Layered europium hydroxide system for phosphorous sensing and remediation

A Layered Lanthanide Hydroxide (LLH) material based on europium (LEuH, Eu₈(OH)₂₀Cl₄.6H₂O) was intercalated with 2,6-naphtalenedicarboxylate (NDC) yielding a material presenting the bright red luminescence characteristic of Eu^{3 +}, both by direct excitation of europium and energy transfer from NDC. The material behaves as a sensor towards anions which display the ability to exchange with NDC. The sensor was tested with several anions (phosphate, sulphate, pyrophosphate, acetate, and tetraborate anions) and the changes in NDC (λ_em = 380 nm) and europium (λ_em = 615 nm) emission intensities upon excitation of NDC (λ_ex = 357 nm), were studied. Phosphate was found to have the highest degree of intercalation and displayed a strong increase (400% fold) on the fluorescence intensity of NDC. The presence of phosphate was further confirmed with Inductively Coupled Plasma-Atomic Emission Spectrometer (ICP-AES). Taking advantage of LEuH selectivity towards phosphate, its applicability in phosphorus remediation was studied presenting high sequestration capacity followed by controlled release of phosphate in three consecutive cycles and improved stability of the LEuH host material. These results highlight the significant potential of LLHs as new scavenging agents for inorganic phosphate.