Achtyl Jennifer L, Vlassiouk Ivan V, Surwade Sumedh P, Fulvio Pasquale F, Dai Sheng, Geiger Franz M
Department of Chemistry, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208, United States.
J Phys Chem B. 2014 Jul 17;118(28):7739-49. doi: 10.1021/jp410298e. Epub 2014 Feb 26.
This work reports thermodynamic and electrostatic parameters for fused silica/water interfaces containing cm(2)-sized graphene ranging from a single layer of pristine graphene to defected graphene. Second harmonic generation (SHG) measurements carried out at pH 7 indicate that the surface charge density of the fused silica/water interface containing the defected graphene (-0.009(3) to -0.010(3) C/m(2)) is between that of defect-free single layer graphene (-0.0049(8) C/m(2)) and bare fused silica (-0.013(6) C/m(2)). The interfacial free energy of the fused silica/water interface calculated from the Lippmann equation is reduced by a factor of 7 in the presence of single-layer pristine graphene, while defected graphene reduces it only by a factor of at most 2. Subsequent SHG adsorption isotherm studies probing the Mg(2+) adsorption at the fused silica/water interface result in fully reversible metal ion interactions and observed binding constants, Kads, of 4(1) - 5(1) × 10(3) M(-1) for pristine graphene and 3(1) - 4(1) × 10(3) M(-1) for defected graphene, corresponding to adsorption free energies, ΔGads, referenced to the 55.5 molarity of water, of -30(1) to -31.1(7) kJ/mol for both interfaces, comparable to Mg(2+) adsorption at the bare fused silica/water interface. Maximum Mg(2+) ion densities are obtained from Gouy-Chapman model fits to the Langmuir adsorption isotherms and found to range from 1.1(5) - 1.5(4) × 10(12) ions adsorbed per cm(2) for pristine graphene and 2(1) - 3.1(5) × 10(12) ions adsorbed per cm(2) for defected graphene, slightly smaller than those of for Mg(2+) adsorption at the bare fused silica/water interface ((2-4) × 10(12) ions adsorbed per cm(2)), assuming the magnesium ions are bound as divalent species. We conclude that the presence of defects in the graphene sheet, which we estimate here to be around 1.3 × 10(11) cm(2), imparts only subtle changes in the thermodynamic and electrostatic parameters quantified here.
这项工作报告了含有厘米尺寸石墨烯的熔融石英/水界面的热力学和静电参数，这些石墨烯范围从单层原始石墨烯到有缺陷的石墨烯。在pH值为7时进行的二次谐波产生（SHG）测量表明，含有有缺陷石墨烯的熔融石英/水界面的表面电荷密度（-0.009(3)至-0.010(3) C/m²）介于无缺陷单层石墨烯（-0.0049(8) C/m²）和裸露熔融石英（-0.013(6) C/m²）之间。根据 Lippmann 方程计算得出，在存在单层原始石墨烯的情况下，熔融石英/水界面的界面自由能降低了7倍，而有缺陷的石墨烯仅使其最多降低2倍。随后对熔融石英/水界面上Mg²⁺吸附进行的SHG吸附等温线研究导致金属离子相互作用完全可逆，原始石墨烯的观测结合常数Kads为4(1) - 5(1)×10³ M⁻¹，有缺陷的石墨烯为3(1) - 4(1)×10³ M⁻¹，对应于以水的55.5摩尔浓度为参考的吸附自由能ΔGads，两个界面均为-30(1)至-31.1(7) kJ/mol，与Mg²⁺在裸露熔融石英/水界面的吸附情况相当。通过对朗缪尔吸附等温线进行古依 - 查普曼模型拟合获得了最大Mg²⁺离子密度，发现原始石墨烯每平方厘米吸附的离子数为1.1(5) - 1.5(4)×10¹²个，有缺陷的石墨烯为2(1) - 3.1(5)×10¹²个，假设镁离子以二价形式结合，略小于Mg²⁺在裸露熔融石英/水界面的吸附量（每平方厘米吸附(2 - 4)×10¹²个离子）。我们得出结论，石墨烯片层中的缺陷（我们在此估计约为1.3×10¹¹ cm²）仅对这里量化的热力学和静电参数产生细微变化。
