Highly-effective removal of methylene blue dye using Cocoa (Theobroma cacao L.) Pods modified with HCl: Optimization using response surface methodology

Abstract

In this study, the cocoa pods modified with hydrochloric acid (CCA) was prepared and used as bio sorbent for methylene blue (MB) removal in aqueous solution. The CCA was characterized by Fourier Transformed Infrared (FT-IR) spectroscopy, Scanning Electron Microscopy (SEM) and pH of point zero charge (pHpzc). The response surface methodology-full factorial design (RSM-FFD) approach was used to investigate the most influential biosorption parameters and optimize their effects on MB adsorbed quantity. The linear and non-linear regression have been used to find the best fit of isotherms and kinetics models. The optimum sorption parameters were found to be 6.0, 240 mg/L and 30 mg for the pH, MB initial concentration and adsorbent dose respectively. Under these optimum conditions, the MB adsorbed quantity was found to be 150.45 mg/g. The RSM-FFD based on the ANOVA revealed that, there was a good fit between the experimental and predicted values respect to the probability (P<0.05) and with 95% degree of confidence. The polynomial equation well explained the synergetic and antagonistic effects of examined factors on MB adsorbed quantity onto CCA. The Freundlich, D.K.R and Temkin isotherms models in one hand, the pseudo-first and pseudo-second order kinetics in order hand gave the best fit for the non-linear MB sorption data. These results demonstrated that, the CCA is a promising, low-cost and eco-friend sorbent for dyes remediation in aqueous medium.