Removal of cationic and anionic azo dyes from aqueous solutions by adsorption on maize stem tissue

• Freundlich and Langmuir isotherm promotes MB and EBT adsorption on MSGT.
• Langmuir capacity of MSGT was found to be 160.84 mg/g for MB at pH 6 (25 °C).
• Langmuir capacity of MSGT was found to be 167.01 mg/g for EBT at pH 2 (25 °C).
• Pseudo-second-order model best describes the absorption process (R2 ≥ 0.9999).
• MSGT is a promising adsorbent for the MB and EBT removal from aqueous solution.

The present investigation reports an effective adsorption of both cationic and anionic azo dyes by maize stem parenchymatous ground tissue with the vascular bundles embedded in it (MSGT), as novel, inexpensive and abundantly available alternative to the other commercial adsorbents. The feasibility of MSGT, for the adsorptive removal of both cationic (Methylene blue – MB) and anionic (Eriochrome black T – EBT) dyes from aqueous solution was evaluated in a batch process. Kinetic of dyes adsorption followed the pseudo second-order equation (R2 > 0.997). The equilibrium data of both MB and EBT adsorption were well correlated by both Freundlich and Langmuir isotherm at initial dye concentration (20–50 mg/L) and pH (2–6) ranges studied. Maximum Langmuir monolayer adsorption capacity of MSGT was found to be 160.84 mg/g for MB at pH 6, and 167.01 mg/g for EBT at pH 2. This study developed mathematical models for the optimization of pH, contact time and initial dye concentration for the adsorption of MB and EBT onto MSGT. Experimental values of the adsorption capacity were in good agreement with the optimum values predicted by the models.