Multifunctional nanostructures of Au–Bi₂O₃ fractals for CO₂ reduction and optical sensing

The development of nanomaterials with multifunctional properties presents a viable business case for potential scale-up of nanomaterial fabrication. Hence, the design and engineering of structures as well as tuning of active sites are crucial in generating multifunctional properties in nanomaterials. In this regard, we demonstrate a three-dimensional (3D) fractal structure of Au–Bi₂O₃ with a fractal dimension (Df) of ≈ 1.80, which is obtained from the small-angle X-ray scattering (SAXS) measurement and through the box counting algorithm. The fractal structures, fabricated via a one-step direct synthesis, gives a homogeneous distribution of catalytically active nanocrystals Au and Bi₂O₃ on a 3D platform with a large active surface area, resulting in a strong enhancement of its localized electric field. Therefore, when applied as a catalyst for electrochemical CO₂ reduction reactions (CO₂RR) and optical gas sensing, the material displays an excellent performance. Specifically, the fractal structure exhibits a high selectivity towards the formation of formate, achieving a very high faradaic efficiency of 97% and high mass-specific formate current density of −54 mA mg⁻¹ at −1.1 V vs. a reversible hydrogen electrode (RHE). Similarly, this structure displayed a plasmonic shift as high as ∼5 nm for 4 vol% acetone sensing with a detection limit of 100 ppm towards different volatile organic compounds (VOCs).