Mechanisms and reusability potentials of zirconium-polyaziridine-engineered tiger nut residue towards anionic pollutants

Access to fresh water, its availability, and its quality are a global challenge to humanity, largely due to human activities in the environment. Thus, global water security has been jeopardized, requiring urgent remediation to safeguard our very existence. Hence, a novel and facilely engineered zirconium and polyethylenimine adsorbent based on tiger nut residue (TNR) was prepared, and its adsorptive capabilities towards a model dyestuff and nutrient were invested through a batch adsorption method. The developed adsorbent, zirconium-polyethylenimine-engineered tiger nut residue (TNR@PEI–Zr) was characterised by scanning electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction analysis, and X-ray photoelectron spectroscopy to understand its morphology and surface chemistry and predict its adsorption mechanism. TNR@PEI–Zr had a pH point of zero charge (pH zpc ) of 6.7. The introduction of salts inhibited the removal efficiency of Alizarin red (AR) and phosphate (PO 4 3– ) in the order of HCO 3 –  > SO 4 2–  > Cl – . Increasing temperatures (293–313 K) favoured the adsorption process at pH 3. The Langmuir model suited the adsorption processes of both AR and PO 4 3– , implying homogenous and monolayer removal of pollutants with a maximal capacity of 537.8 mg·g −1 and 100.5 mg·g −1 at a dose of 0.01 g, respectively. The rate-determining steps of AR and PO 4 3– followed a pseudo-second-order kinetic model and were thermodynamically spontaneous with an increase in randomness at the solid-solution interface. The adsorbent’s recyclability was notable and outperformed most adsorbents in terms of removal efficiency. TNR@PEI–Zr was found to be stable, and its use in practical wastewater decontamination was effective, ecologically acceptable and free of secondary pollution problems.