Synthetic melanin nanoparticles and films are attracting attention due to their simple preparations, low production costs, and wide applications. However, the spontaneous auto-oxidation of melanin precursors of different monomers is more often affected by several factors including the experimental design and the type of melanin precursors. A feasible method has been developed to synthesize melanin from the dihydroxy indole precursor in an aqueous medium at normal conditions.

Here, we prepared two sets of polymeric melanin, one is dispersed nanoparticles in aqueous solution and the other is homogeneous melanin thin films electrodeposited on glass and steel substrates. Both sets were adjusted efficiently to remove dyes contaminants from water samples. Dyes, highly colored organic compounds, are widely used in industries such as textiles, food, tanning, paper, and photoelectrochemical cells. Over usage of these colors causes residues that contaminate drinking water sources and disrupt the natural system. Thus, proper cost-effective treatment options for contaminated wastewater seem essential.

In this project, we tested or newly synthesized melanin against the removal of various dyes including methylene blue and alizarin. Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) analysis were used to characterize the morphology and surface chemistry of melanin nanostructures. Our system has been optimized to enhance the adsorption capacity about 3-fold than normal ranges. Interestingly, the synthesized polymeric melanin moiety can be reused effectively for adsorption and removal of different dyes, indicating the possibility for melanin materials to be utilized in water purification.