| The accelerating advancement of human civilization has brought great challenges to the energy crisis,ecological environment deterioration and water scarcity.Nowadays,nearly half of the produced energy is wasted due to inefficient energy-conversion and energy storage systems.Water contamination and greenhouse effect caused the emission of carbon dioxide during the burning of fossil fuel are also greater threats to human health and the ecosystem.Carbon material,due to their excellent physical chemistry stability show great potential for energy storage,water purification and carbon capture.However,their high-cost preparation,low yield,complicated equipment used,and poor synthesis conditions hindered them in the actual application.Biomass is an ideal precursor of carbon-based material due to their richness in the carbon element,low cost,abundant,and sustainable sources.Consequently,preparation of the carbon-based materials controlled surface properties and pore structure has been arised great attentions from low-cost and renewable biomass by an environment friendly and efficient process,which to achieve "energy"and "ecological environment" friendly coexistence,has become the focus of researchers in recent years.In this paper,we devoted to use corn stalks of agricultural residues and forestry biomass Salix as feedstock to prepare carbon material,which hydrothermal carbonization was used in combination with functional,graphitization and activation of carbon-based materials.We investigated their application in the field of environment and energy.The main research work is as follows:The formation condition,morphology evolution,reaction mechanism and adsorption properties of hydrochars prepared from corn stalk were carried out using a hydrothermal method at 200 ? for 3-44 h.The experimental results showed that 26 h was sufficient time for the producing of hydrochar at 200 ? Batch absorption experiments exhibited that the hydrochar obtained from 26 h reaction is an excellent adsorbent,and its maximum removal efficiency for Cr(VI)is 67%at pH 1.The structure and morphology of Salix-based hydrochar and corn stalks-based hydrochar were completely different.Salix-based hydrochar possessed a molecular sieve-type mesh structure under HTC 220 ? for a period of 26 h,and then the mesh structure of hydrochar had become more and more dense,and finally spongy liked structure has been contiuously formed as the reaction time increase.At the same time,the relative amounts of oxygen and nitrogen functional group have been reached its highest amount on hydrochar surface of HC-26 hydrochar,and its BET specific surface area was bigger than other hydrochar' also,which were beneficial for the adsorption and diffusion of adsorbent.The adsorption of phenol,Ni(II)and Cr(VI)from aqueous solutions onto HC-26 hydrochar has been investigated as well.Batch experiments indicated that adsorption of phenol and Ni(II)were lower than that of Cr(?).Thus,HC-26 hydrochar can be acted as an excellent adsorbent at acidic conditions for Cr(VI),and its maximum removal efficiency for Cr(VI)was 99.84%at pH 1.Salix-based hydrochar is an ideal precursor of activated carbon due to its high numbers of oxygen and nitrogen functional groups and its molecular sieve-type open pore structure.Our goal is to prepare efficient C02 porous carbon adsorbent,preparation of the adsorbent can be divided into two steps:the first step is to dope Nitrogen in situ during HTC in ammonia solution.The second step is to activate hydrochar with KOH or ZnCl2 at 900 ?.The products prepared as above possessed larger BET specific surface area and higher numbers of oxygen and nitrogen functional groups on its surface.Wherein,pore structure of nitrogen-doped porous carbon with ZnCl2 as activator were mainly mesoporous,and pore structure of nitrogen-doped porous carbon with KOH as activator were mainly microporous.Experiment show that the structure and morphology of pore were various with the different proportion of hydrochar and KOH.When mass ratio of hydrochar/KOH reached 1:6,the carbon nanotubes morphology has been formed in nitrogen-doped porous carbon at 900 ?,which exhibited the highest C02 adsorption 110.lmg g-1 at 0.1 bar and 25 ?.As the experiment showed in chapter 4,Hydrochar could be converted to a porous carbon with carbon nanotube morphology under certain conditions.However,porous carbon was mainly in the form of amorphous carbon.Hydrochars were converted to graphitic carbon at 900 ? using nickel nitrate hexahydrate as a graphitization catalyst.The graphitization degree of carbon is close related to HTC reaction time,and graphitization degree increase with the reaction time increase.The morphology of graphite carbon derived from hydrochar was transformed into coil morphology from nanowires when the reaction time was extended from 4 h to 26 h.Electrochemical study showed that graphite carbon has been modified as electrodes to increase electrode's reversibility.Herein,graphite carbons loaded Pt nanoparticles also can be acted as electrodes,they showed highest electrochemical active area and reversibility,which highest electrocatalytic activity for the oxidation of methanol.Hydrochar is an excellent activated carbon precursor.We adopted both traditional and microwave HTC methods of preparation of Salix-based hydrochar in the aqueous solution of ZnCl2.Hydrochars were furtherly activated up to 900 ? for 90 min in the presence of ZnCl2 with different proportion.The results showed that activated carbon derived from microwave hydrochar had a lower BET specific surface area(528.05 m2/g)than traditional method,in spite of microwave hydrochar' BET with higher specific surface area.Micro-or mesoporous structure of activated carbon were adjusted by controlling the amount of ZnCl2 during chemical activation.When the ratio of ZnCl2 and hydrochar is 2:1,activated carbon with a BET specific surface area was 1021.87 m2/g.Electrochemical performance of activated carbon derived from traditional hydrochar was better than that of microwave hydrochar. |
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