Highly Efficient Formation of Visible Light Tunable TiO2-xNx Photocatalysts and Their Transformation at the Nanoscale

Abstract

Using a simple nanoscale exclusive synthesis route, TiO 2 - x N x photocatalysts that can be tuned to absorb across the visible region are produced in seconds at room temperature . The photocatalysts are formed by employing the direct nitridation of anatase TiO 2 nanostructures with alkylammonium salts. Depending on the degree of TiO 2 nanoparticle agglomeration, catalytically active TiO 2 - x N x anatase structured particles are obtained whose absorption onset extends well into the visible region at λ ∼ 550 nm. The introduction of a small quantity of palladium in the form of the chloride or nitrate facilitates further nitrogen uptake, appears to lead to a partial phase transformation, displays a counterion effect when compared also to the acetate, and produces a material absorbing well into the near-infrared. The introduction of palladium via the chloride also facilitates the formation of small tetrahedral and octahedral palladium-based crystallites throughout the TiO 2 - x N x lattice. Surprisingly, no organics appear to be incorporated into the final TiO 2 - x N x products. The resulting photocatalysts readily photodegrade methylene blue and lead to the catalytic oxidation of ethylene as they are placed as gels on surfaces. In contrast to the current nitridation process, which is quite facile at the nanoscale, we observe a much slower nitration of Degussa P25 nanopowders and little or no direct nitridation of micrometer-sized anatase or rutile TiO 2 powders at room temperature. We thus demonstrate an example of how a traversal to the nanoscale can vastly improve the efficiency for producing important submicron materials.