Photocatalytic H2 generation based on noble-metal-free binuclear cobalt complexes using visible-light

Abstract

Two new binuclear cobalt complexes, namely {[Co(dmgH)(dmgH₂)]₂L1} (I) and {[Co(dmgH)(dmgH₂)]₂L2} (II) (dmgH = dimethylglyoximate monoanion; dmgH₂ = dimethylglyoxime, L1 = 1,3-bis(4-pyridyl)propane), L2 = 1,3-bis(imidazol-1-ylmethyl)benzene), have been synthesized by the self-assembly of [Co(dmgH)(dmgH₂)] and L1 or L2, respectively. An efficient photocatalytic system was constructed by combining a noble-metal-free cobalt complex as the catalyst with Eosin Y dye (EY²⁻) as the photosensitizer to give an efficient H₂ generating system under visible-light irradiation (λ > 420 nm) using triethanolamine (TEOA) as a sacrificial electron donor. The maximum amount of H₂ generated was 1013 TON for I and 1134 TON for II over a 2 h irradiation period (λ > 420 nm) under the conditions of pH 8.0, 5% TEOA (v/v), an EY²⁻ concentration of 4.0 × 10⁻⁴ M and a catalyst concentration of 4.0 × 10⁻⁴ M in the mixed solvent system of CH₃CN–H₂O (3 : 1, v/v). In addition, the mechanism of H₂ generation in the photolysis system was briefly discussed.