Comprehensive Studies on Phosphoric Acid Treatment of Porous Titania toward Titanium Phosphate and Pyrophosphate Monoliths with Pore Hierarchy and Nanostructured Pore Surface
Zhu Yang, George Hasegawa, Kazuyoshi Kanamori, Kazuki Nakanishi
Simple post-treatments of the porous titania monolith in varied concentrations of phosphoric acid solution provide a series of monolithic titanium phosphates (TiPs) with a hierarchically porous structure together with exquisite macropore surface. Depending on the reaction condition, platy crystallites composed of either Ti2O3(H2PO4)2∙2H2O, Ti(HPO4)2∙H2O (α-TiP), or Ti2O(PO4)2∙2H2O (π-TiP) are generated on the macropore skeleton via the dissolution and reprecipitation process, which forms distinct wrinkled surface morphologies. In addition, the treatments effectively suppress the shrinkage during drying, leading to the lower bulk density. The post-calcination in air yields porous titanium pyrophosphates preserving the intricate porous architecture in some cases. Notably, the hierarchically porous TiP2O7 monoliths prepared from the α-TiP precursors have a good thermal robustness related to the bulk density.