Sorption of borate onto layered double h

Boric acid is known to be difficult to immobilize because it has a pK_a of 9.23, which means it is present in a molecular form in most aqueous environments and can be changed in the structure and nature with the change of the environmental conditions. Layered double hydroxides (LDHs) are potential sorbents for borate. However, the drawbacks of using LDHs for borate removal are that they are affected by the presence of other anions and are difficult to separate from water. In the present work, novel composites of Mg-Al-V type of LDH, synthesized onto filter papers and then intercalated with gluconate (F-LDH-G) were prepared. LDH with interlayer of carbonate from waters first immobilized onto the surface of filter paper (F-CH-DH-CO3) by in situ hydrothermal crystallization, and then ion-exchanged sequentially with chloride (F-LDH-Cl) followed by gluconate. The influence of the molar ratio of gluconate/LDH and reaction time on F-LDH-G synthesis was explored. Products were characterized by X-ray diffraction, scanning electron microscopy. Fourier transform infrared spectroscopy and nuclear magnetic resonance as well as measurements of borate sorption. The optimal molar ratio of gluconate/LDH and reaction time for borate removal was 24 h in which borate adsorption decreased the pH and increased both the iron sorption density and greater stability than both the original filter paper the filter papers containing other bi-anions. 11B NMR and X-ray results indicated that the predominant mechanism for borate immobilization on F-LDH-G 40-24 is in complexation of gluconate with borate in bischelate and mono-chelate forms. The novel composite is boron-specific and facilitates desalinized/liquid separation.