Response surface modeling and optimization of microcystin-LR removal from aqueous phase by polyacrylamide/sodium alginate–montmorillonite superabsorbent nanocomposite

Abstract

The adsorptive removal of the most commonly occurring cyanobacterial toxin microcystin–LR by polyacrylamide/sodium alginate-modified montmorillonite (PAM/SA-MMT) superabsorbent nanocomposite was investigated through the HPLC/UV system. The process of PAM/SA-MMT preparation and MC-LR adsorption was characterized by scanning electron microscopy, energy dispersive X-ray microanalysis, X-ray diffraction analysis, and Fourier transform infrared spectroscopy analysis. With the application of Box–Behnken statistical experimental design combined with Response surface methodology, the quadratic statistical model was established to predict the interactive effects of pH, weight ratio (wr) of AM to SA, and weight content (wt) of MMT on MC-LR adsorption and to optimize the main controlling parameters. The maximum adsorption capacity was observed with pH 2.5–4.5, wr 55–65, and wt3–5%. The MC-LR adsorption capacity of PAM/SA-MMT increased with increase in temperature from 10 to 40°C. Kinetics were consistent with Pseudo models and revealed that the sorption process could reach the equilibrium within 80 min and involved several different rate-controlling kinetic stages. The Langmuir isotherm model predicted that the theoretical maximum adsorption capacity of PAM/SA-MMT was 32.66 mg g−1. Over 85% adsorption and 80% desorption could be achieved after five regeneration cycles and the recovery of MC-LR reached 92.8% without ionic effect. PAM/SA-MMT superabsorbent nanocomposite was determined as effective, economic, and environmentally benign for MC-LR removal on a large-scale application.