Bio-sourced phosphoprotein-based synthesis of silver-doped macroporous zinc phosphates and their antibacterial properties

The usual sources of phosphorus for metal phosphates are obtained from phosphate rocks, of which resources are depleted. As a substitute for these mineral sources, an original method of synthesis has been developed to prepare macroporous zinc phosphates using casein phosphoprotein. This bio-sourced reactant plays during the synthesis the roles of both a phosphorus source and a reducing agent for silver nanoparticles. Thus, zinc phosphates loaded with different Ag contents (up to 6.4 wt%) are prepared via hydrothermal treatment at 100 °C. Silver nanoparticles co-crystallized with hopeite, Zn3(PO4)2 and/or Zn2P2O7. In addition, casein induces porosity within the zinc phosphate framework and provides macropores (diameter of >50 nm) during calcination. The antibacterial properties against Escherichia coli K12 bacteria of Ag-containing and Ag-free porous zinc phosphates (calcined at 750 °C) were also tested for the first time.