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

Abstract

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 TiO 2 nanotube arrays (TiO 2 NTAs) by a facile hydrothermal process. The resulting N-CQDs decorated TiO 2 NTA heterostructures (N-CQDs@TiO 2 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 TiO 2 NTAs, the N-CQDs-decorated TiO 2 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 H 2 and O 2 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 TiO 2 , imparting a variety of unique applications such as water purification and chemical fuel production. • High quality N-CQDs with size less than 10 nm were derived from silk fibroin. • The heterostructure was obtained through a facile and eco-friendly anodization approach, followed by hydrothermal treatment. • The controlled distribution of N-CQD on TiO 2 can be realized by tuning the concentration of silk fibroin used as precursor. • N-CQDs can effectively facilitate the visible-light harvesting due to the synergistic effect between N-CQDs and TiO 2 NTAs. • The rationally designed TiO 2 based catalysts are sustainable for solar energy conversion and organic pollutant degradation.