| 摘要: | 帶有咪唑官能基的有機硫化物已作為緩蝕劑和生物傳感器受到廣泛的研究，然而它們在電化學界面的吸附狀態尚未被充分探討。本研究透過循環伏安法和原位掃描穿隧式顯微鏡技術，探討了咪唑硫醇MMI(2-mercapto-1-methylimidazole)、苯並咪唑硫醇MBIT(1-methyl-1H-benzimidazole-2-thiol)與MMBI(2-mercapto-5-methylbenzimidazole)分子在金(111)電極上的吸附行為與電位、pH值、陰離子的關係。研究結果闡明，在正電位下，分子以非質子化的形式吸附在金表面上， MMI和MBIT以硫和氮端與金電極鍵結，分子解析度的STM分別顯示了有序的陣列結構與特殊蜂窩結構；在負電位下，分子的金-氮鍵斷裂，導致MMI吸附層的無序化，而MBIT和MMBI以π-π 相互作用力緊密排列，吸附層重組為相似的有序線條結構，此結構重組過程與咪唑官能基的質子化反應密切相關；在更負的電位下，隨著金-硫鍵的斷裂，分子從金表面脫附。由金(111)電極表面的凹洞特徵顯示，分子以典型的硫-金-硫模式吸附於金(111)電極上形成有序結構，而MBIT可能以Au(MBIT)3的模式形成特殊的有序蜂窩結構。此外也觀察到MBIT和MMBI與陰離子的共吸附確實影響了它們的有序吸附結構。
本研究的第二部份揭示了鎳在金電極上的成核和生長過程，以及硫醇分子對鎳沉積的影響。透過長時間的STM掃描，鎳吸附原子穿透到金電極的最上層進而產生鎳-金混和表面，而在金(111)區域進一步沉積鎳將產生多層的moiré pattern。添加MMI分子使鎳在金表面均勻地成核並提前成核電位，形成了平坦的鎳單層，同時MMI與鎳層結合吸附於表面，最終多層鎳以3D方向生長。循環伏安法的結果顯示，添加MMI對鎳的沉積具有顯著的加速效果，鎳的沉積量和效率皆有明顯地提升，推測MMI分子與Ni2+結合形成Ni(MMI)x2+錯合物，有效地傳輸到金電極上進而促進鎳的沉積。相比之下，由於苯環的貢獻，MBIT和MMBI形成了較疏水的阻擋層，不利於Ni(H2O)62+接近金電極表面，進而抑制了鎳的電沉積。本研究揭示了咪唑硫醇分子在金(111)電極上的吸附狀態及其在鎳電鍍過程中的作用，有助於深入理解有機硫化物在電化學界面上的吸附行為，進而幫助開發新型電鍍劑。
;Organic sulfides with imidazole functional groups have been extensively studied as corrosion inhibitors and biosensors. However, their adsorption behavior at the electrochemical interface remains insufficiently explored. In this study, the adsorption behavior of imidazolethiol and benzimidazolethiol molecules, such as 2-mercapto-1-methylimidazole (MMI), 1-methyl-1H-benzimidazole-2-thiol (MBIT), and 2-Mercapto-5-methylbenzimidazole (MMBI), on a Au(111) electrode was investigated using cyclic voltammetry (CV) and scanning tunneling microscopy (STM). The relationship between the adsorption behavior and factors such as potential, pH, and anions was examined.
The results elucidated that the adsorbed MMI and MBIT molecule assumed the unprotonated form, allowing its S- and N-ends to bind with the Au electrode at a positive potential, resulting in ordered array structures and a unique honeycomb structure, respectively, as observed through Molecular resolution STM imaging. At negative potentials, the N-Au bond broke, leading to disorder in the MMI adsorption layer. In contrast, MBIT and MMBI closely packed through π-π interactions, resulting in a similar ordered line structure. This restructuring event was coupled with the protonation of the imidazole functional group. At more negative potentials, the S−Au bond broke, causing the molecules to desorb from the Au electrode. The observation of pitted surface morphology on the Au (111) electrode surface indicated that the molecules adsorbed in a typical S-Au-S motif, forming ordered structures. MBIT possibly formed a unique honeycomb structure as Au(MBIT)3. Additionally, the coadsorption of MBIT and MMBI with anions indeed affected their ordered adsorption structures.
The second part of this study focused on the nucleation and growth process of Ni on the Au electrode and the influence of thiol molecules on Ni deposition. Protracted STM scanning could enable Ni adatoms penetrating the uppermost layer of Au electrode, yielding a Ni-Au mixed surface. Further Ni deposition on the Au(111) domains leads to multilayered moiré patterns. The MMI additive causes uniform Ni nucleation on the Au(111) electrode at a more positive potential than that observed without MMI, forming a smooth Ni adlayer on the Au electrode. Meanwhile, MMI molecules adsorb to the Ni deposit with their –S and –N ends. Bulk Ni deposition with MMI is 3D, resulting in a rolling hill morphology. CV results showed that the addition of MMI significantly accelerated nickel deposition, leading to increased deposition quantity and efficiency. It was speculated that MMI molecules formed Ni(MMI)x2+ complexes, effectively transferred to the Au electrode, and facilitated Ni deposition. In contrast, due to the contribution of the benzene ring, MBIT and MMBI formed hydrophobic barrier layers that hindered the approach of Ni(H2O)62+ to the Au electrode surface, thus suppressing Ni electrodeposition.
This study provided insights into the adsorption states of imidazolethiol molecules on a Au (111) electrode and their role in the Ni electrodeposition process. It contributes to a better understanding of the adsorption behavior of organic sulfides at the electrochemical interface and can aid in the development of novel electroplating agents. |
