In-situ electrochemical doping of nanoporous anodic aluminum oxide with indigo carmine organic dye

• Nanoporous anodic alumina was formed in electrolyte with indigo carmine.
• XPS confirmed the presence of N and S in anodic alumina.
• Raman spectroscopy revealed indigo carmine bands in anodic alumina.
• The higher the voltage, the more indigo carmine was incorporated.

Nanoporous anodic aluminum oxide was formed in sulfuric acid with addition of indigo carmine. During anodizing, the organic dye was incorporated into the porous oxide walls. X-ray photoelectron spectroscopy revealed the presence of nitrogen and sulfur in the anodic aluminum oxide. Two types of incorporated sulfur were found: belonging to the sulfate anions SO42 − of the electrolyte and belonging to the C-SO3− side groups of the indigo carmine. Raman spectroscopy confirmed the incorporation and showed that the inorganic–organic hybrid material inherited optical properties from the indigo carmine. Typical modes from pyrrolidone rings, unique for indigo carmine in the investigated system (650 and 1585 cm− 1), were found to be the strongest for the greatest anodizing voltages used. Despite the indigo carmine incorporation, the morphology of the oxide is still nanoporous and its geometry is still tuned by the voltage applied during aluminum anodization. This work presents an inexpensive and facile approach to doping an inorganic oxide material with organic compounds.