Title

Functional application of iron-based metallic glasses in catalysis technology: Design and mechanism

Date of Award

2017

Degree Type

Thesis

Degree Name

Doctor of Philosophy

School

School of Engineering

First Advisor

Associate Professor Laichang Zhang

Second Advisor

Professor Daryoush Habibi

Field of Research Code

0 9 0 9 1 2

Abstract

In this PhD study, two novel, multifunctional Fe-based metallic glasses (MGs) with the nominal components of Fe78Si9B13 (also known as 1K101) and Fe73.5Si13.5B9Cu1Nb3 (1K107) are manufactured by melt-spinning method to investigate the catalytic performance. The two produced glassy ribbons exhibit advanced catalytic capability when being employed as catalysts for the industrial dye pollutant treatment, presenting a great potential in achieving actual industrilization. Five dyes with different chemical bondings were treated as the targets for monitoring the catalytic efficiency, reusability and the corresponding mechanism.

In the aspect of dye degradation and mineralization efficiency, the individual and combined effects of the various reaction parameters are firstly investigated by employing an orthogonal matrix (L16(45)) experimental methodology. Nearly 100% color removal is achieved within 20 min under premium experimental control. The effects of catalyst dosage, dye concentration, peroxides concentration, light intensity and pH on dye degradation efficiency are fully discussed. The production of high redox radicals, such as hydroxyl radicals (•OH) and sulfate radicals (SO4•−), is investigated by quenching experiments. Total organic carbon (TOC) is employed for investigating the dye mineralization.

In the aspect of sustainability and reusability, the Fe78Si9B13 metallic glass exhibited a superior surface stability and reusability while activating persulfate as indicated by it being used for 30 times while maintaining an acceptable methylene blue (MB) degradation rate. The produced SiO2 layer on the ribbon surface expanded strongly from the fresh use to the 20th used, providing stable protection of the buried Fe. It is the first time to report that SO4•− with a high oxidative potential are successfully activated from persulfate by a Fe78Si9B13 metallic glass.

The catalytic mechanisms using Fe-based MGs as catalysts can be divided into three parts in this work: 1) electron transfer ability, 2) activation rate of peroxides, and 3) pre-adsorption behavirour. For the electron transter ability, the structural relaxation (α-relaxation) by annealing in an amorphous Fe78Si9B13 alloy is studied at the atomic scale to compare the effect of atomic packing structures in amorphous and crystalline catalysts on dye degradation efficiency. The volume fractions of the crystalline structures, such as α-Fe, Fe2Si and Fe2B, in the as-received and annealed MGs are fully characterized. It is found that the randomly atomic packing structure with weak atomic bonding in the as-received metallic glass has an efficient electron transfer capability, presenting advanced superiorities in the aspects of production rate of hydroxyl radicals (•OH), dye degradation rate (k) and essential degradation ability (KSA) for water treatment. The discovery of this critically important work unveils why using MGs as catalysts having higher reactivity than the crystalline materials, and more importantly, provides new research opportunities into the study of synthetic catalysts. For the activation rate of peroxides, Fe78Si9B13 and Fe73.5Si13.5B9Cu1Nb3 MGs are employed for testing the activation rate of •OH. The results revealed that production rate of hydroxyl radicals using these two glassy ribbons is 5 - 10 times faster than other Fe-based catalysts. The likely explanation is that, a) the short-range ordered and long-range disordered atomic structure (weak atomic bonding) in amorphous alloy would cause easier electron activation under UV-Vis light irradiation compared to the crystallized structure (metallic bonding in atoms), b) the enhancement of Fe2+ being in-situ converted from Fe3+ under UV-Vis light irradiation. For the dye pre-adsorption, the quantity of dye adsorption on Fe78Si9B13 and Fe73.5Si13.5B9Cu1Nb3 ribbons is 7.60 mg/g and 0.35 mg/g, respectively, leading to faster dye degradation by using Fe78Si9B13 compared to Fe73.5Si13.5B9Cu1Nb3 ribbons. The equilibrium adsorption data using Fe78Si9B13 ribbon is well fitted to Langmuir and Freundlich isotherms. The calculated qe from the 2nd kinetic model (7.36 mg/g) and qm from Langmuir equation (12.76 mg/g) are very close to the experimental data of 7.6 mg/g and 13.07 mg/g, respectively.

The results suggest that the designed Fe78Si9B13 and Fe73.5Si13.5B9Cu1Nb3 MGs present a superior catalytic performance making them more desirable than the commercial used crystalline Fe-based catalysts. Therefore, this research demonstrates that through proper elemental and atomic structure design it is possible to develop new catalysts with favourable catalytic performance better than the current employed commercial catalysts for the industrial water treatment application.

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