Anatase nanotubes synthesized by a template method and their application as a green photocatalyst

J Mater Sci DOI 10.1007/s10853-010-5044-9

Anatase nanotubes synthesized by a template method and their application as a green photocatalyst
´ I. Tacchini • E. Terrado • A. Anson ´ M. T. Martınez
•

Received: 3 August 2010 / Accepted: 30 October 2010 Ó Springer Science+Business Media, LLC 2010

Abstract Anatase nanotubes were synthesized by a template method from four different titaniumprecursors. Anodized aluminium oxide membranes with a 200-nm pore diameter were used as templates. The resulting nanostructures were characterized by electron microscopies, Raman spectroscopy, X-ray diffraction and nitrogen adsorption. Their photoactivities towards methylene blue dye decomposition were measured and compared with commercial anatase powder (Aldrich, [99%, -325 mesh). Anatasenanotubes obtained from Ti isopropoxide exhibited the longest hollow tubular structures with less amorphous material and the highest surface area, 56 m2 g-1. Despite TiO2 nanotubes showing lower photocatalytic activity than commercial anatase, the possibility of their recovery through several cycles and the feasibility of their utilization in continuous cycling processing make them potential materials ofinterest in green chemistry

Introduction The photoinduced mechanism [1] that takes place in titanium oxide (TiO2) has been studied since the end of the 1960s. This process has been given a wide range of applications in several fields such as photovoltaics [2, 3], environmental photocatalysis [4], and most recently, in the area of superhydrophilicity [5, 6]. Even though all photoinduced phenomenaimply surface bound redox reactions, it is important to note that the type of photochemistry involved in photocatalysis reactions and hydrophilicity
´ ´ I. Tacchini Á E. Terrado (&) Á A. Anson Á M. T. Martınez ´ ´ Instituto de Carboquımica, CSIC, Miguel Luesma Castan 4, 50018 Zaragoza, Spain e-mail: eterrado@icb.csic.es

phenomena is completely different and can occur simultaneously on thesame surface [7]. Absorption of a photon with sufficient energy by a TiO2 crystal leads to a charge separation owing to an electron promotion to the conduction band and a resulting hole in the valence band [8]. The electron–hole pair tends to migrate to the crystal surface. If the pair reaches the surface without recombination, then use can be made of the hole or the electron (depending on the finalapplication), e.g. for electrical current generation in photovoltaic solar cells, for hydrogen production or for antifogging surfaces [2–6]. Another interesting application for TiO2 has been found in the field of self-cleaning surfaces and contaminant destruction. One example of these undesirable substances is dye. Large amounts of dyes are produced by industry every year, and their uncontrolleddischarge into bodies of water can cause drastic damage to the aquatic environment [9]. Dyes are environmentally harmful even at low concentrations because of the induced change in the colour of water. This effect is deeply unpleasant because it limits the access to sunlight by aquatic flora, reducing the photosynthetic action within the ecosystem [10]. Dye elimination is complicated by conventionalwaste water treatments owing to its inherent high values of chemical oxygen demand (COD) and biochemical oxygen demand (BOD). In this context, heterogeneous photocatalysis may be used as an alternative solution for dye degradation, and TiO2 could be a considerable candidate because of its high catalytic efficiency, high chemical stability, low cost and nontoxic nature. However, TiO2 suspensions inwater show high stability, which hinders separation of the catalyst from water and, consequently, its recovery and reuse [11]. A viable solution to this drawback could be found in developing new TiO2-based morphologies in nanostructured materials.

123

J Mater Sci

Anatase and rutile are the photosensitive crystalline phases of TiO2. The required energy for the electron promotion from the...