In the applied mineralogy group these people work:
prof. Ing. František Kovanda, CSc.
doc. Ing. Barbora Doušová, CSc.
Ing. David Koloušek, CSc.
Ing. Michaela Dvořáková, Ph.D.
Szabolcs Muráth, Ph.D.
Ing. Eva Bedrnová (PGS)
- Migration of heavy metals in the environment
- Layered double hydroxides
Zeolites are crystalline hydrated aluminosilicates of alkaline metals alkaline earth metals. The basic of zeolite structure is anionic frame of Si and Al T-atoms, which are tetrahedral coordinated with oxygen atoms. By reason of electrostatic forces it is not possible to make an Al-O-Al bond. Tetrahedrons form single or multipath circles, thereby cavities with diferent size originate in zeolite structure. These cavities are connected by channels. Non-frames cations are not fixed closely and can be changed for another cations. Zeolites are often used in ion-exchange reactions, have unique properties as sorbents and molecular sieves, and play important role in heterogenous catalysis. Zeolites offer in natural localities and a number of it was prepared synthetically.
Structure of zeolites
In the Department of Solid State Chemistry, a synthesis technology was developed based on the hydrothermal reaction of fly-ashes (from power plants) and certified many use-possibilities of these zeolites (heavy metal cations separation, radioactive isotopes separation from wastewater, use in agriculture, etc.).
What do we study about zeolites?
- preparation of so-called geopolymer zeolites (zeolites A, X and P) from brick tablecloths
- separation of water from the water-ethanol system (preparation of absolute alcohol)
- influencing the sensory properties of wine by natural and synthetic zeolites
- recirculation systems for fish farming.
2. Migration of heavy metals in the environment
With anorganic materials hang together possibility of their utilization besides protection of environment, especially as sorbents of toxic substances. research is focused on study of geochemical properties of arsenic and selenium in natural parts of environment. Additional important aspect is study and characterization of structure-chemical properties of natural and synthetic sorbents matching for disposal of these elements from contaminated areas.
Especially toxic oxoanions of arsenic, antimony and selenium, their geochemical properties, stability in waters and soils, transport through the environment.
Natural materials based on oxides of iron, aluminum and manganese, but especially aluminosilicates (clay minerals) in their original and modified form. These materials are being tested as selective sorbents suitable for removing toxic substances from contaminated areas.
The next part of the research is focused on finding the optimal conditions for decontamination of a specific loaded system and designing the appropriate remediation technology.
Leaks of acid mine waters in the Kutná Hora district (high concentrations of arsenic and iron)
Hydride generation atomic fluorescence spectrometry (HG-AFS) on a PSA 10.055 Millennium Excalibur (manufactured by PSAnalytical, Kent, UK), which allows the determination of trace concentrations of these hydride-forming elements within the detection limit of 10 ppt.
3. Layered double hydroxides
Layered double hydroxides (LDHs), known also as hydrotalcite-like compounds or anionic clays, represent a group of important inorganic materials usable in many applications. Their chemical composition can be expressed by the general formula MII1-xMIIIx(OH)2An-x/n×yH2O where MII and MIII are divalent and trivalent metal cations and An- is an n-valent anion. These compounds have a layered crystal structure composed of positively charged hydroxide layers [MII1-xMIIIx(OH)2]x+ and interlayers containing anions and water molecules. The value of x represents a portion of trivalent metal cations substituted in hydroxide layers and usually corresponds to 0.20 < x < 0.35. Layered double hydroxides exhibit anion-exchange properties; a weak bonding between the hydroxide sheets and interlayer anions enables their exchange for the other ones. At moderate temperatures (up to about 500 °C) layered double hydroxides are decomposed to form mixed oxides of MII and MIII metals. These mixed oxides are rehydrated in aqueous solutions; the rehydration process results in reconstruction of the layered LDH structure and intercalation of anions from the solution into interlayers. This unique property of layered double hydroxides can be employed for preparation of compounds intercalated with various anions and polar molecules or in removal of undesirable components from solutions. The often used group name “hydrotalcite-like compounds” is related to the mineral hydrotalcite (Mg6Al2(OH)16CO3×4H2O). A group of other natural minerals with analogous crystal structure has been described and a great number of synthetic compounds, combining various MII and MIII metal cations in hydroxide layers and various anions intercalated in the interlayers, can be prepared.
Structure of double layered hydroxides
Synthetic hydrotalcite is used mainly in the plastics industry, namely as a component of PVC stabilizing compositions and as a neutralizing agent (acid scavenger) in production of polyolefins. Layered double hydroxides can be applied also as nanofillers for synthesizing polymer-based nanocomposites, in which inorganic nanoparticles dispersed in relatively low concentration in the polymer matrix improve its properties. The representative pharmaceutical application of layered double hydroxides is the hydrotalcite-derived antacid. They are also tested as carriers for drugs and other bio-active substances. Layered double hydroxides are widely used in heterogeneous catalysis, mainly as precursors for preparation of mixed oxide-based catalysts. The anion-exchange properties of layered double hydroxides and their ability to recover the layered crystal structure during rehydration of thermally decomposed products may be utilized for adsorption of undesirable contaminants. Layered double hydroxides represent also a host inorganic structure suitable for intercalation of various anions and molecules, resulting in the preparation of hybrid materials with interesting physical and chemical properties.
Preparation of precursors and mixed oxides for heterogeneous catalysis
Our research is focused on preparation of layered double hydroxides of desired chemical composition and thermal treatment of these precursors including a study of the thermal decomposition, formation of oxide phases and their transformation during heating. We are interested also in the deposition of layered double hydroxides and mixed oxides on metal and ceramic supports. The obtained materials are then studied as catalysts for removal of gaseous pollutants, namely the volatile organic compounds and nitrous oxide.
Preparation of layered double hydroxides intercalated with organic components
We are concerned with synthesis of the host structures and their intercalation with organic anions or molecules, especially the active pharmaceutical ingredients; this research is focused on development of new solid dosage forms. The layered double hydroxides intercalated with organic components are studied also in other applications such as preparation of LDH/polymer nanocomposites and photoactive materials. We are interested also in synthesis of other organic-inorganic hybrid materials.
Supported catalyst with active layer of mixed oxide Co-Mn-Al formed by thermal decomposition of double layered hydroxide prepared on anodic oxidized aluminum network
Arrangement of intercalated paracetamol molecules in the intermediate layer of double layered hydroxide