Perovskites in Environmental and Energy Catalysis: Transitioning From Lead-Based to Lead-Free Architectures.

Perovskite materials have emerged as versatile platforms for sustainable photocatalytic and photoelectrocatalytic applications, addressing critical challenges in environmental remediation and clean energy conversion. This Review comprehensively examines oxide perovskites (ABO3), lead-based and lead-free halide perovskites (ABX3, A3B2X9), layered architectures including Ruddlesden-Popper and Dion-Jacobson phases, and perovskite-derived catalysts for pollutant degradation, CO2 reduction, water splitting (HER/OER), and integrated waste-to-fuel conversion. Unlike previous reviews that separately focus on oxide or halide systems or isolated applications, this work establishes a unified environmental-energy catalysis framework that systematically compares diverse perovskite families while emphasizing the transition from Pb-based to Pb-free architectures. Particular attention is given to defect-mediated structure-function relationships, including A/B-site engineering, oxygen and halide vacancy regulation, and heterostructure design, which collectively enhance visible-light harvesting, charge separation, and multielectron redox kinetics. Side-by-side comparisons of lead-based and lead-free systems clarify the catalytic, environmental, and stability implications of Pb substitution. Although Pb-free perovskites offer significant sustainability advantages, challenges related to long-term durability, mechanistic understanding, and scalable synthesis remain unresolved. Future directions involving DFT- and machine learning-guided design, interface engineering, and pilot-scale implementation are highlighted to accelerate the development of next-generation sustainable perovskite catalysts.