Functionalized locust bean pod (Parkia biglobosa) activated carbon for Rhodamine B dye removal

Abstract

Activated carbon prepared from locust bean husk was modified using ortho-phosphoric acid (ALBP) and used to scavenge Rhodamine B (RhB) dye from aqueous solutions. Characteristic features of the adsorbents were investigated using SEM, FTIR, pHpzc and Boehm Titration (BT) techniques respectively. Batch studies were used to determine the influences of contact time, temperature and initial Rh–B dye concentrations. Adsorption data were analysed using four different isotherm models. The maximum monolayer adsorption capacity of 1111.1 mgg-1 was obtained for RhB dye adsorption. The kinetics of the adsorption process was studied using pseudo-first-order, pseudo-second-order Elovich and intraparticle diffusion models respectively. The experimental data was best described by pseudo-second-order kinetic model. Favourability of the process of adsorption was also established by the separator factor (RL) value ranging from 0 and 1, while the mean energy of adsorption (Ea) was 1.12 kJmol-1 suggesting that the removal of Rh–B dye from aqueous solution followed a physisorption process. For the thermodynamic investigations, the positive values of ΔS (280.956 Jmol−1K−1) indicates the affinity of adsorbent for the Rh–B dye uptake and increase randomness at the solid–solution interface during adsorption of Rh–B dye onto the surface of the active sites of ALBP. The negative value of ΔG (-31.892 to -26.355 kJmol-1) depicts the spontaneity and feasibility of the adsorption process. The cost analysis provides a simple proof that ALBP (42.52 USD per kg) is approximately six times cheaper than Commercial Activated Carbon, CAC (259.5 USD per kg). The present study therefore established the suitability of ALBP for effective removal of Rh–B dye from aqueous solutions.