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

Lanthanum (La) (oxy)hydroxides are promising adsorbents for efficient aqueous phosphate (P) removal. The incorporation of cationic hydrogel with La hydroxides represents an effective strategy to improve the dispersion of La–O active sites thereby favoring P adsorption. In this study, a hydrogen (H) bond-capping via organic–inorganic copolymerization strategy was developed for enhancing the dispersion of La–O active sites. This approach significantly enhanced the adsorption capacity of La hydroxide oligomer (LHO) copolymerized cationic hydrogel (LaCCH) to 308.2 mg_P g_La⁻¹. Fixed-bed experiments demonstrated that LaCCH effectively treated over 1098 bed volumes (BV) of synthetic wastewater (1.0 mg_P L⁻¹) containing co-existing ions. Combined analyses using FTIR, Raman, and XPS confirmed that the inner-sphere complexation and formation of LaPO₄·0.5H₂O were crucial to P adsorption. The results of MD simulation implied the weaker intermolecular H bonding between [La(OH)₃] in LaCCH results in a more favorable interaction between [La(OH)₃] and the hydrogel carbon chain. In summary, copolymerization significantly improved the dispersion of La–O active sites, which enhanced P adsorption and demonstrated a strong correlation between the fractal dimension of dispersion and adsorption capacity.