Preparation And Properties Of Enzymatic Hydrolysis Lignin Based Activated Carbon For Electrode

In order to make full use of biomass and bioenergy,enzymatic hydrolysis lignin is extracted from the bioethanol residuals of corn straw.Then,the high added value lignin-based activated carbon(LAC)is activated in one-step by KOH at the temperature of 800 °C.However,the ordered level of LAC framework and its electrical conductivity are still not satisfactory,and thus limiting its application in certain field to some extent.In view of this,in this work,air radio-frequency cold plasma was firstly used to treat LAC,followed by impregnation with metal ions solutions to prepare graphitic carbon under the different pyrolysis temperatures.Emphasis was put on investigating the structure and electrical conductivity of post-graphitization carbons.The effect of the content and distribution of Fe(?)on plasma-modified carbon were investigated.Meanwhile,the electrochemical properties of plasma-treated carbon loaded with Fe(?).The interaction mechanism between modified activated carbon and metal ions was explored,and the optimum process for loading metal ions after modified activated carbon was optimized.Finally,according to optimizing process step by step,the optimized parameters of plasma treatment and the kind of metal ions were adopted for studying the effect of the heating temperature and metal ions on catalyzed-graphitization lignin-based activated carbon.These results can provide theoretical and practical basis for improving the structure and conductivity of amorphous carbon in industry.The results are as following.(1)Enzymatic hydrolysis lignin has high carbon content,low calorific value when raw materials heated.The benzene ring is broken and the final carbon residue is relatively high when lignin is heated.Thus,it can be used as carbon precursor appropriately.The specific surface area of lignin-based carbon activated at 800 °C in one step is higher than those of commercial activated carbons.The pore on the carbon surface is arranged like ?Honeycomb? by scanning electron microscopy(SEM).The electrochemical performance test shows that the lignin-based carbon has high stability in the large charge and discharge current density.The conductivity of lignin-based carbon measured by powder conductivity tester is 6.5 S/cm.(2)The nitrogen and oxygen content on lignin-based carbon surface is increased when lignin-based carbon modified by air plasma.These N-containing and O-based containing functional groups are beneficial for coordinating with metal ions when carbon dipped in the solution.This bonding force depends on the chemical adsorption.The amides and pyrrolic-N on carbon surface provide abundant active sites while the O-containing functional groups bind with metal ions by the ion-exchange reaction.The optimized plasma treatment parameters are determined as the discharge power of 200 W and the process time of 15 min for loading Fe(?)or Ni(?).The total adsorption capacity of modified carbon to Fe(?)or Ni(?)are increased.Meanwhile,the adsorption capacity of modified carbon is higher than that of untreated at the same dipping time,indicating that the air plasma treatment on lignin-based carbon is beneficial on improving the chemical state of carbon surface so as to increasing the adsorption ability of carbon.(3)The lignin-based activated carbon is pretreated by air plasma in the process condition of 200 W and 15 min,followed by impregnating in metal ions with different time.The modified lignin-based carbon/metal ions composite electrode is tested by electrochemical workstation under three electrode system and the results show that: the modified lignin-based carbon after dipping in the metal ion solution up to 270 min show good electrochemical properties.In particular,when the current density is 1 A/g,the specific capacitance of modified lignin-based carbon/metal ions composite electrode reaches 240 F/g.Meanwhile,it has good capacitance retention at high current density(10 A/g).However,the equivalent series resistance of modified carbon loaded with ferric ion is lower than that of modified activated carbon loaded with two nickel ions.This might be related to the activity of the metal ions and their own electrical conductivity.Therefore,ferric ion is chosen as the subsequent catalyst.(4)Plasma-treated activated carbon load with ferric ion in different dipping times,followed by heating at 800 °C for catalyzed-graphitization.The results show that it is a positive correlation between the structure of post-catalyzed carbon and the time of impregnation.The conductivity of post-catalyzed carbon increased by 46.2% compared with the pure lignin-based activated carbon.However,the specific surface area and capacitance of the post-catalyzed carbon are reduced after heating at 900 °C and 1000 °C in impregnation time of 270 min.Fortunately,the ordering degree of structure of post-catalyzed carbons are increased.The sheet graphite microcrystals with lattice stripes stacked on the carbon layer are observed by transmission electron microscopy(TEM).The results of the powder resistivity tester show that the conductivity of catalyzed-graphitization lignin-based activated carbon increased by 64.6% than that of pure lignin-based activated carbon.