Characterization and application of the (NH4)2.5Co0.25PMo12O40 for degradation of orange II under solar light

Abstract

(NH4)2.5Co0.25PMo12O40, an insoluble heteropolysalt, was prepared from H2.5Co0.25PMo12O40 and urea by a dry way. The physical characterizations showed that the compound crystallizes in a Keggin-type structure, with a cubic symmetry, a mesoporous nature and an homogeneous texture. The UV–Visible diffuse reflectance showed two allowed optical transitions, directly at 2.33 eV and indirectly at 1.90 eV. The compound is chemically stable in Na2SO4 electrolyte (0.5 M), test with thiocyanate was negative. The intensity potential (J- E) characetristics showed an irreversible electrochemical system with a weak hysteresis loop. The n-type behavior was determined from the “capacitance−2 – potential” characteristic with a valence band positioned at 6.83 eV under vacuum (+0.18 VSCE), composed of O2−: 2p while the conduction band derives from the Mo6+: 5s wave functions. (NH4)2.5Co0.25PMo12O40 showed a good photoactivity for the degradation of Orange II (OII), a recalcitrant dye, by •OH radicals, under solar light (93 mW cm−2). Thus, a conversion of 58% was achieved in OII solution (10 mg L−1) in 80 min, under solar light and the kinetic obeys to a first order model with a rate constant of (30.776 ± 0.554) × 10−3 min−1 (t1/2 = 23 min).