Quantum chemical and analytical investigations of radionuclide adsorption

Walsh, Daniel and Griffin, John and Kerridge, Andrew (2021) Quantum chemical and analytical investigations of radionuclide adsorption. Masters thesis, Lancaster University.

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Abstract

Generating electricity by the combustion of fossil fuels is one of the largest contributors to worldwide greenhouse gas emissions. To combat climate change, alternative ways of producing and using energy is essential. Nuclear power is one of the lowest carbon-producing technologies for generating electricity and is considered a viable alternative to conventional power stations for the purpose of meeting typical energy demands. Increased utilisation of nuclear power will result in an increased production of nuclear waste. Management, storage and reprocessing of nuclear wastes create radioactive effluent. There are various methods for the treatment of radioactive effluent, however radionuclide adsorption has distinct advantages in comparison to alternative treatment methods. Graphene oxide has the potential to be an exceptional radionuclide adsorbent for the treatment of radioactive effluent. This research is comprised of computational simulations and analytical studies which aim to elucidate the mechanisms of radionuclide adsorption on various graphene oxide surfaces. The computational component involves the creation of models including graphene oxide, reduced graphene oxide and modified analogues of both. The models are based on structures adapted from current scientific literature and theoretical idealised concepts. The models are modified to improve their adsorption affinity and capacity for the selected radioisotopes 137Cs and 90Sr. Ab initio molecular dynamic simulations are performed to observe the interaction between the models and Cs+ and Sr2+ ions in solution. Visualisation of simulated ion trajectories allows for the identification of the location of adsorption of the ions on the model surfaces. The analytical component of this research involves both material characterisation and adsorption experiments. Graphene oxide is prepared via the Hummer's method and subsequently reduced. These were characterised along with externally sourced equivalents. Analytical characterisation was performed using FTIR, Raman spectroscopy, SEM, EDS, and solid-state NMR. Adsorption experiments were conducted by filtering Cs and Sr solutions through each variant of graphene oxide and a standard molecular sieve for comparison. Quantitative analysis to determine adsorption capacities for each material was performed. The identification of the location of ion adsorption on the surface of the externally sourced graphene variants is attempted using solid state NMR. Movement of a Cs+ towards a fluorine functionalised graphene oxide surface in an AIMD simulation suggests potential attraction of a Cs+ to fluorinated functional groups on the modified graphene oxide surface. Carboxyl group instability shown in AIMD simulations on the basal plane of all carboxyl functionalised graphene oxides suggests that carboxyl groups may only occur on the edges of graphene sheets. The removal of carboxyl groups from the surface of all carboxyl functionalised graphene oxide variants and the absence of attraction between Cs+ and Sr2+ to these variants suggests that stable carboxyl functionalisation is a requirement to provide adequate attractive forces for cation adsorption on graphene oxide.