Insights on Interfacial Structure, Dynamics, and Proton Transfer from Ultrafast Vibrational Sum Frequency Generation Spectroscopy of the Alumina(0001)/Water Interface

Abstract

Steady-state and time-resolved vibrational sum frequency generation (vSFG) were used to investigate the structure and dynamics of water at the α-Al 2 O 3 (0001) surface. The vSFG spectra of the OH stretch of water next to the Al 2 O 3 (0001) surface are blue-shifted compared to the Al 2 O 3 (112̅ 0) surface, indicating its weaker hydrogen bonding network. Consequently, the vibrational dynamics of the OH stretch of the neutral Al 2 O 3 ( 0001) surface is two times slower than the neutral Al 2 O 3 (112̅ 0) surface. Furthermore, the vibrational dynamics of the OH stretch of water next to charged Al 2 O 3 surfaces is observed to be faster than that in bulk water and at charged SiO 2 surfaces, which could be due to (a) fast proton transfer dominating the vibrational relaxation and/or, (b) efficient coupling between the OH stretch and the bend overtone via the presence of low frequency (∼3000 cm −1 ) OH stretching modes. Lastly, the addition of excess ions (0.1 M NaCl) seems to have little to no effect on the time scale of vibrational dynamics, which is in contrast with the behavior observed at the silica surface, where addition of excess ions was observed to change the time scale of vibrational relaxation of interfacial water.

Surface Charges at the CaF2/Water Interface Allow Very Fast Intermolecular Vibrational‐Energy Transfer

“…For the water/mineral interface, tr‐SFG has also been used to determine relaxation dynamics . McGuire and Shen performed the first femtosecond tr‐SFG experiments on the water/silica interface.…”

Separating the pH-Dependent Behavior of Water in the Stern and Diffuse Layers with Varying Salt Concentration

“…SFG has been widely utilized to monitor the hydrogen-bonded structure and extent of ordering of interfacial water at a variety of interfaces ranging from amphiphilic films suspended at the air/aqueous interface [12][13][14][15] to mineral oxides like silica [16][17][18][19][20][21][22][23][24] and alumina. [25][26][27] Moreover, SFG has also shown that the presence of salt perturbs the interfacial water structure, with increasing salt concentration leading to a decrease in the amount of ordered water. [18][19][20][22][23] This phenomenon can be attributed to increased screening of the surface potential, thereby decreasing the electrostatic force aligning the water dipoles, which is consistent with EDL models.…”

Oberflächenladungen an der CaF2‐Wasser‐Grenzfläche erlauben eine sehr schnelle intermolekulare Übertragung von Schwingungsenergie

“…Auch für die Wasser/Mineral‐Grenzfläche wurde tr‐SFG verwendet, um die Relaxationsdynamiken zu bestimmen . McGuire und Shen führten die ersten Femtosekunden‐tr‐SFG‐Experimente an der Wasser/Siliciumdioxid‐Grenzfläche durch.…”

“…Für die Grenzfläche Aluminiumoxid/Wasser wurde keine Abhängigkeit der Schwingungsrelaxationsdynamik von H‐gebundenem Wasser gegenüber Oberflächenladung und Ionenstärke gefunden. Darüber hinaus ist die Relaxationsdynamik des Wassers an der geladenen Aluminiumoxid‐Grenzfläche schneller als die von Bulk‐Wasser . Durch diese Studien wurden wichtige Einblicke in die Lebensdauer von Schwingungen erhalten.…”