High‐performance photocatalysts for the selective oxidation of alcohols to carbonyl compounds

Abstract

With an increase in awareness about the need for green chemistry, there is a shift in focus towards identifying eco-compatible technologies that can improve product yield and eliminate the use or generation of hazardous compounds. An immediate practical example of such an approach is the development of sustainable methods for alcohol oxidation as alternatives to the current processes that are energy intensive and rely on ecotoxic chemicals. In this regard, heterogeneous photocatalysis has been identified as a robust technique to catalyze reactions under benign conditions, which would otherwise require harsh synthesis routes. With the advent of materials sciences and nanotechnology, there has been a tremendous increase in the scope of applicability of photocatalysis in fine chemicals synthesis. Though an attractive choice, much of the fundamental information pertaining to catalyst activity, selectivity and reaction conditions for optimum conversion are still to be investigated for most of these systems. To this end, this review will encompass recent achievements in the selective photocatalytic oxidation of alcohols by harnessing solar radiation as a viable source of energy. The discussion will be arranged based on common types of photocatalysts reported in literature, namely metal oxides (eg, TiO 2 and ZnO, Nb 2 O 5), sulphides (eg, CdS, CuS, and Bi 2 S 3), and carbonaceous photocatalysts (eg, g-C 3 N 4). Several such candidates for photocatalysts will be discussed critically with the aim of providing useful insight into developing selective photocatalysts that can oxidize alcohols via eco-friendly pathways along with high yields.

V-Substituted ZnIn2S4: A (Visible+NIR) Light-Active Photocatalyst

“…Therefore, both OH and O 2 − radicals might participate in the mechanism of the final degradation, which should proceed according to the first reaction above. Concerning singlet oxygen, it does not seem to play a large role in photocatalysis [42]; the present authors only know one reference in which it plays a significant role in photocatalysis including a visible light-active sulphide [43]. H 2 O 2 , on the other hand, is much less reactive than OH or O 2 − /HO 2 radicals; it is not likely to have a significant role here.…”

Photo-epoxidation of (α, β)-pinene with molecular O2 catalyzed by a dioxo-molybdenum (VI)-based Metal–Organic Framework

“…This higher conversion obtained in the presence of laser radiation at 406 nm is also attributed to the proximity of this irradiation source to the absorption band associated to the ligand-metal transitions at 403 nm observed in the solid-state UV spectrum presented in figure S3 y S4 in supporting information (SI). These findings are particularly relevant when designing an optimal photocatalytic system [64][65][66][67][68].…”

Development of heterogeneous photocatalystsviathe covalent grafting of metal complexes on various solid supports

“…Additionally, semiconductor-type photocatalysts such as TiO 2 and ZnO typically require UV irradiation for excitation owing to their large band gaps and limited photo response, together with their inconvenient recovery and reuse, which restrict their commercial applications. [33][34][35][36][37][38] The selectivity for the desired product also remains a significant concern due to the involvement of free radical intermediates in UV-induced chemical reactions. This issue becomes acute during the selective oxidation of organic compounds with molecular oxygen (O 2 ), wherein O 2 can be easily attached to free radical intermediates, thus leading to uncontrolled autooxidation products.…”