Operando Synchrotron X-ray Diffraction Studies of Reversible Ag Ion Exchange in a Bismuth Oxide Matrix

Efficient metal ion extraction from seawater and brine systems relies on ion exchange materials, whose performance is governed by structural rearrangements during ion exchange. Herein, we investigate the ion exchange process between NaBiO 3 ·2H 2 O and AgNO 3 in aqueous solution combining three in situ techniques. The formation of Ag-δ-Bi 2 O 3 is directly observed, revealing the structural evolution during the gradual exchange of Na + ions with Ag + ions. Ex situ X-ray diffraction and electron energy loss spectroscopy analyses show that Ag-δ-Bi 2 O 3 gradually transforms back to NaBiO 3 ·2H 2 O at ambient temperature, indicating that the reversible exchange between Na + and Ag + ions is thermodynamically driven. This work directly captures the structural evolution during ion exchange and highlights the critical role of operando methodology.