Adsorptive removal of toxic malachite green from its aqueous solution by Bambusa vulgaris leaves and its acid-treated form: DFT, MPR and GA modeling

Abstract

In the current investigation, bamboo leaves (BL), H2SO4 treated bamboo leaves (SBL), and H3PO4 treated bamboo leaves (PBL) were utilized as biosorbents for the elimination of Malachite Green (MG) from the synthetic medium. The adsorption study was executed under the variation of different experimental conditions like pH, biosorbent dosage, contact time, and the temperature on the MG. Langmuir isotherm fit the adsorption data with maximum monolayer adsorption capacity, 151.735 mg/g at 298 K − 168.339 mg/g at 318 K for PBL. The data fitted the pseudo-2nd -order kinetic model for all three adsorbents with a correlation coefficient greater than 0.99, indicating that chemisorption controls adsorption. The Dubinin-Radushkevich isotherm indicated that the mean sorption energy (E) is a physisorption mechanism. So, the process involves physical sorption as well as chemical sorption processes with negligible sorption energy. The FTIR, Raman Spectra, and 13C NMR results show that different functional groups of cellulose, hemicellulose and lignin are involved in MG elimination. The theoretical studies were applied for a deeper understanding of the adsorption mechanism of MG using semi-empirical quantum chemical calculations. The DFT Calculations yielded valuable information about quantum chemical properties, like EHOMO, ELUMO, electrophilicity, chemical reactivity, dipole moment, and hardness for adsorbent/adsorbate components and the binding energy from adsorbent/adsorbate interactions. Multiple polynomial regression and genetic algorithm also have been successfully applied to predict the removal percentage of malachite green.