• Journal of Korean Society for Atmospheric Environment
• /
• v.19 no.E4
• /
• pp.157-168
• /
• 2003

This study evaluated the technical feasibility of the application of titanium oxide (TiO$_2$) photocatalysis for the removal of VOCs in low ppb concentrations commonly associated with non -occupational indoor air quality issues. A series of experiments were conducted to evaluate four parameters (relative humidity (RH), hydraulic diameter (HD), photocatalytic oxidation (PCO) reactor material (RM), and inlet port size (IPS) of PCO reactor) for the PCO destruction efficiencies of the selected target VOCs. None of the target VOCs presented significant dependency on the RH, which is inconsistent with a few previous studies. However, it is noted that the three parameters (HD, RM and IPS) should be considered for better VOCs removal efficiencies for the application of TiO$_2$ photocatalytic technology for cleansing non -occupational indoor air. The PCO destruction of VOCs at concentrations associated with non-occupational indoor air quality issues can be up to nearly 100％. The amount of CO generated during PCO would be negligible in comparison to the indoor CO levels. These results can make the PCO reactor an important tool in the effort to improve non-occupational indoor air quality.

• Journal of Environmental Science International
• /
• v.13 no.9
• /
• pp.767-777
• /
• 2004

This study evaluated the technical feasibility of the application of $TiO_2$ photocatalysis for the removal of volatile hydrocarbons(VHC) at low ppb concentrations commonly associated with non-occupational indoor air quality issues. A series of experiments was conducted to evaluate five parameters (relative humidity (RH), hydraulic diameter (HD), feeding type (FT) of VHC, photocatalytic oxidation (PCO) reactor material (RM), and inlet port size (IPS) of PCO reactor) for the PCO destruction efficiencies of the selected target VHC. None of the target VHC presented significant dependence on the RH, which are inconsistent with a certain previous study that reported that under conditions of low humidity and a ppm toluene inlet level, there was a drop in the PCO efficiency with decreasing humidity. However, it is noted that the four parameters (HD, RM, FT and IPS) should be considered for better VHC removal efficiencies for the application of $TiO_2$ photocatalytic technology for cleansing non-occupational indoor air. The PCO destruction of VHC at concentrations associated with non-occupational indoor air quality issues can be up to nearly 100%. The amount of CO generated during PCO were a negligible addition to the indoor CO levels. These abilities can make the PCO reactor an important tool in the effort to improve non-occupational indoor air quality.

• Journal of Korean Society on Water Environment
• /
• v.21 no.1
• /
• pp.84-91
• /
• 2005

$TiO_2-catalyst$ suspensions work efficiently in Photocatalytic oxidation (PCO) for wastewater treatment. Nevertheless, once photocatalysis is completed, separation of the catalyst from solution becomes the main problem. The PCO of Cu(II)-EDTA was studied to determine the reusability of the titanium dioxide catalyst. Aqueous solutions of $10^{-4}M$ Cu(II)-EDTA were treated using illuminated $TiO_2$ particles at pH 6 in a circulating reactor. $TiO_2$ was reused in PCO system for treatment of Cu(II)-EDTA comparing two procedures: reuse of water and $TiO_2$ and reuse of the entire suspension after PCO of Cu(II)-EDTA. The results are as follows; (i) Photocatalytic efficiency worsens with successive runs when catalyst and water are reused without separation and filtration, whereas, when $TiO_2$ is separated from water, the reused $TiO_2$ is not deactivated. (ii) The $TiO_2$ mean recovery (%) with reused $TiO_2$ was 86.4%(1.73g/L). Although the mean initial degradation rate of Cu(II)-EDTA and Cu(II) was lower than that using fresh $TiO_2$, there was no significant change in the rate during the course of the three-trial experiment. It is suggested that Cu(II)-EDTA could be effectively treated using an recycling procedure of PCO and catalyst recovery. (iii) However, without $TiO_2$ separation, the loss of efficiency of the PCO in the use of water and $TiO_2$ due to Cu(II), DOC remained from previous degradation and Cu(II)-EDTA added to the same suspension was observed after 2 trials, and resulted in the inhibition of the Cu(II)-EDTA, Cu(II) and DOC destruction.

• Bulletin of the Korean Chemical Society
• /
• v.34 no.4
• /
• pp.1137-1144
• /
• 2013

$TiO_2$ composites with seven different carbon materials (activated carbons, graphite, carbon fibers, single-walled carbon nanotubes, multi-walled carbon nanotubes, graphene oxides, and reduced graphene oxides) that are virgin or treated with nitric acid are prepared through an evaporation method. The photocatalytic activities of the as-prepared samples are evaluated in terms of $H_2$ production from aqueous methanol solution (photo-catalytic reduction: PCR) and degradation of aqueous pollutants (phenol, methylene blue, and rhodamine B) (photocatalytic oxidation: PCO) under AM 1.5-light irradiation. Despite varying effects depending on the kinds of carbon materials and their surface treatment, composites typically show enhanced PCR activity with maximum 50 times higher $H_2$ production as compared to bare $TiO_2$. Conversely, the carbon-induced synergy effects on PCO activities are insignificant for all three substrates. Colorimetric quantification of hydroxyl radicals supports the absence of carbon effects. However, platinum deposition on the binary composites displays the enhanced effect on both PCR and PCO reactions. These differing effects of carbon materials on PCR and PCO reactions of $TiO_2$ are discussed in terms of physicochemical properties of carbon materials, coupling states of $TiO_2$/carbon composites, interfacial charge transfers. Various surface characterizations of composites (UV-Vis diffuse reflectance, SEM, FTIR, surface area, electrical conductivity, and photoluminescence) are performed to gain insight on their photocatalytic redox behaviors.

• Environmental Engineering Research
• /
• v.13 no.4
• /
• pp.171-176
• /
• 2008

Studies on visible-light-driven photocatalysis of air pollutants at indoor air quality (IAQ) levels have been limited. Current study investigated visible-light derived photocatalysis with N-doped and S-doped titanium dioxide ($TiO_2$) for the control of benzene at indoor levels. Two preparation processes were employed for each of the two types of photocatalyst: urea-Degussa P-25 $TiO_2$ and titania-colloid methods for the N-doped $TiO_2$; and titanium isopropoxid- and tetraisopropoxide-thiourea methods for the S-doped $TiO_2$. Furthermore, two coating methods (EDTA- and acetylacetone-dissolving methods) were tested for both the N-doped and S-doped $TiO_2$. The two coating methods exhibited different photocatalytic degradation efficiency for the N-doped photocatalysts, whereas they did not exhibit any difference for the S-doped photocatalysts. In addition, the two doping processes showed different photocatalytic degradation efficiency for both the S-doped and N-doped photocatalysts. For both the N-doped and S-doped $TiO_2$, the photocatalytic oxidation (PCO) efficiency increased as the hydraulic diameter (HD) decreased. The degradation efficiency determined via a PCO system with visible-light induced $TiO_2$ was lower than that with UV-light induced unmodified $TiO_2$, which was obtained from previous studies. Nevertheless, it is noteworthy that for the photocatalytic annular reactor with the HD of 0.5 cm, PCO efficiency increased up to 52% for the N-doped $TiO_2$ and 60% for the S-doped $TiO_2$. Consequently, when combined with the advantage of visible light use over UV light use, it is suggested that with appropriate HD conditions, the visible-light-assisted photocatalytic systems can also become an important tool for improving IAQ.

• Journal of Environmental Health Sciences
• /
• v.30 no.2
• /
• pp.92-97
• /
• 2004

Three methods for VOCs emissions control in indoor air are reduction at the source, ventilation between indoor and outdoor, and removal. The best alternative should be to replace highly emitting sources with sources having low emissions, but the pertinent information on VOCs is not always available from manufactures. Other ways of improving indoor air quality are needed. It is to increase the outside fresh-air flow to dilute the pollutants, but this method would generally provide only a dilution effect without destruction in residence. An ideal alternative to existing technologies would be a chemical oxidation process able to treat large volumes of slightly contaminated air at normal temperature without additional oxidant such as ozone generator and ion generator. Photocatalytic oxidation(PCO) represents such a process. It is characterized by a surface reaction assisted by light radiation inducing the formation of superoxide, hydroperoxide anions, or hydroxyl radicals, which are powerful oxidants. In comparison with other VOCs removal methods, PCO offers several advantages. The purpose of this study was to explore the possibilities for photocatalytic purification of slightly contaminated indoor air by using visible light such as flurescent visible light(FVL). In this study, a PCO of relatively concentrated benzene using common FVL lamps was investigated as batch type and total volatile organic compounds(TVOCs) using a common FVL lamp and penetrated sun light over window. The results of this study shown the possibility of TiO$_2$ photocatalyst application in the area of indoor air quality control.

• Journal of Environmental Science International
• /
• v.17 no.11
• /
• pp.1195-1201
• /
• 2008

Enhancing with non-metallic elemental nitrogen(N) is one of several methods that have been proposed to modify the electronic properties of bulk titanium dioxide($TiO_2$), in order to make $TiO_2$ effective under visible-light irradiation. Accordingly, current study evaluated the feasibility of applying visible-light-induced $TiO_2$ enhanced with N element to cleanse aromatic compounds, focusing on xylene isomers at indoor air quality(IAQ) levels. The N-enhanced $TiO_2$ was prepared by applying two popular processes, and they were coated by applying two well-known methods. For three o-, m-, and p-xylene, the two coating methods exhibited different photocatalytic oxidation(PCO) efficiencies. Similarly, the two N-doping processes showed different PCO efficiencies. For all three stream flow rates(SFRs), the degradation efficiencies were similar between o-xylene and m,p-xylene. The degradation efficiencies of all target compounds increased as the SFR decreased. The degradation efficiencies determined via a PCO system with N-enhanced visible-light induced $TiO_2$ was somewhat lower than that with ultraviolet(UV)-light induced unmodified $TiO_2$, which was reported by previous studies. Nevertheless, it is noteworthy that PCO efficiencies increased up to 94% for o-xylene and 97% for the m,p-xylene under lower SFR(0.5 L $min^{-1}$). Consequently, it is suggested that with appropriate SFR conditions, the visible-light-assisted photocatalytic systems could also become important tools for improving IAQ.

• Proceedings of the Korea Air Pollution Research Association Conference
• /
• 1999.10a
• /
• pp.455-456
• /
• 1999

광촉매산화법(Photocatalytic Oxidation : PCO)은 VOCs(Volatile Organic Compounds)로 오염된 수질과 공기의 질을 개선하는데 있어 기존의 제어기술에서 확인되는 많은 문제점을 해결할 수 있어 최근에 많은 연구가 이루어지고 있는 신진기술이다. 현재 TiO$_2$를 촉매로 이용한 광산화장치의 대상물질로는 염소계 유기화합물중 지하수 오염의 주요인으로 취급되는 TCE가 대부분이다.(중략)

• Journal of Environmental Science International
• /
• v.16 no.7
• /
• pp.785-791
• /
• 2007

The current study evaluated the technical feasibility of the application of titanium dioxide ($TiO_{2}$) photo-catalytic air cleaners for the disinfection of bioaerosols present in indoor air. The evaluation included both laboratory and field tests and the tests of hydraulic diameter (HD) and lamp type (LT). Disinfection efficiency of photocatalytic oxidation (PCO) technique was estimated by survival ratio of bacteria or fungi calculated from the number of viable cells which form colonies on the nutrient agar plates. It was suggested that the reactor coating with $TiO_{2}$ did not enhance the adsorption of bioaerosols, and that the UV irradiation has certain extent of disinfection efficiency. The disinfection efficiency increased as HD decreased, most likely due to the decrease in the light intensity since the distance of the catalyst from the light source increased when increasing the HD. It was further suggested that the mass transfer effects were not as important as the light intensity effects on the PCO disinfection efficiency of bioaerosols. Germicidal lamp was superior to the black lamp for the disinfection of airborne bacteria and fungi, which is supported by the finding that the disinfection efficiencies were higher when the germicidal lamp was used compared to the black lamp in the laboratory test. These findings, combined with operational attributes such as a low pressure drop across the reactor and ambient temperature operation, can make the PCO reactor a possible tool in the effort to improve indoor bioaerosol levels.

• Journal of Korean Society of Environmental Engineers
• /
• v.28 no.3
• /
• pp.316-322
• /
• 2006

The current study evaluated the technical feasibility of the application of $TiO_2$ photocatalysis for the removal of nocotine which has well known as a representative material of environmental tobacco smoke(ETS). Four different preliminary experiments were performed for the evaluation of nicotine removal using photocatalyst-coated construction materials. The photocatalytic removal of nicotine was investigated for five parameters: dry condition of coating tiles, type of coating sol, number of coatings, relative humidity(RH), and input concentrations. Prior to performing the parameter tests, adsorption of nicotine onto the current experimental system was surveyed. All the variables tested in the present study exhibited to influence the photocatalytic decomposition of Nicotine. A dry condition of high temperature and short dry period presented higher photocatalytic oxidation(PCO) efficiency compared to that of low temperature and long dry period. ST-KO3 sol showed higher decomposition efficiency than E-T Sol. The PCO efficiency increased as the number of coating increased. High humidity and low input concentrations exhibited higher PCO efficiency. Consequently, it is noted that the five parameters tested in the present study should be considered for the application of photocatalyst-coated construction materials in cleaning nicotine in ETS.