Formation of Silver Orthophosphate Photocatalytic Layer on Bulk Calcium Phosphate via Surface Precipitation

A mild immersion-based route was developed to immobilize silver orthophosphate (Ag 3 PO 4 ) as a continuous surface layer on calcium phosphate hardened bodies derived from α-tricalcium phosphate (α-TCP, α-Ca 3 (PO 4 ) 2 ) and poly(acrylic acid) solution. The hardened bodies, composed predominantly of dicalcium phosphate dihydrate with residual α-TCP, functioned simultaneously as scaffold and phosphate reservoir, enabling Ag 3 PO 4 formation by surface precipitation in 0.10 mol·L -1 AgNO 3 at room temperature. X-ray diffraction confirmed the crystalline phases, while scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy demonstrated uniform Ag 3 PO 4 coverage on the surface. The analysis also revealed a surface Ag:P ratio of approximately 3:1. In parallel, inductively coupled plasma–atomic emission spectroscopy showed ∼98% Ag + uptake accompanied by Ca 2+ release. Diffuse reflectance spectroscopy with Tauc plot analysis yielded a direct band gap of ∼2.4 eV, consistent with visible-light responsiveness. Under weak blue LED irradiation (470 nm, 5.6 mW·cm -2 ), methylene blue degradation followed pseudo-first-order kinetics with k = 0.23–0.33 h -1 , comparable to reported Ag 3 PO 4 coatings. Post-irradiation diffraction patterns revealed metallic silver, evidencing photoreduction. This simple strategy transforms readily available cement-type substrates into Ag 3 PO 4 -functionalized bulk materials with effective visible-light photocatalytic performance. It thus offers a versatile route for environmental applications, while antibacterial applications remain a prospective direction for future investigation beyond conventional methods restricted to conductive substrates. • Mild immersion route forms Ag 3 PO 4 layers on calcium phosphate cement. • Phosphate hardened bodies act as scaffold and phosphate source for Ag 3 PO 4 growth. • Deposited Ag 3 PO 4 shows direct band gap of ∼2.4 eV under visible light. • Effective MB degradation achieved under weak blue LED irradiation. • Facile and versatile route enables bulk photocatalysts for environmental use.