Treatment of Volatile Organic Compound from Indoor Pollution Source Using Modified Photocatalyst with LED
Date Issued
2006
Date
2006
Author(s)
Lee, Chia-Hsiang
DOI
zh-TW
Abstract
This study investigated the surface modification of photocatalyst and photo-decomposition of volatile organic compounds (VOCs) from indoor pollution source. Formaldehyde, which has the highest concentration among VOCs in the indoor air pollutants, was taken as a model compound. The photocatalyst of Ag/TiO2 was made by the impregnation method. Ti-semiconductor photocatalyst was prepared by precitation method, and expected to change the energy band gap of visible-light-active photocatalyst making it suitable for the wavelengthes of visible light and near UV light.
Regarding the light sources, this study explored the feasibility of the application of the light emitting diode (LED) instead of the traditional light lamp to treat the indoor air pollutant of formaldehyde. The operation parameters, which affect the formaldhyde decomposition in photo-decomposition reaction, were examined. These parameters induded different light sources, photocatalysts and catalytic supports. The modified composed photocatalyst was coated on the glass plates or sticks uniformly. The catalytic effects enhancing the decomposition (ηD) and mineralization (ηM) efficiencies of formaldehyde were studied. Furthermore, the photocatalytic decomposition of formaldehyde at various initial concentrations was elucidated according to the Langmuir-Hinshelwood model.
The results showed that TiNH400 had the finest size of about 30-40 nm and the largest surface area among the modificated photocatalysts examined in this study. In opposition to Ag/TiO2, TiNH400 aggregated more easily to form larger particles with size up to hundreds of nm. The absorption spectra of the TiNH400 indicated a stronger absorption than those of other modificated photocatalysts. Also its absorption spectra were shifted to a lower energy region of about 400-440 nm, which revealed the ability of adsorption of the visible light and near UV light.
The photo-reaction with Ag/TiO2 had better ηD and ηM than those with TiO2 and with UV lamp alone (without catalyst). Under the initial concentration of 500 ppmv formaldehyde, the ηD of formaldehyde reached 82% at 1 h with 365 nm UV lamp (16 W) and 0.05 g Ag/TiO2 coated on glass plates. However, the ηD of formaldehyde became 80% at 1 h with 254 nm UV lamp (16 W) and 0.05 g Ag/TiO2 coated on glass plates. The lamp emitting 365 nm UV was better than that emitting 254 nm UV in this study. Applying the 383 nm UVLED light (Δλ = 18 nm) with 800 mW (20 mW of one LED and 40 totally) and 0.05 g Ag/TiO2 coated on glass plates gave 58% and 65% of ηD at 1 and 7 h, respectively. Using the glass sticks with 0.334 g catalyst instead of the glass plates with 0.05 g catalyst enhanced the ηD to 96% and 95% with 365 nm UV lamp of 16 W and 383 nm UVLED of 800 mW (20 mW of one LED and 40 totally) at 7 h, respectively. The ηM also increased apparently for the case using the glass sticks coated with catalyst. Regarding the humidity effects, the results showed that the ηD increased slightly as relative humidity increased. Using UVLED light as light source in this study can enhance the safety and energy usage efficiency for the application of photocatalytic technology. Thus, this study showed the feasible and potential use of UVLED.
The results also showed that the finally ηD of formaldehyde increased with the higher light energy and shorter wavelength of light sources. Therefore, the ηD in the UV light illumination system was better than that in the visible light illumination system. However, the visible light illumination system still had ηD of 50-60% via LEDs (BLED and WLED). The results of photocatalytic activity of N-doped TiO2 indicated that the photocatalytic activity of the N-doped TiO2 was higher than that of the commercial TiO2 photocatalyst Degussa P25 for the decomposition of formaldhyde under visible light irradiation. It seemed that nitrogen atoms in doped TiO2 polycrystalline powder were responsible for the significant enhancement of the photoactivity of N-doped TiO2 under visible light irradiation. Therefore, the energy effectiveness of LED was higher than those of the traditional lamps. Considering all such advantages of LED and photocatalysts, the potentially high market value for indoor air pollutant cleaners applying the said technology can be anticipated in the near future.
Subjects
揮發性有機物
甲醛
發光二極體
室內污染物
光觸媒改質
可見光光催化
二氧化鈦。
Volatile organic compounds (VOCs)
formaldehyde
light emitting diode (LED)
Ag/TiO2
indoor air pollutant
N-doped TiO2.
Type
thesis
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