Interband transitions in closed-shell vacancy containing graphene quantum dots complexed with heavy metals

Abstract

High-performance optical detection of toxic heavy metals by using graphene quantum dots (GQDs) requires a strong interaction between the metals and GQDs, which can be reached through a functionalization/immobilization procedure or doping effect. However, commonly used surface activation approaches induce toxicity into the analysis system and, therefore, are ineligible from the environmental point of view. Here, we show that artificial creation of vacancy-type defects in GQDs can be a helpful means of intentional control of the active sites available for reaction with cadmium (Cd), mercury (Hg) and lead (Pb). Using restricted density functional theory (DFT) and time-dependent DFT (TD-DFT) methods, we predict the effect of vacancy complexes not previously studied to describe the binding ability of GQDs towards metal adsorbates. We also show that the interband absorption in closed-shell GQDs complexed with Cd, Hg and Pb is strongly dependent on the vacancy type and can be efficiently tuned to attain the desired coloration of the analysis system. The results suggest that the vacancy defects play an important role in governing the hybridization between locally-excited (LE) and charge-transfer (CT) states of the GQDs. Based on the molecular orbital analysis and in-depth knowledge of excited states, the mechanisms underlying the interband absorption are discussed.

Insights into the Electrochemical Behavior of Mercury on Graphene/SiC Electrodes

“…Therefore, this material needs to be modified, possibly through introduction of additional electroactive sites (carbon vacancies, for instance) to attain desirable sensing performance, while maintaining the graphene's quality. As has been shown in our previous work [76], the carbon vacancies can significantly improve the adsorption energy of Hg on graphene.…”

Understanding Graphene Response to Neutral and Charged Lead Species: Theory and Experiment

“…Since neutral Lead species are expected to interact with graphene through the attractive van der Waals forces, the equilibrium Pb adsorption configurations were investigated at PBE1PBE-D3 level of restricted DFT, which includes the empirical dispersion correction [ 61 ] with a 6-31G(d) basis set for carbon and hydrogen atoms as well as a basis set developed by the Stuttgart–Dresden–Bonn group (SDD) for the Lead species [ 62 ]. As has been demonstrated in our previous works [ 63 , 64 , 65 ], such a combination of the method and basis sets gives a possibility to predict van der Waals interaction between elemental heavy metals and graphene. On the other hand, electrostatic interaction between divalent charged Lead species and graphene can be estimated by using B3LYP (Becke, three-parameter, Lee-Yang-Parr) exchange-correlation functional [ 66 ].…”

Nature of photoexcited states in ZnO-embedded graphene quantum dots

“…Geometry optimization of the (ZnO) n C 96−2n systems was performed using Perdew-Burke-Ernzerhof exchange-correlation hybrid functional (PBE0, also called PBE1PBE) 78 , which combines 25% exact Hartree-Fock (HF) exchange with 75% of PBE exchange. PBE0 is a reasonable choice to correctly reproduce the experimentally observed electronic and optical properties of ZnO 79 and GQDs 80,81,82 . To validate the results obtained by PBE0, we performed additional calculations using B3LYP 83 and long-range-corrected functionals like CAM-B3LYP 84 and ωB97XD 85 , respectively.…”

“…PBE0 is a reasonable choice to correctly reproduce the experimentally observed electronic and optical properties of ZnO 79 and GQDs. [80][81][82] To validate the results obtained by PBE0, we performed additional calculations using B3LYP 83 and longrange-corrected functionals like CAM-B3LYP 84 and oB97XD, 85 respectively. 6-31G* basis sets 86 were used for carbon, hydrogen, and oxygen atoms, while the SDD basis set developed by the Stuttgart-Dresden-Bonn group 87 was used for zinc atom.…”