Abstract
This paper presents an overview of recent reports on photocatalytic membrane reactors (PMRs) in organic synthesis as well as water and wastewater treatment. A brief introduction to slurry PMRs and the systems equipped with photocatalytic membranes (PMs) is given. The methods of PM production are also presented. Moreover, the process parameters affecting the performance of PMRs are characterized. The applications of PMRs in organic synthesis are discussed, including photocatalytic conversion of CO2, synthesis of KA oil by photocatalytic oxidation, conversion of acetophenone to phenylethanol, synthesis of vanillin and phenol, as well as hydrogen production. Furthermore, the configurations and applications of PMRs for removal of organic contaminants from model solutions, natural water and municipal or industrial wastewater are described. It was concluded that PMRs represent a promising green technology; however, before the application in industry, additional studies are still required. These should be aimed at improvement of process efficiency, mainly by development and application of visible light active photocatalysts and novel membranes resistant to the harsh conditions prevailing in these systems.
Highlights
Organic synthesis and environmental conversions can be carried out by heterogeneous photocatalysis (PC)
The results described in the present paper evidence that Photocatalytic Membrane Reactors (PMRs) represent a very promising technology of great research and industrial interest
Slurry PMRs can be further classified in integrative-type PMR, where the photocatalytic reaction and the membrane separation take place in one unit, and in split-type PMR, where the photocatalytic reaction and the membrane separation take place in separate units
Summary
Organic synthesis and environmental conversions can be carried out by heterogeneous photocatalysis (PC). (ii) the use of greener and safer catalyst (mainly TiO2 ) avoiding the use of more dangerous heavy metal catalysts; (iii) the use of mild oxidants, such as molecular oxygen; (iv) the possibility to obtain the real destruction of refractory and non-biodegradable contaminants with the formation of innocuous by-products; (v) the requirement of very few auxiliary additives; (vi) the applicability to a wide range of substrates in liquid, solid, and gaseous phases, even if diluted; (vii) the possibility to use renewable solar energy; and (viii) the possibility to couple PC with other physical and chemical technologies Despite these advantages, the costs related to the separation of the heterogeneous photocatalyst and the poor process selectivity represents the major drawbacks limiting PC application at industrial scale [19,20]. The present work gives a critical overview of the recent advantages of PMRs in both organic synthesis and pollutant degradation with a particular focus on the scientific literature of the last 5 years
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