Statistical optimization of Mg-doped UiO-66-NH2 synthesis for resource recovery from wastewater using response surface methodology

Abstract

The response-surface-methodology (RSM) was utilized to enhance phosphate (P) removal effectiveness of a Mg-doped UiO-66-NH2 nanocomposite synthesized via the solvothermal process. The RSM statistically determined the optimum parameters for evaluating and designing the P removal experiments. We investigated the effects of various operating factors of Mg-doped UiO-66-NH2 nanocomposites (such as magnesium concentration, solvothermal temperature, and solvothermal time) on P removal. According to the RSM results, the optimum parameters for Mg-doped UiO-66-NH2 nanocomposite fabrication consist of a magnesium concentration of 1.18 mM, solvothermal temperature of 120 °C, and solvothermal time of 12.69 h. This optimal sample demonstrates a P removal efficiency that is 1.75 times higher than that of pristine UiO-66-NH2. The adsorbent was analyzed with field emission scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and energy-dispersive X-ray spectroscopy. Adsorption kinetics and adsorption isotherms analyses reveal that the pseudo-second-order model (R2 > 0.99) and the Langmuir isotherm (R2 > 0.99) matched well with experimental data, implying that the P removal process was primarily based on chemical interactions. The Langmuir adsorption capacity was calculated to be 68.0 mg P/g or 208.6 mg PO4/g at an equilibrium time of 2 h. Furthermore, the adsorbed P was effectively recovered with different concentrations of sodium hydroxide.