Sol Synthesis Research Articles

Study of Optical and Structural Properties of β-(AlxGa1–x)2O3 Thin Films Grown by Spray Pyrolysis Technique

The work demonstrates the synthesis of thin films of β-(AlxGa1–x)2O3 by spray pyrolysis method. Temperature conditions for sol synthesis are determined to obtain thin films with a specified content of aluminum. The films are studied by scanning electron microscopy, energy-dispersive X-ray spectroscopy and optical spectroscopy. The aluminum content in the fabricated β-(AlxGa1–x)2O3 films is about 3.6 at.%. The optical band gap of the films is determined as 5.0 eV.

Microfluidic Fabrication of Silica Microspheres Infused with Positron Emission Tomography Imaging Agents.

Selective internal radiation therapy (SIRT) is a treatment which delivers radioactive therapeutic microspheres via the hepatic artery to destroy tumorigenic tissue of the liver. However, the dose required varies significantly from patient to patient due to nuances in individual biology. Therefore, a positron emission tomography (PET) imaging surrogate, or radiotracer, is used to predict in vivo behavior of therapeutic Y-90 spheres. The ideal surrogate should closely resemble Y-90 microspheres in morphology for highest predictive accuracy. This work presents the fabrication of positron-emitting silica microspheres infused with PET radiotracers copper, fluorine, and gallium. A quick one-pot synthesis is used to create precursor sol, followed by droplet formation with flow-focusing microfluidics, and finally thermal treatment to yield 10-50 μm microspheres with narrow size distribution. Loading of the infused element is controllable in the sol synthesis, while the final sphere size is tunable based on microfluidic flow rates and device channel width. The system is then employed to make radioactive Ga-68 microspheres, which are tested for radioactivity and stability. The fabrication method can be completed within a few hours, depending on the desired microsphere quantity. A microfluidic system is applied to fabricate silica particles loaded with diverse elemental infusions, including radioactive Ga-68.

Effect of pH on the structure and corrosion protection properties of sol-gel coatings

In this work, effect of pH on the structure and corrosion protection properties of sol-gel coatings were investigated, with a special focus on a broad pH range (pH = 1–10) of sol synthesis process. Viscosity, molecular weight, particle size measurements of sols and structural analysis of sol-gel coatings show the highest condensation degree in pH = 4 samples. Electrochemical, localized electrochemical techniques and morphology characterization demonstrate the best corrosion resistance of pH = 4 coatings. Results reveal that high condensation degree results in a compact and stable three-dimensional sol-gel network with high crosslinking density and less silanol content, providing highly effective corrosion protection.

Photocatalytic TiO2 nanosheets-SiO2 coatings on concrete and limestone: An enhancement of de-polluting and self-cleaning properties by nanoparticle design

In this study, we develop TiO2-SiO2 nanocomposites that can be employed as photoactive coatings to create surfaces with antipollution and self-cleaning properties in urban buildings. In particular, anatase titanium dioxide with a high percentage of {001} facets, commonly called titania nanosheet (TNS), was used as active phase. This approach allows us to improve the antipollution properties of similar sols based on P25. The obtained TNS were intensively characterized by UV–Vis diffuse reflectance absorption, X-Ray diffraction and transmission electron microscopy to rationalize the sol synthesis and fully understand the photocatalytic performances. Our results clearly show that after treating the titania nanosheets with NaOH to remove adsorbed residual fluoride from the synthesis, they can be easily dispersed and the photocatalytic activity is dramatically improved. This material has been shown to effectively reduce concentrations of NOx, soot and organic dyes under simulated sun light radiation.

Synthesis of Thin Titania Coatings onto the Inner Surface of Quartz Tubes and Their Photoactivity in Decomposition of Methylene Blue and Rhodamine B

An evaporation-deposition coating method for coating the inner surface of long (>1 m) quartz tubes of small diameter has been studied by the introduction of two-phase (gas-liquid) flow with the gas core flowing in the middle and a thin liquid film of synthesis sol flowing near the hot tube wall. The operational window for the deposition of continuous titania coatings has been obtained. The temperature range for the deposition of continuous titania coatings is limited to 105–120 °C and the gas flow rate is limited to the range of 0.4–1.0 L min−1. The liquid flow rate in the annular flow regime allows to control the coating thickness between 3 and 10 micron and the coating porosity between 10% and 20%. By increasing the liquid flow rate, the coating porosity can be substantially reduced. The coatings were characterized by X-ray diffraction, N2 chemisorption, thermogravimetric analysis, and scanning electron microscopy. The coatings were tested in the photocatalytic decomposition of methylene blue and rhodamine B under UV-light and their activity was similar to that of a commercial P25 titania catalyst.

Mesoporous tellurium oxide incorporated g-C3N4 for boosted photoinduced – visible-light reduction of Hg(II)

Two-dimensional (2D) tellurium oxide (TeO2) nanoparticles were homogenously incorporated porous graphitic carbon nitride (g-C3N4) utilizing a simple synthesis sol–gel approach in the occurrence of soft and hard templates. The photocatalytic performance of TeO2/g-C3N4 photocatalysts was performed to reduce Hg(II) ions during visible light illumination. α-TeO2 NPs as tetragonal phases are uniformly scattered with small particle size (15 nm) onto layer structure of g-C3N4. The highest photocatalytic performance (100%) within 40 min is 3 %TeO2/g-C3N4 photocatalyst, and it was enhanced 6.66 and 3.7 folds larger than bare g-C3N4 and TeO2. The rate constant of 3 %TeO2/g-C3N4 photocatalyst is fostered nearly 7.6 and 14.3 times larger than the bare TeO2 NPs and g-C3N4. TeO2 with a nanoscale diameter size (∼15 nm) exhibited a higher photoreduction rate and faster kinetics. Such high reduction ability over TeO2/g-C3N4 photocatalyst was ascribed to the advantageous construction of TeO2/g-C3N4 heterojunction, the synergistic effects of TeO2 and g-C3N4 and the enhancement in electron mobility and efficient electrons and holes separation rate. Owing to such advantageous properties, the 2D- TeO2/g-C3N4 photocatalyst presents promising application potentials as a high-performance photoreduction process.

Anti-fog nanocomposite coatings of enhanced durability

Highly porous nanocomposite films were produced at room temperature from SiO2 or TiO2–SiO2 solutions synthesized by a sol–gel route in the presence of oxide nanoparticles. The photocatalytic behavior of titania-based films was controlled at the sol synthesis step, through three parameters: the relative molar concentration between polymeric and condensed silica, the reactivity of the hydrolysis step, and the relative molar concentration of the active component. The reported method allowed ample tuneability of film refractive index, an important parameter for the design of antireflective and multifunctional coatings. Superhydrophilic properties were demonstrated by the samples and, notably, retained for over 30 days. Experimentally mimicking accelerated surface pollution with olive oil and stearic acid, a strong correlation was found between residual organic contamination, quantified by integrating the film absorption FT-IR spectrum over the C–Hn stretching area, and the measured water contact angle (WCA). Strategies for a fast surface cleaning and restoration of the superhydrophilic behavior via a mild oxidizing agent, based on UV exposure or immersion in a NaClO water solution, were investigated.High wettability can also be obtained through the control of the porosity. This effect has been termed nanowicking: the rapid infiltration of water in an interconnected porous network.

Preparation of Modified Silane Composite Emulsion and Its Effect on Surface Properties of Cement-Based Materials

A new type of waterproofing composite emulsion with high silane content and good economic efficiency was synthesized by sol synthesis. The effects of the amount and proportion of the compound emulsifier, amount of tetraethyl orthosilicate, and mixing time on the properties of the emulsifier were investigated. The optimum conditions for the synthesis of a tetraethyl orthosilicate/isobutyl triethoxysilane emulsion were determined. The composite emulsion was characterized by infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, and energy-dispersive spectrometry, along with a series of microscopic testing techniques. It was verified that the composite emulsion was coated on the surface of the paste to form a hydrophobic protective layer. The results show that the composite emulsion can achieve a permeability and impervious effect after coating the concrete material, and microhardness tests prove that the composite emulsion will not reduce the surface hardness of cement-based materials.

The effect of copolymerisation on the performance of acrylate-based hybrid sol-gel coating for corrosion protection of AA2024-T3

The study was focused on the optimisation of the copolymerisation process of acrylate-based hybrid sol-gel coating to obtain long-lasting corrosion protection of AA2024-T3. The coating was synthesised using the radical copolymerisation process of methyl methacrylate (MMA) and 3-methacryloxypropyl trimethoxysilane (MAPTMS) performed under air and nitrogen (oxygen-free) atmospheres, followed by acidic hydrolysis and polycondensation in the presence of silica prepared from tetraethyl orthosilicate (TEOS). The sol synthesis was evaluated at various stages using real-time infrared spectroscopy, multinuclear liquid- and solid-state magnetic resonance spectroscopy and gel permeation chromatography. After deposition on AA2024-T3 substrate and curing, the coating properties were further evaluated by contact profilometer and focused ion beam/scanning electron microscopy coupled with energy-dispersive X-ray spectrometry. The corrosion performance was evaluated in 0.1 M NaCl solution using electrochemical impedance spectroscopy and salt spray chamber testing. The results indicated that the reaction performed in the nitrogen atmosphere increases the degree of the copolymerisation of acrylates groups, resulting in a larger molecular weight of the formed copolymer. After curing, both sol-gels formed continuous, smooth, ∼4 μm thick coatings that provided excellent barrier properties. However, when coating synthesised under nitrogen atmosphere, the coating provided better long-term corrosion resistance reaching almost 1 GΩ cm2 after 6 months immersion in 0.1 M NaCl solution. Superior corrosion resistance was also confirmed in the salt spray chamber where the coating prepared under N2 atmosphere remained unchanged more than 500 hours.

Solvent mediated phase stability and temperature dependent magnetic modulation in BiFeO3 nanoparticles

Phase-pure bismuth iron oxide nanoparticles are reported for the first time based on selection of solvent, during sol–gel synthesis, under as-synthesized conditions and without using any stabilizing agent. Two solvents are being used during sol synthesis i.e. acetic acid and ethylene glycol. Nanoparticles prepared using acetic acid as solvent result in amorphous behavior under as-synthesized conditions, whereas BiFeO3 phase is obtained after calcination at 200 °C. Mixed BiFeO3 and Bi2Fe4O9 phases are obtained for nanoparticles calcined at 300 °C. Nanoparticles prepared using ethylene glycol as solvent result in phase pure BiFeO3 even under as-synthesized conditions and this phase persists after calcination up to 300 °C. Presence and stability of Raman bands corresponding to both E(TO) and A1(TO) show BiFeO3 phase. Nanoparticles with diameter of ~15 nm prepared using ethylene glycol as solvent result in ferromagnetic behavior with saturation magnetization of 9.1 emu/g under as-synthesized conditions due to modulation of spiral spin structure. Decrease in magnetic anisotropy constant is observed with increase in calcination temperature. FC/ZFC curves indicate presence of ferromagnetic domains at 80–300 K and cusp in FC/ZFC data is attributed to pinning of magnetic domains. These interesting properties are useful for advanced applications of bismuth ferrite that is also popular as a multiferroic material.

Modification of Cotton Yarns for Smart Socks Production

The functionality of textiles can be complimented by using a wide variety of modification technologies. This study focuses on textile modification with sol-gel technology as a part of smart sock prototype development. Zinc acetate dehydrate (ZAD) is integrated in sol synthesis and used as modifier thus improving modified cotton yarn mechanical properties and also can prolong time between washing, taking into account modifiers antimicrobial properties. Four hanks of pure cotton yarns with length of 300 m, where modified with silica-based sol with 7,5 wt% ZAD as a modifier. As a part of this study tensile strength and elongation of yarn was determined and changes in liner density were observed. Average yarn linear density increases by 19 % and linear density for knitted samples increases by 2,6 %. Therefore, yarn strength for 80 % of modified samples shows mean value of 2,32 N, that is 17 % higher than unmodified samples.

Preparation of a graphene oxide/faujasite composite adsorbent

Template-free synthesis of faujasite type zeolite was investigated in the presence of graphene oxide (GO) in the synthesis sol. Nano-sized FAU/EMT, nano-sized FAU, and micro-sized FAU can be obtained depending on synthesis conditions such as precursor molar ratios, crystallization temperature, and the use of freeze-drying to alter water content. The obtained GO/Faujasite powder was shaped in the form of a disk by vacuum filtration. The shaped GO/Faujasite powder is electrically conductive (∼0.4 S/m & 2000–3000 Ω/sq), mechanically stable (Young's modulus: ∼7 MPa) and contains micropores, mesopores, and macropores. Furthermore, the GO/Faujasite disk exhibits high methylene blue adsorption capacity and can be regenerated by thermal annealing at 300 °C without significant capacity loss.

From nano- to macro-engineering of ZSM-11 onto thin-felt stainless-steel-fiber: Steam-assisted crystallization synthesis and methanol-to-propylene performance

• Thin-felt ZSM-11/SS-fiber is fabricated via a combined washcoating and SAC method. • Pre-aging treatment of the synthesis sol can facilitate the subsequent SAC growth. • The ZSM-11/SS-fiber catalyst shows the stability improvement for the MTP reaction. • The enhanced mass transfer by microstructured design is paramount for the stability improvement. Thin-felt ZSM-11/stainless-steel(SS)-fiber composites are successfully prepared via a combined washcoating and steam-assisted crystallization (SAC) method. Pre-aging of synthesis sol at a lower temperature of 80 °C can facilitate the zeolite nucleation and subsequent SAC growth at 180 °C. Such synthesis approach realizes the flexible tuning of acidity via adjusting SiO 2 /Al 2 O 3 molar ratio in a wide range, including but not limited from 105 to 425. The as-synthesized ZSM-11/SS-fiber composites are employed as catalysts for the methanol-to-propylene reaction, and the promising thin-felt catalyst with SiO 2 /Al 2 O 3 molar ratio of 200 shows remarkable stability improvement in comparison with its powdered counterpart, due to enhanced zeolite utilization efficiency and heat/mass transfer by the microfibrous-structured design.

On the synthesis of a hierarchically-structured ZSM-5 zeolite and the effect of its physicochemical properties with Cu impregnation on cold-start hydrocarbon trap performance

A hierarchically structured zeolite (self-pillared pentasil; SPP) comprised of MFI nanosheets or lamellae has been synthesized in various Si/Al ratios and mesoporosities. It turns out that a simple removal of ethanol in a synthesis sol resulted in increased mesoporosity, while the additional reduction of water further increased mesoporosity. In addition, we could synthesize the SPP particle with the actual Si/Al ratio as low as ∼23 with a modest mesoporosity. With these hierarchically structured SPP particles, we further conducted copper impregnation on them in order to use as a hydrocarbon (HC) trap. The resulting Cu-impregnated SPPs could not only adsorb HCs in the exit gas stream including water vapor, but also serve as an active oxidizer of HCs. Specifically, Cu-impregnated SPP with an actual Si/Al ratio of ∼22 and medium mesoporosity exhibited very high performance in cold-start trap tests; desirably adsorbing propene and toluene even in the presence of 10 vol% steam, holding them up to higher temperatures (90 °C for propene and 190 °C for toluene), and furthermore, oxidizing the hydrocarbons. The preferred adsorption can be attributed to the larger amount of exchanged Cu2+ ions in SPP particles with a lower Si/Al ratio, while the additional oxidation was due to the CuO particles dispersed on the SPP surface. However, the hydrothermal stability test revealed that the zeolite structure in the Cu-impregnated SPPs was collapsed and transformed into another undesired phase, thus losing the above-mentioned adsorption ability. Nevertheless, the corresponding oxidation performance was well maintained, indicating the robust, active role of the CuO particles.

Hybrid sol–gel coatings based on GPTMS/TEOS containing colloidal SiO2 and cerium nitrate for increasing corrosion protection of aluminium alloy 7075-T6

One of the promising candidates to replace the chromate conversion coatings for corrosion protection of aluminium alloy AA7075 are the hybrid sol–gel coatings. In the present work hybrid silica sol–gel coatings doped with cerium nitrate were prepared and characterized. Tetraethoxysilane (TEOS) and 3-glycidoxypropyl-trimethoxysilane (GPTMS) were used as precursors. Silica SiO2 (Ludox) particles were added to achieve a barrier properties of coating, while Ce(NO3)3·6H2O was added in order to obtain an active corrosion protection. Optimization of sol synthesis was based on the results of ATR-FTIR spectroscopy and UV–vis–NIR spectroscopy. Opening of epoxy rings and completion of hydrolysis and the condensation reactions during the synthesis process were confirmed. Coatings were characterized through thickness, water contact angle, roughness, adhesion, electrochemical properties (potentiodynamic and electrochemical impedance spectroscopy) and the response to prolonged immersion time in 0.1 M NaCl. The high degree of cross-linking of Si–O–Si network structure and high density was achieved during the synthesis of the sol. Moreover, the results showed that the curing process and the incorporation of cerium nitrate into the hybrid sol–gel coating affected to the corrosion properties of the coating. The observed enhancement in corrosion protection properties is attributed to the combination of the barrier properties of the silica matrix with the active protection of the cerium nitrate.

Síntesis, caracterización y evaluación de la resistencia a la corrosión de recubrimientos híbridos Sol-Gel base TEOS/MPS sobre la aleación AA2050-T8

El presente trabajo tuvo como objetivo sintetizar, caracterizar y evaluar la resistencia a la corrosión de recubrimientos híbridos sol-gel base TEOS/MPS, sintetizados sobre la aleación AA2050-T8 (Al-Cu-Li) bajo diferentes condiciones experimentales de polimerización, tales como solvente y tiempo de envejecimiento, así como diferentes relaciones molares de los precursores inorgánico tetraetoxisilano (TEOS) e híbrido 3-metacriloxipropiltrimetoxisilano (MPS). Se monitoreó la evolución de los soles durante el proceso de envejecimiento mediante espectroscopía infrarroja (FT-IR) y ensayos reológicos. Los recubrimientos se obtuvieron mediante dip-coating y fueron caracterizados a través de microscopía electrónica de barrido (MEB-EDX). La evaluación de la resistencia a la corrosión se realizó mediante ensayos de polarización anódica potenciodinámica, en solución aireada 0,1 M de NaCl. Los resultados obtenidos revelaron que, de los tres solventes evaluados, el etanol es el que permite mejor estabilización del precursor híbrido y favorece el proceso de polimerización de los grupos metacrilato del precursor MPS. Por otra parte, la variación de la relación molar TEOS:MPS conlleva a la obtención de recubrimientos más homogéneos y continuos al incrementar la relación del precursor inorgánico. Finalmente, todos los recubrimientos sintetizados mejoraron la resistencia a la corrosión de la aleación AA2050-T8, en especial los sintetizados bajo la relación TEOS:MPS 80:20.

Tuning sol size to optimize organosilica membranes for gas separation

Abstract A series of organosilica sols are prepared by the polymeric sol–gel method using 1, 2-bis(triethoxysilyl)ethane (BTESE) as the precursor. Particle size distributions of the BTESE-derived sols are systematically investigated by carefully adjusting the synthesis parameters (i.e., water ratios, acid ratios and solvent ratios) in the sol process. In certain conditions, increasing the water ratio or the acid ratio tends to cause larger sol sizes and bimodal particle size distributions. However, higher solvent ratios lead to smaller sol sizes and unimodal particle size distributions. The organosilica membranes prepared from the optimized sols show excellent H2 permeances (up to 4.2 × 10− 7 mol·m− 2·s− 1·Pa− 1) and gas permselectitivies (H2/CO2 is 9.5, H2/N2 is 50 and H2/CH4 is 68). This study offers significant insights into the relationship between the sol synthesis parameters, sol sizes and membrane performance.

Moisture absorption properties of hardwood veneers modified by a sol-gel process

Abstract A new invisible nanolevel coating has been developed based on the sol-gel process for veneer finishes. The sol synthesis and its application as a protective agent is described. It could be demonstrated that a combination of organic light stabilizers and sol-gel deposits is feasible and that the resulting hybrid inorganic-organic thin films decrease moisture uptake of hardwood veneers.

Inkjet printing of alumooxide sol for deposition of antireflecting coatings

Subject of Research. This work describes for the first time the formation of antireflective coating on the base of boehmite phase of AlOOH with low refractive index (1.35) by inkjet printing on the nonporous substrate. This method gives the possibility to increase the contrast of colorful interfering images by 32% obtaining by inkjet printing of titanium dioxide sol. The usage of this technology enables to obtain patterns with wide viewing angle and makes them highly stable. Methods. Traditional sol-gel method with peptizing agents and heating for 90oC was applied for sol synthesis. Then the mixture was under sonic treatment for the obtaining of viscous sol. The viscosity was determined by Brookfield HA/HB viscometer, and the surface tension by Kyowa DY-700 tensiometer. Aluminum oxide ink was deposited on polished slides (26×76 mm2, Paul Marienfeld, Germany), over titanium oxide layer. To print titania ink, we use a desktop office printer Canon Pixma IP 2840 and Dimatix DMP-2831. The thickness of an inkjet AlOOH layer after drying in the air and removal of the solvents did not exceed 150 nm with an RI not less than 1.35 in the entire visible range. Results. The stable colloidal ink was obtained for the first time on the base of aluminum oxide matrix with neutral pH. The rheology was regulated by controlling parameters of sol-gel method in the system of aqueous titanium dioxide sol and by adding ethanol that affects the charge of double electrical layer of disperse phase. The controllable coalesce of drops enables to apply antireflection coating within the thickness accuracy of 10 nm. The morphology of particles and the topology of printed structures were analyzed by optical, scanning electron and atomic-force microscopes. Practical Relevance. We have proposed the approach to obtain colorful, interference patterns using two types of high refractive inks with different refractive indexes. The inkjet printing method opens new opportunities for preparing optical waveguides and forming photon-induction panels for new generation of computers.

Cover Picture: Scalable Synthesis of Acidic Mesostructured Silica–Carbon Nanocomposite Catalysts by Rotary Evaporation (ChemCatChem 1/2017)

The Front Cover shows a practical and scalable soft templating synthesis procedure to prepare ordered mesoporous silica-carbon nanocomposites, in which the use of a rotavapor is essential to achieve a fast and reproducible synthesis.In their Communication, R. Zhong et al. demonstrate this convenient method, in which the synthesis sol comprises of green and cheap sucrose as carbon source, besides TEOS as silica source and F127 as the soft template. The porous composites are easily decorated with sulphonic acid groups, and these acid forms show promising applications as acid catalyst for the transformation of biomass-derived substrates to value-added chemicals. More information can be found in the Communication by R. Zhong et al. on page 65 in Issue 1, 2017 (DOI: 10.1002/cctc.201600939).