Selective adsorption of heavy metal ions by different composite-modified semi-carbonized fibers

Highly efficient remediation materials can treat wastewater contaminated by heavy metals. In this study, semi-carbonized plant fiber (Spf) and chemical fiber (Spf) were prepared as the research material. Dodecyl dimethyl betaine and chitosan were used to singly modify semi-carbonized fibers (Sfs). Then, the single-modified Sfs were remodified by sodium alginate to produce composite-modified Sfs. The microscopic morphology of the tested materials was studied by using scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric (TG) analysis, energy dispersion spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and specific surface area (SBET) detection. The selective adsorption effect of the tested materials on water polluted by multiple heavy metals was studied, and the effects of temperature, pH, and ionic strength were compared. SEM, FTIR, and TG results proved that single and composite modifiers were modified on the surface and changed the surface properties of Spf and Scf. The metal ion adsorption capacity of modified Spfs was higher than that of modified Scfs. The maximal adsorption capacity of metal ions on test materials presented the trend of Zn(II) > Cd(II) > Pb(II). The optimum adsorption conditions were 30 °C, pH = 6, and ionic strength of 0.1 mol/L, and the adsorption process was a spontaneous, endothermic, and entropy-increasing reaction. Electrostatic adsorption, precipitation, complexation, and ion exchange were the forms of adsorption for heavy metal ions. SBET and cation exchange capacity of the modified Sfs were the key factors that determine the adsorption capacity of heavy metal ions.