Studies On The Adsorption Properties Of Naphthalene,Phenanthrene,and Pyrene In Original And Modified Activated Carbon

Polycyclic aromatic hydrocarbons?PAHs?are a significant family of environmental pollutants which are composed of two or more fused aromatic rings.Due to the high bioaccumulation and adverse health effects of PAHs,such as light-induced toxic effects,mutagenic,carcinogenic and teratogenic properties,therefore,the development of suitable methods for the removal of PAHs is needed.Activated carbon?AC?is the most common adsorbent used because of its unique and versatile pore structure,large specific surface area,abundant micro and mesoporous structure,and high degree of surface reactivity.Therefore,in this paper,based on the preparation of AC with different raw materials,through applying AC to different adsorption systems or modified to study its adsorption performance,the results are as follows:Firstly,walnut shell was used as raw materia to prepared walnut shell-based activated carbon?WAC?through microwave-assisted KOH activation.The adsorption properties of naphthalene?NAP?and phenanthrene?PHE?onto WAC were studied in both single-and binary-component systems at different pH values.The results showed that pseudo-second-order model better described the kinetic data for all experiment conditions,and that film diffusion was the rate-limiting step in adsorption process.In single-component systems,the adsorption capacity of WAC decreased when the solution pH increased from 3 to 9,and Freundlich isotherm model better depicted the equilibrium data compared with other isotherm models.Relative to single component system,the presence of PHE affected NAP adsorption in binary-component systems,the adsorption amount of NAP decreased from 49.58 mg g^-1 to 39.58 mg g^-1,which was reduced by approximately 20%,and the Sheindorf–Rebhun–Sheintuch model,which is an extended Freundlich model,can be fully fitted the adsorption equilibrium experimental values of WAC for PHE and NAP.The competitive coefficients decreased with the reduces of the mass concentration ratio?r=[NAP/PHE]?.The physical and chemical properties of WAC and polycyclic aromatic hydrocarbons?PAHs?and the?–?complex between the?-electrons of benzene rings of PAHs and active sites on WAC surface may be play major role in competitive adsorption.Secondly,coal-based activated carbon?CAC?was prepared by microwave-assisted KOH activation using pulverized coal as a raw material to explore its adsorption behaviors of naphthalene and pyrene.Batch adsorption experiments showed that the pseudo-second-order kinetics model could better describe the adsorption behavior of pyrene and naphthalene on CAC;film diffusion may be the rate control step;the adsorption process was the spontaneous exothermic reaction and low temperature contributed to the adsorption of pyrene and naphthalene on CAC.The experiments adsorption amount of naphthalene and pyrene on CAC were 67.35 mg g^-11 and 169.32 mg g^-1,respectively.In addition the activation energy Ea<40 kJ mol^-1,indicating that a physical adsorption process.The continuous dynamic column adsorption experiments of pyrene on CAC indicated that the lower flow rate,higher packing layer height and larger packing diameter were not conducive to the breakthrough of the adsorption column bed,which will lead to increased penetration time.Finally,CAC was modified through microwave-assisted cationic surfactants,and the sample with the best adsorption properties was named SAC.The CAC and SAC were characterized by different characterization methods in detail,such as SEM,FTIR and BET.The specific surface area increased from660.60 to 757.19 m² g^-1 and their point of zero charge(pH_PZC)varies from 5.92 to 6.35.The adsorption experiment was carried out by batch technique with variables such as reaction time,adsorbent amount,the pH of solution and the reaction temperature.Results showed that NAP was adsorbed rapidly during the initial 20 min,and thereafter reached adsorption equilibrium after 40 min,and the adsorption amount increased from 152.83 mg g^-11 to 192.50 mg g^-1,which was increased approximately 26.7%.The adsorption kinetics can be well described by the pseuso second-order model and the Freundlich isotherm model better depicted the adsorption isotherms of CAC and SAC.The adsorption process of NAP was spontaneous exothermic process and temperature was found to negatively affect the adsorption capacity.Furthermore,the film diffusion w s confirmed the r te limiting step.The?–?st cking electron donor cceptor interaction,hydrophobic interaction and hydrogen bonding may play key roles in naphthalene adsorption on SAC.