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Degradation of Polycyclic Aromatic Hydrocarbons (PAHs) in Water and Sediments by Field Effect TiO2 Catalysis
UV/titanium dioxide (TiO2) photocatalysis has emerged as a process to degrade various organic contaminants via the formation of OH• radicals. Despite the proven ability to degrade virtually any organic substrate, the drawbacks of UV/TiO2 systems, high energy consumption rates and low energy efficiency, make them unfeasible. For a given quantity of electrical power supplied to the system, there is a loss due to electrical inefficiency, which results from the emission of undesired wavelengths across the spectrum. Of the energy emitted in the useful band of the spectrum, only 1–2% of the emitted photons are absorbed by the catalyst to form electron hole pairs. Another weakness of UV/TiO2 systems is their reliance upon a direct, unobstructed path between the UV source and the catalyst surface, which eliminates the possibility of treating a turbid liquid or sediment that can absorb UV radiation. This hindrance also limits the mass transfer area to the surface, which can be irradiated by the UV source; thus, scientists cannot use packed beds or an extrinsic catalyst with a large surface area.
In the UV/TiO2 process, the primary role of the UV radiation is to generate the electron hole pair on or close to the TiO2 catalyst surface. If the electrons and holes are supplied from an external source, the UV use can be avoided– leading to much higher energy efficiencies. This would permit both the use of packing materials that increase the external geometric surface area, and the treatment of turbid liquids. Therefore, an electrocatalytic TiO2 system could be a promising alternative for destroying Polycyclic Aromatic Hydrocarbons (PAHs) in water and sediments.
Hypothesis
By applying electrical potential, electron hole pairs can be generated at the surface of the positive electrode of an electrochemical reactor. TiO2 coating at the anode surface will act as catalyst for generating hydroxyl radicals that form holes produced due to electrical bias. These radicals are highly reactive and attack the organic substrate at or close to the catalyst's surface.Objectives
We aim to develop an electrocatalytic process, and evaluate the efficiency of its destruction of PAHs in both clean water and artificially-spiked kaolin soil. Kaolin soil is selected for initial investigation of electrochemical degradation of PAHs in sediment. Sediment generally contains around 50% clay materials. Kaolin is selected as a surrogate soil to provide a clean matrix for the degradation studies because it contains 46% clay.Approach
For the proof of concept, we will investigate the destruction of naphthalene in distilled water containing an electrolyte. Subsequent experiments will evaluate the destruction of this PAH in artificially-spiked kaolin soil. If successful, we will then examine phenanthrene and pyrene.PAH oxidation using parallel plate electrodes will be conducted in a closed, electrochemical reactor system, which consists of a plate-type graphite anode and a plate-type stainless steel cathode in an undivided glass cell. The PAH-bearing electrolytic solution will circulate through the reactor, where hydroxyl radicals can oxidize PAHs. The anode of the reactor will be coated with titania (TiO2) fabricated using the sol-gel method based on titanium tetraisopropoxide (TTIP, Aldrich), isopropanol (Fisher Scientific), diethanolamine (DEA), and water. In all experiments, a 0.1 M potassium nitrate (KNO3) solution will be used as the electrolyte for increasing the conductivity of the aqueous system.
PAH degradation by the electrocatalytic reaction process will be evaluated as a balance of the PAHs system total. By monitoring the amounts of PAHs in their residing phases, scientists can determine system efficiency and degradation.
Contact: Souhail Al-Abed (EIMS#135747)