Removal of phosphate from aqueous solution by SiO2-biochar nanocomposites prepared by pyrolysis of vermiculite treated algal biomass

The present work describes the fabrication of SiO2-biochar nanocomposites by pyrolysis of vermiculite treated algal biomass. Physicochemical properties of the SiO2-biochar nanocomposites were studied systematically by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and energy-dispersive X-ray analysis (EDX). Structure and morphology analysis of the sample showed that the SiO2 particles were nanosized and uniformly formed on the carbon surface of the biochar. Effects of initial phosphate concentration, contact time, and pH on the adsorption capacity of SiO2-biochar nanocomposites were investigated in detail. Adsorption experiments revealed that the initial pH of solution could affect the adsorption of phosphate onto the SiO2-biochar nanocomposite. Of the mathematical models used to describe the adsorption kinetics of phosphate removal by the biochars, the pseudo-second-order model showed the best fit. Langmuir isotherm fitted the experimental data of phosphate adsorption onto the biochars better than the Freundlich and Redlich-Peterson adsorption model. Compared to the unmodified biochar, the SiO2-biochar nanocomposite showed a much greater ability to remove phosphate from aqueous solution, probably because the SiO2 particles on the carbon surface served as sorption sites through electrostatic interactions. In addition, the adsorbed SiO2-biochar nanocomposites could be effectively regenerated by NaOH solution. Our results suggest that SiO2-biochar nanocomposites converted from vermiculite-treated algal biomass are promising alternative adsorbents, which can be used to reduce phosphate from water.