Vega Santander, Dariana R.

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    Zeolitic based adsorbents for the removal of siloxanes and derivatives from water
    (2022-06-28) Vega Santander, Dariana R.; Hernández Maldonado, Arturo; College of Engineering; Pagan Torres, Yomaira; Méndez Roman, Rafael; Department of Chemical Engineering; Marin Martin, Carlos
    Low molecular weight siloxanes and derivatives have been identified as problematic compounds in different environments, especially those detected in water bodies. The elimination of these contaminants is essential as it has been determined that they can cause negative impacts on health and the environment. In this matter, two zeolitic based adsorbents were synthesized to verify their potential for the removal of trimethylsilanol (TMS), dimethylsilanediol (DMSD) monomethylsilanetriol (MMST), and dimethyl sulfone (DMSO2). These adsorbent materials possess microporous structures but differ considerably in framework composition (i.e., pure silica zeolite (PSZ) vs. aluminosilicate-AC hierarchical composite). The first adsorbent material was selected for the test based on computational studies on structural interactions between PSZs and siloxanes, a large unidimensional microporous silicate, UTD-1(DON). On the other hand, a functionalized hierarchical Faujasite zeolite/carbon composite (CFAU) was synthesized, combining the hydrophobicity of a carbon phase with a zeolite phase for the effective removal of a series of siloxanes and a derivative. In order to provide electronic fields and enhance specific interactions between de surface and the contaminants, the zeolitic phase of the composite was modified with transition metal cations. The successful synthesis of transition metal functionalized hierarchical zeolites, and its high adsorption capacities toward contaminants from different environments are well documented. Both adsorbent materials (i.e., UTD-1 and CFAU) were fully characterized, and their performance in the siloxanes and derivatives adsorption was evaluated via single and multicomponent batch equilibrium adsorption tests at room temperature neutral pH conditions. Singles component adsorption data showed that UTD-1 has a large uptake capacity toward TMS, and its adsorption mechanism is mainly driven by the interaction with -OH groups present on the UTD-1 surface. Regarding the composite, in general, Ag+-CFAU showed a large uptake capacity toward TMS, DMSD, and DMSO2, but it shows a particular affinity toward DMSO2 mainly due to specific interactions between the metal and this molecule. The multicomponent equilibrium adsorption tests were conducted to understand the interactions between adsorbates and their competition for adsorption sites. These tests revealed that TMS enables significant uptake of other siloxanes and derivatives via co-adsorption.