Photoreaction of Ethanol on TiO₂(110) Single-Crystal Surface

Abstract

The adsorption, thermal, and UV reactions of ethanol over a TiO 2 (110) single-crystal surface have been studied in the presence and the absence of molecular oxygen. Adsorption of ethanol is dissociative at room temperature and gives rise to two C1s peaks of equal intensities (at 285.2 and 286.5 eV) attributed to -CH 3 and -CH 2 O-groups, respectively. The surface coverage at saturation (of the dissociative adsorption mode at 300 K) is close to 0.5 with respect to Ti atoms. Thermal annealing resulted in the disappearance of the C1s signal attributed to both groups (-CH 3 and -CH 2 O-), with negligible oxidation of the ethoxide groups. The decrease of both peaks is not symmetric, it is attributed to water desorption consuming bridging surface oxygen followed by migration of ethoxide species into these defects in the process of healing surface oxygen atoms. Exposures to UV irradiation (3.2 eV) of the ethoxide covered surface in the presence of oxygen at 300 K resulted in considerable decrease of the ethoxide C1s peaks with irradiation time and the formation of a carboxylate peak at about 290 eV. This XPS C1s signal, attributed to both CH 3 COO(a) and HCOO(a) species, is most likely due to oxidation by the photoactive O 2or O 2 2species, formed by capture of the photoexited electrons at the conduction band (Ti 3d). The dependence of the rate of ethoxide decomposition on the O 2 pressure follows the expected Langmuir-Hinshelwood kinetics. The photoreaction cross section was estimated from the decay of the XPS C1s signal (starting from surface saturation) and was found equal to ca. 2 × 10 -18 cm -2 at 1 × 10 -6 Torr of O 2 . This figure compares well with that obtained for acetate decomposition under similar conditions on this same surface.

Ion-Exchange and Cation Solvation Reactions in Ti3C2 MXene

“…3,4 They have been explored in applications from energy storage to water purification to transparent conductive electrodes. 5,6,7,8 Furthermore, spontaneous intercalation of organic molecules (urea, hydrazine, DMF, etc. ), as well as spontaneous and electrochemical intercalation of various cations (Li , Al 3+ ) were previously reported.…”

“…This is especially pertinent now that a number of MXene applications have been explored involving interactions with salt solutions; for example, when MXenes are used in supercapacitors with aqueous electrolytes, 10,13 as sorbents for Pb or Cr ions, 14,15 or membranes for ion sieving, the nature of the cation can play a large role in affecting the sorption efficiency or structure and permeability of the membranes. 6 It has been shown that spontaneous cation intercalation described in reference 10 may lead to changes in MXene surface chemistry, 16 but no systematic studies have been reported. If intercalated cations are structurally inherent in MXenes, controlling their concentrations and understanding their effects on interlayer separation can be crucial for tuning electrochemical energy storage, optical, and ion-exchange properties.…”

Kinetics and Dynamics of Photocatalyzed Dissociation of Ethanol on TiO2(110)

“…Therefore, a lot of surface science techniques have been used to study the fundamental aspects of this important system. For example, the thermal chemistry of ethanol on TiO 2 (110) has been examined by temperature programmed desorption (TPD) [11−13], scanning tunneling microscopy (STM) [14], X-ray photoelectron spectroscopy (XPS) [12,15], * Authors to whom correspondence should be addressed. E-mail: chuanyaozhou@dicp.ac.cn, xmyang@dicp.ac.cn and density functional theory (DFT) calculations [14,16].…”

“…E-mail: chuanyaozhou@dicp.ac.cn, xmyang@dicp.ac.cn and density functional theory (DFT) calculations [14,16]. The photoreaction of ethanol on TiO 2 (110) has also been investigated by TPD and XPS techniques [15,16].…”

“…However, the adsorption of ethanol on the Ti 5c is debatable. Dissociative [12,15,16] and coexistence of both molecu-lar and dissociative [11,13,14] adsorption of ethanol on Ti 5c sites have been proposed. Most recently, TPD and DFT calculations in our laboratory have shown the most stable adsorption state of ethanol on Ti 5c sites is the molecular adsorption.…”