Catalytic carbon-carbon coupling and ceduction using crystalline porous solids for sustainability and environmental applications

Abstract

Three-dimensional porous solid structures, which accrue from the coordination of imidazole-based ion with metal ions and topologically mimic well-known zeolitic materials, afford the potential platform to achieve photocatalytic reactions and organic transformations in environmentally friendly conditions, using transition metals with partially or fully filled 3d orbitals. Cobalt and copper-based zeotypes and metal-organic frameworks (MOFs) have been evaluated for a CrossDehydrogenative Coupling (CDC) reaction under the irradiation of visible light and the presence of molecular oxygen. The highest conversion was obtained for the cobalt-based zeolitic imidazole framework ZIF-9, while the cobalt isomorphously substituted aluminophosphate (CoAlPO-5) did not appear promising. Interesting photocatalytic activities were demonstrated for the copper-based AlPO-5 and MOF.
Aiming to correlate the structural properties to the catalytic performance of the materials, detailed physicochemical and spectroscopic characterization was performed with pXRD, SEM/EDX, BET and ICP. Further investigation of the nature of the active sites was conducted with Electron Paramagnetic Resonance and Diffuse Reflectance UV-VIS. Oxidation states of the transition metals in the scaffolds were identified utilizing XPS, while the occurrence, reversibility and stability between oxidation states were measured in the application of potential with Cyclic Voltammetry to reflect electrochemical behaviour.
ZIF-9 and the rest of the synthesized materials were additionally assessed for catalytic reduction applications with borohydrides. Employed for the conversion of 4-nitrophenol to 4-aminophenol, ZIF-9 outperformed the AlPOs and MOFs and structural & surface characterization was applied to the spent material to probe the changes it undergoes during the reaction. Kinetic studies showed that ZIF-9 performs efficiently as a heterogeneous catalyst, but with the material having been reported for a series of non-catalytic applications in the literature, it was further challenged under dye decolouration reactions. Due to the nature of its structural units, ZIF-9 was applied in aqueous and non-aqueous dye-solutions and achieved decolourisation of Oil-Red-O dye and dyed wastewater.
Overall, ZIF-9, comprising properties from different classes of crystalline porous materials, has superior photocatalytic and catalytic properties for a range of chemical reactions. For this reason, the material has been characterised further for its photocatalytic properties with time-resolved absorption spectroscopy to gain insight into the lifetime of its excited states. Successful modification of its basic structure with graphene suggests an additional role of ZIF-9 in materials’ science and engineering.

More information

Identifiers

ORCID for Robert Raja: orcid.org/0000-0002-4161-7053

Catalogue record

Export record