Colloidal Stability of Silica-Modified Magnetite Nanoparticles: Comparison of Various Dispersion Techniques.
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SUBMITTER: Dzhardimalieva G
PROVIDER: S-EPMC8708453 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Using model catalysts with well-defined particle sizes and morphologies to elucidate questions regarding catalytic activity and stability has gained more interest, particularly utilizing colloidally prepared metal(oxide) particles. Here, colloidally synthesized iron oxide nanoparticles (Fe x O y -NPs, size ?7 nm) on either a titania (Fe x O y /TiO2) or a silica (Fe x O y /SiO2) support were studied. These model catalyst systems showed excellent activity in the Fischer-Tropsch to olefin (FTO) reaction at high pressure. However, the Fe x O y /TiO2 catalyst deactivated more than the Fe x O y /SiO2 catalyst. After analyzing the used catalysts, it was evident that the Fe x O y -NP on titania had grown to 48 nm, while the Fe x O y -NP on silica was still 7 nm in size. STEM-EDX revealed that the growth of Fe x O y /TiO2 originated mainly from the hydrogen reduction step and only to a limited extent from catalysis. Quantitative STEM-EDX measurements indicated that at a reduction temperature of 350 °C, 80% of the initial iron had dispersed over and into the titania as iron species below imaging resolution. The Fe/Ti surface atomic ratios from XPS measurements indicated that the iron particles first spread over the support after a reduction temperature of 300 °C followed by iron oxide particle growth at 350 °C. Mössbauer spectroscopy showed that 70% of iron was present as Fe2+, specifically as amorphous iron titanates (FeTiO3), after reduction at 350 °C. The growth of iron nanoparticles on titania is hypothesized as an Ostwald ripening process where Fe2+ species diffuse over and through the titania support. Presynthesized nanoparticles on SiO2 displayed structural stability, as only ?10% iron silicates were formed and particles kept the same size during in situ reduction, carburization, and FTO catalysis.
| S-EPMC7315821 | biostudies-literature
Project description:BackgroundMesoporous silica (MPS) nanoparticles (NPs), which have a unique pore structure and extremely large surface area and pore volume, have received much attention because of their biomedical application potential. Using MPS NPs for biomedical devices requires the verification of their biocompatibility because the surface area of NPs is one of the most important determinants of toxicity, including the cellular uptake and immune response. We have previously reported that the cytotoxicity and inflammation potential of MPS NPs have been shown to be lower than those of general amorphous colloidal silica (Col) NPs in macrophages, but the low cytotoxicity does not guarantee high biocompatibility in vivo. In this study, we compared the in vivo immunotoxicity of MPS and Col NPs in the mouse model to define the effects of pore structural conditions of silica NPs.Materials and methodsBoth MPS and Col NPs (2, 20, and 50 mg/kg/day) were intraperitoneally administered in female BALB/c mice for 4 weeks, and clinical toxicity, lymphocyte population, serum IgG/IgM levels, and histological changes were examined.ResultsThere was no overt sign of clinical toxicity in either MPS- or Col-treated mice. However, MPS NPs led to significant increases in liver and spleen weight and splenocyte proliferation. Mice treated with MPS NPs showed altered lymphocyte populations (CD3(+), CD45(+), CD4(+), and CD8(+)) in the spleen, increased serum IgG and IgM levels, and histological changes. Despite slight changes in lymphocyte populations in the spleen, Col NPs did not alter other immunological factors.ConclusionThe results indicate that in vivo exposure to MPS NPs caused more damage to systemic immunity than that of Col NPs through the dysregulation of the spleen. The results for in vivo data are inconsistent with those for in vitro data, which show lower cytotoxicity for MPS NPs. These results suggest the importance of verifying biocompatibility both in vitro and in vivo during the design of new nanomaterials.
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Project description:RationaleAntibiotics have been detected worldwide in the aquatic environment. Moreover, certain classes of antibiotics have been repurposed for the management of COVID-19, which increased their use and presence in wastewater. Their occurrence even in low concentrations leads to the development of antibiotic resistance.MethodologyMagnetite pectin nanoparticles (MPNP) were fabricated and compared to an established model of mesoporous silica nanoparticles (MSNP). Our studied adsorbate is levofloxacin, a fluoroquinolone antibiotic, commonly used in managing COVID-19 cases.ResultsThe influence of various factors affecting the adsorption process was studied, such as pH, the type and concentration of the adsorbent, contact time, and drug concentration. The results illustrated that the optimum adsorption capacity for antibiotic clearance from wastewater using MPNP was at pH 4 with a contact time of 4 h; while using MSNP, it was found to be optimum at pH 7 with a contact time of 12 h at concentrations of 10 µg/mL and 16 g/L of the drug and nanoparticles, respectively, showing adsorption percentages of 96.55% and 98.89%. Drug adsorption equilibrium data obeyed the Sips isotherm model.Discussion and conclusionHPLC assay method was developed and validated. The experimental results revealed that the MPNP was as efficient as MSNP for removing the antibacterial agent. Moreover, MPNP is eco-friendly (a natural by-product of citrus fruit) and more economic as it could be recovered and reused. The procedure was evaluated according to the greenness assessment tools: AGREE calculator and Hexagon-CALIFICAMET, showing good green scores, ensuring the process's eco-friendliness.
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Project description:Silica nanoparticles (SNPs) belong to the most widely produced nanomaterials nowadays. Particle size distribution (PSD) is a key property of SNPs that needs to be accurately determined for a successful application. Many single particle and ensemble characterization methods are available for the determination of the PSD of SNPs, each having different advantages and limitations. Since most preparation protocols for SNPs can yield bimodal or heterogeneous PSDs, the capability of a given method to resolve bimodal PSD is of great importance. In this work, four different methods, namely transmission electron microscopy (TEM), dynamic light scattering (DLS), microfluidic resistive pulse sensing (MRPS) and small-angle X-ray scattering (SAXS) were used to characterize three different, inherently bimodal SNP samples. We found that DLS is unsuitable to resolve bimodal PSDs, while MRPS has proven to be an accurate single-particle size and concentration characterization method, although it is limited to sizes above 50 nm. SAXS was found to be the only method which provided statistically significant description of the bimodal PSDs. However, the analysis of SAXS curves becomes an ill-posed inverse mathematical problem for broad size distributions, therefore the use of orthogonal techniques is required for the reliable description of the PSD of SNPs.
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Project description:Highly selective porous films were prepared by spin-coating deposition of colloidal silica nanoparticles on an appropriate macroporous substrate. Silica nanoparticles very homogenous in size were obtained by sol-gel reaction of a metal oxide silica precursor, tetraethyl orthosilicate (TEOS), and using polystyrene-block-poly(ethylene oxide) (PS-b-PEO) copolymers as soft-templating agents. Nanoparticles synthesis was carried out in a mixed solvent system. After spin-coating onto a macroporous silicon nitride support, silica nanoparticles were calcined under controlled conditions. An organized nanoporous layer was obtained characterized by a depth filter-like structure with internal porosity due to interparticle voids. Permeability and size-selectivity were studied by monitoring the diffusion of probe molecules under standard conditions and under the application of an external stimulus (i.e., electric field). Promising results were obtained, suggesting possible applications of these nanoporous films as selective gates for controlled transport of chemical species in solution.
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Project description:An attempt was made to control the surface charge of colloidal silica nanoparticles with 20 nm and 100 nm diameters. Untreated silica nanoparticles were determined to be highly negatively charged and have stable hydrodynamic sizes in a wide pH range. To change the surface to a positively charged form, various coating agents, such as amine containing molecules, multivalent metal cation, or amino acids, were used to treat the colloidal silica nanoparticles. Molecules with chelating amine sites were determined to have high affinity with the silica surface to make agglomerations or gel-like networks. Amino acid coatings resulted in relatively stable silica colloids with a modified surface charge. Three amino acid moiety coatings (L-serine, L-histidine, and L-arginine) exhibited surface charge modifying efficacy of L-histidine > L-arginine > L-serine and hydrodynamic size preservation efficacy of L-serine > L-arginine > L-histidine. The time dependent change in L-arginine coated colloidal silica was investigated by measuring the pattern of the backscattered light in a Turbiscan™. The results indicated that both the 20 nm and 100 nm L-arginine coated silica samples were fairly stable in terms of colloidal homogeneity, showing only slight coalescence and sedimentation.
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Project description:Current paper presents biological effects of magnetite nanoparticles (MNPs). "Relations of MNP' characteristics (zeta-potential and hydrodynamic diameters) with effects on bacteria and their enzymatic reactions were the main focus.". Photobacterium phosphoreum and bacterial enzymatic reactions were chosen as bioassays. Three types of MNPs were under study: bare Fe3O4, Fe3O4 modified with 3-aminopropyltriethoxysilane (Fe3O4/APTES), and humic acids (Fe3O4/HA). Effects of the MNPs were studied at a low concentration range (< 2 mg/L) and attributed to availability and oxidative activity of Fe3+, high negative surface charge, and low hydrodynamic diameter of Fe3O4/HA, as well as higher Fe3+ content in suspensions of Fe3O4/HA. Low-concentration suspensions of bare Fe3O4 provided inhibitory effects in both bacterial and enzymatic bioassays, whereas the MNPs with modified surface (Fe3O4/APTES and Fe3O4/HA) did not affect the enzymatic activity. Under oxidative stress (i.e., in the solutions of model oxidizer, 1,4-benzoquinone), MNPs did not reveal antioxidant activity, moreover, Fe3O4/HA demonstrated additional inhibitory activity. The study contributes to the deeper understanding of a role of humic substances and silica in biogeochemical cycling of iron. Bioluminescence assays, cellular and enzymatic, can serve as convenient tools to evaluate bioavailability of Fe3+ in natural dispersions of iron-containing nanoparticles, e.g., magnetite, ferrihydrite, etc.
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Project description:Using photons to drive chemical reactions has become an increasingly important field of chemistry. Plasmonic materials can provide a means to introduce the energy necessary for nucleation and growth of nanoparticles by efficiently converting visible and infrared light to heat. Moreover, the formation of crystalline nanoparticles has yet to be included in the extensive list of plasmonic photothermal processes. Herein, we establish a light-assisted colloidal synthesis of iron oxide, silver, and palladium nanoparticles by utilizing silica-encapsulated gold bipyramids as plasmonic heat sources. Our work shows that the silica surface chemistry and localized thermal hotspot generated by the plasmonic nanoparticles play crucial roles in the formation mechanism, enabling nucleation and growth at temperatures considerably lower than conventional heating. Additionally, the photothermal method is extended to anisotropic geometries and can be applied to obtain intricate assemblies inaccessible otherwise. This study enables photothermally heated nanoparticle synthesis in solution through the plasmonic effect and demonstrates the potential of this methodology.
| S-EPMC10564728 | biostudies-literature