Ortiz Martínez, Krisiam

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    Transition metal based complexation materials for the selective adsorption of contaminants of emerging and concern and metabolites from aqueous solutions
    (2018) Ortiz Martínez, Krisiam; Hernández Maldonado, Arturo J.; College of Engineering; Martínez Iñesta, María M.; Méndez Román, Rafael; Hwang, Sangchul; Department of Chemical Engineering; Hernández, Samuel
    Since the presence of contaminants of emerging concern (CECs) in different water sources was revealed, the development of more efficient technologies for their removal has been a constant challenge for the scientific community. This is due to the complex chemical nature of these CECs and their ubiquitous presence in the environment at trace levels. Technologies based on separation via adsorption with porous materials could present a potential solution to this quandary, but this can only be guaranteed when the materials’ design is addressed from a bottom-up approach. With the intention of providing efficient alternatives, this work focuses on the development of robust porous material-based adsorbents with flexible and tunable surfaces targeted to the removal of particular CECs (both at parts per million and low parts per billion levels). Ordered mesoporous silica adsorbents (SBA-15) and clays (bentonites) were synthesized and their surfaces were modified with organic moieties (aminosilanes and cationic surfactants) and transition metals (Co2+,Ni2+, Cu2+) by using grafting and ion exchange techniques. These modifications were performed in an effort to provide greater hydrophobicity to these adsorbents. There were also used to introduce coordination complex type interactions with the aromatic rings and/or functional groups of the CECs through electron donation and back-donation at ambient conditions. It was demonstrated that these incorporations gave the materials the ability to form unique interactions with the CECs, significantly improving both adsorption capacity and selectivity. The inclusion of these functionalizations not only enhanced uptake capacity and selectivity but also improved the materials' stability. The resulting hybrid materials were evaluated for the adsorption of different pharmaceutical compounds (i.e., naproxen, carbamazepine, salicylic acid and clofibric acid), stimulants (caffeine), industrial chemicals (bisphenol A) and pesticides (2,4-dichlorophenol) from aqueous solutions via batch and fixed-bed studies. In these tests, the effects of solution pH, the presence of multi-component, metabolites and humic acid (as a model of natural organic matter, NOM) were evaluated through the adsorption capacity, selectivity, and competitiveness in these materials. In general, modified mesoporous silica materials revealed greater adsorption capacity and selectivity towards acidic and anionic pharmaceuticals, especially for naproxen. Multicomponent tests showed a decrease in adsorption capacity due to competition between the CECs for the adsorption sites. However, the modified materials exhibited less competition than its unmodified counterparts, due to the presence of more adsorption sites available to interact with the CECs. On the other hand, modified clay materials showed a greater adsorption capacity and selectivity toward bisphenol A, whereas the co-existence of humic acid at moderate concentrations improved the adsorption capacity of these adsorbates as a result of synergistic effects.