Rice husk charcoal and acid modified rice husk charcoal for efficient adsorption of methyl orange

Abstract

Abstract In this study, methyl orange (MO) was removed from solution using rice husk charcoal (RHC) and acid modified rice husk charcoal (AMRHC). In batch adsorption mode, contact time (1–240 min), pH (3–10), adsorbent dose (1–30 g/L), and initial MO concentration (10–100 mg/L) were investigated. Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were used to characterize the adsorbent's surface morphology and chemistry. At equilibrium, the highest removal of MO by RHC and AMRHC were 89 and 99%, respectively. Removal efficiency increased with increasing adsorbent dose, while the opposite was observed for adsorption capacity because of the availability of unsaturated adsorption sites. RHC and AMRHC were best described by the Freundlich and Langmuir isotherm models, with maximum adsorption capacities of 4.57 and 11.53 mg/g, respectively. The pseudo-second-order kinetic model fitted well for both adsorption and chemisorption, and the process was controlled by multi-step diffusion. Thermodynamic measurements proved that dye adsorption is a spontaneous endothermic process.