Block copolymer templating syntheses of ordered large-pore stable mesoporous aluminophosphates and Fe-aluminophosphate based on an “acid–base pair” route

Abstract

Ordered large-pore (up to 12 nm) and stable mesoporous aluminophosphates (AlPO) have been synthesized by using block copolymer (EO 106PO 70EO 106, Pluronic F127) as a structure-directing agent. The selection of inorganic precursors is based on an “acid–base pair” route. Three acid–base pair, including AlCl 3/H 3PO 4, AlCl 3/OP(OCH 3) 3 and Al(OC 4H 9) 3/PCl 3 are confirmed to be efficient for the assembly of periodic mesoporous frameworks. Ordered 2-D hexagonal mesoporous aluminophosphates can be obtained by using AlCl 3/H 3PO 4 as precursors, while disordered mesoporous aluminophosphates are produced by using AlCl 3/OP(OCH 3) 3 or Al(OC 4H 9) 3/PCl 3 as precursors. BET surface areas and pore sizes of the products vary from 261 to 115 m 2/g and from 9.4 to 12 nm, respectively. The solution and solid state 27Al and 31P MAS NMR were used to characterize the chemical environment of aluminium and phosphorus before and after the formation of mesostructured AlPO products, which simultaneously allows us to evaluate the efficiency of inorganic–inorganic (I–I) interactions (Al–O–P) of different acid–base pair. Both 27Al and 31P MAS NMR results show that among the three acid–base pair, AlCl 3/H 3PO 4 pair interacts more readily with each other than the other two pairs [AlCl 3/OP(OCH 3) 3, Al(OC 4H 9) 3/PCl 3], and tends to form rigid framework before calcination. The detailed structural characterizations reveal that strong I–I interactions (Al–O–P) between inorganic precursors will lead to a final mesoporous material with high structure regularity. This method can also be applied to synthesize iron-incorporated aluminophosphate (FeAlPO) with highly ordered 2-D hexagonal structure. BET surface area and pore size of FeAlPO prepared with Fe/Al=0.1 (molar ratio) are 181 m 2/g and 8.9 nm, respectively. Electron spin resonance (ESR) and UV–vis spectra were employed to characterize the chemical state of Fe 3+ ion.