Iron(II) sulfate crystals assisted mechanochemical modification of microscale zero-valent aluminum (mZVAl) for oxidative degradation of phenol in water.

Microscale zero-valent aluminum (mZVAl) is prone to surface passivation due to formation of the surface Al-(hydr)oxide layer, resulting in short reactive life. To overcome this critical drawback, we developed a mechanochemical ball milling approach to modify and activate commercially available mZVAl assisted by the fragile FeSO·7HO crystals. SEM-EDS and XPS analyses indicated that the particle surface of the mechanochemically modified mZVAl (Fe-mZVAl) was not only fractured with newly formed fresh reactive surfaces, but also attached with a rough layer of Fe-oxides that were uniformly distributed on mZVAl. While pristine mZVAl failed to degrade any phenol, Fe-mZVAl was able to rapidly degrade 88.8% within 90 min (initial phenol = 20 mg/L, pH = 2.50, dosage = 3 g/L) under normal oxic conditions, with a pseudo first-order rate constant of 0.040 min and about 70.0% of phenol mineralized in 8 h. Moreover, Fe-mZVAl also showed prolonged reactive life, and no significant reactivity drop was evident after six cycles of consecutive runs for phenol degradation. The much enhanced reactivity and reactive longevity of Fe-mZVAl are attributed to the critical roles of the surface Fe-oxides, including 1) protecting the newly exposed reactive Al from being oxidized by side reactions, 2) serving as an electron mediator facilitating the electron transfer from the core Al reservoir to the exterior surface, and 3) acting as an Fe source and a heterogeneous catalyst to enable the Fenton (-like) reactions. This study provides a novel and practical approach for preparing Fe-oxides modified mZVAl with enhanced and long-lasting reactivity.