Growth and characterization of CNT–TiO 2 heterostructures (original) (raw)
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Carbon–Inorganic Hybrid Materials: The Carbon-Nanotube/TiO2 Interface
Advanced Materials, 2008
Carbon-inorganic hybrid materials are a new class of functional materials that gained tremendous interest in recent years owing to their exceptional optical, mechanical, electrical, and thermal properties, thus enabling the use in photochemical, catalytic, and electrochemical technologies. [1] Titanium dioxide (TiO 2) is one of the most important transition metal oxides. Its remarkable chemical and physical properties [2] commend it to applications such as gas sensing, [3] photo-chromic devices, [4] photocatalysis (e.g., water and air purification, self cleaning surfaces), [5,6] and ''dye-sensitized TiO 2 solar cells''. [7,8] Generally, for TiO 2 , a large specific surface area is crucial to achieve high (photo)-catalytic activities as well as a good dispersion of adsorbed metals and metal-organic compounds. Thus, the fabrication of TiO 2 with nanometer-scale morphology is of considerable interest. While chemical vapor deposition (CVD) and flame synthesis are possible routes, [9] the sol-gel process provides particularly good control from the molecular precursor to the final product, as well as giving high purity and homogeneity. [10,11] In recent years, there has been considerable progress in the production of novel functional materials by coupling TiO 2 with other inorganic/organic materials. [12,13] For instance, Kamat et al. reported that combining single-walled carbon nanotubes (SWCNTs) with TiO 2 in a photovoltaic device enhanced the photoconversion efficiency from 7 to 15%. [14] A further increase would crucially depend on the improvement of the CNT/TiO 2 interface. CNTs have also been used to improve the mechanical performance of thin-film TiO 2. [15,16] Other workers have dispersed CNTs in a TiO 2 sol [17] and studied the immobilization of TiO 2 on CNTs, [18,19] while CNTs can be applied to the synthesis of various inorganic nanotubes. [13,20,21] Recently, we showed that CNTs could support the anatase coating during its phase transformation into rutile, leading to the first synthesis of rutile nanotubes. [22] CNTs straight from CVD synthesis (pristine CNTs) are hydrophobic and thus need to be functionalized with hydrophilic organic groups to provide attractive interaction with the titanium sol. [13,17] Such groups are typically attached
Synthesis and characterization of carbon nanotubes–TiO 2 nanocomposites
Carbon, 2004
The main objective of this paper is to coat carbon multiwall nanotubes surface with TiO 2 as anatase in view of photocatalytic application for these nanocomposites. Carbon nanotubes were produced by catalytic decomposition of acetylene at 600°C. The coating was performed by a sol-gel method using classical alkoxides as Ti(OEt) 4 and Ti(OPr i ) 4 and by hydrothermal hydrolysis of TiOSO 4 , leading to different TiO 2 morphologies. In using the sol-gel method, nanotubes are coated either with a continuous TiO 2 thin film when the precursor is Ti(OEt) 4 , or with TiO 2 nanoparticles when the precursor is Ti(OPr i ) 4 . By hydrothermal treament, more compact and crystalline nanocomposites are obtained.
Morphology control of CNT-TiO2 hybrid materials and rutile nanotubes
Journal of Materials Chemistry, 2008
Carbon nanotube-inorganic hybrid materials are a new class of functional materials that has gained tremendous interest in recent years due to their exceptional optical, mechanical, electrical and thermal properties. The hydrophobicity of the carbon nanotubes's surface disfavours the adsorption of hydrophilic particles, thus limiting the quality and performance of the hybrid material. We demonstrate that using benzyl alcohol as a surfactant enables TiO 2 to interact with the hydrophobic surface of pristine CNTs without the need of covalent functionalisation. The quality of the TiO 2 coating is strongly affected by various reaction conditions, including the order of mixing, the choice of drying method, and the water concentration. Furthermore, the effect of heat treatment on the crystallisation of amorphous TiO 2 to anatase and the phase transformation from anatase to rutile is discussed in detail. The key achievement of this work is the control of morphology and structure of the TiO 2 coating and, after removal of the CNTs, of the rutile nanotubes, which also allows the production of the ideal CNT-TiO 2 hybrid material for the desired photochemical, catalytic and sensor applications.
Applied Catalysis B-environmental, 2011
Combining carbon nanotubes (CNTs) with TiO 2 at the nano-scale level can promote the separation of the electron-hole charges generated upon irradiation. However, charge separation capability depends on the quality of the interfacial contact between CNTs and TiO 2 , and on the morphological and surface properties of the nanocomposites. In this study, CNT/TiO 2 nanocomposites with tailored uniform core-shell coatings were fabricated from different titania precursors (titanium ethoxide (TEOTi), titanium isopropoxide (TTIP) and titanium butoxide (TBT)) by surfactant wrapping sol-gel method. This method produces a uniform and well-defined nanometer-scale anatase titania (TiO 2 ) layer on individual CNT (multi-walled), producing a mesoporous nanocomposite film. The composites were characterized by a range of analytical techniques including TEM, XRD, BET, TGA and UV-vis to reveal the textural, crystallographic and optical properties of the composites. The nanocomposites produced from the different Ti precursors exhibited significant differences in photocatalytic activity and photocurrent within the experimental range. A thinner TiO 2 layer provides shorter distance for electron transfer to the CNT core enhancing photocatalytic activity (degradation of methylene blue). However, higher CNT content in the composites correlates with higher photocurrents. It is shown that TiO 2 film thickness is the key factor controlling electron transfer and photocatalytic activity in CNT/TiO 2 nanocomposites with a core-shell structure, when the catalyst is applied in an irradiated slurry suspension. However, it is the electronic conductivity of the nanocomposite catalyst film, which increases with CNT content that controls the rate of electron removal from the photocatalyst when it is subject to an external positive bias in an appropriate photo-electrochemical cell. Overall, the CNT/TiO 2 composite prepared from TBT performed significantly better than those prepared from TEOTi and TTIP.
Synthesis of a CNT-grafted TiO2 nanocatalyst and its activity triggered by a DC voltage
Nanotechnology, 2007
Carbon nanotube (CNT)-grafted TiO 2 (CNT/TiO 2 ) was synthesized as an electrically conductive catalyst that exhibits redox ability under electrical excitation besides ultraviolet (UV) irradiation. The CNT/TiO 2 material was synthesized by a two-step process. Ni nanoparticles were photodeposited onto TiO 2 first. The Ni nanoparticles then served as seeds for the growth of CNTs using the chemical vapor deposition (CVD) of C 2 H 2 . The CNT/TiO 2 nanocomposite exhibits strong oxidation activity toward NO gas molecules via both photocatalysis under UV irradiation and electrocatalysis under a DC voltage of 500 V in dark conditions.
Journal of Clean Energy Technologies, 2015
We report the photo-electro-chemical properties of Carbon Quantum Dots (CQD) functionalised TiO 2 nanotube arrays (TNA). The TNA formed by electrochemical anodization of a Ti foil offer highly aligned, vertically oriented nanostructures suitable for photo-catalytic application. These nanostructures are functionalised with CQDs synthesized by the electrochemical etching of graphite and the resultant samples are characterized by high resolution transmission electron microscopy, photo-current and photon-charge conversion efficiency measurements, Mott-Schottky and impedance spectroscopy. The results indicate that the nanotubes with larger diameter can support a higher density of CQDs and hence shows better values for photo-current and light conversion efficiency. Furthermore, these samples offer a lower charge transfer resistance across the semiconductorelectrolyte interface. The CQD functionalised TiO 2 nanotubesarrays with suitable diameter can therefore be used for efficient hydrogen generation by water splitting under the illumination of solar radiation. Index Terms-TiO 2 , carbon quantum dot (CQD), photoelectro-chemical, clean energy.
Synthesis of N-CNT/TiO2 composites thin films: surface analysis and optoelectronic properties
E3S Web of Conferences
In this study, we have investigated the surface analysis and optoelectronic properties on the synthesis of N-CNT/TiO2 composites thin films, using sol gel method for a dye synthetized solar cell (DSSC) which is found to be simple and economical route. The titanium dioxide based solar cells are an exciting photovoltaic candidate; they are promising for the realization of large area devices. That can be synthetized by room temperature solution processing, with high photoactive performance. In the present work, we stated comparable efficiencies by directing our investigation on obtaining Sol Gel thin films based on N-CNT/TiO2, by dispersing nitrogen (N) doped carbon nanotubes (N-CNTs) powders in titanium tetraisopropoxyde (TTIP). The samples were assessed in terms of optical properties, using UV—visible absorption spectroscopic techniques. After careful analysis of the results, we have concluded that the mentioned route is good and more efficient in terms of optoelectronic properties. ...
Carbon nanotubes (CNTs) coated with titanium oxide (TiO2) have generated considerable interest over the last decade and become a promising nanomaterial for a wide range of energy applications. The efficient use of the outstanding electrical properties of this nanostructure relies heavily on the quality of the interface and the thickness and morphology of the TiO2 layer. However, complete surface coverage of the chemically inert CNTs and proper control of the morphology of the TiO2 layer have not been achieved so far. Here, we report a new strategy to obtain ultrathin TiO2 coatings deposited by " Temperature-step " Atomic Layer Deposition (TS-ALD) with complete surface coverage of non-functionalized multiwall carbon nanotubes (MWCNTs) and controlled morphology and crystallinity of the TiO2 film. This strategy consists in adjusting the temperature during the ALD deposition to obtain the desired morphology. Complete coverage of long non-functionalized MWCNTs with conformal anatase layers were obtained by using a low temperature of 60°C during the nucleation stage followed by an increase to 220°C during the growth stage. This resulted in a continuous and amorphous TiO2 layer, covered with a conformal anatase coating. Starting the deposition at 220 °C and reducing to 60 °C resulted in sporadic crystal grains at the CNT/TiO2 interface covered with an amorphous TiO2 layer. The results were accomplished through an extensive study of nucleation and growth of titanium oxide films on MWCNTs of which a detailed characterization is presented in this work.
Advanced Materials, 2011
Titanium dioxide (TiO 2) has been studied extensively due to its attractive physical and chemical properties such as high chemical stability, mechanical resistance, and high optical transmittance in the infrared-visible spectrum. TiO 2 thin fi lms are used for antirefl ection coatings, optical interference fi lters, and optical waveguides. [ 1-3 ] Moreover, they also exhibit interesting photoelectrochemical properties [ 4-7 ] in dye-sensitized solar cells [ 8 , 9 ] and sensor arrays. [ 10 , 11 ] When oxide is deposited onto single-walled carbon nanotubes (SWCNTs), it produces a photodiode effect. This also produces a short-circuit photocurrent due to the reduced kinetic recombination of excitons when a charge is transferred across the interface. [ 12-14 ] Typically, two TiO 2 polymorphs are used. Anatase exhibits a signifi cantly higher photoelectrochemical activity than rutile. This is because the bandgap of anatase (≈ 3.2 eV) is larger than that of rutile (≈ 3.0 eV), resulting in a higher redox potential. Another reason is that anatase has a higher area density of surface hydroxyls, which slows the recombination of photogenerated electron-hole pairs. [ 15 ] However, commercial TiO 2 powders consisting of mixed rutile and anatase, such as Degussa P25, have a higher level of photoelectrochemical activity than single-phase materials. The enhanced photoelectrochemical activity supposedly is due to the spatial charge separation across the anatase/rutile interfaces as a result of a staggered band alignment. [ 16 ] The researchers have found that TiO 2 /MWCNT(multiwalled carbon nanotube) composites show improved photocatalysis [ 17 , 18 ] , but they do not enhance the photocatalytic activity of www.advmat.de www.MaterialsViews.com
2015
ABSTRAK ii ACKNOWLEDGEMENTS iii APPROVAL iv DECLARATION vi LIST OF TABLES x LIST OF FIGURES xi LIST OF SYMBOLS xiii LIST OF ABBREVIATIONS xiv CHAPTER 1 NANOMATERIAL AND NANOTECHNOLOGY 1.1 Introduction 1.2 Problem Statement 1.3 Research Objectives 1.4 Scope of the research 1.5 Significance of the research 1.6 Thesis outline 2 LITERATURE REVIEW 2.1 Introduction 2.2 Titanium dioxide (TiO2) 2.3 Carbon nanotube 2.4 Deposition of TiO2 on CNTs surface 2.5 Characterization of CNTs/TiO2 nanocomposite 2.6 Photocatalytic activity of CNT/TiO2 nanocomposites 2.6.1 Light intensity 2.6.2 pH of the solution 2.6.3 Reaction temperature 2.6.4 Photocatalyst concentration 2.6.5 Concentration of the pollutant 3 THEORY 3.1