Tuning La-O adsorption sites dispersion via hydrogen bond-capping organic-inorganic copolymerization strategy for enhanced phosphate removal

Abstract

The reduction of advanced phosphate (P) levels is crucial for addressing the widespread and severe issue of aquatic eutrophication, which hinges on the development of effective adsorbents. Lanthanum (La)-based materials have been recognized as promising adsorbents for aqueous P removal. These materials are essential for overcoming the challenges posed by low P concentrations, including their inadequate chemical affinity and low utilization rate of active adsorption sites. In this study, a novel strategy for tuning the dispersion of La-O active sites was developed, utilizing hydrogen (H) bond-capping via organic-inorganic copolymerization. This approach significantly enhanced the adsorption capacity of lanthanum hydroxide oligomer (LHO) copolymerized cationic hydrogel (LaCCH) from 56.9 mg/g to 70 mg/g, with consistent La content (14.7-14.9%), compared to La co-precipitated CH (La-CH). Additionally, La usage reached 308.2 mg P/g La. Fixed-bed experiments demonstrated that LaCCH effectively treated over 1098 bed volumes (BV) of synthetic wastewater (1.0 mg P/L) containing co-existing ions. Combined analyses using FTIR, Raman, and XPS confirmed that the inner-sphere complexation and formation of LaPO4·0.5H2O were key to P adsorption. TOF-SIMS and MD simulations further revealed that the pre-oligomerization strategy universally enhances the number of La-O active sites for P adsorption. In comparison to La coprecipitation, La oligomers copolymerized adsorbents significantly reduce the intermolecular hydrogen bonding effect in [La(OH)3], thereby lowering the interaction energy (Ei) between them and promoting the dispersion of La-O adsorption sites, which facilitates improved P removal.