Heterogeneous Photo-Fenton Oxidation

The association of photocatalysis with the Fenton system makes the process more effective and is a very nice example of synergy. Photocatalytic reactions are somehow slow processes that are related to the energy required for transfer of electrons from the valence to the conduction band and quantum efficiency. Fenton reactions are also rather slow processes [84] that are merely associated with the slow back reduction rate of Fe to Fe .  

A number of iron-containing systems, including iron oxides and iron-immobilized materials, have already been developed and investigated for the degradation of organic pollutants [85-88]. 

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Heterogeneous Photo-Fenton Oxidation 489 Semiconductor action versus Heterogeneous photo-Fenton action... 

Herney-Ramirez, J., Vicente, M. and Madeira, L. (2010). Heterogeneous Photo-Fenton Oxidation with Pillared Clay-based Catalysts for Wastewater Treatment A Review, Appl. Catal. B ... 

Catalytic activity of composites B-N-Fe and Si-N-Fe when applying UV radiation in presence of hydrogen peroxide, oxalic acid, and EDTA is determined by formation of photo-Fenton, ferric-oxalate, and Fe-EDTA systems in the solution which leads to generation of the super-oxidant-hydroxyl radicals. At the same time, solutions practically are not polluted by iron. High catalytic activity of the composites is determined by combination of heterogeneous and homogeneous catalyses. 

Among the nonphotochemical AOT s, one can distinguish the oxidation with Oj/OH", Oj/H O, Fenton s processes, electrochemical oxidation, radiolysis, plasma, ultrasonic treatment, etc. Among the photochemical processes, we can find the oxidation in subcritical and supercritical water, photolysis of water in UW, UV/H Oj, UV/O3, UV/H O /Oj, Photo-Fenton s processes, and heterogeneous photocatalysis. 

Fig. 5.8 Examples of oxidative water treatment technologies used in industry, research and development [adapted from FIGAWA (1997), and supplemented by novel methods]. The numbers 1 to 9 refer to the generalized reaction sequences presented in Figure 5-9. a) Oxidation at elevated temperatures between 220°C < T <300°C or supercritical water oxidation at AT >374°C, Ap >221 bar (221000 kPa) (cf Chapter 1) b) oxidation in the presence of bimetallics Fe°/Ni° or Zn°/Ni° (Cheng and Wu, 2001) or heterogeneous oxidation in supercritical water catalyzed by metals Me = Cu, Ag, Au/Ag-alloy c) Fenton reaction at pH <5 d) photo-assisted Fenton reaction, irradiation in the UV-B/VIS range e) the mixture of oxidants O3/H2O2 is called PEROXONE f) ozonation using solid-bed catalysts with conditioned activated carbon (AC) g) vacuum-UV photolysis of water.

Photo-initiated AOPs are subdivided into VUV and UV oxidation that are operated in a homogeneous phase, and in photocatalysis (Fig. 5-15). The latter can be conducted in a homogeneous aqueous phase (photo-enhanced Fenton reaction) or in a heterogeneous aqueous or gaseous phase (titanium dioxide and certain other metal oxide catalysts). These techniques apply UV-A lamps or solar UV/VIS radiation and they are in pre-pilot or pilot status. According to Mukhetjee and Ray (1999) the development of a viable and practical reactor system for water treatment with heterogeneous photocatalysis on industrial scales has not yet been successfully achieved. This is mainly related to difficulties with the efficient distribution of electromagnetic radiation (UV/VIS) to the phase of the nominal catalyst. 

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