Sol-gel Nanoparticles Research Articles

Induced surface photovoltage in TiO2 sol-gel nanoparticles

Induced surface photovoltage in TiO2 sol-gel nanoparticles

Different morphologies on Cu-Ce/TiO2 catalysts for the selective catalytic reduction of NOx with NH3 and DRIFTS study on sol-gel nanoparticles.

The copper-cerium binary oxide catalysts supported by titanium dioxide with nanosphere core-shell structures, nanotube (TNT) core-shell structures, impregnation (imp) nanoparticles and sol-gel nanoparticles were prepared for NH3-SCR of NOx under medium-low temperature conditions. The effect of different morphologies on the Cu-Ce/TiO2 catalysts was comprehensively studied through physicochemical characterization. The results showed that the sol-gel nanoparticles exhibited 100% NOx reduction efficiency in the temperature range of 180-400 °C. Compared with the other catalysts, the sol-gel nanoparticle catalyst had the highest dispersion and lowest crystallinity, indicating that morphology played an important role in the NH3-SCR of the catalyst. The in situ DRIFTS study on the sol-gel nanoparticle catalyst shows that cerium could promote Cu2+ to produce abundant Lewis acid sites, which would significantly increase the adsorption reaction of ammonia on the catalyst surface, thereby promoting the occurrence of the Eley-Rideal (E-R) mechanism. With the Ce-Ti interaction on the atomic scale, the Ce-O-Ti structure enhanced the redox properties at a medium temperature. In addition, cerium oxide enhances the strong interaction between the catalyst matrix and CuO particles. Therefore, the reducibility of the CuO species was enhanced.

Review of Green Synthesis and Anticorrosion Applications for Yttrium Oxide Nanoparticles

Corrosion processes cause considerable losses in industry and the economy. Corrosion inhibitors have been used in both inorganic and organic forms for a long time. Nanomaterials are more effective at preventing corrosion than traditional materials because they have a higher surface-to-volume ratio. Metal oxide nanoparticles (NP) are also novel in a variety of technological applications due to their distinct physical and chemical properties. Due to their higher dielectric constant and thermal stability, yttrium oxide (Y2O3) nanoparticles (NPs) are well known for technical applications. It is frequently utilized in electrochemical applications, photodynamic treatment, and other sectors as a host material for a range of rare-earth alloying elements. As a polarizer, phosphor, biosensor, laser host material, and for bioimaging, Y2O3 NPs has also been employed. Anti-corrosion characteristics of yttrium oxide nanoparticles are appealing regarding the formation of a smooth adsorbed layer on metal surfaces or alloys. This review focuses on Y2O3 NPs promising usage and developments in corrosion-inhibiting applications. The processes of green, chemical, hydrothermal and sol-gel nanoparticle synthesis are discussed.

Structure and spectroscopy characterization of La1-xSmxVO4 luminescent nanoparticles synthesized co-precipitation and sol-gel methods

The Sm-activated orthvanadate nanoparticles with La1-xSmxVO4 (x ≤ 0.3) composition were synthesized by co-precipitation and sol-gel methods. XRD study has shown that synthesized samples are characterized by monoclinic or tetragonal structure as well as their mixture dependently on Sm concentration and methods of synthesis. Influence of method of synthesis on morphology of nanoparticles, their absorption, diffuse reflectance and emission spectra was observed and studied. Luminescence properties and diffuse reflectance spectra of the sol-gel nanoparticles are also depend on Sm concentrations. At least two types of Sm3+ centers were found by emission spectra. These centers have different excitation efficiency by light from the 350–450 nm spectral range. Structures of the centers are discussed taking into account crystal structure, possible defects, morphology of the synthesized nanoparticles and their phase compositions.

A comparative study of magnetic, photocatalytic and dielectric properties of NiO nanoparticles synthesized by sol-gel and composite hydroxide mediated method

Abstract In this study, Nickel oxide (NiO) nanoparticles were synthesized by conventional sol-gel (SG) route using citric acid as an end-capping agent and composite-hydroxide-mediated (CHM) approach. XRD and FTIR confirmed the formation of NiO nanoparticles and the average crystallite size was found to be 68 and 34 nm for SG and CHM method, respectively. Raman spectroscopy revealed higher intensity of one-phonon longitudinal optical (1LO) mode in CHM nanoparticles which is attributed to the presence of defects such as Ni or oxygen vacancies. The two-magnon (2 M) band at 1472 cm−1 confirmed antiferromagnetic (AFM) nature of SG nanoparticles whereas its suppression in CHM nanoparticles indicate superparamagnetic (SPM) nature of the nanoparticles due to decrease in average crystallite size. The magnetic measurements also confirmed the AFM and SPM state of SG and CHM nanoparticles, respectively in accordance with Raman spectroscopy. A sharp and low blocking temperature peak in ZFC/FC also indicates smaller and uniform sized NiO nanoparticles synthesized by CHM method. Optical studies revealed a large value of energy band gap for CHM nanoparticles due to their small average crystallite size and is attributed to quantum confinement effect. A higher photocatalytic performance was observed for CHM nanoparticles due to their large surface area and higher concentration of oxygen vacancies in accordance with Raman spectra. A higher dielectric constant was also observed for CHM nanoparticles due to increased number of grains per unit volume in smaller crystallites. In summary, CHM is one of the most simple synthesis approach that provides fine single-phase NiO nanoparticles at low calcined temperature with improved magnetic, photocatalytic and dielectric properties as compared to SG method.

Improved functional performances of traditional artistic pottery by sol-gel nanoparticles deposition

This work is focused on the realization of a new manufacturing process based on the introduction of TiO2 nanostructured coatings on the surface of red earthenware pottery for domestic use. The aim of the study is to improve the technical properties of the product made from lime and iron-rich clays used to produce traditional artistic Tuscan pottery (Italy). The identified strategy involves the application of nanoparticles onto the surface of ceramic substrates via a sol-gel based process; the initial porosity of the Earthenware promotes the insertion of inert nanoparticles in the outermost part of the ceramic material by simple immersion of bisqueware in the colloidal solutions of nanoparticles. Morphological investigation of the functionalized surfaces has been carried out by scanning electron microscope and atomic force microscopy, while the effectiveness of the treatment was checked by evaluating the water absorption capacity in compliance with the standard method AS-1012.21-1999. The obtained results show a reduction of surface porosity, which turns into a reduced water uptake respect to the traditional pottery, maintaining, at the same time, identical aesthetical characteristics.

YIG based broad band microwave absorber: A perspective on synthesis methods

The fabrication of a thin layer of microwave absorber that operates over a wide band of frequencies is still a challenging task. With recent advances in nanostructure synthesis techniques, considerable progress has been achieved in realizations of thin nanocomposite layer designed for full absorption of incident electromagnetic (EM) radiation covering S to K band frequencies. The primary objective of this investigation is to achieve best possible EM absorption with a wide bandwidth and attenuation >10dB for a thin absorbing layer (few hundred of microns). Magnetic yttrium iron garnet (Y3Fe5O12; in short YIG) nanoparticles (NPs) were prepared by sol–gel (SG) as well as solid-state (SS) reaction methods to elucidate the effects of nanoscale finite size on the magnetic behavior of the particles and hence their microwave absorption capabilities. It is found that YIG prepared by these two methods are different in many ways. Magnetic properties investigated using vibrating sample magnetometry (VSM) exhibit that the coercivity (Hc) of solid-state NPs is much larger (72Oe) than the sol-gel NPs (31Oe). Microwave absorption properties were studied by ferromagnetic resonance (FMR) technique in field sweep mode at different fixed frequencies. A thin layer (∼300μm) of YIG film was deposited using electrophoretic deposition (EPD) technique over a coplanar waveguide (CPW) transmission line made on copper coated RT/duroid® 5880 substrates. Temperature dependent magnetic properties were also investigated using VSM and FMR techniques. Microwave absorption properties were investigated at high temperatures (up to 300°C) both for sol-gel and solid-state synthesized NPs and are related to skin depth of YIG films. It is observed that microwave absorption almost vanishes when the temperature reached the Néel temperature of YIG.

Synthesis and characterization of yttrium iron garnet (YIG) nanoparticles - Microwave material

Magnetic Yttrium Iron Garnet (YIG) nanoparticles (NPs) were prepared by sol–gel (SG) and solid-state (SS) reaction methods to elucidate the nanoscale size on the magnetic behavior of NPs. It is found that YIG prepared by these two methods are different in many ways. The average NP sizes prepared by SG and SS methods were calculated by Scherrer formula from XRD data. SEM images show the change in grain size for both types of NPs. The sintering temperature required to form pure garnet phase is 750°C for SG and 1000°C for SS NPs. The saturation magnetizations (Ms) were 1070 Oe for SG and 1125 Oe for SS NPs, respectively. The coercivity (Hc) of SS NPs are twice larger than SG NPs. This is due to the larger crystal sizes of the SS NPs, hence more crystal boundaries. Dynamic properties were studied by ferromagnetic resonance (FMR) technique in field-sweep and frequency-sweep mode at different fixed frequencies and at different fixed magnetic fields, respectively. Resonance field (Hr) observed to increase linearly with frequency both for SS and SG NPs. The stop-band bandwidth (frequency linewidth) is narrower for SG NPs in comparison to SS NPs. Microwave absorption property make this material as a strong candidate for microwave device applications.

Effects of Tb3+ dopants in the La1−xSrxMnO3 bulk and nanoparticle ferromagnets

Three forms of La,Sr-manganites are synthesized and the role of Tb doping is investigated. First two systems are sol–gel nanoparticles and sintered ceramics of the composition La0.56Tb0.07Sr0.37MnO3, whereas the third system is formed by comparable nanoparticles La0.51Tb0.06Sr0.43MnO3 synthesized in molten salt. The samples show pseudocubic perovskite structure with only small tilts of MnO6 that point to Ibmm symmetry in the bulk and symmetry in nanoparticles. SQUID magnetometry and neutron diffraction reveal a complete FM order of Mn spins in bulk, a reduced order in nanoparticles, and non-zero moments at A sites. Detailed analysis suggests that the dodecahedral coordination of A sites adapts to small terbium size, and the resulting crystal field splitting of Tb3+ yields a singlet ground state. The response to exchange and external fields is characterized as a giant Van Vleck paramagnetism in contrast to the Curie-type behaviour of Tb-based orthoaluminates and orthocobaltites with the quasi-doublet ground state.

Variable emittance behavior of smart radiative coating

Smart radiative coating on yttria stabilized zirconia (YSZ) substrate was prepared by the sol-gel LaSrxMnO3 (x = 0.125, 0.175 and 0.2) nanoparticles and the binder composed of terpineol and ethyl cellulose. The crystallized structure, grain size, chemical compositions, magnetization and the surface morphology were characterized. The thermal radiative properties of coating in the infrared range was evaluated from infrared reflectance spectra at various temperatures. A single perovskite structure is detected in sol-gel nanoparticles with size 200 nm. Magnetization measurement reveals that room temperature phase transition samples can be obtained by appropriate Sr substitution. The influence of surface conditions and sintering temperature on the emittance of coating was observed. For rough coatings with root-mean-square roughness 640 nm (x = 0.125) and 800 nm (x = 0.175) , its emittance increment is 0.24 and 0.26 in in the temperature range of 173–373 K. Increasing sintering temperature to 1673 K, coating emittance variation improves to 0.3 and 0.302 respectively. After mechanical polishing treatment, the emittance increment of coatings are enhanced to 0.31 and 0.3, respectively. The results suggested that the emittance variation can be enhanced by reducing surface roughness and increasing sintering temperature of coating.

Developments in production of silica-based thermoluminescence dosimeters

This work addresses purpose-made thermoluminescence dosimeters (TLD) based on doped silica fibres and sol–gel nanoparticles, produced via Modified Chemical Vapour Deposition (MCVD) and wet chemistry techniques respectively. These seek to improve upon the versatility offered by conventional phosphor-based TLD forms such as that of doped LiF. Fabrication and irradiation-dependent factors are seen to produce defects of differing origin, influencing the luminescence of the media. In coming to a close, we illustrate the utility of Ge-doped silica media for ionizing radiation dosimetry, first showing results from gamma-irradiated Ag-decorated nanoparticles, in the particular instance pointing to an extended dynamic range of dose. For the fibres, at radiotherapy dose levels, we show high spatial resolution (0.1mm) depth-dose results for proton irradiations. For novel microstructured fibres (photonic crystal fibres, PCFs) we show first results from a study of undisturbed and technologically modified naturally occurring radioactivity environments, measuring doses of some 10s of μGy over a period of several months.

Controlling Solid-Gas Reactions at Nanoscale for Enhanced Thin Film Morphologies and Device Performances in Solution-Processed Cu2ZnSn(S,Se)4 Solar Cells.

Using Cu2ZnSn(S,Se)4 (CZTSSe) as a model system, we demonstrate the kinetic control of solid-gas reactions at nanoscale by manipulating the surface chemistry of both sol-gel nanoparticles (NPs) and colloidal nanocrystals (NCs). Specifically, we first identify that thiourea (commonly used as sulfur source in sol-gel processes for metal sulfides) can transform into melamine upon film formation, which serves as surface ligands for as-formed Cu2ZnSnS4 (CZTS) NPs. We further reveal that the presence of these surface ligands can significantly affect the outcome of the solid-gas reactions, which enables us to effectively control the selenization process during the fabrication of CZTSSe solar cells and achieve optimal film morphologies (continuous large grains) by fine-tuning the amount of surface ligands used. Such enhancement leads to better light absorption and allows us to achieve 6.5% efficiency from CZTSSe solar cells processed via a sol-gel process using nontoxic, low boiling point mixed solvents. We believe our discovery that the ligand of particulate precursors can significantly affect solid-gas reactions is universal to solid-state chemistry and will boost further research in both understanding the fundamentals of solid-state reactions at nanoscale and taking advantage of these reactions to fabricate crystalline thin film semiconductors with better morphologies and performances.

Generic Biocombinatorial Strategy to Select Tailor-Made Stabilizers for Sol-Gel Nanoparticle Synthesis.

A generic route for the selection of nanoparticle stabilizers via biocombinatorial means of phage display peptide screening is presented, providing magnesium fluoride nanoparticle synthesis as example. Selected sequence-specific MgF2 binders are evaluated for their adsorption behavior. Peptide-polymer conjugates derived from the best binding peptide are used for the stabilization of MgF2 sol nanoparticles, yielding fully redispersable dry states and improoving processability significantly.

Structural and Magnetic Properties of Ni0.6Zn0.4Fe2O4Ferrite Prepared by Solid State Reaction and Sol-gel

Ni 0.6 Zn 0.4 Fe₂O₄ prepared using solid state reaction and sol-gel methods were compared for their structural and magnetic properties. Due to the much higher annealing temperature used in solid state reaction, the crystalline size was much larger than that of the nanoparticles prepared by sol-gel. The saturation magnetization of sol-gel nanoparticles was higher, and the coercivity was about 2 times larger, compared to the solid state reaction sample. By analyzing the integration intensity of x-ray diffraction peaks (220) and (222), we proposed that the difference in the saturation magnetization might be due to the inversion of cation distribution caused by the different preparation techniques used.

Multifunctional hybrid nanopapers based on bacterial cellulose and sol–gel synthesized titanium/vanadium oxide nanoparticles

The hybrid inorganic/organic nanopapers based on bacterial cellulose and different type of sol–gel synthesized nanoparticles are fabricated. A simple, rapid, low-cost pathway based on a diffusion step of sol–gel nanoparticles into swollen bacterial cellulose membrane via orbital incubator is developed. This alternative pathway allows to keeping intact the 3D network of the bacterial cellulose membrane while sol–gel nanoparticles are formed in situ and anchored on the nanofibers surface. Titanium, vanadium oxide nanoparticles and a mixture of both are used to functionalize bacterial cellulose membrane. Fabricated hybrid inorganic/organic nanopapers are characterized by thermogravimetric analysis, X-ray diffraction spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, MTS mechanical testing, UV–vis spectroscopy, colorimeter and semiconductor analyzer. Synthesized photochromic hybrid nanopapers modified with vanadium and titanium oxide nanoparticles can find potential application as sensitive displays, biosensors and other optical devices.

Assembly of Phosphide Nanocrystals into Porous Networks: Formation of InP Gels and Aerogels

The applicability of sol-gel nanoparticle assembly routes, previously employed for metal chalcogenides, to phosphides is reported for the case of InP. Two different sizes (3.5 and 6.0 nm) of InP nanoparticles were synthesized by solution-phase arrested precipitation, capped with thiolate ligands, and oxidized with H₂O₂ or O₂/light to induce gel formation. The gels were aged, solvent-exchanged, and then supercritically dried to obtain aerogels with both meso- (2-50 nm) and macropores (>50 nm) and accessible surface areas of ∼200 m²/g. Aerogels showed higher band gap values relative to precursor nanoparticles, suggesting that during the process of assembling nanoparticles into 3D architectures, particle size reduction may have taken place. In contrast to metal chalcogenide gelation, InP gels did not form using tetranitromethane, a non-oxygen-transferring oxidant. The requirement of an oxygen-transferring oxidant, combined with X-ray photoelectron spectroscopy data showing oxidized phosphorus, suggests gelation is occurring due to condensation of phosphorus oxoanionic moieties generated at the interfaces. The ability to link discrete InP nanoparticles into a 3D porous network while maintaining quantum confinement is expected to facilitate exploitation of nanostructured InP in solid-state devices.

Two-photon excited luminescence of lanthanide complex in monolithic sol–gel hybrid material

A π-conjugated donor functionalized tris-dipicolinate complex, featuring promising two-photon excited luminescence properties in water was successfully embedded in a monolithic sol–gel material. A complete spectroscopic study unambiguously indicates that the europium complex conserves its integrity in this sol–gel matrix and the improvement of the luminescence lifetime clearly indicates a stabilisation of the complex in the matrix. Biphotonic confocal microscopy measurement shows that the Eu(III) luminescence can be sensitized in the sol–gel material using a two-photon antenna process, which is a first step towards the design of doped sol–gel nanoparticles for two-photon imaging applications.

Fabrication of functional nanostructured coatings by a combined sol–gel and plasma-enhanced chemical vapour deposition method

Nanostructures have a wide range of potential applications in industry because they can impart novel mechanical or functional properties to coatings such as abrasion resistance, UV shielding, superhydrophobicity. In this work we present a method for the fabrication of nanostructured coatings with improved mechanical properties, in which sol–gel nanoparticles are deposited on a surface and embedded in a ceramic film by plasma-enhanced chemical vapour deposition. This synthetic strategy is applied to the fabrication of transparent nanostructured antiscratch coatings.

Pickering emulsions stabilized by anatase nanoparticles

Oil-in-water emulsions can be stabilized by solid particles. These so-called Pickering emulsions are regularly used in many technological applications. Here we describe the efficiency of sol-gel-synthesized anatase nanoparticles with a diameter of 6 nm in stabilizing emulsions. Key parameters were the surface charge of the particles—depending on pH and salt concentration—and their contact angle—depending on the surface groups and the polarity of the oil phase. The effect of these properties on the stability of the emulsions was investigated. The sol-gel nanoparticles were most efficient in stabilizing emulsions at pH 3 (depending on the salt and particle concentration). Highly apolar oil phases (cyclohexane, n-hexane) were required to obtain stable emulsions with the investigated system and addition of salt or hydrophobic coupling molecules in the oil phase, such as long alkyl chain containing phosphonates, increased the stability of the emulsions.

Improved dispersion and mechanical properties of hybrid nanocomposites

Dispersion of nanoparticles and its effect on the mechanical properties were investigated by fabricating nanocomposites via conventional sonication, sol–gel, and a combination of sonication and sol–gel methods. Silica nanoparticles in epoxy produced via sol–gel was procured as Nanopox F 400 to produce silica/epoxy nanocomposite whereas the conventional sonication method was followed to produce alumina/epoxy and carbon nanofibers (CNF)/epoxy nanocomposites. Then, the conventional sonication method was employed in the presence of sol–gel nanoparticles to improve the dispersion quality of conventional dry nanoparticles as well as to increase the particle loading. In the current method, the epoxy with silica nanoparticles produced by the sol–gel method was used as the starting material for sonication. In the subsequent step, particles of the second type were added to the silica/epoxy precursor via sonication. Using this method, two different types of nanoparticles were added to produce hybrid nanocomposites with higher particle loading where alumina and CNF were used as hybridizing particles. TEM micrographs revealed an improved dispersion quality of alumina nanoparticles and CNFs in the presence of very well dispersed silica nanoparticles. The improvement in dispersion was reflected in much improved mechanical properties of the nanocomposites.