Applications Of Biomass-Derived Carbon Materials In Wastewater Treatment And Electrochemistry

Biomass-derived carbon materials are of great potential in applications serving as electrocatalytic materials,supercapacitor electrode materials and high-efficiency adsorbents,because of their low cost,large specific surface area,porous structure,surface functional groups and superior electrothermal stability.In order to overcome challenges in environmental technology and high-efficiency energy storage,this dissertation developed a series of high performance carbon materials by using the abundant environment-friendly biomass as precursors.Various modification methods based on different mechanisms have been explored to optimize the microscopic structure of the derived carbon materials for applications in wastewater treatment and electrochemistry.Technologies of large-scale preparation by an efficient,green and easy-to-operate processes were also discussed.The major conclusions are as follows:(1)A low-cost and high efficiency method is developed to prepare self-doped nitrogen porous carbon nanosheets(NPCNS)with layered porous structures by using leaves of Euonymus japonicas as a precursor.Electrochemical test results show that NPCNS exhibits high electrocatalytic activity for both ORR and OER in alkaline media.Different pyrolysis temperatures(700℃,800,900℃,and 1000℃)are tested to optimize the performance of NPCNS.The samples carbonized at 900℃(NPCNS-900)achieve highest concentration of pyridinium nitrogen,and show best ORR and OER activity.According to the DFT calculation,adsorption energies of O and OH in pyridinium and graphite nitrogen are moderate,which is the key to high ORR and OER catalytic activity.Therefore,the mechanism underlying the high activity of NPCNS-900 is that the distribution of self-doped pyridinium and graphite nitrogen in the porous structures significantly improves the acceptability and transmission of electrons,reducing the reaction resistance.This work shows that NPCNS-900,which can be prepared using a simple method,exhibits excellent electrocatalytic performance and represents a potential candidate in energy technologies such as fuel cells or metal-air batteries.(2)A low-cost,high-efficiency,green and easy-to-operate method for preparing self-doped nitrogen porous carbon materials(NPCs)from C and N-rich leaves of Euonymus japonicas was studied,and applications of NPCs as a high-efficiency adsorbent in dyeing wastewater treatment was also studied.In the adsorption of organic cationic dyes(MB and RhB)and anionic dyes(MO)in dyeing wastewater,the maximum adsorption capacities of NPCs were 626.1,620.7 and 370.8 mg·g-1,respectively.The excellent adsorption performance of NPCs are mainly due to their large specific surface area(1854.06 m2·g-1),suitable pore size distribution(mainly microporous and mesoporous)and self-doped nitrogen(2.59%).In order to illustrate the adsorption law and the internal mechanism,the experimental data were compared with four kinetic models(pseudo-first order,pseudo-second order,intraparticle diffusion and Elovich)and four isotherm models(Langmuir,Freundlich,Temkin and Dubinin-Radushkevich).The fitting basically confirms that the adsorption process is a combination of physical and chemical adsorption,and adsorption is performed through a monolayer.This study represents a environmental friendly and simple method for recycle use of biomass waste as a raw material to prepare high-efficiency adsorbents for treatment of dyeing wastewater.(3)Host-guest interactions were employed in preparing heteroatom-doped biomass-derived carbon materials(HBCMs)through usingβ-cyclodextrin(β-CD)as the C source,MO and MB as the N source and S source.And the capacitive properties of the materials were investigated.HBCMs exhibit good performance as supercapacitor electrode materials.The specific capacitance values of CDC-MO and CDC-MB are 284 and 291.5 F·g-1,respectively,at a current density of 0.5 A·g-1.The cyclic voltammetry curve shows a rectangular-like structure with no redox peaks,good reversibility and stability,suggesting that HBCMs are ideal supercapacitor materials.This work provides a simple and efficient strategy for large-scale production of carbon materials.Given the configurable properties of host and guest molecules,this study also opens up the potential for new HBCMs in supercapacitors.(4)This work explores a low-cost,high-efficiency,green and easy-to-operate method for preparing N-doped biomass-derived carbon materials based on host-guest interactions,and studies applications of the resultant carbon materials in the field of wastewater treatment.A new type of N-doped carbon was prepared by using β-CD as carbon source,P-AZO,MEL,UR and MB as nitrogen source,using host-guest inclusion,through direct hydrothermal carbonization and high temperature activation of host-guest complex.The adsorption capacity of CDC-P-AZO(668.9 mg·g-1 for MB was greater than that of CDC(542.8 mg·g-1),CDC-MEL(573.8 mg·g-1)and CDC-UR(586.3 mg·g-1),mainly due to the large specific surface area(2210 m2·g-1),the appropriate pore size distribution(mainly microporous and mesoporous)and the introduction of N atoms(1.61%).Fitting to kinetic and isotherm models determined that the adsorption process is a physical adsorption and chemical adsorption process through monolayer adsorption,providing a theoretical basis for large-scale production and application of biomass-derived carbon materials。(5)Sodium alginate,a kind of environmental friendly brown algae extracted biomass was employed as precursor for preparing aerogel.Further pyrolysis/carbonization of the aerogel gave rise to sodium alginate carbon aerogel(ETSACA)with a large specific surface area,porous structure,low density and thermal conductivity.And the EISACA were utilized in dyeing wastewater treatment.For comparison purposes,sodium alginate aerogel,pure sodium alginate carbon aerogel(SACA)and direct carbonized sodium alginate powder(SA)were prepared.The adsorption capacity of MB by ETSACA(504.7 mg·g-1)was significantly higher than that of SACA(209.6 mg·g-1)and SA(106.3 mg·g-1),and its excellent adsorption performance was mainly attributed to its large specific surface area(1126.8 m2·g-1),which was superior to that of SACA(767.3 m2·g-1)and SA(222.5 m2·g-1).The method takes advantages of the unique "egg-box" structure of sodium alginate,pyrolysis and carbonization of aerogel,and provides a research basis for the preparation of new three-dimensional porous materials in the fields of fuel cells and lithium ion batteries.