Graduation Semester and Year

2016

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Civil Engineering

Department

Civil Engineering

First Advisor

hyeok Choi

Abstract

Manipulation of physical and chemical properties of matter with nanoscale precision will enhance our ability for fabrication of material with intended characteristics for environmental applications. In this study we presented two main frameworks for addressing non-selectivity issue in TiO2 photocatalysts, which is believed to be a major drawback in full-scale application of this technology. First, a purely physical approach for enhancing selectivity of nanostructured TiO2 photocatalysts toward water target contaminants have been achieved via tailor-designing meso-porous structure of TiO2. This simple, yet effective method is mainly based on size-exclusion as a mean toward preferential decomposition. It was hypothesized controlled mesoporous structure of TiO2 is capable of providing reaction sites for target contaminants while suppressing the access of large-size competing chemicals. Size-sensitivity of this method was evaluated by changing the size range of target contaminants from 1nm (Ibuprofen) to 1.7 nm (Methylene Blue) to 3nm (Microcystin-LR) combined with Humic Acid (HA) as model NOM. In agreement with proposed hypothesize; along with decrease in molecular size of target contaminants, better selectivity was accomplished. Changing the size of HA species proved to affect the selectivity in both porous and non-porous TiO2 particles. Largest size fraction of HA showed the highest selectivity enhancement using porous TiO2 implying the exclusion of competing HA based on physical separation. In agreement with proposed adsorption model, the role of inter-porous structure proved to be more significant in cases with more limitation in surface area i.e. lower catalyst to target contaminants concentration. The role of medium pH as a major contributor to TiO2 surface charge was evaluated in latter part of this study. It was observed, the effect of pH-induced surface charge was significant in terms of adsorption as well as decomposition of ionic organic species. The adsorption behavior shows clear pattern in accordance with ionization state of target contaminant as well as TiO2 surface charge. This proved to be especially efficient in combination with proposed size-exclusion, resulting in considerable recovery in selectivity. From a technical point of view, this study provides basis for designing the physiochemical properties of photocatalysts as well as the reaction conditions for enhanced selective decomposition of target contaminants.

Keywords

Mesoporous TiO2, Selective photocatalysis

Disciplines

Civil and Environmental Engineering | Civil Engineering | Engineering

Comments

Degree granted by The University of Texas at Arlington

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