Crosslinking Modification of Pomelo Peel and Its Pb²⁺ Adsorption Performance

In this study, the alkali-catalyzed crosslinking with formaldehyde was used to modify pomelo peel. The modification process was optimized to improve its Pb²⁺ adsorption performance and to reduce the water-soluble matter. The modified pomelo peel was characterized by scanning electron microscopy, X-ray energy spectrum, Fourier transform infrared spectroscopy and elemental analysis. The findings indicated that taking 1 g pomelo peel for example, the optimized modification process was as follows: 1 mol/L sodium hydroxide solution 20 mL, 37% formaldehyde solution (w/v) 15 mL, reacted at 80 ℃ for 4 h. The modification process made the pomelo peel rougher. Na⁺ exchanges with the protons in the acidic functional groups such as phenolic hydroxyl and carboxyl groups, and K⁺ in the pomelo peel to form sodium salts. During the adsorption process, Pb²⁺ underwent ion exchange with Na⁺ and Ca²⁺. The modification not only greatly increased the Pb²⁺ adsorption performance, but also effectively reduced the chemical oxygen demand of the aqueous extract from the pomelo peel.