Fe⁰ has been found a good material for removing heavy metal from waste water due to high efficiency, low cost, facile operation. But its application has been impeded by its rapidly decreasing reduction rate with increasing treatment time owing to easily oxidization during reduction. This study found that a centi-sized commercial iron turning with a thin layer of amorphous iron oxides (AIO) possesses persistently high Cr⁶⁺ removal rate of 98% in the testing time (36 h). The tribocatalysis arising from the friction between the solution and above-said AIO could account for above-mentioned results. During the first tribocatalysis stage, the electrons of Fe⁰ in iron turning were stimulated to higher energy and more easily went through the interface Fe⁰/AIO, resulting in increasing Cr⁶⁺ reduction efficiency, and the reaction from the Fe⁰ inside AIO to Fe²⁺ and Fe³⁺. During the next tribocatalysis stage, Since there is weak bonding between Fe⁰ and FeO due to lattice mismatch, the surface AIO dropped from iron turning in case of friction. Thus, much more Fe⁰ was exposed to Cr⁶⁺ solution and much higher Cr⁶⁺ removal rate has been obtained. More importantly, the high Cr⁶⁺ removal rate can be persistently kept. It has also been found that iron with larger friction area favors in tribocatalysis than one with less friction area. All in all, this work has found that an effective way-tribocatalysis-to lift the possibility that Fe⁰ go through potential barrier to react with heavy metal ions, and to timely remove the covered materials on the surface of Fe⁰, and therefore resulting in persistently high Cr⁶⁺ removal rate. This work has also given a clear picture for tribocatalysis, facilitating people to understand the mechanism of tribocatalysis.

由于高效率，低成本，操作简便，已发现Fe ⁰是从废水中去除重金属的良好材料。但是，由于在还原过程中容易被氧化，还原速率随着处理时间的增加而迅速降低，从而阻碍了其应用。这项研究发现，在测试时间内（36小时），用无定形氧化铁（AIO）薄层加工的一厘米大小的商用铁车削具有98％的持久高Cr ⁶⁺去除率。由溶液和上述AIO之间的摩擦引起的摩擦催化可以解释上述结果。在第一个摩擦催化阶段，铁车削中的Fe ⁰电子被激发到更高的能量，并且更容易通过界面Fe⁰ / AIO，导致增加的Cr ⁶⁺还原效率，以及AIO内部的Fe ⁰与Fe ²⁺和Fe ^3+的反应。在下一个摩擦催化阶段，由于晶格失配，Fe ⁰和FeO之间的键合较弱，因此在摩擦情况下，表面AIO会因铁的车削而掉落。因此，更多的Fe ⁰暴露于Cr ⁶⁺溶液中，并且获得了更高的Cr ⁶⁺去除率。更重要的是，高Cr ⁶⁺去除率可以持久地保持。还已经发现，具有较大摩擦面积的铁比具有较小摩擦面积的铁更有利于摩擦催化。总而言之，这项工作发现了一种有效的摩擦催化方法，可以消除Fe ⁰穿过势垒与重金属离子发生反应的可能性，并及时清除Fe ⁰表面覆盖的材料，因此Cr ⁶⁺去除率一直很高。这项工作也为摩擦催化提供了清晰的画面，使人们了解了摩擦催化的机理。