Silk fibroin-derived nitrogen-doped carbon quantum dots anchored on TiO₂ nanotube arrays for heterogeneous photocatalytic degradation and water splitting

Bombyx mori silk, a natural nitrogen-rich biopolymer protein, is earth-abundant and sustainable. In this study, nitrogen-doped carbon quantum dots (N-CQDs) derived from Bombyx mori silk fibroin are immobilized onto TiO₂ nanotube arrays (TiO₂ NTAs) by a facile hydrothermal process. The resulting N-CQDs decorated TiO₂ NTA heterostructures (N-CQDs@TiO₂ NTAs) display a maximum incident photon-to-electron conversion efficiency (IPCE) of 32.5% under 450 nm monochromatic light in neutral solution. Compared with pristine TiO₂ NTAs, the N-CQDs-decorated TiO₂ NTAs demonstrate significantly improved photocatalytic efficiency during the degradation of organic contaminants. Furthermore, the constructed heterostructures are used to split water to investigate their photocatalytic promise, yielding the maximum H₂ and O₂ production rates of 30.12 and 14.96 μmol cm⁻² h⁻¹, respectively. Optimizing the N-CQD coating is found to effectively tune the bandgap and up-conversion capability of the heterostructures, enabling unique photon harvest and boosting photocatalytic activity. This study provides a proof of concept that nonmetal, abundant, and sustainable materials can be exploited to enhance the photocatalytic capability of TiO₂, imparting a variety of unique applications such as water purification and chemical fuel production.