Enhanced sonocatalytic degradation of recalcitrant organic contaminants using a magnetically recoverable Ag/Fe-loaded activated biochar composite

Silverorthophosphate (Ag₃PO₄)-iron oxide (Fe₃O₄)@activated biochar (AB) composite was prepared by a co-precipitation method as a sonocatalyst for the degradation of recalcitrant organic contaminants. We characterized Ag₃PO₄–Fe₃O₄@AB to study the physicochemical properties using scanning electron microscopy, porosimetry, a vibrating sample magnetometer, and X-ray photoelectron spectroscopy. The specific surface area increased after loading Ag₃PO₄–Fe₃O₄ on AB compared to AB only. The high magnetic property of Ag₃PO₄–Fe₃O₄@AB was confirmed by vibrating sample magnetometer analysis, which could be attributed to the existence of Fe₃O₄. The Ag₃PO₄–Fe₃O₄@AB demonstrated excellent sonocatalytic performances for the degradation of rhodamine B (RhB) and bisphenol A (BPA) under an ultrasonic (US) irradiation. Synergetic sonocatalytic activity of Ag₃PO₄–Fe₃O₄@AB has been obtained from (i) enhanced pyrolysis conditions of water molecules on the surface of the sonocatalyst through a “hot spot” and (ii) photoinduced separation between electron-hole pairs of Ag₃PO₄ using sonoluminescence. The predominant active radical species was OH•, which was confirmed by a spin trapping study. The US/Ag₃PO₄–Fe₃O₄@AB system demonstrated successful application in the degradation of various organic contaminants including synthetic dyes, endocrine-disrupting compounds/pharmaceutical active chemicals, and chlorinated organic contaminants as well as excellent reusability without a significant loss of sonocatalytic performance.