Natural melanin/TiO2 hybrids for simultaneous removal of dyes and heavy metal ions under visible light

Melanin has attracted researchers' attention in recent years due to its intriguing properties and various applications in different fields. Here, we fabricated a highly efficient photocatalytic material through utilizing the natural melanin (NM) isolated from textile scraps like yak hair wastes. A simple one-step process was employed to synthesize titanium dioxide (TiO2) nanoparticles on the surface of NM. The synthesized NM/TiO2 hybrids exhibited prominent photocatalytic activity for the simultaneous removal of methyl orange (MO) and hexavalent chromium ions (Cr (VI)) under visible light irradiations, which constitute similar to 45 % of the solar light. Our results revealed that NM served as a base material with abundant catechol groups to form C-O-Ti bonds with TiO2 nanoparticles, which narrowed the band gap and broadened the light response of the hybrids. The working mechanism of NM/TiO2 hybrids for the simultaneous removal of dyes (MO) and heavy metal ions (Cr (VI)) was thoroughly explored and proposed. This work highlighted the potential of the NM/TiO2 hybrids for textile dyeing effluent treatment with more efficient utilization of solar spectrum. Our work also opens a pathway for the design of advanced NM-based functional materials from various NM-enriched wastes such as human hair wastes, squid ink, etc.