Batch and fixed-bed adsorption behavior of porous boehmite with high percentage of exposed (020) facets and surface area towards Congo red

Abstract

Five boehmite adsorbents with high percentage of exposed (020) facets and large specific surface area were prepared by the separate nucleation and aging steps (SNAS) method at different rotating speeds, namely B-n (n = rotating speeds) from 500 to 1500 rpm of the rotating liquid film reactor (RLFR). From 500 rpm to 1500 rpm, both specific surface area and percentage of exposed (020) facets increased by ca. 10.8% and 16.9%, respectively. For all the samples, the adsorption behavior followed the pseudo-second-order model and Langmuir isotherm model towards Congo red (CR). The B-1500 sample exhibited the best adsorption performance for CR with the maximum adsorption quantity of 1298.3 mg g⁻¹ in neutral pH solution because of the smallest average particle size (d = 55.6 nm), highest specific surface area (BET = 224.42 m² g⁻¹), and highest percentage of exposed (020) facets (55.18%). In particular, the boehmite pellets shaped with the alginate-assisted moulding method showed promising practical applications for the removal of CR in water through a fixed-bed adsorption column; for example, ca. 600 mL of boehmite pellets including ca. 15.0 g of boehmite powder has the removal efficiency of 75% in 3500 mL of aqueous solution with 100 mg L⁻¹ CR.