Oxidative modifications of rice hull-based carbons for dibenzothiophene adsorptive removal

Four oxidative modifications using concentrated nitric acid, concentrated sulfuric acid, peracetic acid, and hot air, were employed to treat the rice hull (RH) activated by KOH at 750 C, which produced four RH-based carbon materials with different surface chemical properties. The textural structures, surface chemical properties and surface topography were respectively characterized by N₂ adsorption, Boehm titration, Fourier transmission infrared (FT-IR) and scanning electron microscopy (SEM) techniques. Oxidative modifications resulted in changes of both the textural structures and the surface chemistry properties. Experimental results showed that the DBT adsorption behavior of RH-based carbon adsorbents fitted well the Langmuir isotherm equation. The DBT adsorption capacity was strongly influenced by the oxygen containing acid groups on the samples, and an excellent correlation between DBT adsorption capacity and the amount of the strong acid groups was observed, indicating that the amount of the strong acidic groups on RH-based carbons play the most important role in DBT adsorption. It was postulated that the formation of donor-acceptor complexes between the adsorbent and the adsorbate was largely responsible for the significant improvement of the DBT adsorption after oxidative modifications.