Synthesis and characterization of zinc oxide nanoparticles-carbon composite derived from pineapple peel wastes for adsorption of methylene blue from solution and photocatalytic activity

Synthetic dye effluent poses substantial environmental issues due to its toxicity. In this work, a biosorbent derived from pineapple peels and modified with zinc oxide nanoparticles namely ZnONPs/PPWB, was prepared for the removal of cationic dyes, specifically methylene blue (MB), from aqueous solution. The ZnONPs/PPWB composite biosorbent was prepared through a facile green synthesis of zinc oxide nanoparticles utilizing pineapple peel wastes as the source of reducing agent and carbon sources, followed by a calcination at a low temperature of 400 °C for 2 h. The properties of the prepared composite biosorbent were characterized using Brunauer-Emmet-Teller (BET) surface area, scanning electron microscopy (SEM), X-ray diffraction (XRD) and fourier transform infra-red (FTIR) analyses. Several key factors, including pH, initial MB concentration, contact time, and biosorbent dosage as well as photocatalytic activity were investigated. The adsorption of MB on ZnONPs/PPWB is well described by the Freundlich model (R² = 0.9842) and follows the Elovich kinetic model (X² = 0.7390). The calculated maximum adsorption capacity of the ZnONPs/PPWB composite biosorbent (q_max = 65.43 mg/g) was 1.85 folds higher compared to the non-composite biosorbent (PPWB) (q_max = 35.21 mg/g) under the following conditions; adsorbent dose of 10 mg/30 mL, pH 7, and initial MB concentration of 20 mg/L. In addition, under solar irradiation, the composite ZnONPs/PPWB biosorbent exhibited the greater MB removal efficiency than non-irradiated ZnONPs/PPWB. In summary, this work highlights the effectiveness and feasibility of transforming agricultural wastes into ZnONPs/PPWB composite biosorbent for the removal of cationic dyes from wastewater.