Facile synthesis of Fe-doped ZIF-8 and its adsorption of phosphate from water: Performance and mechanism

To remove phosphate from water, a novel Fe-doped ZIF-8 was synthesized as a superior adsorbent. The Fe-doped ZIF-8 was fully characterized using different characterization techniques and it was found that the as-prepared Fe-doped ZIF-8 (denoted as ZIF-(2Zn:1Fe)) showed a polyhedral morphology with a large specific surface area of 157.64 m2/g and an average pore size of 3.055 nm. Analyses using Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction showed that Fe atoms were successfully incorporated into the ZIF-8 skeleton. Batch experiments demonstrated that the molar ratio of Fe and Zn has effects on phosphate adsorption. The adsorption kinetics conformed to a pseudo-second-order model with a high correlation coefficient (R2 = 0.9983). The adsorption isotherm matched the Langmuir model (R2 = 0.9994) better than the Freundlich model (R2 = 0.7501), suggesting that the adsorption of phosphoric acid by ZIF-(2Zn:1Fe) can be classified as a chemisorption on a homogeneous surface. The adsorption amount was 38.60 mg/g. It was found that acidic environments favored the adsorption reaction and the best adsorption was achieved at an initial pH of 2. Inhibition of adsorption by common anions is NO3-> CO32-> SO42-> Cl-. Characterization results indicate that the main mechanism of adsorption is surface complexation interactions.