Periclase-induced generation of flowerlike clay-based layered double hydroxides: A highly efficient phosphate scavenger and solid-phase fertilizer

Global eutrophication and phosphorus (P) crisis raise urgent demands for feasible materials for effective phosphorus removal and recovery from wastewater. In order to render efficient phosphate capture and reclamation, PER@PLDH with a peony-like hierarchical nanostructure was synthesized based on low-cost natural clays via a facile green hydrothermal method. It was the first report on periclase as a structure inducer for designing palygorskite-based nanocomposites with a three-dimensional hierarchical structure. Results of morphologic and spectroscopic analysis confirmed the identity of PER@PLDH synthesized under the periclase/palygorskite mass ratio of 2:1 as a layered double hydroxide composite. PER@PLDH and its calcined derivative PER@PLDO both demonstrated excellent phosphate capture capacities of 229.39 mg P/g and 448.58 mg P/g, respectively, up to 4 times higher than that of the unmodified sample without introducing periclase. High removal rate was also observed in mixed solutions including competing anions and humic acid, resulting in a stringent phosphate-deficient effluent to meet increasingly rigorous discharge standard. Mechanism analysis unveiled the ultrahigh P uptake by PER@PLDH was mainly attributed to the effect of anion exchange while inner-sphere surface complexation dominated the phosphate capture process of PER@PLDO. Remarkably, compared with two commercial fertilizers, the exhausted PER@PLDH after phosphate capture exhibited superior fertilization efficiency via direct use in soils without leaching of toxic metals. These encouraging results highlighted the novel approach of fabricating layered double hydroxides by using low-cost clays. Also, this study provides promising candidates for efficient phosphorus capture and recovery in practical water remediation.