Versatile Preparation Of Carboxylated Multidimensional Carbon Nanomaterials And Their Application On Alleviating Osmotic Stress Of Wheat Seedlings

Carbon nanomaterials(CNMs)and their derivatives have been favored because of their unique properties.To increase water solubility and expand their use in agriculture,pristine CNMs can be modified by hydrophilic functional groups.So far,there is still a lack of research on versatile synthesis technology to prepare the water-soluble multidimensional CNMs application in the field of plant protection.In this paper,zero-/one-/two-dimensional pristine CNMs were modified by nitrene chemistry to obtain water-soluble carboxylated derivatives of multidimensional CNMs.The application in regulating root growth and alleviating osmotic stress of wheat seedlings was also investigated,and the specific contents are as follows:(1)Preparation of azidopropionic acid:It was prepared by the reaction between sodium azide and 3-bromopropionate.(2)Preparation of water-soluble carboxylated derivatives of multidimensional CNMs:A dispersion strategy for dispersing zero-dimensional fullerenes(C₆₀,C₇₀),one-dimensional multi-walled carbon nanotubes(MWCNTs),and two-dimensional graphene using a small amount of polar high-boiling-point solvents,C₆₀/C₇₀/MWCNTs/graphene polyalanine sodium salts were obtained by nitrene reaction with azidopropionic acid followed by alkali treatment,and the resulted produce were marked as C₆₀-COONa,C₇₀-COONa,MWCNTs-COONa,and G-COONa,respectively.It was confirmed by the IR and X-ray photoelectron spectroscopy that the alanine group(s)is successfully bonded to the surface of CNMs.It can be also confirmed by thermogravimetric and XPS analysis that the average molecular formula of C₆₀-COONa,C₇₀-COONa is C₆₀(NCH2CH2COOONa)6,C₇₀(NCH2CH2COONa)4.For MWCNTs-COONa and G-COONa,the average number of appendant alanine groups per thousand carbon atoms is 26 and 116,respectively.Furthermore,MWCNTs-COONa was analyzed by Raman spectroscopy.The ID/IG ratio was found to be 0.78,The ratio is close to that of pristine carbon nanotubes,which indicates that MWCNTs-COONa has less defects.(3)By in vitro ABTS+.radical scavenging experiments,it was learned that C₆₀-COONa,C₇₀-COONa,MWCNTs-COONa,G-COONa can scavenge ABTS+·,and the concentrations were 54,55,59,and 109 ?g·mL-1 to inhibit 50%ABTS+·,respectively.So,the ability to scavenge free radicals ranked by C₆₀-COONa<C₇₀-COONa<MWCNTs-COONa<G-COONa,namely Zero-dimensional CNMs>one-dimensional CNMs>two-dimensional CNMs.(4)The effect of C₆₀-COONa and MWCNTs-COONa on the early growth of wheat seedlings was investigated,and the optimized concentration to promotional effect was validated.The results showed that C₆₀-COONa and MWCNTs-COONa had the most significant effect on root growth at concentrations of 10 and 40 ?g·mL-1,respectively.The root and leaf tissues of wheat seedlings treated with concentration 100 ?g·mL-1 MWCNTs-COONa were analyzed by Raman spectroscopy,It was found that there were G-peaks in root and leaf after treatment,which MWCNTs-COONa can be absorbed by the root and transported to leaf tissue.(5)C₆₀/C₇₀/MWCNTs/G-COONa treatments can alleviate the osmotic stress of wheat seedlings.Using carboxylated CNMs at a concentration of 30 ?g·mL-1 combination wtih 20%PEG-6000 to simulate osmotic-stress culture,the result showed that the root and leaf length of wheat seedlings recovered and significantly alleviate osmotic stress,compared with PEG treatment alone.C₆₀-COONa treatment had the best effect on root growth of wheat seedlings.MWCNTs-COONa treatment had the best effect on wheat seedling leaf growth mitigation,which proved the ability of carboxylated CNMs as plant growth regulators.