High-affinity adsorption leads to molecularly ordered interfaces on TiO ₂ in air and solution

Abstract

Researchers around the world have observed the formation of molecularly ordered structures of unknown origin on the surface of titanium dioxide (TiO) photocatalysts exposed to air and solution. Using a combination of atomic-scale microscopy and spectroscopy, we show that TiO selectively adsorbs atmospheric carboxylic acids that are typically present in parts-per-billion concentrations while effectively repelling other adsorbates, such as alcohols, that are present in much higher concentrations. The high affinity of the surface for carboxylic acids is attributed to their bidentate binding. These self-assembled monolayers have the unusual property of being both hydrophobic and highly water-soluble, which may contribute to the self-cleaning properties of TiO This finding is relevant to TiO photocatalysis, because the self-assembled carboxylate monolayers block the undercoordinated surface cation sites typically implicated in photocatalysis.

Fundamentals of TiO2 Photocatalysis: Concepts, Mechanisms, and Challenges

“…The interaction of H 2 O with R‐TiO 2 (110) in UHV has been largely investigated using a series of experimental techniques, such as TPD, STM, two‐photon photoemission (2PPE), and infrared reflection absorption spectroscopy (IRAS) . It is well‐established that H 2 O molecules dissociatively adsorb at the O v sites (H 2 O v ) and the 〈111〉‐oriented steps, forming OH groups on the O b rows (OH b s) .…”

Small polarons and the Janus nature of TiO2 (110)

“…Refs. [20,[34][35][36][37]. Water dissociation is often affected by specific atomic defects such as oxygen vacancies as mentioned above, impeding conclusive answers for the intrinsic property of the stoichiometric TiO 2 [38][39][40][41][42][43].…”

Structural Properties and Wettability of TiO2 Nanorods

“…Normally the monolayer of carboxylic acid formed on the surface of the TiO 2 makes the TiO 2 film hydrophobic but when we expose the UV light, it decomposes the organic molecules and makes the substrate hydrophilic. Recently, Balajka et al has reported this by utilizing the atomic‐scale microscopy tool to investigate the origin of hydrophilicity of the TiO 2 thin films.…”