Water Soluble Carbon Quantum Dot Sustained Release Nanocapsule And Its Application In Plant Growth

Fluorescent carbon quantum dots(CDs)are widely used in the fields of biosensing,optoelectronic devices,photocatalysis and fluorescent labeling due to their good biocompatibility,stable fluorescence performance and low toxicity.However,CDs are easily annihilated in the solid state,which limits its generalization.In this paper,the synthesis of highperformance CDs nanocapsule and its application in plant growth were studied.The summaries of the related research are as follows:(1)The polymer formed by crosslinking polyvinyl alcohol(PVA)with glutaraldehyde(GA)as shell material,and water-soluble CDs as core material,novel CDs nanocapsule was constructed by a water-in-oil-in-water double emulsion method.The effects of solvent,external water phase PVA content and CDs concentration on the morphology and performance of CDs nanocapsule were investigated.The composition,crystal phase,morphology and the thermal stability of the synthesized nanocapsule were characterized by FTIR,XPS,XRD,SEM,TEM,particle size analysis and TG.The experimental results showed that the nanocapsule synthesized under cyclohexane as organic solvent,1.5% PVA as external aqueous phase and 0.3 mg/mL CDs aqueous solution had an excellent spherical structure and fluorescence intensity.The results of XRD and FTIR indicated that the synthesized CDs nanocapsule had the same amorphous structure as CDs,and the functional group of CDs core surface did not react with the group of PVA shell.The results of SEM,TEM and particle size analysis revealed that the CDs nanocapsule had an obvious spherical core-shell structure with an average particle size of 317.9 nm.TG analysis showed the CDs nanocapsule had better thermal stability than the CDs.The optical property of CDs nanocapsule showed that PVA shell can inhibit the quenching of CDs solid photoluminescence due to the encapsulation and the effective dispersion of CDs.Quantum yield of CDs nanocapsule reached 72.8%.Furthermore,by encapsulating red-emitting CDs,double-fluorescent CDs nanocapsule was obtained since PVA shell can emit effective blue light.(2)Taking lettuce as a model,the effects of CDs nanocapsule on plant growth and physiology were investigated by spraying CDs nanocapsule on the leaves of lettuce.Through comprehensive analysis of the pore structure,sustained release performance of CDs nanocapsule,and its adhesion property as well as the optical property on the leaves,the results showed that CDs nanocapsule had a distinct mesoporous structure with an average pore size of 30 nm,which providing the sustained release channel of CDs,enhancing the absorption of UV light and obtaining a transmittance of more than 80% in the visible light region.In addition,the obtained capsules could effectively adhere to the leaf surface and emit visible light absorbed by chloroplasts,thus enhancing the photosynthesis of plants.The leaves sprayed by 3900 mg / L CDs nanocapsule suspension could obtain the best results,which had the highest net photosynthesis rate and Chl a / b,their contents of soluble sugar,soluble protein and free amino acid increased by 66.02%,22.14%,15.69%,respectively.All the results indicate that the synthesized nanocapsule is used as light fertilizer to spray the foliage to enhance photosynthesis and provides a possible solution for promoting plant growth and physiological processes.