Coupling photocatalysis

Coupling photocatalysis with a physical technologies, such as biological treatment [67, 68], membrane reactor [39] or physical adsorption, the combination does not affect the mechanisms but increases the efficiency of the whole process. 

R. Molinari, L. Palmisano, E. Drioli, and M. Schiavello, Studies on various reactor configurations for coupling photocatalysis and membrane processes in water purification, J. Membr. Sci., 206 (2002) 399-415. 

The major problems occurring in the case of PMRs utilizing pressure driven membrane techniques, such as MF, UF and NF, are permeate flux decline and membrane fouling caused by photocatalyst particles. On the other hand, the deterioration of the permeate flux in the presence of li02 is not observed in the case of PMRs coupling photocatalysis with dialysis, PV and MD. These differences result from the various mechanisms of mass transport in both types of membrane processes. 

Molinari R, Borgese M, DrioU E, Palmisano L and Schiavello M (2002b), Hybrid processes coupling photocatalysis and membranes for degradation of organic pollutants in water , Catal Today, 75,77-85. 

Mozia S, Tomaszewska M and Morawski A W (2007), Photocatalytic membrane reactor (PMR) coupling photocatalysis and membrane distillation—Effectiveness of removal of three azo dyes from water , Catal Today, 129,3-8. 

PMRs coupling photocatalysis with microfiltration (MF) or ultraflltra-tion (UF) have been applied for the degradation of different pollutants, such as pharmaceuticals, humic and fulvic acids, trichloroethylene, bisphe-nol A, chlorophenol, 4-nitrophenol, dyes, as well as for treatment of real dyeing wastewater, synthetic wastewater, grey water and surface waters. 

In Fig. 21.7 a laboratory scale PMR coupling photocatalysis with MF is shown. The PMR was applied for the removal of trichloroethylene (TCE) from water (Choo et al., 2008). The system was composed of a photocatalytic reactor (volume of 700 cm ) and a hollow fiber MF module (effective membrane surface area of 20.7 cm ). A UV-A light source was placed in the inner chamber of the photoreactor, whereas in the outer chamber the solution undergoing the photocatalytic reaction was flowing. Feed from the feed tank was pumped through the photoreactor to the membrane module. The PMR was operated either in batch or in continuous mode. In batch operations, the permeate and retentate were recycled to the photoreactor. In continuous mode, the permeate was discharged and the same volume of the solution was fed into the reactor. Thus the working volume of the photoreactor was maintained at a constant level. 

A PMR that couples photocatalysis with PV was found to be an attractive technology for the simultaneous synthesis and separation of valuable intermediate compounds such as aromatic aldehydes. Nonetheless, before an implementation in full scale, optimization of this system is necessary. 

Sahng HL, Jae HK, Park CB (2013) Coupling photocatalysis and redox biocatalysis toward biocatalyzed artificial photosynthesis. Chem Em J 19 4392-4406... 

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