Mesoporous titania films templated by cellulose nanocrystals: morphological and spectrophotometric properties

A mechanistic study on the synthesis of mesoporous titania films with templating cellulose nanocrystals (CNCs) through a sol–gel process as influenced by CNC content and calcination temperature was made in this work. During calcination, the rutile phase of titania was transformed into the anatase phase with the use of templating CNCs. The CNCs provided heterogeneous nucleation sites for the crystallization of titania, resulting in the formation of more and smaller crystallites with sizes down to 8.8 nm. With the use of CNCs and calcination, specific surface area of titania films increased up to 221.6 m²/g, depending on actual CNC content. All titania films present a monomodal pore size distribution with the pore width varying between 2.5 and 15 nm. The average width of pores originated from the sacrificial CNCs was affected mostly by the calcination temperature rather than CNC content. The content of templating CNCs significantly affected surface area, pore volume, and crystallite size of the film. The degree of absorption in the visible light region consistently increased with increases in the CNC content, suggesting that the CNC-templated titania films can efficiently provide more photocatalytically active sites for light absorption. The morphology, porous structure, phase composition, and optical properties of titania films are controlled by manipulating the process conditions such as CNC content in precursor and calcination temperature.