Preparation of a novel TiO2-based p-n junction nanotube photocatalyst

Preparation of photocatalytic anatase nanowire films by in situ oxidation of titanium plate

Photocatalytic anatase TiO2 nanowire thin films have been prepared by in situ oxidation of Ti plate in a mixture solution of concentrated H(2)O(2) and NaOH, followed by proton exchange and calcination. The morphologies and properties of the titanate and titania films have been investigated by means of field emission scanning electron microscopy, energy-dispersive x-ray spectrometry, high resolution transmission electron microscopy, x-ray diffraction and Raman spectrometry. The mechanism of formation of the porous microstructure has been discussed; it is the result of the balance between dissolution and precipitation. And sodium ions in the solution are needed to combine with titanate species for the nanowire formation. The anatase TiO2 nanowire thin films exhibited enhanced photocatalytic activity and stability in phenol degradation. The combination effects of the porous morphology and nanowire characteristics are favorable for improved photocatalytic performance. This novel nanowire film is promising for practical aqueous purification.

Effects of structure of anodic TiO(2) nanotube arrays on photocatalytic activity for the degradation of 2,3-dichlorophenol in aqueous solution

In this study titanium dioxide nanotube (TNT) arrays were prepared by an anodic oxidation process with post-calcination. The morphology and structure of the TNT films were studied by field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Photocatalytic activity of the TNT films was evaluated in terms of the degradation of 2,3-dichlorophenol in aqueous solution under UV light irradiation. The effects of the nanotube structure including tube length and tube wall thickness, and crystallinity on the photocatalytic activity were investigated in detail. The results showed that the large specific surface area, high pore volume, thin tube wall, and optimal tube length would be important factors to achieve the good performance of TNT films. Moreover, the TNT films calcined at 500 degrees C for 1h with the higher degree of crystallinity exhibited the higher photocatalytic activity than other TNT films calcined at 300 and 800 degrees C. Consequently, these results indicate that the optimization of TiO(2) nanotube structures is critical to achieve the high performance of photocatalytic reaction.

Efficiency of clay--TiO2 nanocomposites on the photocatalytic elimination of a model hydrophobic air pollutant

Clay-supported TiO2 photocatalysts can potentially improve the performance of air treatment technologies via enhanced adsorption and reactivity of target volatile organic compounds (VOCs). In this study, a benchtop photocatalytic flow reactor was used to evaluate the efficiency of hectorite-TiO2 and kaolinite-TiO2, two novel composite materials synthesized in our laboratory. Toluene, a model hydrophobic VOC and a common indoor air pollutant, was introduced in the air stream at realistic concentrations, and reacted under UVA (lamda(max) = 365 nm) or UVC (lamda(max) = 254 nm) irradiation. The UVC lamp generated secondary emission at 185 nm, leading to the formation of ozone and other short-lived reactive species. Performance of clay-Ti02 composites was compared with that of pure TiO2 (Degussa P25), and with UV irradiation in the absence of photocatalyst under identical conditions. Films of clay-TiO2 composites and of P25 were prepared by a dip-coating method on the surface of Raschig rings, which were placed inside the flow reactor. An upstream toluene concentration of approximately 170 ppbv was generated by diluting a constant flow of toluene vapor from a diffusion source with dry air, or with humid air at 10, 33, and 66% relative humidity (RH). Toluene concentrations were determined by collecting Tenax-TA sorbent tubes downstream of the reactor, with subsequent thermal desorption--GC/MS analysis. The fraction of toluene removed, %R, and the reaction rate, Tr, were calculated for each experimental condition from the concentrations measured with and without UV irradiation. Use of UVC light (UV/TiO2/O3) led to overall higher reactivity, which can be partially attributed to the contribution of gas phase reactions by short-lived radical species. When the reaction rate was normalized to the light irradiance, Tr/Ilamda,the UV/TiO2 reaction under UVA irradiation was more efficient for samples with a higher content of TiO2 (P25 and Hecto-TiO2), but notfor Kao-TiO2. In all cases, reaction rates peaked at 10% RH, with Tr values between 10 and 50% higherthan those measured under dry air. However, a net inhibition was observed as RH increased to 33% and 66%, indicating that water molecules competed effectively with toluene for reactive surface sites and limited the overall photocatalytic conversion. Compared to P25, inhibition by coadsorbed water was less significant for Kao-TiO2 samples, but was more dramatic for Hecto-TiO2 due to the high water uptake capacity of hectorite.

Fabrication of highly-ordered TiO(2) nanotube arrays and their use in dye-sensitized solar cells

Highly ordered TiO(2) nanotubes were successfully fabricated using a nanoporous alumina templating method. A modified sol-gel route was used to infiltrate the alumina pores with Ti(OC(3)H(7))(4) which was subsequently converted into TiO(2) nanotubes. The average external diameter, tube lengths, and wall thickness achieved were 295 nm, 6-15 microm, and 21-42 nm, respectively. Diffraction data reveals that the nanotubes consist solely of the anatase phase. Dye-sensitized solar cells using TiO(2) nanotube arrays as the working electrode yielded power conversion efficiencies as high as 3.5% with a maximum incident photon-to-current conversion efficiency of 20% at 520 nm.

Design of BDD-TiO2 hybrid electrode with P-N function for photoelectroatalytic degradation of organic contaminants

P-N hybrid electrode of boron-doped diamond (BDD) and TiO2 were designed and fabricated via selective deposition of TiO2 onto BDD electrode. This hybrid electrode exhibit high photoelectrocatalytic activities toward degradation of acid orange II (AOII) and 2, 4-dichloropheonl (2,4-DCP) due to the P-N effect and high electrocatalytic and photocatalytic activities of BDD electrode and TiO2 particles. The structures of TiO2 and BDD were confirmed by Raman spectra analysis. Atom force microscopy and scanning electron microscopy showed that the TiO2 deposits consist of adherent nanomicro-sized particles, scattered on the BDD substrate. AOII and 2,4-DCP in a solution can be efficiently degraded at the hybrid electrode in the photoelectrocatalysis (PEC) process. Effect of applied bias potentials and solution pH values on AOII and 2,4-DCP degradation were investigated. In the electro-oxidation process, some intermediates such as phenols were detected and they accumulated with the reaction evolution based on the analysis of UV-vis and GC-MS variation. By contrast, phenols intermediates will be degraded with the reaction evolution in the photoelectrocatalysis process. And, organic aromatic and aliphatic carboxylic acids were detected. Furthermore, different degradation mechanism of AOII and 2,4-DCP in the electro-oxidation, photocatalysis, and photoelectrocatalysis is proposed.

Photoreactive TiO2/carbon nanotube composites: synthesis and reactivity

Electron-hole recombination limits the efficiency of TiO2 photocatalysis. We have investigated the efficacy with which anatase/carbon nanotube (CNT) composite materials reduce charge recombination and enhance reactivity. We synthesized nanostructured assemblies composed of different proportions of anatase (5 or 100 nm) and either single-or multi-walled CNTs. The composites were prepared using a simple low temperature process in which CNTs and anatase nanoparticles were dispersed in water, dehydrated at 80 degrees C, and dried at 104 degrees C. The structures of the various TiO2/CNT composites were characterized by scanning electron microscopy (SEM) and their function was tested by phenol oxidation. Charge recombination was compared by measuring the photoluminescence spectra of select composites. We found that a nanostructured composite assembled from the 100 nm anatase and single-walled CNTs (SWCNTs) exhibited enhanced and selective photocatalytic oxidation of phenol in comparison to both pure anatase and Degussa P25. A mechanism for the enhanced reactivity is proposed in which electrons are shuttled from TiO2 particles to the SWCNTs as a result of an optimal TiO2/ CNT arrangement that stabilizes charge separation and reduces charge recombination. In addition, the SWCNT assembly provides better catalyst-support (dispersal and connection) than multi-walled CNTs.

Preparation and activity evaluation of p-n junction photocatalyst NiO/TiO2

p-n Junction photocatalyst NiO/TiO2 was prepared by sol-gel method using Ni(NO3)2.6H2O and tetrabutyl titanate [Ti(OC4H9)4] as the raw materials. The p-n junction photocatalyst NiO/TiO2 was characterized by UV-vis diffuse reflection spectrum, X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The photocatalytic activity of the photocatalyst was evaluated by photocatalytic reduction of Cr2O7(2-) and photocatalytic oxidation of rhodamine B. The results show that, for photocatalytic reduction of Cr2O7(2-), the optimum percentage of doped-NiO is 0.5% (mole ratio of Ni/Ti). The photocatalytic activity of the p-n junction NiO/TiO2 is much higher than that of TiO2 on the photocatalytic reduction of Cr2O7(2-). However, the photocatalytic activity of the p-n junction photocatalyst NiO/TiO2 is much lower than that of TiO2 on the photocatalytic oxidation of rhodamine B. Namely, the p-n junction photocatalyst NiO/TiO2 has higher photocatalytic reduction activity, but lower photocatalytic oxidation activity. Effects of heat treatment on the photocatalytic activity of p-n junction photocatalyst NiO/TiO2 were investigated. The mechanisms of influence on the photocatalytic activity were also discussed by the p-n junction principle.

Nanotechnology and water treatment: applications and emerging opportunities

Nanotechnology, the engineering and art of manipulating matter at the nanoscale (1-100 nm), offers the potential of novel nanomaterials for treatment of surface water, groundwater, and wastewater contaminated by toxic metal ions, organic and inorganic solutes, and microorganisms. Due to their unique activity toward recalcitrant contaminants and application flexibility, many nanomaterials are under active research and development. Accordingly, literature about current research on different nanomaterials (nanostructured catalytic membranes, nanosorbents, nanocatalysts, and bioactive nanoparticles) and their application in water treatment, purification and disinfection is reviewed in this article. Moreover, knowledge regarding toxicological effects of engineered nanomaterials on humans and the environment is presented.

Microwave-assisted synthesis of anatase TiO(2) nanorods with mesopores

Pure anatase TiO(2) nanorods with mesopores were synthesized by a simple and low cost microwave-assisted method when tri-block copolymer was used as a structure stabilization agent and TiCl(4) as metal precursor. TEM investigation showed that larger nanorods were assembled by pearl-necklace-shaped nanorods following an oriented attachment mechanism in a specific direction. A proposed hypothetical scheme showed that the formation of lyotropic titania liquid crystal (TLC) serves a key role in the stabilization of nanorods, and the mesopores on nanorods are derived from the vacancy of inter-particles of nanorods and regions lacking inorganic precursors in the TLC structure. Control experiments showed that microwave treatment plays a key role in the maintenance of original morphologies and mesostructures free from destruction even under high temperature calcinations.