Study on Preparation and Characterization of Pectin/poly-m-phenylenediamine Gel Bead and Its Adsorption Performance on Lead (II)

The pectin bead was prepared from low-ester pectin and CaCl₂ by ion crosslinking method, and then novel pectin/poly-m-phenylenediamine gel bead was prepared by assembling poly-m-phenylenediamine on the surface of pectin gel beads and used for lead (II) adsorption. The structure of pectin/poly-m-phenylenediamine gel bead was characterized by fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), specific surface area and porosity analysis (BET) and energy dispersive X-ray (EDX), and the effects of initial pH, adsorption time, initial concentration of lead (II), dosage of adsorbent and coexistence of other metal ions on the adsorption of lead (II) were investigated. The results showed that compared with pectin gel beads, the specific surface area and thermal stability of pectin/poly m-phenylenediamine gel beads were significantly improved and it had better adsorption performance on lead (II) under the same conditions. Adsorption process was in good agreement with the Langmuir isotherm model and the Pseudo-second-order kinetic model, indicating that the adsorption was monolayer and the adsorption process was dominated by chemical adsorption. The maximum adsorption capacity of pectin/poly-m-phenylenediamine gel beads for lead (II) was 352.03 mg/g, which was much higher than that of pectin gel beads (162.99 mg/g). The coexistence of sodium (I) and calcium (II) had a certain degree of inhibition on the adsorption of lead (II). Under three heavy metal ion systems (lead (II), iron (II), copper (II)), the affinity of pectin/poly-m-phenylenediamine gel beads for heavy metal ions was lead (II)>iron (II)>copper (II). The adsorption mechanisms of lead (II) were the ion exchange between calcium (II) and lead (II), the chelation with oxygen-containing and nitrogen-containing functional groups and electrostatic interaction. After 5 adsorption/desorption cycles, the pectin/poly-m-phenylenediamine gel bead showed good regeneration ability(removal rate was 90%). Pectin/poly-m-phenylenediamine gel beads can be used as an adsorbent to remove lead (II).