ZnS
nanoparticles (NPs) were synthesized using a simple, green, and
reproducible hydrothermal method. Transmission electron micrographs
show polyhedral NPs having an average diameter of 21 nm; whereas the
X-ray diffraction analysis is consistent with the exclusive presence
of cubic ZnS; however no oxide could be detected. A comprehensive
characterization of the NPs’ surface was accomplished through
X-ray photoelectron spectroscopy, diffuse reflectance infrared Fourier
transform spectroscopy (DRIFT), Raman, and thermogravimetric analysis–differential
scanning calorimetry, showing a fairly pure ZnS composition and a
remarkable amount of adsorbed water molecules. The interaction capabilities
of the surface were probed in situ by DRIFT using small molecules
(CO, CO2, methanol, pyridine) as molecular probes. The
same interactions were also theoretically studied with density functional
calculations using a slab model based on the sphalerite ZnS (110)
surface. By comparing theoretical and experimental vibrational shifts,
insights on the nature of the interaction between molecular probes
and surfaces were obtained. Water was found to alter both the structure
as well as the reactivity of the surface, mediating the interaction
of methanol with the surface, and allowing the conversion of CO2 into surface carbonates. Pyridine was instead evidenced to
be able to replace water molecules because of its high adsorption
energy (1 eV) which is in tune with the known pyridine-detection capabilities
of ZnS. No −SH moieties or Lewis acid behavior of the exposed
S atoms were observed.