Photocatalytic processes in membrane reactors

Abstract

Photocatalytic membrane reactors (PMRs) represent an interesting alternative technology useful both in the field of water and air purification and in organic syntheses. The necessity to develop chemical products and industrial processes that reduce or eliminate the use and the generation of toxic substances along with the risk for human health and for environment constitutes the aim of the research efforts based on the principles of green chemistry. Heterogeneous photocatalysis is a technology extensively studied for about three decades, since Fujishima and Honda1 discovered the photocatalytic splitting of water on TiO2 electrodes in 1972, which includes a large range of reactions. When a separation membrane method is coupled with a photocatalytic process, it is possible to obtain a synergistic effect minimizing environmental and economic impacts. In this hybrid system, in fact, the radicals produced by irradiation of the catalyst were exploited to perform partial or total redox reactions leading to selective products or clarified solutions, which can be separated by the membrane. Several characteristics make PMR a green technology, as the safety of the photocatalyst used, the mild operative conditions, the possibility to operate in continuous mode, in which the recovery of the catalyst, the reactions, and the products separation occur in one step, with a remarkable time and cost saving. The choice of an appropriate membrane and the knowledge of the parameters influencing the photocatalytic process represent, therefore, an important step in the design of a PMR. Besides, the possibility to perform the photocatalytic reactions using the solar light makes this process very interesting for future industrial applications.