Amine-grafted walnut shell for efficient removal of phosphate and nitrate

The presence of emerging pollutants such as PO43- and NO3- in water bodies has attracted worldwide concern about their severe effects on water bodies and the health of humankind in general. Therefore, to preserve the health of humankind and environmental safety, it is of the essence that industrial effluents are treated before they are discharged into water bodies. Amine functionalized walnut shells (ACWNS) were synthesized, characterized, and then tested as a novel adsorbent for PO43- and NO3- removal. The effects of pH, dosage, initial phosphate concentration, interference ions, and temperature on the removal of phosphate and nitrate were investigated. Notably, the adsorption of PO43- and NO3- was exothermic and spontaneous, with a maximum uptake capacity of phosphate and nitrate, at 293 K, 82.2 and 35.7 mg g(-1), respectively. The mechanism by which these ions were adsorbed onto ACWNS could be electrostatic interactions and hydrogen bonding. Pseudo-second-order kinetic model fitted the PO43- and NO3- adsorption, while Freundlich and Langmuir models best fitted the PO43- and NO3- adsorption, respectively. Furthermore, in the binary system, the uptake capacity of phosphate decreased by 14.4% while nitrate witnessed a reduction in its uptake capacity of 10.4%. ACWNS has a higher attraction towards both ions and this could be attributed to the existence of a variety of active areas on ACWNS that exhibit a degree of specificity for the individual ions. Results obtained from real water sample analysis confirmed ACWNS as highly efficient to be utilized for practical remediation processes.

Automated summary

The presence of emerging pollutants like PO43- and NO3- in water bodies has raised global concerns about their impact on water bodies and human health. ACWNS, a novel adsorbent, was found to effectively remove phosphate and nitrate, showing exothermic and spontaneous adsorption. The adsorption mechanism is attributed to electrostatic interactions and hydrogen bonding, with ACWNS demonstrating a higher attraction towards the ions.