Green Synthesis of Kaolin-Supported Nanoscale Zero-Valent Iron UsingRuellia tuberosaLeaf Extract for Effective Decolorization of Azo Dye Reactive Black 5

Kaolin-supported nanoscale zero-valent iron (K-NZVI) was synthesized via a green synthesis method, in which leaf extract ofRuellia tuberosawas used as a reducing agent. The synthesized K-NZVI was used for decolorization of Reactive Black 5 (RB5), an azo dye widely used in textile industry. The XRD patterns of the K-NZVI particles show the characteristic peaks of Fe-0, indicating that Fe(0)nanoparticles (NZVI) were successfully synthesized on the kaolin surface. The SEM, TEM images and EDS elemental mapping show that the NZVI particles are well dispersed on the kaolin surface, thus, reducing the extent of NZVI aggregation. Batch experiments for decolorization of RB5 were carried out to investigate the effects of process parameters including solution pH, initial dye concentration and contact time. The results show that high decolorization efficiencies are obtained in acidic pH. Increasing initial dye concentration causes the decolorization efficiency to decrease, whereas increasing contact time results in higher efficiency. Furthermore, after five cycles of reuse of K-NZVI, the decolorization efficiency slightly decreases, indicating high reusability and stability of K-NZVI. The disappearance of the characteristic peaks of RB5 solution recorded by a UV-Vis spectrophotometer indicates cleavage of the azo bonds and, thus, the decomposition of RB5 in the solution. From a kinetic analysis performed at various RB5 concentrations, the decolorization process of RB5 by K-NZVI is well fit by the pseudo-first-order kinetic model.