A new layered hybrid material by hydrothermal assembly of 12-molybdophosphoric acid and 1,10-diaminodecane

Abstract

Organic-inorganic hybrid materials with highly orderly structures have recently attracted substantial attention due to the promising combinative properties of both components [1, 2]. Such organic-inorganic functional materials have been successfully produced by coprecipitation [3, 4], self-assembly [5, 6] and hydrothermal [7, 8] methods. Polyoxometalates (POM) are attractive inorganic components because their molecular structures is retained even while multiple valence states exist [9]. Specifically, Keggin POM [(XM12O40)n−, M = Mo, W; X = P, Si, Fe], which are conveniently described as MO6 octahedra clusters, could be potentially applied as electrode materials [9], photochromic materials [10] and catalysts [11]. Until now, few hybrid materials have been constructed from such hetero-POM because the resulting hybrids usually show amorphous character [12]. In this study, a new layered crystalline hybrid was synthesized under hydrothermal conditions by using 12-molybdophosphoric acid (PMo12) and protonated 1,10-diaminodecane (DAD) as starting materials. The synthesis process was carried out as follows: the acidified mixture (in a molar ratio PMo12 : DAD = 1 : 2) solution (pH = 1.0) was vigorously stirred for 6 h and then kept for 12 h at room temperature. 50 mL of above reactants were transferred into a Teflonlined autoclave and heated to 150 ◦C for 1 day. After cooling for 6 h, the fibrillar solid precipitate was collected by filtration and washed with Milli-Q water several times, and subsequently dried in air at 30 ◦C. The composition of the resultant was determined by elemental analysis (Carlo Erba 1106 analyzer) and thermogravimetric analysis (TGA, Perkin-Elmer 7 Series Thermal Analysis Instrument). Elemental analysis observed: N: 2.51%, C: 9.40%. H: 2.59%, O: 29.77%. TGA curve obtained is given in Fig. 1. Heating to 320 ◦C resulted in 5.8% weight loss, corresponding to dehydration of crystal water from the interlayer space and coordinated to the polyanions. Further heating to 700 ◦C under air flow resulted in 15.6% weight loss, which corresponds to the decomposition of the organic components. The residue is crystalline MoO3 together with little phosphoric oxidate. Experiment results indicate the stoichiometry to be [C10H20(NH2)2]2 · H3PMo12O40 · (H2O)7.5.