On the formation of hydrogen gas on copper in anoxic water

Triple Effects of the Physicochemical Interaction between Water and Copper and Their Influence on Microcutting

Water has been recognized in promoting material removal, traditionally ascribed to friction reduction and thermal dissipation. However, the physicochemical interactions between water and the workpiece have often been overlooked. This work sheds light on how the physicochemical interactions that occur between water (H2O) and copper (Cu) workpiece influence material deformations during the cutting process. ReaxFF molecular dynamics simulations were employed as the primary method to study the atomistic physical and chemical interactions between the applied medium and the workpiece. Upon contact with the Cu surface, H2O dissociated into OH- ions, H+ ions, and traces of O2- ions. The OH- and O2- ions chemically reacted with Cu to form bonds that weakened the Cu-Cu bonds by elongation, while the H+ ions gained electrons and diffused into the Cu lattice as H- ions. The weakening of surface Cu bonds promoted plastic deformation and reduced the difficulty of material removal. Meanwhile, further addition of H2O molecules saw a plateau in hydrolysis and more dominance of H2O physical adsorption on Cu, which weakens the elongation of Cu-Cu bonds. While the ideal case for atomic-scale material removal was found with an optimal number of 240 H2O molecules, the presented Cu material state with more H2O molecules could account for the observations in microcutting. The constricted nature of physical adsorption and hydrogen ion diffusion in the surface layer prevented the propagation of dislocations through the surface, which subsequently caused pinning points to be closer together during chip formation as observed by smaller chip fold widths on the microscale. Theoretical and experimental analysis identified the importance of accounting for physicochemical interactions between surface media and the workpiece when considering material deformations at micronanoscale.

Copper nanoparticles/graphene modified green rusts for debromination of tetrabromobisphenol A: Enhanced galvanic effect, electron transfer and adsorption

The combined effect of copper nanoparticles (Cu NPs) and reduced graphene oxide (RGO) on the reactivity of green rust (GR) towards reductive debromination of tetrabromobisphenol (TBBPA) has been systematically investigated. The removal efficiency of TBBPA increased from 28.78% to 44.70% and the pseudo first-order rate constant (k_obs) increased from 0.002 min^-1 to 0.004 min^-1 when the content of Cu NPs in GR_SO4-Cu NPs increased from 0% to 0.5%. Cu NPs enhanced the reductive reactivity of GR via formation of a galvanic cell and Cu⁰/Cu⁺ redox cycle. The adsorption capacity of RGO towards TBBPA was 13.75 mg/g. The pseudo first-order rate constant for TBBPA removal increased from 0.0341 min^-1 to 0.0866 min^-1 when the RGO content increased from 0 to 2% in GR-Cu NPs-RGO. RGO enhanced the debromination efficiency via enhancing the adsorption of TBBPA and accelerating electron transfer amongst GR, Cu NPs and TBBPA. The increased corrosion current demonstrates the enhanced electron transfer by RGO in GR-Cu NPs galvanic cell. Six-electron transfer process of TBBPA reduction was revealed by rotating disk electrode analysis, which was in line with the final debromination products (Mono-BPA) determined by ion chromatography and liquid chromatography-mass spectrometry.

Molecular and dissociative adsorption of water and hydrogen sulfide at perfect and defective Cu(110) surfaces

The adsorption of H₂O and H₂S onto Cu(110) surfaces lead to considerably different geometries and surface reconstruction and relaxation mechanisms.