Ultrasound-assisted reverse co-precipitation synthesis of biphasic Zn, Ni, or Co spinel ferrite/hematite nanocomposite for the photocatalytic degradation of nitrobenzene

An optimized Iron spinel ferrite (Fe 3 O 4 ) synthesis for the highest catalytic activity by the ultrasonic-assisted reverse co-precipitation (US-RP) method was tested, substituting the divalent cation (Me 2+ ) source from Fe 2+ for Zn 2+ , Ni 2+ or Co 2+ . The respective ZnFe 2 O 4 , NiFe 2 O 4 or CoFe 2 O 4 spinel ferrite nanoparticles were successfully synthesized in this work. The use of this US-RP method employing the ion source MeCl 2 (Me 2+ = Zn 2+ , Ni 2+ or Co 2+ ) yields a magnetic biphasic monocrystalline composite MeFe 2 O 4 /α-Fe 2 O 3 nanomaterial with potential photocatalytic properties. The amount of ferrite in the biphasic composite differed for each ion source, being 25.6%, 34.2%, and 38.2% for the CoFe 2 O 4 < NiFe 2 O 4 < ZnFe 2 O 4 , respectively. With an inverse trend in the magnetic properties, CoFe 2 O 4 > NiFe 2 O 4 > ZnFe 2 O 4 , with a magnetic saturation ( M s ) of 42.5, 28.4, and 2.7 emu g −1 . These magnetic properties were attributed to the differences in the degree of inversion ( δ ) calculated from Raman spectroscopy and Rietveld refinements. As for the photocatalytic potential for nitrobenzene (NB) degradation, the half-life calculated under the tested conditions was in the range of 72 – 113 min, following a reaction mechanism that yields H2O, CO 2 and 4-nitrophenol (4-NPh) as an intermediate product (< 5.65%). Showing an optimal efficiency at a pH = 2 when using the sample containing CoFe 2 O 4 .