Removal of malachite green and toluidine blue dyes from aqueous solution using a clay-biochar composite of bentonite and sweet sorghum bagasse

A clay-biochar composite was prepared through slow \npyrolysis of a mixture of bentonite clay and sweet sorghum \nbagasse. The adsorption of cationic dyes, namely, toluidine \nblue (TB) and malachite green (MG), by the clay-biochar \ncomposite was investigated to determine the adsorption \nmechanism and its sorption potential. Bentonite clay, sweet \nsorghum biochar and the bentonite-biochar composite were \ncharacterized through X-ray fluorescence (XRF), scanning \nelectron microscopy (SEM) and Fourier transform infrared \n(FT-IR) analyses. For the adsorption study, the effects of \nexposure time, initial dye concentration and temperature were \ninvestigated. The findings clearly illustrated the complex \nphysico-chemical properties of the clay-biochar composite \nencompassing distinct features of bentonite clay and biochar, \ntherefore confirming successful preparation. The adsorption of \nMG was found to occur on a heterogeneous surface as \npredicted by the Freundlich isotherm model, while the \nadsorption of TB occurred mostly at a monolayer surface \ndescribed by the Langmuir isotherm model. The adsorption \nequilibrium data was best described by the pseudo-second \norder kinetic model for all adsorbents. The estimated \nadsorption capacity of the clay-biochar composite (12.1255 \nmg/g for MG and 9.9356 mg/g for TB) suggests improved \nadsorption capacity of the biochar after incorporation of clay. \nThe thermodynamic study revealed that the adsorption of dyes \nwas mostly a spontaneous and exothermic process. \nThe adsorbent investigated in this study showed good \npotential for the removal of cationic dyes from aqueous \nsolution and could be considered for the remediation of water \npolluted by industrial effluents