UV- or Visible-Light-Induced Degradation of X3B on TiO₂ Nanoparticles:  The Influence of Adsorption

Abstract

Photodegradation of a textile dye X3B using either UV (λ g 320 nm) or visible light (λ g 450 nm) over three catalysts of highly adsorptive TiO2 nanoparticles in water has been examined. All the adsorption isotherms demonstrated the Langmuir type behavior. The common observation was confirmed that for all the reactions induced by UV or visible light, the apparent initial rate of X3B loss in the aqueous phase increased with the initial equilibrated concentration of X3B. However, this correlation was changed when the rate was determined by the decreased concentration both in the aqueous phase and on the catalyst surface. This increase of real initial rate with the initial equilibrated concentration was observed only in the visible-light-induced reaction over TiO2 of Degussa P25. For all the other reactions, especially under UV irradiation, the real initial rate was found to increase only initially and then decrease with the initial equilibrated concentration. The result suggests that there is a screening effect by the adsorbed dye in the TiO2 photocatalytic reaction and a solution filter effect in the photosensitized reaction. Moreover, the photosensitized photodegradation of X3B was found to be also dependent on the physical properties of TiO2, but interestingly the relative activity among the catalysts was similar to that demonstrated in the photocatalytic reaction.

Treatment options for wastewater effluents from pharmaceutical companies

“…This mechanism requires that the contaminant adsorbs on the catalyst surface as a prerequisite for efficient oxidation (Serpone and Pelizzetti, 1989). Most researchers observe a Langmuir adsorption isotherm and describe the adsorption-desorption process and the reaction rate constant based on the associated Langmuir-Hinshelwood (L-H) model (Xu and Langford, 2001;Rao et al, 2003), which is expressed as:…”

“…In general, adsorption studies are done in the dark and sometimes the adsorption capacity cannot be transferred quantitatively into irradiated systems (Xu and Langford, 2001). Studies indicated that increased adsorption to the catalyst surface translates to increased reaction rates (Xu and Langford, 2001;Rudder et al, 2004).…”

“…In general, adsorption studies are done in the dark and sometimes the adsorption capacity cannot be transferred quantitatively into irradiated systems (Xu and Langford, 2001). Studies indicated that increased adsorption to the catalyst surface translates to increased reaction rates (Xu and Langford, 2001;Rudder et al, 2004). However, it was found that with little difference in adsorption of carbamazepine on the surface of P25 and Hombikat UV100, the reaction rate and photo-adsorption was much higher with P25 as the catalyst (Doll and Frimmel, 2005b).…”

Suspension high velocity oxy-fuel spraying of TiO 2 : A quantitative approach to phase composition

“…Surface area of powder materials is commonly assessed by specific surface area defined as total area to mass of the solid sample and principles of Brunnauer-Emmett-Teller theory [28] are used for its measurement. When the effect of specific surface area on the (sono)photocatalytic activity of TiO2 is investigated, Langmuir-Hinshelwood behaviour [29] is often reported for the rate of photocatalytic reactions [30] and, thus, linear dependence of mass of the adsorbent on the photocatalyst surface (page 30 in [16]) is expected. Effectively, larger specific surface area leads to higher photocatalytic activity.…”

Photophysical and photocatalytic properties of novel M2BiNbO7 (M = In and Ga)

“…Many reports have revealed that the organic dyes could be effectively degraded using the TiO 2 -based photocatalytic process; however, the degradation of a majority of organic dyes are only under UV irradiation except for some dyes, such as alizarin red, which can be degraded under visible light using the TiO 2 -based photocatalysts based on the dyesensitized process. 10,11 Among different dyes, methylene blue dye (MB) is difficult to be decomposed under visible light irradiation and is usually regarded as a model dye contaminant to evaluate the activity of a photocatalyst. 12,13 Up to now, there were only few reports of MB dye degradation under visible light irradiation.…”