Multi-walled carbon nanotubes modified by sulfated TiO2 - A promising support for Pt catalyst in a direct ethanol fuel cell

We report the synthesis of multi-walled carbon nanotubes coated with sulfated TiO₂ (S-TiO₂/MWCNTs) as a promising support for Pt catalyst in a direct ethanol fuel cell. Highly dispersed Pt nanoparticles were supported on the S-TiO₂/MWCNT composites by NaBH₄ reduction procedure (Pt-S-TiO₂/MWCNTs). The presence and nature of the catalyst were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, high-resolution transmission electron microscopy. The size of the sulfated TiO₂ product was about 8 nm, and that of the Pt nanoparticle on the S-TiO₂/MWCNT composites was about 5 nm. The Pt-S-TiO₂/MWCNTs were used to study the electrochemical ethanol oxidation reaction using cyclic voltammetry, chronoamperometry and impedance spectroscopy. The results show that Pt-S-TiO₂/MWCNT catalysts show higher catalytic activity for ethanol oxidation compared with Pt supported on non-sulfated TiO₂/MWCNT composites and commercial Pt/C catalysts.     

Temperature-dependent charge transport in TiO2–multiwalled carbon nanotube composites

Charge transport properties of TiO₂–multiwalled carbon nanotube (MWCNT) composites were investigated. The TiO₂–MWCNT composites were fabricated by spark plasma sintering of a mixture of TiO₂ nanoparticles and MWCNTs. Temperature-dependent electrical conductivities of the composites reveal that the percolation threshold for the MWCNT network is affected by temperature, and that the activation process for electron hopping is also influenced by the percolation. Based on this interdependence, an integrated charge transport model, including both the effects of the percolation and the electron hopping, is proposed for this system.     

Preparation of multi-walled carbon nanotube supported TiO2 and its photocatalytic activity in the reduction of CO2 with H2O

Multi-walled carbon nanotube (MWCNT) supported TiO₂ composite catalysts were prepared by sol-gel and hydrothermal methods. X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy and N₂-adsorption analysis were carried out to characterize the composite catalysts. In using the sol-gel method, the MWCNTs were coated with anatase TiO₂ nanoparticles, and by the hydrothermal method, rutile TiO₂ nanorods were uniformly deposited on the MWCNTs. The photocatalytic activities of the composite catalysts were evaluated by the reduction of CO₂ with H₂O. The results indicate that the addition of an appropriate amount of MWCNTs as supports for TiO₂ could remarkably improve the efficiency of the photocatalytic reaction. The composite catalysts prepared by the sol-gel method lead to the main formation of C₂H₅OH, while HCOOH is found to be the major product on the sample prepared by the hydrothermal method.     

Characterization and photodegradation characteristics of organic dye for Pt–titania combined multi-walled carbon nanotube composite catalysts

Multi-walled carbon nanotubes (MWCNTs), titanium(IV) isopropoxide (TIP) and potassium hexachloroplatinate(IV) (K₂PtCl₆) were used for the preparation of Pt/MWCNT/TiO₂ composites. The composites were comprehensively characterized by Brauer–Emett–Teller surface area, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, energy dispersive X-ray and UV–vis absorption spectroscopy. The photoactivity of the prepared materials under UV irradiation was tested using the conversion of methylene blue (MB) in aqueous solution. According to the results of MB removal experiment, it can be considered that the MB removal effect of the Pt/MWCNT/TiO₂ composites is affected by two kinds of effects: adsorption effect by MWCNTs and photocatalytic effect by TiO₂. Finally, the photocatalytic effect increases due to photo-induced-electron absorption effect by MWCNTs and electron trap effect by Pt metal.     

Botanical Hydrocarbon Sources based MWCNTs Synthesized by Spray Pyrolysis Method for DSSC Applications

The present study aims to synthesize corrosion free counter electrodes for DSSC and evaluate their efficiency in comparison with carbon electrodes. We compare the PCE (Power Conversion Efficiency) of a MWCNT counter electrode DSSC with a carbon coated counter electrode DSSC. MWCNTs are prepared by a spray pyrolysis method and TiO₂ nanoparticles are prepared by aWCT (Wet Chemical Technique). XRD analysis for TiO₂ 2θ = 25.3 shows the presence of anatase phase and 2θ = 25.9 shows the hexagonal graphite structure ofMWCNTs. SEM images of TiO₂ nanoparticles show irregular morphology and for MWCNTs, the SEM image shows the formation of MWCNTS. The exact grain size ofMWCNTs and TiO₂ nanoparticles are studied by TEM analysis. In the DSSC application, MWCNTs coated the DSSC show higher efficiency (2.5 %) than carbon coated DSSC (1.9 %).     

Synthesis of PtRu/carbon nanotube composites in supercritical fluid and their application as an electrocatalyst for direct methanol fuel cells

PtRu nanoparticles were decorated on multi-walled carbon nanotubes (MWCNTs) using H₂PtCl₆ and RuCl₃ as precursors with the aid of supercritical CO₂, and the resulting composites were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy. TEM observation showed that nanoparticles of size about 5 nm were distributed evenly on the MWCNTs, and XRD analysis showed that the particles had a face-centered cubic crystal structure. The loading content of the nanoparticles on the MWCNTs could be adjusted by manipulating the relative ratio of the precursor to MWCNTs. The as-prepared PtRu/MWCNT composites exhibited high activity for methanol electro-oxidation.     

Synthesis of hybrid Pt/TiO2 (anatase)/MWCNTs nanomaterials by a combined sol–gel and polyol process

In the present study, hybrid Pt/TiO₂/MWCNTs nanomaterials are prepared successfully by a combined sol–gel and polyol process. The as-prepared nanomaterials are characterized by X-ray diffraction, high resolution transmission electron microscopy, and thermogravimetry analysis. In addition, its catalytic performance by converting CO into CO₂ is also evaluated. Experimental results show that the hybrid Pt/TiO₂/MWCNTs nanomaterials exhibit a mixture of anatase TiO₂ and Pt phases. Multi-wall carbon nanotubes serve as an excellent supporting material where anatase TiO₂ nanoparticles are decorated with well-distributed Pt nanoparticles. Excellent catalytic performance can be revealed for the hybrid Pt/TiO₂/MWCNTs nanomaterials. When compared with its Pt/TiO₂ counterparts where ～ 100% CO conversion occurred at 150 °C, almost 100% conversion of CO into CO₂ can be observed at a temperature ranged from 30 °C to 100 °C.     

Preparation of nanosized anatase TiO2-coated kaolin composites and their pigmentary properties

Nanosized anatase TiO₂-coated kaolin composites were prepared by the chemical deposition method starting from calcined kaolin and TiCl₄. The resultant TiO₂ nanoparticles on the kaolin surfaces existed in anatase phase after calcination at 200, 400, and 900 °C for 1 h, respectively. The surfaces of the kaolin powders were uniformly coated by a monolayer of TiO₂ nanoparticles. The higher calcination temperature was beneficial to formation of well crystallized anatase TiO₂ nanoparticles. The light scattering indexes of the TiO₂-coated calcined kaolin composites were two times higher than that of the kaolin substrate. XPS analysis shows that TiO₂ coating layers anchored at the kaolin surfaces via the Ti-O-Si and Ti-O-Al bonds.     

Charge transfer properties and photoelectrocatalytic activity of TiO2/MWCNT hybrid

The vertically aligned multiwalled carbon nanotube (MWCNT) arrays on tantalum foils were successfully coated with TiO₂ nanoparticles by a hydrothermal process. The prepared TiO₂/MWCNT hybrid was characterized by scanning electron microscopy and transmission electron microscopy. The charge transfer properties and photocatalytic degradation of rhodamine B with and without bias potential under UV irradiation were investigated. The MWCNTs promoted the separation of photoinduced carriers in the TiO₂, thus enhanced photocatalytic activity. Applying bias potential on the photoanode further enhanced its catalytic activity. The efficient charge transportation and high photoelectrocatalytic activity towards degradation of rhodamine B made this hybrid material promising for photocatalyst and for the development of photoelectrical devices.     

Photocatalytic activity of TiO2 supported on multi-walled carbon nanotubes under simulated solar irradiation

TiO₂ particles supported on multi-walled carbon nanotubes (MWCNTs) were prepared using a sol–gel method to investigate their photocatalytic activity under simulated solar irradiation for the degradation of methyl orange (MO) in aqueous solution. The prepared composites were analyzed using XRD, SEM, EDS and UV–vis absorption spectroscopy. The results of this study indicated that there was little difference in the shape and structure of MWCNTs/TiO₂ composite and pure TiO₂ particles. The composite exhibited enhanced absorption properties in the visible light range compared to pure TiO₂. The degradation of MO by MWCNTs/TiO₂ composite photocatalysts was investigated under irradiation with simulated solar light. The results of this study indicated that MWCNTs played a significant role in improving photocatalytic performance. Different amounts of MWCNTs had different effects on photodegradation efficiency, and the most efficient MO photodegradation was observed for a 2% MWCNT/TiO₂ mass ratio. Photocatalytic reaction kinetics were described using the Langmuir–Hinshelwood (L–H) model. The photocatalyst was reused for eight cycles, and it retained over 95.2% photocatalytic degradation efficiency. Possible decomposition mechanisms were also discussed. The results of this study indicated that photocatalytic reactions with TiO₂ particles supported on MWCNTs under simulated solar light irradiation are feasible and effective for degrading organic dye pollutants.     

The effect of incorporating carbon nanotubes in titania films used for the photocathode protection of 304 stainless steel

Composite films of TiO₂ and multiwall carbon nanotubes (MWCNTs) were prepared on 304 stainless steel (304 SS) by the sol–gel method and heat treatment. Their crystal phase and surface structure were characterized by X-ray diffraction and electron microscopy. The photoelectrochemical performance of the composite films in 3.0% NaCl solution was evaluated by electrochemical measurements under UV irradiation and dark conditions. Since highly conductive MWCNTs in the TiO₂ films can transport the photo-generated electrons easily and quickly to the metal substrate, the MWCNT/TiO₂ composite films exhibited three times the photocurrent and the half the charge transfer resistance of pure TiO₂ films, and provide a much better photocathode protection for 304 SS.     

Preparation of photodegradable polypropylene/clay composites based on nanoscaled TiO2 immobilized organoclay

Photodegradable polypropylene (PP) composites were prepared via melting blending using PP and titanium dioxide (TiO₂) immobilized organically modified montmorillonite (organoclay). TiO₂ immobilized organoclay (TiO₂‐OMT) was synthesized by immobilizing anatase TiO₂ nanoparticles on organically modified clay via sol–gel method. The structure and morphology of TiO₂‐OMT were characterized by XRD and scanning electron microscope (SEM), which showed that anatase TiO₂ nanoparticles with the size range of 8–12 nm were uniformly immobilized on the surface of organoclay layers. Diffuse reflection UV–vis spectra revealed TiO₂‐OMT had similar absorbance characters to that of commercial photocatalyst, Degussa P25. The solid‐phase photocatalytic degradation of PP/TiO₂‐OMT composites was investigated by FTIR, DSC, GPC and SEM. The results indicated that TiO₂‐OMT enhanced the photodegradation rate of PP under UV irradiation. This was due to that immobilization of TiO₂ nanoparticles on organoclay effectively avoided the formation of aggregation, and thereby increased the interface between PP and TiO₂ nanoparticles. After 300 h irradiation, the average molecular weight was reduced by two orders of magnitude. This work presented a promising method for preparation of environment‐friendly polymer nanocomposites. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers.     

Effects of carbon nanotube functionalization on the mechanical and thermal properties of epoxy composites

Chemically functionalized multi-walled carbon nanotube (MWCNT)/bisphenol-A glycidol ether epoxy resin/2-ethyl-4-methylimidazole composites were prepared. MWCNTs were first treated by a 3:1 (v/v) mixture of concentrated H₂SO₄/HNO₃, and then triethylenetetramine (TETA) grafting was carried out. X-ray photoelectron spectroscopy analysis proved the effectiveness of H₂SO₄/HNO₃ treatment and confirmed the TETA functionalization mechanism. Chemical functionalization decreases the crystalline content of MWCNTs, however, it did not greatly disrupt their structure. Transmission electron microscopy showed that there was a TETA thin layer on the MWCNT surface, which contributes to the homogenous dispersion of MWCNTs in epoxy matrix and the improvement of the MWCNT-epoxy interfacial interaction. Thus the impact strength, bending strength and thermal conductivity of the composites are enhanced.     

Visible light photocatalytic degradation of thiophene using Ag–TiO2/multi-walled carbon nanotubes nanocomposite

Ag–TiO₂ nanocatalyst, supported on multi-walled carbon nanotubes, was synthesized successfully via a modified sol–gel method, and the prepared photocatalyst was used to remediate aqueous thiophene environmentally by photocatalytic oxidation under visible light. The prepared Ag–TiO₂/multi-walled carbon nanotubes nanocomposite photocatalyst was characterized through X-ray diffraction, Brunauer–Emmett–Teller (BET), transmission electron microscopy, and UV–vis spectra (UV–vis). The results showed that both Ag and TiO₂ nanoparticles were well-dispersed over the MWCNTs and formed a uniform nanocomposite. Ag doping can eliminate the recombination of electron–hole pairs in the catalyst, and the presence of MWCNTs in the TiO₂ composite can change surface properties to achieve sensitivity to visible light. The optimum mass ratio of MWCNT:TiO₂:Ag was 0.02:1.0:0.05, which resulted in the photocatalyst's experimental performance in oxidizing about 100% of the thiophene in a 600 mg/L solution within 30 min and with 1.4 g L⁻¹ amount of catalyst used.     

PPV/TiO2 hybrid composites prepared from PPV precursor reaction in aqueous media and their application in solar cells

In this work, poly(phenylene vinylene) (PPV) and TiO₂ nanocomposites containing different amounts of TiO₂ were prepared through PPV precursor reaction in aqueous media. The TiO₂ components were introduced into the systems by two methods, i.e. through in situ sol-gel reaction or by mixing commercially available TiO₂ nanoparticles with the PPV precursor before reaction. The composite prepared by mixing commercially available TiO₂ nanoparticles shows perfect crystal character of the anatase TiO₂, but TiO₂ particles severely agglomerate in the PPV matrix. The composite prepared by introducing TiO₂ nanoparticles through the sol-gel reaction shows uniform nanoscale dispersion of anatase TiO₂ in PPV matrix. The UV-vis and FL spectroscopic analyses confirm the formation of the TiO₂/PPV composites and reveal the enhanced PL quenching effect as the TiO₂ content increases. The PPV/TiO₂ composites can show significant photovoltaic response. Better photovoltaic performance is observed for the solar cells prepared by using the in situ sol-gel reaction method.     

Hybridizing MWCNT with nano metal oxides and TiO2 in epoxy composites: Influence on mechanical and thermal performances

In this study, the effects of multi‐walled carbon nanotubes (MWCNT), and its hybrids with iron oxide (Fe₂O₃) and copper oxide (CuO) nanoparticles on mechanical characteristics and thermal properties of epoxy binder was evaluated. Furthermore, simultaneous effects of using MWCNT with TiO₂ as pigment and CaCO₃ as filler for epoxy composites were determined. To investigate effects of nano‐ and micro‐particles on epoxy matrix, the samples were evaluated by TGA and DTA. It was found that the hybrid of MWCNT with nano metal oxides caused considerable increment in the tensile and flexural properties of epoxy samples in comparison to the single MWCNT containing samples at the same filler contents. Significant improvement in the thermal conductivity of epoxy samples was obtained by using TiO₂ pigment along with MWCNT. The TiO₂ pigment also caused considerable improvement in mechanical properties of the epoxy matrix and the MWCNT containing nanocomposite. The best mechanical and thermal properties of epoxy nanocomposites were obtained at 1.5 wt % of MWCNT and 7 wt % of TiO₂ that it should be attributed to particle network forming of the particles which cause better nano/micro dispersion and properties. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43834.     

Influence of MWCTs and nanometal oxide/MWCTs hybrids on the thermal conduction of their acrylic-based nanocomposites

In this study, acrylic-based nanocomposites containing different contents of multi-walled carbon nanotubes (MWCNTs) and metal oxide nanoparticles (i.e., TiO₂, CuO and Fe₂O₃) were fabricated by solvent mixing method. The thermal conductivity of these samples was evaluated. The results indicated that the thermal conductivity of all fabricated samples was significantly improved even at small loading of MWCNTs. It was found that the thermal conductivity was enhanced by increase in MWCNTs content up to 5 wt%. Similarly, the metal oxide nanoparticles caused up to 75 % increment in thermal conductivity at 1.5 wt% of their loading in acrylic film. Contrary to expectations, the thermal conductivity of acrylic film was more increased by nanometal oxides (i.e., TiO₂, CuO and Fe₂O₃) than MWCNTs. The effect of hybridizing of nanometal oxide particles (1.5 wt%) and MWCNTs (1.5 wt%) on thermal conduction was investigated as well. It was found that hybridizing improved thermal conductivities by about 85, 94 and 97 % for Fe₂O₃, TiO₂ and CuO, respectively. Finally, the effects of TiO₂ pigment and CaCO₃ extender on the thermal conductivity of acrylic polymer and nano-TiO₂ acrylic composites were studied. It was found that TiO₂ could increase considerably thermal conduction of its acrylic films and acrylic nanocomposites.     

Ag nanoparticles loaded TiO2/MWCNT ternary nanocomposite: A visible-light-driven photocatalyst with enhanced photocatalytic performance and stability

A visible light active photocatalyst, Ag/TiO₂/MWCNT was synthesized by loading of Ag nanoparticles onto TiO₂/MWCNT nanocomposite. The photocatalytic activity of Ag/TiO₂/MWCNT ternary nanocomposite was evaluated for the degradation of methylene blue dye under UV and visible light irradiation. Ag/TiO₂/MWCNT ternary nanocomposite exhibits (~9 times) higher photocatalytic activity than TiO₂/MWCNT and (~2 times) higher than Ag/TiO₂ binary nanocomposites under visible light irradiation. The enhancement in the photocatalytic activity is attributed to the synergistic effect between Ag nanoparticles and MWCNT, which enhance the charge separation efficiency by Schottky barrier formation at Ag/TiO₂ interface and role of MWCNT as an electron reservoir. Effect of different scavengers on the degradation of methylene blue dye in the presence of catalyst has been investigated to find the role of photogenerated electrons and holes. Simultaneously, the Ag/TiO₂/MWCNT shows excellent photocatalytic stability. This work highlights the importance of Ag/TiO₂/MWCNT ternary nanocomposite as highly efficient and stable visible-light-driven photocatalyst for the degradation of organic dyes.     

The dependence of the photocatalytic activity of TiO2/carbon nanotubes nanocomposites on the modification of the carbon nanotubes

Nanostructural TiO₂/modified multi-wall carbon nanotubes photocatalysts were prepared by hydrolysis of Ti(iso-OC₃H₇)₄ providing chemical bonding of anatase TiO₂ nanoparticles onto oxidized- or amino-functionalized multi-wall carbon nanotubes (MWCNT). The processes of functionalization of the MWCNT and the deposition of TiO₂ influence the photocatalytic activity of the synthesized nanocomposites. The phase composition, crystallite size, and the structural and surface properties of the obtained TiO₂/modified-MWCNT nanocomposite were analyzed from XRD, FEG-SEM, TEM/HRTEM and FTIR data, as well low temperature N₂ adsorption. In the photocatalytic study, the TiO₂/oxidized-MWCNT catalyst showed the highest and the TiO₂/amino functionalized-MWCNT catalysts somewhat lower degradation rates, indicating that the enhancement of photocatalysis was supported by the more effective electron transfer properties of the oxygen- than amino-containing functional groups, which support the efficient charge transportation and separation of the photogenerated electron-hole pairs.     

Hollow porous carbon microspheres obtained by the pyrolysis of TiO2/poly(furfuryl alcohol) composite precursors

Disordered carbon materials with high porosity were prepared through the pyrolysis of TiO₂/poly(furfuryl alcohol) composites, obtained by the sol-gel method. The composites were prepared starting from titanium tetra-isopropoxide (TTIP) and furfuryl alcohol (FA) as precursors. Two different synthetic procedures for our composites were carried out, based on the addition of furfuryl alcohol (FA) before or after the TiO₂ nanoparticles formation. Also, different TTIP/FA ratio was tested. The hybrid materials obtained by both synthetic routes were pyrolyzed, under argon flow, at 900 °C producing novel TiO₂/carbon composites. All samples were characterized by XRD, FT-IR, DR-FTIR, Raman spectroscopy and TEM. Results indicated the effective FA polymerization on TiO₂ (anatase) nanoparticles, and polymer conversion to disordered carbon after the pyrolysis, simultaneously with TiO₂ anatase-rutile phase transition. The resulting TiO₂/carbon composites were treated with HF solution aiming the oxide dissolution, yielding an extremely porous carbon material as insoluble fraction. The morphology of these porous carbon materials is strongly dependent on the synthetic route adopted for the composite precursor, varying from carbon foam to highly ordered hollow microspheres.