Aerosol Gel Research Articles

Transforming scalable synthesis of graphene aerosol gel material toward highly flexible and wide-temperature tolerant printed micro-supercapacitors

The ever-growing demand for portable, bendable, twistable, and wearable microelectronics operating in a wide temperature range has stimulated an immense interest in the development of solid-state flexible energy storage devices using scalable fabrication technology. Herein, we developed additively manufactured graphene aerosol gel-based all-solid-state micro-supercapacitors (MSCs) via inkjet printing with functioning temperature in the range from −15 to +70 °C and exhibiting a super-stable and reliable electrochemical performance using interdigitated finger electrodes and PVA/H3PO4 solid-state electrolyte. The graphene aerosol gel was obtained using a scalable single step synthesis method from a gas phase precursor using a detonation process, producing a nanoscale shell type structure. The fabricated graphene aerosol gel-based solid-state MSC achieved a volumetric capacitance of 376.63 mF cm−3 (areal capacitance of 76.23 μF cm−2) at a constant current of 0.25 μA and demonstrated exceptional cyclic stability (∼99.6% of capacitance retention) over 10 000 cycles. To exploit the mechanical strength of the as-fabricated graphene aerosol gel-based solid-state MSC, its supercapacitive performance was scrutinized under various bending and twisting angles and the results showed excellent mechanical flexibility. Furthermore, to study the electrochemical performance of the as-fabricated graphene aerosol gel solid-state MSC in stringent surroundings, a broad temperature dependent supercapacitive analysis was performed as stated above. The electrochemical results of the as-fabricated graphene aerosol gel based all-solid-state MSC exhibit a highly potential route to develop scalable and authentic future miniaturized energy storage devices for IoT based smart electronic appliances.

Graphene nanosheets from the controlled explosion of aromatic hydrocarbons

Explosions of benzene, toluene and xylenes were carried out in a 16.7 L chamber in the presence of O2 at different fuel-rich molar ratios such that an aerosol of elemental carbon was produced. The product was a powder at higher precursor oxygen content and an aerosol gel at lower oxygen where the carbon yield was larger. The explosion temperature was measured by a spectrometer that detected black body, Planck radiation from the incandescent carbon, the analysis of which indicated temperatures in the range 2000–2500 K. The product collected was characterized by Raman, X-ray diffraction, Brunauer, Emmett and Teller (BET) specific surface area, high-resolution transmission electron microscopy (HRTEM), etc. HRTEM and Raman showed two product types: amorphous soot at a lower explosion temperature and few-layer graphene at a higher explosion temperature. BET showed that the graphene sample is highly porous and has a specific surface area of 388 m2/g. We conclude that chamber explosion of aromatic hydrocarbons can produce graphene, and the high explosion temperature during the reaction is the primary reason graphene is formed rather than soot.

Synthesis and properties of VPO catalysts for oxidation of n-butane to maleic anhydride

Bulk and supported vanadium-phosphorus oxide VPO catalysts were synthesized by traditional and barothermal methods. It was shown that the use of aerosil as a support for the VPO phase, depending on the time of its introduction into the reaction mixture. It can lead to the formation of catalyst precursor of vanadyl hydrogen phosphate VOHPO4 0.5H2O, or a phase of vanadyl pyrophosphate (VO)2P2O7 as already the catalytically active phase for selective oxidation of n-butane to maleic anhydride. The use of a modified aerosil gel formed from pyrogenic aerosol, as a support for the VPO phase, leads to the formation of VOHPO4∙0.5H2O phase. It has been found that the nature of support affects the features of formation of VOHPO4∙0.5H2O phase, in particular, the ratio of crystallographic planes in resulting VPO phase. The use of aerosil as a support leads to a decrease in the relative content of the basal plane, while use of aerosil gel leads to an increase in the relative content of the basal plane in applied VPO phase. The catalytic properties of bulk and supported VPO samples were studied in the selective oxidation of n-butane to maleic anhydride in standard (1.7 vol.%) and enriched (3.4 vol.%) n-butane mixtures. It has been found that in an enriched n-butane mixture for bulk samples, the n-butane conversion and selectivity for maleic anhydride are sharply reduced. It has been found that supported VPO samples have a higher specific rate of n-butane oxidation and higher productivity compared to bulk samples. It was shown that use of barothermal synthesis and aerosol gel as a support made it possible to increase the selectivity of maleic anhydride, which is associated with an increase in the relative content of the basal plane of VPO phase. The achieved improved catalytic properties of VPO catalysts supported with aerosol gel make recycling technology promising. This can make the production of maleic anhydride more economical.

Synthesis of turbostratic nanoscale graphene via chamber detonation of oxygen/acetylene mixtures

AbstractA study of the detonation synthesis method to make graphene and the properties of the resulting graphene is presented. The gaseous precursors are mixtures of oxygen and acetylene with oxygen/carbon molar ratios of O/C = 0.25 to 0.75. Chamber pressure and temperature data indicate pressures ≤ 300 psi and temperatures of 2550 ± 100K after initiation of the reaction mixture. The graphene material collected from the chamber after the detonation was characterized by Raman, XRD (X‐ray diffraction), BET, SEM (scanning electron microscopy), TEM (transmission electron microscopy), and so on. The material properties divide into two groups: low O/C (≤ 0.45) and high O/C (≥ 0.5). Low O/C graphene appears as a low density, aerosol gel with ∼8 weakly associated, disordered turbostratic layers with a lateral extent of 20 to 30 nm. High O/C graphene appears as a denser powder with ∼30 weakly associated turbostratic layers, with a lateral extent of 100 to 200 nm. We conclude, as we have previously, that the high detonation temperature during the reaction is the primary reason that graphene is formed rather than soot. Differentiation into two types of graphene products is hypothesized to be a result of aggregation kinetics to form a static gel that pre‐empts layering (stacking) when O/C is low.

Zirconia coatings deposited by novel plasma‐enhanced aerosol–gel method

The sol–gel technique is well known and widely used for manufacturing coatings. An aerosol–gel method is a modification of the classic sol–gel process. Preparation of coatings by this technique involves the formation of an aerosol and its deposition on the coated surfaces, where the aerosol droplets merge into a continuous layer. In this work, an aerosol–gel routine, enhanced with a low‐temperature plasma discharge, was used to produce zirconia coatings on different substrates. Low‐temperature plasma was used for preactivation of substrate surfaces prior to the sol deposition, and for treatment of deposited layers. The obtained coatings were characterized using optical, electron (SEM), and atomic force (AFM) microscopes, a contact‐angle device, a scratch tester, a grazing‐incidence X‐ray diffractometer (GIXRD), and an infrared spectrometer (FTIR). The results showed a significant influence of substrate plasma pretreatment on the formation and morphology of zirconia thin films. A noticeable effect of low‐temperature plasma treatment on the structure and properties of the obtained coatings was also presented. These results allow possible applications of this method for the preparation of zirconia coatings on temperature‐sensitive substrates to be predicted.

Plasma enhanced aerosol–gel deposition of Al2O3 coatings

Abstract The new plasma enhanced aerosol–gel technique has been used for alumina films preparation, in this work. This process integrates aerosol–gel deposition of films and their plasma treatment in one reactor. The alumina films deposited by aerosol–gel method on Si substrate were plasma or thermally treated. The influence of deposition and condensation conditions on properties of the films was studied. Produced coatings were characterized in terms of surface morphology (SEM, AFM) as well as crystalline and chemical structure (FTIR, XRD). Plasma discharge used for modification of the substrates prior to the deposition process improved homogeneity of produced coatings. Coatings obtained at room temperature exhibit boehmite structure which was transformed into γ-Al 2 O 3 after annealing. A similar transformation was induced by low temperature oxide plasma discharge treatment for sufficiently thin coatings.

Plasma enhanced aerosol–gel method: a new way of preparing ceramic coatings

The sol–gel process is widely used for the production of powders, coatings and bulk materials. However, being a wet-chemical technique, it has certain limitations related to properties of aqueous colloidal solution, especially when applied as a coating. The most frequently used methods, such as dip- and spin-coating, are difficult to apply onto more complex substrates. In these cases, the aerosol–gel deposition method can be regarded as the solution of this problem. In the present article, a novel plasma enhanced aerosol–gel method of coatings production is presented. A novelty of this method is based on an integration of the aerosol–gel deposition of thin films and their low temperature plasma treatment. Owing to the above, all stages of the coatings production process—substrate preparation, film deposition, and its plasma treatment, can be carried out in a single reactor. The design and operational scheme of such device is presented in this work. Using this device, thin coatings were first deposited on substrates and then plasma treated. The effect of deposition and plasma discharge conditions on morphology and chemical structure of the films has been studied. It was found that plasma treatment had a substantial influence on all the examined properties of the aerosol–gel deposited coatings.

Aero-sol–gel synthesis and photovoltaic properties of mesoporous TiO2 nanoparticles

Highly mesoporous TiO2 nanoparticles were synthesized by using a combination of aero-sol–gel and aqueous washing processes. By varying the mass fraction of NaCl templates in the TiO2–NaCl composite nanoparticles, we examined the formation of mesoporous TiO2 nanoparticles with optimized surface area and pore volume distributions. Then, the photovoltaic properties of the resulting mesoporous TiO2 nanoparticles were systematically investigated by forming a photovoltaic active layer of these nanoparticles on the photoanode of dye-sensitized solar cells (DSSCs). The mesoporous TiO2 nanoparticle-based DSSCs fabricated in this study showed an improved short circuit current densities and power conversion efficiencies compared to solid TiO2 nanoparticle-based DSSCs (the values increased from 2.02±0.11 to 8.16±0.51mA/cm2 and from 1.07±0.21% to 3.88±0.33%, respectively). This improvement is due to an increase in the amount of inorganic dye (N719) adsorption in the mesoporous TiO2 nanoparticles with a specific surface area of 184m2/g and an average pore size of 5nm. These specially designed mesoporous TiO2 nanoparticles have great potential as an effective dye-supporting and electron-transfer medium and can help improve the photovoltaic performance of DSSCs.

Microstructure-Controlled Aerosol–Gel Synthesis of ZnO Quantum Dots Dispersed in SiO2 Nanospheres

ZnO quantum dots dispersed in a silica matrix were synthesized from a TEOS:Zn(NO(3))(2) solution by a one-step aerosol-gel method. It was demonstrated that the molar concentration ratio of Zn to Si (Zn/Si) in the aqueous solution was an efficient parameter with which to control the size, the degree of agglomeration, and the microstructure of ZnO quantum dots (QDs) in the SiO(2) matrix. When Zn/Si ≤ 0.5, unaggregated quantum dots as small as 2 nm were distributed preferentially inside SiO(2) spheres. When Zn/Si ≥ 1.0, however, ZnO QDs of ∼7 nm were agglomerated and reached the SiO(2) surface. When decreasing the ratio of the Zn/Si, a blue shift in the band gap of ZnO was observed from the UV/Visible absorption spectra, representing the quantum size effect. The photoluminescence emission spectra at room temperature denoted two wide peaks of deep-level defect-related emissions at 2.2-2.8 eV. When decreasing Zn/Si, the first peak at ∼2.3 eV was blue-shifted in keeping with the decrease in the size of the QDs. Interestingly, the second visible peak at 2.8 eV disappeared in the surface-exposed ZnO QDs when Zn/Si ≥ 1.0.

Formation of Light-weight Low-density Materials via Gas Phase Aerosol Gelation

ABSTRACTWe have demonstrated that gas phase explosive combustion can lead to nanoparticle aerosols with sufficiently large volume fraction to cause a volume spanning gel to form on the order of ten’s of seconds. The term “aerosol gel” was coined to name these materials. So far we have made aerosol gels of carbon and silica. These aerosol gels are similar to well-known, liquid-phase, sol-gel synthesized aerogels.

Aerosol Gelation: Synthesis of a Novel, Lightweight, High Specific Surface Area Material

We demonstrate that an aerosol can gel. This gelation is then used for a one-step method to produce an ultralow density porous carbon material. This material is named an aerosol gel because it is made via gelation of particles in the aerosol phase. The carbon aerosol gels have high specific surface area (200–350 m 2 /g), an extremely low density (2.5–5.0 mg/cc) and a high electrical conductivity, properties similar to conventional aerogels. The primary particles of the carbon aerosol gels are highly crystalline with a narrow (002) graphitic X-ray diffraction peak. Key aspects to form a gel from an aerosol are large volume fraction, ca. 10 −4 or greater, and small primary particle size, 50 nm or smaller, so that the gel time is fast compared to other characteristic times.

The role of salt in nanoparticle generation by salt-assisted aerosol method: Microstructural changes

We described the possible roles of an inert salt such as NaCl in spray pyrolysis and aerosol–gel syntheses of nanoparticles. We demonstrated that the salt acts primarily as a filler to inhibit further agglomeration of preexisting SiO 2 sols as well as co-precipitated CuO particles. Depending on the contents of the salt, we observed that the microstructures of nanoparticles range from nano dots to mesoporous particles. During the aerosol–gel reaction, in particular, the salt could accelerate the reaction faster. Possible mechanisms will be discussed in detail.

Up-conversion emission in rare earth-doped Y 2Ti 2O 7 sol–gel thin films

Yttrium titanate (YTO) thin films doped with rare earth elements have been deposited using the aerosol–gel process. The up-conversion emission (UPE) of films doped with erbium and/or thulium has been studied with respect to the film crystallization degree and rare earth concentration. The effects of ytterbium codoping have been considered as well. Mechanisms that control UPE of YTO films are discussed with respect to the experimental conditions. It is shown that films, which selectively emit in the blue ( 1G 4→ 3H 6 transition of thulium ions), green ( 2H 11/2→ 4I 15/2 and 4S 3/2→ 4I 15/2 transitions of erbium ions), or red ( 4F 9/2→ 4I 15/2 transition of erbium ions), can readily be achieved.

Luminescence properties of ORMOSIL films doped with terbium complexes

Luminescence properties of sol–gel SiO2–TiO2 ORMOSIL films doped with various terbium complexes were studied. 3-(Trimethoxysilyl) propyl methacrylate and tetraisopropyl-orthotitanate complexed with methacrylic acid were used as sol–gel precursors for film deposition. In situ rare earth complexation was performed through the direct incorporation of TbCl3 and 1,10-phenanthrolin (Phen), phthalic acid (Phta), or 2,2′-bipyridyl (Bipy) ligand in the sol–gel precursor solution. ORMOSIL coatings were deposited using the aerosol–gel process, which is an original deposition method based on the sol–gel polymerization of a liquid film produced from an ultrasonically sprayed aerosol. ORMOSIL films containing terbium complexes exhibited a strong green emission, which was intensified through post-treatment temperature optimization. The highest photoluminescence intensities were measured on films doped with Tb(Phen)3+ complex and heat treated at 150°C, while films doped with Tb(Bipy)3+ complex and heat-treated at the same temperature exhibited the longest lifetimes.

Microstructure and photoluminescence properties of sol–gel Y2−xErxTi2O7 thin films

Abstract Optically active Y2−xErxTi2O7 (YETO) thin films have been successfully deposited using the aerosol–gel process. The effects of post-deposition rapid thermal annealing and conventional thermal annealing heat-treatments have been investigated. The corresponding thin film microstructure is described and discussed in terms of crystallisation degree, mean crystallite size, and porosity. Strong photoluminescence (PL) at 1.53 μm is observed under 980 nm excitation. PL properties are found to depend closely on the film crystallisation degree. PL emission spectra exhibit sharp peaks for crystalline films and a wide band for amorphous ones. PL decay curves are also very closely related to the film microstructure and the corresponding lifetimes range between 2 and 7 ms for a similar erbium concentration.

Aerosol–gel deposition of photocurable ORMOSIL films doped with a terbium complex

Photocurable SiO 2 –TiO 2 ORMOSIL films have been deposited using the aerosol–gel process. 3-(trimethoxysilyl) propylmethacrylate and tetraisopropyl-orthotitanate complexed with methacrylic acid were used as sol–gel precursors. Doping with a terbium:sulphosalicylic acid complex was also studied to test the deposition of optically active photocurable films. Photopolymerization and photoluminescence properties of the films are reported. The results demonstrate the potential of UV-writing of aerosol–gel deposited active thin films.

Aerosol–gel deposition and spectroscopic characterization of pyrochlore films heavily doped with erbium ions

Abstract Optically active films in the Y2Ti2O7–Er2Ti2O7 (YETO) system have been deposited using the aerosol–gel process. Photoluminescence properties closely depend on the film crystallization degree. Dilution of erbium ions within a crystalline Y2Ti2O7 matrix (YETO solid solution) allows preventing photoluminescence concentration quenching induced by short range distance interactions. Consequently, heavily doped films with good photoluminescence properties can be obtained. First studies of a YETO-derived microcavity demonstrate the potential of YETO films for integrated optics applications.

Biological evaluation of aerosol–gel-derived hydroxyapatite coatings with human mesenchymal stem cells

The bioactive properties of hydroxyapatite (HAP) are evaluated for applications involving the enhancement of biocompatible prostheses by seeding human pluripotent mesenchymal stem cells (MSCs). The in vitro response of human MSCs seeded on aerosol–gel HAP coatings is addressed in this work. The processing of the HAP coatings has been carried out by the aerosol–gel technique using calcium nitrate and triethylphosphate as starting precursors. The characterization of the coatings was carried out by using transmission electron microscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, energy disperse X-ray microanalysis, and surface force microscopy, which confirmed the high performance of the HAP coatings. In vitro tests show that human MSCs adhere to aerosol–gel-derived HAP coatings and show proliferation signals on these surfaces.

Microstructural study of aerosol–gel derived hydroxyapatite coatings

Highly porous aerosol–gel derived hydroxyapatite (HAP) coatings have been prepared from calcium nitrate and phosphoric acid based sols. Precursor solutions were prepared by filtering the suspension formed during the ultrasonic slurring of the reactants mixture. The coatings deposited on Si wafers were studied after sintering at different temperatures by using Fourier transform infrared spectroscopy, X-ray diffraction, energy disperse microanalysis and scanning electron microscopy. The composition, structure and morphology of the coatings sintered at 650 °C were found to fit highly porous HAP. That is considered of great relevance since the deposition parameters are compatible with the processing of bioactive coatings on load bearing metallic substrates.

Surface Modification of Cyclic Olefinic Copolymers for Bio-Mems Microfluidic Devices

AbstractCyclic Olefin copolymers (COC) are a new class of polymers that may prove to be extremely useful in injection molding of micron scale fluidic devices. In microfluidic devices it is desirable to have a hydrophilic surface such as in flow driven by capillary action. However, such hydrophilic surfaces tend to display protein deposition when contacted with blood unlike hydrophobic surfaces. Alternatives to capillary action are then needed to control fluid flow for hydrophobic surfaces. Our goal in this research is to tune the slightly hydrophobic COC surfaces through simple surface modifications that are amenable to injection molding and other processing methods. In this study, the surface of an injection molded microfluidic component made from COC was modified in order to change the surface properties important to bio-fluidic devices. Some of the techniques used in this study were plasma treatments and ASG (aerosol gel) coating. Plasma treatments were conducted by using O2, CF4 and their combination gas. O2 treated surfaces became hydrophilic with increasing time of treatment. Combining O2 and CF4 made the surfaces more hydrophobic compared to CF4 only. The structural changes after the plasma treatments were examined by ATR (Attenuated Total Reflectance) spectroscopy. Titania and silica particles from the ASG process were synthesized from titanium iso-propoxide and tetraethoxysilane, respectively. Titania coated surfaces became more hydrophilic and the silica coated surfaces did not have much change in their surface characteristics. The hydrophobicity of the plastic surfaces was measured by their contact angle with water. The implication of these treatments on bio-fluidic devices and their adaptation to the injection molding process will also be discussed.