Light-Driven Hydrogen Generation from Microemulsions Using Metallosurfactant Catalysts and Oxalic Acid

Abstract

A unique microemulsion-based photocatalytic water reduction system is demonstrated. Iridium- and rhodium-based metallosurfactants, namely, [Ir(ppy)(dhpdbpy)]Cl and [Rh(dhpdbpy)Cl]Cl (where ppy = 2-phenylpyridine and dhpdbpy = 4,4'-diheptadecyl-2,2'-bipyridine), were employed as photosensitizer and proton reducing catalyst, respectively, along with oxalic acid as a sacrificial reductant in a toluene/water biphasic mixture. The addition of 1-octylamine is proposed to initiate the reaction, by coupling with oxalic acid to form an ion pair, which acts as an additional surfactant. Concentration optimizations yielded high activity for both the photosensitizer (240 turnovers, turnover frequency (TOF) = 200 h) and catalyst (400 turnovers, TOF = 230 h), with the system generating hydrogen even after 95 h. Mechanistic insights were provided by gas-phase Raman, electrochemical, and luminescence quenching analysis, suggesting oxidative quenching to be the principle reaction pathway.

Asymmetric Catalysis in Liquid Confinement: Probing the Performance of Novel Chiral Rhodium–Diene Complexes in Microemulsions and Conventional Solvents

“…Over the last decade homogeneous metal catalysis has strongly benefited from microemulsions due to improved solubility of reactants and mass transport as compared with conventional solvents or biphasic reaction media . Most work has focused on industrially relevant transition‐metal‐catalyzed reactions in microemulsions, such as Rh‐catalyzed hydrogenations and hydroformylations, Rh‐ and Pd‐catalyzed disproportionation of dihydroarenes, Rh‐catalyzed cyclotrimerizations of alkynes, photocatalytic water splitting with Ir and Rh complexes, as well as biocatalytic reactions . Besides the use of various enzymes surprisingly little work has been carried out on homogeneous asymmetric catalysis in microemulsions.…”

Air-Sensitive Photoredox Catalysis Performed under Aerobic Conditions in Gel Networks

“…Nature uses confined and compartmentalized environments such as organelles to carry out chemical reactions under mild conditions with precise control of kinetics and selectivity. Over the last few decades, this has served as an inspiration to develop artificial nanoreactors based on directed self-assembly of small molecules through noncovalent interactions. − Within this context, photochemistry can benefit from confined spaces, , for example, when performed in mesoporous inorganic materials, microemulsions, micelles, , vesicles, polyelectrolyte nanoparticles, foams, and gels. , The confinement may improve photochemical processes by influencing key aspects such as light absorption and the lifetime of redox intermediates. , Among the above-mentioned confined media, physical or supramolecular gels are typically made of low molecular weight (LMW) compounds, so-called gelators, self-assembled through noncovalent interactions (e.g., hydrogen bonding, van der Waals, charge transfer, dipolar, p-p stacking), which usually provides reversible gel-to-sol phase transitions as a response to external stimuli. The solid-like appearance and rheological behavior of these materials result from the immobilization of the liquid (major component) into the interstices of a self-assembled matrix (minor component) through high surface tension and capillary forces, making the liquid pools different from homogeneous solutions .…”

Recent Advancements and Future Prospects in Ultrathin 2D Semiconductor-Based Photocatalysts for Water Splitting

“…Subsequently, the research field is also expanding fast and attracting lots of scientists from chemistry and material science to physics and computational science. For example, chemists devote themselves to developing molecular photosensitizers and catalysts as well as establishing the relationship between the structure of materials and the corresponding property for H 2 production systems [34][35][36][37]. For material scientists, they try their best to design and synthesize new architecture materials with high photocatalytic performance [38][39][40].…”