Horizontal Attenuated Total Reflectance Fourier Transform Infrared and X-ray Photoelectron Spectroscopy Measurements of Water Adsorption on Oxidized Tin(II) Sulfide (SnS) Surfaces.

Tin(II) sulfide (SnS) is considered to be a promising optoelectronic material due to its narrow band gap, strong optical absorption, low cost and nontoxic and chem. inert characteristics. As an inherently stable compd., SnS surfaces are expected to be hydrophobic by nature. However, exposure of pristine SnS surfaces to air inevitably leads to surface oxidn. which can affect the mineral's dissoln., reactivity, optical and electronic properties as well as hydrophobicity. In the present study, water adsorption measurements on oxidized SnS thin films were performed using horizontal attenuated total reflection Fourier transform IR (HATR-FTIR) spectroscopy. XPS anal. allowed for characterization of the SnS surface compn. before water vapor exposure and identification of any changes that occurred to the surface after water vapor exposure. XPS results are consistent with water adsorption occurring on SnS surfaces contg. hydroxyl and carbonate groups. Addnl., XPS anal. showed that exposure of SnS to water vapor resulted in no significant changes to the original surface compn. Quant. water adsorption measurements using HATR-FTIR spectroscopy show that the oxidized SnS surface exhibits a slightly hydrophilic nature, demonstrating multilayer water adsorption at high relative humidity (RH) values. Exptl. water adsorption data were fit using the Brunauer-Emmett-Teller (BET) and Freundlich adsorption models. From these model fits, details of monolayer water adsorption and the water adsorption mechanisms were extd. to provide a better understanding of gas/surface adsorption on oxidized SnS surfaces. Results suggest that water adsorption on SnS powder occurs in three distinct regimes, including sub-monolayer water adsorption up to monolayer coverage at 13% RH, followed by filling of mesopores (13-76% RH) and finally multilayer water adsorption ( > 76% RH) via filling of macropores. This study represents the first report of in situ water adsorption measurements on SnS as a function of relative humidity, illustrating how oxidized surface species can alter the hydrophobic nature of SnS surfaces. [on SciFinder(R)]