Spectral tuning of biotemplated ZnO photonic nanoarchitectures for photocatalytic applications

The photocatalytic activity of a flat surface can be increased by micro-
and nanostructuring the interface to increase the area of the contact
surface between the photocatalyst and the solute, moreover, optimize
charge carrier transfer. Further enhancement can be achieved by using
photonic nanostructures, which exhibit photonic band gap (PBG).
Structurally colored butterfly wings offer a rich “library” of PBGs in the
visible spectral range which can be used as naturally tuned sample sets
for biotemplating. We used conformal atomic layer deposition (ALD) of ZnO
on the wings of various butterfly species (Arhopala asopia, Hypochrysops
polycletus, Morpho sulkowskyi, Polyommatus icarus) possessing structural
color extending from the near UV to the blue wavelength range, to test the
effects arising from the nanostructured surfaces and from the presence of
different types of PBGs. Aqueous solutions of rhodamine B were used to
test the enhancement of photocatalytic activity that was found for all ZnO
coated butterfly wings. The best reaction rate of decomposing rhodamine B
when illuminated with visible light was found in 15 nm ZnO coated M.
sulkowskyi wing the reflectance of which had the highest overlap with the
absorption band of the dye and had the highest reflectance intensity.