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Selenium reduction on Ni-Fe bimetallic nanoparticles: effect of process variables on reaction rates

机译：镍铁双金属纳米颗粒上的硒还原：工艺变量对反应速率的影响

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The use of bimetallic nanoparticles (BNPs) for contaminant reduction has gained prominence in recent years. In this work, the effect of initial selenium concentration, BNP loading, dissolved oxygen and pH on selenium reduction using Ni-Fe BNPs was investigated in batch kinetic and equilibrium studies. Equilibrium studies revealed that maximum selenium uptake was obtained at near neutral pH. Reaction kinetics of Se(VI) and Se(IV) reduction on Ni-Fe BNPs was best described Langmuir-Hinshelwood kinetics, with first order at low Se concentrations and zero order at high Se concentrations. For both selenium species, complete removal was obtained within 1 h of contact time. Reaction rates for Se(VI) were higher than that of Se(IV), indicating a two-step reduction process. With increase in Ni-Fe loading (i.e., increase in number of active surface sites), reaction rates also increased linearly, suggestive of an adsorption-controlled rate-limiting step. Deviation from linearity was observed due to the deactivation of the Ni-Fe catalysts. The presence of dissolved oxygen did not significantly affect Se reduction rates. Reduction of selenate, Se(VI), and selenite, Se(IV), on Ni-Fe BNPs occurred primarily due to: (1) adsorption of Se species on the active surface sites; (2) chemical reduction reactions on the surface and (3) sorption of the reduced Se species.
机译：近年来，使用双金属纳米颗粒（BNP）来减少污染物的作用日益突出。在这项工作中，在分批动力学和平衡研究中，研究了初始硒浓度，BNP含量，溶解氧和pH对使用Ni-Fe BNP还原硒的影响。平衡研究表明，在接近中性pH值时可获得最大的硒吸收量。用Ni-Fe BNPs还原Se（VI）和Se（IV）的反应动力学最好地描述了Langmuir-Hinshelwood动力学，在低硒浓度下为一阶，在高硒浓度下为零阶。对于这两种硒，在接触时间内1小时即可完全去除。 Se（VI）的反应速率高于Se（IV），表明还原过程分为两步。随着Ni-Fe负载量的增加（即，活性表面位点数量的增加），反应速率也线性增加，表明吸附控制的限速步骤。由于镍铁催化剂的失活，观察到线性偏差。溶解氧的存在不会显着影响硒的还原速率。 Ni-Fe BNP上硒酸盐Se（VI）和亚硒酸盐Se（IV）的减少主要是由于：（1）硒在活性表面位点上的吸附； （2）表面上的化学还原反应和（3）还原硒物种的吸附。

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