From catalysis by metals to bifunctional photocatalysis

Abstract

Catalysis by metals'', was transposed to ''Bifunctional Photocatalysis'', based on noble metals deposited on titania. Both, participation (i) of the photo-active oxidic support and (ii) of the deposited metal have been successfully analyzed, delimited and associated. For both reactions involving hydrogen (Cyclopentane-Deuterium Isotope Exchange (CDIE) and alcohol dehydrogenation), the respective roles of electrons and holes were clearly put in evidence. The photogenerated electrons were found to be spontaneously transferred to the metal nano-particles because of the alignment of the Fermi levels of both solid phases. They neutralize protons H + (or deuterons D + ) into atoms before their recombination and evolution of dihydrogen (or HD). Simultaneously, photogenerated holes h + neutralize anionic species in oxidation reactions responsible for the activation of organic molecules. These two anionic species were OD ) deuteroxyl surface groups in CDIE and alcoholate anions RO ) in alcohol dehydrogenation, respectively. Both reactions exhibited a stoichiometric threshold which was exceeded several hundreds of times, clearly defining the real catalytic character of both reactions. The titania-deposited noble metals appeared as auxiliaries or co-catalysts working independently of UV-irradiation for making the reaction run catalytically. Eventually, the concepts of bifunctional photocatalysis were applied to account for interphasic photocatalytic processes such as hydrogen transfer, electron transfer, photosensitization in the visible via CdS addition.

Environmental green chemistry as defined by photocatalysis

“…This belongs to the field of bifunctional photocatalysis using TiO 2 -deposited noble metal catalysts [13].…”

“…Conventional catalysis by metals is not selective at all in alkane-deuterium isotopic exchange [13].…”

Detoxification of wastewater containing five common pesticides by solar AOPs–biological coupled system

“…Among the different approaches to pesticide elimination, advanced oxidation processes (AOPs) have been recognized as especially efficient compared to conventional technologies, mainly phase-separation (adsorption processes, stripping techniques) and other methods which destroy the contaminants www.elsevier.com/locate/cattod Catalysis Today 129 (2007) [69][70][71][72][73][74][75][76][77][78] (chemical oxidation/reduction) [5][6][7][8]. AOPs are characterized by the production of hydroxyl radicals ( OH), which are able to oxidise and mineralize almost any organic molecule, yielding CO 2 and inorganic ions.…”

Environmental photocatalysis: Perspectives for China

“…However, above a certain value depending on the photoreactor, the reaction rate r becomes proportional to  1/2 , indicating strong electron-hole recombination. These two regimes have been independently demonstrated by Egerton et al [26] and the author [27,28].…”