A Facile Approach for Controlling the Orientation of One- Dimensional Mesochannels in Mesoporous Titania Films Feng Shan, † Xuemin Lu,* ,† Qian Zhang, † Jun Wu, † Yuzhu Wang, ‡ Fenggang Bian, ‡ Qinghua Lu,* ,† Zhaofu Fei, § and Paul J. Dyson § † School of Chemistry and Chemical Engineering, the State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University, Shanghai 200240, P.R. China ‡ Shanghai Synchrotron Radiation Facility, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 200240, P.R. China § Institut des Sciences et Ingé nierie Chimiques, Ecole Polytechnique Fé de ́ rale de Lausamne (EPFL), CH-1015, Lausanne, Switzerland * S Supporting Information ABSTRACT: Controlling of the orientation of meso- channels in mesostructured thin films is important for the development of novel molecular devices and, in particular, generating vertically aligned mesochannels with respect to the substrate plane is extremely challenging for nonsili- ceous materials. We describe a facile and highly effective air flow method, which is able to control the unidirectional alignment of titania mesochannels in a desired direction (e.g., parallel, perpendicular, or oblique) on a large scale, via manipulation of the air flow rate and incident angle. The titania mesochannels were characterized by TEM, SEM, SAXRD, and GISAXS. The unidirectional, vertically aligned mesostructured titania films were found to exhibit excellent ion conductivity. P olymer-templated mesostructured organic/inorganic hy- brid materials and their corresponding calcined meso- porous derivatives provide a route to prepare a large range of mesostructures with tailor-made properties. 1 The fine control of one-dimensional (1D) channels of such mesomaterials in a certain direction is of considerable interest due to the demand for novel molecular-scale devices. 2 Previous attempts have been made to develop mesostructured films with uniform pore orientation, and the alignment of mesochannels parallel to the substrate surface has been achieved with silica films using external fields 3 and anisotropic surfaces, 4 thereby affording materials with macroscopically anisotropic properties. 5 Com- pared to parallel mesochannels in mesoporous films, vertical alignment of mesochannels with respect to the surface is much more difficult to achieve, although highly desirable, because such ordered mesoporous structures can provide transmission channels for electrons, ions, and fluids, which are especially suited to solar cells, fuel cells, separation technologies, etc. 6 In spite of intensive efforts, only a few examples describing the preparation of vertically aligned mesochannels have been reported. Magnetic fields of the order of 10-30 T 3c,7 and confinement in anodized alumina channels 6b have been used to generate vertical channels in mesoporous thin films, but these methods are limited to small areas. Mesoscale epitaxial-like growth may be used to obtain vertical alignment of channels, 6d,8 but alignment over an entire surface has not been achieved. Vertical channels were obtained in silica films via cathodic electrodeposition; however, the thickness of the ordered mesoporous film is limited to the range 40-150 nm. 3e Moreover, most of these pioneering studies have focused on silica frameworks. In an excellent and recent review on mesoporous films the major challenges in this field were identified, which include the precise control of 1D mesochannels in any direction and the realization of well-ordered alignments of mesoporous thin films based on materials other than silica. 2b,9 In this contribution we describe a simple and effective method that addresses these two major challenges, thus allowing the preparation of uniaxially oriented mesoporous titania films in any uniaxial alignment direction via the manipulation of the magnitude and incident direction of a shear-force in a hot-air flow. This approach builds on our previous work in which silica mesochannels oriented in parallel were obtained. 3f To precisely control the orientation of the mesopores in the film two parameters need to be controlled, the incident angle of the air jet with respect to the surface plane and the rate of solvent evaporation, the latter is determined by the temperature and the air flow rate. To demonstrate the approach, drops of a titania sol precursor were pipetted directly onto a clean silicon wafer to form a liquid film, and then a jet of hot air at a constant temperature of 70 °C was applied over the substrate surface for 10 s (the air flow speed was varied from 9.5-5.5 m/ s, and the incident angle α was varied from 0-70°; α refers to the incident angle subtended between the substrate plane and the incident air flow), followed by aging at 20 °C for 24 h under a controlled humidity of ∼70-80%. On the basis of comparisons to literature data, 10 the obtained titania films were shown to comprise 2D hexagonal mesophase (p6mm). Transmission electron microscopy (TEM) of the powders scraped off the films and small-angle X-ray diffraction (SAXRD) of films annealed at 200 °C further confirm the 2D hexagonal structure (Figure 1), with a lattice spacing of d = 9.4 nm. Examination of these films by cross-sectional TEM revealed that the gas flow rate effectively controls the alignment of the Received: September 15, 2012 Published: December 5, 2012 Communication pubs.acs.org/JACS © 2012 American Chemical Society 20238 dx.doi.org/10.1021/ja309168f | J. Am. Chem. Soc. 2012, 134, 20238-20241