Effectivity of Indonesian Rice Husk as an Adsorbent for Removing Congo Red from Aqueous Solutions

Abstract

Indonesian rice husk biochar (RH-BC) was prepared by pyrolysis method at 500°C and characterized using X-ray diffraction, Fourier-transform infrared spectroscopy, surface-area-specific analysis by Brunauer-Emmett-Teller, and scanning electron microscopy. The RH-BC were used as adsorbents for enhancing the adsorption of Congo red compared to pristine rice husk (RH) in aqueous solutions. The results of characterization through surface-area-specific analysis showed the surface area of RH-BC (72.25 m2/g) was ten times higher than RH (7.08 m2/g) owing to high-temperature treatment. The results of the adsorption study showed that the RH and RH-BC followed the pseudo-second-order kinetic model and the Freundlich isotherm equation with maximum adsorption capacities of 85.470 mg/g and 72.993 mg/g for the RH-BC and RH, respectively. The thermodynamic parameters of adsorption indicated spontaneous and endothermic processes. The reusability of the adsorbents (RH and RH-BC) showed that they are potentially suitable for extracting Congo red from aqueous solution up to three adsorption-desorption cycles. Their performance sharply decreases after the fourth and fifth cycles.