Removal of Direct Blue-86 dye from aqueous solution using alginate encapsulated activated carbon (PnsAC-alginate) prepared from waste peanut shell

The alginate encapsulated activated carbon (PnsAC-alginate), prepared from waste peanut shell was used as an adsorbent for the removal of Direct Blue-86 (DB-86) from aqueous solutions. The effects of temperature, extraction time, adsorbent dose, dye concentration and solution pH on the adsorption of DB-86 onto PnsAC-alginate were studied. Central composite design coupled with response surface methodology (RSM) was used to optimize the adsorption feed conditions in order to achieve maximum dye removal efficiency. The statistical analysis revealed that for maximum dye removal efficiency, the optimal conditions were adsorbent dose of 24.65 g L-1, DB-86 dye concentration of 125.5 mg L-1 and pH of 3.1. Under the optimized conditions, experimental dye removal efficiency (98.4 +/- 0.1%) agreed closely with the predicted results, indicating the suitability of RSM in optimizing the feed conditions. SEM-EDX, TEM, XRD, BET, and FTIR analyses showed the surface morphology of the adsorbents and confirmed the adsorption of DB-86 onto PnsAC-alginate. The experimental results revealed about 7% enhancement of dye removal efficiency compared to that with unmodified PnsAC adsorbent. The adsorption kinetics of DB-86 was well described by Pseudo second order kinetic model with intra-particle and film diffusion mechanisms. Langmuir isotherm model provided the best fit to the adsorption equilibrium data, obtaining maximum dye adsorption capacity of 21.6 +/- 0.9 mg g(-1). Estimation of thermodynamic parameters revealed that adsorption process was feasible with spontaneous and endothermic in nature. The present study demonstrated that use of PnsAC-alginate adsorbent might be cost effective and suitable alternative for removal of DB-86 dye from aqueous solutions.