The aim of my thesis was to seek the possibility of using clays with positively or negatively charged surfaces to solve certain environmental problems. An experimental part of the thesis was planned, in which I wanted to prepare a zinc-chromium double hydroxide deposited on a glass surface in the form of a thin layer, and further check its adsorption efficiency for binding a certain dye. Due to circumstances connected with epidemic situation, I was not able to do the experimental work, so I focused on the theoretical part of my diploma work. Some current environmental problems and the possible methods to solve them with charged clays are described.
Charged clays are classified as cationic or anionic depending on the charge of the clay layers. The charged surface results in their ability to bind ions with opposite charge from the environment (water or soil) to their solid surface. This is useful, for example, in the development of a novel fertilizer or in the purification of sewage from livestock operations, in the prevention of algal blooms in freshwater by removing phosphate ions from the water, in the treatment of arsenic-containing drinking water, and in the removal of dyes from textile industry wastewater. Layered double hydroxides have another useful ability, they are photocatalytically active and can catalyze the decomposition of some organic molecules, such as textile azo dyes.
There are many analytical methods that are useful for research in the mentioned field. UV-Vis spectroscopy is useful for studying adsorption and photocatalytic efficiency of charged clays. X-ray diffraction is used to confirm the phase obtained after the synthesis of the material, and the changes in the structure after thermal treatment and rehydration. It is known that layered double hydroxides have a so-called memory effect, which means that the layered structure collapses after thermal treatment but rebuilds after rehydration. Thermal treatment at very high temperatures prevents the complete reconstruction of the layer structure after rehydration.