Adsorption difference between Cu²⁺ and Zn²⁺ on sodium dodecyl sulfate/ chitosan-modified semi-carbonized fibers

Semi-carbonized polyacrylonitrile fiber (Spf) was modified with 50% and 100% sodium dodecyl sulfate (SDS) to prepare SDS-modified Spf (SDS-Spf) to explore the adsorption effect of heavy-metal ions on composite-modified fiber materials. Then, SDS-Spf was compositely modified with chitosan (CS) in different proportions (0%, 25%, 50%, and 100%) to obtain SDS and CS-modified Spf (SDS/ CS-Spf). The isotherm adsorption characteristics of Cu2+ and Zn2+ on different SDS-Spfs and SDS/ CS-Spfs were studied by batch method, and the effects of temperature, pH, and ionic strength on the adsorption were analyzed. The following results were obtained: (1) the adsorption isotherms of Cu2+ and Zn2+ on the tested samples all conformed to the Langmuir model, with the maximum adsorption capacity maintained at 1,007.60-1,156.03 (Cu2+) and 856.08-970.50 mmol/kg (Zn2+). They showed a trend of SDS/CS-Spf > SDS-Spf > Spf. (2) At 10 degrees C-30 degrees C, the adsorption amount of Cu2+ and Zn2+ on the tested materials increased with increasing temperature, and the adsorption exhibited a spontaneous, endothermic, and entropy-increasing process. (3) High pH facilitated the adsorption of Cu2+ and Zn2+ on the tested materials in the pH range of 2-6. With the increase in ionic strength, the adsorption amount of Cu2+ and Zn2+ increased first and then decreased, reaching the peak value at an ionic strength of 0.1 mol/L. (4) The pH, cation exchange capacity, and specific surface area of the different SDS/CS-Spfs determined the adsorption amount of Cu2+ and Zn2+.