纳米Fe_3O_4负载铜绿假单胞菌吸附U(VI)的热力学与动力学研究

Dynamic and thermodynamic study on U(VI) adsorption onto nano-Fe_3O_4 immobilized Pseudomonas aeruginosa

探讨纳米Fe3O4负载铜绿假单胞菌吸附铀的动力学与热力学过程,以及相关反应的速率控制过程。结果表明:纳米Fe3O4负载铜绿假单胞菌对U(VI)的吸附过程符合准二级动力学模型(R2≥0.9995);膜扩散和粒子内部扩散是吸附的控制步骤;Bangham模型拟合结果表明粒子内部扩散不是唯一的速率控制步骤,而液相边界层和粒子外部传质过程对吸附的影响不能忽略;表观活化能为15.705kJ/mol。热力学试验结果表明:纳米Fe3O4负载铜绿假单胞菌对U(VI)的吸附服从Langmuir、Freundlich等温模型,表明吸附是一个单层覆盖与多层吸附相结合的过程;在298 K、303 K、308 K下Langmuir模型拟合最大吸附量分别为92.483 mg/g、103.875 mg/g、107.918 mg/g;吸附过程ΔH>0、ΔS>0、ΔG<0,表明吸附过程自发进行,为吸热过程,存在着各种化学键力和范德华力作用,化学吸附与物理吸附过程共存。

The paper is to provide our dynamic and thermodynamic analysis of U（VI） adsorption onto Pseudomonas aeruginosa loaded by nano-Fe304, in which we explored the dynamics, thermodynamics, particle diffusion types, activation energy and rate-controlling steps. As is known, Pseudomonas aeruginosa loaded by nano-Fe304 has a great effect on the adsorption of uranium. The results of our analysis indicate that such kind of adsorption depends significantly on all the above-mentioned parameters. Moreover, the adsorptive kinetics has also proved to be in close accord with the quasi-second-order model （R2〉 0.9995）. Fitting diffusion model well eotdirmed that liquid flim diffusion and intra-particle diffusion is the controlling step of ad- sorption; Bangham model yielded a somewhat good fit （R2 0.9455）, showing that the intra-particle diffusion was not the only rate-controlling step, the influence of liquid phase boundary layer and particle external mass transfer processes on adsorption couldn＇t be ig- nored either. The experimental data have been described by the four theoretical adsorption isotherms, i.e., the Langmuir, Freundlich, Temkin and D - R. The results of our experiments also show that the adsorptive behavior of uranium onto nano-Fe304 is well fit for the Langmuir and Freundlich isotherm models, which implies that the ad- sorption process involves both the monolayer cover and muhilayer ad- sorption. Langmuir adsorptive capabilities were found to be 92.483 mg/g, 103.875 mg/g and 107.918 mg/g at 298 K, 303 K and 308 K, respectively. In addition, the adsorptive capability actually in- creases with the increase of the temperature. The Langmuir and Fre-undlich coefficients, RL and 1/n, their values are in the range of 0 1, indicate that the loading Pseudomonas aeruginosa loaded by nano- Fe304 tends to be an attractive composite material for removing the u- ranium. We have also evaluated the thermodynamic parameters, such as AH, AS and A G for the adsorption, the positive values of AH and AS, whereas the negative values of AG indicate that the ad- sorption has taken place spontaneously and emtothermically, in which there exist all kinds of chemical bond force and Van Der Waals h）rce with the adsorption mechanism taking place in a mixed way, includ- ing physisorption and chemisorption.