Abstract
Photocatalytic organic synthesis/conversions and water treatment under visible light are a challenging task to use renewable energy in chemical transformations. In this review a brief overview on the mainly employed visible light photocatalysts and a discussion on the problems and advantages of Vis-light versus UV-light irradiation is reported. Visible light photocatalysts in the photocatalytic conversion of CO2, conversion of acetophenone to phenylethanol, hydrogenation of nitro compounds, oxidation of cyclohexane, synthesis of vanillin and phenol, as well as hydrogen production and water treatment are discussed. Some applications of these photocatalysts in photocatalytic membrane reactors (PMRs) for carrying out organic synthesis, conversion and/or degradation of organic pollutants are reported. The described cases show that PMRs represent a promising green technology that could shift on applications of industrial interest using visible light (from Sun) active photocatalysts.
Highlights
The development of advanced green chemical technologies and processes in organic synthesis and environmental conversions has become one of the most important challenges for chemical researchers in the last decades [1,2] and, for the ones using heterogeneous photocatalysis (HPC).Too much interest is devoted on using the solar source as a non-exhaustible energy and, in this aspect, visible light photocatalysts play a very crucial role.Many conventional catalytic processes for chemical production usually employ toxic and hazardous substances as catalysts or solvents, they are not very sustainable in terms of resources, environmental impact and energy efficiency [1,2,3,4]
Advancements in photocatalytic materials research have allowed the development of various materials, e.g.: adsorbents incorporated in membrane technologies, photocatalysts combined with magnetic material and coated on optical fibers
Previous studies on photocatalytic reduction as well as partial and total oxidation of organics on membrane reactors have shown the great potential of this technology but they ostly involve the use of UV light
Summary
Many conventional catalytic processes for chemical production usually employ toxic and hazardous substances as catalysts or solvents, they are not very sustainable in terms of resources, environmental impact and energy efficiency [1,2,3,4]. Photocatalytic reactions generally utilize semiconductors to directly absorb photons above their band gap energy and produce carriers consisting of electrons and holes, promoting oxidation and reduction reactions [1,2,3,4,6]. The produced electron/hole couple can undergo two different fates: (i) the couple can quickly recombine, in the bulk or on the surface of the semiconductor, releasing the accumulated energy as heat or photons; (ii) the couple can migrate to the surface of Catalysts 2020, 10, 1334; doi:10.3390/catal10111334 www.mdpi.com/journal/catalysts
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