Key Laboratory of Northwest Water Resource, Environment and Ecology, MOE, Xi'an University of Architecture and Technology, Xi'an 710055, China.
Shaanxi Key Laboratory of Environmental Engineering, Xi'an University of Architecture and Technology, Xi'an 710055, China.
Environ Sci Technol. 2021 Nov 2;55(21):14639-14648. doi: 10.1021/acs.est.1c04463. Epub 2021 Oct 14.
In this work, aggregation of graphene oxide (GO) in synthetic surface water at high pH was elaborated, and experimental characterizations and molecular dynamics simulations were employed to uncover the mechanisms. According to previous studies, aggregation of GO is supposed to be impossible at high pH considering the deprotonation of functional groups on GO and the increased electrostatic repulsions. However, significant aggregations and a reversed trend in zeta potential at high pH were observed. One of the mechanisms was that the promoted metal adsorption at high pH can offset the negative charges generated by the deprotonation. Additionally, the stripping of oxidation debris (OD) on GO also contributes to the unexpected trend in the aggregation behavior and zeta potential. GO consists of lightly oxidized functionalized graphene (FG) sheets and highly oxidized OD. Upon the increase of pH and the deprotonation of functional groups on FG and OD, OD was stripped from FG, which decreased the electrostatic repulsions between FG sheets and accelerated the aggregation. The stripped ODs may recombine to FG edges and bridged FG sheets, which also contribute to the aggregation. Upon the stripping of OD and microstructure transformation of FG, FG-water-OD aggregates formed. According to this study, the aggregation of GO was accompanied by deprotonation of functional groups, metal adsorption, and surface property transformation triggered by the stripping of ODs and should be considered during the development of GO-related nanomaterials and the evaluation of its environmental impact.
在这项工作中，详细阐述了在高 pH 值的合成地表水中文物氧化石墨烯（GO）的聚集，并用实验表征和分子动力学模拟来揭示其机制。根据之前的研究，考虑到 GO 上的官能团去质子化和增加的静电斥力，GO 在高 pH 值下应该不可能聚集。然而，在高 pH 值下观察到了显著的聚集和zeta 电位的反向趋势。其中一个机制是，高 pH 值下促进的金属吸附可以抵消由去质子化产生的负电荷。此外，GO 上氧化碎片（OD）的剥落也导致了聚集行为和 zeta 电位的意外趋势。GO 由轻度氧化的官能化石墨烯（FG）片和高度氧化的 OD 组成。随着 pH 值的升高和 FG 和 OD 上官能团的去质子化，OD 从 FG 上剥落，这降低了 FG 片之间的静电斥力并加速了聚集。剥落的 OD 可能重新结合到 FG 边缘并桥接 FG 片，这也有助于聚集。随着 OD 的剥落和 FG 的微观结构转变，形成了 FG-水-OD 聚集物。根据这项研究，GO 的聚集伴随着官能团的去质子化、金属吸附以及由 OD 剥落引发的表面性质转变，在开发 GO 相关纳米材料和评估其环境影响时应予以考虑。
