Heterogeneous degradation of toxic organic pollutants by hydrophobic copper Schiff-base complex under visible irradiation

Abstract

A hydrophobic complex of Cu2+[bis-salicylic aldehyde-o-phenylenediamine], Cu-SPA, was prepared and used as a heterogeneous photocatalyst to degrade organic pollutants in water under visible irradiation (λ ⩾ 420 nm) at neutral pH. The structure of complex was characterized by using nuclear magnetic resonance (NMR), elemental analysis, IR and UV-vis spectrometries. Degradation of Rhodamine B (RhB), Sulforhodamine B (SRB) and Benzoic acid (BA) in water were used as model reactions to evaluate the photocatalytic activities of Cu-SPA. The results indicated that RhB and SRB were easily adsorbed on the hydrophobic surface of Cu-SPA from aqueous solution (the maximum adsorption amount: Qmax = 11.09 and 8.05 μmol/g, respectively). Under visible irradiation, RhB and SRB were decolorized completely after 210 and 240 min, respectively, and BA was removed completely after 5 h. The efficiency of H2O2 was > 95%, in contrast to that of the reaction without catalyst or light (< 20%). In water soluble medium, the hydrophobic Cu-SPA can be used more than 6 cycles. ESR results and the behavior of cyclic voltammetry showed that, in the reaction process, Cu2+-SPA was reduced to intermediate state Cu+-SPA firstly, which was extremely unstable and reacted rapidly with H2O2, leading to high reactive oxygen species (·OH radical ) to degrade the substrate.