Kinetic Studies of Photocatalytic Degradation in a TiO₂ Slurry System:  Distinguishing Working Regimes and Determining Rate Dependences

Abstract

A systematic analysis has been carried out to distinguish "kinetic" and "transport" limited regimes for photocatalytic degradation in a TiO 2 slurry system using benzoic acid as a model component. Experiments were performed to investigate the effect of both monoparametric (e.g., catalyst loading, circulation rate, and initial concentration) and biparametric (e.g., catalyst loading and circulation rate, initial concentration of solute, and light intensity) on the degradation rate to differentiate the kinetic regime from the transport regime. It is shown that there is no external mass-transfer limitation at any catalyst loading, but at high catalyst loading, there exist both internal mass-transfer limitation and light limitation. The domain of kinetic limitation, the domain of internal mass-transfer limitation (particle agglomeration effect), and the domain of light transport limitation (shielding effect) were distinguished. Experimental results demonstrate a significant difference in the rate values between the "optimal catalyst loading" regime and the kinetic regime. The true kinetic dependences of the photocatalytic degradation rate on light intensity and the substance initial concentration were determined.

Experimental investigation of Taylor vortex photocatalytic reactor for water purification

“…The above three model compounds are selected, as their reaction rate constants are an order of magnitude different from each other. The intrinsic reaction rate constant (k r ) of Benzoic acid is circa 13 s −1 (Mehrotra et al, 2003), which is higher than Eosin B (k r = 0.4 s −1 ) (Zhou and Ray, 2003), which in turn is much higher than Orange II dye (k r = 0.017 s −1 ). When the catalyst is immobilized onto a surface, a sequence of events control the overall photocatalytic degradation rate.…”

“…7 clearly shows that the degradation rate of Benzoic acid is slower than the other two-model compounds, Orange II and Eosin B, particularly slow at low Reynolds number inspite of the fact that intrinsic reaction rate constant is higher than the other two model compounds. This is due to the fact that adsorption of benzoic acid on TiO 2 is very small (Mehrotra et al, 2003) compared to the other two components, and according to Eq. (7), both adsorption rate and external mass transfer becomes the rate-controlling step.…”

Kinetic Concepts of Heterogeneous Photocatalysis

“…As sufficient catalyst loading is reached, agglomerates are believed to be formed whose size R, can be estimated using Eq. 2.90 (Mehrotra et al 2003).…”

Photocatalytic Degradation of Phenol and Phenol Derivatives Using a Nano-TiO2 Catalyst: Integrating Quantitative and Qualitative Factors Using Response Surface Methodology

“…The impact of various factors on photocatalytic reactions has been reported in many studies; however, few studies have examined the interaction effects of different variables on process performance. Studies assessing the impact of interaction factors on TiO 2 photocatalysis are limited [25,26] and in an effort to address this knowledge gap, this work will examine the effects of TiO 2 particle size, temperature and the chemical structure of similar structures (phenol and mono-substituted isomers (cresol isomers)) on the photocatalytic degradation rate.…”