Preparation of Ag foam catalyst based on in-situ thermally induced redox reaction between polyvinyl alcohol and silver nitrate with supercritical CO2 foaming technology

The preparation process of a traditional metal foam catalyst is cumbersome, energy-intensive, and difficult to scale production, which restricts its development. In this work, the potential of polyvinyl alcohol (PVA) as a polyhydroxy reductant was explored. We used the thermally induced redox reaction between PVA and silver nitrate (AgNO3), combining with supercritical carbon dioxide (ScCO2) foaming technology, proposing an innovative idea for preparing the micron-sized Ag foam catalyst. Firstly, through the compound plasticizing effect of H2O and AgNO3, using CO2 as foam agent, the PVA/AgNO3 composite foams with uniform structure could be prepared below 100 °C. The maximum cell density could reach 5.39*109 cells/cm3 and the average cell size could reach 8.27 μm. Then, using the PVA matrix as a reductant and self-sacrifice template, silver ions could be quickly in-situ reduced at lower temperature (160–210 °C), the resulting silver particles could self-assemble into a foam-like skeleton structure. The Ag foams have an adjustable porous structure with a cell size of 4.01–16.30 μm and a ligament size of 1.08–2.82 μm. Applying it as a catalyst to promote the reduction of 4-nitrophenol (4-NP), the catalytic reaction rate constant is 10 times that of existing commercial Ag foam. The prepared Ag foam catalyst has the advantages of less dosage, easy recovery and good stability. Also, it has great application potential in the sensing, biomedicine, heat conduction and other fields.