Preparation of multicolored carbon quantum dots using HNO 3 /HClO 4 oxidation of graphitized carbon
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Preparation of multicolored carbon quantum dots using HNO3/HClO4 oxidation of graphitized carbon Chao Tan1, Songlin Zuo1,a), Yunyang Zhao2
, Baoshou Shen3
1
College of Chemical Engineering, Jiangsu Provincial Key Lab for the Chemistry and Utilization of Agro-forest Biomass, Nanjing Forestry University, Nanjing 210037, China 2 Institute of Applied Physics and Materials Engineering, Joint Key Laboratory of the Ministry of Education, University of Macau, Macau 999078, China 3 Department of Environmental Engineering, College of Urban and Environmental Sciences Northwest University, Xi’an 710127, China a) Address all correspondence to this author. e-mail: [email protected] Received: 31 May 2019; accepted: 7 August 2019
The microstructure of carbon quantum dots (CQDs) has a great influence on their fluorescence properties. Here, different microstructures of CQDs were synthesized by the selective oxidation of graphitized activated carbon using HNO3/HClO4 as the oxidant. We characterized the microstructure and surface chemistry of the CQDs, and the results show that the degree of graphitization of activated carbon has a significant effect on the structure and fluorescence properties of the obtained CQDs. The fluorescence of the CQD solution can be tuned from yellow to green by regulating the degree of graphitization of the activated carbon by heat treatment at high temperature (up to 2500 °C). Moreover, the increased degree of graphitization of the raw carbon precursor is beneficial for significantly reducing the fluorescence self-absorption quenching of the concentrated CQD solution. Importantly, the as-prepared CQDs have no cytotoxicity and can be used as bioimaging agents.
Introduction Carbon quantum dots (CQDs) are a new type of carbon nanomaterial with particle sizes ,10 nm and have attracted an increasing amount of attention due to their photoluminescence performance since their discovery from carbon nanotubes in 2004 [1]. When compared to traditional metal quantum dots, CQDs show great potential for wide application in the fields of fluorescent probes [2], bioimaging [3], and medical diagnosis [4], because of their excellent photochemical stability, low toxicity and good biocompatibility. In general, CQDs can be synthesized using two approaches, bottom-up and top-down. In the bottom-up process, CQDs are obtained from small-molecular weight substances, such as citric acid [5], amino acids [6], and glucose [7], using hydrothermal synthesis [8, 9]. Disadvantages of this process are as follows: it needs high temperature (for hydrothermal), expensive raw materials, and so on. In the top-down process, raw carbon materials are reduced to the size of CQDs using physical or chemical methods, such as chemical oxidation [10], electrochemical oxidation [11], laser etching [12], and arc discharge [13]. Compared with the bottom-up method, this process usually
ª The Author(s) 2019
uses cheap and environment friendly precursors, so it is widely used by many researchers. The fluorescence properties of CQDs are mainly determined by their
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