Insights into Copper Sulfide Formation from Cu and S K edge XAS and DFT studies.
Sara A AzzamAlexey BoubnovAdam S HoffmanTirso López-AusensNicole ChiangGriffin CanningPhilippe SautetSimon R BareDante A SimonettiPublished in: Inorganic chemistry (2020)
An understanding of the fundamentals of the reaction between CuO with trace amounts of H2S to form CuS products is critical for the optimal utilization of this process in sulfur removal applications. Unfortunately, CuS is a complex material, featuring various Cu2-xS compounds (with 0 ≤ x ≤ 1), distorted crystal phases, and varying electronic structures and coordination environments of Cu and S ions. In this work, we combine ex situ and in situ X-ray absorption spectroscopy (XAS) at S and Cu K edges, fixed bed sorption experiments, DFT simulations, and other characterization techniques to speciate the CuS products formed at different temperatures (298-383 K) and from CuO sorbents with different crystallite sizes (2.8-40 nm). The results of our analysis identify the formation of a distorted CuS layer at the surface of CuO crystals with disulfide groups with shorter Cu-S bonds and higher delocalization of the positive charge of the Cu center into (S1-)2. This distorted CuS layer dominates the XAS signal at lower temperatures (298-323 K) and at the initial stages of sulfidation at higher temperatures (353 and 383 K) where conversion is low (<40%). First-principles atomistic simulations confirm the thermodynamic favorability of the formation of surface (S1-)2 on both CuO (111) and (1̅11) surfaces, providing further support for our experimental observations. Furthermore, these simulations reveal that the presence of disulfide bonds stabilized surface hydroxyl groups, leading to lower Gibbs Free Energies of their surface migration.
Keyphrases
- aqueous solution
- molecular dynamics
- density functional theory
- high resolution
- metal organic framework
- computed tomography
- magnetic resonance imaging
- gene expression
- cystic fibrosis
- escherichia coli
- single cell
- photodynamic therapy
- genome wide
- heavy metals
- molecular dynamics simulations
- simultaneous determination
- biofilm formation
- crystal structure
- liquid chromatography
- data analysis