Research On Synthesis And Application Of N-doped Biomass Carbon Dots And Its Composite

Carbon dots?CDs?generally refer to zero-dimension fluorescentnanoparticles of less than 10 nm size with unique fluorescent properties,oxidation reducing,electron transfer properties,excellent water solubility and biocompatibility.CDs are potential alternative of toxicsemiconductor quantum dots or traditional organic fluorescent molecule in the biological sensing,drug delivery,photocatalysis and photoelectric device.Traditional preparations to obtain CDs are complicate in procedure,poor in yield,highly-dependent on equipment and doping agents.Biomass is rich in carbon,nitrogen and oxygen element,and is easy and cheap to get,which is ideal resource to obtain excellent carbon dots through green and simple synthesis process.The dissertation holds a deep research on the effect of various N-doping agents on the chemical structure and fluorescents properties of biomass-based carbon dots and the respective inner mechanism.On the other hand,carbon dots with superb properties are applied in biomarkers,biological sensors and macromoleculenanotechnology,which successfully realizesvalue-added conversion of biomass and expands potentialapplication of carbon dots.The detailed information is listed as follows:1.Various biomass carbon dots were synthesis through the hydrothermal/solventthermal method with different structure nitrogen doping reagent.The N-doped biomass CDs therefore were investigated in details by comparing their fluorescent performance and the chemical structure variation.Here the doped nitrogen exists in a form of amino group,pyridine nitrogen and pyrrolic nitrogen thus reducing the surface defect and forming a new energy level,which ultimately accelerate the electron-hole radiation recombination and improve the fluorescent properties.UCDs prepared from 5%urea-doping system has QY as high as 32.64%,which is double the value of that AGCDs.Depending on the formation of the molecular luminescence center,the yellow luminescent YCDs were successfully prepared by introducing 1,5-diaminonaphthalene.NCDs with high yield,excellent water solubility,stability and up conversion were prepared with PEG surface modification?QY=22.16%?.Moreover,the modified CDs can serve as nano drug carrier through coupling reaction with hydrophobic azelaic acid.This novel prodrug with increased water solubility was able to label and target tumour cells and give responsive release under enzyme stimulus.2.Fluorescent lignin CDs are prepared by one-pot hydrothermal treatment with ammonia water as solvent and N-doping agent.Results show that the introduced N-dopeing exsited in a form of amimo.Surface amination modification can improve the surface state fluorescence emission.The CDs were obtained by hydrothermal treatment?200?,12 h?with the 2.5%ammonia water.Compared to control experiment?1.49%?,the as-prepared has a higher QY?10.4%?and stable fluorescent properties in neutral environment.Thus,lignin CDs were introduced as fluorescent probe.And here we firstly found this probe can reversible respond to high-valence ions and ascorbic acid.Fe³⁺and ascorbic acid were introduced into lignin CDs sensing model to investigate the mechanism of fluorescent“on-off-on”phenomenon.The reversible control on the fluorescence change is proved by the formation and dissociation of CDs/metal chelates.Based on the phenomenal“on-off-on”response,we have successfully applied the respect sensing properties in human serum sensing and logic gate information transferation.3.Hydrogen bonding strengthened hydrogel was prepared by using acrylic acid as monomer and CDs as physical crosslinker under APS-induced free radical polymerization.CDs were embedded into the structure of hydrogel as physical crosslinker and hydrogen bonding donor by strong interaction between amino group/hydrogen group and carboxyl group,thus improving the mechanical properties.Under 90%compressive strain,when the CDs content was 0.05 g,PAA/CDs composite hydrogel has the maximum compression strength and modulus of 2.30 Mpa and 15.39 Mpa,respectively.Subsquently,LDH were introducing the gels serving as synergistic hydrogen bonding donor.The PAA/CDs/LDH composite hydrogels reached the optimal tensile properties?tensile strength of 61.42 KPa and modulus of 53.59 KPa?.The breaking elongation was 347.85%,which increased nearly 10times comparing to blank experiment.Different to CDs,LDH can undergo directional rearrangement against tensile strain and play a toughening role.CDs and LDH are synergistic and complementary in improving the mechanism properties of composite hydrogels,endowing composite hydrogel a higher strength as well as toughness.Moreover,those as-prepared composite hydrogel have comparable fluorescent properties as CDs solution and show excellent swelling ability in water.This additive advantage are promising in labeling,pollutants absorbing practical filed.4.Strengthened fluorescent hydrogels are successfully prepared by blending three functional nanoparticles:nano-cellulose,CDs and LDH into PAA hydrogels.As a physical cross point,CDs participate in the construction of three-dimensional network structure and maintain the original fluorescence performance of CDs.With proper contents of all additives?5 wt%APS,2 mL CNF,50 mg CDs,20 mg LDH?,hydrogel compression strength and compression modulus increased to a maximum of 222.09 KPa and 827.90 KPa,respectively.Then,the strengthed fluorescent hydrogel were ultilised to build three-dimensional biological sensing model.An typical"on-off-on"biosensor was successfully built based on Fe³⁺-PA or Au³⁺-GSH pairs.The reversible fluorescence control is realizes by metal ions-induced quenching and reducing agents-induced recovering.The sensitive hydrogel enable quantitative detection of metal ions(Ksv(Fe³⁺)=328.96 M^-1,Ksv(Au³⁺)=258.54 M^-1)and biological small molecules(Ksv?PA?=925.24 M^-1,Ksv?GSH?=4350.68 M^-1),which are potential in further practical applications.