Chemical transformation and dissociation of amino acids on metal sulfide surface: Insights from DFT into the effect of surface vacancies on alanine-sphalerite system

How Do Surface Defects Change Local Wettability of the Hydrophilic ZnS Surface? Insights into Sphalerite Flotation from Density Functional Theory Calculations

“…While one of these undercoordinated sulfur atoms interacts with the hydrogen from water, the other one forms a new S–S bond (find the S3–S4 bond in the III Zn case in Figure ) with the nearest sulfur atom from the surface downward hill layer after water adsorption. The further postrelaxation of the ZnS surface changes the coordination number of the twofold sulfur atom to threefold (i.e., the S3 atom), which is believed to be another reason for the better stability of water molecules on the Zn-deficient surface …”

“…In the case of the sulfur-deficient slab, the surface undergoes a large relaxation by forming metallic Zn–Zn bonds, which is shown to be the most energetically favorable configuration compared to other modes (see Zn–Zn bonds in the II S sample of Figure ). We observed a similar surface reconstruction scheme for the alanine/sulfur-deficient complex . Similar to the previous result obtained for the alanine/ZnS system, the H 2 O molecule is adsorbed around the vacancy site with a Zn–O population of 0.18.…”

“…The higher H-bond population for the S2 ... H2 is also noticeable by a large H-bond angle of 173.5°, very close to the maximum effective value of 180°. Removing a zinc atom from the surface leaves the upper hill surface layer with two twofold coordinated sulfur atoms, which are attractive sites for an electrophilic moiety of the adsorbates . While one of these undercoordinated sulfur atoms interacts with the hydrogen from water, the other one forms a new S–S bond (find the S3–S4 bond in the III Zn case in Figure ) with the nearest sulfur atom from the surface downward hill layer after water adsorption.…”

“…To study the effect of surface defects on the water/ZnS interactions, we considered the same vacancy types used in our previous investigation for the alanine/ZnS system . Three different deficiencies, namely, sulfur vacancy, zinc vacancy, and double congruent neighboring vacancies, were assumed to exist on the outermost surface layer (Figure ).…”

“…We followed the systematic procedure we introduced in our previous work to construct the initial configuration of adsorbates on the ZnS (110) surface . In this regard, the grand canonical Monte Carlo (GCMC) method was used to search for the possible adsorption sites of water molecules on the surface.…”