Polyaniline-decorated Macadamia nutshell composite: an adsorbent for the removal of highly toxic Cr(VI) and efficient catalytic activity of the spent adsorbent for reuse

Herein, a novel polyaniline-decorated lignocellulose composite adsorbent made by modifying macadamia nutshells (MNS) with polyaniline (PANI) for the uptake of Cr(VI) is reported. The as-synthesised MNS–PANI was characterised using Fourier transform infrared spectroscopy, X-ray diffraction analysis, thermogravimetric analysis, field emission scanning electron microscopy, energy-dispersive X-ray analysis, transmission electron microscopy and Brunauer–Emmett–Teller surface area analysis. Batch adsorption experiments were carried out to investigate the adsorptive behaviour of MNS–PANI with Cr(VI). The uptake of Cr(VI) was well described by a pseudo-second-order kinetics model, while the adsorption isotherm best fitted the Langmuir model with a maximum adsorption capacity of 384.6 mg/g at 45 °C. Thermodynamic parameters obtained revealed endothermic and spontaneous uptake of Cr(VI) by MNS–PANI. The spent adsorbent was further applied for the photocatalytic degradation of ciprofloxacin, and 86% of the pharmaceutical was efficiently degraded within 80 min.