True doping levels in hydrothermally derived copper-doped ceria Mužina, Katarina; Kurajica, Stanislav; Dražić, Goran ...
Journal of nanoparticle research : an interdisciplinary forum for nanoscale science and technology,
07/2021, Letnik:
23, Številka:
7
Journal Article
This work brings a thorough investigation of hydrothermally derived ceria nanoparticles doped with copper in a wide range of concentrations: Cu
x
Ce
1-x
O
2
, where
x
= 0, 0.1, 0.2, 0.3, 0.4, and ...0.5, respectively. X-ray diffraction (XRD) analysis showed no additional phases for all samples up to
x
= 0.4, which exceeds the maximum amount of copper incorporated into ceria without the appearance of copper oxide phase reported in the literature. However, the inductively coupled plasma mass spectrometry (ICP-MS) and energy-dispersive X-ray spectroscopy (EDS) analyses showed that copper is incorporated into the ceria crystal lattice in amounts far lower than the nominal. Nevertheless, the addition of copper has a significant influence on the ceria properties. The size of the obtained nanoparticles was determined by transmission electron microscopy (TEM) and it decreases with the increase of the copper amount from 6 nm for the pure sample to 3.8 nm for the 40 mol. % Cu-doped CeO
2
sample. In accordance with the small particle size, the specific surface area, determined from nitrogen adsorption–desorption isotherms at 77 K, is in the range of 196 to 222 m
2
g
−1
. The increase in the copper amount also causes the reduction of the band gap, as determined by UV–Vis reflectance analysis (UV–Vis DRS), and an increase of reducibility, as proven by temperature-programmed reduction by hydrogen (H
2
-TPR).
The aim of this work was to determine how different types of alkaline pretreatment influence the properties of waste almond and hazelnut nutshell, as well as their compatibility with model inorganic ...geopolymer matrixes for the formation of biocomposites with potential use in civil engineering. For alkaline pretreatment, 3, 6 and 9% NaOH water solutions and milk of lime were used under different temperature and time conditions. The rise in the crystallinity index was confirmed by X-ray powder diffraction analysis, while the corroboration of the removal of amorphous and undesirable components was demonstrated through Fourier-transform infrared spectroscopy. Furthermore, the effectiveness of the pretreatments was confirmed via simultaneous differential thermal and thermogravimetric analysis, and the positive change in the morphology of the surface of the waste nutshell (WN) and the deposition of the desired phases was established using scanning electron microscopy. Surface free energy and adhesion parameters were calculated using the Owens, Wendt, Rabel and Kaelble method for WN as fillers and geopolymers as model novel inorganic binders. This research indicates that the 6% NaOH treatment is the optimal pretreatment process for preparing WN as the filler in combination with potassium and metakaolin geopolymer that has been cured at room temperature.
Using a combustion synthesis, the range of achievable textures is broader than using conventional synthesis methods and can be controlled more successfully. As a tool allowing the achievement and ...control of desired textures, here we bring about wet chemistry synthesis using aluminium nitrate nonahydrate (ANN) precursor systematically combined with different fuels (amino acids). The amino acids; glycine (G), alanine (A) and asparagine (N) have been specifically selected in order to show the role of gradual increase in their: (1) molar mass, (2) enthalpy of combustion, (3) amine groups content and (4) ratio to ANN. Detailed (micro) structural and thermal characterisations confirm that the nanocrystalline character and thermomechanical stability were not diminished in the course of this synthesis. The conditions leading to development of different morphologies from gels to powders were found to be heavily under the influence of fuel/oxygen ratio, i.e. of the smouldering versus flaming mechanism of the combustion. Higher content of nitrates (predominately from amino-rich amino acids) strongly promoted auto-combustion behaviour. As-derived alumina precursors have been thermally treated at various temperatures (quenched and soaked), to monitor γ- and α-alumina crystallisation, with respect to the development of morphology. Different texture types have been observed, such as porous wormhole, porous and porous expanded flakes. Higher fuel levels promote specific surface increase. This combustion synthesis allows facile tailoring of nanocrystalline γ-alumina with different morphological features, whereas samples having optimal parameters were suitable for catalyst support application on behalf of rapid sorption performance.
In this work, we bring the first large-scale study of grain growth kinetics of copper-doped ceria nanoparticles. Since most of the notable applications of ceria nanoparticles, such as catalysis or ...solid oxide fuel cells, require its use at elevated temperatures, particle agglomeration and aggregation occur, which diminish the favorable properties of ceria. Doping with copper was chosen as a strategy for the increase of ceria thermal stability. Pure ceria and ceria doped with 10, 20, 30 and 40 mol.% of copper were prepared by hydrothermal synthesis, thermally treated at temperatures in the range between 300 and 700 °C at various annealing times and analyzed using X-ray diffraction analysis and transmission electron microscopy. An isothermal grain growth kinetics analysis was conducted based on the crystallite sizes calculated through the Scherrer equation in order to determine the influence of copper doping on ceria thermal stability. Three temperature ranges with different grain growth regimes and kinetic parameters were defined. The activation energies increase, while the grain growth exponents decrease from low to high temperature range, which is in concordance with the change in the growth mechanism from diffusion to Ostwald-Ripening. It was established that the thermal stability of ceria does not solely depend on the lattice defects introduced by copper, but also on microstructure, porosity and sample preparation. Still, the addition of copper has a positive influence on thermal stability of ceria up to 650 °C, and the sample with 40 mol.% of added copper has the slowest grain growth in the full studied temperature range.
This study presents a novel method for the development of TiO2/reduced graphene oxide (rGO) nanocomposites for photocatalytic degradation of dyes in an aqueous solution. The synergistic integration ...of rGO and TiO2, through the formation of Ti–O–C bonds, offers an interesting opportunity to design photocatalyst nanocomposite materials with the maximum absorption shift to the visible region of the spectra, where photodegradation can be activated not only with UV but also with the visible part of natural solar irradiation. TiO2@rGO nanocomposites with different content of rGO have been self-assembled by the hydrothermal method followed by calcination treatment. The morphological and structural analysis of the synthesized photocatalysts was performed by FTIR, XRD, XPS, UV-Vis DRS, SEM/EDX, and Raman spectroscopy. The effectiveness of the synthesized nanocomposites as photocatalysts was examined through the photodegradation of methylene blue (MB) and rhodamine B (RhB) dye under artificial solar-like radiation. The influence of rGO concentration (5 and 15 wt.%) on TiO2 performance for photodegradation of the different dyes was monitored by UV-Vis spectroscopy. The obtained results showed that the synthesized TiO2@rGO nanocomposites significantly increased the decomposition of RhB and MB compared to the synthesized TiO2 photocatalyst. Furthermore, TiO2@rGO nanocomposite with high contents of rGO (15 wt.%) presented an improved performance in photodegradation of MB (98.1%) and RhB (99.8%) after 120 min of exposition to solar-like radiation. These results could be mainly attributed to the decrease of the bandgap of synthesized TiO2@rGO nanocomposites with the increased contents of rGO. Energy gap (Eg) values of nanocomposites are 2.71 eV and 3.03 eV, when pure TiO2 particles have 3.15 eV. These results show the potential of graphene-based TiO2 nanocomposite to be explored as a highly efficient solar light-driven photocatalyst for water purification.
Zirconium-doped ceria is a promising and extensively researched catalytic material with notable use in three-way catalytic converters, the oxidation of volatile organic compounds and solid oxide fuel ...cells. In this work, pure and zirconium-doped ceria nanoparticles (Ce1−xZrxO2, where x = 0, 0.1, 0.2, and 0.3) were prepared by combustion synthesis using glycine as the fuel and cerium and zirconium nitrate as oxidants. The obtained powders were characterized using X-ray powder diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, differential thermal and thermogravimetric analysis, UV–Vis diffuse reflectance spectroscopy, and X-ray photoelectron spectroscopy. The combustion temperature increases with the increase in zirconium content in the samples, but the XRD patterns exclusively show ceria diffraction peaks. The crystallite sizes are in the range from 25.2 to 11.7 nm, and do not vary substantially after thermal treatment, indicating the good thermal stability of the prepared nanocatalysts. XPS analysis showed that the surface amount of zirconium is lower than the nominal and that the ceria sample with 10 mol. % of zirconium has a higher amount of oxygen vacancies than the 30 mol. % Zr-doped sample. The 10 mol. % Zr-doped sample displays the best catalytic activity in the BTEX (benzene, toluene, ethylbenzene, and o-xylene) oxidation process.
The aim of this work was to derive γ-alumina from gels prepared by hydrolysis of aluminum (Al) sec-butoxide (Asb) chelated with ethyl acetoacetate (Eaa) in various ratios and to determine the effect ...of Eaa on the properties of obtained alumina. Gels and γ-alumina were investigated by nuclear magnetic resonance, X-ray diffraction, scanning electron microscopy and N2 adsorption–desorption isotherms. The results show that the Eaa/Asb ratio greatly affects the gelation process. At higher Eaa/Asb ratios, hydrolysis resistant tris(ethyl acetoacetate)aluminum (III) is formed, causing a less complete gelation process. Aluminum coordination in samples varies from six-fold coordination in tris(ethyl acetoacetate)aluminum (III) to less defined five-fold coordinated sites of Al in the gel. Thermal treatment at 800 °C for 2 h induces γ-Al2O3 crystallization. A partial transformation to α-Al2O3 is observed after thermal treatment at 900 °C for 2 h for some samples. Transformation to α-Al2O3 after thermal treatment at 1000 °C for 2 h is complete for all samples. In addition to thermal stability of samples, the Eaa/Asb ratio also influences morphology of γ-Al2O3 crystallized at 800 °C. In samples with lower Eaa/Asb ratio, particles appear compact, but are cavernous for samples with higher Eaa/Asb ratios.
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•The ethyl acetoacetate to Al sec-butoxide ratio greatly affects the gelation process.•At higher acetoacetate/butoxide ratio, chelate is formed, causing incomplete gelation.•Al coordination varies from six-fold in chelate to five-fold in the gel.•Acetoacetate to butoxide ratio influences thermal stability of γ-Al2O3.•Morphology and texture are dependent on parent gel structure.
Silver nanowires were prepared by the polyol process with ethylene glycol as a solvent and reducing agent, silver nitrate as a silver source, polyvinylpyrrolidone as a growth-directing agent, ...stabilizer and agglomeration prevention agent, and copper chloride as a growth control agent. The product was characterized by UV–Vis spectroscopy, scanning electron microscopy, and X-ray diffraction. The biocidal activity of silver nanowires was investigated using the disc diffusion method on the bacteria Bacillus subtilis and Pseudomonas aeruginosa and the fungi Aspergillus niger and Candida albicans. X-ray diffraction and scanning electron microscopy showed that, in addition to silver nanowires, the product also contains quasi-spherical silver nanoparticles and some silver chloride. Based on the results of UV–Vis spectroscopy and scanning electron microscopy, it was estimated that the diameter of the nanowires is 200–300 nm. Nanowires have shown weak bactericidal and good fungicidal activity. Silver nanowires showed particularly good activity in inhibiting the growth of Candida albicans.
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