Preparation of porous carbon-doped TiO2 film by sol–gel method and its application for the removal of gaseous toluene in the optical fiber reactor
Introduction
As volatile organic compounds (VOCs) have attracted concern due their harmful effects on human health, research has focused on their removal in recent years. Most VOCs have distinct volatility, solubility, and chemical stability since they are aromatic compounds with a benzene ring [1]. Toluene is extensively used as a solvent for coating, adhesive, and painting in industrial fields as a major VOC [2]. Gaseous toluene is known to cause skin disease and respiratory problems even at low concentration. Among the many reports on various removal processes for gaseous toluene, the photo-oxidative removal of gaseous toluene has demonstrated the highest effectiveness [3], [4].
In the last few decades, the degradation of toluene by titanium dioxide (TiO2) as a photocatalyst has attracted much attention as a promising method for air purification due to its easy handling [5], [6], [7], [8], [9], [10], [11], [12], [13], [14]. Many researchers have studied the effects of relative humidity, input flow rate, input toluene concentration, residence time, UV wavelength, and reaction temperature on gaseous toluene by using TiO2. However, removal efficiency of gaseous toluene by using the aforementioned works was not improved. It is more reasonable to increase removal efficiency of gaseous toluene with carbon-doped TiO2 (C-TiO2) film than other sensitizer at a low cost. Kisch and Sakthivel [15] prepared 3-types of C-TiO2 by the hydrolysis of titanium tetrachloride with tetrabutylammonium hydroxide, whose band-gap energy were 3.02 eV, 3.11 eV, and 3.17 eV by containing 2.98%, 0.42%, and 0.03% carbon, respectively. Wang et al. [16] synthesized C-TiO2 by inducing carbon in the TiO2 structure as a carbon source of methyl methacrylate and Ren et al. [17] prepared mesoporous C-TiO2 by using glucose as a carbon source. These C-TiO2 showed higher photocatalytic activity than undoped TiO2 under visible light irradiation. Xiao et al. [18] found that sintering temperature had a close relationship with photodegradation capability of C-TiO2 and PE of methylene blue at 400 °C was much higher than that at 800 °C.
In this paper, we prepared porous C-TiO2 films with a higher specific surface area to enhance PE of gaseous toluene. Specific surface area of TiO2 was controlled by adding HPC content. PE of gaseous toluene was investigated by thickness of TiO2 film, added solvents, HPC content, and photodegration time using C-TiO2 film.
Section snippets
Preparation of porous carbon-doped TiO2 film
Tetra-titanium-isopropoxide (TTIP, with the purity over 98%, Junsei Chem. Co. Ltd., Japan), hydroxyl-propyl-cellulose (HPC, Aldrich, USA), either propylene-glycol-monomethyl-ether (PGME, Samchun, Korea), ethylene-glycol-monomethyl-ether (EGME, Shinyo Pure Chemical, Japan), and carbon particle (Aldrich, U.S.A) were used as raw materials for the synthesis of porous C-TiO2.
The porous, carbon-doped TiO2 is synthesized as shown in Fig. 1.
After adding 2 g TTIP and 0.145–0.726 g HPC into 40 g solvent,
Effect of TiO2 film thickness on the photodegradation of gaseous toluene
TiO2 film was immobilized on the optical fiber by dip-coating and Fig. 3 shows the SEM images of the TiO2 film thickness with from one to five coating applications.
For the 1-, 2-, 3-, 4- and 5-time coatings, the film thickness of TiO2 was 1.6 μm, 2.6 μm, 3.2 μm, 4.0 μm, and 4.2 μm, and the solid-weight coated on the fiber was 1.59 mg m−2, 1.62 mg m−2, 2.64 mg m−2, 2.97 mg m−2, and 3.05 mg m−2, respectively.
Fig. 4 shows the PE of gaseous toluene as the TiO2 film thickness was varied by the number of coatings.
Conclusions
With the goal of enhancing PE of gaseous toluene, the carbon-doped TiO2 (C-TiO2) film with a higher specific surface area was prepared. EGME was better than PGME and ethanol as a solvent in improving specific surface area of TiO2. The surface specific area was controlled by HPC concentration over the range from 0.145 g to 0.435 g at 40 g EGME, but not above 0.435 g. Although PE of gaseous toluene was 77–79% with TiO2 film of 55 m2 g−1 at constant thick of 3.2-μm, it was 85–87% with C-TiO2 film of 230 m
Acknowledgements
This study was supported by the Ministry of Environment, Republic of Korea (Project no. 013-071-053).
References (25)
- et al.
J. Mol. Catal. A
(2002) - et al.
J. Hazard. Mater.
(2007) - et al.
Chemosphere
(2004) - et al.
Appl. Catal. B
(2007) - et al.
Catal. Today
(1999) - et al.
Appl. Catal. B
(2001) - et al.
Appl. Catal. B
(2002) - et al.
J. Photochem. Photobiol.
(2003) - et al.
Thin Soild Films
(2006) - et al.
Appl. Catal. B
(2007)
Catal. Today
J. Hazad. Mater.
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