Fluorescent organic semiconducting dots (OSDs) with tunable particle size and surface functionality are synthesized from lignite by chemical oxidation method followed by ultra-sonication techniques and dialysis. The defects and oxygen functionalities play a vital role in the photoluminescent property of the synthesized nanoparticles along with quantum confinement effect. These nanomaterials are suitable for imaging and chemical sensing applications as there is no photobleaching and quenching even after a continuous UV exposure of 24 hours and storage of 2 years. The excellent excitation dependent luminescence of the synthesized carbon dots can be utilized for making a low-cost carbon-based sensor for Cu2+ metal ions sensing. The OSDs show good ratiometric fluorescent sensing and can be used as a reliable probe for the detection of Cu2+ ions. They exhibit excellent detection limit of copper ion in acidic solution to a very low concentration of 0.0089 nM. The fluorescent nanodots synthesized from such an abundant and cost-effective precursor exhibiting high copper ion sensitivity is being reported for the first time.
Lignite is an abundantly utilized feedstock for the facile synthesis of fluorescent carbon dots and carbon nanomaterials. Its value is appreciated as an energy source for combustion for long time. Herein we report a novel top-down strategy to synthesis lignite based fluorescent nano carbon structures by combined acidic oxidation and chemical reflux. The nanocarbon crystallites in lignite are converted to oxygenated nano carbon dots and graphene sheets. They exhibited stable fluorescence property in the visible region depending on their size, functionalities and defects which were highly stable in all the pH conditions. These nanocarbon structures are an effective probe for fluorescent sensing of label-free and selective detection of glucose ions with detection limit as low as 0.125 mM, promising real-world sensor applications. These findings establish a scalable method for the production of fluorescent carbon based glucose sensor from lignite.
Coal is a natural energy resource which is mainly used for energy production via combustion. Coal has nanocrystals embedded in it, formed during the coalification process, and is an ideal precursor for nano-carbon dots and diamonds. Herein, we report a facile top-down method to synthesise nanodots and diamonds of the size of 5 nm to 10 nm from three different types of coal by simple chemical leaching. TEM analysis revealed the formation of a mixture of carbon dots, graphene layers, and quantum dots in bituminous coal and sub-bituminous coal. Raman analysis confirmed the existence of synthesized nanodiamond and nano-carbon mixed phase with defects associated with it. It is concluded that graphene quantum dots, nanodiamonds, graphene sheets and carbon dots present in coal can be extracted by simple chemical treatment. These structures can be tuned to photoluminescent material for various optoelectronic applications or energy harvesting devices like super capacitors.
In present paper, a facile method is reported to extract mixed phase nanometre-sized carbon sheets from sub-bituminous coal. The lattice constants (La and Lc) of sub-bituminous coal were calculated to be 4.82 and 1.41 nm, respectively. The aromatic layers and average number of carbon atoms in the aromatic lamellae were estimated as 5 and 8, respectively. The obtained graphene sheets exhibits broadened D and G band in addition to a very broad 2D bump. Defect to graphitic ratio is found to be 0.54 indicating less disorder in graphene nanomaterial formed. This is further corroborated by (ID/ID') ratio which was observed to be 3.40, confirming the defect has originated from boundary. The SEM analysis reveals the formation of large number of carbon layers with different shape in the nanometer scale range. Formation of graphene dots in the shape of hexagonal, spherical, graphene layers and corn shaped carbon nanotubes are noticed in the TEM image.
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