Abstract
Photocatalytic membrane reactors (PMR), with immobilized photocatalysts, play an important role in process intensification strategies; this approach offers a simple solution to the typical catalyst recovery problem of photocatalytic processes and, by simultaneous filtration and photocatalysis of the aqueous streams, facilitates clean water production in a single unit. The synthesis of polymer photocatalytic membranes has been widely explored, while studies focused on ceramic photocatalytic membranes represent a minority. However, previous reports have identified that the successful synthesis of polymeric photocatalytic membranes still faces certain challenges that demand further research, e.g., (i) reduced photocatalytic activity, (ii) photocatalyst stability, and (iii) membrane aging, to achieve technological competitiveness with respect to suspended photocatalytic systems. The novelty of this review is to go a step further to preceding literature by first, critically analyzing the factors behind these major limitations and second, establishing useful guidelines. This information will help researchers in the field in the selection of the membrane materials and synthesis methodology for a better performance of polymeric photocatalytic membranes with targeted functionality; special attention is focused on factors affecting membrane aging and photocatalyst stability.
Highlights
The wide use of chemicals in our society contributes to the accumulation of a huge amount of pollutants in the environment
The incorporation of two semiconductors forms a hybrid photocatalyst, where the photo-generated electrons can flow from more negative to less negative fermi energy (EF ) in conduction band (CB), while holes flow from more positive to less positive EF in valence band (VB) at the interface to prevent charge recombination. These new materials have been mostly used in slurry-type reactors and when it comes to photocatalytic membranes inorganic supports [91] or self-standing catalysts [92]
At high concentration of other hand, at high concentration of photocatalyst, due to the strong interaction between the photocatalyst, due to the strong interaction between the photocatalyst nanoparticles and the polymer photocatalyst nanoparticles and the polymer molecules, the viscosity increases abruptly, the polymer molecules, the viscosity increases abruptly, the polymer solution changes its nature from Newtonian to solution changes its nature from Newtonian to non-Newtonian fluid and the membrane formation is non-Newtonian fluid and the membrane formation is governed by the kinetics, that is radically slowed governed by the kinetics, that is radically slowed down reducing the pore radius and membrane down reducing the pore radius and membrane porosity
Summary
The wide use of chemicals in our society contributes to the accumulation of a huge amount of pollutants in the environment. A rigorous and methodological analysis of how the immobilization method of the photocatalyst in the membrane affects all those parameters needs to be done to ascertain their impact on the overall performance of the functional membrane, in terms of flux properties and photocatalytic activity [4]. This is the first attempt reported in the literature to critically review the information on photocatalytic polymeric membranes so far applied to the treatment of waters and wastewaters polluted with POPs or model organic pollutants; the analysis has been focused to identify the influence of (i) the polymer and photocatalyst selection and, (ii) the methodology of membrane
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