Study On Preparation And Application Of Lignocellulosic Biomass-based Carbon Quantum Dots

Lignocellulosic biomass is a resource rich in carbon content.Using its own high-carbon characteristics to prepare carbon materials with special functions can realize high-value utilization of bioresources.Carbon quantum dots(CQDs)is a novel carbon nanomaterial with a diameter of less than 10 nm.CQDs have attracted much attention in the fields of fluorescence probe,biological imaging,and photocatalysis due to the advantages of good water solubility,low toxicity,stable photoluminescence,and low chemical activity.In this study,CQDs,N-CQDs and N,P-CQDs were prepared by hydrothermal treatment using bleached softwood Kraft pulp(BSKP)as carbon source by doping elements,and N,P-CQDs with different molecular weights were obtained through gradual dialysis.Meanwhile,N,P-CQDs/g-C3N4 was prepared with N,P-CQDs and g-C3N4,and applied to photocatalytic degradation of lignin model.Firstly,CQDs,N-CQDs and N,P-CQDs were prepared by doping with ammonia or diammonium phosphate during the hydrothermal treatment of BSKP as the carbon source,and three kinds of CQDs were characterized(N,P-CQDs-500,N,P-CQDs-1000,N,P-CQDs-3500).The results showed that the fluorescence intensity of N,P-CQDs was much higher than that of CQDs and N-CQDs;In the study,the metal ions selectivity of resultant N,P-CQDs were investigated,the results showed that N-CQDs have good fluorescence quenching effect on Fe3+and Fe2+,while N,P-CQDs only have good sensitivity to Fe3+.Secondly,N,P-CQDs-3500,N,P-CQDs-1000,and N,P-CQDs-500 were obtained by fractionation through gradual dialysis,respectively,and used as fluorescent probes for detecting metal ions and cell imaging.The results showed that the N,P-CQDs-500 and N,P-CQDs-1000 have the strongest fluorescence intensity in the pH of 6.0 and 3.0,respectively,while N,P-CQDs-3500 were stable in the pH range of 2.0-8.0.The diameters of N,P-CQDs-3500,N,P-CQDs-1000,and N,P-CQDs-500 were all less than 10 nm,and there were no obvious lattice structure.The N,P-CQDs had good selectivity for Fe3+,and N,P-CQDs-500 had a certain fluorescence selectivity for Fe2+.The detection limits of N,P-CQDs-500 for Fe3+and Fe2+ were 1.28 and 3.07 mmol/L,respectively,and the linear ranges were 0-0.362 and 1.36-4.97 mmol/L,respectively.N,P-CQDs-3500 showed good fluorescence in H1650,HEPG,HelaS3,Raji,and RPMI8226 cells.Finally,N,P-CQDs/g-C3N4 was synthesized by ultrasonic and liquid phase deposition,and applied to photocatalytic degradation of lignin model.The results showed that N,P-CQDs could be uniformly distributed on the SCN surface.The BET surface areas of CN,SCN and S-SCN-2 were 14.17,21.62 and 17.62 m2/g,respectively.The fluorescence intensity decreased from 5700 a.u.of CN to 500 a.u.of C-SCN-2,and the band gap width decreased from 2.85 eV to 2.79 eV.The degradation of lignin model by C-SCN-2 reached 95.50%.The results showed that the designed C-SCN-2 composite material would be a potential and efficient photocatalyst for lignin.