$\mathrm{Bi_{2}O_{2}CO_{3}}$ Growth at Room Temperature: In Situ X-ray Diffraction Monitoring and Thermal Behavior

The room-temperature formation of bismuth oxycarbonate (Bi$_{2}$O$_{2}$CO$_{3}$) from Bi$_{2}$O$_{2}$CO$_{3}$ in sodium carbonate buffer was investigated with in situ powder X-ray diffraction (PXRD) in combination with electron microscopy and vibrational spectroscopy. Time-resolved PXRD measurements indicate a pronounced and rather complex pH dependence of the reaction mechanism. Bi$_{2}$O$_{2}$CO$_{3}$ formation proceeds within a narrow window between pH 8 and 10 via different mechanisms. Although a zero-dimensional nucleation model prevails around pH 8, higher pH values induce a change toward a diffusion-controlled model, followed by a transition to regular nucleation kinetics. Ex situ synthetic and spectroscopic studies confirm these trends and demonstrate that in situ monitoring affords vital parameter information for the controlled fabrication of Bi$_{2}$O$_{2}$CO$_{3}$ materials. Furthermore, the β → α bismuth oxide transformation temperatures of Bi$_{2}$O$_{2}$CO$_{3}$ precursors obtained from different synthetic routes differ notably (by min 50 °C) from commercially available bismuth oxide. Parameter studies suggest a stabilizing role of surface carbonate ions in the as-synthesized bismuth oxide sources. Our results reveal the crucial role of multiple preparative history parameters, especially of pH value and source materials, for the controlled access to bismuth oxide-based catalysts and related functional compounds