Removal of Crystal Violet from aqueous solution by biofibers

Abstract

The adsorption characteristics of activated biochar fibers, which have been prepared from biofibers obtained from the cladodes of Opuntia ficus-indica, for the removal of the basic dye Crystal Violet (CV) from aqueous solutions, have been investigated prior and after chemical modification of the fibers (e.g., carbonization and following oxidation of the fibers). The effect of the initial concentration, contact time and temperature on the removal of CV was investigated in order to elucidate the adsorption process. According to the experimental results, the oxidized biochar fibers (ACF) present the highest adsorption capacity (qmax >> 50 mg g–1) for the dye, followed by the non-treated (F, qmax = 54 mg g–1) and the carbonized (CF, qmax = 27 mg g–1) fibers. The increased adsorption capacity of ACF is attributed to the carboxylate moieties present on the fibers surface, which in addition to the cation–π interactions favor the affinity of ACF for the cationic dye. Generally, the CV adsorption by the biofibers is a two-step process and carbonization of the biofibers results in significantly faster adsorption kinetics, which could be attributed to channel freeing due to thermal treatment. In the case of the oxidized biochar fibers, the channel freeing to such an extent that diffusion of the dye within those biochar fibers is only of minor relevance. In addition, in all cases, the adsorption is an endothermic, entropy-driven process.