Textural and catalytic properties of combinational micro-mesoporous octatitanate fibers prepared by solvothermal soft chemical process

Protonic octatitanate fibers with novel combinational micro-mesoporous structures were prepared by using solvothermal soft chemical process in glycerine. Potassium titanate of K₂Ti₄O₉, which has a fibrous morphology and microstructures organized with K₂O-rich melt on mesoscale, was used as a precursor. In the first step, the potassium titanate precursor was treated with an acidic solution to obtain layered protonic tetratitanate. In the second step, the layered protonic tetratitanate was treated in glycerine under mild conditions to transfer the layered structure to the tunnel-like structure of protonic octatitanate fibers. Textural and catalytic properties of the protonic octatitanate fibers were investigated. They are fibers (0.5-1.5 μm in diameter and 10-20 μm in length) consisting of nanowhiskers with the average diameter of around 30 nm. The nanowhiskers further consist of microporous nanorods (around 3 nm in diameter and 5-10 nm in lengths) and nanoslits (1-2 nm in width and up to 8 nm in length). In addition, mesopores with diameters in main ranges of 1-4 and 20-40 nm exist within the octatitanate fibers. The solvotherthermally treated octatitanate fibers exhibit highly photocatalytic activity for the photodegradation of methyl orange. The interfacial charge transfer is also quickened because of a large amount of surface active sites and adsorbed reactants of O₂, hydroxyl OH, glycerine, and methyl orange. The number and strength of surface acid sites on the octatitanate fibers were measured quantitatively by the technique of microcalorimetric adsorption, using ammonia as the probe molecule. The octatitanate fibers prepared by thermal treatment in air exhibit the very strong acidity with an initial heat of 145 kJ/mol and coverage of 1100 μmol/g for the adsorption of NH₃, showing potential application in solid acid catalysis.