Photon-independent NaOH/H2O2‒based degradation of rhodamine-B dye in aqueous medium: Kinetics, and impacts of various inorganic salts, antioxidants, and urea

Abstract

The present study reports an advantageous approach over the photon-dependent advanced oxidation processes (AOPs) such as UV or visible light dependent homogeneous or heterogeneous photocatalysis. Herein, we investigated the potential of a homogeneous cum alkali-catalyzed H2O2 decomposition based oxidation process (NaOH/H2O2 process) for the degradation of rhodamine-B (RhB) dye present in aqueous medium. The degradation of RhB follows pseudo-first-order reaction kinetics with rate constant (kavg.) = 0.0745 min−1 (R2 ≥ 0.99) for 0.15 M NaOH and 1500 ppm (about 0.044 M) H2O2 concentrations. In addition, the degradation of RhB via NaOH/H2O2 process is found to be significantly influenced by the concentration of H2O2 as per the correlation: kobserved min-1=5.55×10-5min-1.ppm-1×CH2O2ppm, at a fixed dose of NaOH (0.15 M) that controls the total reaction pH (>11). Moreover, compared with other AOPs, this method requires moderate conditions with low-cost raw materials, and there are no temperature gradients and H2O2 stabilizers’ requirements. However, this process has shown selective effectiveness for the degradation of cationic dyes. Besides this, NaOH/H2O2 process is hardly influenced by the presence of inorganic anions (Cl−, PO43−, SO42−, NO3−, and CO32−), except bicarbonate ions (HCO3−) that have shown a significant decrement in the RhB degradation efficiency. Furthermore, the typical doses of antioxidants and urea are also found to be quite impuissant to diminish this process.