Rooibos tea waste binary oxide composite: An adsorbent for the removal of nickel ions and an efficient photocatalyst for the degradation of ciprofloxacin.

ABSTRACT

In this study, rooibos tea waste (RTW) incorporated with a binary oxide (BO; Fe2O3-SnO2) has been reported for the first time as a highly efficient adsorbent material for the elimination of Ni(II) ions. The as-synthesised rooibos tea waste-binary oxide (RWBO) composite adsorbent was characterised using miscellaneous techniques such as FTIR, XRD, SEM, EDX, TGA, BET, and XPS. The RWBO was then tested for the removal of Ni(II) in a batch adsorption experiment. The composite adsorbent showed a great removal efficiency of about 99.75% for Ni(II) ions at 45 °C, 180 min agitation time, pH 7, and dosage of 250 mg. The adsorption process was found to be endothermic and spontaneous. Also, the spent adsorbent [RWBO-Ni(II)] was found to be solar light active with a narrow band gap of 1.4 eV. It was further used as a photocatalyst for the photocatalytic abatement of 10 mg/L ciprofloxacin with an extent of degradation of 83% obtained after 150 min. In addition, the extent of mineralisation of the ciprofloxacin by the spent adsorbent as obtained from the TOC data was found to be 64%. Overall, the RWBO composite adsorbent lends itself as an efficient, eco-friendly and promising material for environmental remediation.