Synthesis and phosphate uptake behavior of Zr4+ incorporated MgAl-layered double hydroxides

We synthesized Zr4+ incorporated MgAl-layered double hydroxides, Mg(AlZr)-LDH(A) (where A denotes a counteranion in the interlayer space and is expressed as CO3 for carbonate and Cl for chloride ions), with different molar ratios of Mg/(Al + Zr). Then we characterized their uptake behavior toward phosphate ions. CO3-type tertiary LDH materials synthesized at room temperature show low crystallinity, whereas the highly crystalline Cl-type tertiary LDH, [Mg0.68Al0.17Zr0.14(OH)2][Cl0.26⋅(CO3)0.04⋅1.24H2O], was synthesized for the first time using a hydrothermal treatment at 120 °C. The distribution coefficients (KdKd) of oxo-anions were measured with a mixed solution containing trace amounts of the anions. The selectivity sequences were Cl−, NO−3 < SO2−4 ≪ HPO2−4 for CO3-type materials and SO2−4 < HPO2−4 

(a) Ion exchange of HPO2−4 with CO2−3 in the interlayer space followed by cross-linking with two Zr(IV) centers in the neighboring layers liberating two OH− ions, (b) while for H2PO−4, ion exchange is followed by bonding of each H2PO−4 ion with one Zr(IV) center in the layer.Figure optionsDownload as PowerPoint slide