Adsorption-enhanced reductive degradation of methyl orange by Fe73.3Co10Si4B8P4Cu0.7 amorphous alloys

Abstract

Cobalt alloying for Fe83.3Si4B8P4Cu0.7 amorphous alloy can enhance the decolorization performances of azo dye wastewater. Co substitutions in amorphous Fe83.3-xCoxSi4B8P4Cu0.7 (x = 0, 10, 20 and 40 at.%) alloys play a positive role in improving the decolarization efficiencies of methyl orange azo dyes (MO). Amorphous Fe73.3Co10Si4B8P4Cu0.7 alloy has better abilities to break –N=N– bonds of MO than Fe83.3Si4B8P4Cu0.7, Fe63.3Co20Si4B8P4Cu0.7 and Fe43.3Co40Si4B8P4Cu0.7 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 Fe43.3Co40Si4B8P4Cu0.7 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 (kSA) of MO degraded by Fe73.3Co10Si4B8P4Cu0.7 ribbons is confirmed to be 0.69, 3 times higher than that of zero-valent Fe powders and Fe83.3Si4B8P4Cu0.7 ribbons. The degradation pathways of MO by amorphous Fe73.3Co10Si4B8P4Cu0.7 alloy different from those by Fe83.3Si4B8P4Cu0.7 and Fe43.3Co40Si4B8P4Cu0.7 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 Fe73.3Co10Si4B8P4Cu0.7 alloy are governed by adsorption-enhanced reductive degradation mechanism.