Two different types of nanoscale zero-valent iron (nZVI) were synthesized according to the same standard procedure: reduction of dissolved Fe(II) with sodium borohydride – one starting from a commercial iron salt having pro analysi (p.a.) purity, and another from microscale iron with an extraordinary degree of purity, derived from the decomposition of iron pentacarbonyl. The ZVI samples exhibited similar hydrodechlorination activities towards hexachlorobenzene as an example for higher chlorinated aromatics and carbon tetrachloride as an aliphatic model substance. However, only the sample derived from the iron salt (p.a.) was able to dechlorinate monochlorobenzene (MCB) at a measurable rate whereas the nZVI derived from the very pure precursor (nZVI_pure) did not show this ability. Closer inspection lead us to the finding that the observed activity could be attributed to a Ni content as small as 0.005 wt.-% of the former nZVI sample which was named nZVI_impure accordingly. It was demonstrated that such a small amount of Ni develops its catalytic activity for the hydrodechlorination of MCB only under acidic conditions. Although acidic conditions might not be common for studies with ZVI, higher Ni contents (e.g. of reagent grade iron sources) could have an influence under ambient conditions.

两种不同类型的纳米尺度零价铁（的nZVI）根据相同的标准方法合成：还原溶解的Fe（II）的硼氢化钠-一个从具有商业铁盐开始亲analysi（PA）的纯度，和另一由五羰基铁分解产生的具有极高纯度的微型铁。ZVI样品对六氯苯具有类似的加氢脱氯活性，例如，高级氯代芳烃和四氯化碳为脂族模型物质。但是，只有衍生自铁盐（pa）的样品才能以可测量的速率将一氯苯（MCB）脱氯，而衍生自非常纯前体（nZVI）的nZVI_纯）没有显示此功能。更仔细的检查使我们得出以下发现：观察到的活性可能归因于前nZVI样品的0.005 wt .-％的Ni含量，后者被相应地称为nZVI_不纯。证明了如此少量的Ni仅在酸性条件下才发展出其对MCB加氢脱氯的催化活性。尽管酸性条件对于ZVI研究可能并不常见，但较高的Ni含量（例如试剂级铁源）可能会在环境条件下产生影响。