Polymer assisted ultrafiltration of AO7 anionic dye from aqueous solutions: Experimental design, multivariate optimization, and molecular docking insights

Abstract

The removal of toxic dyes from contaminated waters by ultrafiltration can be enhanced by the addition of water-soluble binding polymers. Herein, we report results of the complexation-ultrafiltration process applied to remove the anionic dye (Acid-Orange 7, AO7) from aqueous solutions using polyethyleneimine (PEI) as a chelating agent. Factors influencing the process were pH of feed solution, the polymer-to-dye ratio (r), and initial dye concentration (C0). A central-composite design of experiments was employed to investigate the effects of factors on the rejection efficiency and permeate flux. In this respect, we used commercial membranes (ultrafiltration discs, Ultracel® 10kDa) made of regenerated cellulose. The data-driven modeling and optimization of polymer assisted ultrafiltration process was performed with the aid of multiple regression analysis and genetic algorithms, respectively. The single-objective optimization (SOO) disclosed the conditions (pH 5.69, r = 2.46, C0 = 83 mg/L) that yielded a high rejection efficiency (99.02%). Instead, the multi-objective optimization (MOO) revealed the Pareto front. This suggested a feasible domain of factors (pH: 4.00–5.67, r: 1.55–2.49, C0: 50–83 mg/L) that provided an acceptable compromise between the rejection efficiency and permeate flux. In addition, a composite membrane (made of polysulfone and nanoclay) was tested under optimal conditions, unveiling superior rejection efficiency equal to 99.62%. Moreover, insights about molecular interactions (between AO7, PEI, and polysulfone) were unraveled by automatic docking simulations.