Modification of Chitosan-Pectin Beads Adsorbent and Its Application for the Removal of Pb (II) from C-phycocyanin

Chitosan-pectin gel beads (CPB) have high potential for removing heavy metals from food. This study aimed to improve their stability, recyclability, and adsorption capacity by modified CPB with gelatin (Gel) and carboxymethyl cellulose sodium (CMC). The structural characteristics of the modified CPBs were characterized using Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TG), Zeta potential, scanning electron microscopy (SEM), pore size distribution analysis (BET), X-ray photoelectron spectroscopy (XPS), specific surface area analysis. The adsorption-resolution conditions of modified CPB were optimized, and their actual removal efficiency for Pb(II) in C-phycocyanin was evaluated. Results showed that CMC-modified CPB (CMC-CPB) had higher thermal stability, rougher and more porous surface, larger specific surface area (20.28±1.35 m²/g), lower zeta potential, stronger metal ion adsorption capacity, and higher regeneration efficiency compared with CPB and Gel-CPB. FTIR showed the functional group of CPB had significant difference after modification, and the main group in CPB were carboxyl, hydroxyl, and amino groups. TG analysis presented the thermal stability of CMC-CPB was higher than that of CPB and Gel-CPB. XPS analysis showed CMC-CPB had the strongest absorption peak for Pb(II). The optimal pH and temperature for the three adsorbents (CPB, Gel-CPB, and CMC-CPB) to remove Pb(II) were 6.0 and 60 ℃, respectively. The Pb(II) adsorption process of all three adsorbents fit the Langmuir isotherm model (R²=0.9543~0.9811) and the pseudo-second-order kinetic model (R²=0.9963~0.9991), and the adsorption process belonged to the monolayer chemical adsorption, involving the complexation of -COO, -OH, -CO-NH, and Pb(II). Based on the Langmuir model curve, the maximum adsorption capacity (q_max) of CMC-CPB for Pb(II) was 69.37 mg/g, significantly higher than that of Gel-CPB and CPB (P<0.05). Combing application effect of three adsorbents in C-phycocyanin, CMC-CPB showed a great prospect to efficiently remove Pb(II) in food of algae and C-phycocyanin at low-cost and environment friendly.