Thanh-Dong Pham

Feasibility of Silver Doped TiO2/Glass Fiber Photocatalyst under Visible Irradiation as an Indoor Air Germicide

This study investigated the feasibility of using Ag-TiO2 photocatalyst supported on glass fiber (Ag-TiO2/GF) prepared by a sol-gel method as an indoor air germicide. An experimental model was designed to investigate the bacterial disinfection efficiency of Staphylococcus (Staph), the most popular bacterium in hospitals in Korea, by the Ag-TiO2/GF photocatalyst. The silver content in Ag/TiO2 was altered from 1 to 10% to investigate the optimal ratio of Ag doped on TiO2/glass fiber (TiO2/GF) for photocatalytic disinfection of Staph. This study confirmed that Ag in Ag-TiO2/GF could work as an electron sink or donor to increase photocatalytic activity and promote the charge separation of electron-hole pairs generated from TiO2 after photon absorption. Ag also acts as an intermediate agent for the transfer of photo-generated electrons from the valence band of TiO2 to an acceptor (O2 gas) to promote photo-oxidation processes. The photocatalytic disinfection activity of Ag-TiO2/GF under visible light increased with the increase in silver content up to 7.5% and then slightly decreased with further increasing silver content. The highest disinfection efficiency and disinfection capacity of Staph using 7.5% Ag-TiO2/GF were 75.23% and 20 (CFU∙s−1∙cm−2) respectively. The medium level of humidity of 60% ± 5% showed better photocatalytic disinfection than the lower (40% ± 5%) or higher (80% ± 5%) levels.

Effects of Ag doping on the photocatalytic disinfection of E. coli in bioaerosol by Ag–TiO2/GF under visible light

Ag doped TiO2/glass fibers (Ag-TiO2/GF) were prepared and used for photocatalytic disinfection of Escherichia coli (E. coli) in an indoor air environment. The prepared photocatalysts were characterized using scanning electron microscope (SEM) for morphology, X-ray diffraction (XRD) for microstructure, UV-Visible diffuse reflectance spectra (DRS) for optical properties and X-ray photoelectron spectroscopy (XPS) to determine elemental state. The optimized weight fraction of TiO2 in the TiO2/glass fiber (TiO2/GF) was 3%. The silver content in Ag/TiO2 was altered from 1% to 10% to investigate the optimal ratio of Ag doped on the TiO2/GF for the photocatalytic disinfection of E. coli. Doped Ag enhanced the electron-hole separation as well as charge transfer efficiency between the valance band and the conduction band of TiO2. The generated electron-hole pairs reacted with water and molecular oxygen to form strong oxidative radicals, which participated in the oxidation of organic components of E. coli, resulting in bacterial death. The photocatalytic disinfection activity under visible light increased with the increase in silver content up to 7.5% and then decreased slightly with further increasing Ag content. Among the three humidity conditions used in this study (40±5%, 60±5%, 80±5%), the highest disinfection ratio of E. coli by the photocatalytic system was observed in the intermediate humidity level followed by the high humidity level. Using the 7.5% Ag-TiO2/GF and the intermediate level of humidity (60±5%), the highest disinfection ratio and disinfection capacity of E. coli were 93.53% and 26 (CFU/s cm(2)), respectively.

Novel adsorption and photocatalytic oxidation for removal of gaseous toluene by V-doped TiO2/PU under visible light

In this study, V was used as a dopant to defect into the TiO2 lattice, leading to formation of Ti(3+) and V(4+) in the lattice. The presence of Ti(3+) and V(4+) introduced into the TiO2 lattice increased the electron-hole pair generation capacity and electron-hole pair separation efficiency of the TiO2, leading to enhancement of the photocatalytic activity of the photocatalyst. Porous polyurethane (PU) was used to immobilize the V-doped TiO2 by creating chemical bonds. The use of porous substrate contributed to the increased adsorption ability of the enhanced photocatalyst, as well as expanded its application for the removal of toluene from aerosols. Under dark conditions, the V-TiO2/PU only exhibited adsorption ability for toluene treatment in aerosol. Under visible light conditions, the V-TiO2/PU exhibited high photocatalytic oxidation ability for the removal of toluene in aerosol. The photocatalytic oxidation ability was found to depend on the V to TiO2 ratio. The optimal V content in V/TiO2 for enhancing the photocatalytic activity of TiO2 was determined to be 6 wt%. Even under visible light irradiation, the 6% V-TiO2/PU sample could photocatalytically remove 80% of the toluene in 200-ppmV inlet gas, while 89.3% of the removed amount was mineralized into CO2 and H2O.

Novel integrated approach of adsorption and photo-oxidation using Ag–TiO2/PU for bioaerosol removal under visible light

Abstract We investigated a novel approach by synthesizing an integrated material, which could act as both adsorbent and photocatalytic material, for bioaerosol purification under visible light conditions. Agwas used as a dopant agent to enhance photocatalytic activity of TiO2, leading to high photocatalytic activity of the doped TiO2 even under visible light. Under visible light, the doped TiO2 photocatalyst could produce oxy radicals, oxidative agents, that participate in oxidation reactions to decompose important organic components of bacteria, leading to death or removal of bacteria from an aerosol. Adsorption property was integrated into the enhanced TiO2 photocatalyst by using polyurethane (PU), a honeycomb structure material, as a substrate for coating process of the doped TiO2. Three materials including pristine PU, TiO2 coating on PU (TiO2/PU), and Ag-doped TiO2 coating on PU (Ag–TiO2/PU) were used to remove Escherichia coli in an aerosol under visible light. Under dark conditions, the removal capacities of E. coli in the aerosol by PU, TiO2/PU, and Ag–TiO2/PU were 1.2×105, 2.7×105, and 6.2×105 (CFU/cm3), respectively. Under visible light irradiation, the removal capacities of E. coli in an aerosol by PU, TiO2/PU, and Ag–TiO2/PU were 1.2×105, 2.7×105, and 1.8×106 (CFU/cm3), respectively. The improvement of the removal capacity by TiO2/PU and Ag–TiO2/PU, versus PU, is due to adsorption alone and the combination of adsorption plus photocatalytic activity, respectively.

Advanced removal of toluene in aerosol by adsorption and photocatalytic degradation of silver-doped TiO2/PU under visible light irradiation

We synthesized a novel Ag–TiO2/PU material for the effective removal of gaseous toluene by both adsorption and photocatalytic degradation. The Ag particles, which were distributed on the TiO2 surface, and the Ag dopants, which were incorporated into the TiO2 lattice, increased the electron–hole pair separation efficiency of TiO2. Therefore, Ag–TiO2/PU exhibited high photocatalytic degradation of toluene even under visible light. Porous polyurethane (PU) was used to immobilize the enhanced TiO2, to increase the adsorption capacity of the photocatalyst. The synthesized Ag–TiO2/PU removed gaseous toluene even under dark conditions via adsorption. The removal of gaseous toluene by Ag–TiO2/PU under visible light conditions was due to the combination of both adsorption and photocatalytic degradation. The oxygen content in the gas stream insignificantly affected the toluene adsorption by the Ag–TiO2/PU. However, the photocatalytic degradation of toluene by Ag–TiO2/PU increased with increasing oxygen content and stabilized when the oxygen content exceeded 15%. These results suggest that ambient air can be used economically as an oxygen source for the photocatalytic degradation of gaseous toluene by Ag–TiO2/PU under visible light conditions. Under visible light irradiation, 6% Ag–TiO2/PU, which was the Ag/TiO2 ratio that optimized the photocatalytic degradation activity of TiO2, removed 85.2% of the toluene in 100 ppm inlet gas, of which 90.3% was mineralized into CO2 and H2O.

Advanced removal of C. famata in bioaerosols by simultaneous adsorption and photocatalytic oxidation of Cu-doped TiO2/PU under visible irradiation

Abstract Polyurethane (PU), a honeycomb structure material, was used as a substrate onto which TiO2 and Cu–TiO2 were deposited in order to integrate the adsorption property to the photocatalysts. TiO2 deposited on PU (TiO2/PU) and Cu-doped TiO2 deposited on PU (Cu–TiO2/PU) were synthesized and applied to the removal of Candida famata (C. famata), a frequently encountered airborne yeast. The removal capacities of C. famata by PU, TiO2/PU and Cu–TiO2/PU were 1.5×105, 3.2×105 and 6.9×105 (CFU/cm3) under dark condition and 1.5×105, 3.3×105 and 1.8×106 (CFU/cm3) under visible light irradiation, respectively. PU and TiO2/PU seemed to exhibit only an adsorption ability for removing C. famata in aerosols under both dark and visible light. The C. famata removal capacity of Cu–TiO2/PU under visible light was increased 2.6-fold compared to that under dark condition. This significant increase was attributed to the Cu dopant, which enhanced the electron–hole separation efficiency and capacity of TiO2, resulting in the high photocatalytic activity of Cu–TiO2/PU under visible light.