BiFeO₃ Nanoparticles Embedded on α-MoO₃ Nanorods: A Heterostructure for Oxygen Vacancy-Driven Photocatalytic Activity and Gas Sensing

The rapid development of human civilization has influenced the rising demand for sustainable energy sources, and deteriorating air quality has elevated the risk of toxic-gas exposure. This encourages the development of efficient nanomaterials capable of seamlessly combining multiple functions and adapting to various application areas. However, establishing a generalized strategy for achieving the multipurpose applications of nanomaterials has always been a challenge. Herein, a type-II heterojunction has been designed with BiFeO 3 nanoparticles embedded on α-MoO 3 nanorods to demonstrate highly efficient multifunctional properties for photocatalytic activity and gas sensing. The optimized heterostructure exhibits ∼8.3-folds higher current density (∼12 μA/cm 2 ) and 12-folds enhanced photocatalytic H 2 generation (340 μmol g –1 ) under visible-light irradiation, surpassing the benchmark for MoO 3 -based systems. Moreover, 145% improvement in H 2 S sensing performance (∼98% to 100 ppm) with a rapid response/recovery time of 4.7/14 s has been achieved. The proposed growth mechanism suggests that, BiFeO 3 nanoparticles sitting on top of α-MoO 3 nanorods facilitate the formation of interface, creating defects in the system to overcome the shortcomings of bare α-MoO 3 as a water-splitting catalyst. Band-edge modification (with wide-band-gap α-MoO 3 nanorods, and narrow-band-gap BiFeO 3 nanoparticles) and tuned oxygen vacancy concentration have a synergetic effect on enhanced performance. A potential gradient at the interface of two semiconductors generates a built-in electric field facilitating charge transfer, as reflected in the lower R ct value. The oxygen vacancies act as electron traps, which reduce the charge recombination and improve visible-light absorption. Consequently, it boosts the photocatalytic efficiency and creates myriads of active sites for H 2 S adsorption. This work provides a generalized route for designing a band-gap-engineered α-MoO 3 /BiFeO 3 heterostructure that exhibits multifunctional activity originated from enriched oxygen vacancies to address the need for green-energy and environmental air-quality monitoring.