Synthesis And Azo Dye Degradation Properties Of Iron-based Amorphous Alloys

Due to their unique soft magnetic and corrosive resistant properties, iron-based amorphous alloys have attracted great attention since its discovery in 1970 s. Very recently, it is found that some iron-based amorphous alloys could be used as zero-valent iron to rapidly discolorate the azo dyes and exhibit promising application in wastewater treatment. However, for now, there are still many problems to be resolved, such as the kinetic process, internal mechanism, effects of composition and environmental virables. In this study, beginning with the Fe-B binary amorphous alloys, three kinds of iron-based amorphous alloys were studied to explore their kinetic processes, internal mechanisms and effects of composition and so on.Through the studies on the Fe-B binary amorphous alloys, it is found that Fe84B16 amorphous alloy ribbons could be more reactive than its crystalline counterparts and 300 mesh iron powders. Under the same neutral conditions, the surface normalized reaction rate constant of Fe 84B16 amorphous alloy ribbons in degrading Direct Blue 6 could be 1.8 and 89 times that of its crystalline counterparts and the 300 mesh iron powders, respectively. Through U V-vis and mass spectra, it is found that the degradation mechanism of Fe-B binary metallic glasses is the same as the crystalline zero-valent iron. Further analysis shows that the high degradation ability of Fe-B amorphous alloys is ascribed to the metastable amorphous structure and the addition of boron, which could enhance the reactivity and promote the formation of an incompact and easy to be detached oxide layer on the surface.The degradation studies with Fe-Si-B amorphous alloys show that Fe-Si-B possess superior degradation ability in treating azo dyes containing wastewater. Under the same conditions, the surface normalized reaction rate constants of commercial Fe-Si-B amorphous alloys in degrading Direct Blue 6, Orange II and Methly Orange could be 60, 1300 and 37000 times that of 300 mesh iron powders, respectively. Further analysis show that the internal mechanism of Fe-Si-B amorphous alloys in degrading azo dyes is the same as the Fe-B binary amorphous alloys. And the high degradation rate is also due to the amorphous structure and the addition of metalloids. Through mechanical crashing, the Fe-Si-B amorphous alloy powders were obtained and used to test its degradation ability. The results show that although the activation energy of powders is far higher than the original ribbons, the observed reaction rate constant of powders in degrading Direct Blue 6 is around 2- 10 times than that of the original ribbons. And the repeatability of the 300-500 mesh Fe-Si-B powders showed that after 5 cycles of degradation process, the reactivity of powders remains unchanged.Last, the experiments with a series of Finemet amorphous alloy ribbons showed that the surface normalized reaction rate constant of Finemet amorphous alloy ribbons in degrading Orange II is around 100 times that of 300 mesh iron powders, but far less than Fe-B and Fe-Si-B amorphous alloys. Further analysis showed that the addition of metallic elements would enhance the density of th e oxide layer formed on the surface which would inhibit the electron transfer during the reductive reaction. Thus the degradation mechanism of Finemet amorphous alloys is mainly the adsorption rather than reducvie reaction found before. Further studies with over heated ribbons found that the precipited crystallites would disrupt the dense oxide layer and enhance the degradation ability of Finemet amorphous alloys.