Study on the Structure and Properties of Sodium Lignosulfonate-graphene Quantum Dots with Different Molecular Weights
The relative molecular weight was an important factor affecting the performance of polymers.Four types of sodium lignosulfonate-graphene quantum dots(SL/GQDs)were prepared using sodium lignosulfonate with different relative molecular weights and citric acid as raw materials.The prepared SL/GQDs solutions were labeled as SL/GQDs1-SL/GQDs4,corresponding to relative molecular weights of undefined,5 000,10 000,and 50 000,respectively.Optical properties,structures,and morphologies of the four composite quantum dots were compared and analyzed using UV-visible spectroscopy,infrared spectroscopy,transmission electron microscopy,and fluorescence spectroscopy,respectively.The results showed that the surface of SL/GQDs was rich in hydrophilic groups such as carbonyl and hydroxyl groups.The average particle sizes of SL/GQDs1-SL/GQDs4 were 1.34,1.78,2.13,and 2.26 nm,respectively.The composite quantum dot SL/GQDs4 with a relative molecular weight of 50 000 exhibited the best overall performance and the strongest photo-induced luminescence effect.Therefore,SL/GQDs4 was selected for the detection of metal ions.It was found that SL/GQDs4 showed good selectivity and sensitivity towards different metal ions,and Fe3+could still be detected in the coexistence system of different metal ions,which could serve as a fluorescent probe for Fe3+detection.Furthermore,the addition of Fe3+resulted in fluorescence quenching effect in SL/GQDs4.When Fe3+concentrations were in the range of 10-400 µmol/L,there was a good negative correlation between Fe3+concentration and fluorescence intensity(F/F0).The Stern-Volmer linear regression equation obtained by data fitting was F/F0=0.893 66-0.001 19C(Fe3+),with R2 of 0.98.
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