Activated carbon from agricultural by-products for the removal of Rhodamine-B from aqueous solution

Bagasse pith (BP) has been utilized for activated carbon preparation using H3PO4 (BPH) or KOH (BPK) as a chemical activating agent followed by carbonization at 500 °C. The physicochemical properties of activated carbon were carried out. The effectiveness of carbon prepared in adsorption of Rhodamine B (RhB) has been studied as a function of adsorbent type, pH, particle size, agitation time, temperature, initial dye concentration, and desorption. The results obtained showed that the adsorb ability of (RhB) to the BPH is higher than that of the BPK carbon by approximately 10 folds (198.6 and 21.5 mg g−1, respectively). Kinetic studies show that the adsorption of RhB proceeds according to the pseudo-second-order. The intra-particle diffusion was identified to be the rate-limiting step in addition to the film diffusion. The adsorption was analyzed using 5 isotherm models (Langmuir, Freundlich, Temkin, Harkins-Jura, and Halsey isotherm equations). The highest values of r2 were obtained with Langmuir (0.997). The adsorption capacity, qm, was 263.85 (mg g−1) at initial pH 5.7 for the particle size 0.25 nm and equilibrium time of 240 min at a temperature of 20 °C and initial dye concentration range of 100-600 (mg l−1). Temperature effect proves that the adsorption is endothermic with ΔH = 4.151 (kJ mol−1), ΔS = 65.786 (J mol−1 K−1) and a decrease in Gibbs energy (ΔG = −7.939 to −26.729 kJ mol−1). Desorption studies were carried out using water medium, HCl and NaOH with desorption of 2.7, 5.4 and 7.8%, respectively of adsorbed RhB confirming the chemical adsorption mechanism of the dye. This adsorbent was found to be both effective and economically viable.