Synthesis and characterization of chitosan-pyrazoloquinoxaline Schiff bases for Cr (VI) removal from wastewater

Two novel chitosan Schiff bases namely chitosan pyrazolo[3,4-b]quinoxaline Schiff base (Ch-PQ₁) and chitosan phenyl-1H-pyrazolo[3,4-b]quinoxaline Schiff base (Ch-PQ₂) were synthesized as a modification of chitosan in order to increase its ability in heavy metal removal from wastewater. Their structures were characterized by FT-IR spectroscopy, TGA analysis and X-ray diffraction. They were tested for the removal of hexavalent chromium from synthetic samples. In addition pH conditions, polymer dosage, Cr (VI) initial concentration and contact time were studied as a key factor for the adsorption process. Kinetic studies of the removal process were also clarified. Furthermore, experimental equilibrium data were fitted to Langmuir and Freundlich adsorption isotherms. Both chitosan Schiff bases showed high removal efficiency, the result indicated that Cr (VI) removal using Ch-PQ₁ and Ch-PQ₂ was 96.4% and 98.8% respectively.