Neklyudov Vadim V, Khafizov Nail R, Sedov Igor A, Dimiev Ayrat M
Laboratory for Advanced Carbon Nanomaterials, Kazan Federal University, 18 Kremlevkaya str., 420008 Kazan, Russian Federation.
Department of Physical Chemistry, Kazan Federal University, 18 Kremlevkaya str., Kazan 420008, Russian Federation.
Phys Chem Chem Phys. 2017 Jul 5;19(26):17000-17008. doi: 10.1039/c7cp02303k.
One of the main advantages of graphene oxide (GO) over its non-oxidized counterpart is its ability to form stable solutions in water and some organic solvents. At the same time, the nature of GO solutions is not completely understood; the existing data are scarce and controversial. Here, we demonstrate that the solubility of GO, and the stability of the as-formed solutions depend not just on the solute and solvent cohesion parameters, as commonly believed, but mostly on the chemical interactions at the GO/solvent interface. By the DFT and QTAIM calculations, we demonstrate that the solubility of GO is afforded by strong hydrogen bonding established between GO functional groups and solvent molecules. The main functional groups taking part in hydrogen bonding are tertiary alcohols; epoxides play only a minor role. The magnitude of the bond energy values is significantly higher than that for typical hydrogen bonding. The hydrogen bond energy between GO functional groups and solvent molecules decreases in the sequence: water > methanol > ethanol. We support our theoretical results by several experimental observations including solution calorimetry. The enthalpy of GO dissolution in water, methanol and ethanol is -0.1815 ± 0.0010, -0.1550 ± 0.0012 and -0.1040 ± 0.0010 kJ g, respectively, in full accordance with the calculated trend. Our findings provide an explanation for the well-known, but poorly understood solvent exchange phenomenon.
氧化石墨烯（GO）相较于其未氧化的对应物的主要优势之一在于它能够在水和一些有机溶剂中形成稳定的溶液。与此同时，GO溶液的性质尚未被完全理解；现有的数据稀少且存在争议。在此，我们证明GO的溶解度以及所形成溶液的稳定性不仅如通常所认为的那样取决于溶质和溶剂的内聚参数，而且主要取决于GO/溶剂界面处的化学相互作用。通过密度泛函理论（DFT）和量子拓扑原子分子理论（QTAIM）计算，我们证明GO的溶解度是由GO官能团与溶剂分子之间形成的强氢键所赋予的。参与氢键形成的主要官能团是叔醇；环氧化物仅起次要作用。键能值的大小明显高于典型氢键的键能值。GO官能团与溶剂分子之间的氢键能按以下顺序降低：水＞甲醇＞乙醇。我们通过包括溶液量热法在内的若干实验观察结果来支持我们的理论结果。GO在水、甲醇和乙醇中的溶解焓分别为-0.1815±0.0010、-0.1550±0.0012和-0.1040±0.0010 kJ/g，完全符合计算趋势。我们的发现为众所周知但理解不足的溶剂交换现象提供了解释。
