Adsorption behavior and mechanism of Pb(II) on a novel and effective porphyrin-based magnetic nanocomposite

Abstract

Core-shell porphyrin-based magnetic nanocomposites with multi-functional groups were synthesized and used as effective adsorbents and crystal nuclei for removing Pb(II) from water. The effect of initial Pb(II) concentration (C0), equilibrium time and experimental temperature on the adsorption capacity has been investigated. Under the optimized conditions, the removal rate of Pb(II) can reach 84.3% only within 5 min, more efficient than similar adsorbents. In addition, the maximum adsorption capacity of FST is up to 798.34 mg/g, which is much higher than previously reported results for removing Pb(II) in aqueous solution. Furthermore, the adsorption mechanisms were proposed based on the results of field emission scanning electron microscopy (FE-SEM), ultraviolet-visible spectroscopy (UV–vis) and X-ray diffraction tests. The adsorption processes could be well described by pseudo-second-order kinetic model regardless of C0. However, when C0 was <19.2 mg/L, the adsorption process was a favorable monolayer interaction, controlled by the coordination between Pb(II) and porphyrin. When the C0 was at the range of 19.2–512 mg/L, adsorption was multilayer interaction, and the process was controlled by crystallization and limiting solubility. Moreover, density functional theory (DFT) calculations have been used to study the optimal functional group towards Pb(II), which revealed that the adsorbability of tetrapyrrolic core to Pb(II) was better than that of NH, CO and SiOSi in porphyrin. This study provides a facile method for removal of Pb(II) from aqueous solutions and offers theoretical and practical guidance on new adsorbent designs for selective removal of heavy metal ions.