Preparation of room temperature phosphorescence carbon dots of xylan and their anti-counterfeiting applications
Due to the drawbacks of complexity,high cost,and toxicity associated with conventional room temperature phosphorescent(RTP)materials like pure-organic phosphorescent materials or metal-containing inorganic phosphorescent materials,carbon dot-based RTP materials have attracted widely attention because of their simple synthesis process,favorable photostability,and low biotoxicity compared to conventional phosphorescent materials in recent years.The unique properties of carbon dot based RTP materials have made them highly versatile and sought-after in various applications,including anti-counterfeiting,information encryption,sensors,and bioimaging.The dissolving pulp and viscose fiber industries produce a significant quantity of hemicellulose annually,which is a by-product characterized by a straight-chain xylan structure.However,the effective development and utilization of this by-product pose an urgent challenge for enterprises.To address this issue,this study focused on the preparation of photoluminescent xylan carbon dots(X-CDs)from industrial xylan through the one-pot hydrothermal reaction involving its dissolution in NaOH solution.The transmission electron microscopy(TEM)analysis revealed that the X-CDs exhibited a spherical-like morphology,with an average particle size of 3 nm,and displayed typical diffraction fringes associated with a graphitic carbon lattice.Fourier transform infrared spectroscopy(FT-IR)and X-ray photoelectron spectroscopy(XPS)tests showed that the main constituent elements of X-CDs were C and O,and carbonyl functional groups were presented on the surface,and the n → π*transition generated by X-CDs can effectively promote intersystem crossing to produce room temperature phosphorescence.X-CDs exhibited fluorescence in both solution and solid state,but did not show afterglow effects,since the triplet state exciton was easily quenched by the environment.The incorporation of X-CDs into polyvinyl alcohol(PVA)resulted in the generation of phosphorescent afterglows at room temperature,which exhibited excitation wavelength-dependent phenomenon.Furthermore,after ceasing the 365 nm UV irradiation,the prepared X-CDs-PVA composite film emitted naked eye-visible afterglow up to 2.5 s under ambient conditions,with a phosphorescence lifetime of 338.2 ms.Moreover,this film displayed a remarkable phosphorescence quantum yield of 6.19％when excited at 365 nm.This observation indicated that the PVA matrix can provide rigid hydrogen bonding environment and effectively restricted the rotation and vibration of the luminescent center,thereby suppressing the quenching of excitons in the triplet state.X-CDs and PVA mixture solution can be used as ink,which can be applied in the fields of anti-counterfeiting and information encryption.This study provides new ideas for the design of practical anti-counterfeiting materials and broadens the scope of utilization of xylan.
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