Influence of Volcanic Sand Surface Hydroxyl Groups on the Heterogeneous Catalytic Ozonation of Methylene Blue Contaminated Waters

Abstract

In this work, the influence of volcanic sand surface hydroxyl groups (Me-OH₂⁺, Me-OH, Me-O^-) on the catalytic ozonation of methylene blue contaminated waters is experimentally assessed. Single ozonation, pure adsorption, and combined processes were tested here at laboratory scale, using untreated and modified (with 2.44 M HCl) Chilean volcanic sand samples. Results show that the rate of MB removal by heterogeneous ozonation is much greater than the simple addition of single ozonation and adsorption. Pseudo-first order rate constants in the range 0.2 - 6.0 × 10^-3 (s^-1) were obtained at pH 8, and greater rates were observed in the case of modified volcanic sand. Surface hydroxyl groups on metal oxides of volcanic sand would act as active sites for the adsorption of reacting species, as well as initiators and/or promoters of ozone decomposition reactions. Finally, the process rate increased with pH, and maximum MB removal rates were observed at pH above the pH of the point of zero charge (pH_PZC), suggesting that higher catalytic activity could be due to deprotonated hydroxyl groups.