Novel transformations amongst mesostructured VPO phases synthesized through surfactant assisted organization from an exfoliated solution of VOPO4·2H2O

A series of mesostructured VPO phases have been synthesized from a solution of VOPO4·2H2O exfoliated in 2-propanol with CTAB as the structure directing agent with different aging periods of 30 min, 1 day, 3 days and 6 days. The mesostructured phases have been characterized by both small angle and wide angle XRD, FTIR, TGA, XPS, TPR and TPD studies. It is observed that initially a CTAB incorporated mesostructured phase with an interlayer spacing of 25.2 Ǻ is obtained in which the vanadium phosphorus ratio is 1:0.1 in contrast to 1:1 in the starting VPO phase. On subsequent aging for one day the mesostructured phase remains essentially unchanged but becomes more crystalline. On further aging for 3 days and 6 days however, the incorporated CTAB gradually leaches out and the phosphorus content of the phases increases until a new VPO phase is obtained on aging for 6 days. This is in contrast to what has been reported earlier wherein mesostructured VPO phases obtained using CTAB are known to undergo transformation between lamellar, hexagonal and cubic phases on aging. Interestingly the TPR and TPD studies show that the CTAB incorporated into the mesostructured VPO phase decomposes to produce H2 at about 400 °C and CO at around 800 °C, suggesting thereby that the methylene groups in CTAB are decomposed into hydrogen and carbon at 400 °C and the liberated carbon is oxidised to CO presumably by the lattice oxygen at 800 °C.