The Study On Preparation And Performance Of Starch-based Porous Carbons

Energy is a special resource.According to the possibility of regeneration,it can be divided into two categories on earth: nonrenewable resources and renewable resources.At present,in the world's primary energy production and consumption,ranked first is the oil,followed by coal and natural gas.With a lot of oil,coal,natural gas and other fossil resources reserves dwindling and followed by a large number of harmful gases and greenhouse gases emissions such as CO₂?NO₂?SO₂,the world faces energy and environmental issues double increase,these problems have become the focus of attention in modern society,therefore,searching for new alternative energy sources is of great significance to the development of the world's energy.Nowdays,it is generally believed that the use of renewable biomass resources gradually replace petroleum chemical products can effectively help to solve the environmental problems and develop a sustainable society.Biomass is an inexpensive,readily available,environmentally friendly renewable resource,it is the only available carbon source in renewable resources,it is also an ideal precursor of high-performance carbon materials,therefore,the use of renewable resources of biomass as raw materials to reduce or replace nonrenewable resources of fossil fuels to prepare a series of high value-added of carbonaceous materials is the future direction of the global development.Starch is one of the biomass resources,as a kind of natural polysaccharide compounds,it has the advantages of low cost,abundant source,green environmental protection,can be regenerated etc.Starch and its derivatives are widely used in food,pharmaceutical,biological,chemical,textile,papermaking,water treatment and many other industries.In this paper,corn starch was used as the precursor of carbonaceous materials,H₃PO₄ as activating reagent,various porous carbons have been prepared by different synthesis methods,the corresponding application performance of porous carbons have been studied in detail,the main research contents for the following several aspects:1.High-performance porous carbons were synthesized from corn starch by a two-step process: hydrothermal carbonization and chemical activation with H₃PO₄.The as-prepared porous carbons were characterized by scanning electron microscopy,powder X-ray diffraction,fourier transform infrared spectra,C,H,N,O,S analyzer,N2 adsorption/desorption,cyclic voltammetry and galvanostatic charge/discharge techniques.The effects of activation conditions on the morphology,microstructure and electrochemical performance of porous carbons were thoroughly investigated.The resulting porous carbons showed a high specific surface area of 1188 m2 g^-1 and a large pore volume of 1.40 cm3 g^-1.The specific capacitance and energy density were up to 143.6 F g^-1 and 19.9 Wh kg^-1,respectively.After 5000 charge/discharge cycles,the specific capacitance still retained above 99% of its initial capacitance,there was only less than 1% loss of its initial capacitance.2.High-performance porous carbons were synthesized from corn starch by a one-step process of chemical activation with H₃PO₄.The as-prepared porous carbons were characterized by scanning electron microscopy,powder X-ray diffraction,fourier transform infrared spectra,C,H,N,O,S analyzer,N2 adsorption/desorption,cyclic voltammetry and galvanostatic charge/discharge techniques.The effects of activation conditions on the morphology,microstructure and electrochemical performance of porous carbons were thoroughly investigated.The optimum conditions were as follows: activation temperature was 500 ?,activation time was 1 h and the H₃PO₄:hydrochar ratio was 4:1?g/g?.The specific surface area and pore volume were as large as 1167 m2 g^-1 and 1.80 cm3 g^-1,respectively.The specific capacitance and energy density were as high as 161.7 F g^-1 and 22.5 Wh kg^-1,respectively.After 5000 charge/discharge cycles,the specific capacitance is 152.7 F g^-1,still retained above 94% of its initial capacitance.3.Comparison of structure properties of porous carbons prepared by different synthesis methods showed that porous carbons with relatively well-developed porosity were synthesized from corn starch through directly activated by H₃PO₄.So chose porous carbon prepared by this method under the optimum conditions to study the adsorption performance on Cu²⁺?Pb²⁺ and Cd²⁺ from aqueous solution,besides,commercial activated carbon was used for comparative analysis.The influence of experimental parameters such as ion concentration,adsorption time,solution p H,adsorbent dose and temperature on adsorption were explored.The adsorption capacity of Cu²⁺?Pb²⁺ and Cd²⁺ was compared.Adsorption kinetics and adsorption isotherm models were also investigated.It demonstrated that homemade starch-based porous carbon presented good adsorption performance and high cost performance compared with commercial activated carbon.Both adsorption capacity of heavy metal ions followed the order of Pb²⁺>Cu²⁺>Cd²⁺,all the adsorption behaviors were followed the pseudo-second order kinetic model and Langmuir isotherm model,also could be considered as monolayer chemical adsorption.This paper was used the biomass of corn starch as raw material,H₃PO₄ as activating reagent,through lots of experiments and series of characterization methods,studied on the application performance of porous carbons prepared by different synthesis methods.The results showed that corn starch-based porous carbons had excellent electrochemical performance and adsorption performance,the good electrochemical performance can be applied in the field of energy storage such as supercapacitor electrode materials,the good adsorption performance can be applied in the field of environmental protection such as adsorbent materials.In a word,a new method for preparing porous carbons from starch by using H₃PO₄ as an activator was proposed,which provided a new route for the application of porous carbons in electrode materials and adsorbents.