针铁矿吸附诺氟沙星特征的研究

Characteristics of norfloxacin sorption on goethite

根据OECD Guideline 106批平衡实验.分别研究了pH值对针铁矿吸附诺氟沙星的动力学特征和吸附量的影响以及诺氟沙星的吸附热力学特征,并探讨了其可能吸附机理.结果表明,不同pH值(3.5,5.0,5.6和6.2)时,诺氟沙星在经历了约6h的快速吸附阶段后,均进入缓慢吸附阶段,吸附平衡时间为48h.伪二级动力学方程能够较好地描述不同pH值条件下诺氟沙星针铁矿上的吸附动力学特征.影响吸附量大小的pH值依次为5.6>5.0>6.2>3.5,主要决定于诺氟沙星和针铁矿的不同形态间的乘积之和,针铁矿表面的吸附作用主要以诺氟沙星的兼性离子为主.吸附等温线较好地符合Freundlich方程,温度从15℃升高到35℃时,拟合系数1/n从0.43升至0.61,表明温度升高减弱了针铁矿对诺氟沙星的非线性吸附.ΔH0=-39.45kJ/mol和ΔG0<0表明吸附是自发进行的放热过程,且以离子交换为主,同时可能存在着偶极间作用力和氢键力等作用.ΔS0<0表明吸附过程中熵在减小.

The kinetics characteristics and sorption amount under different pH conditions（i.e.pH=3.5,5.0,5.6 and 6.2） and the thermodynamics characteristics of norfloxacin（NOR） sorption on goethite（α-FeOOH） were determined by batch equilibrium experiments according to OECD Guideline 106 in this study.The sorption mechanisms were also found out.Results showed that the sorption of NOR on α-FeOOH began from a rapid stage with continuing for approximately 6 h,and then followed with a slow stage until a 48 h of sorption equilibrium time.Sorption kinetic curves fit a pseudo second-order kinetic model well at different pH.The sorption amount of different pH corresponded to the decreasing order of 5.6 〉5.0〉 6.2〉 3.5,which depended on the sum of the products concentrations obtained from different species of α-FeOOH and NOR at respective pH value.This result also indicated that the order of sorption amount was mostly attributed to the sorption of NORH2± on the surface of α-FeOOH.The Freundlich model could compatibly describe sorption isotherm of NOR on α-FeOOH.The 1/n of the isotherm fitted by the Freundlich model increased from 0.43 to 0.61 with increasing temperature from 15 ℃ to 35 ℃,which indicated that an increase in temperature could reduce the nonlinear sorption of NOR on α-FeOOH.Results with-39.45 kJ/mol of ΔH0 and less than 0 of ΔG^0 revealed that the sorption of NOR on α-FeOOH was a spontaneously exothermic process.The exchange of ion was a dominant sorption mechanism for NOR sorption on α-FeOOH,while the H-bonding and dipole force were other possible sorption mechanisms.Less than 0 of ΔS^0 indicated an entropy decrease during the sorption process.