A design of experiment approach to the sol-gel synthesis of titania monoliths for chromatographic applications

A design of experiement approach is described for the optimization of the microscopic morphology of macro-mesoporous titania monoliths that were elaborated for the chromatographic enrichment of phosphorylated compounds. The monolithic titania gels were formed via an alkoxy-derived sol-gel route in association with a phase separation mechanism. The synthesis was performed at mild temperatures of gelation using starting mixtures of titanium n-propoxide, hydrochloric acid, N-methylformamide, water, and poly (ethylene oxide). The gelation temperature and the chemical compositions of N-methylformamide, water, and poly (ethylene oxide) were chosen as the most relevant experimental factors of the sol-gel process. Using the sizes of the skeletons and macropores as morphological descriptors of the dried porous monoliths, the statistical analyses simultaneously revealed the effects and interactions between the different factors. Crack-free TiO ₂ monolithic rods of 8 to 10 cm long with well-defined co-continuous macropores and micro-structured skeletons were obtained after selection of the sol-gel parameters and optimization of the drying and heat-treatment steps of the gels. The bimodal texture of the rods exhibited macropores of 1.5 μm and mesopores centered at 5.2 nm with a total surface area of 140 m ² g ^-1. The ability of the macro-mesoporous titania rods to selectively bind phosphorylated compounds was demonstrated for O-phosphoamino acids (P-Ser, P-Thr, P-Tyr).