Molecular dynamic simulation and DFT computational studies on the adsorption performances of methylene blue in aqueous solutions by orange peel-modified phosphoric acid

Abstract

Adsorptive removal of methylene blue dye (MB) from aqueous medium using orange peels treated with phosphoric acid (OP-H 3 PO 4 ) was examined. The OP-H 3 PO 4 was characterized using Fourier transform Infra-red spectroscopy, X-ray diffraction, scanning electron microscopy, Energy Dispersive X-ray Spectroscopy, and thermogravimetric analysis. The effect of different process parameters, namely contact time, initial dye concentration, initial solutions pH, and temperature effect were examined. Equilibrium experimental data were fitted by Langmuir, Freundlich, Redlich-Peterson (R-P) and Sips isotherm models. For the two-parameter models, the data fitted well with the Langmuir isotherm model suggesting a monolayer adsorption of the dye onto the homogeneous adsorbent surface. However, regarding the three-parameter models, for the whole temperature range, both the sips and the Redlich-Peterson models showed high correlation factors, indicating that calculated data were close to those found experimentally and suggesting that MB adsorption occurs on both homogeneous and heterogeneous surfaces of OP-H 3 PO 4 The present study revealed that OP-H 3 PO 4 is an effective and efficient adsorbent for the removal of basic dyes from aqueous solution. In addition, quantum chemical calculations realized with density functional theory (DFT) method were successfully considered to correlate the experimental results. Moreover, the molecular dynamics simulations (MDS) were used to simulate the interactions between the MB molecule and the OP-H 3 PO 4 (110) surface, indicating that the MB molecule adsorbs onto the OP-H 3 PO 4 (110) surface in a nearby horizontal position. • High adsorption potential of OP-H3PO4, about 307.63 mg/g at 25 °C. • Adsorption kinetics shows that the pseudo-second-order model was the most reliable to describe experimental data. • The equilibrium data indicates that both Sips and Langmuir models could represent the MB uptake onto OP-H 3 PO 4. • The results of the ionic strength effect showed that the competition between the MB dye and the Na + ions led to a decrease in the amount adsorbed.