Preparation Of Coal-based Activated Carbon By Microwave Activation And Its Application In Naphthalene, Phenanthrene, And Pyrene Adsorption

Polycyclic aromatic hydrocarbons (PAHs) are persistent organic pollutants. The nature oftheir difficult biodegradation caused great harm to the environment and they are notefficiently removed by conventional physicochemical methods. Activated carbon (AC) isconducive to adsorb non-polar organic compounds and the compounds with unsaturatedbonds, due to their developed pore structure and huge specific surface area. Our research takeadvantage of abundant coal resource of Xinjiang as raw materials, coal-based activated carbon(CAC) with high adsorption performance was prepared by microwave activation and itsapplication in the typical PAHs (naphthalene, phenanthrene, and pyrene) adsorption. Theresults of the study are as follows:The optimum preparation conditions of anthracite-based activated carbon (anthracite-AC)are KOH as activating agent, coal alkali ratio of1:3, microwave time of12min, andmicrowave power of700W. The optimum preparation conditions of smokey coal-basedactivated carbon (smokey-AC) are KOH as activating agent, coal alkali ratio of1:2,microwave time of8min, and microwave power of700W. The optimum preparationconditions of changyan coal-based activated carbon (changyan-AC) are KOH as activatingagent, coal alkali ratio of1:1.5, microwave time of8min, and microwave power of700W.The three optimal CAC on its adsorption capabilities for methylene blue (MB) and iodinewere investigated. Their adsorption capacity as: anthracite-AC﹥smokey-AC﹥changyan-AC.The coal alkali ratio, microwave time, and microwave power have great influence on thesurface structure of CAC. The BET surface area, pore area, pore volume, and average porediameter of the optimal CAC were identified to be1770.49m2/g,508.87m2/g,0.61m3/g and2.82nm, respectively. The surface of CAC with a large number of pores and specific surfacearea was developed after activator activation. With increased coal alkali ratio, microwave time,and microwave power, the number of lactonic groups decreased and pHPZCincreased.Naphthalene, phenanthrene, and pyrene adsorption onto CAC was a two-stage process.The first stage was fast adsorption, and the second stage was slow adsorption. The increase oftemperature resulted in the decrease in the adsorption rate and amount. The increase of theamount of activated carbon resulted in the increase in the adsorption rate and decrease in adsorption amount. The adsorption rate decreases and adsorption amount increases as theinitial concentration increases. With the increase of initial pH solution, the adsorption amountchanged little. Agitation had little effect on adsorption. Naphthalene, phenanthrene, andpyrene adsorption were described well by the Langmuir model and indicated that theadsorption was surface. The kinetic results indicated that adsorption was described by thepseudo-second-order equation and suggested that the adsorption involved chemicalinteraction.The maximum adsorption amount of Naphthalene, phenanthrene, and pyrene adsorptiononto the optimal anthracite-AC were73.04mg/g,87.05mg/g, and91.43mg/g, respectively.The maximum adsorption amount of Naphthalene, phenanthrene, and pyrene adsorption ontothe optimal smokey-AC were59.24mg/g,84.13mg/g, and88.20mg/g, respectively. Themaximum adsorption amount of Naphthalene, phenanthrene, and pyrene adsorption onto theoptimal changyan-AC were58.71mg/g,82.52mg/g, and87.10mg/g, respectively. Theadsorption capacity as: anthracite-AC﹥smokey-AC﹥changyan-AC. The adsorption progressis controlled by hydrophobicity and the molecules with more aromatic rings showed asignificantly higher adsorptive affinity.