Chemie | Biochemie | Medizin
Silja Van Vliet, 2005 | Boll, BE
The concentration of various heavy metals in wastewater has increased during the last decades. Metal ions can be harmful for the environment and are also precious materials. Therefore it is beneficial to remove or gain them from wastewater. In this thesis, metal-organic frameworks (MOFs) and biosorption as adsorption techniques have been examined. The highly porous zirconium-based MOFs, UiO-66(Zr) and UiO-66(Zr)-NH2, were synthesized and tested for their adsorption efficacy of gold, which was up to 51 %. Furthermore, saccharomyces cerevisiae as biosorbent has been used for the adsorption of copper and aluminum. In average, the yeast accumulated 73.4 % of copper and 29.6 % of aluminum. These values are promising for future research and application.
Introduction
The questions treated in this thesis were:
i) What are metal-organic frameworks (MOFs) and how good is their functionality for water purification from metal contaminants?
ii) What is biosorption and how efficient is S. cerevisiae as biomaterial for the removal of different metal contaminants from water?
iii) How can the two methods – metal-organic frameworks and biosorption – be compared?
Methods
Two metal-organic frameworks (MOFs), UiO-66(Zr) and UiO-66(Zr)-NH2, were synthesized with a chemical synthesis method. The material was characterized by nitrogen adsorption isotherm and powder X-ray diffraction. A gold adsorption experiment was conducted using tetrachloroauric acid (100 ppm) as adsorbate and the zirconium-MOFs as adsorbent.
For the biosorption experiment, baker’s yeast and spent brewer’s yeast were washed with deionized water and partially pretreated with ethanol, then frozen. The copper and aluminum adsorption efficacy was tested using coppersulfate pentahydrate and aluminumsuflate decaoctahydrate as adsorbate, each with an initial concentration of 100 ppm.
The remaining metal concentrations were measured with inductively coupled plasma optical emission spectroscopy (ICP-OES).
Results
The characterizations showed the MOFs’ structure and their accessible surface area (1500 m2g-1 for UiO-66(Zr) and 1100 m2g-1 for UiO-66(Zr)-NH2). In 20 hours of incubation, UiO-66(Zr) adsorbed 23 % of the gold whereas UiO-66(Zr)-NH2 could remove 51 %.
Saccharomyces cerevisiae adsorbed in average 73.4 % copper and 29.6 % aluminum in 1 hour incubation time. The living brewer’s yeast was even able to remove 98 % of copper.
Discussion
With the chemical synthesis, two MOFs with zirconium as central atom and (2-amino) terephthalic acid as linker were synthesized. The type of adsorption these MOFs do is physisorption. UiO-66(Zr)-NH2 had, likely due to the amine group, a higher removal efficacy.
The metal accumulation on biomass is possible through ion exchange between the yeast’s cell wall and the metal cations. The effect of the pretreatment stayed unclear. S. cerevisiae seems to be selective, but to proof this, the conducted experiments have to be repeated to reach significance.
Conclusions
Both water purification techniques worked, so the first two questions raised could be answered positively. To compare the MOFs and biosorption and be therefore able to answer the third question, further experiments have to be conducted. The production of MOFs is currently expensive and energy-consuming, but as there is much research going on, these costs might be reduced. Yeast is a waste product of the brewing process and therefore very beneficial for economy and environment. In both cases, MOFs and biosorption, the metal concentration after the adsorption process was still higher than the legal maximum value of the Swiss drinking water regulation. Nevertheless, the results show that with more research these methods have great potential.
Würdigung durch den Experten
Prof. Dr. Beat Zehnder
Silja Van Vliet untersuchte im Hinblick auf Abwasserreinigung die Extraktion von drei ausgewählten Schwermetallen aus wässrigen Lösungen. Als Adsorbentien dienten einerseits Hefekulturen und andererseits selbst synthetisierte zirkonorganische Frameworks. Die anspruchsvolle Organisation, die präzise Ausführung, Auswertung, Interpretation und Dokumentation der umfangreichen und komplexen Arbeit erledigte sie sorgfältig und qualitativ hochstehend. Der Einstieg in naturwissenschaftliches Arbeiten ist Silja Van Vliet gelungen.
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Gymnasium Köniz-Lerbermatt
Lehrer: Dr. Daniel Meierhans