Surface-modification of γ-Al2O3 pellets with organic phosphonic acids-quaternary ammonium compounds for adsorptive nitrate removal from water

The increased discharge of nitrate into natural waters, particularly in agriculturally impacted areas, has become a major challenge in water treatment because elevated nitrate concentrations are harmful to both human health and environmental equilibria. Therefore, the objective of this study is to present a novel method for the efficient adsorptive removal of nitrate from water. Regenerable γ-Al 2 O 3 -based adsorbers were prepared by surface functionalization with phosphonate-based quaternary ammonium modifiers synthesized in a two-step reaction. At an initial nitrate concentration of 50 mg L ‒1 , nitrate uptake increased rapidly to about 3.3 mg g ‒1 within 60 min and reached a plateau of about 3.45 mg g ‒1 after 120 min. Langmuir capacities ranged from 9.7 to 13.2 mg g ‒1 , with the highest value obtained for C2TMABr-modified Al 2 O 3 . Competing anions reduced nitrate uptake, with sulfate showing a substantially stronger inhibitory effect than chloride. Regeneration with 16.13 mmol L ‒1 NaCl restored about 95% of the initial adsorption performance after 30 min, and the C2TMABr-modified adsorber retained 93 ± 2% of its initial capacity over the last seven of ten adsorption–desorption cycles. These results show that phosphonate-functionalized γ-Al 2 O 3 pellets provide moderate nitrate uptake combined with practical separability, modifier-dependent selectivity, and good regeneration stability.