Construction And Properties Of Glycosyl-Based Carbon Quantum Dots/PVA Composites Room Temperature Phosphorescent Materials

Room temperature phosphorescent?RTP?materials can store part of the energy under the irradiation of external excitation light.After the external excitation light is turned off,it can be released in the form of visible light.Due to the special luminous properties of RTP materials,it has potential development prospects in advanced anti-counterfeiting,biological imaging,chemical sensing and other fields.However,the traditional RTP materials are mainly concentrated on rare earth elements and organic materials containing heavy metals or pure organic materials.Carbon quantum dots?CQDs?as new fluorescent nanomaterials,has a wide range of applications in biological imaging,chemical sensing,light emitting diodes,anti-counterfeiting,because of the excellent optical properties,good biocompatibility,low toxicity,and photobleaching resistance.The thesis focuses on the preparation of RTP materials based on CQD.The thesis also studies their luminous properties and practical applications in related fields.The main research contents of the paper are summarized as follows:?1?The NCQDs solution was prepared by introducing external nitrogen-containing compounds using glucose as a carbon source with simple green hydrothermal carbonization method.The composite RTP materials were prepared by mixing NCQDs and polyvinyl alcohol?PVA?matrix.Under UV light irradiation,the NCQDs solution emits blue fluorescence,however,the NCQDs/PVA composite materials emit blue fluorescence under UV light irradiation,and emit blue-green phosphorescence at room temperature after turning off the ultraviolet light.And the FTIR spectrum of the NCQDs solution shows that the surface of the NCQDs contains C=N/C=O functional groups,which can form hydrogen bonds with a large number of hydroxyl groups on the surface of the matrix PVA.The non-radiative relaxation of the functional groups on the NCQDs surface can be suppressed by hydrogen bonding,further obtaining long afterglow NCQDs/PVA composite RTP materials.On the one hand,the obtained RTP materials was successfully used in advanced anti-counterfeiting fields as luminescence ink.On the other hand,the obtained NCQDs/PVA film and aerogel materials with a life of up to 416 and 442ms,making them potential applications in ion detection and gas sensing.?2?CQDs was prepared from Schisandra chinensis polysaccharide?SCP?as the only carbon source through ecofriendly hydrothermal carbonization method.Then the CQDs/PVA composite film material with a lifetime of 271.2ms was prepared by coating method with PVA matrix.And the water-soluble SCP is extracted from Schisandra chinensis fruit via ethanol precipitation,which has the natural molecular structure of nitrogen containing polysaccharides.Therefore,the in-situ green synthesis of RTP materials based on CQDs have successfully prepared without the need to introduce external nitrogen-containing compounds.At the same time,the luminescence mechanism of the prepared RTP material was explored:the prepared CQDs/PVA composite film material has a small energy level difference?0.32eV?,which is conducive to the occurrence of the ISC process and further promotes the generation of the RTP effect.The FTIR and XPS spectra show that the surface of CQDs contains a large number of C=O/C=N functional groups.After being compounded with PVA matrix,the surface functional groups of CQDs are inhibited from rotating and vibrating through hydrogen bonding,which is conducive to spin coupling,and stabilize the triplet excited state,finally promote the RTP effect.?3?The CQDs solution prepared from SCP emits blue fluorescence under 350 nm irradiation of excitation light.It exhibits excellent optical stability,pH value?pH=3-12?and ionic stability,and the fluorescence can be quenched in the presence of metallic iron ions(Fe³⁺).The CQDs/PVA composite film emits blue fluorescence under ultraviolet light,and emits green room-temperature phosphorescence when the UV lamp is turned off.However,in the presence of Fe³⁺,the fluorescence and room-temperature phosphorescence of the CQDs/PVA film are quenched at the same time.When the concentration of Fe³⁺in the range of 0.1-2mM,the lowest detection line is 0.57?M.The quenching of fluorescence and phosphorescence can be directly observed by the naked eye when the CQDs/PVA composite film exposed in the condition of Fe³⁺.At the same time,the optical intensity and luminescent life of CQDs/PVA composite film are almost unchanged when it placed in the air for half a year.Thus,it has good optical stability,which makes it have greater application in practical visualization of iron ion detection potential.