Nkoh Nkoh Jackson, Yan Jing, Hong Zhi-Neng, Xu Ren-Kou, Kamran Muhammad Aqeel, Jun Jiang, Li Jiu-Yu
State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, P.O. Box 821, Nanjing, China; University of Chinese Academy of Sciences, Beijing, 100049, China; Department of Chemistry, University of Buea, P.O. Box 63, Buea, Cameroon.
State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, P.O. Box 821, Nanjing, China.
Colloids Surf B Biointerfaces. 2019 Nov 1;183:110450. doi: 10.1016/j.colsurfb.2019.110450. Epub 2019 Aug 22.
Extracellular polymeric substances (EPS) contain a vast number of functional groups which can provide sorption sites for heavy metal cations in solution, however, the mechanisms for the interaction of EPS with various metal cations were not well understood. In this study, the sorption potential of EPS from Pseudomonas fluorescens for different cations was investigated. The changes of electrokinetic properties that occurred on the surface of EPS once they adsorbed these cations were also studied using zeta potential measurements as a function of pH and cation concentration. The adsorption data fitted Freundlich isotherm better than Langmuir and D-R isotherms. The interactions of the cations with EPS were favourable with the separation factor K < 1. Under different pH conditions, the zeta potential of EPS in the different cation solution followed the order: Fe(III) (at pH ≤ 5.0) > Al(III) > Cu(II) > Mn(II) > Ni(II)≈Cd(II) > Ca(II) > EPS, while with respect to the initial cation concentration, the zeta potential of EPS was in the order: Fe(III) > Al(III) > Cu(II) > Cd(II) > Ni(II)≈Mn(II)≈Ca(II). The effect of cation sorption on the surface charge of EPS increased with pH as well as cation concentration. The thermodynamic analysis demonstrated that besides the sorption of Fe which was exothermic, all the other cations were adsorbed through an endothermic process. The ΔS revealed that most of the cations interacted with EPS through the formation of inner-sphere complexes. The ATR-FTIR analyses confirmed that complexation occurred between the cations and functional groups on the surface of EPS. The zeta potential of EPS shifted to positive value direction due to sorption of cations on EPS, indicating that the specific interactions were involved in the sorption process. This study enhances our understanding of EPS aggregation and heavy metal bio-sorption through the electrokinetic mechanism. The results will provide useful references for immobilization of heavy metals and alleviation of Al toxicity in acidic soils.
胞外聚合物（EPS）含有大量官能团，可为溶液中的重金属阳离子提供吸附位点，然而，EPS与各种金属阳离子相互作用的机制尚未得到充分了解。在本研究中，研究了荧光假单胞菌的EPS对不同阳离子的吸附潜力。还使用zeta电位测量研究了EPS表面吸附这些阳离子后发生的电动性质变化，该变化是pH和阳离子浓度的函数。吸附数据拟合Freundlich等温线比Langmuir和D-R等温线更好。阳离子与EPS的相互作用是有利的，分离因子K<1。在不同pH条件下，不同阳离子溶液中EPS的zeta电位顺序为：Fe（III）（pH≤5.0时）>Al（III）>Cu（II）>Mn（II）>Ni（II）≈Cd（II）>Ca（II）>EPS，而对于初始阳离子浓度，EPS的zeta电位顺序为：Fe（III）>Al（III）>Cu（II）>Cd（II）>Ni（II）≈Mn（II）≈Ca（II）。阳离子吸附对EPS表面电荷的影响随pH和阳离子浓度的增加而增加。热力学分析表明，除了Fe的吸附是放热的外，所有其他阳离子都是通过吸热过程吸附的。ΔS表明大多数阳离子通过形成内球络合物与EPS相互作用。ATR-FTIR分析证实阳离子与EPS表面的官能团之间发生了络合。由于阳离子在EPS上的吸附，EPS的zeta电位向正值方向移动，表明吸附过程涉及特定的相互作用。本研究通过电动机制增强了我们对EPS聚集和重金属生物吸附的理解。研究结果将为酸性土壤中重金属的固定和铝毒性的缓解提供有用的参考。
