Box Behnken Design in the Optimization of Rhodamine B Adsorption onto Activated Carbon Prepared from Delonix regia Seeds and Pods

Abstract

The uptake of Rhodamine B (RhB) dye onto chemically prepared activated carbon from Delonix regia pods (DPAC) and seeds (DSAC) by response surface methodology was investigated. The activated carbons were prepared with 1 M nitric acid and characterized by BET FTIR, SEM and EDX. The results obtained revealed that the prepared activated carbons DPAC and DSAC with pore diameter 4.04 nm and 3.48 nm respectively possess mesoporous structures. Optimization of the four operating variables viz; concentration, adsorbent dosage, contact time, and pH on RhB adsorption were examined using Box Behnken design (BBD). The maximum removal efficiency of RhB from aqueous solution was achieved at 99.16% and 98.36% for DSAC and DPAC respectively with an initial RhB concentration of 55 mg/L, 0.1 g dosage, pH 12, and 725 min for both adsorbents. The actual values of 99.16% (DSAC) and 98.36% (DPAC) compared with predicted values 101.7% (DSAC) and 99.40% (DPAC) have a good agreement and this confirms the suitability of the proposed model. The adsorption process fitted best into the Freundlich isotherm model. The adsorption process was adequately described by the pseudo-second-order kinetics model. Intra-particle diffusion appears to control the adsorption process but is not the only rate-limiting step.