Graphene quantum dots (GQDs) are zero-dimensional materials that exhibit characteristics of both graphene and quantum dots. Herein, we report a rapid, relatively green, one-pot synthesis of size-tunable GQDs from graphene oxide (GO) by a sonochemical method with intermittent microwave heating, keeping the reaction temperature constant at 90 °C. The GQDs were synthesized by oxidative cutting of GO using KMnO4 as an oxidizing agent within a short span of time (30 min) in an acid-free condition. The synthesized GQDs were of high quality and exhibited good quantum yield (23.8%), high product yield (>75%), and lower cytotoxicity (tested up to 1000 μg/mL). Furthermore, the as-synthesized GQDs were demonstrated as excellent fluorescent probes for bioimaging and label-free sensing of Fe(III) ions, with a detection limit as low as 10 × 10–6 M.

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Direct visualization of soft organic molecules like cellulose is extremely challenging under a high-energy electron beam. Herein, we adopt two ionization damage extenuation strategies to visualize the lattice arrangements of the β-(1→4)-D-glucan chains in carboxylated nanocellulose fibers (C-NCFs) having cellulose II crystalline phase using high-resolution transmission electron microscopy. Direct imaging of individual nanocellulose fibrils with high-resolution and least damage under high-energy electron beam is achieved by employing reduced graphene oxide, a conducting material with high electron transmittance and Ag + ions, with high electron density, eliminating the use of sample-specific, toxic staining agents, or other advanced add-on techniques. Furthermore, the imaging of cellulose lattices in a C-NCF/TiO 2 nanohybrid system is accomplished in the presence of Ag + ions in a medium revealing the mode of association of C-NCFs in the system, which validates the feasibility of the presented strategy. The methods adopted here can provide further understanding of the fine structures of carboxylated nanocellulose fibrils for studying their structure−property relationship for various applications.

Metrics & MoreArticle Recommendations(1) We note that the TEM images for the carboxylated nanocellulose fiber (C-NCF) sample given in published article (Figure S1d and S1e, Supporting Information) are ambiguous due to its short length morphology resulted from an experimental error that occurred in the batchwise preparation. We regret for this error and we have provided the reimaged TEM data (Figure 1) for the C-NCF sample. Although the length is not on the micrometer scale, the calculation of percentage crystallinity from the XRD pattern in the published article (Figure S5, Supporting Information) supports the fibrous nature nanocellulose.