Adsorptive removal of methylene blue and acid orange 7 by hexadecyltrimethylammonium bromide modified rice husk

Abstract

The feasibility of rice husk (RRH) and surfactant modified rice husk (SMRH) to adsorb cationic dye, methylene blue (MB) and acid orange 7 (AO7) from aqueous solution was studied. SMRH was prepared by reacting RRH with different initial concentrations (1.0, 2.5 and 4.0 mM) of cationic surfactant quaternary ammonium compound, hexadecyltrimethylammonium bromide (HDTMABr). RRH and SMRH were characterized using Fourier transform infrared (FTIR) spectroscopy to determine surface functional group and effect of surfactant modification on the structure of RRH. Adsorption studies were performed in a series of batch experiment and effect of initial dye and HDTMABr concentrations on the adsorption capacity of RRH and SMRH were evaluated. The results showed that the removal of MB was higher for RRH compared to SMRH meanwhile AO7 removal was higher for SMRH compared to RRH. Modification of rice husk by cationic surfactant was proven to decrease the adsorption site for MB. On the other hand, the presence of surfactant on SMRH increased the adsorption site and allows more adsorption to occur for AO7. The equilibrium data were better described by Langmuir isotherm with maximum adsorption capacity for MB was 100.0 mg/g and 200.0 mg/g for AO7. In conclusion, the modification of rice husk by HDTMABr decreased the adsorption towards cationic dye but increased the adsorption towards anionic dye.