Raman evidence of the interaction between multiwalled carbon nanotubes and nanostructured TiO2

Nanocomposites of carbon nanotubes and titanium dioxide (TiO₂) have attracted much attention due to their photocatalytic properties. Although many examples in the literature have visualized these nanocomposites by electron microscopic images, spectroscopic characterization is still lacking with regard to the interaction between the carbon nanotube and TiO₂. In this work, we show evidence of the attachment of nanostructured TiO₂ to multiwalled carbon nanotubes (MWNTs) by Raman spectroscopy. The nanostructured TiO₂ was characterized by both full‐width at half‐maximum (FWHM) and the Raman shift of the TiO₂ band at ca 144 cm⁻¹, whereas the average diameter of the crystallite was estimated as approximately 7 nm. Comparison of the Raman spectra of the MWNTs and MWNTs/TiO₂ shows a clear inversion of the relative intensities of the G and D bands, suggesting a substantial chemical modification of the outermost tubes due to the attachment of nanostructured TiO₂. To complement the nanocomposite characterization, scanning electronic microscopy and X‐ray diffraction were performed. Copyright © 2011 John Wiley & Sons, Ltd.     

In situ Radical Copolymerization in Presence of Surface‐Modified TiO2 Nanoparticles: Influence of a Double Modification on Properties of Unsaturated Polyester (UP) Nanocomposites

In the preparation of nanocomposites, there is competition between the dispersion of nanoparticles and the formation of agglomerates. In this study, radical copolymerization of ethyl acrylate and methyl methacrylate initiated by 2,2‐azobis (isobutyro) nitrile (AIBN) was performed, in the presence of titanium oxide (TiO₂) nanoparticles modified in a new approach; a good dispersion of the nanoparticles in the unsaturated polyester (UP) matrix was obtained. The TiO₂ nanoparticles were exposed to 3‐(methacryloxy) propyl trimethoxy silane as the coupling agent. The presence of coupling agent‐grafted TiO₂ nanoparticles in the copolymerization process resulted in the formation of a polymeric layer on the surface of the TiO₂ nanoparticles (doubly modified‐TiO₂). The grafting of coupling agent molecules and consequently copolymer macromolecular chains onto the surface of TiO₂ nanoparticles was investigated using Fourier transform infrared (FTIR) analysis. It found that the formation of an acrylate layer on the surface of nanoparticles was successful. Then, unsaturated polyester (UP)/TiO₂ nanocomposites were prepared. The morphology was studied using transmission electron microscopy (TEM). Mechanical properties and ultraviolet visible (UV/VIS) spectroscopy of various samples, including the doubly modified‐TiO₂ nanoparticles, with different nanoparticle inclusions and the unmodified‐TiO₂ nanoparticles, were also investigated. The results showed the doubly modified‐TiO₂ nanoparticles, compared to those of unmodified‐TiO₂, had better nanoparticle dispersion causing improvement in the mechanical properties and UV shielding.     

Synthesis and characterization of “mulberry”-like Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/multiwalled carbon nanotube nanocomposites

Nanocomposites composed of multi-wall carbon nanotubes (MWNTs) and Fe₃O₄ nanoparticles were fabricated using solvothermal method. Transmission and scanning electron microscopy, energy dispersive spectroscopy, and X-ray powder diffraction measurements confirmed that these mulberry-like Fe₃O₄ microparticles which were combined with the MWNTs in a random pattern are constructed with tiny nanocrystallites (12 nm in average diameter). The magnetic properties of the Fe₃O₄/MWNTs nanocomposites were measured using a vibrating sample magnetometer. Results showed that the Fe₃O₄/MWNTs nanocomposites exhibited superparamagnetism at room temperature and possessed a lower saturation magnetization (around 27.6 emu/g) than that of the pure Fe₃O₄ nanoparticles (around 33.7 emu/g). The Fe₃O₄/MWNTs nanocomposites have potential applications in engineering and medicine.     

Synthesis and characterization of multi–wall carbon nanotubes supported-hydrated iron phosphate cathode material for lithium–ion cells by a novel homogeneous precipitation method

Iron phosphate (FePO₄) is a promising candidate for the cathode material in lithium-ion cells due to its easy synthesis and low cost. However, the intrinsic drawbacks of FePO₄ material (i.e., the low electronic conductivity and the low lithium-ion diffusion coefficient) result in poor capacity. To overcome the shortcomings, multi-wall carbon nanotubes (MWNTs) supported hydrated iron phosphate nanocomposites (FePO₄·2H₂O/MWNTs) are prepared using a novel homogeneous precipitation method. Meanwhile, the formation mechanism of highly dispersed and ultrafine FePO₄·2H₂O nanoparticles is discussed in detail. Electrochemical measurements show that FePO₄·2H₂O/MWNTs nanocomposites have a superior discharge capacity and stability. For example, FePO₄·2H₂O/MWNTs nanocomposites exhibit a high initial discharge capacity (129.9?mAhg^?1) and a stable capacity retention (114.3?mAhg^?1 after 20 cycles). The excellent electrochemical performance is attributed to the small particle size of FePO₄·2H₂O nanoparticles, the good electronic conductivity of MWNTs, and the three-dimensional conductive network structure of FePO₄·2H₂O/MWNTs nanocomposites.     

The effect of SiO2 and TiO2 nanoparticles on physical properties of SrFe12O19 nanoparticle

In order to obtain SrFe₁₂O₁₉ nanoparticles, thermal treatment method was employed, and afterwards SiO₂ and TiO₂ nanoparticles were embedded in SrFe₁₂O₁₉ matrix SrFe₁₂O₁₉ nanoparticles. The SiO₂ and TiO₂ nanoparticles' effects were set in SrFe₁₂O₁₉ matrix and experimental techniques which include, transmission electron microscopy (TEM), x-ray diffraction (XRD), fourier transform infrared spectroscopy (FT-IR), x-ray analysis (EDX) and field emission scanning electron microscope (FESEM) were used in studying the physical properties of the prepared nanoparticles. The precise DASF method (derivation of absorption spectrum fitting) was employed in examining the optical properties. The addition of SiO₂ and TiO₂ nanoparticles to SrFe₁₂O₁₉ matrix resulted in the reduction of energy band gap values in compare with the SrFe₁₂O₁₉ nanoparticles. The chemical analysis of SrFe₁₂O₁₉/SiO₂, SrFe₁₂O₁₉ nanoparticles, and SrFe₁₂O₁₉/TiO₂ nanocomposites was carried out using energy dispersion X-ray analysis (EDX). Ferromagnetic behaviors were demonstrated by SrFe₁₂O₁₉ nanoparticles, SrFe₁₂O₁₉/SiO₂ and SrFe₁₂O₁₉/TiO₂ nanocomposites, and the behaviors were validated through the use of a vibrating sample magnetometer (VSM). A wasp-waist was observed through hysteresis loop of SrFe₁₂O₁₉/SiO₂ nanocomposites, implying the presence of the two magnetic phases; soft and hard ferromagnetic.     

Analysis of fiber optic SPR sensor utilizing platinum based nanocomposites

SPR based fiber optic sensor using nanocomposite is presented. Nanocomposites comprising of Pt nanoparticles with various volume fractions embedded in dielectric matrices of TiO₂ and SnO₂ are considered. Sensitivity enhances with increase in thickness of nanocomposite and volume fraction of nanoparticles for both nanocomposites. Optimized thicknesses are obtained to be 40 and 50 nm for Pt–TiO₂ and Pt–SnO₂ nanocomposites respectively while optimized volume fraction is found to be 0.85 for both nanocomposites. 40 nm thick Pt–TiO₂ nanocomposite based sensor with 0.85 volume fraction possesses utmost sensitivity.     

Physicochemical and photocatalytic activities of self-assembling TiO2 nanoparticles on nanocarbons surface

TiO₂ nanoparticles were self-assembled on three different dimensional nanocarbon (SWCNT, C₆₀ and graphene) surfaces by a uniform thermal reaction. The effective anchoring of TiO₂ nanoparticles on the nanocarbon surfaces was characterized by FT-IR, XRD, XPS, TEM, Raman spectroscopy, PL and UV-Vis. By investigating the effect of different carbon nanostructures on TiO₂ photocatalyst system, we found that the enhancing photocatalytic activities of nanocarbon/TiO₂ (NT) nanocomposites have still related to great adsorbability and effective charge transfer by nanocarbon introduced, however, no more insights can be provided for peculiar properties on different nanostructures, although graphene by itself has an excellent structure and morphology.     

Structural, photochemical and photocatalytic properties of zirconium oxide doped TiO2 nanocrystallites

Composite photocatalysts composed of TiO₂ and ZrO₂ have been prepared via the sol-gel method. The as-prepared nanocomposites are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-vis spectrometry and fluorescence emission spectra. The results shows that TiO₂/ZrO₂ nanocomposites are composed of mainly anatase titania and tetragonal ZrO₂. Incorporating TiO₂ particles with ZrO₂ plays an important role in promoting the formation of nanoparticles with an anatase structure and leads to decreased fluorescence emission intensity. Most of the TiO₂/ZrO₂ nanocomposites exhibited comparable photocatalytic activity compared with commercial TiO₂ for the degradation aqueous methyl orange (MO) under ultraviolet irradiation, while the composite with Zr/Ti mass ratio of 15.2% shows the highest photocatalytic performances. Furthermore, the as-prepared nanocomposites can be reused with little photocatalytic activity loss. Without any further treatment besides rinsing, the photocatalytic activity of TiO₂/ZrO₂ (15.2%) composites is still higher than after five-cycle utilization.     

Microwave absorption properties of 50% SrFe12O19–50% TiO2 nanocomposites with porosity

SrFe₁₂O₁₉–TiO₂ nanocomposites are usually used for absorbing microwaves in military and civil applications. In this work, microwave absorption properties of porous SrFe₁₂O₁₉ nanocomposites with 50% weight ratio of TiO₂ have been investigated. 50% TiO₂–50% SrFe₁₂O₁₉ nanocomposites were prepared by a controlled hydrolysis of titanium tetraisopropoxide in which SrFe₁₂O₁₉ nanoparticles were synthesized by a sol–gel auto combustion route. The morphology, crystalline structure and crystallite size of SrFe₁₂O₁₉–TiO₂ nanocomposites were characterized by field emission scanning electron microscopy and X-ray powder diffraction. The magnetic measurements were carried out with a vibrating sample magnetometer. The microwave absorption was measured by a Vector Network Analyzer. The microwave absorption results indicated that the reflection losses for specimens with 52%–56% porosity and thicknesses of 1.8, 2.1 and 2.6 mm were not very low but minimum reflection loss for a specimen with 4.2 mm thickness reached upto −33 dB.     

Optical Limiting Properties of Two Soluble Polymer/Multi-Walled Carbon Nanotube Composites

Two soluble polymer grafted multi-walled carbon nanotubes （MWNTs）, including poly（N-vinylcarbazole）-MWNTs and poly（methyl methacrylate）-MWNTs, are synthesized. Their nonlinear optical properties and opticaJ limiting （OL） performances are investigated by z-scan method with 527nm nanosecond laser pulses. These grafted MWNTs dissolved in chloroform show much better optical limiting performance than those of MWNTs and C60 in toluene solution. Nonlinear absorption and nonlinear scattering mechanism are taken into consideration for explaining the observed results. The comparison of the experimental results shows that nonlinear absorption is the dominant mechanism for OL performance of these new samples.     

A new one-step synthesis method for coating multi-walled carbon nanotubes with iron oxide nanorods

A facile solution-chemical method has been developed to be capable of covering a multiwalled carbon nanotube (MWNTs) with iron oxide nanorods without using any bridging species. MWNTs in this composite were decorated randomly by α-Fe₂O₃ nanorods with diameters in the range of 3–5 nm and lengths of 15–30 nm. The formation route to anchor α-Fe₂O₃ nanorods onto MWNTs was proposed as the intercalation and adsorption of iron ions onto the wall of MWNTs, followed by the nucleation and growth of α-Fe₂O₃ nanorods. α-Fe₂O₃/MWNTs nanocomposites show specific high Brunauer–Emmett–Teller surface areas. The photocatalytic activity experiment indicated that the prepared α-Fe₂O₃/MWNTs nanocomposites exhibited a higher photocatalytic activity for the photocatalytic decolorization of rhodamine B aqueous solution under the visible-light illumination than the single phase α-Fe₂O₃ samples. This methodology made the synthesis of MWNTs-nanorods composites possible and may be further extended to prepare more complicated nanocomposites based on MWNTs for technological applications.     

Preparation and characterization of polyethylene/TiO2 nanocomposites

The rheological behaviour, dispersion, crystallization behavior, mechanical properties, fracture surface morphology of polyethylene (PE)/TiO₂ nanocomposites prepared by melt compounding were investigated using rheometer, energy dispersive X-ray spectrometer (EDX), polarized microscopy, impact tester, universal testing machine and field-emission scanning electron microscopy (FE-SEM). The rheological analysis indicated a fine dispersion of TiO₂ during the melt compounding. The large scaled surface dispersion of TiO₂ nanoparticles was revealed by the EDX composition distribution maps. The introduction of 2.0 wt% TiO₂ in composites improved the mechanical properties significantly compared to neat PE, and resulted in 45% increase in notched impact strength. Moreover, the further analysis and discussion showed the mechanical properties of the composites were controlled by the dispersion conditions of TiO₂ and its nucleating effect on PE crystallization.     

Novel carbon nanotube iron oxide magnetic nanocomposites

A novel magnetic nanocomposite of γ-Fe₂O₃ nanoparticles decorated multiwalls carbon nanotubes (MWNTs) was synthesized for the first time by a simple chemistry precipitation method. The structure and morphology of the composite was characterized by X-ray powder diffractometer (XRD), TEM and EDS. The results of XRD and TEM show that γ-Fe₂O₃ nanoparticles is immobilized on the side wall of the MWNTs, the size of most of the particle is <5 nm.The EDS analysis shows that the atomic ratio of Fe to O is 2:3. The magnetization curves of the MWNTs and γ-Fe₂O₃ decorated MWNTs were measured by VSM at room temperature, which indicate that the saturated magnetization (Ms), remanence (Mr) and coercivity (Hc) of the decorated MWNTs are much larger than those of MWNTs, and the decorated MWNTs exhibit well magnetic properties.     

ZnO–TiO2 nanocomposites formed under submerged DC arc discharge: preparation,characterization and photocatalytic properties

A rutile TiO₂ (α-TiO₂) and hexagonal wurtzite ZnO nanocomposite was directly and synchronously synthesized via arc discharge method submerged in de-ionized water. In correlation with the detailed characterization of the morphology, and crystalline structure of the prepared ZnO–TiO₂ nanocomposites, the UV–visible and photoluminescence properties were studied. X-ray diffraction and transmission electron microscopy investigations revealed the co-existence of α-TiO₂ and hexagonal wurtzite ZnO phases with the ZnO and α-TiO₂ nanoparticles are in nanorod and nanospheres morphologies, respectively. The diameters of the synthesized nanocomposite particles are in the range of 5–70 nm. Interestingly, the as-prepared ZnO–TiO₂ nanocomposite shows better photocatalytic activity for photodegradation of the methylene blue dye than both of pure ZnO and TiO₂ nanocatalyts. This work would explore feasible routes to synthesize efficient metal or/and metal oxide nanocomposites for degrading organic pollutants, gas sensing or other related applications.     

Hybrid nanostructured materials with tunable magnetic characteristics

Novel titanium oxide (TiO₂) nanoparticles were fabricated via a modified propanol drying step. These nanoparticles were loaded with anti-cancer drug paclitaxel (PTX) to yield PTX-TiO₂ nanocomposites. The nanocomposites were characterized for their size and surface morphology employing nanoparticle tracking analysis (NTA) and scanning electron microscopy (SEM). The SEM images showed spherical particles with smooth surface and narrow size distribution of ~30–40 nm, which was also supported by NTA analysis data. The drug loading efficiency of the air-dried nanoparticles was observed to be ~63.61 % while those prepared through propanol-induced drying step showed ~69.70 %, thereby demonstrating higher efficiency of the latter. In vitro pH-dependent release of the loaded PTX was observed with higher release at acidic pH compared with physiological pH. Cell uptake studies suggested of time-dependent internalization of nanocomposites with significant improvement in uptake by increasing incubation time from 2 to 24 h, as evidenced by flow cytometry. Further, the cell viability as a measure of anti-cancer activity revealed that cell viability upon exposure to PTX only was 40.5 % while that of PTX-TiO₂ nanocomposite showed 21.6 % viability after 24 h, suggesting better anti-cancer efficacy of nanocomposites. Apoptosis studies revealed that cells treated with PTX-TiO₂ nanocomposites possessed more amount of apoptotic bodies as compared to those treated with PTX only.     

Hydrothermal synthesis of CdTe quantum dots–TiO2–graphene hybrid

CdTe–TiO₂–graphene nanocomposites were successfully synthesized via a simple and relatively general hydrothermal method. During the hydrothermal environment, GO was reduced to reduced graphene oxide (RGO), accompanying with the anchoring of TiO₂ nanoparticles on the surface of RGO. In the following process, CdTe quantum dots (QDs) were then in situ grown on the carbon basal planes. The morphologies and structural properties of the as-prepared composites were characterized by X-ray diffraction, Raman spectroscopy, transmission electron microscopy and fluorescent spectroscopy. It is hoped that our current work could pave a way towards the fabrication of QDs–TiO₂–RGO hybrid materials.     

The electrical conductivity properties of polythiophene/TiO2 nanocomposites prepared in the presence of surfactants

A composite of polythiophene (PT) and nano-titanium dioxide (TiO₂), possessing core–shell structure, was synthesized via oxidative polymerization of thiophene using FeCl₃ in the presence of three different surfactants: anionic, cationic, and nonionic. The morphology of the obtained composite materials was investigated by SEM, proving the core–shell structure of the prepared nanocomposite. The formation and thermal stability of the PT onto TiO₂ nanoparticles were confirmed by FTIR and TGA analyses, respectively. XRD data show all of composite materials were amorphous structures. The electrical properties of the nanocomposites were investigated in the presence of surfactant materials, and the best semiconductor property was observed for PT/TiO₂-anionic system. This difference in the conductivity has been attributed to differences in the stability of the composites.     

Improvement in thermo mechanical and optical properties of in situ synthesized PMMA/TiO2 nanocomposite

In this paper, transparent thin films of nano titania filled Poly(methyl methacrylate) (PMMA) composites were synthesized by solvent casting method using tetra hydro furan as a solvent, with in situ nonaqueous ‘sol-gel’ transformation involving the mixing of titanium isopropoxide (as sol-gel precursor) and methanol. The present research work is focused at studying the effect of titania loading on optical and mechanical behavior of transparent nano hybrid thin films. The effect of nano Titanium dioxide (TiO₂) loading on PMMA morphology was studied by using a scanning electron microscope (SEM). Bowl shaped structures were obtained in pure PMMA thin film, which were deformed on incorporation of TiO₂ nanoparticles. This nanocomposite exhibits enhanced optical and mechanical properties. The peak of UV absorption is blue shifted to 261 and 266?nm with the incorporation of TiO₂. At this wavelength, the absorption is increased up to approximately 397%. The nanocomposites exhibit increased tensile strength up to 40% and modulus up to 16%. Tg of PMMA increased from 84.8 to 86.7?°C on adding 1.25% TiO₂ nanoparticles.     

Synthesis of titania/carbon nanocomposites by polymeric precursor method

Here we describe a single chemical route to obtain highly dispersed nanometric Ni particles embedded in titania/carbon matrixes (amorphous and crystalline). The synthesis of these nanocomposites is based on a polymeric precursor method. The metallic Ni nanoparticles (1-15 nm) were obtained in a single process. We also present the results of photocatalytic experiments involving a series of nanocrystalline composites based on TiO₂/carbon with embedded Ni nanoparticles as nanocatalysts for rhodamine 6G degradation in aqueous solution and investigate the effects of the structure and properties of the nanocomposites on their photocatalytic applications. The effect of the different annealing treatments on the formation of TiO₂ nanophases (anatase and/or rutile), the size of Ni particles and the role of the residual carbon phase on the final solid are also described.     

Nanotitania-coated multi-walled carbon nanotube composite by facile colloidal processing route for photocatalytic applications

Multi-walled carbon nanotubes (MWCNTs) and titanium dioxide nanocomposites (MWCNTs/TiO₂) were fabricated by a simple novel colloidal processing route and tested as a photocatalyst for degradation of methylene blue under UV irradiation. The novel idea behind this work is to make MWCNTs and TiO₂ nanoparticle suspensions separately highly oppositely charged and utilize the electrostatic force of attraction between two entities to deposit nanotitania onto MWCNTs surface. Particle charge detector, scanning electron microscopy, transmission electron microscope, energy dispersive X-rays, X-rays diffraction (XRD), and Raman spectroscopy were used to characterize the composite. XRD and Raman spectroscopic analysis showed the crystalline structure of deposited TiO₂ over MWCNTs surface structure as anatase phase. It was found that MWCNTs/TiO₂ composite structure have much higher photocatalytic activity compared to TiO₂ nanoparticles. The composite material developed may find potential applications in the degradation of organic pollutants in aqueous medium under UV irradiation.