Control of magnesium containing vanadium mesoporous materials

Magnesium containing vanadium mesoporous materials were synthesized using vanadium(V) oxide and magnesium nitrate as sources and cetyltrimethylammonium bromide (CTAB) and the mixture of CTAB and hexadecylamine (HDA) as templates. The effects of the Mg/V molar ratio and the surfactant concentration in the initial batches, the pH employed, and the length of aging time on the structural properties of the synthesized materials were investigated. Both CTAB alone and the mixture CTAB + HDA were effective in templating magnesium containing vanadium mesoporous materials, with a larger average pore size in the latter case. The degree of crystallinity of the mesoporous V-Mg-O was found to increase with increasing surfactant concentration in the initial batches. However, a too large amount of surfactant increased tremendously the viscosity of the system, generating difficulties in the preparation. At a given pH, the degree of crystallinity of the mesoporous materials increased with increasing Mg/V molar ratio in the initial batch attaining a maximum followed by a decrease. At a given Mg/V molar ratio in the initial batch, the degree of crystallinity increased with increasing pH, passed though an optimum for a pH = 7, and then decreased. The analysis of the composition of the mesoporous materials revealed that the amount of magnesium included in the samples was small and increased only slightly with increasing amount in the initial batches; the increase of the pH increased, however, much more the amount of Mg included in the mesoporous materials. The stability toward heating at various temperatures increased with increasing amount of magnesium in the samples. Possible explanations for the effects found are suggested.