The heterogeneous activation of PMS by cobalt has

Fig. 5. SMZ degradation in the presence of different catalysts. Reaction conditions: [SMZ] = 5 mg L−1, [PMS] = 10 mg L−1, catalyst = 0.5 g L−1, pH 6.3, and 0.01 M NaClO4.Figure optionsDownload full-size imageDownload as PowerPoint slide
Taking standard thermodynamic parameters into consideration, PMS activation in the presence of Cu2+Cu2+ probably starts with the formation of the Cu2+-(HO)OSO3- complex (Eq. (4)) [19]. Through one VCH 222 transfer inside the complex, ·SO4- can be generated, which is accompanied by the production of Cu3+-OH-Cu3+-OH- (Eq. (5)). Given that the reduction potential of Cu3+Cu3+/Cu2+Cu2+ (E0 = 2.3 V [37]) is much higher than that of SO52-/·SO5- (1.1 V [8]), Cu3+-OH-Cu3+-OH- can be reduced to Cu2+-OH-Cu2+-OH- by HSO5- through redox reactions (Eqs. (6) and (7)), producing sulfate radicals for SMZ degradation:equation(2)Co3++HSO5-→Co2++·SO5-+H+equation(3)Co2++HSO5-→Co3++·SO4-+H2Oequation(4)Cu2+-OH-+HSO5-→Cu2+-(HO)OSO3-+OH-equation(5)Cu2+-(HO)OSO3-→Cu3+-OH-+·SO4-equation(6)Cu3+-OH-+HSO5-→Cu2+-·OOSO3-+H2Oequation(7)Cu2+-·OOSO3-+2H2O→Cu2+-OH-+O2+2·SO4-+2H+