Porous cross-linked materials formed by oligomeric aluminium hydroxides and α-tin phosphate
The intercalation of the tridecameric polyhydroxyaluminium Keggin-type cation, formally [AlO4Al12(OH)24(OH2)12]7+, into α-Sn(HPO4)2·H2O via the colloidal tetramethylammonium-exchanged intermediate α-Sn[NMe4]0.9–1.0H1.1–1.0(PO4)2·4H2O and the alumina-pillared materials obtained after calcination are described. Two different intercalated precursor materials are obtained, depending on whether the Keggin ion inserted derives from the commercial product (‘Chlorhydrol’) or from the polyhydroxyaluminium cation generated in situ. Calcination leads to materials differing in free heights and in alumina contents. Their surface areas (B.E.T., N2, 77 K) are quite high: 190 m2 g–1[chlor-SnP (400 °C)] and 228 m2 g–1[Al13-SnP (400 °C)]. Pore-size calculations show them to be mainly mesoporous, but with some micropore contribution (> 50% of pores in width range 15–40 Å). The higher microporosity of the former with respect to the latter is ascribed to lateral-order differences between the alumina pillars.
High cation-exchange capacities (for Co2+, Ni2+ and Cu2+) confirm that both solids are porous and have more accessible interlayer sites than does the parent material. Optical spectra of the transition-metal ion-exchanged materials indicate that the sites available in the two solids differ, and that both differ from those present in the starting α-tin phosphate. Site geometries are suggested.