Multi-application of fennel (Foeniculum vulgaris) seed composites for the adsorption and photo-degradation of methylene blue in water

This work reports on synthesis of fennel-based composites and their feasibility to remove and photo-degrade methylene blue dye from aqueous solution. Pristine fennel seeds (PFS) was impregnated with iron(III) oxide nanoparticles (Fe2O3 NP) and iron(III)-1,2,3,4-tetracarboxylic acid (Fe-TCA) to yield the composites fennel seeds-nanoparticles (FS-NP) and fennel seeds-tetracarboxylic acid (FS-TCA), respectively. Scanning electron microscope (SEM) images revealed that the surface of the adsorbents appeared to have a rough texture with cavities. Fourier transform infrared spectroscopy (FTIR) spectra confirmed the presence of −OH, −C=O, −COC, −COOH and −CO groups that could easily bind to the dye. The physicochemical characteristics such as cation exchange capacity (CEC) and Brunauer, Emmett and Teller (BET) surface area were enhanced after impregnation compared with PFS. The maximum adsorption capacity recorded at pH 10 for PFS was 13.2 mg/g while for FS-NP and FS-TCA was 32.8 and 42.9 mg/g, respectively This was ascribed to chemical interaction such as hydrogen bond, electrostatic attraction and π-π stacking. The isotherm and kinetic data were best described by Freundlich and pseudo-first order models. Thermodynamic parameters (∆Ho and ∆Go) showed spontaneity and endothermicity respectively. The positive values of ΔSo suggests that there was increased level of freedom at solid/liquid interface. PFS showed no activity for photocatalytic degradation properties while PF-NP and PF-TCA recorded 58.9 and 48.6% efficiencies, respectively. The data revealed that pseudo-second order described the photocatalytic processes of MB better than pseudo-first order kinetics