Hydrodynamic cavitation for exfoliation of carbon dots from coal
Using coal as a precursor to prepare carbon nanomaterials is of high significance for the clean and resource utilization of coal.Carbon dots show great potential in many application fields owing to their excellent performance.However,current chemical and physical methods for preparation of coal-based carbon dots have some shortcomings,such as the use of chemicals,expensive equipment,and difficult to scale production.Therefore,it is urgent to develop a green and scalable preparation method.Herein,using anthracite as a precursor,hydrodynamic cavitation was first applied for the exfoliation of coal-based carbon dots.The morphological results showed that the carbon dots were quasi-spherical with an average size of 2.1nm and graphitic lattice structure.XPS and FTIR spectra demonstrated the carbon dots mainly compose of C and O elements and had abundant oxygen-containing groups on the surface,which caused good dispersion in aqueous solution.Due to its special core-shell structure,the carbon dots exhibited unique fluorescence properties.It showed two fluorescent peaks of blue and yellow emission under excitation wavelength of 360nm.When the wavelength was less than 360nm,the blue emission was dominant in fluorescence spectrum.Otherwise,the yellow fluorescence was dominant.In addition,as the excitation wavelength increased,the blue peak showed dependent behaviors,while the yellow emission was basically unchanged.The successful preparation of the carbon dots provided a new physical basis for the investigation of the fluorescence mechanism with double emission and the transition and conversion between the two emission peaks.More importantly,the research results would provide new ideas and methods for green,efficient,low-cost,continuous and large-scale preparation of carbon dots,as well as the high-value utilization of coal resources.
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