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18. Influence of N doping on structural and photocatalytic properties of hydrothermally synthesized TiO2/carbon composites

Author

Maletić Marina M., Kalijadis Ana M., Lazović Vladimir, Trifunović Snežana, Babić Biljana M., Dapčević Aleksandra, Kovač Janez, and Vukčević Marija M.

Subjects
tio2/carbon composites, n-doping, surface properties, photocatalytic properties, pharmaceuticals, Chemistry, QD1-999
Abstract

N-doped TiO2/carbon composites (TiO2/CN) with different nitrogen content, were obtained starting from titanium isopropoxide and glucose, and by varying the amount of melamine, added to starting reaction mixture. For comparison, an undoped sample (TiO2/C) was also prepared. Structural and surface characteristics were determined through scanning electron microscopy, thermogravimetric analysis, elemental analysis, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction and nitrogen adsorption– desorption isotherms. The photocatalytic activity of TiO2/CN composites was examined via photocatalytic degradation of methylene blue and multiclass pharmaceuticals from water solution. It was found that N doping of TiO2/carbon composites induced changes in structural and surface characteristics of TiO2/CN composites, improving their adsorption, but decreasing photocatalytic efficiency. Nevertheless, TiO2/CN0.05 composite obtained by the hydrothermal synthesis in the presence of glucose and 0.05 g melamine showed the highest efficiency for removing selected pharmaceuticals and methylene blue from aqueous solutions through the combined processes of adsorption in the dark, and photocatalytic degradation under UV and visible irradiation.

Published
2023
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28. Effects of Hydrogen Dissociation During Gas Flooding on Formation of Metal Hydride Cluster Ions in Secondary Ion Mass Spectrometry.

Author

Ekar, Jernej, Markelj, Sabina, Mozetič, Miran, Zaplotnik, Rok, and Kovač, Janez

Subjects
SECONDARY ion mass spectrometry, COMPLEX ions, METAL clusters, NUCLEAR reactions, ALLOYS, DEPTH profiling
Abstract

The application of hydrogen flooding was recently shown to be a simple and effective approach for improved layer differentiation and interface determination during secondary ion mass spectrometry (SIMS) depth profiling of thin films, as well as an approach with potential in the field of quantitative SIMS analyses. To study the effects of hydrogen further, flooding of H2 molecules was compared to reactions with atomic H on samples of pure metals and their alloys. H2 was introduced into the analytical chamber via a capillary, which was heated to approximately 2200 K to achieve dissociation. Dissociation of H2 up to 30% resulted in a significant increase in the intensity of the metal hydride cluster secondary ions originating from the metallic samples. Comparison of the time scales of possible processes provided insight into the mechanism of hydride cluster secondary ion formation. Cluster ions presumably form during the recombination of the atoms and molecules from the sample and atoms and molecules adsorbed from the gas. This process occurs on the surface or just above it during the sputtering process. These findings coincide with those of previous mechanistic and computational studies. [ABSTRACT FROM AUTHOR]

Published
2024
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45. Phloroglucinol-Based Carbon Quantum Dots/Polyurethane Composite Films: How Structure of Carbon Quantum Dots Affects Antibacterial and Antibiofouling Efficiency of Composite Films

Author

Marković, Zoran M., Milivojević, Dušan, Kovač, Janez, Todorović Marković, Biljana, Marković, Zoran M., Milivojević, Dušan, Kovač, Janez, and Todorović Marković, Biljana

Abstract

Nowadays, bacteria resistance to many antibiotics is a huge problem, especially in clinics and other parts of the healthcare system. This critical health issue requires a dynamic approach to produce new types of antibacterial coatings to combat various pathogen microbes. In this research, we prepared a new type of carbon quantum dots based on phloroglucinol using the bottom-up method. Polyurethane composite films were produced using the swell–encapsulation–shrink method. Detailed electrostatic force and viscoelastic microscopy of carbon quantum dots revealed inhomogeneous structure characterized by electron-rich/soft and electron-poor/hard regions. The uncommon photoluminescence spectrum of carbon quantum dots core had a multipeak structure. Several tests confirmed that carbon quantum dots and composite films produced singlet oxygen. Antibacterial and antibiofouling efficiency of composite films was tested on eight bacteria strains and three bacteria biofilms.

Published
2024

46. Alkaline electrochemical oxygen reduction boosted by trimetallic palladium–copper–gold nanoparticles

Author

Obradović, Maja D., Lačnjevac, Uroš Č., Radmilović, Vuk V., Gavrilović-Wohlmuther, Aleksandra, Kovač, Janez, Rogan, Jelena R., Stevanović, Sanja I., Radmilović, Velimir R., Gojković, Snežana Lj., Obradović, Maja D., Lačnjevac, Uroš Č., Radmilović, Vuk V., Gavrilović-Wohlmuther, Aleksandra, Kovač, Janez, Rogan, Jelena R., Stevanović, Sanja I., Radmilović, Velimir R., and Gojković, Snežana Lj.

Abstract

A Pd-Cu-Au/C nanocatalyst with a low content of Cu (8.2 at %) and Au (4.4 at %), and an average crystallite size of about 2 nm was synthesized by employing a one-pot two-steps borohydride reduction method in the presence of sodium citrate, characterized by energy-dispersive X-ray spectroscopy, X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy and examined for the oxygen reduction reaction (ORR) in an alkaline solution. Pd/C and Pd-Cu/C catalyst with 17 at % Cu, which were synthesized by the same method, and a commercial Pt/C were used for comparison. In addition, Pd-Cu-Au/C and Pd-Cu/C nanocatalysts were treated in acid with a purpose of their dealloying. The electrochemically active surface area of Pd was determined from COads desorption. It was found that the ORR on all catalysts follows first order kinetics with respect to O2 with four electrons transferred per O2 molecule. The catalysts were subjected to a short-term cycling stability test. Pd-Cu/C and Pd-Cu-Au/C were more active for ORR than Pd/C and Pt/C. The acid-treated catalysts exhibited higher activity compared to their untreated counterparts; both initially and after the stability test (up to 1.7 times in specific activity and 2 times in mass activity). The catalyst with the highest specific and mass activity after the stability test was the acid-treated Pd-Cu-Au/C which surpassed Pd/C by a factor of up to 2.5 in specific activity and 5.7 in mass activity. It was concluded that the acid treatment leads to a major dissolution of Cu from the nanoparticles, thus leaving a highly disordered Pd structure exhibiting increased activity for the ORR, while Au stabilizes Pd structure contributing to better performance after the stability test.

Published
2024

47. Antibacterial and Antibiofouling Activities of Carbon Polymerized Dots/Polyurethane and C60/Polyurethane Composite Films

Author

Marković, Zoran M., Budimir Filimonović, Milica, Milivojević, Dušan, Kovač, Janez, Todorović-Marković, Biljana, Marković, Zoran M., Budimir Filimonović, Milica, Milivojević, Dušan, Kovač, Janez, and Todorović-Marković, Biljana

Abstract

The cost of treatment of antibiotic-resistant pathogens is on the level of tens of billions of dollars at the moment. It is of special interest to reduce or solve this problem using antimicrobial coatings, especially in hospitals or other healthcare facilities. The bacteria can transfer from medical staff or contaminated surfaces to patients. In this paper, we focused our attention on the antibacterial and antibiofouling activities of two types of photodynamic polyurethane composite films doped with carbon polymerized dots (CPDs) and fullerene C60. Detailed atomic force, electrostatic force and viscoelastic microscopy revealed topology, nanoelectrical and nanomechanical properties of used fillers and composites. A relationship between the electronic structure of the nanocarbon fillers and the antibacterial and antibiofouling activities of the composites was established. Thorough spectroscopic analysis of reactive oxygen species (ROS) generation was conducted for both composite films, and it was found that both of them were potent antibacterial agents against nosocomial bacteria (Klebsiela pneumoniae, Proteus mirabilis, Salmonela enterica, Enterococcus faecalis, Enterococcus epidermis and Pseudomonas aeruginosa). Antibiofouling testing of composite films indicated that the CPDs/PU composite films eradicated almost completely the biofilms of Pseudomonas aeruginosa and Staphylococcus aureus and about 50% of Escherichia coli biofilms.

Published
2024

48. Designing the thermal processing of Ba(Ti0.8Zr0.2)O3–(Ba0.7Ca0.3)TiO3 thin films from an ethylene glycol-derived precursor.

Author

Konsago, Sabi William, žiberna, Katarina, Ekar, Jernej, Kovač, Janez, and Malič, Barbara

Abstract

Lead-free ferroelectric 0.5Ba(Ti0.8Zr0.2)O3–0.5(Ba0.7Ca0.3)TiO3 (BZT–BCT) thin films on platinized silicon substrates are prepared by a chemical solution deposition route. The solution chemistry involves the use of ethylene glycol and ethanol as solvents for alkaline earth acetates and transition metal alkoxides, respectively. The thermal decomposition of the BZT–BCT xerogel, the crystallization process of BZT–BCT thin films, and their homogeneity are investigated. In the xerogel, the decomposition of the organic residues occurs between 290 °C and 514 °C, followed by the formation of carbonate groups and their decomposition between 580 °C and 775 °C. In the thin films, the sequence of drying and pyrolysis steps, and the concentration of the coating solution influence the formation of carbonate groups and their decomposition upon annealing. Extending the drying and pyrolysis times from 2 minutes to 15 minutes and lowering the concentration of the coating solution from 0.2 M to 0.1 M contribute to an easier thermal decomposition of the carbon residues. Time-of-flight secondary ion mass spectrometry analysis reveals that upon rapid thermal annealing, the decomposition of the carbonate residues in a few tens of nanometres thick BZT–BCT film proceeds from the top downwards, resulting in a pure perovskite phase faster in the thinner films than in thicker ones. The about 100 nm thick BZT–BCT film annealed at 850 °C exhibits a columnar microstructure with a homogeneous distribution of elements across the thickness of the film. [ABSTRACT FROM AUTHOR]

Published
2024
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