Nitrate removal from aqueous solution using watermelon rind derived biochar-supported ZrO2 nanomaterial: Synthesis, characterization, and mechanism

Abstract

Recently, biochar has attracted tremendous research interest for environmental applications. In this study, biochar-derived watermelon rind (WM) was produced via optimal pyrolysis at 500 °C for 2 h, and then improved the adsorption capacity by Zirconium oxide nanoparticles (ZrO2 NPs). The WM@ZrO2 was characterized using X-ray diffraction (XRD), Scanning electron microscopic - Energy-dispersive X-ray spectroscopy (SEM-EDS), and Fourier transform infrared (FTIR). The adsorptive capacities of synthesized ZrO2 NPs were investigated for nitrate as a function of pH, adsorbent dosage, contact time, initial adsorbate concentration, and pyrolysis temperature in the batch experiment. The results showed that a Langmuir isotherm and a pseudo-second-order kinetics model were the best-fit for experimental nitrate data in its non-linear form as correlation coefficients (R2) were 0.985 and 0.998, respectively. The maximum adsorption capacity for the Langmuir isotherm model was 15.196 mg g−1. The proposed mechanism, including electrostatic attraction and ligand exchange, played a dominant role in nitrate adsorption. After testing with the real domestic wastewater, the removal of nitrate for WM@ZrO2 was achieved at 78 %, which was equivalent to the adsorption capacity of 8.1 mg g−1 of adsorbent. Overall, the WM@ZrO2 is proposed as a promising, effective, and environmentally friendly adsorbent in removing nitrate from an aqueous solution.

Keywords

• Nitrate
• ZrO2
• Biochar
• Watermelon rind
• Pyrolysis