Preparation and photophysical properties of ellagic acid afterglow aerogel
Ellagic acid(EA)was used as a chromophore in sodium alginate(SA),which was crosslinked and gelated with bivalent metal ions such as Zn2+and Ca2+.The resulting gel was freeze-dried to obtain green afterglow aerogel(EA@SA).Photophysical properties of EA@SA aerogel were analyzed.The results showed that the phosphorescence emissions of EA@SA-Zn,EA@SA-Ca,EA@SA-Sr and EA@SA-Ba aerogels were 275.71,157.59,123.92 and 144.56 ms,respectively.EA@SA-Zn aerogels exhibited the longest phosphorescent lifetime among them.This may be attributed to the fact that different bivalent metal ions formed coordination polymers with sodium alginate of varying structures,which affected the localized action of ellagic acid within the sodium alginate matrix,and subsequently in-fluenced the photophysical properties of aerogels.The bivalent metal ions crosslinked with sodium alginate formed a rigid matrix structure,which had a better limiting effect on ellagic acid.Therefore,EA@SA aerogels had stronger phosphorescence emission and longer phosphorescence life.With an increased concentration of bivalent metal ions(such as Zn2+),the phosphor lifetime of the aerogel increased.When the number of bivalent metal ions crosslinked with sodium alginate reached saturation,the phosphor lifetime did not continue to increase.The measured fluorescence spectra and fluorescence lifetime showed that the fluorescence emission center of EA@SA-Zn aerogel was at 430 nm,and the fluorescence lifetime reached 5.87 ns.The SEM test results showed that the EA@SA-Zn aerogel presented a network porous structure and the structure was relatively loose.The abundant pore structure provided a good substrate environment for EA molecules.At the same time,the element mapping of EA@SA-Zn aerogels showed that C,O,Zn and Cl were evenly distributed on its surface,which indicated that Zn2+was fully crosslinked with sodium alginate,and EA@SA-Zn aerogels were successfully prepared.The prepared EA@SA-Zn aerogel was placed in different hu-midity environments,and the phosphor intensity and phosphor lifetime decreased with the increase of relative humidity.Under high temperature conditions,water evaporated from the aerogel and restored the hydrogen bond be-tween EA and SA,which effectively inhibited non-radiative transition of EA molecules,resulting in restored phosphor intensity and lifetime.The phosphorescence lifetime of aerogel was increased from 142.44 to 214.15 ms,and the aerogel can still maintain good phosphorescence emission.Furthermore,EA@SA-Zn aerogel showed excellent phosphorescence emission in acetonitrile(ACN),ethanol(EtOH),tetrahydrofuran(THF)and dichloromethane(DCM)organic sol-vents,with respective phosphorescence lifetimes of 254.76,260.14,266.64 and 268.67 ms,respectively.The prepared EA@SA-Zn aerogel can still observe the green afterglow emission after 30 d,and had phosphorescence stability.Final-ly,the afterglow line loaded with EA@SA-Zn aerogel was prepared and applied in the fields of embroidery and anti-counterfeiting,which expanded the application field of natural polyphenol preparation of afterglow materials.
ellagic acidsodium alginateaerogeldivalent metal ionroom temperature phosphorescence
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