Publications by authors named "Vlastimil Matějka"

9 Publications

  • Page 1 of 1

Modification of Graphitic Carbon Nitride with Hydrogen Peroxide.

Nanomaterials (Basel) 2020 Sep 3;10(9). Epub 2020 Sep 3.

Department of Chemistry, VŠB-Technical University of Ostrava, 70800 Ostrava, Czech Republic.

Graphitic carbon nitride (GCN) was synthetized by heating melamine and then it was thermally exfoliated for 1-3 h in air. Both bulk and exfoliated GCN nanomaterials were treated in the 10-30% aqueous solutions of HO for us to study their modification. The light absorption properties were observed by the reddish color and the red-shifts of their UV-Vis spectra. The content of oxygen increased and hydrogen peroxide was supposed to partially oxidize C-OH groups to C=O ones and to form C-O-C groups instead of edge C-NH-C ones. The GCN structure changes were not observed. However, a surface modification of the GCN materials was recognized by their changed photocatalytic activities tested by means of Acid Orange 7 (AO7) and Rhodamines B (RhB), zeta-potentials, and neutralization titration curves.
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http://dx.doi.org/10.3390/nano10091747DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7559342PMC
September 2020

The Effect of Temperature and Milling Process on Steel Scale Utilized as a Pigment for Ceramic Glaze.

Materials (Basel) 2020 Apr 12;13(8). Epub 2020 Apr 12.

Třinecké železázárny, a.s, Průmyslová 1000 Staré Město, 739 61 Třinec, Czech Republic.

This study is focused on the evaluation of the re-utilizability of scale originated during the steel casting and steel rolling processes as a pigment for glazes. Non-oiled scale with FeO as the major phase were used as a coloring component of transparent glaze matrix in: (i) as received state, (ii) thermally pre-treated at 700 and 900 °C, (iii) mechanically treated in planetary ball mill (60, 120 and 240 min) and (iv) mechanically treated in vibratory disc mill (60 and 120 min). Prepared glazes were applied on the surface of ceramic tiles prepared from a commercially available white ceramic slurry. The resulting tiles with given glaze were thermally treated at 800, 900 and 1060 °C. The pigments were characterized by X-ray powder diffraction method (XRD), X-ray fluorescence spectroscopy (XRF), granulometry (PSD), thermogravimetric analysis (TG) and differential thermal analysis (DTA), scanning electron microscopy (SEM/EDAX). The color of the samples was described by the coordinates L*a*b* from CIELAB color space. The results showed that the non-oiled scale is suitable as the pigment for ceramic glazes. Careful control of the scale treatment process (mechanical as well as thermal) together with the temperature of final glaze firing is necessary to obtain the glaze of desired color and quality.
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http://dx.doi.org/10.3390/ma13081814DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7216004PMC
April 2020

Photocatalytic Degradation of Selected Pharmaceuticals Using g-CN and TiO Nanomaterials.

Nanomaterials (Basel) 2019 Aug 23;9(9). Epub 2019 Aug 23.

Department of Chemistry, VŠB Technical University of Ostrava, 17. listopadu 2172/15, 700 33 Ostrava, Czech Republic.

Exfoliated graphitic carbon nitride (g-CN) and two commercially available nanomaterials from titanium dioxide (P25 and CG300) were tested for the photocatalytic degradation of paracetamol (PAR), ibuprofen (IBU), and diclofenac (DIC). Prior to photocatalytic experiments, the nanomaterials were characterized by common methods, such as X-ray diffraction (XRD), UV-VIS diffuse reflectance spectroscopy (DRS), Fourier transformed infrared spectroscopy in attenuated total reflection mode (FTIR-ATR), transmission electron microscopy (TEM), physisorption of nitrogen, and dynamic vapor adsorption (DVS) of water. The sizes and specific surface area (SSA) of the TiO nanoparticles were 6 nm and 300 m·g for CG300 and 21 nm and 50 m·g for P25. The SSA of g-CN was 140 m·g. All photocatalytic experiments were performed under UV (368 nm), as well as VIS (446 nm) irradiation. TiO P25 was the most active photocatalyst under UV irradiation and g-CN was the most active one under VIS irradiation. Photodegradation yields were evaluated by means of high performance liquid chromatography (HPLC) and reaction intermediates were identified using gas chromatography with mass detection (GC-MS). Paracetamol and ibuprofen were totally removed but the intermediates of diclofenac were observed even after 6 h of irradiation. Some intermediates, such as carbazole-1-acetic acid, 2,6-dichloraniline, and hydroxylated derivates of diclofenac were identified. This study showed that g-CN is a promising photocatalyst for the degradation of pharmaceuticals in an aqueous environment, under visible light.
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http://dx.doi.org/10.3390/nano9091194DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6780102PMC
August 2019

Microstructure, Optical and Photocatalytic Properties of TiO₂ Thin Films Prepared by Chelating-Agent Assisted Sol-Gel Method.

J Nanosci Nanotechnol 2016 Jan;16(1):504-14

Single and multilayer TiO₂ thin films coated on two types of soda-lime glass substrates (microscope slides and cylinders) were prepared by a chelating agent-assisted sol-gel method, using ethyl acetoacetate as a chelating agent, dip-coating and calcination at 500 °C for 2 h in air. Phase composition, microstructural, morphological and optical properties of thin films were comprehensively investigated by using XRF, advanced XRD analysis, Raman and UV-vis spectroscopy and AFM. It was found out that the thickness of thin films increases linearly with increasing number of deposited layers, indicating a good adhesion of the titania solution to a glass substrate as well as to a previously calcined layer. 1 layer film crystallized to anatase-TiO₂(B) mixture with minor/negligible amount of nanosized brookite, 2-4 layers films crystallized to anatase-brookite-TiO₂(B) mixture. In contrast to other multilayers films, 4 layers film was highly inhomogeneous. The different phase composition of thin films was clarified based on the crystallization via titanate/s and metastable monoclinic TiO₂(B) as a consequence of several phenomena; the diffusion of Na⁺ ions from a soda-lime glass substrate, acidic conditions and repeated thermal treatment. The multilayer films were in average highly transparent (80-95%) in the visible light region with the sharp absorption edge in the UV light region. Additionally, the photocatalytic properties of selected multilayer films were compared in AO7 photodegradation. Photocatalytic experiments showed that thicker 4 layers film of tricrystalline anatase-brookite-TiO₂(B) phase mixture was similarly active as thinner 3 layers film of similar phase composition, which may be a consequence of the inhomogeneity of the thicker film.
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http://dx.doi.org/10.1166/jnn.2016.10684DOI Listing
January 2016

Photocatalytical nanocomposites: a review.

J Nanosci Nanotechnol 2014 Feb;14(2):1597-616

This review focuses on photocatalytically active nanocomposites that are based on the photoactive nanoparticles, or nanostructured particles captured on the surface of the different powderized carriers. Nanosized and nanostructured oxides and sulfides with selected metal cations (Ti, Zn, Cd, Fe, etc.) are intensively studied as the photocatalysts for different purposes. The nanodimension of these particles brings several disadvantages, among them being the negative impact on human health, which is a widely discussed topic nowadays. The nanoparticles can permeate through living tissue and enter living cells and thus a strong effort focused on diminishing this problem is the subject of research activities by many groups. One possible way to achieve control of the nanoparticles' mobility is capturing them on the surface of suitable particulate carriers with dimensions on the order of tenths and hundredths of microns whereas this approach leads to formation of new composite material. Clay minerals, silicates, carbonaceous materials, and other particulate matter are intensively studied for these purposes and proper selection of the substrate can bring additional functionality to the final composite. Very often the photoactivity, antibacterial properties, electrical conductivity, and other properties are significantly enhanced in the case of this kind of composite materials. Strong adhesion between the nanoparticles and the surface of the selected substrate is essential for the stability of the final composites. Characterization of the adhesion energies using laboratory experiments is quite difficult and molecular modeling can bring valuable information about the character of interactions at the interface of nanoparticles and substrate.
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http://dx.doi.org/10.1166/jnn.2014.9081DOI Listing
February 2014

On airborne nano/micro-sized wear particles released from low-metallic automotive brakes.

Environ Pollut 2011 Apr 17;159(4):998-1006. Epub 2011 Jan 17.

Technical University Ostrava, Nanotechnology Center, Ostrava-Poruba, Czech Republic.

The paper addresses the wear particles released from commercially available "low-metallic" automotive brake pads subjected to brake dynamometer tests. Particle size distribution was measured in situ and the generated particles were collected. The collected fractions and the original bulk material were analyzed using several chemical and microscopic techniques. The experiments demonstrated that airborne wear particles with sizes between 10 nm and 20 μm were released into the air. The numbers of nanoparticles (< 100 nm) were by three orders of magnitude larger when compared to the microparticles. A significant release of nanoparticles was measured when the average temperature of the rotor reached 300°C, the combustion initiation temperature of organics present in brakes. In contrast to particle size distribution data, the microscopic analysis revealed the presence of nanoparticles, mostly in the form of agglomerates, in all captured fractions. The majority of elements present in the bulk material were also detected in the ultra-fine fraction of the wear particles.
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http://dx.doi.org/10.1016/j.envpol.2010.11.036DOI Listing
April 2011

Structural ordering of organovermiculite: experiments and modeling.

J Colloid Interface Sci 2007 Sep 11;313(1):281-7. Epub 2007 May 11.

Nanotechnology Center, VSB-Technical University of Ostrava, 17 Listopadu 15, 708 33 Ostrava-Poruba, Czech Republic.

The ordering of three different sizes of quaternary ammonium salts (QUATs) has been studied with respect to concentration of guests in the host's interlayer gallery. From the modeling, we could verify that small molecules of n-butylammonium salt build a monolayer structure in the vermiculite gallery without reference to concentration. On the other hand, the larger molecules of dodecyltrimethylammonium and dioctadecyldimethylammonium salts are responsive to the numbers of their molecules in the interlayer space of the host, building mono- or bilayered structures. Supersaturated structure of both QUATs keep an arrangement of alkyl chains nearly perpendicular to silicate layers, while only saturated samples exhibit tilted alkyl chains in the gallery. The ordering changes bring out the calculation of mean crystallite size. Low values of the nonbond energy of supersaturated forms predict that those organovermiculites will readily exfoliate, e.g., in polymer/clay nanocomposite.
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http://dx.doi.org/10.1016/j.jcis.2007.04.007DOI Listing
September 2007

Preparation of Mg-vermiculite nanoparticles using potassium persulfate treatment.

J Nanosci Nanotechnol 2006 Aug;6(8):2484-8

Institute of Material Chemistry, VSB - Technical University Ostrava, 17 Iistopadu 15/2172, 70833 Ostrava-Poruba, Czech Republic.

Delamination/exfoliation process of the Mg-vermiculite (Letovice, Czech Republic), particles with size less than 5 microm, was studied after potassium persulfate treatment and compared with known method utilized hydrogen peroxide treatment. X-ray powder diffraction (XRPD) patterns showed that treatment of Mg-vermiculite with different molar concentration of potassium persulfate: c = 0.02, 0.04, and 0.08 mol x dm(-3) at the temperature 60 degrees C for 2 hr caused reduction of relative intensity (I(rel.)) of the basal 001 diffraction to the 15%, 9%, and 4%, respectively, compared to intensity of 001 diffraction of untreated Mg-vermiculite (I(rel.) = 100%). On the other hand I(rel.) of the 001 diffraction of Mg-vermiculite after treatment with 30% and 50% (c = 9.8 and 17.4 mol x dm(-3)) hydrogen peroxide at the 60 degrees C for 2 hr decreased only to I(rel.) = 36% and 32%, respectively. Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) verified effect of potassium persulfate treatment on structure degradation which is connected with higher degree of delamination/exfoliation of the particles and their cracking into nano-sized particles.
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http://dx.doi.org/10.1166/jnn.2006.536DOI Listing
August 2006

Preparation of vermiculite nanoparticles using thermal hydrogen peroxide treatment.

J Nanosci Nanotechnol 2006 Mar;6(3):726-30

Institute of Materials Chemistry, Technical University Ostrava, 17. listopadu 2172, 708 33 Ostrava-Poruba, Czech Republic.

Powdered natural Mg-vermiculite (Letovice, Czech Republic), with the formula (Mg0.35K0.02Ca0.01) (Mg2.39Fe0.51(3+)Fe0.02(2+)Al0.08) (Si2.64Al1.33Ti0.03) O10(OH)2 x 4.97H2O and particle size < 5 microm, was used for the investigation of exfoliation after hydrogen peroxide and/or microwave treatment (600 W). A sample heated in the microwave oven for 40 min exhibits a 11% mass loss and reduction of the 001 peak intensity in the X-ray diffraction pattern. The basal 001 peak intensity of untreated Mg-vermiculite sample (/001 = 100%) drops to 35% in the microwave treated sample. Only the sample treated for 5 h at 80 degrees C fully rehydrated after 120 min at room temperature. A more pronounced reduction of the 001 peak intensity (to 8%) was observed after hydrogen peroxide treatment of the sample at 25 degrees C. The combination of a five-hour hydrogen peroxide treatment at 80 degrees C and subsequent microwave heating leads to an effective extinction of the 001 diffraction in the XRD pattern. The 001 diffraction profile becomes very diffuse with peak intensity less than 1%. The degree of reduction of the 001 diffraction intensity also depends on the time and temperature of hydrogen peroxide treatment and on the peroxide concentration. An even more pronounced reduction of the peak intensity is caused by exfoliation of particles to nano-domains coupled with a randomization of the c-axes.
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http://dx.doi.org/10.1166/jnn.2006.116DOI Listing
March 2006