Impurity Defect Induced Ferromagnetism Investigation of SiO2-Supported NiO Particles

This study examines amorphous SiO2-supported NiO particles by nickel concentration and calcination temperature arrangement to determine photoluminescence emission peaks and magnetic properties. Conventional co-precipitation with thermal calcination was used to produce NiO nanoparticles. Cubic NiO crystallization with single phase was improved by doubling the nickel concentration by calcination at 500 ºC and 600 ºC. Average crystalline size of 72 nm was obtained in the samples where double nickel concentration with calcination temperature at 600 ºC. Granular forms have been observed in all samples, and nickel clusters were shown in the samples where the nickel concentration is twice as high. Green band emission intensity increases with improved NiO crystallinity due to surface oxygen vacancies at 505 nm. It is interesting to observe ferrimagnetism for SiO2-supported NiO particles calcined at 500 ºC. From these results, optimal synthesis procedure and reduction in nucleation growth of NiO nanoparticles was achieved by double nickel concentration with calcination temperature at 600 ºC. Resumen. Este estudio examina partículas de NiO soportadas en SiO2. El estudio comprende la variación de la concentración de níquel y la temperatura de calcinación para determinar los picos de emisión de fotoluminiscencia y las propiedades magnéticas. Se utilizó la coprecipitación convencional con calcinación para producir nanopartículas de NiO. Se mejoró la cristalización cúbica de NiO con fase única al duplicar la concentración de níquel y calcinación a 500 ºC y 600 ºC. Se obtuvo un tamaño cristalino promedio de 72 nm en las muestras donde se duplicó la concentración de níquel con temperatura de calcinación a 600 ºC. Se observaron formas granulares en todas las muestras, y se encontraron agregados de níquel en las muestras donde la concentración de níquel fue el doble. La intensidad de la banda de emisión aumenta con la cristalinidad de NiO debido a las vacantes de oxígeno en la superficie. Es interesante observar el ferrimagnetismo de las partículas de NiO soportadas en SiO2 calcinadas a 500 ºC. A partir de estos resultados, se logró un procedimiento de síntesis óptimo y la reducción del crecimiento de nucleación de nanopartículas de NiO mediante una concentración doble de níquel con una temperatura de calcinación de 600 ºC.

Preparation of Ceria-Coated Silica Nanoparticles and Their Chemical Mechanical Planarization Performance on Si-Face 6H-SiC Substrates

Ceria-coated silica (SiO2/CeO2) composite abrasives were prepared through a novel homogeneous precipitation method using commercial silica (SiO2) sol as the silicon resource and cerium nitrate (Ce(NO3)3) and hexamethylenetetramine (HMT) aqueous mixtures as coating precursors. The phase composition, nano-topography, size distribution, and chemical structure of as-prepared particles were characterized by X-ray diffraction, transmission electron microscopy, Zetasizer Nano ZS90 and Fourier infrared spectra. In addition, the possible coating mechanism was discussed. Then, chemical mechanical planarization behaviors of SiO2 sol, ceria (CeO2) sol, and the novel abrasives and on Si-face (0001) 6H-SiC were investigated by atomic force microscopy. The results indicated that the composite particles were mono-dispersed nano-spheres composed of amorphous SiO2 core and cubic fluorite CeO2 shell, possessing complete core-shell structure and particle size of about 110 nm. CeO2 shell (10 nm) grew on the surface of SiO2 core by formation of Ce-O-Si chemical bonds, forming stable core-shell structure. SiO2/CeO2 composite abrasives provided an exponentially high material remove rate (MRR) of 1207 nm/h and an impressive surface finish with roughness average (Ra) 0.216 nm due to its active chemical property and unique structure.

BaGdF5 Nanophosphors Doped with Different Concentrations of Eu3+ for Application in X-ray Photodynamic Therapy

X-ray photodynamic therapy (XPDT) has been recently considered as an efficient alternative to conventional radiotherapy of malignant tissues. Nanocomposites for XPDT typically consist of two components—a nanophosphor which re-emits X-rays into visible light that in turn is absorbed by the second component, a photosensitizer, for further generation of reactive oxygen species. In this study, BaGdF5 nanophosphors doped with different Eu:Gd ratios in the range from 0.01 to 0.50 were synthesized by the microwave route. According to transmission electron microscopy (TEM), the average size of nanophosphors was ~12 nm. Furthermore, different coatings with amorphous SiO2 and citrates were systematically studied. Micro-CT imaging demonstrated superior X-ray attenuation and sufficient contrast in the liver and the spleen after intravenous injection of citric acid-coated nanoparticles. In case of the SiO2 surface, post-treatment core–shell morphology was verified via TEM and the possibility of tunable shell size was reported. Nitrogen adsorption/desorption analysis revealed mesoporous SiO2 formation characterized by the slit-shaped type of pores that should be accessible for methylene blue photosensitizer molecules. It was shown that SiO2 coating subsequently facilitates methylene blue conjugation and results in the formation of the BaGdF5: 10% Eu3+@SiO2@MB nanocomposite as a promising candidate for application in XPDT.

Activity Trends in the Propane Dehydrogenation Reaction Catalyzed by MIII Sites on an Amorphous SiO2 Model: A Theoretical Perspective

One class of particularly active catalysts for the Propane Dehydrogenation (PDH) reaction are well-defined M(III) sites on amorphous SiO2. In the present work, we focus on evaluating the catalytic trends of the PDH for four M(III) single-sites (Cr, Mo, Ga and In) on a realistic amorphous model of SiO2 using density functional theory-based calculations and the energetic span model. We considered a catalytic pathway spanned by three reaction steps taking place on selected MIII–O pair of the SiO2 model: σ-bond metathesis of propane on a MIII–O bond to form M-propyl and O–H group, a β-H transfer step forming M–H and propene, and the H–H coupling step producing H2 and regenerating the initial M–O bond. With the application of the energetic span model, we found that the calculated catalytic activity for Ga and Cr is comparable to the ones reported at the experimental level, enabling us to benchmark the model and the methodology used. Furthermore, results suggest that both In(III) and Mo(III) on SiO2 are potential active catalysts for PDH, provided they can be synthesized and are stable under PDH reaction conditions.

Formation of Aligned α-Si3N4 Microfibers by Plasma Nitridation of Si (110) Substrate Coated with SiO2

Plasma nitridation of an amorphous SiO2 layer on Si (110) substrate can form well-aligned α-Si3N4 crystallites in fibrous morphology. Nitriding is performed at a temperature in the range of 800–1000 °C by using microwave plasma with a gas mixture of N2 and H2. Raman spectroscopy shows the characteristics of an α-Si3N4 phase without other crystalline nitrides. As shown by scanning electron microscopy, the formed α-Si3N4 microfibers on the Si substrate can be in a dense and straight array nearly along with Si <11¯0>, and can have a length over 2 mm with a diameter in the range of 5–10 μm. Structural characterization of scanning transmission electron microscopy in cross section view reveals that the elongated α-Si3N4 crystallites are formed on the surface of the nitrided SiO2/Si (110) substrate without any interlayers between Si3N4 and Si, and the longitudinal direction of α-Si3N4 appears mainly along <112¯0>, which is approximately parallel to Si <11¯0>.

Porosity of Calcium Silicate Hydrates Synthesized from Natural Rocks

In this work, the suitability of natural raw materials with various modifications of SiO2—granite sawing waste (quartz) and opoka (a mixture of cristobalite, tridymite, quartz, and an amorphous part)—for the 1.13 nm tobermorite and xonotlite synthesis is examined, and their specific surface area, pore diameter and volume, and the predominant pores are determined. Hydrothermal syntheses were carried out at 200 °C for 12 and 72 h from mixtures with a molar ratio of CaO/SiO2 = 1.0. X-ray diffraction analysis, simultaneous thermal analysis, and scanning electronic microscopy were used, which showed that in the lime–calcined opoka mixture the formation of crystalline calcium silicate hydrates takes place much faster than in the lime–granite sawing waste mixture. The high reactivity of amorphous SiO2 results in the rapid formation of 1.13 nm tobermorite and xonotlite (12 h). According to Brunauer, Emmet and Taller (BET) analysis data, this product features a specific surface area of ~68 m2/g, a total pore volume of 245·10−3 cm3/g, and has dominating 1–2.5 nm and 5–20 nm diameter pores. This porosity of the material should provide good thermal insulation properties of the products made from it as no air convection occurs in the fine pores.

Cobalt Oxide on a Nanoporous TUD-1 Catalyst for Methylene Blue Dye Interaction DFT Studies and Degradation

Fenton and Fenton-like advanced oxidation processes (AOP) have been substantially utilized in wastewater treatment for the removal of organic contaminants. The present investigation explores the catalytic activity of cobalt dispersed over nanoporous silicate material (CoO/TUD-1), TUD-1, for the Fenton-type degradation of methylene blue (MB) dye present in wastewater, with hydrogen peroxide (H2O2) as an oxidant. The catalyst, which was prepared using the hydrothermal method, was characterized using analytical and spectroscopic techniques, such as X-ray diffraction (XRD), N2 adsorption–desorption isotherms, UV-visible diffuse reflectance (DR), scanning electron microscope (SEM), transmission electron microscopy (TEM) and Fourier transform infrared (FTIR). The results indicated that the CoO/TUD-1 possessed three-dimensional structures with a high surface area and a pore diameter capable of the uniform dispersion of cobalt species. Density functional theory (DFT) simulations were performed to study the most stable tetra coordinate adsorption configuration of a single Co atom on amorphous SiO2. To understand the geometric and electronic structure of this configuration, electron density differences, Bader charge, and partial density of states were examined. The results obtained from the DFT calculations confirmed the occurrence of electron transfer from the Co atom to the amorphous SiO2. The calculated adsorption energy was found to be -1.58 eV, which indicated that the MB dye was strongly adsorbed by parallel configuration mode and degraded more easily. Further, the addition of a 0.1g/L dose of the prepared CoO /TUD degraded the MB dye effectively (~95%) within 240 min of contact. Thus, CoO/TUD-1 is a potential material for the removal of organic contaminants and the degradation of dyes in wastewater treatment.