Graphene Quantum Dot - Titania Nanoparticle Composite for Photocatalytic Water Splitting
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Graphene Quantum Dot - Titania Nanoparticle Composite for Photocatalytic Water Splitting Sowbaranigha Chinnusamy Jayanthi1, Ravneet Kaur1 and Folarin Erogbogbo1 1 Department of Biomedical, Chemical and Materials Engineering, San Jose State University, San Jose, CA 95112, U.S.A.
ABSTRACT Graphene quantum dots (GQDs) of different sizes were synthesized by the top-down approach, using charcoal as the precursor material. Size and absorption characteristics of synthesized GQDs were analyzed using Transmission Electron Microscopy (TEM), Atomic Force Microscopy (AFM), Photoluminescence Spectroscopy (PL), and UV-vis Spectroscopy. The results showed that GQDs with an average height of 8.5 nm, synthesized at a relatively lower temperature of 85°C, exhibited higher UV and visible light absorption. GQD concentration was varied to form 0.5, 1, 2.5, and 5 wt.% GQD-titania (TiO2) nano composites. Surface morphology of the composite was examined using Scanning Electron Microscopy (SEM). Photocatalytic activity of the samples was assessed from methylene blue dye degradation in UV irradiation at 340nm. A distinguishable trend for pure TiO2 and composites at various concentrations were observed. INTRODUCTION Titania or TiO2 is a promising semiconductor material for photocatalytic water splitting, because it is non-toxic, stable, and cost effective [1]. However, TiO2 as a photo anode material faces some significant challenges, such as poor absorption of visible light, high carrier recombination, and limited charge-carrier transport [2,3]. Many researchers have attempted to overcome these limitations and significantly enhance the photocatalytic property by combining TiO2 with different carbon based nanoparticles [2,4,5]. In particular, GQDs are reported to exhibit bandgap tunability and enhance light absorption by including the UV and also the visible regions of the electromagnetic spectrum [6,7]. GQD nanostructures exhibit band gap tunability based on their size and have the potential to enhance the photo absorption in TiO2. Thus far, GQDs have been synthesized from expensive precursor materials, such as graphene oxides and fullerenes or using non-scalable lithography techniques [8-10]. In the present study, GQDs are synthesized by a wet chemical method using inexpensive bird charcoal as the starting material. The feasibility to vary the size and, hence the absorption bands of GQDs, by modifying the synthesis temperature is demonstrated. TEM and AFM images are used to examine the lateral and vertical size distribution of GQD samples. In addition, UVvis spectroscopy was used to examine the absorption edges of different sized GQDs and the impact of GQDs on the photocatalytic performance of TiO2.
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EXPERIMENT GQDs were synthesized following the modified protocol of Ye et al. and Peng et al. [11,12] using
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