Physico-chemical assessment of [Mg-Al-PO4]-LDHs obtained by structural reconstruction in high concentration of phosphate

• Published in: Colloids and surfaces. A, Physicochemical and engineering aspects Vol. 497; pp. 53 - 62
• Main Authors: Bernardo, Marcela P., Moreira, Francys K.V., Colnago, Luiz A., Ribeiro, Caue
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 20-05-2016
• Subjects: Adsorption; Assessments; Controlled release; Intercalation; Magnesium; Memory effect; Phosphates; Precipitation; Recycling; Slow release fertilizer; Surface area; Surface chemistry; CD; RNA; FT-IR; [Mg-Al]c; BET; LDH; NMR; Precipitation; JCPDS; DNA; Slow release fertilizer; SEM; Surface area; Memory effect; PXRD
• ISSN: 0927-7757; 1873-4359
• DOI: 10.1016/j.colsurfa.2016.02.021

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•MgAl-LDHs can serve as host matrixes to control the release of PO43− ions.•The memory effect was explored to increase the intercalation capacity of MgAl-LDHs.•Adsorption and precipitation are concomitant mechanisms in the PO43− uptake.•The PO43− release was better described by the Higuchi model with R2=0.92.•MgAl-LDHs returned to a pure LDH phase composition after PO43− desorption.
We report that hydrotalcite-like LDHs ([Mg-Al]-LDHs) can act as host matrixes for controlled release of phosphate. The memory effect was successfully employed to incorporate high loadings of PO43− into [Mg-Al]-LDHs. The intercalation of PO43− anions was confirmed to occur by XRD measurements at a 1:2.5 Al3+:PO43− molar ratio. We uncover a strong concentration dependence of PO43− adsorption process in reconstructed LDHs in which intercalation and precipitation happen as coexisting steps. This was confirmed by 27Al and 31P solid state NMR. Regardless of the adsorption mechanism, the PO43− release from [Mg-Al]-LDHs was successfully confirmed. The Higuchi model provided the best fit for the release profile, with R2=0.92. All [Mg-Al]-LDHs returned to a pure LDH phase composition after PO43− desorption, thereby exhibiting a recycling capacity for slow phosphate release applications.