Miguel Salaices

Experimental evaluation of photon absorption in an aqueous TiO2 slurry reactor

This study presents an experimental evaluation of photon absorption in a TiO2 slurry medium using an annular photoreactor. This photoreactor was equipped with several windows placed at equidistant axial positions. Tubular black collimators and inner polished-aluminum collimators were attached to these windows to measure the total transmitted radiation and the transmitted non-scattered radiation. Experiments were developed with six TiO2 commercial powders having differences in particle size, agglomerate particle size in water suspension, and specific surface area. Modeling allowed to establish that the forward-transmitted radiation can be represented by the difference of two exponential decay functions accounting respectively for the total transmitted radiation and the transmitted non-scattered radiation. These two exponentials are functions of particle concentration and extinction coefficients, with the extinction coefficient for the transmitted radiation being strongly affected by the particle agglomerate size.

Novel Photocatalytic Reactors for Water and Air Treatment

The development of water and air treatment systems based on heterogeneous photocatalysis is an area of major technical importance (Blanco and Malato, 1993; Matthews, 1993; Ollis et al., 1989; Pelizzetti et al., 1992). Harada et al., (1999) have stated, “... the design of highly efficient photocatalytic systems is of vital interest and one of the most desirable yet challenging goals in the research of environmentally friendly catalysts”. There is general agreement that an important obstacle in the development of highly efficient photocatalytic reactors is the establishment of effective reactor designs for intermediate and large-scale use, as demanded by industrial and commercial applications. To achieve a successful commercial implementation, several reactor design parameters must be optimized, such as the photoreactor geometry, the type of photocatalyst and the utilization of radiated energy. A fundamental issue regarding the successful implementation of photocatalytic reactors is the transmission of irradiation in a highly scattering and absorbing medium composed of water and fine TiO2 particles.

The Irradiation Field in Photocatalytic Reactors

The evaluation of absorption photon rates in slurry reactors is a rather challenging task since light can experience a combination of reflection, scattering and absorption in the TiO2 particle suspension.

Establishing Photocatalytic Kinetic Rate Equations: Basic Principles and Parameters

Heterogeneous photocatalysis is a promising new alternative method for the removal of organic pollutants in water (Carey, 1976). The degradation of organic pollutants in water, using irradiated dispersions of titanium dioxide, is a growing area of both fundamental and applied research.

Kinetic Modeling of the Photocatalytic Reaction Network: The Parallel-Series Approximation

Photocatalytic oxidation of phenol has been studied at a laboratory scale by several researchers (Al-Ekabi and Serpone, 1988; Matthews and McEvoy, 1992; Okamoto et al., 1985b; Tseng and Huang, 1990; Wei and Wan, 1992; Winterbottom et al., 1997). Phenol is a chemical species difficult to convert in conventional bio-treatment processes. Phenol is also a very useful model contaminant in photocatalytic research for ranking reactor performance.

Photocatalytic Degradation of Air Borne Pollutants

Heterogeneous photocatalytic oxidation of organic air contaminants is a promising technology that offers distinct advantages. These advantages include potential lower operating costs, the elimination of treatment reagents or electron acceptors, the possible recovery, regeneration and reuse of the photocatalyst and finally its widespread applicability for the complete mineralization of organic compounds (Miller and Fox, 1993; Suri et al., 1993). Cabrera et al., (1994) indicated that almost any organic pollutant, and many inorganic ones, could be completely mineralized or separated by means of heterogeneous photocatalysis. Additionally, photocatalytic technology can be used in conjunction with solar radiation (Suri et al., 1993) at close to ambient temperature (Cassano et al., 1995; Falconer and Magrini-Bair, 1998; Miller and Fox, 1993). Photocatalysis also shows important prospects for certain air treatment applications, given that the observed apparent quantum efficiencies can be in excess of 100% (Ibrahim and de Lasa, 2003).

The Energy Efficiency Factors in Photocatalytic Processes

Heterogeneous photocatalysis on metal oxide semi-conductors has been shown to be effective in degrading organic pollutants in gaseous and aqueous streams (Fox and Dulay, 1993; Hoffmann, et al., 1995). In photocatalysis, the definition of energy yield parameters describing the light utilization efficiency is very critical (Fox, 1988).

Photocatalysts, Radiation Sources and Auxiliary Equipment for Photocatalysis

A successful implementation of photocatalysis requires very efficient catalysts, illumination sources and reactors. In addition, auxiliary equipment for photocatalytic reactors is of major importance to assess the effectiveness of the reactor and of the kinetic reactor modeling. This requires proper characterization of the near-UV lamps used, in the case of artificially powered photocatalytic reactors, and the characterization of the photons absorbed in the photocatalytic reactor unit.

Advances and Perspectives for Photocatalysis

Photocatalysis is a new advanced oxidation process based on the irradiation of semiconductor materials, normally TiO2, with UV light having a wavelength smaller than 390 nm. Heterogeneous photocatalysis has emerged as a promising technology that could be instrumental in eliminating pollutants from air and water streams.

Water Decontamination of Organic Species: Modeling Reaction and Adsorption Processes

Modeling photocatalytic reaction processes requires careful consideration of reaction and adsorption phenomena. In order to establish the importance of these matters, experiments can be developed using model pollutants such as methylene blue, phenol, 2-chlorophenol, 2,4-dichlorophenol, catechol (or 1,2 benzenediol), and pyrogallol (or 1,2,3 benzenetriol), each having quite different behaviours of adsorption and reaction.