Dye-Sensitized Photoelectrosynthesis Cells for Benzyl Alcohol Oxidation Using a Zinc Porphyrin Sensitizer and TEMPO Catalyst

Abstract

based DSPEC using a zinc porphyrin (ZnP) sensitizer and a TEMPO organo-catalyst that quite efficiently catalyzes light driven oxidation of methoxybenzyl alcohol into aldehyde. Two dyads ZnP-TEMPO, differing by the anchoring group (carboxylic acid and hydroxamic acid) on ZnP, were prepared and their electrochemical, absorption, emission properties were recorded and quantum chemical modelling was realized. The photovoltaic performances in DSSCs were first examined in order to optimize the dyeing conditions and compare the relative efficiencies of the compounds. The dyads substituted with TEMPO outperform the reference zinc porphyrin lacking TEMPO with a much higher Jsc and Voc. The photocatalytic properties after immobilization on TiO 2 nanocrystalline films towards para-methoxy benzyl alcohol oxidation were explored in borate buffer and in acetonitrile electrolyte. In borate buffer, the optimal pH was 8 and using the dyad ZnP-TEMPO anchored with hydroxamic acid, para-methoxy benzaldehyde was selectively produced with average photocurrent density of 200 A/cm 2 , a faradaic efficiency of 82%, a TON of 26, and a TOF of 47 h -1 . In acetonitrile in presence of 0.1 M of N-methyl-imidazole, the same dyad gives an average photocurrent density of about 100 A/cm 2 , a faradaic efficiency of 76%, a TON of 13, and a TOF of 24 h -1 . The stability of the anchor is crucial in acetonitrile electrolyte, where the dyad is quite soluble, since only the dyad functionalized with hydroxamic acid is compatible with these organic solvent conditions. Overall this study paves the way to the development of more efficient and probably more stable TiO 2 based DSPECs for alcohol oxidation that could advantageously complement those devoted to water oxidation.

Beyond Water Oxidation: Hybrid, Molecular-Based Photoanodes for the Production of Value-Added Organics

“…More interestingly, the hybrid system turns out to be effective in the photo-oxidation of natural lignin in the acetone solution, with measured J of ∼130 μA/cm 2 under comparable experimental conditions. Odobel et al reported the synthesis of a molecular triad based on a ruthenium tris (bipyridine) complex as the photosensitizer, connected on one side to the TEMPO alcohol oxidation catalyst and on the other side to a naphthalenedicarboxyanhydride dicarboximide (NDADI) electron acceptor ( Figure 1H ) ( Nikoloudakis et al, 2021 ). When attached onto nano- ITO, the triad effectively mediates the oxidation of para -methoxybenzyl alcohol in a pH 10 carbonate buffer solution on visible light irradiation at a bias of +0.4 V versus SCE.…”

“…The lower oxidation power required for the transformation of organics can open new opportunities for a plethora of porphyrin dyes which usually require ring functionalization to achieve potentials suitable for water oxidation. Within this framework, one elegant system was recently proposed by Odobel et al, combining a zinc porphyrin and a TEMPO catalyst onto a TiO 2 semiconductor ( Figure 2A ) ( Nikoloudakis et al, 2021 ). The system was successfully applied in the photoelectrochemical oxidation of benzyl alcohol derivatives in the presence of methyl imidazole as the base, with better performances observed in aqueous borate buffer with respect to the acetonitrile solution.…”

“… Hybrid systems discussed in Section 3 based on noble-metal–free and organic components. (A) Adapted with permission from Nikoloudakis et al (2021 ). Copyright 2021 American Chemical Society.…”

“…Copyright 2020 American Chemical Society. (H) Reprinted with permission from Nikoloudakis et al (2021 ). Copyright 2021 John Wiley and Sons.…”

Unraveling the Unique Role of Methyl Position on the Ring-Opening Barrier in Photocatalytic Decomposition of Xylene Isomers

“…Volatile organic compounds (VOCs) are generated and released extensively from modern industries such as petroleum refining, chemical raw material production, and electronic equipment manufacturing. − Xylene isomers ( m -, p -, and o -xylene), as a class of typical aromatic VOCs, are particularly hazardous in causing severe diseases and endangering the ecological environment. − As one of the indispensable technology for air purification, the massive application of photocatalysis in the decomposition of VOCs confirms its great potential. − However, the rapid deactivation is almost inevitable against the accumulation of ring-containing intermediates on the photocatalyst surface during VOC decomposition reactions. − It is definite that the ring-opening reaction is considered to be the rate-determining step for the complete decomposition of aromatic VOCs pollutants. − Thus, the subtle mechanism of the ring-opening reaction requires a comprehensive investigation for the development of deactivation-resistant photocatalysts.…”