Toward combining graphene and QDs: Assembling CdTe QDs to exfoliated graphite and nanographene in water

Herein, we report for the first time on a full-fledged investigation of water-soluble CdTe quantum dots (QD) that are immobilized onto exfoliated graphite (EG) and/or nanographene (NG). Particular emphasis was placed on a top-down preparation of stable aqueous dispersions–starting from natural graphite rather than graphene oxide–while preserving the intrinsic properties of graphene. To this end, we circumvented the harsh conditions commonly employed for the pre-exfoliation (i.e., Hummers method). First, a hydrophobic–hydrophobic/π–π stacking motif was tested between EG and pyrene, to which QDs are covalently attached (QD-pyrene). Second, we employed the combination of hydrophobic–hydrophobic/π–π stacking and electrostatic interactions to build up hierarchical structures composed of NG, positively charged pyrene (pyrene+), and negatively charged QDs. The novel nanohybrids—QD-pyrene/EG and QD/pyrene+/NG—were characterized with specific emphasis on electron-transfer chemistry. In fact, both assays provide kinetic and spectroscopic evidence that support electron transfer dynamics that vary, however, between EG and NG as a reflection of the different degree of graphite exfoliation.