The competitive adsorption of clofibric acid (CFA) and sulfamethoxazole (SMX) on amine-organosilane-modified periodic mesoporous organosilicas (PMOs) along with the coexistence of actual complex of dissolved organic matter (DOM) were systematically investigated. The effects of amine-silane units (1N-, 2N-, and 3N-silane) and the molar loading ratios of amine-silane units (10%, 25%, and 40% of organosilica precursor) were evaluated. 3 N-Silane’s loading rate at 40% provided the highest amine group density and \(\:{pH}_{zpc}\) , resulting in the highest adsorption performance of CFA and SMX. Adsorption rate and capacity of CFA were better than those of SMX, which closely correlated with the hydrogen bonding, attractive electrostatic interaction, and hydrophobic partitioning corresponding to the \(\:\text{log}{K}_{ow}\) and \(\:pK_{a}\) values of the adsorbates. Compared to SMX, CFA’s adsorption onto 40% and 3N-magnetized PMO performed higher competitive adsorption, and solution pH had a lower effect on it. Hydrophilic-like DOM may interact with CFA and SMX only in the aqueous phase, resulting in adsorption reduction in a mixed-solute solution. Interestingly, hydrophobic-like DOM can be co-adsorbed and promote the adsorption of SMX in a mixed-solute solution through multilayer adsorption. While coexisting with the actual mixed DOM complex, the competitive adsorption capacity of CFA was reduced and that of SMX increased. However, a reduction in the CFA adsorption capacity of 3 N-magnetized PMO after regeneration by ethanal extraction was detected due to the collapse of the organosilica structure.
