Effect of Modification of Rice Husk-Derived Porous Carbon and Silica on Benzene Vapor Adsorption Kinetics

Porous carbon and silica, which can be used as inexpensive adsorbents for air purification to remove volatile organic compounds (VOCs) and for solvent recovery, can be co-produced from rice husk ash (RHA). These materials are attractive due to their well-developed micro- and mesoporous structure and modifiable surface properties. The effect of various types of modification of RHA-derived adsorbents on the adsorption kinetics of VOCs is still poorly understood. In this study, porous carbons are subjected to alkaline activation, activation in a nitrogen stream, and amination in an autoclave, while silica is modified with γ‑APTES. The effect of various types of modification on the adsorption kinetics of benzene vapors is studied by a set of methods: X-ray photoelectron spectroscopy (XPS), elemental analysis, low-temperature nitrogen adsorption, scanning electron microscopy, and laser diffraction of particle dispersions. Intraparticle diffusion rates and activation energies for adsorption/desorption processes are calculated. The dependence of diffusion rate on vapor pressure is measured for carbon subjected to alkaline activation in a nitrogen stream, which is the most promising adsorbent.