Synthesis And Application Of Carbon Quantum Dots Based On Lignin Which Pretreated By P-TsOH

As a new type of carbon-based zero-dimensional material with excellent water solubility,biocompatibility and light stability,carbon quantum dots have significant advantages over traditional organic fluorescent dyes and semiconductor quantum dots.They have broad development prospects in biological imaging,tracking drug release and nanoelectronic devices and so on.Lignin is the largest natural aromatic polymer substance in the world.Less than 5% of lignin was modified for commercial or industrial use,but the majority of it was burned or discharged as black liquid.Due to its high carbon content,aromatic conjugate structure,surface functional group modification and other features,lignin has the advantage of preparing fluorescent carbon quantum dots.At present,one of the main reasons for limiting the high value utilization of lignin is its high impurity content.In order to obtain high-purity lignin,the effect of pretreatment process on the purity and structure of lignin was studied,and the optimization pretreatment process was established with p-toluenesulfonic acid(p-TsOH)which was purification agent.Lignin-doped carbon quantum dots,which were prepared from purified lignin,were combined with PNIPAM/PVA hydrogels to prepare pH/temperature dual responsive hydrogels.The application of lignin-doped carbon quantum dots in hydrogels was explored.The morphology,optical properties of lignin-doped carbon quantum dots and the properties of hydrogels were studied systematically.Compared with alkali dissolution-acidic precipitation,the purified lignin,which pretreated with p-TsOH,had higher purity(up to 99.38% which was based on Sigma Lignin),greater phenolic hydroxyl content(up to 4.12 mmol/g)and higher sulfonation degree(up to 2.16 mmol/g).It also had better dispersibility,too.Lignin-doped carbon quantum dots with a quantum yield of 43.9% were prepared by hydrothermal method using lignin,which pretreated with p-TsOH,as a carbon source.Surface defects caused by doping nitrogen could not only increase the quantum yield,but also prolong their fluorescence lifetime(higher than the fluorescence lifetime of carbon quantum dots prepared from lignin in the existing literature).They had a graphene-like crystal structure with a lattice spacing of 0.21 nm.They were dispersed in water as spherical-like nanoparticles with a particle diameter of 2-5 nm.In the range of 1?pH?10,the fluorescence intensity of carbon quantum dots had a linear relationship with the pH value.pH/temperature dual responsive multifunctional hydrogels were constructed using lignin-doped carbon quantum dots,as pH fluorescent probes,and PNIPAM,as temperature-responsive polymers.Their temperature sensitivity and internal pore size could be controlled by the dosage of PVA.In the range of 1?pH?7,the fluorescence intensity of the dual responsive hydrogels exhibited a certain linear relationship with pH value,so they were expected to be applied to tissue engineering scaffolds,drug carriers and so on.This paper focused on the pretreatment,modification and application of lignin,which provided a new possibility to reduce environmental pollution and broaden the application of lignin.