Shtepliuk Ivan, Khranovskyy Volodymyr, Yakimova Rositsa
Department of Physics, Chemistry and Biology, Linköping University, SE-58183, Linköping, Sweden.
Phys Chem Chem Phys. 2017 Nov 22;19(45):30445-30463. doi: 10.1039/c7cp04711h.
Exploring graphene quantum dots (GQDs) is an attractive way to design novel optical and electrochemical sensors for fast and reliable detection of toxic heavy metals (HMs), such as Cd, Hg and Pb. There are two main strategies for achieving this: (i) surface modification of an electrochemical working electrode by nanoscale GQDs and (ii) using a GQD solution electrolyte for optical sensing. Further development of these sensing technologies towards reaching or exceeding the WHO permissible limits implies deep understanding of the interaction between GQDs and HMs in different dielectric media. Solvent is expected to be one of the key factors affecting the binding ability of the GQDs to HMs and their electronic and optical properties. Here we show that the solvent-solute interaction changes the geometrical configuration, stability and absorption spectra of zigzag/armchair-edged GQDs after complexation with neutral and charged HM species. We observe physisorption behavior of Cd and Hg adatoms on the sp surface with a solvent-mediated enhancement of the binding energy with increasing solvent polarity. For Pb adatoms, an opposite picture is revealed. We find that the solvent effect also manifests itself in weakening of the chemisorption strength in the HM cation-π system with increasing dielectric constant of the solvent. Thus, a solvent engineering strategy based on control of the dielectric permittivity can be a promising approach to reach the desired binding energy in the HM@GQDs and to provide high sensitivity and selectivity of both optical and electrochemical sensors to toxic HMs we are interested in.
探索石墨烯量子点（GQDs）是设计新型光学和电化学传感器以快速可靠地检测有毒重金属（HMs）（如镉、汞和铅）的一种有吸引力的方法。实现这一目标有两种主要策略：（i）通过纳米级GQDs对电化学工作电极进行表面修饰，以及（ii）使用GQD溶液电解质进行光学传感。将这些传感技术进一步发展以达到或超过世界卫生组织的允许限值，意味着要深入了解GQDs与不同介电介质中HMs之间的相互作用。溶剂有望成为影响GQDs与HMs结合能力及其电子和光学性质的关键因素之一。在这里，我们表明溶剂 - 溶质相互作用改变了锯齿形/扶手椅形边缘GQDs与中性和带电HM物种络合后的几何构型、稳定性和吸收光谱。我们观察到镉和汞吸附原子在sp表面的物理吸附行为，随着溶剂极性增加，结合能通过溶剂介导得到增强。对于铅吸附原子，呈现出相反的情况。我们发现，随着溶剂介电常数的增加，溶剂效应还表现为HM阳离子 - π体系中化学吸附强度的减弱。因此，基于控制介电常数的溶剂工程策略可能是一种有前景的方法，以在HM@GQDs中达到所需的结合能，并为我们感兴趣的有毒HMs提供光学和电化学传感器的高灵敏度和选择性。
