NAP-XPS Probes the Electronic Structure of the Mg-Al-Cl Layered Double Hydroxide upon Controlled Hydration

The hydration of [Mg2Al(OH)6]+[Cl-, yH2O] LDH was investigated by volumetric water adsorption, X-ray diffraction, Fourier Transformed Infrared (FTIR) sepctroscopy, and Near Ambient Pressure X-ray Photoelectron Spectroscopy (NAP-XPS). It was demonstrated that water uptake into interlayer region can be quantified by NAP-XPS. The LDH's electronic structure is assessed for increasing relative humidity (RH) up to 0.044. The Cl 2p level appears essentially unaffected by water uptake, but as supported by DFT calculation, H-bonds between chloride and water induce Cl 3p orbitals splitting. At RH = 0.7, LDH is covered by a water film that contains Mg and Cl species but no Al. Soft X-ray radiolysis of hydrated Cl species induces the formation of oxidized Cl species.