Adsorption of ion pairs onto graphene flakes and impacts of counterions during the adsorption processes

作者：Zhu, Chang; Yun, Jiena; Wang, Qian; Yang, Gang^*

来源：Applied Surface Science, 2018, 435: 329-337.

DOI：10.1016/j.apsusc.2017.11.105

• Adsorption configuration
• Counterion effects
• Electron transfer
• Density functional theory calculations
• Edge-functionalization

Although cations and anions are two integral constituents for all electrolytes, adsorption of ion pairs onto carbonaceous materials gains obviously less attention than adsorption of only cations or anions. Here DFT calculations are employed finding that four adsorption configurations emerge for KI onto graphene flakes (GF) instead of three for the other ion pairs. Reservation of ionic bonds is critical to their stabilities, and the bilateral configurations, where GFs couple with both cations and anions, are disfavored due to rupture of ionic bonds. Relative stabilities of two vertical configurations can be regulated and even reversed through edge-functionalization. Surprisingly, the horizontal adsorption configurations, which are global energy minima as long as present, are non-existent for a majority of ion pairs, and their existence or not is determined by the adsorption differences between halide ions and alkali ions (Delta E-ad). Counterions effects for both cations and anions increase with the atomic electronegativities and cations correspond to stronger counterion effects; e.g., Li+ added on the other side of GFs promotes the adsorption of F-more pronouncedly than edge-functionalization. Mechanisms of electron transfers are also discussed, and three alteration patterns by counterions are observed for each type of adsorption configurations. Furthermore, addition of counterions causes band gaps to vary within a wider range that may be useful to design electronic devices.

• 出版日期2018-3-30
• 单位西南大学