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

Abstract

In this study, rice husk (RRH) was modified with surfactant (SMRH) to remove dyes in batch mode and was compared with unmodified rice husk (RRH). SMRH was prepared by mixing the RRH with different concentrations of cationic surfactant Hexadecyltrimethylammonium Bromide (HDTMABr). All samples were then characterized with Fourier Transform-Infrared Spectroscopy (FTIR). Screening experiment was done by comparing adsorption capacity of SMRH and RRH toward several anionic and cationic dyes with concentration of dyes at 50 mg/L. From the experiment, RRH and SMRH show affinity towards cationic and anionic dyes, respectively. The adsorptive potential of the adsorbents was further investigated towards methylene blue (MB) and acid orange 7 (AO7) with different concentration of dyes solution (5.0 - 1000.0) mg/L and different concentration of HDTMABr modified rice husk (1.0, 2.5 and 4.0) mM. Langmuir and Freundlich isotherms were used to describe adsorption isotherms. The results shows that the removal of AO7 was higher for SMRH compared to RRH meanwhile MB removal was higher for RRH compared to SMRH. Modification of rice husk by surfactant was proven to decrease the adsorption site for MB. On the other hand, the presence of surfactant on the SMRH increases the adsorption site and allows more adsorption to occur for AO7. The equilibrium data were better described by Langmuir isotherm with maximum adsorption capacity of AO7 was 200.0 mg/g and 100.0 mg/g for MB. In conclusion, the modification of rice husk by HDTMABr decreased the adsorption towards cationic dyes but increased the adsorption towards anionic dyes.