Density functional theory simulation for Cr(VI) removal from wastewater using bacterial cellulose/polyaniline.

Herein, for the first time, the adsorption mechanism of HCrO4- and CrO42- (as models of Cr(VI)) by bacterial cellulose (BC), polyaniline (PANI), and BC/PANI was performed using Density Functional Theory (DFT) in both acidic and neutral pH. For this purpose, three forms of neutral, partially (pp), and fully protonated (fp) were assumed for PANI in neutral and acidic media to elucidate the influence of pH. The results indicated that the formation of hydrogen bonds (H-bond) had the main contribution in the adsorption of CrO42- and HCrO4- onto both BC and PANI. Besides, the adsorption energy of PANI was nearly 3 times as much as BC in both acidic and neutral pH. The design of the BC/PANI complex improved the stability of PANI by increasing in HOMO-LUMO energy gap from 1.1 eV to 1.97 eV. The establishment of more H-bonds, and the appearance of two different types of H-bonds, O⋯H and N⋯H, and their smaller distances (average 1.5 Å), were observed in HCrO4-/BC-fp-PANI complexes, while one type of hydroxyl H-bond (average 2 Å) was detected in CrO42-/BC-pp-PANI. It proved the adsorption of Cr(VI) is more favorable in acidic pH. The small value of charge transferred (-0.001-0.01) showed that interfacial interaction was governed by physisorption.