Synthesis And Properties Of Carbon Dots From Xingjiang Hongshaquan Coal And Its Liquid Products Of Biodegradation

As an emerging zero-dimensional fluorescent carbon nanomaterials,carbon dots(CDs)have been widely used in biomedical,energy storage,chemical sensing,and other fields,because of their excellent optical properties,low toxicity,excellent biocompatibility,low cost,and easy preparation.The high stability and fast response of CDs lead to the potential application of CDs in chemical sensing.In this research,low-rank coal and its biodegradation product have been used as selected carbon sources to synthesize a series of CDs by simple and convenient preparation methods.The composition and optical properties of CDs have been studied,and their applications in the field of pH and temperature sensing were further explored.The main research contents are as follows:(1)Synthesis of C-CDs using Xinjiang Hongshaquan coal as carbon sourceUsing Xinjiang Hongshaquan coal as the carbon source and selecting DMF as the reaction solvent,blue-green luminescent coal-based carbon dots(C-CDs)with a fluorescence quantum yield of 19.1%were successfully prepared.And the effects of reaction conditions on the fluorescence properties of the C-CDs were investigated.The surface state of C-CDs was analyzed,and the results showed that the surface of C-CDs was rich in N/O contained functional groups.C-CDs showed good temperature responsing fluorescence during the heating process in the temperature range of 20 to 95℃,and the fluorescence intensity of C-CDs showed a good linear correlation with the solution temperature(R2=0.993).In addition,the fluorescence intensity of C-CDs had a good linear relationship with the pH value of the C-CDs solution,and the correlation coefficient was 0.972(pH=1～3)and 0.992(pH=1～13),respectively.Moreover,the fluorescence response of C-CDs to temperature and pH had good reversibility.(2)Synthesis of L-CDs using liquid products of biodegradation of coal as carbon sourceThe one-step hydrothermal method was used to prepare coal-biodegradation liquid product-based carbon dots(L-CDs)with an average size of 3.4 nm and good dispersibility.And by controlling the reaction conditions,L-CDs with controllable fluorescence properties in the emission range of 414～535.5 nm were prepared,and the highest fluorescence quantum yield was 24.1%.The structure of L-CDs was characterized,and the results showed that the carbon core of L-CDs was composed of sp2 and sp3 hybrid carbons.The time-resolved fluorescence decay curve showed that the luminescence of L-CDs is caused by different fluorophores or energy levels in L-CDs.In addition,the prepared L-CDs showed good light stability,metal-ion stability,time stability and good salt resistance,and their fluorescence properties showed obvious pH and temperature sensitivity,when the pH value of the solution was between 3 and 8 when the temperature of the solution was between 30 and 65℃,the fluorescence intensity of L-CDs solution showed a good linear correlation with the pH value and temperature of the solution,and the correlation coefficient(R2)was 0.991 and 0.995,respectively.Furthermore,the fluorescence response of L-CDs to pH and temperature of the solution had good reversibility.