Experimental design approaches in the optimization of sorption potential of nano biomass derived from walnut shell for the removal of Malachite Green

In the recent years, researchers have focused on the production of activated carbons from agricultural waste material as biomass because of their purity, stability of its resources and cheap prices for the removal of water pollutant. Dye waste water including malachite green (MG) is one of the significant pollutant source and is made by various industries including textile, pigment, leather, food, cosmetics manufacturing, rubber, paper printing and cotton [1]. MG is also used in aquaculture as an effective topical antiparasitic and antiprotozoan [2]. MG is a cationic triphenylmethane dye which is extremely toxic and harmful for human [3], hence scientists have worked on the MG properties and its influence on the human health and mammals [4]. Activated carbon based on walnut shell as a biomass material was synthesized and successfully applied for the removal of malachite green (MG) dye from aqueous solution. This biomass was characterized by several techniques such as Fourier transform infrared (FT-IR) spectroscopy, Transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET), Dynamic light scattering (DLS) and X-ray diffraction (XRD). Crucial operating parameters were screened and optimized by response surface methodology (RSM), in batch study considering removal efficiency as response. A five-level, three-factor central composite design (CCD) has been employed to determine the influence of operating parameters such as initial concentration of MG (16.5-33.5 mg L-1), nano biomass dose (16.5- 33.4 mg) and contact time (13.0-47.0 min) on MG uptake from aqueous solution. Results showed that about 100% elimination was attained at initial MG concentration of 33.3 mg L-1, nano biomass dose of 33.3 mg and contact time of 20.0 min. Four adsorption isotherms, including the Langmuir, Freundlich, Temkin and Dubinin–Kaganer–Radushkevich (DKR) isotherm models were used to analyze the experimental data and the results indicated the Langmuir isotherm was suitable to describe the adsorption behaviors. Finally the pseudo second order kinetic model described the MG sorption process with a well-fitting (R2 = 0.9897).