Insoluble matrix proteins from shell waste for synthesis of visible-light response photocatalyst to mineralize indoor gaseous formaldehyde.

HCHO is the most concerned indoor air pollutant that photocatalytic degradation is a feasible approach. To achieve efficient and complete degradation of HCHO under visible light irradiation, heteroatoms are usually doped in TiO2. But using natural materials as a dopant instead of expensive and toxic chemicals to fertilize TiO2 remains challenging. This paper proposes a sustainable and green approach to synthesize an efficient N, Ca co-doped TiO2 photocatalyst (TIMP) by using the insoluble matrix proteins (IMPs) extracted from abalone shell. TIMP-0.8 achieves near completely degradation HCHO within 45 min under visible light at ambient temperature and exhibits superior stability after 7 cycles. TIMP-0.8 has monodispersity with smaller diameter, high porosity, abundant defects and high adsorption affinity for surface hydroxyls compared with pure TiO2. With the assistance of IMPs, the rate-determining step of HCHO degradation changes from -COOH oxidation to spontaneous decomposition of HCO3-, significantly facilitating the elimination and mineralization of HCHO. Overall, IMPs from abalone shell are natural surfactant, bio-templet, and dopant for TiO2 modification, contributing to desirable visible-light photocatalytic performance for HCHO degradation. This paper provides new insight for high-value utilization of waste shell and photocatalytic indoor purification.