Preparation And Application Of Bayberry-kernel-based Nitrogen-doped Mesoporous Carbon

In order to cope with the problem of energy shortage and heavy metal pollution,this study used green environmentally-friendly bayberry-kernel liquefaction as a carbon source instead of the phenol,triblock copolymer as template,TEOS as silicon source and melamine as nitrogen source,assisted by EISA method to achieve ternary co-assembly.We have successfully prepared nitrogen-regulated series and different template series of bayberrykernel-based nitrogen-doped mesoporous carbon,and comprehensively studied its application in capacitors,electrochemical sensors and adsorption.All samples were characterized by modern analytical methods,such as nitrogen absorption-desorption isotherm,scanning electron microscope,energy spectrum element surface distribution,transmission electron microscopy,Fourier transform infrared spectroscopy,X-ray photoelectron spectroscopy,X-ray diffraction,Raman spectroscopy.The bayberry-kernel-based nitrogen-doped mesoporous carbon has abundant pores,partially graphitized ordered structures and cross-connected pores,and rich nitrogen and oxygen functional groups.By controlling the amount of melamine added from 0 g to 20 g,the amount of nitrogen doping was adjusted,and the percentage of nitrogen atoms increased from 0.41 at.%to 4.39 at.%.The carbon lattice produced more defects and the average pore diameter increased,although the increase in nitrogen doping resulted in a decrease in the pore order,specific surface area and pore volume of the material.The addition of 20 g of melamine introduced a high nitrogen doping amount while maintaining a wide range of ordered structures,having the advantages of ordered pores and high value of nitrogen doping.Comparing MCN20-F127-7 and MCN20-F127-9,it can be seen that when the highest carbonization temperature changed from 700℃ to 900℃,the nitrogen content decreased from 4.39 at.%to 3.18 at.%,but the BET specific surface area and pore volume increased,providing more effective reaction surface area;and more graphitic carbon and graphitic nitrogen were produced in the carbon lattice at 900℃.Using Pluronic F127,F108 and P123 as templates respectively,adding 20 g of melamine,and a wide range of ordered carbons with two-dimensional hexagonal(p6mm),body-centered cubic(Im3m)and spherical structures were prepared at 900℃.Among them,MCN20-P123-9 has the highest nitrogen content(3.44 at.%)and the largest specific surface area(1442 m2 g-1),with the most defective nitrogen atoms and high degree of graphitization.The synthesis mechanism of bayberrykernel-based nitrogen-doped mesoporous carbon was proposed.In the application of supercapacitors,it can be found that the specific capacitance of MCNx-F 127-7 at 1 A g-1 increased from 82.5 F g-1 to 125.3 F g-1 as the amount of melamine added increased from 0 g to 20 g.Meanwhile,the cyclic voltammetry performance was improved,and the impedance was significantly reduced,indicating that the increase of nitrogen doping can effectively improve the capacitance performance of the nitrogen-doped mesoporous carbon.Pseudo-capacitance was produced by quinone-like C=O,Pyridinic-N and Pyrrolic-N to increase the specific capacitance of the materials.MCN20-P123-9 has the highest specific capacitance and a specific capacitance of 197.4 F g-1 at a current density of 1 A g-1,it can still maintain 52.68%of that at 1 A g-1 when the current density was 50 A g-1,indicating better rate capability.The capacitance retention of MCN20-P123-9 can still reach 93.1%of the initial value after 3000 cycles at 10 A g-1,indicating high cycle stability.The utilize of P123 as a template to prepare the bayberry-kernel-based nitrogen-doped mesoporous carbon can introduce more nitrogen-containing functional groups and maintain a high specific surface area.In the application of electrochemical sensors,the high-sensitivity electrochemical sensor was constructed by using different template series of bayberry-kernel-based nitrogendoped mesoporous carbon modified glassy carbon electrode for the detection of lead ions in aqueous solution.MCN20-P123-9@GCE has a larger active electrochemical area and a smaller electron transfer resistance than MCN20-F127-9@GCE and MCN20-F108-9@GCE,owing to MCN20-P123-9 having interpenetrating cross-linked micro/mesoporous structure,high nitrogen atomic percentage,more Pyridinic-N,Graphitic-N and Graphitic-C.The optimal conditions for MCN20-P123-9@GCE to detect lead ions was as following:the solution was HAc-NaAc with pH=4.2,the deposition potential was-1.2 V,the dispersion dose was 5 μL,and the deposition time was 200 s.There was a good linear relationship between the peak current and lead ion concentration(R2=0.997),the linear range of measurement was 10-1000 μg L-1,and the limit of detection was 2.1 μg L-1.MCN20-P1239@GCE also had good stability and reproducibility.The recovery rate ranged from 96.3%to 102.7%when detecting actual water samples such as landscape lake water and tap water.In the application of adsorption,the increase of nitrogen doping amount played an important role in improving the adsorption capacity of Pb(Ⅱ),which helped to introduce more nitrogen-containing groups onto the bayberry-kernel-based nitrogen-doped mesoporous carbon.It could form an effective complexation with heavy metal ions,thereby improving the adsorption capacity.At pH=5.5,the bayberry-kernel-based nitrogen-doped mesoporous carbon has reached the optimal adsorption capacity.MCN20-F127-7 and MCN20-P123-9 had the Langmuir adsorption amount of 35.657 mg g-1 and 62.189 mg g-1 at 25℃,respectively.The shorter PEO segment of P123 facilitated the retention and conversion of melamine into an effective nitrogen-containing functional group during the synthesis process.The nitrogen doping greatly enhanced the surface polar alkalinity of the materials,contributing the complex sites for adsorbing heavy metal ions.The Langmuir isotherm model and the Pseudo-second-order kinetic equation were more suitable for describing the adsorption behavior of the adsorption of lead ions in aqueous solution by the bayberry-kernelbased nitrogen-doped mesoporous carbon,and it was confirmed that the adsorption process is mainly chemical adsorption,including ion exchange,electrostatic interaction and complexing.A possible adsorption mechanism diagram was proposed.MCN20-P123-9 showed high adsorption stability after multiple lead adsorption-desorption processes.The results of competitive ion adsorption showed that the presence of common alkali metals in water hardly affects the adsorption performance of lead ions,indicating that the modified sample MCN20-P123-9 can be used as an adsorbent to remove lead ions in wastewater.