Synthesis and Properties of Fluorescent Carbon Dots from Anthracite and g-C3N4

Author:Li Ming Yu

Supervisor:qiu jie shan


Degree Year:2019





As an emerging new class of fluorescent nanomaterials,carbon dots(CDs)have drawn an increasing attention due to their tunable emission wavelengths,high photostability against photobleaching,excellent photostability,good biocompatibility and low toxicity.They are easy to achieve low-cost production in comparison with semiconductor quantum dots and other fluorescent nanoparticles.It is of great importance to choose a superior carbon precursor and synthesis route at molecular level,which result in CDs with designed structure and optical properties,and further contribute to fluorescent CDs with superior performance for practical application.Besides,it is also a great guidance to the design and construction of carbon-based functional materials.In the present work,the thesis is primarily focused on synthesis of low-cost and photoluminescence(PL)-controllable CDs from anthracite and bulk graphitic carbon nitride(g-C3N4).The preparation route is confirmed according to different structure and physicochemical properties of the precursors,of which the major results are summarized as follows.A facile acidic oxidation strategy has been developed for producing fluorescent CDs with rich oxygen-containing functional groups from Jincheng anthracite by acidic oxidation method.Surface grafting of the CDs is achieved by chemical grafting with a series of organic amine molecules.It is found that the solubility and the optical properties of CDs vary with and depend on their surface chemistry to some degree.The quantum yield(QY)of the as-made CDs is only 0.73%by using Rodamine B as a standard.In contrast,the QY of the organic amine-grafted anthracite-derived CDs increases dramatically.Among the suface-modified CDs available now,ethylenediamine-grafted CDs possess an obviously enhanced PL with a QY of 18.6%by using Rodamine B as a standard,a 24.5 times increase in comparison with that of the pristine CDs,indicative of potential applications in various optical materials and devices.Fluorescent nitrogen-doped CDs(N-CDs)are synthesized by a facile one-pot solvothermal approach from Taixi anthracite in dimethyl formamide(DMF).The as-prepared N-CDs show a strong PL with a high quantum yield of 47%by using Rodamine B as a standard.Besides,the N-CDs also exhibit a singlet oxygen generation behavior with a quantum yield of 19%by using Ir(ppy)2bpy as a reference.Benefiting from superior dispersion of light components in DMF and easy exfoliation of smaller sp2-carbon structures from the anthracite,the N-CDs synthesized by solvothermal approach exhibit a relatively fewer oxygen containing functional groups and more conjugated structures.Therefore,radiative recombination of the electron-hole pairs is dominated,thus leading to a relatively high QY.Ultrasmall ultraviolet(UV)-emissive g-C3N4 nanodots(CNNDs)can be synthesized by melamine polymerization to form the bulk g-C3N4,followed by acidic oxidation of the as-made g-C3N4,hydrothermal treatment of the acidified g-C3N4 and liquid exfoliation in sequence.The as-made CNNDs with an average size of 1.6 nm deliver an emission peak with a blue shift to the UV range.The possible reason is ascribed to the quantum confinement effect of the ultrasmall structure.The quantum yield is ca.2%by using 2-aminopyridine as a standard.Besides,owing to the electron-rich and Lewis base-like structure,the as-made CNNDs can serve as a highly sensitive fluorosensor for selective and label-free detection of Fe3+ ions.