Mesoporous La-based nanorods synthesized from a novel IL-SFME for phosphate removal in aquatic systems

Abstract La-based nanorods with large mesopores were synthesized at a low temperature (35 °C) in a reverse surfactant-free microemulsion (SFME). The SFME consisted of hydrophilic ionic liquid (IL) propylammonium formate (PAF), hydrophobic IL 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF6), and protic IL diethylammonium formate (DEAF), corresponding to the water phase, oil phase, and amphi-solvent, respectively. This IL-SFME, as a new microemulsion, was formed by the three ionic liquids without any volatile organic solvents. The morphology and properties of the La-based material were investigated utilizing transmission electron microscope, X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, specific surface analysis, and zeta potential measurements. The obtained complex was lanthanum methanoate La(COOH)3 which exhibited a large specific BET surface area (47.71 m2/g) and high pHpzc (11.63), assuming a remarkable removal ability on phosphate in aqueous solutions within a wide range of pH values. This paper presents a facile, non-toxic, and energy-efficient route of the material, owing to the absence of both surfactant and high temperature treatment usually adapted in other literatures. The adsorption of the La(COOH)3 nanorods for phosphate was investigated by changing adsorbent dosage, initial phosphate concentration, contact time, and pH value. The sorption kinetics and isotherms of phosphate on the La-based adsorbent could be explained by the pseudo second-order and Langmuir model, respectively. The maximum adsorption capacity of the product was 381.6 mg PO43–/g, evidently higher than usual phosphate adsorbents. The study on the mechanism revealed that the adsorption mainly comes from the precipitation, electrostatic interaction, and ligand exchange. The adsorbed phosphate could nearly be desorbed by NaOH solution for reusability. To summarize, the synthesized mesoporous La-based nanorods unfolds a promising application in the phosphate adsorption.