Selective capture of Ge(IV) by chitosan functionalized with pomegranate peel polyphenol extract: Kinetic, dynamic mass transfer and mechanism insight

In this work, chitosan was modified by extracting the polyphenols rich in pomegranate peels to prepare the bio-composite material (PPPs-CS), which was applied to capture the dispersed metal germanium (Ge(IV)) in wastewater. The experimental results indicate that PPPs-CS exhibits the best adsorption performance for Ge(IV) at pH 7.0 with a dosage of 0.7 g/L. The adsorption behavior conforms to the pseudo-second-order kinetics and the Langmuir model, with the maximum adsorption capacity fitted by the Langmuir model reaching 71.34 mg/g. The results of dynamic adsorption mass transfer simulations showed that the capture behavior of PPPs-CS on Ge(IV) was dominated by the chemical adsorption of monomolecular layer. The adsorption partition coefficient of PPPs-CS for Ge(IV) with coexisting metal ions of Mn(II), Cd(II), Ca(II) and Ga(III) was as high as 11.23 L/g, exhibiting a selectivity coefficient more than 3.5 times higher than that of competing ions and demonstrating superior selectivity. After five adsorption-desorption cycles, the capture rate was still greater than 87 %. DFT calculations indicated that the uptake of Ge(IV) by PPPs-CS might be due to the ion exchange and complexation between the catechol groups on the surface of the PPPs-CS and Ge(OH) 4 . The pomegranate peel polyphenols could effectively improve the diversity and chemistry of the active sites for Ge(IV) binding by chitosan and enhance the specific recognition performance for Ge(IV). Overall, PPPs-CS has significant advantages and potential as environmentally friendly and cost-effective materials for the recovery of Ge(IV) from wastewater.