One-Step Synthesis of N-Doped Graphene Quantum Dots from

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One-Step Synthesis of N-Doped Graphene Quantum Dots from Chitosan as a Sole Precursor Using Chemical Vapor Deposition Subodh Kumar, Tarik Aziz, Olga Girshevitz, and Gilbert Daniel Nessim J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.7b05494 • Publication Date (Web): 03 Jan 2018 Downloaded from http://pubs.acs.org on January 3, 2018

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The Journal of Physical Chemistry

One-Step Synthesis of N-Doped Graphene Quantum Dots from Chitosan as a Sole Precursor Using Chemical Vapor Deposition Subodh Kumar, SK Tarik Aziz, Olga Girshevitz, and Gilbert D. Nessim* Department of Chemistry, Bar Ilan Institute for Nanotechnology and Advanced Materials (BINA), Bar Ilan University, Ramat-Gan 52900, Israel. E-mail: [email protected]

ABSTRACT We present a simple, environment-friendly, and fast synthesis of nitrogen-doped graphene quantum dots (N-GQDs) on copper foil by chemical vapor deposition using exclusively chitosan, a cheap and non-toxic biopolymer, as a carbon and nitrogen precursor. We characterized the synthesized N-doped graphene quantum dots using Raman spectroscopy, XPS, AFM, HRTEM and HRSEM and found them to be in the range 10-15 nm in diameter and 2-5 nm-thick with 4.2 % of maximum nitrogen content. The proposed growth mechanism process includes three key steps: (1) decomposition of chitosan into nitrogen-containing compounds, (2) adsorption of reactive species (HCN) on the copper surface, and (3) nucleation to form N-doped graphene quantum dots. The synthesized N-GQDs exhibit photoluminescence (PL) emission in the visible band region, thus making them suitable for applications in nano-optoelectronics.

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INTRODUCTION Numerous carbon nanomaterials (0D, 1D, 2D and 3D) have been developed with exceptional thermal, chemical, mechanical, and electrical properties.1-7 Graphene, a 2D nanostructure, and its derivatives are materials of interest owing to its excellent electronic,8 magnetic,9 optical,10 and electro-catalytic properties.11 These properties can be tailored by changing its shape,12 size,13 intrinsic structure,14 and surface functional groups.15 Graphene sheets with lateral dimensions of less than 100 nm and less than 10 layers exhibit quantum confinement effect and edge effects and are called graphene quantum dots (GQDs).16 These GQDs generally consist of sp2/sp3 carbon and oxygen-based functional groups. Graphene quantum dots have received wide attention owing to their unique properties such as strong luminescence, high solubility, biocompatibility, and low cytotoxicity; they have been applied in the field of drug delivery,17 catalysts,18 bioimaging19 and photovoltaics.20 Graphene quantum dots doped with hetero-atoms exhibit amended properties and provide a means to design and fabricate new devices.21-24 The nitrogen atom, owing comparable atomic size as the carbon atom, has been widely used as an ideal dopant for graphene-based carbon materials to confer graphene with semiconducting properties. Incorporation of nitrogen atoms in the graphene lattice causes polarization in the carbon network owing to its higher electronegativity, thereby influencing the electronic and optical properties.25-26 The well- known way to synthesize nitrogen-doped graphene quantum dots (N-GQDs) is to first convert graphitic material into nitrogen-doped graphene-based material (N-reduced graphene oxide or N-doped CNTs) into sheets followed by its chemical cutting into N-GQDs by harsh oxidation using concentrated acids (H2SO4 and HNO3).27-28 There are other efficient approaches to produce NGQDs, such as hydrothermal,29 microwave,30 electrochemical treatment26 of graphene oxide


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using different nitrogen source, and stepwise organic synthesis.31 These N-GQDs generally possess oxygen and nitrogen functional groups. However, the use of harmful and corrosive acids and the tedious synthesis process make these methods not suitable from a sustainability point of view. Chemical vapor deposition (CVD) is an alternative technique for the fabrication of luminescent GQDs, while controlling the size and number of graphene layer per quantum dot.3233

However, to our knowledge, there is no report on the direct synthesis of nitrogen-doped

graphene quantum dots (N-GQDs) using CVD yet. Here, we propose a low-temperature, onestep CVD synthesis process using chitosan, a non-toxic green precursor. Chitosan is the second most abundant biopolymer in nature and has received considerable interest in recent decades mainly due to its low-cost, non-toxicity, biocompatibility, and multifunctional properties.34 It is mainly composed of 2-amino-2-deoxy-D-glucopyranose units and exhibits ~7 % nitrogen content. However, owing to its low reactivity and no solubility in organic solvents, chitosan is the least exploited biomass source.35 Thermal analysis has shown that chitosan starts to decompose at a temperature higher than 220 °C.36 Moreover, thermal decomposition of chitosan is well documented in the literature.37-38 Recently, we reported a thermal approach to synthesize nitrogen-doped reduced graphene oxide using chitosan as a nitrogen source to introduce N atoms into the resultant reduced graphene oxide in a single step, basically using chitosan as a nitrogen-doping source.39 In this new work, the thermal decomposition of chitosan provides both the carbon that will form the graphene quantum dots and the nitrogen that will dope the quantum dots. Both steps occur concurrently to synthesize N-GQDs directly on copper foil via a simple, one-step atmospheric pressure CVD method at a comparatively lower temperature.



EXPERIMENTAL Materials and Gases Chitosan and copper foil were purchased from Sigma Aldrich and Alfa Aesar respectively. Chitosan was used after drying at 100 °C under argon atmosphere. The copper foil was also cleaned by dipping it in acetic acid and then washed with water, isopropanol, and acetone using sonication. Compressed cylinder tanks of argon gas and hydrogen gas were procured from Gas Technologies with the purity of 99.999%. An atmospheric-pressure three-zone furnace fitted with quartz tube with an internal diameter of 22 mm was used for the synthesis of N-GQDs.40-41 The furnace temperatures were measured by the built-in furnace thermocouples and flows of argon and hydrogen gases were maintained using electronic mass flow controllers.

Characterization Techniques A high-resolution scanning electron microscope (HRSEM), FEI, Magellan 400Li, operating at 18 keV comprising energy dispersive X-ray spectrometer (EDS) system for elemental analysis was used to determine the surface morphology and elemental analysis of synthesized N-GNDs. Atomic Force Spectroscopy measurements (AFM) were carried out using a Bio FastScan scanning probe microscope (Bruker AXS). The measurements were performed under environmental conditions. The resolution of the images was 512 samples/line. For image processing and analysis, the Nanoscope Analysis Software was used. We applied the “flatting” and “planefit” functions before analyzing the AFM images. X-ray photoelectron spectroscopy (XPS) analysis was performed in a Kratos AXIS-HS spectrometer, using a monochromatized Al Kα source. All XPS measurements were carried out at room temperature, under vacuum of 1.03.0 × 10-9 Torr. Raman spectra of synthesized materials were collected in a back scattering


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configuration at room temperature using a micro-Raman spectrometer HR 800 (Jobin Yvon Horiba) with 532 nm excitation source and a microscope objective (50X, Olympus LWD). The ultraviolet visible (UV-Vis) absorption spectra of N-GQDs was recorded on Cary 300 UVVisible absorbance spectrophotometer to determine the optical absorption in the wavelength range of 200-800 nm with resolution of 1 nm. Fluorescence emission spectra of N-GQDs were recorded on Cary Eclipse Fluorescence emission photometer. The structural analysis of the N-GQDs were investigated with the use of a 200 KV thermionicgun transmission electron microscope (TEM, Joel 2100). We prepared the samples for high resolution transmission electron microscopy (HRTEM) by sonicating the copper foil in isopropanol and by depositing a few drops of the resulting suspension on a TEM copper grid. The morphological and structural studies of the N-GQDs were performed using conventional selected area diffraction (SAED) with 300 nm aperture.

Synthesis of N-Doped Graphene Quantum Dots (N-GQDs) The synthesis of N-GQDs was performed using an atmospheric chemical vapor deposition (CVD) system using solely chitosan as carbon and nitrogen source under argon and hydrogen atmosphere. A schematic representation of the N-GQDs synthesis process is shown in Figure 1. In a typical experiment, chitosan (500 mg) and copper foil (30 mm × 20 mm × 0.25 mm) were positioned in the quartz tube of the CVD furnace in the Zone 1 and in the Zone 3, respectively. Firstly, we annealed the copper foil under Ar and H2 gaseous mixture at 1000 °C for one hour while positioning the chitosan outside the heated zone of the furnace with a fan blowing on the exposed quartz tube to keep the chitosan at room temperature. The flows of Ar and H2 were respectively set at 100 and 300 sccm. The annealing step was followed by a growth step. This



gas mixture was flown while the furnace heating zones 1 and 2 were ramped to 250 °C and 300 °C, respectively. Once the set temperatures of both zones were reached, the quartz tube was shifted, thus positioning the chitosan in the Zone 1 and the copper foil in the Zone 3. To start the growth process, the temperature of the Zone 1 was increased from 250 to 300 °C, while maintaining the Zone 3 temperature set at 300 °C. After reaching 300 °C in the Zone 1, the growth process continued for 3 additional minutes. The flows of Ar and H2 were respectively set at 30 and 150 sccm during the growth process. After the growth was completed, the quartz tube was shifted out of the furnace to slowly cool down to room temperature under a flow of argon before removing the sample from the furnace.

Figure 1: Schematic diagram for the synthesis of N-GQDs

RESULTS AND DISCUSSION Thermal decomposition of chitosan includes de-polymerization of chitosan chains and decomposition of pyranose rings through dehydration and deamination.42 These reactions result


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in the formation of various nitrogen-containing volatile compounds such as acetonitrile, furan, pyrrole, pyridine and pyrazine derivatives.43 Moreover, it is a complex process involving various chemical reactions, leading to the disintegration of intramolecular forces and the breaking of the molecular structure of nitrogen-containing compounds accompanied by the exclusion of small molecular gases such as HCN, C2H2, NH3, CO and CO2.44-46 The mechanistic way in which CNTs and graphene grow from the interaction of hydrocarbons species and with a catalytic metal surface may resemble what is happening here.47 It is well accepted that triple bonded C-C species are produced as a byproduct during the thermal decomposition of hydrocarbons and are found to be active species for the high yield growth of CNTs.48 However, Pint et al. have demonstrated that HCN, the decomposition byproduct of acetonitrile and pyridine, are more reactive species compared to C2H2 for the super growth of SWCNTs.49 According these studies, we presume that triple-bonded HCN obtained by chitosan pyrolysis are the active species and the whole growth process mainly includes three steps; (1) decomposition of chitosan into nitrogen-containing compounds; (2) adsorption of reactive species (HCN) on the copper surface, (3) and nucleation to form N-doped graphene quantum dots. We assume that initially, HCN arrives to the surface of a Cu film and decomposes to yield carbon atoms, which can diffuse to the interface between film and substrate leading to the nucleation and growth of buried layers.50-51 The presence of water, formed by the decomposition of chitosan, during the growth44 could be responsible for etching the edges of the graphene domains, simultaneously to nitrogen-doping, thus leading to the formation of N-GQDs. The etching behavior of water and oxygen impurities during graphene growth is well documented in the literature. 52-54 We characterized the prepared N-GQDs using different techniques such as HRSEM, HRTEM, AFM, EDX, XPS, Raman and Fluorescence spectroscopy. We used HRSEM to analyze the



morphology of the N-GQDs on copper foil. Figures 2b and 2c clearly show the presence and distribution of N-GQDs on the copper foil after growth at different magnification. In order to investigate the effect of growth time on the morphology and the size of the N-GQDs, we increased the growth time from 3 to 5 minutes. Consequently, we observed larger nitrogendoped graphene quantum dots with sizes of 40-50 nm (Figure S1, Supplemental information). However, further increases of the growth time did not affect the size and thickness of the NGQDs. From this, we infer that the chitosan completely decomposed in 5 min.

Figure 2: HRSEM images of a) pristine copper foil; b) and c) copper foil after 3 min growth at 300 °C with different magnification.

HRTEM images of the N-GQDs transferred on a copper grid (Fig. 3a), indicate aggregates of NGQDs with overlapped boundaries revealing a size distribution between 10-15 nm. These aggregates are the result of sample preparation, where the N-GQDs were transferred from the copper foil to a HRTEM copper grid using sonication and dropcasting. However, the lattice fringes of the N-GQDs can be clearly observed. Selected area electron diffraction (SAED) was used to map the crystallographic orientation of the aggregated domains, showing that N-GQDs are polycrystalline in nature. The calculated inter-planar distances of 0.288, 0.236 and 0.179 nm from the SAED image correspond to the (002), (100), and (102) planes respectively, which is comparable with the results reported in the previous literature.32, 55-56 Multiple spots appearing in


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the SAED patterns indicate that there are rotational stacking faults within the region measured.57 This is due to back-folding of edges, intrinsic rotational stacking faults, overlapping domains, or from a boundary region where the two domains meet and have different crystallographic orientations.

Figure 3: a) HR-TEM Image of N-GQDs transferred on Copper grid; b) and their corresponding SAED pattern We performed AFM to identify the number of stacked graphene layers in an individual N-GQD by measuring its thickness. The AFM images and the corresponding thickness profiles shown in Figure 4a indicate that the samples consisted of few-layer graphene sheets. We estimated the thickness of individual N-GQDs to be in the 2-5 nm range, which corresponds to the thickness of 4-10 graphene sheets.58 However, the thickness of individual N-GQDs significantly increased to 20-28 nm when we increased the growth time to 5 minutes (Figure S2, Supplemental information). From the combined information of HRSEM and AFM, we can conclude that the



size and the thickness of individual N-GQDs increased for increasing growth time, when the same amount of chitosan was provided.

Figure 4: a) AFM image of N-GNDs on copper foil with thickness profile (inset); b) Raman spectrum

The Raman spectra of N-GQDs on copper foil showed two characteristic peaks centered at 1350 cm-1 and 1585 cm-1, which are attributed to the D band and G band respectively (Figure 4b). The D band generally arises due to the defects in the form of sp3 carbon. However, the G band is observed due to the sp2 carbon of graphitic domains and the in-plane vibration of sp2 carbon bonded atoms. We calculated the integral intensity ratio of D and G bands (ID/IG ratio) to be 1.05, which indicates a large number of defects presents in the form of edges and surface functionalized moieties in the N-GQDs. This may also indicate partially disoriented and stacking of graphene sheets in the N-doped graphene quantum dots. Moreover, the broad nature of the D band suggests structure distortion caused by intercalation of nitrogen atoms into its graphitic lattice planes.26


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We performed XPS analysis to elucidate the surface chemical nature of N-GQDs. Survey scan shows predominant C1s and O1s peaks at 285.2 and 531.9 eV. A pronounced N1s peak at 399.5 eV was also observed confirming the presence of nitrogen in the synthesized N-GQDs (Figure 5a). These results also support the EDX analysis (not presented here). The high resolution XPS spectra in C1s region exhibited mainly two characteristic peak components at binding energy 285.1 and 288.5 eV revealing the presence of graphitic and oxidized carbon respectively.

Figure 5: a) XPS survey scan; b) high resolution C1s XPS spectra; c) high resolution N1s XPS spectra of N-GNDs and d) schematic diagram of single-layer of N-GQDs.



This C1s peak is further deconvoluted into C=C, C-N/C-O and C=O/COOH components to determine the existence of C-N bond. We observed additional resolved peak centered at 286.2 eV, which is an apparent indication of C-N bond formation. Moreover, the scan on the N1s region gave two predominant peaks at 399.8 and 401.0 eV due to the presence of pyrrolic and graphitic N content, and one minor peak at 398.5 due to the pyridinic N content, respectively. However, amine can also be present because also ammonia can be formed from the decomposition of chitosan.44 The position of the energy peak of N-amine overlaps with the known position of the N-pyrrolic compound,59 thus rendering accurate deconvolution of its peak difficult. We estimated the N/C atomic ratio, which is found to be 6.0 %, higher than those NGQDs prepared by other method.26, 60 We preformed UV-Vis absorption spectra for the N-GQDs to determine the optical band gap. Absorption spectra of the synthesized N-GQDs are displayed in Figure 6a. We observed a strong absorption band at around 270 nm, which is blue-shifted by 50 nm with respect to that of N-free GQDs,20 ascribed to the π-π* transition of C=C. In addition, we also absorbed a broad band at 335 nm in the ultra-violet region tailing up to 600 nm, which generally arise due to the nitrogen doping,61 and used to determine the bandgap of the N-GQDs by Tauc-Plot, extrapolating the line tangent to the plotted (Ahv)^2 vs. hv curve (Figure 6a, insertion). The value associated with the point of intersection of the line tangent with the horizontal axis (hv axis) indicated a 3.46 eV optical bandgap of N-GQDs, which is in good agreement with similar values reported in the literature.62


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Figure 6: a) Absorption spectra with inserted Tauc-Plot for band gap calculation; b) PLE and PL spectra of N-GQDs on copper foil

We obtained the photoluminescence (PL) spectrum directly from the N-GQDs on copper foil excited at 333 nm (Figure 6b). The PL spectrum shows a comparatively narrow sharp peak at 448 nm with full width half maximum 15 nm compared to those of N-GQDs synthesized by chemical methods.60 Even though our N-GQDs have much narrower emission peaks, the result is in good agreement with the work of Yang et al., of graphene oxide quantum dots grown on silicon.33 These results indicate that the as-synthesized N-GQDs possess interesting optoelectronic properties.

CONCLUSION We successfully synthesized N-GQDs on copper foil using as carbon and nitrogen precursor only chitosan, a cheap and nontoxic biopolymer, by a simple, fast and eco-friendly low-temperature atmospheric pressure CVD technique. We suggest the plausible steps of the synthesis mechanism and assume that water, formed by the decomposition of chitosan, allows the growth of N-GQDs



instead of graphene sheets on the surface of the copper foil. The synthesized N-GQDs exhibited n-doped graphene layers with an average diameter of 10-15 nm. The size and density of the NGQDs can be effectively tailored by controlling the growth time. In addition, N-GQDs on copper foil emit a sharp and strong luminescence at a wavelength of 448 nm rendering them suitable for optoelectronic applications.

ASSOCIATED CONTENT Supporting Information. Supporting Information Available: This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author * Tel. +972 3 7384540. E-mail: [email protected] Notes The authors declare no competing financial interest.

ACKNOWLEDGEMENTS S.K. acknowledge the Planning and Budgeting Committee of the Council for Higher Education for his PBC Post-Doctoral Fellowship. G.D.N. would also like to thank the Israel Science Foundation, VATAT and the Israel Prime Minister’s Office fuel alternatives initiative for partial funding of this study under the Israel Research center for Electrochemical Propulsion (INREP).


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REFERENCES (1)

Qian, H.; Greenhalgh, E. S.; Shaffer, M. S.; Bismarck, A. Carbon Nanotube-Based Hierarchical Composites. J. Mater. Chem. 2010, 20, 4751-4762. (2) Lin, C.-Y.; Zhao, Z.; Niu, J.; Xia, Z. Synthesis, Properties and Applications of 3d Carbon Nanotube– Graphene Junctions. J. Phys. D: Appl. Phys. 2016, 49, 443001. (3) Balandin, A. A. Thermal Properties of Graphene and Nanostructured Carbon Materials. Nat. Mater. 2011, 10, 569-581. (4) Geim, A. K.; Novoselov, K. S. The Rise of Graphene. Nat. Mater. 2007, 6, 183-191. (5) Velasco-Santos, C.; Martínez-Hernández, A. L.; Fisher, F. T.; Ruoff, R.; Castaño, V. M. Improvement of Thermal and Mechanical Properties of Carbon Nanotube Composites through Chemical Functionalization. Chem. Mater. 2003, 15, 4470-4475. (6) Shen, J.; Zhu, Y.; Yang, X.; Li, C. Graphene Quantum Dots: Emergent Nanolights for Bioimaging, Sensors, Catalysis and Photovoltaic Devices. Chem. Commun. 2012, 48, 3686-3699. (7) Nessim, G. D. Properties, Synthesis, and Growth Mechanisms of Carbon Nanotubes with Special Focus on Thermal Chemical Vapor Deposition. Nanoscale 2010, 2, 1306-1323. (8) Neto, A. C.; Guinea, F.; Peres, N. M.; Novoselov, K. S.; Geim, A. K. The Electronic Properties of Graphene. Rev. Mod. Phys. 2009, 81, 109. (9) Matte, H. R.; Subrahmanyam, K.; Rao, C. Novel Magnetic Properties of Graphene: Presence of Both Ferromagnetic and Antiferromagnetic Features and Other Aspects. J. Phys. Chem. C 2009, 113, 9982-9985. (10) Avouris, P. Graphene: Electronic and Photonic Properties and Devices. Nano Lett. 2010, 10, 4285-4294. (11) Zhou, X.; Qiao, J.; Yang, L.; Zhang, J. A Review of Graphene-Based Nanostructural Materials for Both Catalyst Supports and Metal-Free Catalysts in Pem Fuel Cell Oxygen Reduction Reactions. Adv. Energy Mater. 2014, 4. (12) Whitby, R. L. Chemical Control of Graphene Architecture: Tailoring Shape and Properties. ACS Nano 2014, 8, 9733-9754. (13) Ma, T.; Liu, Z.; Wen, J.; Gao, Y.; Ren, X.; Chen, H.; Jin, C.; Ma, X.-L.; Xu, N.; Cheng, H.-M. Tailoring the Thermal and Electrical Transport Properties of Graphene Films by Grain Size Engineering. Nat. Commun. 2017, 8. (14) Singh, A. K.; Ahmad, M.; Singh, V. K.; Shin, K.; Seo, Y.; Eom, J. Tailoring the Electrical Properties of Graphene Layers by Molecular Doping. ACS Appl. Mater. Interfaces 2013, 5, 5276-5281. (15) Tang, Q.; Zhou, Z.; Chen, Z. Graphene-Related Nanomaterials: Tuning Properties by Functionalization. Nanoscale 2013, 5, 4541-4583. (16) Buzaglo, M.; Shtein, M.; Regev, O. Graphene Quantum Dots Produced by Microfluidization. Chem. Mater. 2015, 28, 21-24. (17) Liu, Z.; Robinson, J. T.; Sun, X.; Dai, H. Pegylated Nanographene Oxide for Delivery of WaterInsoluble Cancer Drugs. J. Am. Chem. Soc. 2008, 130, 10876-10877. (18) Jin, H.; Huang, H.; He, Y.; Feng, X.; Wang, S.; Dai, L.; Wang, J. Graphene Quantum Dots Supported by Graphene Nanoribbons with Ultrahigh Electrocatalytic Performance for Oxygen Reduction. J. Am. Chem. Soc. 2015, 137, 7588-7591. (19) Zhu, S.; Zhang, J.; Qiao, C.; Tang, S.; Li, Y.; Yuan, W.; Li, B.; Tian, L.; Liu, F.; Hu, R. Strongly GreenPhotoluminescent Graphene Quantum Dots for Bioimaging Applications. Chem. Commun. 2011, 47, 6858-6860. (20) Li, Y.; Hu, Y.; Zhao, Y.; Shi, G.; Deng, L.; Hou, Y.; Qu, L. An Electrochemical Avenue to GreenLuminescent Graphene Quantum Dots as Potential Electron-Acceptors for Photovoltaics. Adv. Mater. 2011, 23, 776-780.



(21) Li, S.; Li, Y.; Cao, J.; Zhu, J.; Fan, L.; Li, X. Sulfur-Doped Graphene Quantum Dots as a Novel Fluorescent Probe for Highly Selective and Sensitive Detection of Fe3+. Anal. Chem. 2014, 86, 1020110207. (22) Zhang, L.; Zhang, Z.-Y.; Liang, R.-P.; Li, Y.-H.; Qiu, J.-D. Boron-Doped Graphene Quantum Dots for Selective Glucose Sensing Based on the “Abnormal” Aggregation-Induced Photoluminescence Enhancement. Anal. Chem. 2014, 86, 4423-4430. (23) Yang, S.; Sun, J.; He, P.; Deng, X.; Wang, Z.; Hu, C.; Ding, G.; Xie, X. Selenium Doped Graphene Quantum Dots as an Ultrasensitive Redox Fluorescent Switch. Chem. Mater. 2015, 27, 2004-2011. (24) Tang, L.; Ji, R.; Li, X.; Bai, G.; Liu, C. P.; Hao, J.; Lin, J.; Jiang, H.; Teng, K. S.; Yang, Z. Deep Ultraviolet to near-Infrared Emission and Photoresponse in Layered N-Doped Graphene Quantum Dots. ACS Nano 2014, 8, 6312-6320. (25) Yeh, T. F.; Teng, C. Y.; Chen, S. J.; Teng, H. Nitrogen-Doped Graphene Oxide Quantum Dots as Photocatalysts for Overall Water-Splitting under Visible Light Illumination. Adv. Mater. 2014, 26, 32973303. (26) Li, Y.; Zhao, Y.; Cheng, H.; Hu, Y.; Shi, G.; Dai, L.; Qu, L. Nitrogen-Doped Graphene Quantum Dots with Oxygen-Rich Functional Groups. J. Am. Chem. Soc. 2011, 134, 15-18. (27) Li, M.; Wu, W.; Ren, W.; Cheng, H.-M.; Tang, N.; Zhong, W.; Du, Y. Synthesis and Upconversion Luminescence of N-Doped Graphene Quantum Dots. Appl. Phys. Lett. 2012, 101, 103107. (28) Qian, Z.; Zhou, J.; Chen, J.; Wang, C.; Chen, C.; Feng, H. Nanosized N-Doped Graphene Oxide with Visible Fluorescence in Water for Metal Ion Sensing. J. Mater. Chem. 2011, 21, 17635-17637. (29) Hu, C.; Liu, Y.; Yang, Y.; Cui, J.; Huang, Z.; Wang, Y.; Yang, L.; Wang, H.; Xiao, Y.; Rong, J. One-Step Preparation of Nitrogen-Doped Graphene Quantum Dots from Oxidized Debris of Graphene Oxide. J. Mater. Chem. B 2013, 1, 39-42. (30) Zheng, B.; Chen, Y.; Li, P.; Wang, Z.; Cao, B.; Qi, F.; Liu, J.; Qiu, Z.; Zhang, W. Ultrafast AmmoniaDriven, Microwave-Assisted Synthesis of Nitrogen-Doped Graphene Quantum Dots and Their Optical Properties. Nanophotonics 2017, 6, 259-267. (31) Yan, X.; Cui, X.; Li, L.-s. Synthesis of Large, Stable Colloidal Graphene Quantum Dots with Tunable Size. J. Am. Chem. Soc. 2010, 132, 5944-5945. (32) Hassanien, A. S.; Shedeed, R. A.; Allam, N. K. Graphene Quantum Sheets with Multiband Emission: Unravelling the Molecular Origin of Graphene Quantum Dots. J. Phys. Chem. C 2016, 120, 21678-21684. (33) Huang, K.; Lu, W.; Yu, X.; Jin, C.; Yang, D. Highly Pure and Luminescent Graphene Quantum Dots on Silicon Directly Grown by Chemical Vapor Deposition. Part. Part. Syst. Charact. 2016, 33, 8-14. (34) Rinaudo, M. Chitin and Chitosan: Properties and Applications. Prog. Polym. Sci. 2006, 31, 603632. (35) Kumar, M. N. R. A Review of Chitin and Chitosan Applications. React. Funct. Polym. 2000, 46, 127. (36) Grząbka-Zasadzińska, A.; Amietszajew, T.; Borysiak, S. Thermal and Mechanical Properties of Chitosan Nanocomposites with Cellulose Modified in Ionic Liquids. J. Therm. Anal. Calorim. 2017, 1-12. (37) Zawadzki, J.; Kaczmarek, H. Thermal Treatment of Chitosan in Various Conditions. Carbohydr. Polym. 2010, 80, 394-400. (38) Georgieva, V.; Zvezdova, D.; Vlaev, L. Non-Isothermal Kinetics of Thermal Degradation of Chitosan. Chem. Cent. J. 2012, 6, 81. (39) Kumar, S.; Gonen, S.; Freidman, A.; Elbaz, L.; Nessim, G. D. Doping and Reduction of Graphene Oxide Using Chitosan-Derived Volatile N-Heterocyclic Compounds for Metal-Free Oxygen Reduction Reaction. Carbon 2017, 120, 419-426.


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(40) Teblum, E.; Itzhak, A.; Shawat-Avraham, E.; Muallem, M.; Yemini, R.; Nessim, G. D. Differential Preheating of Hydrocarbon Decomposition and Water Vapor Formation Shows That Single Ring Aromatic Hydrocarbons Enhance Vertically Aligned Carbon Nanotubes Growth. Carbon 2016, 109, 727-736. (41) Somekh, M.; Shawat, E.; Nessim, G. D. Fully Reproducible, Low-Temperature Synthesis of HighQuality, Few-Layer Graphene on Nickel Via Preheating of Gas Precursors Using Atmospheric Pressure Chemical Vapor Deposition. J. Mater. Chem. A 2014, 2, 19750-19758. (42) Rybarczyk, M. K.; Lieder, M.; Jablonska, M. N-Doped Mesoporous Carbon Nanosheets Obtained by Pyrolysis of a Chitosan–Melamine Mixture for the Oxygen Reduction Reaction in Alkaline Media. RSC Adv. 2015, 5, 44969-44977. (43) Zeng, L.; Qin, C.; Wang, L.; Li, W. Volatile Compounds Formed from the Pyrolysis of Chitosan. Carbohydr. Polym. 2011, 83, 1553-1557. (44) Qiao, Y.; Chen, S.; Liu, Y.; Sun, H.; Jia, S.; Shi, J.; Pedersen, C. M.; Wang, Y.; Hou, X. Pyrolysis of Chitin Biomass: Tg–Ms Analysis and Solid Char Residue Characterization. Carbohydr. Polym. 2015, 133, 163-170. (45) Imamura, G.; Saiki, K. Synthesis of Nitrogen-Doped Graphene on Pt (111) by Chemical Vapor Deposition. J. Phys. Chem. C 2011, 115, 10000-10005. (46) Hore, N.; Russell, D. Radical Pathways in the Thermal Decomposition of Pyridine and Diazines: A Laser Pyrolysis and Semi-Empirical Study. J. Chem. Soc., Perkin Trans. 2, 1998, 0, 269-276. (47) Puretzky, A. A.; Merkulov, I. A.; Rouleau, C. M.; Eres, G.; Geohegan, D. B. Revealing the Surface and Bulk Regimes of Isothermal Graphene Nucleation and Growth on Ni with in Situ Kinetic Measurements and Modeling. Carbon 2014, 79, 256-264. (48) Plata, D. L.; Meshot, E. R.; Reddy, C. M.; Hart, A. J.; Gschwend, P. M. Multiple Alkynes React with Ethylene to Enhance Carbon Nanotube Synthesis, Suggesting a Polymerization-Like Formation Mechanism. ACS Nano 2010, 4, 7185-7192. (49) Pint, C. L.; Sun, Z.; Moghazy, S.; Xu, Y.-Q.; Tour, J. M.; Hauge, R. H. Supergrowth of NitrogenDoped Single-Walled Carbon Nanotube Arrays: Active Species, Dopant Characterization, and Doped/Undoped Heterojunctions. ACS Nano 2011, 5, 6925-6934. (50) Chen, W.; Cui, P.; Zhu, W.; Kaxiras, E.; Gao, Y.; Zhang, Z. Atomistic Mechanisms for Bilayer Growth of Graphene on Metal Substrates. Phys. Rev. B 2015, 91, 045408. (51) Nie, S.; Wu, W.; Xing, S.; Yu, Q.; Bao, J.; Pei, S.-s.; McCarty, K. F. Growth from Below: Bilayer Graphene on Copper by Chemical Vapor Deposition. New J. Phys. 2012, 14, 093028. (52) Asif, M.; Tan, Y.; Pan, L.; Li, J.; Rashad, M.; Usman, M. Thickness Controlled Water Vapors Assisted Growth of Multilayer Graphene by Ambient Pressure Chemical Vapor Deposition. J. Phys. Chem. C 2015, 119, 3079-3089. (53) Li, J.; Wang, D.; Wan, L.-J. Unexpected Functions of Oxygen in a Chemical Vapor Deposition Atmosphere to Regulate Graphene Growth Modes. Chem. Commun. 2015, 51, 15486-15489. (54) Choubak, S.; Levesque, P. L.; Gaufres, E.; Biron, M.; Desjardins, P.; Martel, R. Graphene Cvd: Interplay between Growth and Etching on Morphology and Stacking by Hydrogen and Oxidizing Impurities. J. Phys. Chem. C 2014, 118, 21532-21540. (55) Fan, T.; Zeng, W.; Tang, W.; Yuan, C.; Tong, S.; Cai, K.; Liu, Y.; Huang, W.; Min, Y.; Epstein, A. J. Controllable Size-Selective Method to Prepare Graphene Quantum Dots from Graphene Oxide. Nanoscale Res. Lett. 2015, 10, 55. (56) Sadhukhan, M.; Bhowmik, T.; Kundu, M. K.; Barman, S. Facile Synthesis of Carbon Quantum Dots and Thin Graphene Sheets for Non-Enzymatic Sensing of Hydrogen Peroxide. RSC Adv. 2014, 4, 49985005. (57) Warner, J. H.; Rümmeli, M. H.; Gemming, T.; Büchner, B.; Briggs, G. A. D. Direct Imaging of Rotational Stacking Faults in Few Layer Graphene. Nano Lett. 2008, 9, 102-106.



(58) Shearer, C. J.; Slattery, A. D.; Stapleton, A. J.; Shapter, J. G.; Gibson, C. T. Accurate Thickness Measurement of Graphene. Nanotechnology 2016, 27, 125704. (59) Pels, J.; Kapteijn, F.; Moulijn, J.; Zhu, Q.; Thomas, K. Evolution of Nitrogen Functionalities in Carbonaceous Materials During Pyrolysis. Carbon 1995, 33, 1641-1653. (60) Dey, S.; Govindaraj, A.; Biswas, K.; Rao, C. Luminescence Properties of Boron and Nitrogen Doped Graphene Quantum Dots Prepared from Arc-Discharge-Generated Doped Graphene Samples. Chem. Phys. Lett. 2014, 595, 203-208. (61) Shi, B.; Zhang, L.; Lan, C.; Zhao, J.; Su, Y.; Zhao, S. One-Pot Green Synthesis of Oxygen-Rich Nitrogen-Doped Graphene Quantum Dots and Their Potential Application in Ph-Sensitive Photoluminescence and Detection of Mercury (Ii) Ions. Talanta 2015, 142, 131-139. (62) Liu, Q.; Guo, B.; Rao, Z.; Zhang, B.; Gong, J. R. Strong Two-Photon-Induced Fluorescence from Photostable, Biocompatible Nitrogen-Doped Graphene Quantum Dots for Cellular and Deep-Tissue Imaging. Nano Lett. 2013, 13, 2436-2441.


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One-Step Synthesis of N-Doped Graphene Quantum Dots from

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