| Summary: | We create ordered arrays of shape-selective gold-titania composite nanomaterials at the mesoscale (100 µm to 5 mm) by a combination of both bottom-up and top-down approaches for exquisite control of the size, shape, and arrangement of nanomaterials. Lithographic techniques along with wet chemical synthetic methods were combined to create these composite nanomaterials. The photocatalytic activity of these TiO<sub>2,</sub> TiO<sub>2</sub>-Au and SiO<sub>2</sub>-TiO<sub>2</sub>-Au nano-composite mesoscale materials was monitored by the photodegradation of a model analyte, methyl orange, under UV and visible (Vis) illumination. Bare TiO<sub>2</sub>- and SiO<sub>2</sub>-TiO<sub>2</sub>-coated pillar arrays showed significant activity toward methyl orange in UV light with degradation rates on the order of 10<sup>−4</sup>–10<sup>−3</sup> min<sup>−1</sup>. The photocatalytic activity of these arrays was also found to depend on the nanoparticle shape, in which particles with more edges and corners were found to be more reactive than spherical particles (i.e., the photocatalytic activity decreased as follows: diamonds > squares > triangles > spheres). SiO<sub>2</sub>-TiO<sub>2</sub>-Au nano-composite pillar arrays were tested in both UV and Vis light and showed increased activity in Vis light but decreased activity in UV light as compared to the bare semiconductor arrays. Additionally, the Au nanorod-functionalized nanoarrays exhibit a strong shape-dependence in their photocatalytic activity toward methyl orange degradation in Vis light.
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