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

Abstract

The uptake of Rodamine B (RhB) dye onto chemically prepared activated carbon from Delonix regia pods (DPAC) and seeds (DSAC) by response surface methodology were investigated. The activated carbons were prepared with 1 M nitric acid and characterized by Brunauer–Emmett–Teller (BET) surface area analysis, Fourier transform infrared (FTIR) spectroscopy, Scanning electron microscopy (SEM) and Energy dispersed x-ray spectroscopy (EDX). The results obtained revealed that the prepared activated carbons DPAC and DSAC possess mesoporous structure. Optimization of the four operating variables viz; concentration, adsorbent dosage, contact time, and pH on RhB adsorption were examined using Box Behnken design (BBD). A maximum removal efficiency of RhB from aqueous solution was achieved at 99.16% and 98.36% for DSAC and DPAC respectively with initial concentration of 55 mg/L, 0.1 g dosage, pH 12 and 725 min for both adsorbents. Comparing the actual values 99.16% (DSAC) and 98.36% (DPAC) with predicted values 101.7% (DSAC) and 99.40% (DPAC) having good agreement confirms the suitability of the proposed model. The adsorption process fitted best into Freundlich isotherm model when compared with Langmuir and Temkin isotherm. The adsorption process was adequately described by pseudo-second order kinetics model. Intra-particle diffusion appears to control the adsorption process but is not the only rate limiting step.