The Synthesis Of Functionalized Graphene And Carbon Dots And Their Applications In Sensors

Graphene, a one-atom layer of graphite, possesses a unique two-dimensional structure and excellent mechanical, thermal, and electrical properties, and thus has been widely applied in the design of devices of micro-nano-electronics, optoelectronics, novel composite materials and sensing materials. Compared with the conventional quantum dots, fluorescent carbon dots(CDs) are more promising for the application in biology labelling and life science owing to their unique properties such as large two-photon absorption crosssection, high chemical inertness, facile functionalization, high resistance to photobleaching, low toxicity, and good biocompatibility.As a part of the project supported by the National Nature Science Foundation of China(NO. 21173070) and the Innovator Foundation of the Colleges and Universities of Henan Province(No. 124200510014), the preparation of the functionalized graphene composites and carbon dots were carried out through chemical reduction and hydrothermal method in this thesis. The composition and structure of these carbon-based nanomaterials were characterized by electron microscopy, the X-ray photoelectron spectra, and so on. Furthermore, the relationships between the compositions, morphologies and structures of these carbon-based nanomaterials and their properties were primarily explored, and the applications of the as-prepared carbon-based nanomaterials in the sensors field were also studied. The main contents are as follows:1. A facile approach was developed to prepare ionic liquid functionalized graphene(IL-G) composite using 1-butyl-3-methylimidazolium 2-amino-3-mercaptopropionic acid salt([Bmim][Cys]) ionic liquid as a reducing reagent and functionalization reagent. The composition and structure of IL-G composites were characterized by AFM, FESEM, RM, CVs and so on. The obtained ionic liquid functionalized graphene composites showed good dispersibility and long-term stability in water, DMF, and DMSO solvents, and exhibited a superior electrical conductivity due to the high ionic conductivity of the ionic liquid and the synergistic effect of graphene and the ionic liquid. The materials were employed to modify glass carbon electrode for sensing application. The modified electrodes showed excellent sensitivity and selectivity for detection of CT and HQ. It is believed that the developed approach potentially opens up a simple, fast and environment-friendly route to prepare graphene-based composites with broad application prospects.2. A method was reported for the simultaneous determination of dopamine(DA) and uric acid(UA) in the presence of ascorbic acid(AA) using a glassy carbon electrode modified with the as-prepared IL–G(IL–G/GCE). The IL–G/GCE possessed excellent electrocatalytic activity toward the oxidation of AA, DA, and UA. The separations of oxidation peak potentials for AA–DA, DA–UA, and AA–UA were 147, 145 and 292 mV, respectively. The electrochemical sensor showed excellent selectivity, stability, a wide linear range and low detection limit for the simultaneous determination of DA and UA in the presence of AA, suggesting that the proposed modified electrode is a good candidate for the simultaneous determination of DA and UA. Moreover, the electrochemical sensor was applied successfully to the determination of DA and UA in real urine samples using the standard addition method, with recoveries of 97.0–103.8%.3. A simple, low cost, and green approach was developed to prepare water-soluble, nitrogen-, sulfur-, and phosphorus-co-doped carbon dots(N/S/P-CDs) by one step hydrothermal treatment of cucumber juice. It was also found that a higher reaction temperature favors the formation of N/S/P-CDs with smaller size and longer wavelength of photoluminescence emissions. The resultant N/S/P-CDs possessed uniform morphology, size of less than 10 nm, plentiful O and N functional groups as well as a limited amount of P and S functional groups, and exhibited good luminescence stability, high resistance to photobleaching, high solubility, and excitation-dependent emission behavior. Moreover, the N/S/P-CDs were applied as a fluorescent probe for the detection of Hg2+ ion, with a high sensitivity and good selectivity.4. A simple, low cost, and green approach was developed to prepare water-soluble, nitrogen-, and sulfur-co-doped carbon nanoparticles(N/S-CDs) by one step hydrothermal treatment of the mixed solution of GO and pyritinol hydrochloride, without any additives such as acids, bases, and an organic-solvent. The resultant N/S-CDs possessed uniform morphology, size of less than 10 nm, and exhibited good luminescence stability, high resistance to photobleaching, high solubility, and excitation-dependent emission behavior. It was also found that the presence of GO favors the formation of N/S-CDs with higher quantum yield(32.2%). Moreover, the N/S-CDs were applied as a fluorescent probe for the detection of Hg2+ ion. The fluorescent probe showed excellent selectivity and a wide linear range for the determination of Hg2+ ion. The developed approach would potentially open up a simple and environment-friendly route to prepare heteroatom-co-doped CDs with broad application prospects.