A Facile Synthesis of Graphene Quantum Dots via Size-Selective Precipitation and Their Application in GQD-layer Modified
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A Facile Synthesis of Graphene Quantum Dots via Size-Selective Precipitation and Their Application in GQD-layer Modified DSSC Jaehoon Ryu1 and Jyongsik Jang1 1 School of Chemical and Biological Engineering, College of Engineering, Seoul National University (SNU), Seoul, Korea. ABSTRACT A novel approach to synthesize highly luminescent graphene quantum dots (GQDs) with well-defined sizes was explored based on simple oxidation of herringbone-type carbon nanofibers (HCNFs) and size-selective precipitation. In addition, the upconversion properties of GQD were investigated by applying GQD in working electrode of dye-sensitized solar cells (DSSCs). INTRODUCTION Techniques to engineer the bandgap in graphene have attracted significant attention for applications in graphene-based electronics [1]. To date, diverse strategies for the formation of a bandgap in graphene structures have been developed, including graphene quantum dots (GQDs) and graphene nanoribbons (GNRs) [2]. Among graphene nanostructures, GQDs have recently emerged as a potential candidate for fluorescent probes in bioimaging and semiconductor materials in electronic devices due to their unique characteristics, such as high surface area, large diameter, and enhanced surface grafting using the π– π conjugated network or surface groups [3]. Interestingly, GQDs also exhibit upconversion photoluminescence (PL) properties, making them a valuable platform for photoelectrochemical cells. To date, diverse synthetic strategies for GQDs have been developed, including electronbeam lithography, ruthenium-catalyzed C60 transformation, and hydrothermal and electrochemical approaches [4]. However, a dialysis process was required in most previous methods for the removal of additives or unreacted residual materials. Nevertheless, dialysis limits the size separation of GQDs with a diverse range of size. Furthermore, this technique typically takes several days, entails high cost, and requires additional steps for the removal of excess amount of solvent. Thus, it is necessary to develop an efficient and facile strategy for the synthesis of GQDs of various sizes. In this poster, we propose a simple and reliable approach for fabricating well-defined and low size distribution GQDs based on the oxidation of herringbone-type carbon nanofibers (HCNFs) and size-selective precipitation, which quickly separated nanometer-sized GQDs from the bulk GQD solution without a time-consuming dialysis process. This novel and facile approach describes the tailoring of PL emission of GQDs by varying the oxidation temperature and sedimentation velocity, which effectively produced GQDs of varying sizes. Additionally, the upconversion properties of GQD were determined and the response mechanism of the upconversion GQD-layer-modified working electrode in dye-sensitized solar cells (DSSCs) was investigated. In particular, the optimized GQD-layer modified DSSC led to ca. 9.4 % enhanced short circuit current density (Jsc) with long-wavelength absorption bands at 850 nm. The synthesized GQDs proved to be a f
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