Date of Award

May 2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Engineering

First Advisor

Chris Yuan

Committee Members

Yin Wang, Junhong Chen, Deyang Qu, Benjamin Church

Keywords

Lithium ion battery, nanomaterial, titanium oxide, water treatment, zirconium oxide

Abstract

Clean water and energy shortage problems are pressing issues human facing today, as they not only cause many problems including public health and environmental deteriorations, but also threaten sustainable development of human society. It is urgent and critical to address and solve these problems.

Among various technologies, photocatalysis and adsorption applications in water and wastewater catch a lot of attention in recent years, for their low costs and for no requirement for chemical additives or thermal inputs. Photodegradation of contaminants by nanomaterials as catalysts is an important method in water and wastewater treatment. The adsorption is mainly through complexation between dissolved metals and the oxygen in metal oxides. Nano-adsorbents offer significant improvement with extremely high specific surface area and associated sorption sites, short intraparticle diffusion distance, tunable pore size and surface chemistry. Metal oxides such as iron oxide, titanium oxide, aluminum oxide and zirconium oxide are effective, low cost adsorbents for heavy metals and radionuclides.

Same as the situation of clean water supply, energy shortage is another urgent problem. As energy demand and consumption of conventional fossil fuel increase constantly, the resulting energy crisis and environmental problems caused by combustion of fossil fuel drive us to look for more sustainable energy sources. Renewable energy resources appear to be an effective and promising solution. To overcome the variability for better renewable energy utilization, suitable energy storage devices are required.

Nanotechnology and nanomaterials are actively pursued to both improve existing technologies and develop new technology. TiO2 nanomaterials have been intensively investigated in various applications, as photoelectrode, catalyst, sensor, energy storage. TiO2 nanomaterials possess fascinating properties such as biological and chemical inertness, photostability, low cost, nontoxicity and superior oxidization ability. However, the wide electronic band gap and fast electron recombination rate limit the photocatalytic application and energy conversion efficiency of TiO2 nanomaterials. Though TiO2 can retain capacity at fast charge/discharge rates, and it is also electrochemical stable in common electrolytes and lack of harmful solid-electrolyte interfacial layer, the capacity of TiO2 is relatively low. Zirconium oxide has valuable chemical and physical properties, including high melting point, mechanical and thermal resistance, low electrical conductivity, biocompatibility, chemical inertness (resistant to oxidant agent and acids/bases, non-toxic, and not dissolvable in water) is a widely used inorganic material. ZrO2 is practical applied in fuel-cell technology, catalyst or catalyst support, oxygen sensor, thermal-barrier coatings and so on.

In this study, different modification strategies are carried out to improve the performance of TiO2 and ZrO2 in water treatment and energy storage applications. There are three objectives in this proposal. The first objective is to demonstrate high-efficiency photocatalysts using innovative hybrid nanostructures that consist of Pt nanoparticles and rGO co-modified three-dimensionally ordered microporous (3DOM) TiO2. The excellent charge-separation property and high adsorption capacity of rGO increased the charge carrier lifetime and affinity to organic molecules. The introduction of Pt nanoparticles increased spectral response to visible light through surface plasmon resonance and suppressed charge recombination. This study entails the synthesis and characterization of Pt/rGO-TiO2 for application in methyl orange photodegradation. The second objective of this study is to demonstrate high-performance Lithium-ion battery electrode using hybrid nanomaterials consist of Fe2O3 nanospindles assembled on 3DOM TiO2 with carbon coating. The carbon coated TiO2@Fe2O3 material showed good electrochemical performance with exhibits a large reversible capacity about 570 mAh g-1, which is about four times of the reversible capacity of 3DOM TiO2. In addition to the high reversible capacity, the obtained material also exhibits good cycle performance and superior rate capacity. This rationally designed composite benefits from both good stability of TiO2, high capacity of Fe2O3, and good electron conductivity of carbon. The third objective is to study zirconium modified clays as absorbents of phosphate from aqueous solution. Comparing three clays, zirconium modified MT (2:1), VT (2:1) and KT (1:1) exhibit different structure and surface properties, and thus performance differently toward phosphate adsorption. The adsorption kinetics data of phosphate on zirconium modified clays could be well described by the pseudo-second-order model, indicating that the adsorption was through chemisorption. The experimental equilibrium data of phosphate adsorption on modified clays were fitted better by Langmuir isotherm model than the Freundlich, implying monolayer adsorption. The effect of water chemistry (pH, co-existing anions, ionic strength, DOC) was also studied. These low-cost, abundant and effective are easily synthesized and have potential for practical wastewater treatment.

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