Crystal Structure Elucidation of Reduced Dawson-Type Polyoxometalates Guides Sustainable Fabrication of Ag/Graphene Nanocomposites with Catalytic Performance

The structural elucidation of highly reduced polyoxometalates (POMs) and their structure-reducibility relationships have persisted as pivotal challenges in materials chemistry, driven by their multielectron redox capabilities. Herein, we present the synthesis and crystallographic characterization of two distinct reduced Wells-Dawson POMs, Na₄(NH₄)₆[P₂W^VI₁₄W^V₄O₆₂]·10H₂O (red-P₂W₁₈) and (NH₄)₇[P₂W^VI₁₇W^VO₆₂]·9H₂O (int-P₂W₁₈), which serve as dual-functional agents for the green fabrication of a three-dimensional silver/graphene nanocomposite (rGO/P₂W₁₈-Ag). This in situ reduction strategy provides an environmentally benign alternative by eliminating toxic organic reagents and enabling rapid synthesis. The optimized nanocatalyst demonstrates exceptional catalytic activity in 4-nitrophenol reduction, achieving a rate constant (<i>k</i>) of 0.085 s^-1, which is 58-fold higher than that of conventional Ag/GO systems. Mechanistic studies reveal synergistic interplay between the POM's electron-sponge behavior and Ag nanoparticles' catalytic sites, which is further validated by DFT calculations and spectroscopic monitoring.