Abstract：
Calcium (Ca2+) and phosphorous (PO43-) significantly influence the form and effectiveness of nitrogen (N), however, the precise mechanisms governing the adsorption of ammonium nitrogen (NH4+-N) and nitrate nitrogen (NO3--N) are still lacking. This study employed batch adsorption experiments, charge distribution and multi-site complexation (CD-MUSIC) models and density functional theory (DFT) calculations to elucidate the mechanism by which Ca2+ and PO43- affect the adsorption of NH4+-N and NO3--N on the goethite (GT) surface. The results showed that the adsorption of NH4+-N on the GT exhibited an initial increase followed by a decrease as pH increased, peaking at a pH of 8.5. Conversely, the adsorption of NO3--N decreased with rising pH. According to the CD-MUSIC model, Ca2+ minimally affected the NH4+-N adsorption on the GT but enhanced NO3--N adsorption via electrostatic interaction, promoting the adsorption of ≡FeOH-NO3- and ≡Fe3O-NO3- species. Similarly, PO43- inhibited the adsorption of ≡FeOH-NO3- and ≡Fe3O-NO3- species. However, PO43- boosted NH4+-N adsorption by facilitating the formation of ≡Fe3O-NH4+ via electrostatic interaction and site competition. DFT calculations indicates that although bidentate phosphate (BP) was beneficial to stabilize NH4+-N than monodentate phosphate (SP), SP-NH4+ was the main adsorption configuration at pH 5.5-9.5 owing the prevalence of SP on the GT surface under site competition of NH4+-N. The results of CD-MUSIC model and DFT calculation were verified mutually, and provide novel insights into the mechanisms underlying N fixation and migration in soil.
摘要：
钙(Ca2+)和磷(PO43-)显著影响氮(N)的形态和有效性,然而,仍然缺乏控制铵态氮（NH4-N）和硝酸盐氮（NO3--N）吸附的精确机制。本研究采用分批吸附实验，电荷分布和多位点络合（CD-MUSIC）模型和密度泛函理论（DFT）计算阐明了Ca2和PO43-影响NH4-N和NO3-N在针铁矿（GT）表面吸附的机理。结果表明，随着pH值的增加，GT对NH4-N的吸附呈先增加后下降的趋势。在pH值为8.5时达到峰值。相反，随着pH的升高,NO3--N的吸附量下降。根据CD-MUSIC模型,Ca2+对NH4+-N在GT上的吸附影响最小，但通过静电相互作用增强了NO3--N的吸附，促进εFeOH-NO3-和εFe3O-NO3-物种的吸附。同样，PO43-抑制εFeOH-NO3-和εFe3O-NO3-物种的吸附。然而,PO43-通过静电相互作用和位点竞争促进εFe3O-NH4的形成来促进NH4-N的吸附。DFT计算表明，虽然双齿磷酸盐（BP）比单齿磷酸盐（SP）更有利于稳定NH4-N，SP-NH4是pH5.5-9.5时的主要吸附构型，因为在NH4-N的位点竞争下，GT表面上普遍存在SP。CD-MUSIC模型和DFT计算结果相互验证,并为土壤中氮固定和迁移的机制提供了新的见解。
