Selective Photocatalytic Activities of Amino Acids/Peptide-Ti3C2Tx-TiO2 Composites Induced by Calcination: Adsorption Enhancement vs Charge Transfer Enhancement

A ternary component photocatalyst composed of amino acids/peptide, Ti3C2Tx, and TiO2 was created by incorporating peptide chains of wool keratin between T i3C2Tx nanosheets and TiO2 nanoparticles through the combination of both low-temperature vibration-assisted grinding process for making Ti3C2Tx nanosheets and hydrothermal synthesis process for producing TiO2 nanoparticles. The as-obtained amino acid/peptide-Ti3C2Tx-TiO2 (P-T-T) composite was further calcined under nitrogen gas protection condition to produce calcined P-T-T composite photocatalysts (CP-T-T). The photocatalytic properties of the control Ti3C2Tx-TiO2 (T-T), P-T-T, and calcined P-T-T (CP-T-T) composites were evaluated by examining their performance in the photodegradation of C.I. Reactive Blue 194 dye, tetracycline hydrochloride, and levofloxacin antibiotics. First-principles calculations were performed to verify the experimental results. It was concluded that in comparison with the T-T and P-T-T composites, the CP-T-T composite showed a significantly better photocatalytic activity in the decomposition of C.I. Reactive Blue 194. This was ascribed to the large Brunauer–Emmett–Teller (BET) specific surface area, the presence of micropores and mesopores, the narrowed band gap with an internal electric field (IEF), and the intimate contacts among the peptide, Ti3C2Tx, and TiO2, which resulted in the fast transfer and separation of charge carriers in the photocatalytic activity of the composite. The P-T-T and CP-T-T composite photocatalysts have shown different photodegradation pathways when degrading the C.I. Reactive Blue 194 dyes. The peptide chains of wool keratin led to the redistribution of the electron accumulation and depletion on the peptide, Ti3C2Tx, and TiO2, which changed the direction of IEF in the composite. It is interestingly noted that, when degrading C.I. Reactive Blue 194, the P-T-T composite photocatalysts showed an adsorption-mediated photocatalytic degradation while CP-T-T composite photocatalysts showed an charge transfer-mediated photocatalytic degradation.