Abstract
The present work gives a critical overview of the recent progresses and new perspectives in the field of photocatalytic membranes (PMs) in photocatalytic membrane reactors (PMRs), thus highlighting the main advantages and the still existing limitations for large scale applications in the perspective of a sustainable growth. The classification of the PMRs is mainly based on the location of the photocatalyst with respect to the membranes and distinguished in: (i) PMRs with photocatalyst solubilized or suspended in solution and (ii) PMRs with photocatalyst immobilized in/on a membrane (i.e., a PM). The main factors affecting the two types of PMRs are deeply discussed. A multidisciplinary approach for the progress of research in PMs and PMRs is presented starting from selected case studies. A special attention is dedicated to PMRs employing dispersed TiO2 confined in the reactor by a membrane for wastewater treatment. Moreover, the design and development of efficient photocatalytic membranes by the heterogenization of polyoxometalates in/on polymeric membranes is discussed for applications in environmental friendly advanced oxidation processes and fine chemical synthesis.
Highlights
Membrane reactors (MRs) are multifunctional reactors that are characterized by the combination of a reaction with a membrane separation processes
When a membrane is combined with a photocatalytic process the MR is indicated as photocatalytic membrane reactor (PMR) [11] and it can be designed in two main configurations, depending from the catalyst confinement [12,13,14]: (i) photocatalytic membrane reactors (PMRs) with solubilized or suspended photocatalyst; and, (ii) PMRs with photocatalyst immobilized in/on a membrane
In the case of PMRs that operated under cross-flow filtration mode, where the feed solution is continuously recirculated tangentially to the membrane, the recirculation flow rate is an important operating parameter affecting the photocatalytic performance of the system
Summary
Membrane reactors (MRs) are multifunctional reactors that are characterized by the combination of a (catalytic) reaction with a membrane separation processes. MRs are specific example of reactive separations well responding to the requests of the PI strategy, coupling a reaction with a membrane separation process, at equipment level, but by realizing functional synergies between the operations involved [6] This synergic combination can have several advantages in comparison with traditional reactors depending on the specific functions performed by the membrane [8]. When a membrane is combined with a photocatalytic process the MR is indicated as photocatalytic membrane reactor (PMR) [11] and it can be designed in two main configurations, depending from the catalyst confinement [12,13,14]: (i) PMRs with solubilized or suspended photocatalyst; and, (ii) PMRs with photocatalyst immobilized in/on a membrane Both configurations present specific advantages and limitations depending from the specific application.
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