National Research Council Research Associate , Athens, Georgia United States.
Environ Sci Technol. 2014 Jan 21;48(2):961-9. doi: 10.1021/es403247k. Epub 2014 Jan 8.
Interactions of graphene oxide (GO) with silica surfaces were investigated using a quartz crystal microbalance with dissipation monitoring (QCM-D). Both GO deposition and release were monitored on silica- and poly-l-lysine (PLL) coated surfaces as a function of GO concentration and in NaCl, CaCl2, and MgCl2 as a function of ionic strength (IS). Under favorable conditions (PLL-coated positive surface), GO deposition rates increased with GO concentration, as expected from colloidal theory. Increased NaCl concentration resulted in a greater deposition attachment efficiency of GO on the silica surface, indicating that deposition of GO follows Derjaguin-Landau-Verwey-Overbeek (DLVO) theory; GO deposition rates decreased at high IS, however, due to large aggregate formation. GO critical deposition concentration (CDC) on the silica surface is determined to be 40 mM NaCl which is higher than the reported CDC values of fullerenes and lower than carbon nanotubes. A similar trend is observed for MgCl2 which has a CDC value of 1.2 mM MgCl2. Only a minimal amount of GO (frequency shift <2 Hz) was deposited on the silica surface in CaCl2 due to the bridging ability of Ca(2+) ions with GO functional groups. Significant GO release from silica surface was observed after adding deionized water, indicating that GO deposition is reversible. The release rates of GO were at least 10-fold higher than the deposition rates under similar conditions indicating potential high release and mobility of GO in the environment. Under favorable conditions, a significant amount of GO was released which indicates potential multilayer GO deposition. However, a negligible amount of deposited GO was released in CaCl2 under favorable conditions due to the binding of GO layers with Ca(2+) ions. Release of GO was significantly dependent on salt type with an overall trend of NaCl > MgCl2 > CaCl2.
采用石英晶体微天平（QCM-D）监测耗散，研究了氧化石墨烯（GO）与二氧化硅表面的相互作用。分别在二氧化硅和聚赖氨酸（PLL）涂层表面监测了 GO 的沉积和释放过程，研究了 GO 浓度以及 NaCl、CaCl2 和 MgCl2 中离子强度（IS）对这两个过程的影响。在有利条件下（带正电的 PLL 涂层表面），GO 的沉积速率随 GO 浓度的增加而增加，这与胶体理论相符。增加 NaCl 浓度会导致 GO 在二氧化硅表面的沉积附着效率增加，这表明 GO 的沉积符合德加古林-朗道-维尔威（DLVO）理论；然而，由于大的聚集体形成，在高 IS 下 GO 的沉积速率降低。GO 在二氧化硅表面的临界沉积浓度（CDC）确定为 40 mM NaCl，这高于报道的富勒烯和碳纳米管的 CDC 值，低于碳纳米管。在 MgCl2 中观察到类似的趋势，其 CDC 值为 1.2 mM MgCl2。由于 Ca（2+）离子与 GO 官能团的桥接能力，在 CaCl2 中仅沉积了少量 GO（频率变化<2 Hz）。加入去离子水后，观察到大量的 GO 从二氧化硅表面释放，表明 GO 的沉积是可逆的。在相似条件下，GO 的释放速率至少是沉积速率的 10 倍，这表明 GO 在环境中具有较高的释放和迁移能力。在有利条件下，GO 大量释放，这表明 GO 可能存在多层沉积。然而，在有利条件下，在 CaCl2 中，由于 GO 层与 Ca（2+）离子的结合，沉积的 GO 几乎没有释放。GO 的释放明显依赖于盐的类型，总体趋势为 NaCl>MgCl2>CaCl2。
