Microwave-assisted fabrication of porous flower-like pseudo-boehmite and high-efficiency phosphate removal from water: batch and fixed-bed column continuous operation

Abstract

It is of great interest and importance to explore low-cost, high-efficiency adsorbents for phosphate removal. Herein, we developed a microwave-assisted hydrothermal method to fabricate three-dimensional, flower-like pseudo-boehmite adsorbents using a separate nucleation and aging steps (SNAS) method. We carefully investigated their adsorption behavior toward phosphate in aqueous solution. The morphologies were controlled by adjusting the feeding ratios of the aluminium salt to the alkali in the reaction system, resulting in different pore structures and varying degrees of exposure of the (020) facet. The adsorption behavior followed the Elovich kinetic model and the Langmuir isotherm model based on the correlation coefficient. High doping of aluminium salt promoted the specific surface area by 32.7% and increased the (020) facet exposure by 59.6%. Among the three samples, notably, sample A-1/10, obtained with a molar ratio of Al³⁺ to NaOH of 1 : 10, demonstrated the largest specific surface area (430.67 m² g⁻¹) and the greatest proportion (19.25%) of the exposed (020) facet. Sample A-1/10 exhibited high phosphate removal performance in an acidic solution (pH 3), with the highest adsorption capacity of 158.58 mg g⁻¹. Furthermore, the fixed-bed adsorption column removed 95% of phosphate in a continuous operation system with alginate-assisted pseudo-boehmite beads, consisting of 75% pseudo-boehmite. These results indicate a promising avenue for practical applications in phosphate removal.