Abstract
Insights into the adsorption mechanisms of salicylate on goethite, especially its competition with catechol, can further our understanding of the fate and transport of natural organic matter analogues in the environment. The adsorption process was investigated using multiple complementary techniques including batch adsorption experiments, flow-cell ATR-FTIR measurement, and DFT calculations. The macroscopic results show that increasing pH and ionic strength had an adverse effect on salicylate adsorption because of electrostatic interactions. Salicylate formed an inner-sphere complex in a mononuclear monodentate configuration with carboxylate bound to the iron atom on goethite surface within pH 5–9. The electrostatic outer-sphere complex could be observed under high salicylate concentrations and low ionic strength. In the competitive adsorption of salicylate and catechol, their individual interfacial complexes coexisted and competed with each other. The surface salicylate could be replaced by catechol during adsorption under neutral and basic pH conditions. Accordingly, the macroscopic adsorption capacity of salicylate was depressed in the binary system.
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