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

https://doi.org/10.1016/j.jiec.2011.02.010Get rights and content

Abstract

In this paper, we prepared the carbon-doped TiO2 (C-TiO2) film to enhance photodegradation efficiency (PE) of gaseous toluene under UV light. PE was affected by thickness of TiO2 film, specific surface area of TiO2, and carbon content doped on TiO2. The highest value of PE was 76% with 3.2-μm-thick film. By adding 0.435 g HPC, the maximum specific surface area of TiO2 was 230 m2 g−1 and PE with porous TiO2 film was 85–87% in 30 min. The specific surface area of conventional TiO2 was 55 m2 g−1 and PE with normal TiO2 film was 77–79%. To increase higher photodegradation capability of TiO2 under UV light, carbon was doped on TiO2 by sol–gel and combustion method. PE of gaseous toluene with porous carbon-doped TiO2 was 91–94% in 30 min and this was more enhanced by 18–19% than that with conventional TiO2. By-products derived from the photocatalytic oxidation of toluene were mostly amyl formate and ethyl formate, which are non-toxic.

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)

  • M.B. Kang et al.

    J. Mol. Catal. A

    (2002)
  • R. Jothiramalingam et al.

    J. Hazard. Mater.

    (2007)
  • J. Jeong et al.

    Chemosphere

    (2004)
  • A. Kubacka et al.

    Appl. Catal. B

    (2007)
  • G. Martra et al.

    Catal. Today

    (1999)
  • A.J. Maira et al.

    Appl. Catal. B

    (2001)
  • H. Einaga et al.

    Appl. Catal. B

    (2002)
  • Z. Pengyi et al.

    J. Photochem. Photobiol.

    (2003)
  • F. Bosc et al.

    Thin Soild Films

    (2006)
  • N. Keller et al.

    Appl. Catal. B

    (2007)
  • V. Tomasic et al.

    Catal. Today

    (2008)
  • J. Mo et al.

    J. Hazad. Mater.

    (2009)
  • Cited by (30)

    • Working principle and application of photocatalytic optical fibers for the degradation and conversion of gaseous pollutants

      2022, Chinese Chemical Letters
      Citation Excerpt :

      Furthermore, to reduce the bandgap and extend the absorption band in the visible light range, non-metal doping with carbon results in attractive photocatalytic properties since the substitution of oxygen with carbon atoms results in new energy states in the TiO2 bandgap [50–52]. In particular, the bandgap energy of C/TiO2 can be downregulated to 3.02 eV with 2.98% carbon [50], which can overcome the low UV transmission of plastic optical fibers. Thus, 3.2 mm thick C/TiO2-coated plastic optical fibers showed a high photodegradation efficiency (76%) for toluene under a 500 W Hg lamp with peak wavelengths of 300, 405, and 436 nm.

    • Photocatalytic TiO<inf>2</inf>-based coatings for environmental applications

      2021, Catalysis Today
      Citation Excerpt :

      Kim et al. demonstrated that carbon-doped TiO2 (C-TiO2) film under UV light converted gaseous toluene in amyl formate and ethyl formate, which are non-toxic. A reactor containing optical fibers, externally coated, by dip coating, with a TiO2 film [140]. Strini et al. mentioned that TiO2 thin films possess a photocatalytic capacity, 3–10 times higher than bare TiO2 (3 % catalyst content) mixed into cementitious materials [144].

    • Transition metal oxide-based materials for visible-light-photocatalysis

      2021, Nanostructured Materials for Visible Light Photocatalysis
    View all citing articles on Scopus
    View full text