Removal of Naproxen, Salicylic Acid, Clofibric Acid, and Carbamazepine by Water Phase Adsorption onto Inorganic-Organic-Intercalated Bentonites Modified with Transition Metal Cations

Inorganic-organic-intercalated (IO) bentonites were modified with Co2+, Ni2+, or Cu2+ to create adsorbents for the removal of relevant emerging contaminants (naproxen, salicylic acid, clofibric acid, and carbamazepine) from water, overcoming challenges associated with low concentration and polar nature of these contaminants by relying on weak chemical complexation interactions. Characterization of the materials via X-ray diffraction, porosimetry, scanning electron microscopy, thermal gravimetric analysis, and Fourier transform infrared spectroscopy indicated general structural integrity and a metal loading that increases as follows: Ni < Cu < Co. Single-point adsorption experiments were done at room temperature with different pH conditions and using an initial adsorbate concentration of 14 ppm. In general, the transition metal-modified IO bentonites displayed adsorption capacities that varied depending on the type of metal, pH, and nature of the adsorbate. The largest adsorption capacity was observed for salicylic acid, probably because of its smaller footprint. In addition, it appears that the presence of some functional groups plays an important role during the adsorption of a particular adsorbate, possibly indicating complexation with the transition metal. For carbamazepine, although the observed adsorption loadings are comparable to those of other adsorbents discussed elsewhere, the modification of the IO bentonites does not appear to enhance the unmodified material capacity. This could be due to the absence of key functional groups in this particular adsorbate.