有机改性蒙脱土对萘的吸附机制和影响因子

Investigating Adsorption of Naphthalene to Organo-Modified Montmorillonites and Influencing Factors

我国场地土壤中多环芳烃(PAHs)污染或PAHs-重金属复合污染是常见的污染类型,对公众健康与环境构成巨大威胁.本研究利用耗散型石英晶体微天平(QCM-D)技术和批量吸附实验,探究实验室制备的2种有机改性黏土对萘的吸附机制,以及萘与Cu^2+共存时黏土颗粒吸附情况.结果表明,25℃时,十六烷基三甲基溴化铵改性蒙脱土(CTAB-SMF)的吸附等温线符合Freundlich模型(R^2>0.92,n>1),说明其对萘的吸附位点具有多样性,在较高萘平衡浓度(ce=1 mmol·L^-1)下吸附分配系数Kd为SMF的13.4倍;3-巯基丙基三甲氧基硅烷改性蒙脱土(TMSP-SMF)的吸附等温线符合Langmuir模型(R^2>0.96),在较高萘平衡浓度(ce=1 mmol·L^-1)下吸附分配系数Kd为SMF的1.14倍.说明2种有机改性黏土对萘的吸附效果优于SMF颗粒.3种黏土颗粒对萘的吸附焓在-30^-10 kJ·mol-1之间,均为自发物理吸附.溶液离子强度升高抑制了SMF吸附萘,但对改性黏土吸附萘无显著影响.萘平衡浓度较低(ce=0.1 mmol·L^-1)时,Cu^2+的存在使TMSP-SMF对萘的吸附效果增加了3倍;同时萘能促进2种改性黏土对Cu^2+的吸附.本研究通过原位在线QCM-D检测了黏土对萘的吸附机制,结果与批量吸附实验结果一致:CTAB-SMF对萘的吸附位点主要为黏土层间的改性剂基团,TMSP-SMF则位于黏土颗粒表面的改性剂基团.本项研究结果显示,QCM-D技术是一种有效的原位在线表征黏土膜吸附有机污染物的方法,2种有机改性的黏土颗粒可作为应用于PAHs或PAHs-重金属复合污染场地的修复材料.

There are many sites contaminated by polycyclic aromatic hydrocarbons(PAHs)or combined PAHs-heavy metal in China,which pose serious health-risks to local people and environments.Dissipative quartz crystal microbalance(QCM-D)was applied to investigate the adsorption of naphthalene to two organic-modified smectite clays(cetyltrimethyl ammonium bromide modified montmorillonite,CTAB-SMF,and 3-mercapto propyl trimethoxy silane modified montmorillonite,TMSP-SMF)and original SMF,together with batch adsorption experiments.The results,based on in-situ online QCM-D experiments,showed that the adsorption sites of CTAB-SMF on naphthalene were mainly CTAB grouped between the interlayers of clay particles,while TMSP-SMF’s were TMSP grouped on the surfaces of clay particles.The isotherms of naphthalene adsorption to CTAB-SMF fitted well(R^2>0.92)with the Freundlich model,while the adsorption isotherms to TMSP-SMF and SMF fitted well with the Langmuir model(R^2>0.96).The parameters of CTAB-SMF(n>1)indicated that the adsorption sites of naphthalene to CTAB-SMF were heterogeneous and the adsorption increases at higher equilibrium concentration.The adsorption capacity qmax of TMSP-SMF is significantly greater than that of SMF(P<0.05).Based on the calculation,the value ofΔHobs for these three clays(CTAB-SMF,TMSP-SMF,and SMF)were within the range of-30 to-10 kJ·mol-1,which indicated that it was a spontaneous exothermic physical process.The solution ionic strength could decrease the adsorption of naphthalene to SMF,but had limited effects on naphthalene adsorption to the two organo-modified clay particles.The existence of Cu^2+in the solution could enhance naphthalene adsorption to the three particles,and naphthalene could improve Cu^2+adsorption to these two modified clays.The results of this study show that QCM-D is a useful technique to indicate the changes of clay film during the process of adsorption,and the two organo-modified clay particles have the potential to be remediation materials to remediate PAHs or PAHs-heavy metal-contaminated sites.