LAUSR

Surface chemistry of solids is the fundamental for processes on solid surfaces and properties of solid surfaces, such as heterogeneous catalysis, electrochemistry, corrosion, thin film growth, sensing, friction and lubrication [1]. Understanding surface chemistry of solids is not only of great scientific interest, but also of important technological value for optimizing surface properties and processes. Due to the complexity of solid surface structures, it is challenging to unambiguously elucidate the surface chemistry of surface properties and processes at a molecular level. For example, catalytic CO oxidation to CO2, a simple chemical reaction, has exhibited complex reaction mechanisms far more than expected [2]. However, there also exist surface properties and processes of solids whose surface chemistry turns out to be simple and beautiful. For example, due to the high affinity for carboxylic acids via their bidentate binding, the surface of TiO2 exposed to air and solution was found to selectively adsorb atmospheric carboxylic acids that are typically present in parts-per-billion concentrations while to effectively repel other adsorbates, such as alcohols, that are present in much higher concentrations [3]. The resulting self-assembled carboxylate monolayers have the unusual property of being both hydrophobic and highly water-soluble, which may contribute to the self-cleaning properties of TiO2. Very recently, Zheng, Jiang, Fu and co-workers [4] reported the formation of a surface coordination layer on Cu foils hydrothermally treated in an aqueous solution of sodium formate at 200 °C capable of efficiently passivating oxidation of Cu. The surface of untreated Cu turned fully dark after being kept in 0.1 M NaOH at 25 °C for 8 h, while the Cu foil after formate treatment retained its metallic lustre under the same conditions (Figure 1(a, b)). Quantitative electrochemical measurements demonstrated that the oxidative corrosion rate of formate-treated Cu in 0.1 M NaOH was reduced by 20-fold compared to bare Cu. Interestingly, the anti-corrosion effect of treatment with formate solution depended sensitively on the Cu surface structure, readily achieved for Cu(110) single crystal surfaces but not for Cu(111) and (100) single crystal surfaces (Figure 1(c)). STM characterizations showed the presence of large-scale Cu(110) single-crystalline domains on the formate-treated Cu foils with a perfect Cu(110)-c(6×2) superlattice identical to what observed on the formate-treated Cu(110) single crystal surface (Figure 1(d–f)), and the structure models of the paddlewheel dinuclear Cu(II) formate complex and the Cu(110) surface co-passivated by [Cu(μ-HCOO)(OH)2]2 and O 2−