In-situ tracking CO₂-assisted isothermal-isobaric synthesis of self-assembled Bi-based photocatalyst using novel SAXS/XRD/XAFS combined technique

The synthetic path of a catalyst determines its morphology, species, and performance, and in-situ monitoring the catalyst formation process is fascinating and challenging. Herein, a newly developed synchrotron radiation small-angle X-ray scattering/X-ray diffraction/X-ray absorption fine structure (SAXS/XRD/XAFS) combined technique was used to in-situ monitor the isothermal-isobaric synthesis process of CO₂-assisted (BiO)₂CO₃ (BOC) photocatalyst, and the atomic near-neighbor structure, crystalline structure and nanoscale particle size evolution with reaction time were simultaneously captured. The results show that both polyvinyl pyrrolidone and CO₂ formed uniformly-distributed nano-sized scatterers in the Bi-based precursor solution, presenting short-range ordered structures to a certain extent. The as-prepared BOC catalytic particles underwent the evolution process of initial Bi(OH)₃ precipitate, early-stage formed KBiO₂ molecules, intermediate amorphous (BiO)₄CO₃(OH)₂ nanoparticles, and finally crystallized flower-like BOC particles self-assembled by nanosheets. The flower-like BOC particles, Bi/BOC composite, and Bi nanospheres were further prepared with different synthesis paths. Flower-like BOC particles showed the best photocatalytic degradation performance of RhB. Scavenger experiment and theoretical calculation revealed the photocatalytic mechanisms of BOC. This work has implications for path-dependent synthesis of other catalysts.