• 关键词：MOF-Fe  亚硒酸根  磷酸根  共存  竞争性吸附

• 基金项目：国家自然科学基金（No.41561053，21767009）

• 王锐
• 湖北民族学院化学与环境工程学院, 恩施 445000

• 许海娟
• 湖北民族学院化学与环境工程学院, 恩施 445000

• 魏世勇
• 湖北民族学院化学与环境工程学院, 恩施 445000

• 吴德勇
• 湖北民族学院化学与环境工程学院, 恩施 445000

• 摘要：通过系列吸附实验，研究了磷酸盐（Pi）共存对MOF-Fe吸附亚硒酸盐（Se（Ⅳ））的影响.结果表明，不加Pi的吸附体系（Pi/Se=0）中，Langmuir和Freundlich模型对MOF-Fe等温吸附Se（Ⅳ）的数据的拟合度都较高；体系中加入与Se（Ⅳ）等物质的量浓度的Pi（Pi/Se=1）以后，等温吸附过程只适合用Freundlich模型拟合.与Pi/Se=0体系相比，Pi/Se=1体系中MOF-Fe对Se（Ⅳ）的最大吸附容量降低了68%，而吸附亲和力和吸附异质性却明显增强.Pi/Se=0和1的两种体系中，MOF-Fe对Se（Ⅳ）的吸附平衡时间分别为160 min和40 min，二级动力学方程可很好地描述两种体系的动力学吸附过程，液膜扩散和颗粒内扩散是吸附反应的主要速率控制因子.两种体系中，MOF-Fe对Se（Ⅳ）的平衡吸附量均随着温度的升高而降低，吸附均属于自发放热且有序度降低的过程.与Pi/Se=0体系相比，Pi/Se=1体系中MOF-Fe对Se（Ⅳ）的平衡吸附量受温度影响更为明显，这说明升高温度增强了Pi对Se（Ⅳ）吸附在MOF-Fe上的竞争强度；Pi/Se=1体系中MOF-Fe对Se（Ⅳ）的吸附自由能ΔG^θ略微增大，而焓变ΔH^θ和熵变ΔS^θ均明显减小，这说明Pi共存导致MOF-Fe对Se（Ⅳ）的化学吸附贡献增强.吸附体系pH从4.0升高至8.0时，Pi/Se=0和1体系中MOF-Fe对Se（Ⅳ）的平衡吸附量分别降低了7%和37%.当增大体系中Pi的浓度时，MOF-Fe对Se（Ⅳ）的平衡吸附量呈指数模型降低并稳定于最大吸附量的30%，这表明MOF-Fe对Se（Ⅳ）的吸附中约70%的比例可归属为可逆吸附.可见，Pi/Se=1体系中MOF-Fe对Se（Ⅳ）的吸附可分为可逆和不可逆吸附，其中，可逆吸附受Pi的竞争作用影响而明显降低，不可逆吸附则不受共存Pi的影响.

• Abstract：The influence of phosphate (Pi) on selenite (Se(Ⅳ)) adsorption by MOF-Fe was investigated through the batch adsorption experiments that were conducted under different conditions. Results showed that in the system without Pi (Pi/Se=0) the isothermal adsorption data for Se(Ⅳ) by MOF-Fe could be well fitted by both Langmuir and Freundlich models (R²=0.9855~0.9863). As for the system with a molar ratio of Pi/Se(Ⅳ)=1 (Pi/Se=1), Freundlich model fitted the adsorption data better than Langmuir model, and the determination coefficients (R²) of the two models were 0.9746 and 0.9374, respectively. Compared with the Pi/Se=0 system, the maximum adsorption capacity of Se(IV) by MOF-Fe in the Pi/Se=1 system decreased by 68%, while the adsorption affinity and adsorption heterogeneity enhanced significantly. In the two systems of Pi/Se=0 and 1, the equilibrium times of Se(IV) adsorption by MOF-Fe were 160 min and 40 min, respectively. The pseudo-second-order model was very suitable to describe the dynamic process of Se(IV) adsorption by MOF-Fe in the two systems, and film diffusion and intraparticle diffusion were the main rate control factors of the adsorption reactions. In the two systems, the amount of Se(IV) adsorbed on MOF-Fe decreased with increasing the temperature, and the adsorption process was spontaneous and the disorder after adsorption increased. Compared with the Pi/Se=0 system, the adsorption of Se(IV) by MOF-Fe in the Pi/Se=1 system was more sensitive to the temperature, indicating that the competitive adsorption of Se(IV) by Pi increased with increasing the temperature. In the Pi/Se=1 system, the adsorption free energy of Se(IV) by MOF-Fe increased slightly, while the enthalpy and entropy reduced greatly, indicating that the coexistence of Pi increased the chemical adsorption of Se(IV) by MOF-Fe. Increasing the pH from 4.0 to 8.0, the adsorption of Se(IV) by MOF-Fe in the Pi/Se=0 and 1 systems decreased by 7% and 37%, respectively. When the initial concentration of Pi was increased, the adsorption amount of Se(IV) by MOF-Fe was exponentially reduced, and then stabilized at about 30% of the maximum adsorption amount. This showed that about 70% of the maximum adsorption amount of could be attributed to the reversible for the Se(IV) adsorption by MOF-Fe. Therefore, the adsorption of Se(IV) by MOF-Fe in the Pi/Se=1 system might include reversible and irreversible reactions, and the reversible reaction was significantly reduced due to the competitive effect of Pi, while the irreversible adsorption was hardly affected by the coexistence of Pi.

• Key words：MOF-Fe  selenite  phosphate  coexistence  competitive adsorption

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