  Titanium dioxide (TiO$_2$) thin films are commonly used as photocatalytic
materials. Here, we enhance the photocatalytic activity of devices based on
TiO$_2$ by combining nanostructured glass substrates with metallic plasmonic
nanostructures. We achieve a three-fold increase of the catalyst's surface area
through nanoscale three-dimensional patterning of periodic conical grids, which
creates a broadband optical absorber. The addition of aluminum and gold
activates the structures plasmonically and improves the optical absorption in
the TiO$_2$ films to above 70% in the visible and NIR spectral range. We
demonstrate the resulting enhancement of the photocatalytic activity with
organic dye degradation tests under different light sources. Furthermore, the
pharmaceutical drug Carbamazepine, a common water pollutant, is reduced in
aqueous solution by up to 48% in 360 minutes. Our approach is scalable and
potentially enables future solar-driven wastewater treatment.
