Dramatically Enhanced Phenol Degradation on Alkali Cation‐Anchored TiO₂/SiO₂ Hybrids: Effect of Cation‐π Interaction as a Diffusion‐Controlling Tool in Heterogeneous Catalysis

Abstract

Cation‐π interaction is an intermolecular interaction between the face of a π system and an adjacent cation, which brings about a change in molecular dynamics of organic reactants in catalysis. In this study, a series of alkali metal cations‐anchored TiO2/SiO2 hybrid catalysts were prepared based on organo‐functionalized MCM‐41 mesoporous silica, in order to examine the effect of cation‐π interaction in heterogeneous catalysis. Immobilizing heavier alkali metal cations on surface‐functionalized carboxylic acid ion‐exchange sites provided a dramatic impact on diffusion properties of aromatic molecules, which led to a significant enhancement in photocatalytic degradation of phenol in water under ultraviolet light irradiation, whereas such an enhancement was not observed in degradation of cyclohexanol without π electrons. A distinct relationship was observed between the catalytic activities and adsorption energies determined by thermogravimetric analysis, which evidenced a role of the cation‐π interaction as a diffusion‐controlling tool in this reaction system.

Cation−π Interactions in Organic Synthesis

“…Recently, the authors found that a series of alkali metal cation-anchored TiO 2 /SiO 2 hybrid catalysts significantly enhanced the degradation of phenol under UV irradiation, suggesting that a cation−π interaction acts as a diffusioncontrolling tool in such reaction systems. 442 4.2.2. Photochemical Reactions.…”

Functionalized Ordered Mesoporous Silicas (MCM-41): Synthesis and Applications in Catalysis

“…In 2017, Yamashita et al [124], prepared TiO 2 /MCM-41 catalyst with alkali metal cations embebed (Li + , Na + , K + , Rb + , Cs + ) within its pores. In this regard, a previous post-modification of the MCM-41 with carboxylic acid groups was needed.…”

“…Schematic illustration of alkali metal cations-anchored mesoporous silica with catalytic centres. Reproduced with permission from[124]. Copyright 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.…”