High-resolution solid-state magic-angle spinning nuclear magnetic resonance studies on the thermal decomposition of the layered antimony hydrogen phosphate, HSb(PO4)2·2H2O
Abstract The antimony hydrogen phosphate, HSb(PO 4 ) 2 ·2H 2 O, was synthesised using an ion-exchange method from the crystalline KSb(PO 4 ) 2 precursor. The synthesised H 1 SbP 2 ·2H 2 O material was then studied using 31 P and 1 H Magic-angle Spinning Nuclear Magnetic Resonance (MAS NMR) techniques. MAS NMR indicated that the synthesised phosphate consisted of Q 3 -type phosphate tetrahedra (i.e.; PO 4 ) which were protonated in all cases. This was thought to be caused by the dynamic equilibrium between the mobile interlayer water and the protons randomly attached to alternate phosphate groups as H–O–(PO 3 )–R groups in the structure. Simultaneous TG and DTA thermogravimetry revealed a constant mass loss up to a temperature of 600°C in the TG curve and a series of well defined thermal events in the DTA curve. Scanning electron microscopy revealed that the KSb(PO 4 ) 2 was formed by the so-called `deck of cards' mechanism. This technique also revealed that the ion-exchange to HSb(PO 4 ) 2 ·2H 2 O resulted in delamination of the phosphate. BET (N 2 ) analysis of the synthesised material suggested a surface area of ca. 6.8 m 2  g −1 and a range of pore sizes.