Degradation studies of Rhodamine B in the presence of UV/H₂O₂

The photo-oxidation of Rhodamime B was carried out in the presence of H₂O₂ using UV light. The effects of dye concentration, pH, H₂O₂ dose and irradiation time were studied. These parameters strongly influenced the degradation of the dye. As expected, the increase of initial dye concentration decreased the percentage decoloration. Likewise increasing H₂O₂ concentration also increased the dye decoloration upto a certain limit after which it starts decreasing. The optimum operating conditions of the method were found to be [Dye] = 10 μM; [H₂O₂] = 1.67 mM at pH 7. Under these conditions, a maximum of 73% decoloration of the dye was achieved. The decoloration pattern obeyed the first-order kinetics and was used to calculate apparent rate constants for dye decoloration. The actual breakdown of the dye was confirmed using HPLC and GC/MS analyses. Preliminary results show that the low molecular weight aliphatic alcohols and acids are some of the degradation products of Rhodamine B. The influence of dye assisting chemicals such as NaCl, NaNO₃, Na₂SO₄ and Na₂CO₃ on photodecoloration of the dye was also investigated. Addition of these chemicals inhibited the percent decoloration as well as the rate of dye degradation. The reaction mechanism is discussed in terms of OH^• radical scavenging by these ions.