Study of the Microstructure of Amorphous Silica Nanostructures Using High-Resolution Electron Microscopy, Electron Energy Loss Spectroscopy, X-ray Powder Diffraction, and Electron Pair Distribution Function

First-Principles Prediction of Amorphous Silica Nanoparticle Surface Charge: Effect of Size, pH, and Ionic Strength

The quantification of surface charge properties of silica nanoparticles is essential for several applications. To determine these properties, many experimental and theoretical methods have been introduced, which are time-consuming and/or challenging to use. In this study, a first-principles approach is developed to determine the surface charge properties of amorphous silica nanoparticles against the nanoparticle size, pH, and ionic strength without relying on experimental data. An amorphous silica nanoparticle of 1.34 nm diameter is simulated by using integrated molecular dynamics and Monte Carlo methods. A detailed analysis of the nanoparticle structure is provided by analyzing the types of silanol groups on the surface. Moreover, a model is developed to estimate the probability distribution of the surface silanol groups based on the nearest neighbor distances and the diameter of the nanoparticle to determine the number of surface silanols on larger nanoparticles. Thereafter, a computational chemistry approach is used to calculate the acid dissociation constants of the corresponding deprotonation reactions. The calculated constants and the point of zero charge value are in excellent agreement with experiments. The surface charge properties of the nanoparticle with various diameters are then estimated by using a mean-field model at different pH and ionic strength values. The results of the developed model are compared to the Poisson-Boltzmann equation as a reference model. The developed model predictions agree well with the reference model for low and mid-electrolyte concentrations (1 and 10 mM) and small nanoparticles (smaller than 100 nm). However, the developed model seems to qualitatively predict the surface charge properties more accurately than the Poisson-Boltzmann model for high electrolyte concentrations.

Reduced Sodium Portions Favor Osteogenic Properties and Cytocompatibility of 45S5-Based Bioactive Glass Particles

Besides its favorable biological properties, the release of sodium (Na) from the well-known 45S5-bioactive glass (BG) composition (in mol%: 46.1, SiO2, 24.5 CaO, 24.5 Na2O, 6.0 P2O5) can hamper its cytocompatibility. In this study, particles of Na-reduced variants of 45S5-BG were produced in exchange for CaO and P2O5 via the sol-gel-route resulting in Na contents of 75%, 50%, 25% or 0% of the original composition. The release of ions from the BGs as well as their impact on the cell environment (pH values), viability and osteogenic differentiation (activity of alkaline phosphatase (ALP)), the expression of osteopontin and osteocalcin in human bone-marrow-derived mesenchymal stromal cells in correlation to the Na-content and ion release of the BGs was assessed. The release of Na-ions increased with increasing Na-content in the BGs. With decreasing Na content, the viability of cells incubated with the BGs increased. The Na-reduced BGs showed elevated ALP activity and a pro-osteogenic stimulation with accelerated osteopontin induction and a pronounced upregulation of osteocalcin. In conclusion, the reduction in Na-content enhances the cytocompatibility and improves the osteogenic properties of 45S5-BG, making the Na-reduced variants of 45S5-BG promising candidates for further experimental consideration.

SiO2 Modification of Silicon Carbide Membrane via an Interfacial In Situ Sol-Gel Process for Improved Filtration Performance

Silicon carbide (SiC) membrane has emerged as a promising class of inorganic ceramic membranes with many advantageous attributes and has been used for a variety of industrial microfiltration (MF) processes. The state-of-the-art industrial manufacturing of SiC membranes based on the particle sintering method can only achieve an average pore size that ranges from 40 nm to a few micrometers, which is still unsatisfactory for ultrafiltration (UF) applications. Thus, the pore size control of SiC membranes remains a focus of continuing study. Herein, we provide an in situ sol-gel modification strategy to tailor the pore size of SiC membranes by a superficial deposition of SiO2 onto the membrane surface and membrane pore channels. Our in situ sol-gel modification method is simple and effective. Furthermore, the physical characteristics and the filtration performance of the membrane can easily be controlled by the in situ reaction time. With an optimal in situ reaction time of 30 min, the average pore size of the membrane can be reduced from macropores (400 nm) to mesopores (below 20 nm), and the retention ability for 20 nm fluorescent PS microspheres can be improved from 5% to 93%; the resultant SiC/SiO2 composite membranes are imparted with water permeance of 77 L·m-2·h-1·bar-1, improved anti-protein-fouling properties, excellent performance, and anti-acid stabilities. Therefore, modified SiC/SiO2 membranes based on the in situ sol-gel process have great potential as UF membranes for a variety of industrial processes.

Revealing the Impact of Micro-SiO2 Filer Content on the Anti-Corrosion Performance of Water-Borne Epoxy Resin

Due to green development in recent years, water-borne epoxy resins (WBE) have become increasingly popular since they generate the lowest level of volatile organic compounds (VOC) during curing. However, because of the large surface tension of water, it is easy to produce voids and cracks during the curing process of the coating. An electrochemical strategy was used in this study to assess the impact of different SiO2 content on the corrosion performance of a WBE coating, in which micron spherical SiO2 particles were synthesized in a liquid phase reduction. The results showed that the synthesized micron spherical SiO2 particles were about 800 ± 50 nm in diameter and in an amorphous state. By hydrophilizing the surfaces of these SiO2 particles, uniform dispersion in an aqueous solvent and a WBE can be achieved. It is important to note that adding a small or excessive amount of SiO2 to a coating will not improve corrosion resistance and may even reduce corrosion resistance. With the appropriate modification of SiO2, corrosion resistance of composite coatings is greatly enhanced, as is the adhesion between the coatings and the metallic substrates. Because the appropriately modified SiO2 can effectively fill the pores that are formed during the curing process, a corrosive medium is less likely to react with the matrix when the medium comes into contact with the matrix. Based on their incorporation content of 3 wt.%, their corrosion resistance is the best after 16 cycles of AC-DC-AC accelerated corrosion tests.

Recovery of Valuable Materials from End-of-Life Photovoltaic Solar Panels

The disposal of end-of-life (EOL) photovoltaic solar panels has become a relevant environmental issue as they are considered to be a hazardous electronic waste. On the other hand, enormous benefits are achieved from recovering valuable metals and materials from such waste. Eventually, physical and chemical processing will become the most important stages during the recycling process. A physical treatment including crushing, grinding, and screening was achieved, and it was observed that a fine fraction of -0.25 mm had the maximum percentage of the required materials. Moreover, the optimum chemical treatment conditions were adjusted to reach the maximum recovery of silver, aluminum, and silicon. The synthesis of silicon oxide, silver oxide, alunite, and K-Alum from leachant solution was performed through a simple route. The structural and morphological properties of the prepared materials were defined by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and field emission scanning electron microscopy (FESEM).

Acquisition and evaluation procedure to improve the accuracy of SAED

The achievement of this work is that fine tuning of experimental and evaluation parameters can improve the absolute accuracy and reproducibility of selected area electron diffraction (SAED) to 0.1% without using internal standard. Due to the proposed procedure it was possible to reach a reproducibility better than 0.03% for camera length between sessions by careful control of specimen height and illumination conditions by monitoring lens currents. We applied a calibration specimen composed of nanocrystalline grains free of texture and providing narrow diffraction rings. Refinements of the centre of the diffraction pattern and corrections for elliptic ring distortions allowed for determining the ring diameters with an accuracy of 0.1%. We analyze the effect of different error sources and reason the achieved absolute accuracy of the measurement. Application of the proposed evaluation procedure is inevitable in case of multicomponent nanocomposites or textured materials and/or having close diffraction rings where application of automated procedures is limited. The achieved accuracy of 0.1% without internal standard is approaching that of routine laboratory XRD, and reduction of instrumental broadening due to the elaborated evaluation procedure allows for separation of close reflections, provides more reliable ring width and thus improved input parameters for further nanostructure analysis as demonstrated on dental enamel bioapatite.

Behavior of Silica Nanoparticles Synthesized from Rice Husk Ash by the Sol-Gel Method as a Photocatalytic and Antibacterial Agent

Silica nanoparticles (SiO₂ NPs) are one of the most well-studied inorganic nanoparticles for many applications. They offer the advantages of tunable size, biocompatibility, porous structure, and larger surface area. Thus, in this study, a high yield of SiO₂ NPs was produced via the chemical treatment of rice husk ash by the sol-gel method. Characteristics of the prepared SiO₂ NPs were validated using different characterization techniques. Accordingly, the phase, chemical composition, morphological, and spectroscopic properties of the prepared sample were studied. The average particle size of the SiO₂ NPs was found to be approximately 60-80 nm and the surface area was 78.52 m²/g. The prepared SiO₂ NPs were examined as photocatalysts for the degradation of methyl orange (MO) dye under UV irradiation. It was found that the intensity of the characteristic absorption band of MO decreased gradually with exposure time increasing, which means the successful photodegradation of MO by SiO₂ NPs. Moreover, the antibacterial activity of obtained SiO₂ NPs was investigated by counting the coliform bacteria in the surface water using the most probable number (MPN) index method. The results revealed that the MPN of coliform bacteria untreated and treated by SiO₂ NPs was estimated to be 170 CFU/100 mL and 10 CFU/100 mL, respectively, resulting in bacterial growth inhibition of 94.12%.

Fabrication, Design and Characterization of 1D Nano-Fibrous SiO2 Surface by a Facile and Scalable Method

In this paper, new 1D nano-fibrous SiO2 with functionalized surfaces is prepared. First, the effect of dispersion on the morphology and the surface properties of the silica SiO2 compounds are investigated. Second, energy dispersive spectrometer (EDS) and variable pressure scanning electron microscope (VP-SEM) show typically pure and fibrous texture on the surface of SiO2. Third, the presence of the bridging oxygen stretching vibration Si–O–Si, as well as the increase in the intensity ratio between Si-OH band and Si-O-Si are revealed by (FTIR) spectroscopy. Furthermore, X-ray diffraction (XRD) validates the conservation of the SiO lattice after chemical treatment through the KOH for both dispersed and non-dispersed samples. In addition, the shift of the XRD main peak (101) is in good agreement with the FTIR results showing the shift of Si-O-Si peak and the increase in the intensity ratio of Si-OH/Si-O-Si. The dispersed SiO2 sample exhibits a promising functionalized surface with satisfactory results in terms of silica nanofibers crystallinity and chemical composition. As a result, gigh resolution transmission electron microscopy (HR-TEM) data corroborate the claim of the presence of SiO2 nanofibers on the surface from 20nm to 250nm. New nano-fibrous SiO2 surfaces will be used to improve interfacial bonding strength between SiO2 compounds and polymer (or organic materials).

Schiff base functionalized silica gel for simultaneous separation and preconcentration of Cu(II), Ni(II), and Cd(II) in pharmaceuticals and water samples

A method for separation and preconcentration of Cu(II), Ni(II), and Cd(II) using N-N'-bis(5-methoxsalicylidene)-2-hydroxy-1,3-propanediamine modified silica gel was improved for aqueous samples and pharmaceuticals. Determination of the analytes was achieved by inductively coupled plasma optic emission spectrometry. The experimental conditions including pH value, sample volume, eluent type and volume, sorbent mass, sample, and eluent flow rates were optimized with univariate and multivariate optimization tools. The relative standard deviations of the method were 2.9% for Cu(II), 3.0% for Ni(II), and 3.3% for Cd(II) with recovery values between 98.8 ± 3.2-101.5 ± 3.0%. The limits of detection were found to be 62.4, 39.5, and 28.2 ng L-1 for Cu(II), Ni(II), and Cd(II), respectively. The accuracy of the suggested procedure was tested with the certified reference material (Certipur ICP multi-element standard solution IV) and addition-recovery experiments. The method was successfully applied to eye drop, anesthetic, serum, tap water, mineral water, and spring water samples.

Magnetic nanostructures functionalized with a derived lysine coating applied to simultaneously remove heavy metal pollutants from environmental systems

The pollution of environmental systems with heavy metals is becoming a serious problem worldwide. These contaminants are one of the main issues in sludge (which is considered waste) and can even have harmful effects if the sludge is not treated properly. Thus, the development of a novel functional magnetic nanoadsorbent based on a derived lysine is reported here, which can be efficiently applied for metal removal from sludge. Magnetic nanoparticles were coated with silica layer and further modified by covalent bonding of derived lysine. The morphology of the nanomaterial, its nano-size and the silica layer thickness were analyzed by transmission electron microscopy. The successful silanization of the lysine derivative to the silica-coated magnetic nanostructures was investigated by several physicochemical characterization techniques, while the magnetic properties were measured with a vibrating sample magnetometer. The synthesized nanostructures were used as adsorbents for simultaneous removal of most critical heavy metals (Cr, Zn, Cu) from real complex sludge suspensions. The main practical adsorption parameters, pH of the native stabilized sludge, adsorbent amount, time, and adsorbent regeneration were investigated. The results show promising adsorption properties among currently available adsorbents (the total equilibrium adsorption capacity was 24.5 mg/g) from the sludge with satisfactory nanoadsorbent reusability and its rapid removal. The stability of the nanoadsorbent in the sludge, an important but often neglected practical parameter for efficient removal, was verified. This work opens up new possibilities for the development of high-quality magnetic nanoadsorbents for metal pollutants applied in various complicated environmental fields and enables waste recovery.