Ligand‐Assisted Assembly Approach to Synthesize Large‐Pore Ordered Mesoporous Titania with Thermally Stable and Crystalline Framework

Abstract

A novel ligand‐assisted assembly approach is demonstrated for the synthesis of thermally stable and large‐pore ordered mesoporous titanium dioxide with a highly crystalline framework by using diblock copolymer poly(ethylene oxide)‐b‐polystyrene (PEO‐b‐PS) as a template and titanium isopropoxide (TIPO) as a precursor. Small‐angle X‐ray scattering, X‐ray diffraction (XRD), transmission electron microscopy (TEM), high‐resolution scanning electron microscopy, and N2‐sorption measurements indicate that the obtained TiO2 materials possess an ordered primary cubic mesostructure with large, uniform pore diameters of about 16.0 nm, and high Brunauer–Emmett–Teller surface areas of ∼112 m2 g−1, as well as high thermal stability (∼700 °C). High resolution TEM and wide‐angle XRD measurements clearly illustrate the high crystallinity of the mesoporous titania with an anatase structure in the pore walls. It is worth mentioning that, in this process, in addition to tetrahydrofuran as a solvent, acetylacetone was employed as a coordination agent to avoid rapid hydrolysis of the titanium precursor. Additionally, stepped evaporation and heating processes were adopted to control the condensation rate and facilitate the assembly of the ordered mesostructure, and ensure the formation of fully polycrystalline anatase titania frameworks without collapse of the mesostructure. By employing the obtained mesoporous and crystallized TiO2 as the photoanode in a dye‐sensitized solar cell, a high power‐conversion efficiency (5.45%) can be achieved in combination with the N719 dye, which shows that this mesoprous titania is a great potential candidate as a catalyst support for photonic‐conversion applications.

A general ligand-assisted self-assembly approach to crystalline mesoporous metal oxides

“…Moreover, uncontrolled hydrolysis and condensation of transition metal sources, such as alkoxides, can result in poorly structured materials due to the rapid formation of dense, cross-linked inorganic networks. Carboxylic acid-containing ligands can be used as structure-directing agents in soft-templating approaches 17,18 , and the ligand-assisted EISA method developed by Deng and coauthors provides a new idea for the synthesis of stable and crystalline mesoporous oxides 19 . Although great advances have been made in the synthesis of several mesoporous transition metal oxides, the development of a universal method to synthesize thermally stable and highly crystalline mesoporous metal oxides is still a great challenge.…”

Mesoporous Titania: Synthesis, Properties and Comparison with Non-Porous Titania

“…To further control the hydrolysis and condensation of the Ti precursor during the assembly process, addition of ligands like acetic acid [45] and acetylacetonate [46] usually leads to more ordered and/or more stable materials.…”

Ordered meso-/macroporous silica and titania films by breath figure templating in combination with non-hydrolytic sol–gel processing

“…In addition, the formed transition metal oxides are prone to crystallization at temperatures at which the material is calcined, thus often resulting in pore collapse. To overcome this problem, Wiesner et al and Zhao et al developed a method in which amorphous carbon derived from block-copolymer templates acts as rigid support [13,14]. Other promising approaches to maintain the mesoporous arrangement are (i) the reduction of the water content to improve the nucleation rate of the titania nanoparticles or (ii) the application of templates, which support larger pore sizes and therefore a more robust titania gel structure [15,16].…”