Mechanistic insights into synergistic co-removal of Cr(VI) and Cu(II) by polyethyleneimine-chitosan/imidazolium-polysulfone composite beads from simulated electroplating rinse wastewater

Efficient and simultaneous removal of chromium(VI) oxyanions and heavy metal cations from complex electroplating rinse wastewater remains a major challenge. In this study, polyethyleneimine-chitosan/imidazolium-polysulfone composite beads (denoted as CSPF) were fabricated by integrating polyethyleneimine-modified chitosan powder (CSPI) with imidazolium-functionalized polysulfone (IMPSF) via a phase inversion method. The resulting CSPF beads was applied to simultaneously remove Cr(VI) and Cu(II) from simulated electroplating rinse wastewater. In a single-metal system at pH 5, CSPF exhibited maximum adsorption capacities of 89.3 mg g −1 for Cu(II) and 251.4 mg g −1 for Cr(VI). In the Cr(VI)/Cu(II) binary system, a notable co-removal synergy was observed, with adsorption capacities of CSPF increasing by 193.3% for Cu(II) and 39.7% for Cr(VI) compared to the single-metal system. The presence of other coexisting inorganic anions further significantly enhanced the adsorption of Cu(II) by CSPF. The promotion effect of different anions on Cu(II) adsorption follow the order of HCrO 4 − > H 2 PO 4 − ≈ SO 4 2 − >> NO 3 − ≈ Cl − . This trend is consistent with the extent to which they elevate the final solution pH and Cu 2p 3/2 binding energy after adsorption, and is further confirmed by DFT calculations. These results indicate that a unique electrostatic shielding–proton transfer synergistic mechanism is the key factor responsible for the synergistic co-removal of Cu(II) and Cr(VI) from complexed wastewater. Column cycling experiments demonstrated that CSPF could continuously and efficiently remove both Cu(II) and Cr(VI) from the simulated electroplating rinse wastewater, along with good reusability.