Thermodynamically-Selective Metathesis and Salt-Mediated Syntheses of Monoclinic BiVO4.

Inorganic compound synthesis is often guided by phase diagrams; however, phase diagrams alone do not predict reaction selectivity. Here, computational thermodynamic screening of solid-state reaction networks identifies which phase diagrams and thus which low-temperature metathesis and salt-assisted synthesis pathways are selective for monoclinic bismuth vanadate (BiVO4) when additional elements are permitted to be included into the reaction. From this, three different selective reactions are identified: 1) ternary metathesis (AVO3 + BiOCl), 2) assisted metathesis (BiCl3 + A2CO3 + V2O5), and 3) salt-mediated reactions of the binary oxides (Bi2O3 + V2O5) with alkali chlorides (ACl), for A = Na, K. All six reactions yielded monoclinic BiVO4 at 500 °C with less than 1 mol % impurities. Potassium-based systems required shorter reaction times than the sodium counterparts for complete reactions, following the selectivity predictions. These results validate thermodynamic reaction-network screening as a reliable route to phase-pure functional oxides.