부산대학교 도서관

Recognized by researchers as a promising treatment tool, photocatalysis has been used in combination with other treatment technologies in recent years, with the aim to enhance the mineralization of recalcitrant organic pollutants. However, there remains a substantial gap in our understanding of the band structure and radiocatalytic properties of photocatalysts within radiation treatment systems using high energy sources. This research aims to conduct a foundational investigation into the band structure, electrical, radiochemical, and radiocatalytic properties of photocatalysts suitable for a radiation treatment system for mineralizaiton of recalcitrant organic chemicals such as sulfamethoxazole.Despite the promising aspects of photocatalysis, its practical application often confronts limitations due to several technical issues related to the energy band gap of photocatalysts, particularly in systems using sunlight and UV. Some photocatalysts with large energy band gap have been successfully used in the radiocatalytic systems using gamma radiation and electron beam. However, there has been little systematic studies for band structure and electrical properties of an appropriate radiocatalyst in the radiation treatment. Kinetic studies were conducted to evaluate the properties (conduction band, valence band, energy band gap, electron mobility, and stability) of catalysts suitable for the radiocatalytic system using high energy sources and the radiocatalytic oxidation performance for sulfamethoxazole (SMX). The lower the CB potential and/or the higher the VB potential was, the higher the oxidation performance of a catalyst was. Unlike the photocatalytic process (activating the catalysts with energy band gaps lower than 6.2 eV), the radiation system using a gamma ray could activate the catalyst with a comparatively large energy band gap (< 1,240 keV). TOC removal efficiency for SMX (30 mg/L) with Al2O3 (2 g/L) as a radiocatalyst was enhanced up to 83.9% at an absorbed dose of 5 kGy, compared to the control (radiation treatment without catalysts) showing 6.6% TOC removal efficiency at the same condition. The stabilities of metal oxide catalysts were much higher (low self-degradation of 0.0006−0.01% at 50 kGy) than those (0.07−0.44% at 50 kGy) of metal sulfide catalysts. Since S2− is less electronegative than O2−, the VB holes of metal sulfide catalyst are more prone to self-degradation. The radiation technology has a wide range of selection for catalysts, and can be an effective alternative-treatment system for the mineralization of recalcitrant organic chemicals.This study aimed to investigate the adsorption effects of electron scavengers (H2O2 and S2O82−) on the oxidation performance for the mineralization of SMX in the radiation treatment using catalysts (Al2O3, TiO2). Hydrogen peroxide (H2O2) as an electron scavenger showed weak adsorption onto the catalysts (0.012 mmol/g-Al2O3 and 0.004 mmol/g-TiO2, respectively), leading to an increase in the TOC removal efficiency of SMX by 12.3% with Al2O3 and 8.0% with TiO2. However, the high S2O82− adsorption onto Al2O3 (0.266 mmol/g) showed a decrease in the TOC removal efficiency of SMX from 76.2% to 30.2%. Al2O3 used in the radiocatalytic treatment without any electron scavengers promoted a high direct decomposition of SMX through high adsorption of SMX onto the catalyst compared to TiO2. However, competitive adsorption on Al2O3 was observed between SMX and S2O82− in the radiocatalytic system using an electron scavenger, which reduced the oxidative catalytic performance due to significant S2O82− adsorption onto the surface of Al2O3. In contrast, TiO2 with low adsorption properties showed low SMX and electron scavenger adsorption compared to Al2O3, which promotes indirect decomposition as a dominant reaction.Al2O3 balls were used as catalysts in radiocatalytic systems to overcome the disadvantages of photocatalyst powders (e.g., separation and recovery of photocatalyst powders). The 1-mm Al2O3 ball size was the most effective, with 82.8% of the TOC removal of SMX at an absorbed dose of 30 kGy compared to other sized Al2O3 balls used. Using H2O2 enhanced the oxidation performance of the Al2O3 balls but was less economically effective than not using it. In addition, organic matter was found to inhibit the oxidation performance of Al2O3 balls more than inorganic ions. The TOC removal efficiency of Al2O3 balls was reduced to 24.5% after 7 cycles without water cleaning. However, when the Al2O3 balls were periodically cleaned, stable wastewater degradation was achieved after 7 cycles, with an average TOC removal efficiency of 56.7%. While further research may be necessary to optimize the performance and cost-effectiveness of a radiation catalyst system using Al2O3 balls, the results suggest it has potential as an alternative treatment system for TOC removal in wastewater.