The azo dye accounts for the major part of annual dye production. It was widely used in textile, paper and decoration applications. In general, about 15% of azo dye was released to the wastewater without treatment after consumption. They were stable in air and were hazardous to the nature. The most difficult and crucial step of azo dye treatment is the splitting of ‘-N=N-’ bond to two amino groups. Once that is done, the aromatic amine could be used to feed micro-organisms, which helps degrading the amine to harmless substances. Recently, the Fe-based amorphous powder was applied as reducing agent to cleave azo bond. The powder in glassy state was metastable and thus the activation energy of the reaction was lower than that if the crystalline counterpart was used. Moreover, the types and fractions of constituent atoms in the Fe-rich amorphous solid can vary in wide ranges so that the reactions mechanisms and kinetics can be fine-tuned.
The aim of this work is to design Fe-rich amorphous structures for fast reduction of the azo bond. The glassy alloy designed based on competitive atomic-cluster model was synthesized and characterized. The decolourization of model azo dye Orange G (OG) solution at room temperature was used for comparing the effectiveness of the zero-valent iron (ZVI) species in different Fe-based glassy alloys. The fresh color of OG aqueous solution makes it easy to monitor the concentration by UV-Vis spectrum. The previously reported Fe78B14Si8 sample, pure iron powder and the clusters of Fe11Y3 and Fe8B2 were selected to make a comparison. The Fe66.3B16.6Y17.1 amorphous structure designed in this work exhibited excellent effectiveness for OG decolourization compared with those of the other Fe-based alloys samples under the same testing conditions. We demonstrated the consumption of ZVI destabilized the local atomic arrangement of Fe66.3B16.6Y17.1 glassy alloy and resulted in phase separation of Fe on the sample surface. A catalytic effect was generated spontaneously during the Fe separation and contributed to the fast decolourization. This observation was in accordance with the result of kinetic study, and it was supported by the cyclic decolourization experiments.
In the second part of this work, the Fe66.3B16.6X17.1 (Zr, Nb) amorphous structures designed based on cluster line model were synthesized and compared with Fe66.3B16.6Y17.1 in the OG decolourization. The motivations to replace Y with Zr and Nb are the lower materials cost and potentially good decolourization ability. XRD and XPS were employed to characterize the structures and electronic structures of Fe66.3B16.6X17.1 (Y, Zr, Nb) samples, and compared with those reported for Fe78B14Si8. The results demonstrated that the high reactivity of Fe66.3B16.6Y17.1 was related to the complex clusters’ structures, which result in the weaker interactions between constituent atoms. The relative intensity of mj = -3/2 peak of Fe2p3/2 XPS spectra was found to have good predictability to the decolourization ability.
This work provided a new strategy to design multi-functional metallic materials and indicated their promising future in applications. It also proved that the local structure of the amorphous solid had significant influence on the properties. The correlations between the structure and properties of the samples investigated in this work were discussed in terms of the differences in structure and bonding of Fe-rich amorphous solid.