Acceleration comparison between Fe~(2+)/H2O2 and Co~(2+)/oxone for decolouration of azo dyes in homogeneous systems

摘要

In this work, we have studied the decolouration of 0.10 mM methyl orange in the presence of (1) H2O2, (2) oxone, (3) the combination of Fe~(2+)/H2O2, (4) the combination of Co~(2+)/oxone, (5) the combination of Co~(2+)/ H2O2, (6) the combination of Fe~(2+)/oxone. Under the experimental conditions, the data show that H2O2 itself cannot oxidize methyl orange, oxone itself can oxidize methyl orange; all combinations can oxidize methyl orange. The acceleration sequence is: Co~(2+)/oxone > oxone > Fe~(2+)/oxone > Fe~(2+)/H2O2 > Co~(2+)/ H2O2 > H2O2 (no effect). The roles of Fe~(2+) and Co~(2+) are catalysts, through recycling-catalysis of M~(2+) (M = Fe, Co) in the combination of M~(2+)/oxidant (M = Fe, Co; oxidant = H2O2, oxone), a great quantity of HO- are generated, active HO· can attack methyl orange molecules and accelerate the decolouration of methyl orange. The accelerations from the combinations of oxone and different Co~(2+)-salts (CoSO4, CoCl2, Co(NO3)2, CoAc2) are almost the same for the decolouration of the azo dye methyl orange (with one azo bond) or congo red (with two azo bonds).