Adsorption-enhanced reductive degradation of methyl orange by Fe_73.3Co₁₀Si₄B₈P₄Cu_0.7 amorphous alloys

Cobalt alloying for Fe_83.3Si₄B₈P₄Cu_0.7 amorphous alloy can enhance the decolorization performances of azo dye wastewater. Co substitutions in amorphous Fe_83.3-xCo_xSi₄B₈P₄Cu_0.7 (x = 0, 10, 20 and 40 at.%) alloys play a positive role in improving the decolarization efficiencies of methyl orange azo dyes (MO). Amorphous Fe_73.3Co₁₀Si₄B₈P₄Cu_0.7 alloy has better abilities to break –N=N– bonds of MO than Fe_83.3Si₄B₈P₄Cu_0.7, Fe_63.3Co₂₀Si₄B₈P₄Cu_0.7 and Fe_43.3Co₄₀Si₄B₈P₄Cu_0.7 alloys, and is able to degrade MO to mainly form sulfanilic acid anions with trace amounts of intermediate products with higher complete degrees. The rate determining step of MO degradation is the surface adsorption on amorphous Fe_43.3Co₄₀Si₄B₈P₄Cu_0.7 alloy, and the intermediate degradation products with –N=N– bonds are dominantly formed with small amount of sulfanilic acid anions. The highest surface-area normalized rate constant (k_SA) of MO degraded by Fe_73.3Co₁₀Si₄B₈P₄Cu_0.7 ribbons is confirmed to be 0.69, 3 times higher than that of zero-valent Fe powders and Fe_83.3Si₄B₈P₄Cu_0.7 ribbons. The degradation pathways of MO by amorphous Fe_73.3Co₁₀Si₄B₈P₄Cu_0.7 alloy different from those by Fe_83.3Si₄B₈P₄Cu_0.7 and Fe_43.3Co₄₀Si₄B₈P₄Cu_0.7 alloys have been clarified on basis of the UV–Vis and HPLC-MS data. The experimental results manifest that the degradation performances are enhanced by Co substitutions due to the sharp decrease of reaction activation energies and the improvements of adsorption performances. The mechanism changes from reduction degradation to adsorption-determined degradation modes with increases of Co concentrations. MO degradations on amorphous Fe_73.3Co₁₀Si₄B₈P₄Cu_0.7 alloy are governed by adsorption-enhanced reductive degradation mechanism.