Torres Cabán, Roberto José

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    Adsorption of pollutants by spent-coffee-grounds composite beads
    (2020-05-19) Torres Cabán, Roberto José; Vega Olivencia, Carmen A.; College of Arts and Sciences - Sciences; Román Velázquez, Félix R.; Rivera Portalatín, Nilka; Mina Camilde, Nairmen; Department of Chemistry; Román Pérez, Rosa I.
    The use of heavy metals in technological applications has led to detrimental effects on the environment. Activated carbon is commonly used to remove pollutants but it is expensive. Therefore, the research of low-cost alternatives derived from organic wastes is being considered. This study considers the use of Calcium Alginate/Spent Coffee Grounds (CA–SCGs) composite beads to adsorb heavy metals from aqueous solutions. The studied metals were Cu2+, Ni2+ and Cd2+ at concentrations from 10 ppm to 100 ppm. CA–SCGs beads were made of alginate and spent coffee grounds. They were compared with calcium alginate beads (CA beads) and spent coffee grounds (SCGs) in terms of capacity and rate of adsorption. Three cycles of adsorption/desorption were done for Cd2+ and Ni2+. The beads were characterized by Scanning Electron Microscopy coupled with an energy-dispersive X-ray spectroscopy (SEM–EDX), Fourier-transform infrared spectroscopy (FT–IR), Raman spectroscopy, and point of zero charge. Langmuir, Freundlich, and Sips models and a pseudo-second-order kinetic equation were used. Sips model showed the best correlation with the adsorption of CA–SCGs beads with capacities of adsorption of 91.18 mg/g for cadmium, 42.06 mg/g for copper and 20.96 mg/g for nickel. The major advantage of SCGs and CA-SCGs beads versus CA beads is that the adsorption sites of SCGs showed faster adsorption and larger percentages of removal, especially in the lower range of concentrations (10 ppm to 30 ppm). Ion exchange of divalent metals is the main mechanism of adsorption of CA but adsorption onto deprotonated carboxyl and phenolic sites can be the dominant mechanism of SCGs. Paracetamol is one of the most often detected pharmaceutical products in surface water. Paracetamol in the environment can have potential harmful effects. Activated carbon is also an effective adsorbent of paracetamol but it is expensive. Chitosan-Spent Coffee Grounds beads (Chitosan–SCGs beads) were studied to remove paracetamol from an aqueous solution. Cyclic Voltammetry technique was used due its good signal for paracetamol and the wider range of concentrations than can be used without any further process of the sample. The maximum adsorption capacity predicted by the Sips model was 12.71 mg/g.