COMPARISON OF THE EFFICIENCY OF DIFFERENT DETECTORS OF THE SCANNING ELECTRONIC MICROSCOPE «MIRA-LMH» FOR STUDYING MICROSTRUCTURE OF NANOMATERIALS

На первом этапе были синтезированы объекты исследования - диоксид кремния методом Штобера, где в качестве прекурсора использовали тетраэтоксисилан, и нанокомпозит ZnO - Au золь-гель методом с использованием в качестве прекурсора 2 - водного ацетата цинка. На втором этапе, микроструктуру и морфологию полученных образцов исследовали методом растровой электронной микроскопии на сканирующем электронном микроскопе «MIRA-LMH» фирмы «Tescan» с применением как классического детектора вторичных электронов, так и дополнительных детекторов - внутрилинзового детектора вторичных электронов и детектора отраженных электронов. В результате исследований установлено, что при использовании детектора вторичных электронов получаются изображения с топографическим контрастом и практически без шумов. При использовании внутрилинзового детектора вторичных электронов создаются изображения только материального контраста, без влияния рельефа поверхности. Также использование данного детектора позволило получить высококачественные изображения с большим разрешением на расстоянии от образца 5 мм. При использовании детектора отраженных электронов с рабочим расстоянием до образца 8 мм и увеличении разрешающей способности микроскопа, полученные изображения имеют низкий контраст границ, но представляют композиционную информацию с высокой чувствительностью. Таким образом, установлено, что внутрилинзовый детектор вторичных электронов, с рабочим расстоянием до образца 5 мм, является оптимальным для получения четких изображений микроструктры поверхности наноматериалов при многократном увеличении. At the first stage, the objects of study were synthesized - silicon dioxide by the Stober method, where tetraethoxysilane was used as a precursor, and a nanocomposite ZnO - Au by the sol-gel method using the aqueous zinc acetate dihydrate as a precursor. At the second stage, the microstructure and morphology of the obtained samples were investigated by scanning electron microscopy on a «MIRA-LMH» scanning electron microscope (Tescan company) using both a classical secondary electron detector and additional detectors - intralens secondary electron detector and back-scattered electrons detector. As a result of the research, it was found that when using the secondary electron detector, practically no noise images with topographic contrast are obtained. When using the intralens secondary electron detector, images of only material contrast are created, without the influence of the surface relief. Also, the use of this detector made it possible to obtain high-quality images with a high resolution at a distance of 5 mm from the sample. When using a back-scattered electrons detector with a working distance to the sample of 8 mm and increasing the resolution of the microscope, the resulting images have low border contrast, but represent compositional information with high sensitivity. Thus, it was found that the intralens secondary electron detector with a working distance of 5 mm to the sample is optimal for obtaining clear images of the microstructure of the surface of nanomaterials at multiple magnifications.

Removal of Oil Pollution in water using hydrophobic silica

Nowadays the contamination in waters by oily substances turns out to be a problem of world-wide scope and although some methods of removal of oils in water exist; these present some limitations; therefore, this project proposes the use of hydrophobic silicas as absorbent materials for oily substances. Modified silicas (R-SiO2) were synthesized using the Stöber method, modifying the surface by co-condensation. Tetraethyl-orthosilicate (TEOS) and two surface modifiers were used as silica former: Methyl-trimethoxysilane (MeTEOS) and n-octyl-triethoxysilane (nOctyl-TEOS). The R-SiO2 were characterized by infrared spectroscopy identifying the modifying groups and their hydrophobicity was qualitatively evaluated according to the change in solubility in water. Finally, the removability of an automotive motor oil was evaluated by determining the amount of oil removed per gram of modified silica.

Optical Properties of Doxorubicin Hydrochloride Load and Release on Silica Nanoparticle Platform

Silica nanoparticles (SiO2 NPs) synthesized by the Stober method were used as drug delivery vehicles. Doxorubicin hydrochloride (DOX·HCl) is a chemo-drug absorbed onto the SiO2 NPs surfaces. The DOX·HCl loading onto and release from the SiO2 NPs was monitored via UV-VIS and fluorescence spectra. Alternatively, the zeta potential was also used to monitor and evaluate the DOX·HCl loading process. The results showed that nearly 98% of DOX·HCl was effectively loaded onto the SiO2 NPs’ surfaces by electrostatic interaction. The pH-dependence of the process wherein DOX·HCl release out of DOX·HCl-SiO2 NPs was investigated as well. For comparison, both the free DOX·HCl molecules and DOX·HCl-SiO2 NPs were used as the labels for cultured cancer cells. Confocal laser scanning microscopy images showed that the DOX·HCl-SiO2 NPs were better delivered to cancer cells which are more acidic than healthy cells. We propose that engineered DOX·HCl-SiO2 systems are good candidates for drug delivery and clinical applications.

Investigating Methylene Blue Removal from Aqueous Solution by Cysteine-Functionalized Mesoporous Silica

In this study, mesoporous silica nanoparticles (MSNs) were synthesised using the Stober method and functionalised with cysteine (MSN-Cys) for removal of Methylene Blue (MB) from aqueous solution using the batch method. The adsorbent nanoparticles were characterised by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), FTIR, BET, and TGA. Several influential factors on the adsorption of MB onto the surface of MSN-Cys particles were investigated, including pH, initial concentration, and contact time. The adsorption capacity of MB from aqueous solution increased from circa 70 mg/g MSN-Cys in acidic media to circa 140 mg/g MSN-Cys in basic media. Adsorption isotherms and kinetic models of adsorption were used to clarify the adsorption process. The measured adsorption isotherm was fitted with a Freundlich model for all solutions, and the kinetic model was determined to be pseudo-second-order.

Molecularly imprinting polymer sensor for the detection of testosterone and endocrine disrupting chemicals in environmental and biomedical applications

Molecular imprinting is one of the promising techniques that have been used recently to detect trace contaminants in aqueous solution. This technique is based on the fact that the target compound is present during the polymer synthesis which gives an opportunity for the molecularly imprinted polymers (MIP) to rebind the target molecule selectivity after removal. In this thesis, it was used to detect a hormone (testosterone) in water and blood samples. The procedures are straightforward, fast, and use simple equipment. The detection of the template was carried out by using HPLC and UV-Vis. The MIP starts by preparing a template for the polymer morphology from a silica particle deposition on the glasses slides. At the beginning of this research, the silica particles were prepared by using the Stober method and then commercial silica particles were used. Bulk polymerization was used to prepare the polymer. Two types of solvent (porogen) have been applied. The composition of the prepolymerization solution was optimized. The smart sensor was used first as a self-standing film to characterize and validate. After that, the sensor was deposited on a Poly (methyl methacrylate) (PMMA) slide as a support material which made it easy to use and regenerate. The selectivity and sensitivity of the sensor to the target (testosterone) were studied. The sensor has the potential to detect testosterone not only in a water sample but also in blood samples. In addition, this sensor has the potential for integration into a microdevice for on-site and online monitoring. Such a sensor could be easily used by an inexperienced operator. In this work, the sensor was developed to detect the target with a very low concentration in blood samples. Different endocrine disrupted chemicals were used to compete for the target and to test the potential interference effect. Several human blood samples were utilized to investigate the sensor selectivity. Also, the recoverability of the sensors was studied. The detection of endocrine-disrupting chemicals by traditional methods was complicated, expensive and time-consuming. This research studied the affinity of eight EDCs to the testosterone sensor. In addition, the relation between the classification of chemicals depend on relative binding affinity (RBA) which calculated from other sources to the classification that were got from the sensor were compared to investigate any relationship between. Based on the results of the study, the chemicals were classified into 4 categories, according to their response: strong affinity (T), moderate (CHL, VIN, EST, and FLU), weak (BPA, DDE, and DCP), and inactive (DDT). Also, the percent activity showed that the selected chemicals had lower adsorption to the binding site of the sensor in comparison with testosterone. The results showed that 57 [percent] of our classification was identical with Fang classification which means that our sensor can be used as a pre method to study the affinity of EDCs binding to AR.

Selective and Efficient Olefin Epoxidation by Robust Magnetic Mo Nanocatalysts

Iron oxide magnetic nanoparticles were synthesized with different sizes (11 and 30 nm). Subsequently they were shelled with a silica layer allowing grafting of an organic phosphine ligand that coordinated to the [MoI2(CO)3] organometallic core. The silica layer was prepared by the Stöber method using either mechanical (both 11 and 30 nm nanoparticles) or ultrasound (30 nm only) stirring. The latter nanoparticles once coated with silica were obtained with less aggregation, which was beneficial for the final material holding the organometallic moiety. The Mo loadings were found to be 0.20, 0.18, and 0.34 mmolMo·g−1 for MNP30-Si-phos-Mo,MNP11-Si-phos-Mo, and MNP30-Sius-phos-Mo, respectively, with the ligand-to-metal ratio reaching 4.6, 4.8, and 3.2, by the same order, confirming coordination of the Mo moieties to two phos ligands. Structural characterization obtained from powder X-ray diffraction (XRD), scanning electron microscopy (SEM)/ transmission electron microscopy (TEM) analysis, and Fourier-transform infrared (FTIR) spectroscopy data confirmed the successful synthesis of all nanomaterials. Olefin epoxidation of several substrates catalyzed by these organometallic nano-hybrid materials using tert-butyl hydroperoxide (tbhp) as oxidant, achieved very good results. Extensive testing of the catalysts showed that they are highly active, selective, recyclable, and efficient concerning oxidant consumption.

Fabrication of Double Emission Enhancement Fluorescent Nanoparticles with Combined PET and AIEE Effects

The major challenge in the fabrication of fluorescent silica nanoparticles (FSNs) based on dye-doped silica nanoparticles (DDSNs) is aggregation-caused fluorescence quenching. Here, we constructed an FSN based on a double emission enhancement (DEE) platform. A thio-reactive fluorescence turn-on molecule, N-butyl-4-(4-maleimidostyryl)-1,8-naphthalimide (CS), was bound to a silane coupling agent, (3-mercaptopropyl)-trimethoxysilane (MPTMS), and the product N-butyl-4-(3-(trimethoxysilyl-propylthio)styryl)-1,8-naphthalimide (CSP) was further used to fabricate a core–shell nanoparticle through the Stöber method. We concluded that the turn-on emission by CSP originated from the photoinduced electron transfer (PET) between the maleimide moiety and the CSP core scaffold, and the second emission enhancement was attributed to the aggregation-induced emission enhancement (AIEE) in CSP when encapsulated inside a core–shell nanoparticle. Thus, FSNs could be obtained through DEE based on a combination of PET and AIEE effects. Systematic investigations verified that the resulting FSNs showed the traditional solvent-independent and photostable optical properties. The results implied that the novel FSNs are suitable as biomarkers in living cells and function as fluorescent visualizing agents for intracellular imaging and drug carriers.

Effect of the Preparation Method on the Physicochemical Properties and the CO Oxidation Performance of Nanostructured CeO2/TiO2 Oxides

Ceria-based mixed oxides have been widely studied in catalysis due to their unique surface and redox properties, with implications in numerous energy- and environmental-related applications. In this regard, the rational design of ceria-based composites by means of advanced synthetic routes has gained particular attention. In the present work, ceria–titania composites were synthesized by four different methods (precipitation, hydrothermal in one and two steps, Stöber) and their effect on the physicochemical characteristics and the CO oxidation performance was investigated. A thorough characterization study, including N2 adsorption-desorption, X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDS), transmission electron microscopy (TEM) and H2 temperature-programmed reduction (H2-TPR) was performed. Ceria–titania samples prepared by the Stöber method, exhibited the optimum CO oxidation performance, followed by samples prepared by the hydrothermal method in one step, whereas the precipitation method led to almost inactive oxides. CeO2/TiO2 samples synthesized by the Stöber method display a rod-like morphology of ceria nanoparticles with a uniform distribution of TiO2, leading to enhanced reducibility and oxygen storage capacity (OSC). A linear relationship was disclosed among the catalytic performance of the samples prepared by different methods and the abundance of reducible oxygen species.

Morphological and Structural Properties of Amino-Functionalized Fumed Nanosilica and Its Comparison with Nanoparticles Obtained by Modified Stöber Method

In industry, silica nanoparticles (NPs) are obtained by the fuming and the precipitation method. Fumed silica NPs are commonly used in the preparation of nanocomposites because they have an extremely low bulk density (160–190 kg/m3), large surface area (50–600 m2/g), and nonporous surface, which promotes strong physical contact between the NPs and the organic phase. Fumed silica has fewer silanol groups (Si–OH) on its surface than the silica prepared by the Stöber method. However, the number of –OH groups on the fumed silica surface can be increased by pretreating them with sodium hydroxide (NaOH) before further surface modification. In this study, the effectiveness of the NaOH pretreatment was evaluated on commercial fumed silica NPs with a surface area of 200 m2/g. The number of surface –OH groups was estimated by potentiometric titration. The pretreated fumed NPs, and the precipitated NPs (prepared by the Stöber method) were modified with 3-aminopropyltriethoxysilane (APTES) to obtain A200S and nSiO2-APTES, respectively. The NPs were characterized using electron dispersive scanning (EDS), scanning electron microscopy (SEM), dynamic light scattering (DLS), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), X-ray diffraction (XRD), BET (Brunauer–Emmett–Teller) analysis, and ζ-potential. XRD confirmed the presence of the organo-functional group on the surface of both NPs. After the amino-functionalization, the ζ-potential values of the nSiO2 and A200 changed from −35.5 mV and −14.4 mV to +26.2 mV and +11.76 mV, respectively. Consequently, we have successfully synthesized functionalized NPs with interesting, specific surface area and porosity (pore volume and size), which can be attractive materials for chemical and energy industries.

Structural Colors Based on Amorphous Arrays Comprised Solely of Silica Particles

In this study, structural colors were fabricated by producing an amorphous array with atypical silica particles. The colors were controlled by an array of silica particles with different sizes. In previous research, the process required inducement of the amorphous array, which was complex. Meanwhile, in this paper, we proposed a simple one-step process. First, spherical silica nanoparticles were synthesized using the sol-gel process of the Stöber method. Atypical silica particles that induced an amorphous array were produced by adding a small amount of phenol-formaldehyde resin. Subsequently, the colloidal silica was converted to a powder using a convection oven. The characteristics of the synthesized silica particles were confirmed using a scanning electron microscope (SEM). All the synthesized silica powders obtained structural colors. Finally, the silica powders were dispersed in deionized (DI) water and coated on a glass slide. We confirmed that the silica particles showed different structural colors depending on the size of the particles. We also found that the color was highly independent of the viewing angle.