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An Investigation into the Adsorption Behavior of Aqueous Metal Ions to Graphene Oxide and Archaeal Surfaces

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posted on 2016-07-15, 00:00 authored by Allison R. Showalter

Remediation and prevention of environmental contamination by toxic metals is an ongoing issue. Halophilic archaeon Halobacterium noricense could be involved with the future potential transport of toxic metals stored in transuranic waste in a salt mine at the Waste Isolation Pilot Plant (WIPP) near Carlsbad, New Mexico, USA. Additionally, improving water filtration systems is necessary to prevent toxic metals from circulating through the water supply. Graphene oxide (GO) is a highly sorptive material for a variety of heavy metals under different ionic strength conditions over a wide pH range, making it a promising candidate for use in metal adsorption from contaminated sites or in filtration systems. We present X-ray absorption fine structure (XAFS) spectroscopy results investigating the binding environment of Cd(II), U(VI) and Pb(II) ions onto multi-layered GO. In addition, cadmium sorption isotherm experiments and XAFS experiments were used to determine how Cd(II) adsorbs to the surface of H. noricense.

This study shows that the binding environment of each metal onto the GO is unique, with different behaviors governing the adsorption as a function of pH. For Cd(II) adsorption to GO, the same mechanism of electrostatic attraction between the GO and the Cd+2 ions surrounded by water molecules prevails over pH range 4.9-8.1. The adsorption of the U(VI) to the GO is through a covalent, inner-sphere bond, showing only subtle changes as a function of pH from 4.0-8.5. Pb(II) adsorption to GO changes with pH across range 5.0-8.3 where the lower pH conditions are dominated by electrostatic, outer-sphere adsorption, while higher pH conditions are dominated by covalent, inner-sphere adsorption.

Adsorption isotherm results show that the amount of Cd(II) adsorption to archaeon H. noricense is relatively constant across the pH range of 5.5-7.5. The XAFS results indicate that the active binding areas on the archaeal cell wall are sulfur sites, with the binding mechanism likely to be via inner-sphere binding with sulfhydryl groups. This would suggest Cd(II) binding to H. noricense will be limited by the surface sulfur sites,

History

Date Modified

2017-06-05

Defense Date

2016-07-08

Research Director(s)

Bruce Bunker

Committee Members

Jeremy Fein Justin Crepp Sylwia Ptasinska

Degree

  • Doctor of Philosophy

Degree Level

  • Doctoral Dissertation

Language

  • English

Program Name

  • Physics

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