The band gap properties of graphene quantum dots (GQDs) arise from quantum confinement effects and differ from those in semimetallic graphene sheets. Tailoring the size of the band gap and understanding the band gap tuning mechanism are essential for the applications of GQDs in opto-electronics. In this study, we observe that the photoluminescence (PL) of the GQDs shifts due to charge transfers between functional groups and GQDs. GQDs that are functionalized with amine groups and are 1-3 layers thick and less than 5 nm in diameter were successfully fabricated using a two-step cutting process from graphene oxides (GOs). The functionalized GQDs exhibit a redshift of PL emission (ca. 30 nm) compared to the unfunctionalized GQDs. Furthermore, the PL emissions of the GQDs and the amine-functionalized GQDs were also shifted by changes in the pH due to the protonation or deprotonation of the functional groups. The PL shifts resulted from charge transfers between the functional groups and GQDs, which can tune the band gap of the GQDs. Calculations from density functional theory (DFT) are in good agreement with our proposed mechanism for band gap tuning in the GQDs through the use of functionalization.

RGO flakes are homogeneously dispersed in a Cu matrix through a molecular-level mixing process. This novel fabrication process prevents the agglomeration of the RGO and enhances adhesion between the RGO and the Cu. The yield strength of the 2.5 vol% RGO/Cu nanocomposite is 1.8 times higher than that of pure Cu. The strengthening mechanism of the RGO is investigated by a double cantilever beam test using the graphene/Cu model structure.

The scalable preparation of two-dimensional hexagonal boron nitride (h-BN) is essential for practical applications. Despite intense research in this area, high-yield production of two-dimensional h-BN with large-size and high solubility remains a key challenge. In the present work, we propose a scalable exfoliation process for hydroxyl-functionalized BN nanoplatelets (OH-BNNPs) by a simple ball milling of BN powders in the presence of sodium hydroxide via the synergetic effect of chemical peeling and mechanical shear forces. The hydroxide-assisted ball milling process results in relatively large flakes with an average size of 1.5 μm with little damage to the in-plane structure of the OH-BNNP and high yields of 18%. The resultant OH-BNNP samples can be redispersed in various solvents and form stable dispersions that can be used for multiple purposes. The incorporation of the BNNPs into the polyethylene matrix effectively enhanced the barrier properties of the polyethylene due to increased tortuosity of the diffusion path of the gas molecules. Hydroxide-assisted ball milling process can thus provide simple and efficient approaches to scalable preparation of large-size and highly soluble BNNPs. Moreover, this exfoliation process is not only easily scalable but also applicable to other layered materials.

Since the first discovery of carbon nanotubes (CNTs) in 1991, a window to new technological areas has been opened. [1] One of the emerging applications of CNTs is the reinforcement of composite materials to overcome the performance limits of conventional materials. [2,3] Recent developments in CNT/polymer composites have shown the potential for improving the strength of polymers, [2] and this finding has encouraged researchers to use carbon nanotubes as reinforcements for metal and ceramic matrices.[4±7] However, because of the difficulties in distributing CNTs homogeneously in a metal or ceramic matrix by means of traditional composite processes, it has been doubted whether CNTs can really reinforce metals or ceramics.[4±7] Here we report on a CNTreinforced Cu matrix nanocomposite, fabricated by a novel fabrication process called ªmolecular-level mixingº; this nanocomposite shows extremely high strength, several times higher than the matrix. The novel process for fabricating CNT/Cu composite powders involves suspending CNTs in a solvent by surface functionalization, mixing Cu ions with the CNT suspension, drying, calcination, and reduction. This process produces CNT/Cu composite powders, whereby the CNTs are homogeneously implanted within the Cu powders. The CNT/Cu nanocomposite, consolidated by spark plasma sintering of CNT/Cu composite powders, is shown to possess three times the strength of the Cu matrix and to have twice the Young's modulus. This extraordinary strengthening effect of carbon nanotubes in metal is higher than that of any other reinforcement ever used for metal-matrix composites. Several researchers have attempted to fabricate CNT-reinforced metal-or ceramic-matrix composite materials by COMMUNICATIONS

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