Interaction of Magnesium Ions with Pristine Single-Layer and Defected Graphene/Water Interfaces Studied by Second Harmonic Generation
Interaction of Magnesium Ions with Pristine Single-Layer and Defected Graphene/Water Interfaces Studied by Second Harmonic Generation
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DOI：
10.1021/jp410298e
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发表时间：
2014-07-17
影响因子：
3.3
通讯作者：
Geiger, Franz M.
中科院分区：
文献类型：
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作者：
Achtyl, Jennifer L.;Vlassiouk, Ivan V.;Geiger, Franz M.
本研究报告了含有厘米(2)大小的石墨烯的熔融二氧化硅/水界面的热力学和静电参数，范围从单层原始石墨烯到缺陷石墨烯。在pH 7下进行的二次谐波产生（SHG）测量表明，含有缺陷石墨烯的熔融二氧化硅/水界面的表面电荷密度(-0.009(3)至-0.010（3)C/m(2)）介于无缺陷单层石墨烯(-0.0049（8)C/m(2)）和裸熔融二氧化硅(-0.013（6)C/m(2)）之间。根据Lippmann方程计算的熔融二氧化硅/水界面的界面自由能在单层原始石墨烯存在时降低了7倍，而缺陷石墨烯最多只降低了2倍。随后的SHG吸附等温线研究探测了Mg2+在熔融二氧化硅/水界面上的吸附，结果发现了完全可逆的金属离子相互作用，并观察到结合常数K-ads，对于原始石墨烯为4(1)- 5(1)× 10(3) M-1，对于缺陷石墨烯为3(1)- 4(1)× 10(3) M-1，对应于吸附自由能，δ G(ads)，参考水的55.5摩尔浓度，在两个界面上为-30(1)至-31.1(7)kJ/mol。与Mg2+在裸熔融二氧化硅/水界面的吸附相当。根据符合Langmuir吸附等温线的Gouy-Chapman模型获得了最大Mg2+离子密度，发现原始石墨烯每厘米(2)吸附1.1(5)- 1.5(4)× 10（12）个离子，缺陷石墨烯每厘米(2)吸附2(1)- 3.1(5)× 10（12）个离子，略小于裸熔融二氧化硅/水界面上Mg2+吸附的离子密度（（2-4）× 10（12）个离子每厘米(2)），假设镁离子以二价形式结合。我们得出的结论是，石墨烯片上的缺陷，我们估计在1.3 X 10(11) cm(2)左右，只会给热力学和静电参数带来细微的变化。
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 Mg2+ adsorption at the fused silica/water interface result in fully reversible metal ion interactions and observed binding constants, K-ads, of 4(1) - 5(1) x 10(3) M-1 for pristine graphene and 3(1) - 4(1) x 10(3) M-1 for defected graphene, corresponding to adsorption free energies, Delta G(ads), referenced to the 55.5 molarity of water, of -30(1) to -31.1(7) kJ/mol for both interfaces, comparable to Mg2+ adsorption at the bare fused silica/water interface. Maximum Mg2+ 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) X 10(12) ions adsorbed per cm(2) for pristine graphene and 2(1) - 3.1(5) x 10(12) ions adsorbed per cm(2) for defected graphene, slightly smaller than those of for Mg2+ adsorption at the bare fused silica/water interface ((2-4) x 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 X 10(11) cm(2), imparts only subtle changes in the thermodynamic and electrostatic parameters quantified here.