Chitosan modified sugarcane bagasse biochar for the adsorption of inorganic phosphate ions from aqueous solution

Abstract

Recently, a variety of bio-composites have been reported as biosorbents for nutrients removal in aqueous solutions. The preference for biosorbents in nutrient removal is based on their advantages in terms of cost-effectiveness, and biodegradability properties. Herein, sugarcane bagasse was selected as a feedstock to produce a biochar that was used as biosorbent for the removal of phosphate ions from aqueous solution. However, raw biochar possesses a surface with negative charges, which makes it less effective in the adsorption of phosphate ions. The chitosan biopolymer was employed as a modifying agent to enhance the adsorption capacity of sugarcane bagasse biochar, and epichlorohydrin was also added to increase the stability of the bio-composite. Fourier-transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), Energy Dispersive X-Ray (EDX), Brunauer-Emmet-Teller (BET), and X-ray diffraction (XRD) were employed to ascertain characteristics of bio-composite in terms of functional groups, morphology, surface area and crystallinity respectively. During the experimental work, it was observed that the addition of chitosan and epichlorohydrin enhanced the adsorption capacity of the bio-composite. Experimental data best fitted to the Liu adsorption isotherm, demonstrating the surface of biosorbent was heterogeneous, and the predicted maximum adsorption was 37.2 mg/g. In addition, the experimental data best fitted to the pseudo first-order kinetic model and pseudo second-order kinetic model depending on the initial concentration of phosphate ions, indicating the mechanism of adsorption was both through the physisorption and chemisorption. Moreover, the phosphate was easily desorbed from the surface of biosorbent, and thus makes the prepared bio-composite reusable. Furthermore, the biosorbent was tested in real wastewater samples, and the removal percentage was 40.23 %, and 2.93 %, for pH 3 and pH 8, respectively. Poor removal, especially at higher pH was attributed to insufficient active sites as well as the competition from other pollutants. Therefore, these findings show that the biosorbent will have maximum performance at acidic conditions.