Cr(VI) and Pb(II) capture on pH-responsive polyethyleneimine and chloroacetic acid functionalized chitosan microspheres

•PEI-ECH-CMCS microspheres were first fabricated via elaborate three-step reactions.•PEI-ECH-CMCS microspheres of 24.79 μm in size had smooth spherical surfaces.•New sorbent had pH-responsive swelling features, beneficial to pollutants’ capture.•Adsorption capacity for Cr(VI) or Pb(II) was higher than the counterparts reported. PEI-ECH-CMCS microspheres (MPs) were first constructed via elaborately programmed procedures. Fourier transform infrared spectroscopy, conductometric titration, Brunauer−Emmett−Teller, X-ray diffraction, pH at zero point of charge (pHzpc), scanning electron microscopy, X-ray photoelectron spectroscopy, and swelling results demonstrated that chitosan-based adsorbent had ample −NH2 and −COOH, specific surface area of 29.040 m2/g, porous 3D architectures, pHzpc of 4.2, uniform spherical surfaces, narrow size distribution (19–33 μm), and pH-responsive swelling features, advantageous to Cr(VI) and Pb(II) capture. Adsorption parameters were obtained from batch experiments and pH 3 and 5 were chosen for Cr(VI) and Pb(II) capture. Pseudo-second-order kinetic and Liu isotherm models well interpreted adsorption behavior, and thermodynamic, isotherm, and kinetic studies revealed an exothermic, spontaneous, monolayer, and chemical adsorption process. Maximum adsorption capacity for Cr(VI) or Pb(II) was 331.32 or 302.56 mg/g, exceeding CS-based adsorbents reported. Excellent reusability and feasibility were evidenced by adsorption capacity loss < 12.10% and high removal efficiency for Cr(VI) (95.79%) and Pb(II) (91.40%) in synthetic effluents. Finally, potential adsorption mechanisms were proposed.