Cabrera Lafaurie, Wilman A.

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    Synthesis and characterization of porous inorganic adsorbents for the removal of PPCPs via complexation and size exclusion principles
    (2013) Cabrera Lafaurie, Wilman A.; Hernández Maldonado, Arturo J.; College of Engineering; Hernández Rivera, Samuel P.; Martínez Iñesta, María M.; Velazquez Figueroa, Carlos; Department of Chemical Engineering; Cáceres Valencia, Pablo G.
    Pharmaceutical and personal care products (PPCPs) are considered emerging contaminants that present great challenges for their remediation from water systems. Unfortunately, traditional water treatment methods are not suitable for the complete and efficient removal of PPCPs. Recent initiatives to overcome these limitations include, among other things, the removal of PPCPs using adsorption methods that could be easily implemented in traditional treatment facilities. The effort dedicated in the present work was focused on Faujasite synthetic zeolites (type Y) and inorganic-organic pillared clays (IOCs) adsorbents. Upon proper modification, these materials combined essential characteristics (i.e., hydrophobicity, stability, surface functionalization, etc.) in a synergistic way and suitable for the selective removal of groups of small to mid-size PPCPs. IOCs and Faujasite-type synthetic zeolite were modified via incorporation of transition metals (Co2+, Ni2+ or Cu2+) and a cationic surfactant (cetylpyridinium; CPY+) to induce enhanced adsorbate–adsorbent interactions at ambient temperature. In general, the incorporation of the transition metals onto IOCs enhanced the equilibrium adsorption capacities at acidic and natural pH, particularly at low PPCP concentrations. Moreover, non-equilibrium adsorption of salicylic acid, clofibric acid, carbamazepine and caffeine from water onto as-prepared and partially calcined transition metal containing IOCs fixed-beds revealed that both the multicomponent uptakes and selectivities were influenced by the type of transition metal employed and hydrophobicity of the adsorbate surface. For the modified zeolites, the adsorption equilibrium data showed that the best capacities were achieved when a transition metal/surfactant combination was employed. The salicylic acid equilibrium adsorption capacities, for example, increased as follows: (Ni2+, CPY+)-Y < (Na+, CPY+)-Y < (Co2+, CPY+)-Y < (Cu2+, CPY+)-Y. A remarkable selectivity toward salicylic acid over carbamazepine was evident in all cases, but the capacity for the latter also varied upon modification of the zeolite.
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    Adsorption of Hexahydro-1,3,5-Trinitro-1,3,5-Triazina (RDX) on soil and clay mineral surfaces
    (2008) Cabrera Lafaurie, Wilman A.; Mina, Nairmen; College of Arts and Sciences - Sciences; Hernández Rivera, Samuel P.; Muñoz, Miguel A.; Department of Chemistry; Benítez, Jaime
    Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) is an energetic compound that is commonly used as a military explosive. Studies indicate that nitroamines compounds, particularly those exhibiting several NO2 groups or other electronwithdrawing substituents, may adsorb strongly and reversibly from aqueous solutions to natural clay minerals. To determine the fate and transport mechanisms of explosives contained on buried landmines it is essential to understand the adsorption process on soil and clay minerals. In this research, the adsorption behavior of RDX was evaluated in soil samples and clay fractions from the Ap, and A horizons of the Jobos Series at Isabela, Puerto Rico and the University of Puerto Rico Mayaguez (UPRM campus). The clay fraction was separated from the other soil components by centrifugation. We analyzed the mass of solute sorbed per unit mass of soil at equilibrium (µg/g) and the aqueous equilibrium phase solute concentration (L/kg) using high-performance liquid chromatography (HPLC). Adsorption coefficients (Kd ) for the RDX–soil and RDXclay interaction were determined. The adsorption process for RDX-soil was described by the Freundlich model. The higher adsorption coefficient was observed in the UPRM soil (0.99 L/Kg). The Freundlich algorithm also described the adsorption process for RDX-clay interaction. The relative adsorption capacity of the clays for RDX was higher in the A horizon (4.42 L/Kg). These results suggest that adsorption by soil organic matter predominates over adsorption on clay minerals when significant soil organic matter content is present. It was also found that properties like cation exchange capacity, surface area, type of exchangeable cations and clay minerals present in the clay fractions are important factors in the adsorption of RDX on clay and soils. The experimental adsorption enthalpy (∆Hads = -18.46 KJ/mol) found for the RDX-soil interaction, suggests that these interactions are of the Van der Waals type.