Bingguang Zhang

Selective Oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid Using O2 and a Photocatalyst of Co-thioporphyrazine Bonded to g-C3N4

Selective oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) is one of the key reactions for producing chemical commodities from biomass and their derivatives. The challenge for this reaction is to develop an efficient catalytic process that can be conducted under mild conditions (room temperature and atmospheric pressure, using oxygen molecules in air as the oxidant) and a recyclable catalyst. Herein we report a photocatalyst of cobalt thioporphyrazine (CoPz) dispersed on g-C3N4 (abbreviated as CoPz/g-C3N4), which exhibits excellent catalytic activity toward the selective oxidation of HMF into FDCA under simulated sunlight using oxygen molecules in air as a benign oxidant. For example, an FDCA yield of 96.1% in an aqueous solution at pH = 9.18 is achieved at ambient temperature and air pressure. At lower pH (4.01), the product generated is 2,5-diformylfuran. Hence, it is possible to control the reaction outcome by control of the pH of the reaction system. g-C3N4 itself is not a suitable catalyst for the selective oxidation because under the experimental conditions g-C3N4 generates hydroxyl radicals that initiate processes that oxidize HMF directly to CO2 and H2O. CoPz on the other hand activates O2 to give singlet oxygen (1O2), which more controllably oxidizes HMF to FDCA albeit at a more moderate yield (36.2%). The strong interaction between the CoPz and g-C3N4 in the CoPz/g-C3N4 catalyst is experimentally evidenced, which not only improves accessibility of the CoPz sites and makes the catalyst recyclable but also disables the hydroxyl radical generation by g-C3N4 and promotes 1O2 generation on the CoPz sites, significantly enhancing the catalytic performance. This study demonstrates the potential for efficient non-noble metal photocatalysts for organic transformations driven by sunlight.

Synergistic photocatalytic performance of cobalt tetra(2-hydroxymethyl-1,4-dithiin)porphyrazine loaded on zinc oxide nanoparticles

A new ZnO/CoPz(hmdtn)4 composite as a highly efficient photocatalyst was successfully prepared by cobalt tetra(2-hydroxymethyl-1,4-dithiin)porphyrazine (CoPz(hmdtn)4) impregnated onto the surface of ZnO nanoparticles, the photocatalytic performance of ZnO/CoPz(hmdtn)4 under both simulated sunlight and visible light (λ ≥ 400 nm) irradiation was assessed by degradation of Rhodamine B (RhB) and phenol in aerated conditions. The ZnO/CoPz(hmdtn)4 manifested much higher photocatalytic activity than pure ZnO and pure CoPz(hmdtn)4, originating from the synergistic effect between CoPz(hmdtn)4 and ZnO. Furthermore, the XPS analysis revealed that there may be strong interaction between CoPz(hmdtn)4 and ZnO. Thereby ZnO/CoPz(hmdtn)4 with excellent stability can maintain high photocatalytic activity over five runs on the basis of the reusability test. The active species generated in the photocatalytic system were verified by electron spin resonance (ESR) technology. A possible mechanism of the synergistic effect between CoPz(hmdtn)4 and ZnO was also proposed.

Photocatalyst of Annulated Binuclear Thioporphyrazine-Enhancing Photocatalytic Performance by Expansion of π-electron System

A novel planar binuclear zinc hexa(2,3-bis(butylthio)) porphyrazine (bi-ZnPz(SBu)6) sharing one benzene ring has been synthesized. In order to assess the photocatalytic activity of bi-ZnPz(SBu)6, it was loaded on neutral Al2O3 to form a composite photocatalyst bi-ZnPz(SBu)6@Al2O3, then the degradation of rhodamine B (RhB) in an aerated suspension under simulated sunlight was carried out. It was discovered that the photocatalytic activity of bi-ZnPz(SBu)6 is two times higher than that of its mononuclear counterpart. A possible mechanism was proposed through theoretical calculation by density functional theory (DFT) and detection of reactive oxygen species by electron spin resonance (ESR) technology. The results show that the HOMO–LUMO energy gap (ΔEH–L) of bi-ZnPz(SBu)6 is much smaller than that of its mononuclear counterpart, which is beneficial to the excitation of energy and electron under irradiation of light. Super-powerful signals of singlet oxygen (1O2) formed by bi-ZnPz(SBu)6 indicated that the energy transfer capacity of bi-ZnPz(SBu)6 was enhanced significantly under irradiation of light while the electron transfer capacity was decreased due to the weakening of the contribution from the active S atoms in the thiobutyl groups in the periphery to the HOMO. This work introduces a novel and promising biomimetic antenna molecule, whose excellent light-harvesting capacity will be favored and admired in the field of solar cells, photocatalysis and photodynamic therapy.

Selective oxidation of benzyl alcohols to benzoic acid catalyzed by eco-friendly cobalt thioporphyrazine catalyst supported on silica-coated magnetic nanospheres

A novel magnetically recoverable thioporphyrazine catalyst (CoPz(S-Bu)8/SiO2@Fe3O4) was prepared by immobilization of the cobalt octkis(butylthio) porphyrazine complex (CoPz(S-Bu)8) on silica-coated magnetic nanospheres (SiO2@Fe3O4). The composite CoPz(S-Bu)8/SiO2@Fe3O4 appeared to be an active catalyst in the oxidation of benzyl alcohol in aqueous solution using hydrogen peroxide (H2O2) as oxidant under Xe-lamp irradiation, with 36.4% conversion of benzyl alcohol, about 99% selectivity for benzoic acid and turnover number (TON) of 61.7 at ambient temperature. The biomimetic catalyst CoPz(S-Bu)8 was supported on the magnetic carrier SiO2@Fe3O4 so as to suspend it in aqueous solution to react with substrates, utilizing its lipophilicity. Meanwhile the CoPz(S-Bu)8 can use its unique advantages to control the selectivity of photocatalytic oxidation without the substrate being subjected to deep oxidation. The influence of various reaction parameters on the conversion rate of benzyl alcohol and selectivity of benzoic acid was investigated in detail. Moreover, photocatalytic oxidation of substituted benzyl alcohols was obtained with high conversion and excellent selectivity, specifically conversion close to 70%, selectivity close to 100% and TON of 113.6 for para-position electron-donating groups. The selectivity and eco-friendliness of the biomimetic photocatalyst give it great potential for practical applications.