Preparation And Properties Of Luminescent Hydrogel Based On Coal Pitch Carbon Dots

Luminescent hydrogels have been widely used in clinical research and biomedicine due to their in-situ and real-time detection capabilities.Researchers are accustomed to using a gel factor that has its own luminescent properties to prepare a luminescent hydrogel,or to introduce luminescent substances（such as rare earth ions）into a polymer hydrogel network to prepare a luminescent hydrogel.However,both gel factors and lanthanides have toxicity and poor biocompatibility.In contrast,carbon quantum dots（C-dots）have excellent biocompatibility,chemical stability and high light stability.Therefore,C-dots have a broad application prospect in the biomedical field.In this paper,coal tar pitch carbon quantum dot（C-dot）and modified agarose（AG）hydrogel were successfully prepared,and a kind of luminescent hydrogel with good mechanical and self-healing properties was prepared by combining the two hydrogels.The details are as follows:（1）C-dots with blue fluorescence were prepared by hydrogen peroxide etching with coal tar pitch as carbon source.The morphology,particle size distribution,structure and surface valence of carbon quantum dot（C-dot）were characterized by transmission electron microscopy（TEM）,fourier transform infrared spectroscopy（FT-IR）and X-ray photoelectron spectroscopy（XPS）.The results show that the coal tar pitch C-dot were spherical with particle size of 2-5 nm and abundant functional groups such as-COOH and-OH on the surface.The effects of hydrogen peroxide concentration,temperature and reaction time on the fluorescence quantum yield of C-dots were discussed.Under the optimal conditions,the fluorescence quantum yield of coal pitch C-dot reached 16.67%.The fluorescence properties of C-dot were studied.Under the excitation of ultraviolet light,C-dot emited blue fluorescence and had up-conversion characteristics.C-dot exhibited good fluorescence stability in the range of p H 3.0-9.0.Strong acid and strong base would lead to fluorescence quenching,and the fluorescence intensity of C-dot increased with the increasing polarity of solvent（2）AG/PVA/CB[7]dual-network hydrogel was prepared by using natural polymer AG as the first physical crosslinking network,polyvinyl alcohol（PVA）as the second physical crosslinking network,and cucurbituril[7]（CB[7]）as the crosslinking agent.The morphology,structure,crystallization and crosslinking mode of AG/PVA/CB[7]hydrogel were characterized and analyzed by SEM,FT-IR and XRD.Moreover,it was determined that the interaction between PVA,AG and CB[7]was mainly in the form of hydrogen bond,and also a small number of macromolecular microcrystals exist simultaneously.The effects of components and freeze-thaw times on the mechanical properties of hydrogels were investigated.When the freeze-thaw cycle times was within a certain range（1-5 times）,the mechanical properties of the system increased with the increase of the freeze-thaw cycle times.And the addition of the crosslinking agent CB[7]improves the mechanical properties of the hydrogel,the maximum tensile strength was 0.37MPa.The self-healing properties of AG/PVA/CB[7]hydrogel and the effect of CB[7]on the self-healing properties of the hydrogel were studied by weighing method,and the self-healing efficiency was 40.8%.The sol-gel transition properties of the AG/PVA/CB[7]hydrogel were investigated.The hydrogel was transformed into a sol state at high temperature（>75°C）and strong acid(>5mol·L^-1).（3）C-dot/AG/PVA/CB[7]luminescent hydrogel was prepared with coal tar C-dot as the luminescent factor.SEM and FT-IR techniques were used to characterize the morphology,structure and crosslinking manners of AG/PVA/CB[7]hydrogel.Moreover,it was determined that the interaction between C-dot and gel network is mainly in the form of hydrogen bond.The effects of C-dot and hydrogel on the properties of the gel were studied.The results showed that the introduction of C-dot enhanced the mechanical properties of hydrogels,weakened the self-healing properties of hydrogels,made the swelling equilibrium time of hydrogels longer.Moreover,the combination of the C-dots and hydrogel shifted the fluorescence emission wavelength by 33nm.The cytotoxicity of C-dot/AG/PVA/CB[7]luminescent hydrogel was investigated.The results showed that the hydrogel was non-toxic to SVREC cells.Finally,the luminescence mechanism of C-dot/AG/PVA/CB[7]hydrogel was discussed,which is consistent with the surface functional group effect.