Use of response surface methodology to develop and optimize the composition of a chitosan-polyethyleneimine-graphene oxide nanocomposite membrane coating to more effectively remove Cr(VI) and Cu(II) from water.

Response surface methodology (RSM) was successfully used to optimize the amounts of chitosan (CS), polyethyleneimine (PEI), graphene oxide (GO), and glutaraldehyde (GLA) to produce a multifunctional nanocomposite membrane coating able to remove positively and negatively charged heavy metals, such as Cr(VI) and Cu(II). Batch experiments with different concentrations of the four coating components (GO, CS, PEI and GLA) on cellulose membranes were carried out with solutions containing 10 ppm Cr(VI) and Cu(II) ions. Reduced quadratic equations for the Cr(VI) and Cu(II) removals were obtained based on the observed results of the batch experiments. The numerical analysis resulted in an optimized solution of 30-min soaking in CS, 1.95% PEI, 1000 ppm GO and 1.68% GLA with predicted removals of 90±10 % and 30±3% for Cr(VI) and Cu(II), respectively, with a desirability of 0.99. This mathematically optimized solution for the coating was experimentally validated. To determine the best membrane material for the coating, stability of the nanocomposite coating was determined using attenuated total reflectance - infrared (ATR-IR) spectroscopy in eight membrane materials before and after exposure to four solutions with different water chemistries. The glass microfiber (GMF) membranes were determined to be one of the best materials to receive the coating. Then, the coated GMF filter was further investigated for the removal of Cr(VI) and Cu(II) in single and binary component solutions. Results showed that the coatings were able to remove successfully both heavy metal ions, suggesting its ability to remove positively and negatively charged ions from water.