Carbon–silica composite bio-sorbents with a high density of oxygen-containing sites for efficient methylene blue adsorption

Abstract

There is a growing trend to employ agricultural waste/by-products (AWBs) as substrates for the development of dye bio-sorbents, and surface modification plays a vital role in improving the sorption of dye by raw AWBs. However, the fabrication of low-cost and high-performance bio-sorbents that can effectively adsorb dye remains a great challenge. Herein, a new rice husk-based nanoporous carbon–silica composite bio-sorbent was prepared via a combinational method of sulfuric acid-assisted low-temperature carbonization and ammonium persulfate oxidization treatment. The morphology and surface chemistry were investigated using N2 adsorption–desorption, Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) techniques. The influences of pH, adsorption kinetics, adsorption isotherms and the recycling test were thoroughly investigated. It was demonstrated that the adsorbent can effectively adsorb methylene blue (MB) from an aqueous system. Moreover, RH-C-ox could be regenerated effectively and recycled five times by using ethanol solutions. Equilibrium adsorption data were fitted to Langmuir and Freundlich models, and the data are more consistent with the Langmuir isotherm equation than the Freundlich model. The maximum monolayer capacity obtained from the Langmuir isotherm was 340.1 mg/g.