Dye‐Sensitized Heterogeneous Photocatalysts for Green Redox Reactions

Abstract

Conversion of sunlight into chemical energy has been the subject of intense research efforts in recent years, due to the possibility to store the enormous amount of energy continuously provided by the Sun in the form of useful “solar fuels”. To allow such process, suitable photocatalysts are required, which are usually obtained by combination of different inorganic materials or by self‐assembly of molecular components on semiconductor surfaces: accordingly, they are capable to carry out several different processes such as light harvesting, substrate binding, electron transport, storage and transfer. Among the photocatalytic systems developed to date, heterogeneous dye‐sensitized semiconductors decorated with various electrocatalysts received particular attention, thanks to their favorable properties of tunable absorption spectrum, high stability and adaptability to different reactions. In this paper, we will review some selected examples of application of such photocatalysts to two main reactions, namely H+ reduction to H2 and CO2 conversion to C1‐building blocks (CO, formate), which are among the most important transformations in the field of so‐called “artificial photosynthesis”.

Ancillary Ligand Effects on Heteroleptic IrIII Dye in Dye‐Sensitized Photocatalytic CO2 Reduction: Photoaccumulation of Charges on Arylated Bipyridine Ligand and Its Control on Catalytic Performance

“…To validate the carbon origin of CO 2 reduction,w ec arried out an isotope-labelinge xperiment for the mixed homogeneous system ( tBu IrP-t Bu + + ReC) and binaryh ybrid system ( tBu IrP-Ph Si + + TiO 2 /ReC) in 13 CO 2 -saturated DMF-d 7 -D 2 Om ixed solvent (3.0 vol% D 2 O) containing 0.10 m BIH. After irradiation, the emergence of as harp signal at d~184 ppm in 13 CNMR spectrum directly indicates the successful 13 CO 2 -to- 13 CO conversion. The 13 Ci sotope abundance (> 98.7 %) characterized by gas chromatography mass spectrometry (GC-MS) further supports that the CO evolution originated from the injected CO 2 gas ( Figures S18 and S19).…”

“…After irradiation, the emergence of as harp signal at d~184 ppm in 13 CNMR spectrum directly indicates the successful 13 CO 2 -to- 13 CO conversion. The 13 Ci sotope abundance (> 98.7 %) characterized by gas chromatography mass spectrometry (GC-MS) further supports that the CO evolution originated from the injected CO 2 gas ( Figures S18 and S19). In addition, as shown in Figure S20 in Supporting Information, the 13 CNMR spectrum of the irradiated homogeneous sample reveals as harp signal at d 162 ppm corresponding to the resonance of H 13 CO 3…”

“…[9][10][11][12][13] In particular, the dye-sensitized photocatalytic (DSPC) system, featured as an efficient visible light energy collectionb yt he introduction of organic/organometallic component,h as received much attention due to its convenience in puttinge ach component in one platform for efficient electron flow from photosensitizing unit to ac atalytic site. [13][14][15][16][17][18][19][20][21] Above all, light harvesting component has been known to be the mostf ragile under the prolonged photolytic condition for CO 2 reduction and decimates photocatalytic activity accordingly, [22,23] so that developing a stable photosensitizer is prerequisite to secure durable opera-tion of the DSPC system.A mong molecular photosensitizers, organometallic complexes are superior to electron-donor and -acceptor type organic dyads for the following reasons:( 1) the readily accessible long-lived,l ow-energy triplet excited states that enable photochemical transformationsi nm any applications, [22,[24][25][26][27] (2) easys ynthetic tunability by substitution of the cyclometallating (C^N) and chelating (N^N) ligand,w hichc onsequently allows energy modulation of the lowest electronic transition, [24,[28][29][30] and (3) tunable periphery group of metal complex (i.e.,a dding anchoring group required for immobilization to diverse functional surfaces), which is necessary for practical applicationw hile maintaining the natureo ft he lowest excited state and the originalc oordination sphere of am etal complex intact. [19,31,32] Such versatilep roperties have been manifested in Ir III , [19,[24][25][26][27][28]…”

“…Recently, the development of multi‐component hybrid photo‐catalyst has shown enhanced catalytic performance and broken the stalemate of CO 2 photoreduction catalysis within the realm of developing either photosensitizer or photocatalyst separately, or engaging both at a binary or ternary catalytic system [9–13] . In particular, the dye‐sensitized photocatalytic (DSPC) system, featured as an efficient visible light energy collection by the introduction of organic/organometallic component, has received much attention due to its convenience in putting each component in one platform for efficient electron flow from photosensitizing unit to a catalytic site [13–21] . Above all, light harvesting component has been known to be the most fragile under the prolonged photolytic condition for CO 2 reduction and decimates photocatalytic activity accordingly, [22, 23] so that developing a stable photosensitizer is prerequisite to secure durable operation of the DSPC system.…”

“…Alarmed by abnormal climates worldwide caused by unbridled carbon dioxide emission (CO 2 ), research on the solar‐light‐driven reduction technology of CO 2 is a top agenda in chemistry and related environmental science [1–8] . Recently, the development of multi‐component hybrid photo‐catalyst has shown enhanced catalytic performance and broken the stalemate of CO 2 photoreduction catalysis within the realm of developing either photosensitizer or photocatalyst separately, or engaging both at a binary or ternary catalytic system [9–13] . In particular, the dye‐sensitized photocatalytic (DSPC) system, featured as an efficient visible light energy collection by the introduction of organic/organometallic component, has received much attention due to its convenience in putting each component in one platform for efficient electron flow from photosensitizing unit to a catalytic site [13–21] .…”