Thesis topic proposal
Examination of chemical properties of complexes formed between toxic heavy metals and humic substances dissolved in aqueous systems


Institute: University of Pannonia
Doctoral School of Chemistry and Environmental Sciences

Thesis supervisor: Erzsébet Szabóné Bárdos
Location of studies (in Hungarian): Environmental and Inorganic Photochemistry Research Group, Center for Natural Sciences, University of Pannonia
Abbreviation of location of studies: PETTK

Description of the research topic:

Humic substances have chemically heterogeneous compositions, they are macromolecules rich in functional groups. They can be considered intermediate products of organic matter mineralization, but are relatively resistant to chemical degradation. They can be found in soils, surface and ground waters, and, according to recent research, also in atmospheric aerosols.
Based on their solubility, we distinguish water-soluble fractions (fulvic acid - solubility in water does not depend on pH, humic acid - soluble in the alkaline range) and water-insoluble fractions (hymatomelanic acid - only soluble in alcohol, humin - completely insoluble).
Humic substances have a significant impact on the properties of natural water systems because they play a direct role in the formation of the physical and chemical environment of water, which ultimately determines its biological composition. Through their diverse functional groups, they increase the solubility, mobility, and reactivity of pollutants, and they can also catalyze their degradation under the influence of sunlight. Humic substances can bind heavy metals (e.g. cadmium, silver, lead, zinc) and aromatic hydrocarbons, thus reducing their toxicity and negative impact on aquatic organisms.
Due to its solubility in natural waters, fulvic acid is the most important fraction, however, due, humic acid cannot be neglected either because of its complex-forming properties; it can effectively participate in detoxification processes.
Humic substances are generally not preferred in wastewater treatment as they reduce the efficiency of the treatment and result in high COD (TOC) values remaining in the water. Although in the first step of wastewater treatment, most of the humic substances are trapped in the sludge, the other part of the dissolved organic matter migrates through all the steps of the technological line. However, there are companies that specifically recommend humic acids to reduce the toxic heavy metal content of wastewater.
Only a few pieces of literature deal with the chemical properties of the complexes formed by humic substances with toxic heavy metals as well as with the effects of various environmental factors (e.g. light) on the complexes.
The aim of the doctoral research is to critically explore the literature background of the topic, to review the applied procedures and methods, and to characterize natural and synthetic humus materials in general (elemental composition, molecular size distribution, functional groups, etc.). The conditions of complex formation with some selected heavy metals should be investigated in detail.
Another part of the work is the exploration of the properties of the formed complexes (stability, reactivity). The photochemical stability and activity of both humic substances and their complexes with heavy metals, as well as their role and impact on the environment, must be studied using light sources emitting in different wavelength ranges.
It is expected that the obtained results will provide important pieces of information for the interpretation of the complex behavior of humus materials, they will promote the extension of their usability, e.g., in agricultural preparations and water treatment.

Required language skills: English
Number of students who can be accepted: 1

Deadline for application: 2023-01-31

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