Heterogeneous Photocatalytic Process Research Articles

Photocatalytic kinetics of phenol and its derivatives over UV irradiated TiO 2

In recent years, photocatalytic degradation mediated by illuminated TiO 2 has received considerable attention as an alternative for treating polluted water. In the present study, a new two-phase swirl-flow monolithic-type reactor was used to study the kinetics of heterogeneous photocatalytic processes. Photocatalytic degradation of phenol, 4-chlorophenol (4-CP) and 4-nitrophenol (4-NP) both in aqueous suspensions and over immobilized Degussa P25 TiO 2 has been studied in laboratory scale. Experiments were conducted to investigate the effects of parameters such as catalyst dosage, pollutant concentration, temperature, partial pressure of oxygen, UV light intensity, catalyst-layer thickness, circulation flowrate and catalyst annealing temperature. Simple model for predicting the optimal catalyst dosage in aqueous suspensions for different photo-systems was proposed. Pseudo first-order kinetics with respect to all the parent compounds was observed. Experimental data obtained under different conditions were fitted with kinetic equation to describe the dependency of degradation rate as a function of the above mentioned parameters. Consequently, kinetic parameters were experimentally determined. Adsorptive properties of all the organics were also experimentally measured and fitted with Langmuir equation. The extreme low surface coverage of the organics on the catalyst may be one of the main factors that result in the low efficiency of the photocatalytic process. Besides, mass transfer of organics and oxygen in the photocatalytic process has also been discussed in detail.

Degradation of organic pollutants in water by photochemical reactors

The degradation of glycolic acid in aqueous media was performed by homogeneous photochemical and heterogeneous photocatalytic processes using different kinds of chemical reactors. The efficiency of the degradation processes was evaluated by measuring both the reactant conversion and the decrease of the total organic carbon (TOC) of the solution. The best results were obtained by using a continuous reactor with a fixed supported photocatalyst.

Photodegradation kinetics of 4-nitrophenol in TiO 2 suspension

A new two-phase swirl-flow monolithic type reactor was designed to study the kinetics of heterogeneous photocatalytic processes on semiconductor catalysts. Most of the earlier work investigated the effects of various parameters on the initial degradation rate (or the formation of CO 2) of the pollutants. In the present study, photomineralization of 4-nitrophenol (4-NP) sensitized by Degussa P25 TiO 2 in aqueous solution has been investigated as a function of the following different experimental parameters: initial concentration of pollutant (C S0), light intensity ( I a), partial pressure of oxygen ( p O 2 ), catalyst concentration, pH, chloride ion and temperature. The kinetic expression obtained can be described by the following formula r s= k 0 exp (− E/ RT) I α β K O 2 p O 2 /(1+ K O 2 p O 2 ) K s C s/(1+ K s C s 0). The apparent overall activation energy for 4-NP obtained was 7.42 kJ mol −1 by fitting the above equation with experimental data and the values for β, K O2 and K s were 0.84, 9.98 atm −1 and 0.075 ppm −1 respectively. The kinetic equation can predict the concentration of 4-NP during the entire degradation process at pH value of 4.3 and TiO 2 concentration of 2 g l −1, and is therefore, more meaningful. It can be used in the development of large-scale photocatalytic reactor and optimization of experimental conditions for any particular studies. Furthermore, the photodegradation of 4-NP on two different catalysts (P25 and UV100) was compared and the photonic efficiency of the process has also been investigated.

Novel swirl‐flow reactor for kinetic studies of semiconductor photocatalysis

AbstractA new two‐phase swirl‐flow monolithic‐type reactor was designed to study the kinetics of heterogeneous photocatalytic processes on immobilized semiconductor catalysts. True kinetic rate constants for destruction of a textile dye were measured as a function of wavelength of light intensity and angle of incidence, catalyst layer thickness, and the effect of absorption of light by liquid film on the overall rate of photocatalytic degradation. Photocatalytic activities of two commercially available TiO2 catalysts (Degussa P25 and Hombikat UV 100) were also compared for different light intensities and catalyst layer thickness. Residence time distribution and mass‐transfer limitations were evaluated. This new reactor appears to be an attractive choice for kinetic studies of heterogeneous photocatalysis.

Solar photocatalytic processes for the purification of water: State of development and barriers to commercialization

Semiconductor-based photocatalytic processes for removing hazardous chemicals from contaminated water have been studied for nearly 20 years. One goal of this research is to use the sun as the light source. This article assesses the state of development of solar heterogeneous photocatalytic processes for treating contaminated water and identifies key barriers that must be overcome for the technology to achieve commercial success. Some industry members estimate that the cost of using solar technology for waste treatment will need to be less than half the cost of a “conventional” technology in order to gain market acceptance. The number of applications that are near commercial viability could be expanded with significant progress in the improvement of the photo-efficiency of the photocatalytic process.

A Proposal for the Quantitative Assessment of Heterogeneous Photocatalytic Processes

A critical assessment of the parameters needed for the correct comparison of activity and efficiency of various heterogeneous photocatalytic systems is presented in the present paper. Two parameters are to be evaluated in order to compare different photocatalytic systems. The first parameter, the "intrinsic reaction rate" (ri), allows one to have information on the specific catalytic reactivity, while the second one, the "rate of photon absorption" (rpa), allows the evaluation of the capacity of absorbing photons. From the knowledge of these two parameters the "quantum yield" (qy), which indicates the efficiency of the absorbed photons for promoting a reaction event, can be determined. The phenol photodegradation reaction, carried out in aqueous dispersions of polycrystalline (anatase) TiO2, has been used as a test reaction in order to determine the ri, rpa, and qy values of powdered specimens from different preparation methods and sources.