The combination of heterogeneous photocatalysis with chemical and physical operations: A tool for improving the photoprocess performance

Abstract

Heterogeneous photocatalysis is a process of great potential for pollutant abatement and waste treatment. In order to improve the overall performance of the photoprocess, heterogeneous photocatalysis is being combined with physical or chemical operations, which affect the chemical kinetics and/or the overall efficiency. This review addresses the various possibilities to couple heterogeneous photocatalysis with other technologies to photodegrade organic and inorganic pollutants dissolved in actual or synthetic aqueous effluents. These combinations increase the photoprocess efficiency by decreasing the reaction time in respect to the separated operations or they decrease the cost in respect of heterogeneous photocatalysis alone, generally in terms of light energy. Depending on the operation coupled with heterogeneous photocatalysis, two categories of combinations exist. When the coupling is with ultrasonic irradiation, photo-Fenton reaction, ozonation, or electrochemical treatment, the combination affects the photocatalytic mechanisms thus improving the efficiency of the photocatalytic process. When the coupling is with biological treatment, membrane reactor, membrane photoreactor, or physical adsorption, the combination does not affect the photocatalytic mechanisms but it improves the efficiency of the overall process. The choice of the coupling is related to the type of wastewater to be treated. A synergistic effect, giving rise to an improvement of the efficiency of the photocatalytic process, has been reported in the literature for many cases.

Effect of key parameters on the photocatalytic oxidation of toluene at low concentrations in air under 254+185nm UV irradiation

“…or through the formation of H 2 O 2 and its subsequent photolysis by irradiation of ozone in water with near-UV light (λ > 300 nm), which produces H 2 O 2 quantitatively [29]:…”

The constraints of transition metal substitutions (Ti, Cr, Mn, Co and Ni) in magnetite on its catalytic activity in heterogeneous Fenton and UV/Fenton reaction: From the perspective of hydroxyl radical generation

“…3). The positive effect of UV light on the improvement of • OH generation was ascribed to the iron recycling caused by the photochemical reduction of ferric ions, and accordingly promoted the Fenton reaction [32]. The kinetic process of • OH generation also could be divided into two stages (Table 2).…”

The progress of catalytic technologies in water purification: A review

“…However, for the application at large scale, the main limitation is to find electrode materials with specific characteristics to make the process competitive. Ti/PbO 2 , Ti/SnO 2 , Ti/IrO 2 , glassy carbon are generally used (Augugliaro et al, 2006). A series of TiO 2 -modified β-PbO 2 electrodes were prepared using co-deposition method and characterized by SEM and XRD (Li et al, 2005(Li et al, , 2006a(Li et al, , 2006b).…”

“…The oxidation process at BDD anodes involves the production of . OH radicals scarcely adsorbed at the BDD surface: they consequently desorb and can attack the organic pollutant (Augugliaro et al, 2006). Moreover, the BDD electrode exhibit ptype semiconductor properties.…”