Kaolin-supported nanoscale zero-valent iron for removing cationic dye-crystal violet in aqueous solution

The degradation of crystal violet in aqueous solution was investigated using kaolin-supported zero-valent iron nanoparticles (K-nZVI). It was found that K-nZVI with a ratio of kaolin: zero-valent iron nanoparticles (nZVI) at 1:1 was most effective in removing crystal violet. Batch experiments show that more than 97.29 % crystal violet was degraded using K-nZVI, while only 24.36 % was removed using nZVI after reacting for 7 min, where the solution contained 100 mg L-1 crystal violet at pH 6.5. This is due to a decrease in aggregation of Fe-0 nanoparticles and enhanced their reactivity in the presence of kaolin, which was confirmed by the characterization using scanning electron microscopy. X-ray diffraction shows the formation of iron oxide and hydroxide, while UV-Vis spectral shows that the absorption peak of crystal violet was reduced, as well as Fourier transform infrared shows that new bands were formed after K-nZVI reacting with crystal violet. These suggest that degradation of crystal violet by K-nZVI include the oxidation of iron, the adsorption of crystal violet onto the K-nZVI, the transformation of crystal violet to leuko-crystal violet, and finally the cleavage of C=C bond.