Spectroscopic characterization, X-ray molecular structures and cyclic voltammetry study of two (piperazine) cobalt(II) meso-arylporphyin complexes. Application as a catalyst for the degradation of 4-nitrophenol

Hydrogen Evolution Reaction, Electrochemical CO2 Reduction, and Oxidative Photodegradation of Organic Dyes Catalyzed by Co(II) Trimethoxy-Meso-Arylporphyrin

In search of robust catalysts for redox transformations such as the hydrogen evolution reaction (HER) or CO2 to CO reduction, we stepped on the previously reported meso-tetrakis(3,4,5-trimethoxyphenyl)porphyrinato cobalt(II) complex [Co(TTMPP)]. We prepared [Co(TTMPP)] in good yields and characterized it by IR, UV-vis absorption, photoluminescence spectroscopy, and cyclic voltammetry (CV). The [Co(TTMPP)] was used as a homogeneous catalyst for the electrochemical formation of H2 (HER) in DMF (N,N’-dimethylformamide)/TFA (trifluoroacetic acid) and DMF/EtN3BF4 solutions, with high faradic efficiencies (FE). Additionally, the reduction of CO2 to CO in DMF under a CO2 atmosphere was catalyzed in DMF/TFE (TFE = 2,2,2-trifluoroethanol) and DMF/PhOH with high FE and only traces of H2 as a by-product. Turnover frequencies of 15.80 or 9.33 s−1, respectively were determined from CV experiments or controlled potential electrolysis in the presence of 1eq. TFE. They were lower with PhOH as proton source with 13.85 or 8.31 s−1, respectively. Further, [Co(TTMPP)] as a solid catalyst (suspension) allowed the photodecomposition of the organic dyes methylene blue (MB) and rhodamine B (RhB) using H2O2 under visible light irradiation. The photocatalyst was photostable over five cycles. A photocatalytic mechanism was proposed based on trapping experiments of reactive oxygen species.

Synthesis of New Cobalt(III) Meso-Porphyrin Complex, Photochemical, X-ray Diffraction, and Electrical Properties for Photovoltaic Cells

The present work describes the preparation and characterization of a new cobalt(III) porphyrin coordination compound named (chlorido)(nicotinoylchloride)[meso-tetra(para-chlorophenyl)porphyrinato]cobalt(III) dichloromethane monosolvate with the formula [Co^III(TClPP)Cl(NTC)]·CH₂Cl₂ (4). The single-crystal X-ray molecular structure of 4 shows very important ruffling and waving distortions of the porphyrin macrocycle. The Soret and Q absorption bands of 4 are very red-shifted as a consequence of the very distorted porphyrin core. This coordination compound was also studied by fluorescence and cyclic voltammetry. The efficiency of our four porphyrinic compounds-the H₂TClPP (1) free-base porphyrin, the [Co^II(TClPP)] (2) and [Co^III(TClPP)Cl] (3) starting materials, and the new Co(III) metalloporphyrin [Co^III(TClPP)Cl(NTC)]·CH₂Cl₂ (4)-as catalysts in the photochemical degradation was tested on malachite green (MG) dye. The current voltage of complexes 3 and 4 was also studied. Electrical parameters, including the saturation current density (J_s) and barrier height (ϕ_b), were measured.

CO2 to CO Electroreduction, Electrocatalytic H2 Evolution, and Catalytic Degradation of Organic Dyes Using a Co(II) meso-Tetraarylporphyrin

The meso-tetrakis(4-(trifluoromethyl)phenyl)porphyrinato cobalt(II) complex [Co(TMFPP)] was synthesised in 93% yield. The compound was studied by 1H NMR, UV-visible absorption, and photoluminescence spectroscopy. The optical band gap Eg was calculated to 2.15 eV using the Tauc plot method and a semiconducting character is suggested. Cyclic voltammetry showed two fully reversible reduction waves at E1/2 = −0.91 V and E1/2 = −2.05 V vs. SCE and reversible oxidations at 0.30 V and 0.98 V representing both metal-centred (Co(0)/Co(I)/Co(II)/Co(III)) and porphyrin-centred (Por2−/Por−) processes. [Co(TMFPP)] is a very active catalyst for the electrochemical formation of H2 from DMF/acetic acid, with a Faradaic Efficiency (FE) of 85%, and also catalysed the reduction of CO2 to CO with a FE of 90%. Moreover, the two triarylmethane dyes crystal violet and malachite green were decomposed using H2O2 and [Co(TMFPP)] as catalyst with an efficiency of more than 85% in one batch.