Preparation Of Nitrogen And Phosphorus Doped Carbon Dots And Their Application In Growth Regulation Of Water Spinach

Carbon dots(CDs),as an emerging nanomaterial,have been increasingly used in agriculture in recent years due to their non-toxicity,biocompatibility,and tunable advantages.At present,the application of CDs in plants mainly focuses on the transport and accumulation in plants and the impact of CDs on plant growth and yield.However,there are few related studies on the effects of CDs on plant growth quality and physiological characteristics.Based on this,a long-wavelength emission of nitrogen-phosphorus doped carbon dots(N,P-CDs)was prepared in this thesis.The luminescence mechanism of long-wavelength emission of N,P-CDs was deeply studied,and the effects of different N,P-CDs treatments on the growth,quality and physiological characteristics of water spinach were also discussed.The main findings are as follows:(1)Long-wavelength emitting N,P-CDs with an emission peak at 626 nm were synthesized by a one-step hydrothermal method with o-phenylenediamine and phosphoric acid as precursors.Using the controlled variable method,the effects of the amount of precursor,reaction time,and temperature on the relative quantum yield of CDs was explored.The best reaction conditions were determined to be 540.7 mg of o-phenylenediamine and 1 m L of phosphoric acid at 160℃ for 6 h,and finally,N,P-CDs with a relative fluorescence yield of 15.27% were obtained.The stability test of N,P-CDs shows that the carbon dots have strong resistance to photobleaching,salt-resistance,and stability in acid and alkali environments.Through X-ray photoelectron spectroscopy(XPS),transmission electron microscopy(TEM),and other characterization results,it is found that the reason why the increase of phosphoric acid content leads to the shift of N,P-CDs to the long-wavelength direction is mainly related to the degree of graphitization,the content and species of surface functional groups.(2)Using water spinach as the research object.The water spinach seeds were immersed in different concentrations of N,P-CDs solution,and it was found that 25 mg/L N,P-CDs solution could effectively promote the germination of seeds.The prepared N,P-CDs were added to water spinach hydroponic solution with different concentrations(root treatment).The results showed that water spinach grow best when the concentration of N,P-CDs was 100 mg/L in the root system.Under the treatment of this concentration,the growth of water spinach increased to a certain extent compared with the blank group.The dry and fresh weight of the aerial part increased by 67.32% and90.70% respectively,and the dry and fresh weight of the underground part increased by64.59% and 104.90% respectively.The 100 mg/L concentration treatment was also most beneficial to the improvement of the quality of water spinach,and the relative content of soluble sugar,which is a product of photosynthesis,increased by 81.08%.Photosynthetic parameters and the value of photosynthetic pigments also showed a positive effect,and the growth trend of photosynthetic pigments was particularly obvious.The values of all physiological indexes were concentration-dependent with N,P-CDs.(3)The effect of N,P-CDs on the growth of water spinach was explored by spraying carbon dots as a material for enhancing light capture on water spinach leaves.The results showed that the optimal concentration of N,P-CDs sprayed on water spinach leaves was 50 mg/L.N,P-CDs as a light harvester made the photosynthetic parameters and photosynthetic pigment values of water spinach showed a trend of increasing first and then decreasing,and increased within the appropriate concentration range.Based on the enhancement of photosynthesis,50 mg/L concentration treatment was also most beneficial to the improvement of water spinach quality.The contents of soluble sugar,soluble protein,flavonoids,total phenols,and anthocyanins increased by 36.49%,48.14%,77.95%,57.78%,and 70.97%,respectively,while the contents of MDA and nitrate decreased accordingly.At the same time,the yield and root vigor of water spinach increased to a certain extent,and the root vigor increased by 74.75%.Finally,this paper compared the effects of two different treatments on the growth regulation of water spinach and found that the positive effect of root treatment was more obvious.The application of the two treatments on plants is of great significance to agricultural production.