Optimisation of mercury adsorption by ZIF-8 from aqueous solutions through response surface methodology
Masoomeh Torabideh, Morteza Khalooei, Ahmad Rajabizadeh, Hossein Abdipour, Sedigheh Zeinali
Abstract
Mercury is one of the most toxic heavy metals. Various techniques have been used to remove it from water sources. Among these, adsorption is a low-cost and effective method to remove mercury even in very low concentrations. One of the adsorbents that has gained considerable popularity recently is the zeolite imidazolate framework-8 (ZIF-8). In this study, after the synthesis of ZIF-8, its properties were determined using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and field emission electron microscopy (FESEM). Temperature (25–61 °C), contact time (5–85 min), adsorbent dosage (0.1–0.9 g/L), pH (2–10), and initial mercury concentration (24- mg/L) were investigated. The optimal conditions for the adsorption method were determined using the response surface methodology (RSM). The optimal conditions for mercury elimination included a primary mercury concentration of 4 mg/L, a temperature of 61°C, adsorbent dose (0.5 g/L), and a pH of 7; the elimination efficiency under these conditions was 91.66%. The adsorption equilibrium data were analysed using Langmuir and Freundlich isotherm models, and the Langmuir model was found to be consistent with the adsorption isotherm (R2 = 0.9363). The adsorption kinetics closely matched the pseudo-second-order model (R2 = 0.9998). These results indicate that the nanoporous adsorbent ZIF-8 can successfully eliminate mercury from aqueous environments.