Layered perovskite Bi7Fe2Ti2O17Cl: Universally efficient photo-piezocatalysis and mechanismic insight into the origin of polarity

Sillén-Aurivillius-type Bi-based photocatalysts have been drawing extensive attention as effective photocatalysts due to their intrinsic merits, including layered crystal structure, unique electron configuration, and tunable constitution. High-crystalline and well-developed Bi₇Fe₂Ti₂O₁₇Cl nanosheets are prepared using the moderate molten salt method. It exhibits a strong piezoelectric response and efficient photo-piezocatalytic activity towards various organic contaminants, with rhodamine B (RhB) degradation rates as high as 96 %. It also can remove highly concentrated and mixed wastewater consisting of tetracycline hydrochloride (TC), ciprofloxacin (CIP), chloramphenicol hydrochloride (TCT), and enrofloxacin (ENX). In particular, the catalyst demonstrates moderate removal efficiency towards refractory pollutants, including bisphenol A (BPA), paracetamol (APAP), and chlorphenamine (CPA). This can be attributed to the high-crystalline and robust polarity of Bi₇Fe₂Ti₂O₁₇Cl that is favorable for the key-steep of charge separation and migration. More importantly, it is revealed that the polarity of Bi₇Fe₂Ti₂O₁₇Cl mainly originated from the middle two perovskite layers in the four-sandwiched structure, with the dipole moment of perovskite layers adjacent to [Bi₂O₂]²⁺ layers offset. This work synthesizes a highly efficient photo-piezo catalyst to settle the environmental issue and provides new insights into the generation of piezoelectric response of Sillén-Aurivillius-type materials.