Effect of bronsted base on topological alteration of rice husk as an efficient adsorbent comparative to rice husk ash for azo dyes

Abstract

Rice husk (RH) is a notable fraction of lingo-cellulosic waste of paddy rice, abundantly available in rice-producing countries. In the last few years, rice husk ash, one of the processed products of the husk, has gained attention as an adsorbent. The present study the first time elucidates the adsorption kinetics of sodium hydroxide-treated rice husk, without recovering the dissolved sugars, onto cationic dye. The goal of the study was to investigate the implications of the alkali treatment on rice husk composition and structure and to compare its adsorption potential with rice husk ash. The effects of different concentrations of a base (2%, 4%, and 6%) and temperatures (25ºC, 70ºC, and 100ºC) were considered. Surface modification was assessed utilizing Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM), followed by adsorption studies of malachite green using chemically modified rice husk (MRH) and rice husk ash (RHA). The results showed that even a mild treatment (4% NaOH) produces visible changes in the topology and bond vibrations. Although similar trends were observed in the case of adsorbent MRH and RHA, adsorbent I (MRH) proved to be an efficient adsorbent as compared to adsorbent II (RHA). MRH and RHA followed the pseudo second-order of reaction. The R2 value for RHA (0.8619 and 0.838) and MRH (0.038 and 0.987) in Langmuir and Freundlich isotherms suggested that RHA follows the principle of monolayer, whereas MRH shows the heterogeneity of binding sites.