A new perovskite-type NdFeO₃ adsorbent: synthesis, characterization, and As(V) adsorption

Nanocrystalline NdFeO₃ perovskite oxide was prepared by the combustion method using polyvinyl alcohol (PVA) and corresponding metal nitrate precursors under optimum process conditions, using a solution with a pH of 2, a metal/PVA molar ratio of 1:3, and a calcination temperature of 600 °C, and was characterized by x-ray diffraction, scanning electron microscopy, transmission electron microscopy, Brunauer–Emmett–Teller nitrogen adsorption and desorption, energy dispersive x-ray spectroscopy, Fourier transform infrared spectroscopy, laser Raman spectroscopy, and thermogravimetric and differential thermal analysis. The synthesized perovskite NdFeO₃, which had an average size of 20 nm and a relatively high surface area of 20 m² g⁻¹, was investigated for adsorbing hazardous arsenate from aqueous solution. Arsenate adsorption by perovskite NdFeO₃ is a pH-dependent process with a high adsorption capacity at pH levels between 4 and 7 and a maximum As(V) adsorption capacity of 126.58 mg g⁻¹, higher than most arsenate adsorbents reported in the literature. Kinetic and equilibrium data of reaction under the experimental conditions are best described by a pseudo-second-order and the Langmuir isotherm equation. The values of enthalpy, Gibbs free energy and entropy changes (ΔH⁰ = +63.916 kJ mol⁻¹, ΔG⁰ = −6.551 kJ mol⁻¹ to −14.021 kJ mol⁻¹ at T = 283−313 K, ΔS⁰ = +0.249 kJ mol⁻¹ K⁻¹) suggested that the reaction was endothermic, spontaneous, and took place with increasing entropy. (paper)