High Efficiency Phosphate Removal Was Achieved by Lanthanum-Modified Mesoporous Silica Aerogels with Cellulose-Guided Templates

Abstract

Removing excess phosphate from environmental water is extremely important to reduce eutrophication. In this study, cellulose nanocrystals (CNCs) were utilized as biological templates, and the SA-La-X was synthesized by calcination with lanthanum modification. Some characterization techniques were used to confirm the impregnation of La on the surface of mesoporous silica aerogel (SA). The obtained aerogels SA-La-5, 10, and 25 had large specific surface areas (262.69, 251.23, and 197.18 m2 g-1), and average pore sizes of aerogels SA-La-5, 10, and 25 were 5.14, 4.85, and 4.71 nm, respectively. The results manifested that sample SA-La-5 with the molar ratio of Si/La of 5:1 presented the maximum adsorption capacity of 42.08 mg g-1. Meanwhile, SA-La-X exhibited less La leaching, good stability, and strong selectivity for phosphate. Through the adsorption isotherm, the phosphate adsorption over SA-La-X samples followed the Langmuir model, and the kinetic experiment demonstrated that the adsorption process fitted the pseudo-second-order models. The phosphate adsorption mechanism of SA-La-X was detected by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and X-ray diffraction (XRD), and it was found that the binding mechanism of the adsorbent and phosphorus included electrostatic adsorption, surface precipitation, and ligand exchange. Among them, electrostatic and ligand exchange were considered to be the main ways to selectively adsorb phosphate at pH 3.0. At the same time, the prepared SA-La-X with a cylindrical shape was easy to separate without causing secondary pollution to the water system, which would be the promising adsorbent for phosphate adsorption in the water environment to reduce eutrophication.