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  • 423 Reads
High surface-area cathodes for aluminum ion batteries
Published: 16 April 2018 by MDPI in 1st International Online Conference on Nanomaterials session Devices & Energy

Lithium ion batteries (LIBs) are highly efficient. They have high capacities and long cycle lives with coulombic efficiencies of over 98%. With their immense success, they now find use in many applications, for example, electric vehicles (EVs). The increasing demand puts a lot of pressure on lithium and cobalt reserves as these metal oxides (LiCoO2) form the basic component of LIB electrode. Furthermore, the typical electrolyte in LIBs is flammable rendering these batteries hazardous. Any damage to the cell (like thermal runaway reactions, direct electrode contact) leads to short circuits, sometimes leading to an explosion!

Aluminum ion batteries (AIBs) are cheap and non-flammable alternatives to LIBs. They can be easily recycled. The theoretical energy density of aluminum is higher than lithium and hence, it may exceed the current performance of LIBs. Graphite is the most commonly used cathode in AIBs. Its layered structure helps in insertion/extraction of electrolyte ions (AlxCly) or Al3+ into the cathode. However, most of the AIBs have a low electrode potential and a short cycle life. We will present new high-surface area cathode nanomaterials that will lead to better performing AIBs. Some of the tested cathodes have shown an improved cycle life and a much better electrode potential (~2.0 V).

  • Open access
  • 3553 Reads
Exploring the effects of nanoparticle incorporation on the mechanical properties of hydrogels.
Published: 16 April 2018 by MDPI in 1st International Online Conference on Nanomaterials session Materials

Recent studies have expanded our understanding of the effects of nanoparticles on hydrogel mechanical properties. However, further studies are needed to validate the generality of the findings, as well as to determine the exact mechanisms behind the enhancements afforded by the incorporation of nanoparticles. In this study, we performed rotational rheological characterizations of chemically crosslinked poly(acrylamide) hydrogels incorporating silica nanoparticles to better understand the role of nanoparticles on the enhanced properties of hydrogel nanocomposites. Our results indicate that the increases in elastic moduli due to the addition of nanoparticles depend strongly on particle size and concentration, as well as the overall concentration of the hydrogel. Moreover, we find that incorporating nanoparticles can lead to enhancements in hydrogel elastic moduli greater than the maxima obtainable through purely chemical crosslinking. Finally, our data indicates a strong role for pseudo-crosslinking mediated by non-covalent interactions between the nanoparticles and hydrogel polymers on the observed reinforcements. Collectively, our results shed further insight into the role of nanoparticles on enhancements of mechanical properties of polymers and may thereby facilitate engineering specific mechanical properties in a wide range of hydrogel nanocomposite systems.

  • Open access
  • 231 Reads
Tunable work function and optical nonlinearity of nanocomposites
Published: 16 April 2018 by MDPI in 1st International Online Conference on Nanomaterials session Materials

We fabricated Au nanoparticles on the surface of TiO2 by photo-reduction method. The structural property of film is investigated using transmission electron microscopy technique. The surface plasmon resonance absorption peaks of TiO2 and Au-TiO2 were recorded using Shimadzu (UV-2450) UV-visible spectrophotometer. The work function of films was measured by scanning Kelvin probe microscopy (SKP5050) from KP technology, United Kingdom. The nonlinear optical refractive index and nonlinear optical absorption coefficient of Au-TiO2 nanocomposites were simultaneously measured using z-scan technique.

The nonlinear optical response of Au-TiO2 nanocomposites is due to pure electronic transfer effects in Au nanoparticles. The observed nonlinearity is due to the dielectric constant of Au, which is due to the surface plasmon resonance and surface polarization between Au nanoparticles and TiO2. The dielectric constant of Au shows maximum value at 532 nm wavelength (2.33 eV). Surface plasmon resonance effect of Au nanoparticles is directly related to the metal dielectric constant, therefore it is increased. The increase in surface plasmon rsonance of Au-TiO2 nanocomposites can be observed from UV-visible absorption spectra. The optical nonlinearity depends strongly on the dielectric constant of Au. Therefore, the optical nonlinearity increases with the increase in surface plasmon resonance peak. The absorption peak of surface plasmon resonance at 544 nm is inversely proportional to the work function. Therefore, we can say that the Au dopant decreases the work function that effectively increases the surface plasmon resonance absorption peak at 544 nm, so that the nonlinear response is enhanced. The systematic change in the work function with Au concentration plays a major role in optical nonlinearity. The estimated optical nonlinearity was found to increase from 3.80×10-6 to 9.69×10-6 esu with increase in Au concentrations from 0 to 1.0x10-2 mole. This observed increment in nonlinearity is due to the enhancement of local electric field created by excitation of surface plasmon resonance that affects the work function. Therefore, the surface plasmon resonance and work function help in tuning the optical nonlinearity. The tunable nonlinear optical response of the Au-TiO2 nanocomposites may find applications in nonlinear optics at wavelength 532 nm and the development of materials for generating the higher order harmonics.

  • Open access
  • 244 Reads
Polymer top covered Bragg reflectors as optical humidity sensors
Published: 23 August 2018 by MDPI in 1st International Online Conference on Nanomaterials session Devices & Energy

Bragg reflectors are multi-layered systems of sequentially deposited low and high refractive index materials with quarter-wavelength optical thicknesses exhibiting structural colors due to the presence of high reflection band in the visible spectral range. If Bragg reflector is covered with film sensitive to external stimuli then the change in the environment could be easily detected by monitoring the change of Bragg reflector’s transmittance or reflectance spectra.

In the present study as a sensitive material we use linearly branched copolymer containing poly(N,N-dimethyl acrylamide) and Poly(ethylene oxide) blocks deposited in the form of thin films by spin-coating method. The required thickness is pre-optimized through theoretical modelling in order to achieve the highest sensitivity. Two types of Bragg reflectors, having different optical contrast and operating wavelengths are implemented as transducers of humidity changes. The first one consists of sequentially deposited SiO2 and Nb2O5 films prepared by sol-gel and spin-coating methods. The second one comprises alternating dense and porous Nb2O5, the last prepared with addition of organic template. Single films and Bragg reflectors are characterized by transmittance measurements at different humidity levels in the range from 5 to 95 % relative humidity (RH). The influence of number of the layers in the stack, the operating wavelength and optical contrast on the sensitivity is studied. The potential and advantages of using top covered Bragg reflector as humidity sensor with simple optical read-out are demonstrated and discussed.

Acknowledgments: The financial support of Bulgarian National Science Fund, grant number DN08-15/14.12.2016 is highly appreciated. R. Georgiev acknowledges World Federation of Scientists for fellowship and project DFNP-17-97/28.07.2017 of the Program for career development of young scientists.

  • Open access
  • 154 Reads
Nanoparticle Intestinal Transport Characterization Using In Vitro Co-Culture Models
Published: 27 August 2018 by MDPI in 1st International Online Conference on Nanomaterials session Bio & Medicine

Introduction: The Caco-2 adenocarcinoma cell line has been used extensively for the past couple of decades in nutrient and drug transport studies as an adequate in vitro model of the intestinal mucosa. However, due to the over-expression of tight junction protein complexes, Caco-2 monolayers fail to provide a reliable estimation in terms of in vivo paracellular permeability of small hydrophilic compounds. To address this issue, we co-cultured Caco-2 and HT29-MTX (mucus-secreting cell-line) to ensure a tunable model and emulate the intestinal transport of two classes of nanoparticles.

Methods: We exposed Caco-2/HT29-MTX of different seeding ratios, cultured on Transwell® systems, to non-cytotoxic concentration levels (20 μg/mL) of Si/SiO2 quantum dots and iron oxide (α-Fe2O3) nanoparticles. Transepithelial electric resistance was measured before and after exposure, and monolayer permeability (Peff) was assessed via the paracellular marker Lucifer Yellow. At regular intervals during the 3-hour transport study, samples were collected from the basolateral compartments for nanoparticle detection and quantitative testing. Cell morphology characterization was done by phalloidin-FITC/DAPI labelling, and Alcian Blue/eosin staining was performed on insert cross-sections in order to compare the intestinal models and evaluate the production of mucins.

Results: Morphological alterations of the Caco-2/HT29-MTX (7:3 ratio) co-cultures were observed at the end of the transport study compared to the controls. The nanoparticle suspensions tested did not diffuse across the intestinal model and were not detected in the receiving compartments, due to their tendency to precipitate at the monolayer surface level and form visible aggregates. Our preliminary results indicated the need for further nanoparticle functionalization in order to appropriately assess intestinal absorption in vitro. The intestinal models used in this study have been shown to adequately screen for prospective candidate carrier-type materials and gauge the transport dynamics of nanoparticles.

Acknowledgements: This work was supported by the project no. 77/2018 NANO-BIO-INT.

  • Open access
  • 73 Reads
NH4F modified Al-SBA-15 materials for esterification of valeric acid to alkyl valerates.
Published: 27 August 2018 by MDPI in 1st International Online Conference on Nanomaterials session Devices & Energy

In the present work, SBA-15 aluminosilicate materials were modified for their use as catalysts in the valeric acid esterification. Firstly, Al-SBA-15 material were functionalised by ball milling with several niobium loadings (0.25-1 wt.%) and, eventualy, by incipient wetness impregnation with several F- loadings, using ammonium fluoride as salt precursor. The catalyst herein synthesised were characterised by XRD, N2 porosimetry and DRIFT among others with a special emphasis to the acidic properties, which were evaluated by titration using pyridine and 2,6-dimethylpyridine. The prepared materials shown form moderate to high catalytic activities in the microwave-assisted transformation of valeric acid to ethyl valerate via esterification. Unexpectedly, the incorporation of niobic acid nanoparticles on the aluminosicates lead to a decrease in the conversion without finding any trend related with the metal loading. On the contrary, the incorporation of fluoride anions either on Al-SBA-15 or on Nb1%/Al-SBA-15 leads to a linear increase in valeric acid conversion with the F- content. The increase on valeric acid conversion has been the same independently if the modification with fluoride anions has been performed over Al-SBA-15 or Nb1%/Al-SBA-15. Thus, it can be concluded that F- modified mesoporous aluminosilicates are efficient catalyst for the transformation of valeric acid into alkyl valerate esters as renewable fuels.

  • Open access
  • 154 Reads
Synthesis and characterization of graphene oxide derivatives via functionalization reaction with hexamethylene diisocyanate
Published: 30 August 2018 by MDPI in 1st International Online Conference on Nanomaterials session Synthesis

Graphene oxide (GO), the oxidized form of graphene, shows unique properties such as strong mechanical strength, high electrical and thermal conductivity, amphiphilicity and surface functionalization capability that make it very attractive in various fields ranging from medicine to optoelectronic devices and solar cells. However, its insolubility in non-polar and polar aprotic solvents hinders some applications. To solve this issue, novel functionalization strategies are pursued. In this regard, the current study deals with the preparation and characterization of hexamethylene diisocyanate (HDI)-functionalized GO. Different reactions conditions were tested to optimize the functionalization degree (FD), and detailed characterizations were conducted via elemental analysis, Fourier-transformed infrared (FT-IR) and Raman spectroscopies to confirm the success of the functionalization reaction. The morphology of HDI-GO was investigated by transmission electron microscopy (TEM), which revealed an increase in the flake thickness with increasing FD. The HDI-GO showed a more hydrophobic nature than pristine GO and could be suspended in polar aprotic solvents such as N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP) and dimethyl sulfoxide (DMSO) as well as in some low polar/non-polar solvents like tetrahydrofuran (THF), chloroform and toluene; further, the dispersibility improved upon increasing FD. Thermogravimetric analysis (TGA) results confirmed that the covalent attachment of HDI greatly improves the thermal stability of GO, ascribed to the crosslinking between adjacent sheets, which is interesting for a variety of applications including long-term electronics and electrothermal devices. The HDI-GO could further react with other organic molecules or polymers via the remaining oxygen groups, which makes them ideal candidates as nanofillers for high-performance GO-based polymer nanocomposites.

  • Open access
  • 160 Reads
Monoclinic zirconium oxide nanostructures having tunable band gap synthesized under extremely non-equilibrium plasma conditions
Published: 30 August 2018 by MDPI in 1st International Online Conference on Nanomaterials session Synthesis

Zirconium oxide (ZrO2) is a wide and direct band gap semiconductor having potential to be used in making fuel cells, protective coatings for mirrors and optoelectronic devices. The optoelectronic devices fabricated on ZrO2 span wide optical range depending on the band gap of ZrO2 material. The band gap of ZrO2 can be tuned by fabricating it to nanoscale. In this paper, we synthesized the ZrO2 nanostructures on quartz substrate using ZrO2 ions produced by the ablation of ZrO2 pellet due to high temperature, high density and extremely non-equilibrium argon plasma in a modified dense plasma focus device. Uniformly distributed monoclinic ZrO2 nanostructures of average dimension ~ 14 nm have been obtained as found from X-ray diffraction and Scanning electron microscopy studies. The monoclinic phase of ZrO2 nanostructures is further confirmed from photoluminescence (PL) and Raman spectra. PL spectra show peaks in ultra-violet (UV) and near-UV regions with tunable band gap of nanostructures. Similar tunability of band gap has been observed from absorption spectra. The obtained structural, morphological and optical properties are correlated to investigate the potential applications of ZrO2 nanostructures in optoelectronic devices.

  • Open access
  • 111 Reads
Inks development for 3D printing cathode of Li-ion microbatteries
Published: 30 August 2018 by MDPI in 1st International Online Conference on Nanomaterials session Devices & Energy

Due to the demand for wearable and implantable microelectronic devices (MED), there is a growing interest in the development of thin-film lithium-ion microbatteries (LiBs) with high-energy density. The high cost of production is an issue restraining thin-film LIBs wide application. Inkjet printing is a method of applying materials to the substrate surface: ink droplets formed on piezoelectric nozzles fall on the substrate, whereafter evaporation of the solvent thin layer of film is formed. The proposed technology can simplify the production of LiBs for MED and reduce their cost.

The present work reports results of inkjet printing 3D cathodes development for LiBs. The 3D printed cathodes were produced with using synthesized Li-rich cathode material (Li1.2+xMn0.54Ni0.13Co0.13O2, 0<x<0.05) which has a larger capacity (>250 mAh/g) in comparison with the materials used in modern lithium-ion cells.

For LIB electrode printing the non-aqueous solvent based inks were used. The prepared cathode material was dispersed in N-methyl-2-pyrrolidone. The effect of various additives such as ethylene glycol, diethylene glycol, glycerin, propylene glycol on the viscosity and stability of the ink was studied. Inkjet printing was performed with the use of Dimatix Material Printer 2831. Substrate temperature, number of layers and other parameters were varied to determine the optimal printing conditions.

  • Open access
  • 105 Reads
Atomic layer deposition of Li-Me-O thin films as electrode materials for nanodevices power sources
Published: 30 August 2018 by MDPI in 1st International Online Conference on Nanomaterials session Devices & Energy

Nowadays the development of nanoscale power sources with a long battery life is required for novel nanoelectronic devices, such as wireless sensors, biomedical implants, smart cards and others. Lithiated metal oxides (Li-Me-O) are widely used in Lithium-ion batteries (LIBs). Depending on the type of metal Li-Me-O can be applied as cathode, anode or electrolyte materials. Atomic layer deposition (ALD) is an excellent method for synthesis of a different type of thin films LIBs materials due to its precision control over thickness, purity, and uniformity over large areas. In this study, Li-Sn-O and Li-Al-O thin films were synthesized by ALD as the anodes and solid-state electrolyte materials for thin films power sources. It was shown that prepared thin film anodes demonstrate exceptional cyclability at a fast discharge rate. Specific capacity decrease at the increase of discharge rate up to 40 times is less than 20 %. The present work reports results of films investigation with the use of spectral ellipsometry, X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectrometry.

This research was supported by the Russian Science Foundation grant (project No 18-73-10015).

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