Collisional Electron Transfer Route between Homogeneous Porphyrin Dye and Catalytic TiO₂/Re(I) Particles for CO₂ Reduction

Abstract

Dye detachment issue in the TiO 2 -mediated dye-sensitized photocatalytic system engenders an electron injection route based on collisional quenching between the detached solution-phase dye and dispersed n-type TiO 2 particles, in addition to the general fast electron injection pathway from dye chemisorbed on TiO 2 . For porphyrinsensitized hetero-binary hybrids prepared by mixing a solution-phase Zn porphyrin sensitizer (ZnP) and heterogeneous Re(I) molecular catalystimmobilized TiO 2 particles (TiO 2 /Re(I)), we found that without any dye immobilization on the TiO 2 surface, the dissolved porphyrin dye can effectively transport its excited-state electrons to the heterogeneous catalytic TiO 2 /Re(I) particles via a collisional electron transfer pathway, which is relatively unstudied and thus an interesting topic in the dye-sensitized semiconductor photocatalytic system. The better light-harvesting ability of porphyrin in solution and the TiO 2induced stabilization of the molecular Re(I) catalyst raised the photochemical CO 2 -to-CO conversion activity of the semiheterogeneous system (porphyrin + TiO 2 /Re(I) catalyst) above that of the homogeneous system (porphyrin + Re(I) catalyst) and the heterogeneous ternary hybrid (porphyrin/TiO 2 /Re(I) catalyst).

Inorganometallic Photocatalyst for CO2 Reduction

“…In addition, as it has been suggested that Mott–Schottky analysis is not suitable for characterizing bulk TiO 2 nanoparticles with a high concentration of defects, the E fb values of TiO 2 were further estimated using the spectroelectrolysis technique discovered by Grätzel et al, whereby the number of electrons in the CB at a given applied potential can be determined employing visible/near-infrared absorption spectroscopy. The measured E fb values were within a similar range as those commonly obtained using Mott–Schottky analysis, illustrating the significant proton dependence of the E fb level arising from the establishment of a proton adsorption–desorption equilibrium. − In practical terms, this spectroelectrolysis technique is the most reliable for determining the E fb of polycrystalline TiO 2 materials, which are commonly used in TiO 2 -based hybrid systems. Figure shows a comparison of the excited-state energies of the organic and organometallic components (photosensitizer and catalyst, respectively) and the band energetics of TiO 2 , which can be varied with different Brønsted acid additives and is determined using the spectroelectrolysis analysis tool.…”

“…In our recent reports, we have demonstrated that collisional ET from the solvated porphyrin dye to the heterogeneous TiO 2 semiconductor suspended in a reaction solution can serve as a major ET route under conditions wherein the free dye and heterogeneous TiO 2 /catalyst particles coexist in a single reaction vessel (Figure 7). 32 The high activation energies for the collisional electron injection process (57−58 kJ/mol, solvated porphyrin dye → TiO 2 ), which were quantified by means of Arrhenius analysis, indicate that the ET is inefficient because of the low probability of collisions between the solutionphase anionic dye (porphyrin •− ) and heterogeneous TiO 2 particles. 35 However, our photolysis and photodynamic study results demonstrated that the long lifetime of the reductively quenched porphyrin dye (porphyrin •− , τ ∼ minutes), readily obtained in the presence of excess electron donor, can overcome the slow heterointerfacial ET kinetics, effectively increasing the collisional quenching probability of porphyrin •− toward the TiO 2 surface.…”

“…Schematic representation of the TiO 2 -mediated MIOM system showing the process of ET from the photosensitizer to the reduction-catalyst-anchored TiO 2 semiconductor. Adapted from ref . Copyright 2020 American Chemical Society.…”

“…(b) High activation energies for the collisional electron injection process (∼58 kJ/mol, solvated dye → TiO 2 particles) derived from the inefficient ET from the solution-phase porphyrin dye to the heterogeneous TiO 2 particles. Adapted from refs and . Copyright 2020 and 2021, respectively, American Chemical Society.…”

Photochemical CO2-to-Formate/CO Conversion Catalyzed by Half-Metallocene Ir(III) Catalyst and Its Mechanistic Investigation

“…The relatively lower conversion activities of the ternary hybrid can be understood in terms of the lower light-harvesting activity of TiO 2 -bound IrP derived from the considerable light-scattering effects of TiO 2 particles floating in reaction solvent, unlike the homogeneous system. 50,51 The enhanced durability of the ternary hybrid is attributed to the retarded photodegradation of the photosensitizing unit by TiO 2 heterogenization (Figures S11 and S12), as demonstrated by our previous reports. 41,43,46,50,51 This is reminiscent of similar findings in the case of ternary hybrids based on Re(I) catalyst (dye/TiO 2 /Re(I) catalyst).…”