases upon hydrolysis and then decreases after long durations of hydrolysis. The optimal extraction time was found to be around 40 min during hydrolysis at 45 °C with 65% sulfuric acid. The thermal stability was found to decrease as the hydrolysis time increased. The electrophoretic mobility of the CNC suspensions was measured using the zeta potential, and it ranged from −8.7 to −95.3 mV.

Synthesis and Efficient Visible Light Photocatalytic Hydrogen Evolution of Polymeric g-C3N4 Coupled with CdS Quantum Dots

Abstract: Novel CdS quantum dot (QD)-coupled graphitic carbon nitride (g-C3N4) photocatalysts were synthesized via a chemical impregnation method and characterized by X-ray diffraction, transmission electron microscopy, ultraviolet–visible diffuse reflection spectroscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and photoluminescence spectroscopy. The effect of CdS content on the rate of visible light photocatalytic hydrogen evolution was investigated for different CdS loadings using platinum as a cocatalyst in methanol aqueous solutions. The synergistic effect of g-C3N4 and CdS QDs leads to efficient separation of the photogenerated charge carriers and, consequently, enhances the visible light photocatalytic H2 production activity of the materials. The optimal CdS QD content is determined to be 30 wt %, and the corresponding H2 evolution rate was 17.27 μmol·h–1 under visible light irradiation, ∼9 times that of pure g-C3N4. A possible photocatalytic mechanism of the CdS/g-C3N4 comp...

Synthesis and characterization of magnetite nanoparticles via the chemical co-precipitation method

Abstract: Magnetite nanoparticles were synthesized via the chemical co-precipitation method using ammonium hydroxide as the precipitating agent. The size of the magnetite nanoparticles was carefully controlled by varying the reaction temperature and through the surface modification. Herein, the hexanoic acid and oleic acid were introduced as the coating agents during the initial crystallization phase of the magnetite. Their structure and morphology were characterized by the Fourier transform infrared spectroscopy (FTIR), the X-ray diffraction (XRD) and the field-emission scanning electron microscopy (FE-SEM). Moreover, the electrical and magnetic properties were studied by using a conductivity meter and a vibrating sample magnetometer (VSM), respectively. Both of the bare magnetite and the coated magnetite were of the cubic spinel structure and the spherical-shaped morphology. The reaction temperature and the surface modification critically affected the particle size, the electrical conductivity, and the magnetic properties of these particles. The particle size of the magnetite was increased through the surface modification and reaction temperature. In this study, the particle size of the magnetite nanoparticles was successfully controlled to be in the range of 10–40 nm, suitable for various biomedical applications. The electrical conductivity of the smallest particle size was 1.3 × 10−3 S/cm, within the semi-conductive materials range, which was higher than that of the largest particle by about 5 times. All of the magnetite nanoparticles showed the superparamagnetic behavior with high saturation magnetization. Furthermore, the highest magnetization was 58.72 emu/g obtained from the hexanoic acid coated magnetite nanoparticles.

Nano-FTIR absorption spectroscopy of molecular fingerprints at 20 nm spatial resolution.

Abstract: We demonstrate Fourier transform infrared nanospectroscopy (nano-FTIR) based on a scattering-type scanning near-field optical microscope (s-SNOM) equipped with a coherent-continuum infrared light source. We show that the method can straightforwardly determine the infrared absorption spectrum of organic samples with a spatial resolution of 20 nm, corresponding to a probed volume as small as 10 zeptoliter (10–20 L). Corroborated by theory, the nano-FTIR absorption spectra correlate well with conventional FTIR absorption spectra, as experimentally demonstrated with poly(methyl methacrylate) (PMMA) samples. Nano-FTIR can thus make use of standard infrared databases of molecular vibrations to identify organic materials in ultrasmall quantities and at ultrahigh spatial resolution. As an application example we demonstrate the identification of a nanoscale PDMS contamination on a PMMA sample.

Fourier Transform Infrared Spectroscopy for Natural Fibres

Abstract: Infrared spectroscopy is nowadays one of the most important analytical techniques available to scientists. One of the greatest advantages of the infrared spectroscopy is that virtually any sample in any state may be analyzed. For example, liquids, solutions, pastes, powders, films, fibres, gases and surfaces can all be examined with a judicious choice of sampling technique. The review by Annette, Sudhakar, Ursula and Andrea [1-2] also demonstrates the applicability of dispersion infrared spectroscopy for natural fibres studies.

AFM-IR: Combining Atomic Force Microscopy and Infrared Spectroscopy for Nanoscale Chemical Characterization

Abstract: Polymer and life science applications of a technique that combines atomic force microscopy (AFM) and infrared (IR) spectroscopy to obtain nanoscale IR spectra and images are reviewed. The AFM-IR spectra generated from this technique contain the same information with respect to molecular structure as conventional IR spectroscopy measurements, allowing significant leverage of existing expertise in IR spectroscopy. The AFM-IR technique can be used to acquire IR absorption spectra and absorption images with spatial resolution on the 50 to 100 nm scale, versus the scale of many micrometers or more for conventional IR spectroscopy. In the life sciences, experiments have demonstrated the capacity to perform chemical spectroscopy at the sub-cellular level. Specifically, the AFM-IR technique provides a label-free method for mapping IR-absorbing species in biological materials. On the polymer side, AFM-IR was used to map the IR absorption properties of polymer blends, multilayer films, thin films for active devices such as organic photovoltaics, microdomains in a semicrystalline polyhydroxyalkanoate copolymer, as well as model pharmaceutical blend systems. The ability to obtain spatially resolved IR spectra as well as high-resolution chemical images collected at specific IR wavenumbers was demonstrated. Complementary measurements mapping variations in sample stiffness were also obtained by tracking changes in the cantilever contact resonance frequency. Finally, it was shown that by taking advantage of the ability to arbitrarily control the polarization direction of the IR excitation laser, it is possible to obtain important information regarding molecular orientation in electrospun nanofibers.

Graphene oxide: the mechanisms of oxidation and exfoliation

Abstract: Graphene oxides (GOs) with large sheets and more perfect aromatic structure were prepared by a novel modified Hummers method. We demonstrated that the graphite did not need to be oxidized to such a deep degree as described in Hummers method because the space distance increased little when the oxidation proceeded to a certain extent and the obtained graphite oxides (GTOs) could be fully exfoliated to single layers with high thermal stability. The oxidation mechanism and chemical structure model of GO were proposed by analyzing the evolution of the functional groups with oxidation proceeded based on thermogravimetric analysis, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. The layer spacing calculated by molecular dynamics simulations coincided with the X-ray diffraction results. Furthermore, the size distribution and thickness of GOs were also studied. The results confirmed that the GOs prepared by the modified method were fully exfoliated to uniform single layers, and this method may be important for efficient exfoliation of GTO to GO and large-scale production of graphene.

One-step reverse precipitation synthesis of water-dispersible superparamagnetic magnetite nanoparticles

Abstract: Hydrophilic functionalization of nanoparticle surface is essential for their biomedical applications. Herein, we report a facile one-step reverse precipitation method to synthesize water-dispersible, biocompatible, and carboxylate-functionalized superparamagnetic magnetite (Fe3O4) nanoparticles with the help of biocompatible sodium citrate salt. Transmission electron microscope (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), zeta potential measurement, dynamic light scattering (DLS), and superconducting quantum interference device (SQUID) were used to characterize the as-prepared magnetite nanoparticles. The size of the as-prepared magnetite nanoparticles was tuned from 27 ± 3.8 to 4.8 ± 1.9 nm by changing the sodium citrate concentration from 25 to 125 mM. The sodium citrate concentration also influenced the water-dispersible stability of the as-prepared magnetite nanoparticles, which was due to the electrostatic repulsion.

One-step hydrothermal synthesis of N-doped TiO2/C nanocomposites with high visible light photocatalytic activity.

Abstract: N-doped TiO2 nanoparticles modified with carbon (denoted N–TiO2/C) were successfully prepared by a facile one-pot hydrothermal treatment in the presence of L-lysine, which acts as a ligand to control the nanocrystal growth and as a source of nitrogen and carbon. As-prepared nanocomposites were characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, ultraviolet–visible (UV–vis) diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), electron paramagnetic resonance (EPR) spectra, and N2 adsorption–desorption analysis. The photocatalytic activities of the as-prepared photocatalysts were measured by the degradation of methyl orange (MO) under visible light irradiation at λ ≥ 400 nm. The results show that N–TiO2/C nanocomposites increase absorption in the visible light region and exhibit a higher photocatalytic activity than pure TiO2, commercial P25 and previously reported N-doped TiO2 photocatalysts. We have demonstrated that the nitrogen was doped into the lattice and the carbon species were modified on the surface of the photocatalysts. N-doping narrows the band gap and C-modification enhances the visible light harvesting and accelerates the separation of the photo-generated electrons and holes. As a consequence, the photocatalytic activity is significantly improved. The molar ratio of L-lysine/TiCl4 and the pH of the hydrothermal reaction solution are important factors affecting the photocatalytic activity of the N–TiO2/C; the optimum molar ratio of L-lysine/TiCl4 is 8 and the optimum pH is ca. 4, at which the catalyst exhibits the highest reactivity. Our findings demonstrate that the as-obtained N–TiO2/C photocatalyst is a better and more promising candidate than well studied N-doped TiO2 alternatives as visible light photocatalysts for potential applications in environmental purification.

In situ synthesis and enhanced visible light photocatalytic activities of novel PANI–g-C3N4 composite photocatalysts

Abstract: Novel polyaniline–graphitic carbon nitride (PANI–g-C3N4) composite photocatalysts with different PANI:g-C3N4 ratios were synthesized by “in situ” deposition oxidative polymerization of aniline monomer in the presence of g-C3N4 powder cooled in an ice bath. The resulting PANI–g-C3N4 composite photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), ultraviolet-visible diffuse reflection spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS) and photoluminescence spectroscopy (PL). The photoelectrochemical measurements were performed using several on–off cycles of visible light irradiation. The photocatalytic activities of the novel photocatalysts were evaluated using methylene blue as a target pollutant. The PANI–g-C3N4 composites exhibit obviously enhanced photocatalytic performance under visible light irradiation, which is much higher than that of TiO2 (P25). The synergistic effect between PANI and g-C3N4 is found to lead to an improved photo-generated carrier separation. A possible photocatalytic mechanism of PANI on the enhancement of visible light performance is proposed to guide further improvement of their photocatalytic activity.

Graphene oxide-iron oxide and reduced graphene oxide-iron oxide hybrid materials for the removal of organic and inorganic pollutants

Abstract: Graphene oxide (GO) and reduced graphene oxide (RGO) were both decorated with iron oxide nanoparticles and were characterized by scanning and transmission electron microscopy, powder X-ray diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The adsorption of Pb(II), 1-naphthol, and 1-naphthylamine, as representatives of inorganic and organic pollutants, on GO-iron oxides and RGO-iron oxides was investigated. The results showed that the GO-iron oxide material was a good adsorbent for Pb(II) but not for 1-naphthol and 1-naphthylamine due to oxygen-containing groups on the surface, whereas the RGO-iron oxide material was a good adsorbent for 1-naphthol and 1-naphthylamine but not for Pb(II). The adsorption of 1-naphthol and 1-naphthylamine on RGO-iron oxides was an endothermic and spontaneous process. Both materials can be easily separated by magnetic separation.

Hydrophobic cellulose nanocrystals modified with quaternary ammonium salts

Abstract: An environmentally friendly procedure in aqueous solution for the surface modification of cellulose nanocrystals (CNCs) using quaternary ammonium salts via adsorption is developed as inspired by organomodified layered silicates. CNCs with a high carboxylate content of 1.5 mmol g−1 were prepared by a new route, direct hydrochloric acid hydrolysis of 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-oxidized nanofibrillated cellulose from a softwood pulp, and characterized by atomic force microscopy (AFM) and X-ray diffraction (XRD). Four quaternary ammonium cation surfactants bearing long alkyl, phenyl, glycidyl, and diallyl groups were successfully used to modify CNCs carrying carboxylic acid groups as characterized by Fourier transform infrared spectroscopy (FTIR). The modified CNCs can be redispersed and individualized in an organic solvent such as toluene as observed by scanning transmission electron microscopy (STEM). One may envision removing excess surfactant to obtain CNC with a monolayer of surfactant. The toluene suspension of the modified CNCs showed strong birefringence under crossed polars but no further chiral-nematic ordering was observed. The model surface prepared by the CNCs modified with quaternary ammonium salts bearing C18 alkyl chains showed a significant increase in water contact angle (71°) compared to that of unmodified CNCs (12°). This new series of modified CNCs can be dried from solvent and have the potential to form well-dispersed nanocomposites with non-polar polymers.

Two-dimensional Fourier transform electronic spectroscopy

Abstract: Two-dimensional Fourier transform electronic spectra of the cyanine dye IR144 in methanol are used to explore new aspects of optical 2D spectroscopy on a femtosecond timescale. The experiments reported here are pulse sequence and coherence pathway analogs of the two-dimensional magnetic resonance techniques known as COSY (correlated spectroscopy) and NOESY (nuclear Overhauser effect spectroscopy). Noncollinear three pulse scattering allows selection of electronic coherence pathways by choice of phase matching geometry, temporal pulse order, and Fourier transform variables. Signal fields and delays between excitation pulses are measured by spectral interferometry. Separate real (absorptive) and imaginary (dispersive) 2D spectra are generated by measuring the signal field at the sample exit, performing a 2D scan that equally weights rephasing and nonrephasing coherence pathways, and phasing the 2D spectra against spectrally resolved pump–probe signals. A 3D signal propagation function is used to correct the...

A series of furan-aromatic polyesters synthesized via direct esterification method based on renewable resources

Abstract: A series of furan-aromatic polyesters were successfully synthesized via direct esterification method starting from 2,5-furandicarboxylic acid, ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, and 1,8-octanediol and characterized by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (1H NMR), X-ray diffraction (XRD), differential scanning calorimeter (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), tensile tests, and so on. The preliminary evidence clearly showed that direct esterification method was rewarding and worthy to synthesize these furan-aromatic polyesters. The densities of furan-aromatic polyesters were ranging from 1.19 to 1.38 kg/m3. The FTIR and 1H NMR confirmed their expected structures in detail. The results of XRD showed that these furan-aromatic polyesters were crystalline polyesters. The results of DSC, TGA, DMA, and tensile tests showed that they behaved as thermoplastic polyester, had satisfactory thermal and mechanical properties, and their thermal stabilities were quite similar to that of corresponding benzene-aromatic polyesters. The results of contact angle measurement showed that they were hydrophilic. The properties above showed that furan-aromatic polyesters based on renewable resources could be a viable alternative to their successful petrochemical benzene-aromatic counterpart. Furthermore, they could be used as biopolymer materials according their satisfactory thermal and mechanical properties and hydrophilicity in the future. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Facile preparation of nitrogen-doped graphene as a metal-free catalyst for oxygen reduction reaction.

Abstract: Nitrogen-doped graphene (nG) is a promising metal-free catalyst for oxygen reduction reaction (ORR) on the cathode of fuel cells. Here we report a facile preparation of nGviapyrolysis of graphene oxide with melamine. The morphology of the nG is revealed using scanning electron microscopy and transmission electron microscopy while the successful N doping is confirmed by electron energy loss spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. The resulting nG shows high electrocatalytic activity toward ORR in an alkaline solution with an onset potential of −0.10 V vs.Ag/AgCl reference electrode. The nG catalyzed oxygen reduction exhibits a favorable formation of watervia a four-electron pathway. Good stability and anti-crossover property are also observed, which are advantageous over the Pt/C catalyst. Furthermore, the effect of pyrolysis temperature on the structure and activity of nG is systematically studied to gain some insights into the chemical reactions during pyrolysis.

Hexagonal and cubic Ni nanocrystals grown on graphene: phase-controlled synthesis, characterization and their enhanced microwave absorption properties

Abstract: Hexagonal close-packed Ni (h-Ni) nanocrystals and face-centered cubic Ni (c-Ni) nanoflowers with uniform size and high dispersion have been successfully assembled on graphene nanosheets (GN) via a facile one-step solution-phase strategy under different reaction conditions, where the reduction process of graphite oxide (GO) sheets into GN was accompanied by the generation of Ni nanocrystals. The reduction of GO by this method is effective, which was confirmed by X-ray diffraction (XRD), Fourier transform infrared (FTIR) and Raman spectroscopy and is comparable to conventional methods. The phase and morphology of nickel can be easily tuned by varying the reaction temperature and solvent. It was shown that the as-formed h-Ni nanocrystals with a diameter as small as 3 nm are grown densely and uniformly on the graphene sheets, and as a result the aggregation of the h-Ni nanocrystals was effectively prevented. In addition, c-Ni nanospheres assembled by c-Ni nanocrystals with a size of 15 nm were also uniformly deposited on the graphene sheets. The investigation of the microwave absorbability reveals that the three Ni/GN nanocomposites exhibit excellent microwave absorbability, which is stronger than the corresponding Ni nanostructures.