Adsorption and photoactivity performances of copper(II)–benzene‐1,3,5‐tricarboxylate (Cu‐BTC) and zeolitic imidazolate framework (ZIF‐8): effect of humidity

Abstract

AbstractBACKGROUNDIn this study, adsorption properties and photocatalytic activities of Cu‐BTC and ZIF‐8 are explored using an anionic dye, methyl orange (MO), and a cationic dye, methylene blue (MB). Effect of humidity on the stabilities and performances of Cu‐BTC and ZIF‐8 is controlled under 40%, 67% and 84% relative humidity (RH) conditions. Cu‐BTC, ZIF‐8 and humidified samples are characterized by various techniques.RESULTSHumidified samples do not exhibit new X‐ray diffraction (XRD) peaks and significant variations in scanning electron microscopy images and UV–visible diffuse reflectance (UV–Vis DRS) spectra. After degradation experiments, XRD, X‐ray photoelectron spectra and UV–Vis DRS confirm the coexistence of Cu1+ and Cu2+ in Cu‐BTC and the formation of ZnO in ZIF‐8. Reduction in surface area measurements and detection of N and S signals in energy‐dispersive X‐ray analysis prove interaction of MO and MB. Adsorptions of MO and MB are proposed via electrostatic attraction, π–π interaction and hydrogen bonding and conform to pseudo‐second‐order kinetics. Langmuir and Freundlich models describe the adsorption isotherms of MO and MB. Ligand‐to‐metal charge transfer process is principally responsible for the photoactivities of Cu‐BTC and ZIF‐8. Cu‐BTC (84% RH) and ZIF‐8 (84% RH) exhibit the highest performances, following Langmuir–Hinshelwood kinetics. Stability tests of Cu‐BTC, ZIF‐8 and humidified samples imply their reuse abilities.CONCLUSIONThis study correlates structural characteristics and adsorption abilities/photocatalytic performances of Cu‐BTC and ZIF‐8. Results may offer new ideas for the improvement of metal–organic frameworks as adsorbents and photocatalysts. © 2023 Society of Chemical Industry.