Bimetallic Centers with Open Coordination Sites and Magnetic Nanocomposites for Water Remediation

Karen Ventura, University of Texas at El Paso

Abstract

The development of effective, renewable and environmentally friendly energy sources is essential to supply the growing global energy demands. The use of fossil fuels to fulfill those energy demands have led to the increase of greenhouse gases and water contamination. The extraction of oil and gas requires a large amount of pressurized water, resulting in contaminated water as a byproduct. Meanwhile, ensuring access to clean water is one of the greatest global challenges of this century. ^ The following study is presented in three sections. In the first section, a bimetallic system with open coordination sites that can be used as a platform for the activation of small molecules has been synthesized. Small molecule activation is important to synthesize more energy dense compounds that can later serve as chemical fuels. A quadruply bonded complex W2(DippF) 2K2 with a W2(0) core was synthesized and structurally characterized. The observed W-W distance of 2.407(1) Å, which is longer than previously reported quadruply bonded complexes. DFT calculations were used to elucidate the electronic structure of the unprecedented complex having a D2h symmetry, resulting in a molecular orbital configuration of σ2π2π2δ 2δ2δ2*2 where the HOMO is the δ*. ^ To prepare future generations for the development of new energy sources, we have designed a four-hour physical chemistry laboratory to introduce upper division students to electrochemistry concepts, including mixed-valency and electron-transfer (ET), using cyclic and differential pulse voltammetries. In this laboratory practice, students use a ferrocene dimer consisting of two ferrocene centers covalently bonded through a dimethylethylene bridge as a platform for the measurement of inner-sphere ET. The degree of electronic communication between the ferrocene redox centers is measured by the magnitude of the equilibrium constant of the comproportionation reaction that yields the mixed valent ferrocene dimer. Students measure the difference in E 1/2 from the electrochemistry of the ferrocene dimers and categorize these ferrocene dimers according to the Robin-Day classification. ^ The use of fossil fuels have left a negative environmental impact in sources of fresh water. Water contamination is the result of the use of fracking techniques to extract oil and gas. In an attempt to approach this issue a series of highly efficient water contaminant adsorbents were developed using Ni3(BTC)2 and Co3(BTC)2 metal-organic frameworks (MOFs) and Fe3O4 magnetic nanoparticles (MNPs) to functionalize graphene oxide (GO). XRD results show high crystallinity of the prepared nanomaterials and the successful decoration of Ni3(BTC) 2 and Co3(BTC)2 MOFs over the GO substrate (BTC = benzene-1,3,5- tricarboxylic acid). SEM and TEM imaging show the successful formation of nanoscale MOFs and Fe3O4 MNPs over GO. IR spectroscopy supports the characterization and successful preparation of the Fe3O4/MOF@GO hybrid nanocomposites. The prepared adsorbents were used to sorb methylene blue (MB) as a model for common organic pollutants in water and common ions from a brackish water model (Na +, Ca2+, Mg2+, SO4 –2, SiO3–2). The adsorption capacity for methylene blue of the prepared nanocomposites is improved by an average of 30.52 and 13.75 mg/g for the Co and Ni composite, respectively, when compared to the MOFs parent materials. The adsorption capacity for sulfates improves by 92.1 mg/g for the Co composite and 112.1 mg/g for the Ni composite, when compared to graphene oxide. This adsorption capacity enhancement is attributed to suppressed aggregation through increased dispersive forces in the MOFs due to the presence of GO, formation of nanoscale MOFs over the GO platform, and the hindering of stacking of the graphene layers by the MOFs. Leaching tests show that the release of Co and Ni ions to water is reduced from 105.2 and 220 ppm, respectively, in the parent MOF materials to 0.5 and 16.4 ppm, respectively, in the nanocomposites. These findings show that the newly developed adsorbents can sorb organic pollutants, and target sulfate and silicate anions, which makes them suitable candidates for water and wastewater treatments^

Subject Area

Chemistry

Recommended Citation

Ventura, Karen, "Bimetallic Centers with Open Coordination Sites and Magnetic Nanocomposites for Water Remediation" (2017). ETD Collection for University of Texas, El Paso. AAI10742927.
https://digitalcommons.utep.edu/dissertations/AAI10742927

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