MODELING COMPETITIVE ADSORPTION OF PHOSPHATE AND SALICYLATE ON THE GOETHITE (210) SURFACE

The long-term goal of our research is to provide the foundational knowledge necessary to design management practices to significantly increase phosphorus (P) use efficiency in agroecosystems. A recent meta-analysis encompassing 162 soil sites distributed worldwide showed that P availability was controlled by iron and aluminum (oxy)hydroxide and organic C content in both acidic and non-acidic soils. This suggests that the P and C cycles are coupled by their interactions on metal (oxy)hydroxide surfaces. Understanding these interactions is critical to preserving ecosystems processes that sustain human, plant, animal and microbial populations.

The experimental component of this research addresses the need to ascertain the amount of competition and reversibility of adsorption as a function of adsorbate concentration and pH. To determine the actual molecular speciation of the adsorbates under each condition, we have performed ATR-FTIR spectroscopic analysis of the samples of the crop residue-derived lignin in the wet and dry states. DFT calculations complement the ATR-FTIR spectra. We have determined possible surface complexes with the lowest potential energy as bidentate binuclear. This result provides a preliminary prediction as to the structure of the adsorbate. Configurations were subjected to frequency analyses (after potential energy minimizations of the structures) in both VASP (3-D periodic) and Gaussian 16 calculations, and the model results compare favorably with experiment.