Adsorptive features of banana (Musa paradisiaca) stalk-based activated carbon for malachite green dye removal

Chemically prepared activated carbon derived from banana stalk (BSAC) was used as an adsorbent to remove malachite green (MG) dye from aqueous solution. BSAC was characterised using thermogravimetric analyser, Brunauer Emmett Teller, Fourier transform infrared spectrometry, scanning electron microscopy, pH_pzc, elemental analysis and Boehm titration. The effectiveness of BSAC in adsorbing MG dye was studied as a function of pH, contact time, temperature, initial dye concentration and repeated desorption–adsorption processes. pH_pzc of BSAC was 4.5 and maximum dye adsorption occurred at pH 8.0. The rate of dye adsorption by BSAC was very fast initially, attaining equilibrium within 120 min following a pseudo-second-order kinetic model. Experimental data were analysed by Langmuir, Freundlich and Dubinin–Raduschevich isotherms. Equilibrium data fitted best into the Langmuir model, with a maximum adsorption capacity of 141.76 mg·g^?1. Δ G ⁰ values were negative, indicating that the process of MG dye adsorption onto BSAC was spontaneous. The positive values of Δ H ⁰ and Δ S ⁰ suggests that the process of dye adsorption was endothermic. The regeneration efficiency of spent BSAC was studied using 0.5 M HCl, and was found to be in the range of 90.22–95.16% after four cycles. This adsorbent was found to be both effective and viable for the removal of MG dye from aqueous solution.