Quaternary-nitrogen functionalized carbonaceous adsorbent derived from coffee grounds for nitrate removal from aqueous solution

With the rapid development of agriculture and industrialization, nitrate (NO₃^-) contamination has become an increasingly severe global environmental issue. In this study, a nitrogen-doped porous carbon material (Cf-U1Z1-450) was synthesized using coffee grounds as the carbon precursor, with quaternary nitrogen (N-Q) species successfully incorporated <i>via</i> urea-assisted doping. Structural characterization confirmed the effective introduction of N-Q groups, which significantly enhanced the material's adsorption performance. Batch adsorption experiments revealed that Cf-U1Z1-450 exhibited a maximum nitrate adsorption capacity of 0.62 mmol/g under acidic conditions (pH 3). Even under neutral to alkaline conditions (pH 7-11), it still showed considerable uptake, suggesting that N-Q groups remained active at higher pH. Furthermore, fixed-bed column adsorption experiments demonstrated regeneration ability and adsorption stability, with the saturated adsorption capacity remaining nearly unchanged after five adsorption-desorption cycles. These results indicate the crucial role of N-Q functional groups in improving nitrate removal and biomass-derived carbon materials modified with N-Q hold potential for application in nitrate-contaminated water treatment.