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  • Open access
  • 44 Reads
Gel-Phase Reduction of Graphene Oxide Coatings by L-Ascorbic Acid

Reduced Graphene Oxide (r-GO) has physical-chemical properties similar to graphene and therefore it can be used for most of the graphene technological applications. The r-GO is produced by chemical or thermal reduction of graphene oxide (GO). GO is a high water-soluble organic compound that can be easily processed in form of aqueous/alcoholic ink to produce thick self-standing films (i.e., GO paper) or thin coatings supported on a variety of substrates (e.g., polymers, cellulose, glass, silicon, etc.). The best GO reduction technique is depending on the substrate chemical/thermal stability, and in the case of thermally unstable substrates (e.g., cellulose) the chemical approach is mandatory. However, traditional reductants, like hydrazine and phenyl-hydrazine, are highly active and therefore detrimental for the substrate. Among the mild reducing agents, L-ascorbic acid (L-aa) a green chemical reductant, has been widely investigated for GO reduction in aqueous solutions. Here, L-aa has been used to convert a GO gel-phase to r-GO by (i) swelling the GO phase with hot water, in order to allow L-aa permeation inside its lamellar structures by diffusion, and (ii) periodically restoring the reductant on the GO layer surface. According to the morphological-structural characterization (SEM, XRD, FT-IR, contact angle measurements, etc.), the proposed approach allowed GO conversion to r-GO preserving a thin GO interfacial layer essential for a good adhesion.

  • Open access
  • 21 Reads
Enhanced efficiency of inverted perovskite solar cells by passivating hole transport layer with POSS
Bo-Tau Liu, Hong-Ru Lin

The energy crisis and environmental pollution are attracting increasing attention, which made many countries implement a series of preferential policies for renewable energy. Among them, solar photovoltaic technology, which can convert solar light into electrical energy, is one of the most feasible methods for renewable energy. It not only improves environmental problems but also reduces dependence on fossil fuels. In recent years, perovskite solar cells has reviewed promising potential in solar photovoltaics owing to low process energy consumption, large-scale production, low cost, simple fabrication process, light weight, flexibility, etc. Polyhedral oligomeric silsesquioxane (POSS) possessing a hollow-cage or semi-cage structure is a new type of organic-inorganic hybrid nanoparticles. POSS combines the advantages of inorganic components and organic components to become one of the most important materials. When POSS is well dispersed in the polymer matrix, it can effectively improve the thermal, mechanical, magnetic, acoustic, and surface properties of the polymer. In this study, the POSS was spin-coated as a ultra-thin passivation layer to optimize a nickel-oxide hole layer, which made perovskite solar cells feature high open circuit voltage. Experimental results showed that Coating an appropriate POSS amount to form an ultra-thin passivation layer could effectively suppress the surface defects of perovskite layers, reduce the recombination of the electron and hole, and increase the short-circuit current. As a result, the power conversion efficiency increased from 13.30 to 15.58%, enhanced by 17%.

  • Open access
  • 19 Reads
Effect of microwave heating on the sol-gel process of silica gels
Samantha Flores López, Sara Fernández Villanueva, Miguel Montes Morán, Guillermo Cruz, Julian G. Garrido, Ana Arenillas
Published: 10 November 2020 by MDPI in 2nd International Online-Conference on Nanomaterials session Poster

Synthesis of silica gels with tailored textural properties using the sol-gel process has been extensively studied. However, even with the inclusion of several steps and special techniques, the entire conventional procedure is still complex and time-consuming for their large scale production. The use of microwave heating could be an effective alternative. Until now, this technology has been only used for the drying step, but it could be applied to the whole process in order to reduce the synthesis time. In the present study, silica xerogels were prepared via acid-basic synthesis from different mixtures of TEOS, ethanol and HCl (used as silica precursor, solvent and catalyst respectively). Conventional and microwave heating were applied to the precursor solutions at different exposure configurations to evaluate the effect of this technology at each step on the sol-gel process. Porosity characterization showed a positive effect of microwaves on the silica gel structure. The analysis of these porosity results evidence for the first time interactions between microwave radiation and functionalities of the reactants, offering not only a reduction around 90% of the synthesis time, but also the possibility of using moderate operating conditions and a simple process for the synthesis of silica gels.

  • Open access
  • 19 Reads
Formation of carbon nanofibers under moderate synthesis of carbon gels

Carbon nanomaterials with different structures (i.e. fibers, tubes, spheres) have been widely studied in the last decades for many applications in the fields of energy, electronics, catalysis and bio-nanotechnology with promising results. The synthesis of these materials includes methodologies such as catalysis, vapor- or electro-deposition and the use of templates; however, it is still necessary to develop effective processes for their mass production. On the other hand, carbon gels are considered very interesting materials for a wide range of applications due to their textural and chemical properties. But certainly, the most valued property of this kind of materials is the ease when tuning their morphology and porous properties. The sol-gel chemistry is controlled by parameters including the type and amount of reactants, solvents, catalyst and temperature; that influence the nucleation, growth and interconnectivity of the resultant network. From a precursor mixture of resorcinol-formaldehyde, and the selection of moderate synthesis conditions (i.e. atmospheric pressure and temperatures under 90°C), this work shows how the heating process during the synthesis alters the morphology of the carbon gel, changing from the typical polymeric nodules to the formation of nanofibers.

  • Open access
  • 12 Reads
Development and Characterization of polyaniline/ Hexamethylene Diisocyanate-Modified Graphene Oxide Nanocomposites

Polyaniline (PANI) is a cheap and widely used conducting polymer due to its exceptional electrical and optoelectronic properties. However, it is insoluble in conventional organic solvents and degrades at high temperatura. To improve the performance of PANI, carbon-based nanomaterials such as graphene, graphene oxide (GO) and their derivatives can be incorporated in a PANI matrix. In this work, hexamethylene diisocyanate-modified GO has been used as reinforcement to prepare PANI/HDI-GO nanocomposites by means of in situ polymerization of aniline in the presence of HDI-GO followed by ultrasonication and solution casting. The effect of the HDI-GO functionalization degree and concentration on the final properties of the nanocomposites has been explored by scanning electron microscopy (SEM), Raman spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), tensile tests, and four-point probe measurements. An homogenous dispersion of the HDI-GO nanosheets has been found as well as very strong PANI-HDI-GO interactions via pi-pi stacking, H-bonding, and hydrophobic and electrostatic charge-transfer complexes. A continuos improvement in thermal stability and electrical conductivity was found with increasing nanomaterial concentration, the increments being larger with increasing HDI-GO degree of functionalization. The nanocomposites showed a very good combination of rigidity, strength, ductility and toughness. The approach developed herein opens up a versatile route to prepare multifunctional graphene-based nanocomposites with conductive polymers for a broad range of applications including photovoltaic organic solar cells.

  • Open access
  • 11 Reads
mRNA structuring for stabilizing mRNA nanocarriers and improving their delivery efficiency
Satoshi Uchida, Kyoko Koji, Naoto Yoshinaga, Yuki Mochida, Taehun Hong, Horacio Cabral

For in vivo application of mRNA therapeutics, development of mRNA nanocarriers that protect mRNA from enzymatic degradation is needed. While current nanocarrier development focuses on fine-tuning chemical structure of its components, including lipids and polymers, herein, we propose a novel strategy to design stable mRNA carriers by structuring mRNA inside the nanocarriers. Firstly, several mRNA strands were crosslinked with each other using RNA crosslinkers that hybridize to mRNA strands, to prepare mRNA nanoassemblies (NAs). Interestingly, NAs preserved their translational activity, because of selective NA dissociation inside cells through 5´ cap-dependent translation. Then, we mixed NAs with poly(ethylene glycol) (PEG)-polycation block copolymers to prepare core-shell-structured polyplex micelles (PMs), composed of PEG shell and mRNA containing core. Notably, PM loading NAs (NA/m) exhibited enhanced stability against enzymatic attack and polyion exchange reaction compared to that loading naïve mRNA (naïve/m). According to mechanistic analyses, NA/m possessed a shell with denser PEG layer and a core with more condensed mRNA compared to naïve/m, which may contribute to PM stabilization. As a result, NA/m induced more efficient protein expression after introduction to cultured cells and mouse brain, compared to naïve/m. Further notably, the improved functionality of NA/m was observed in 3 types of mRNA, demonstrating versatility of our strategy. While newly developed materials need long processes before their clinical approval, our strategy is effective in improving stability and mRNA introduction efficiency of existing mRNA carriers just by structuring mRNA without the use of additional materials, holding great promises for future clinical applications.

  • Open access
  • 18 Reads
Heterojunction Generation between Copper Oxide and Single-Walled Carbon Nanotubes Leading to Nano-cauliflower Chemical Assembly for Enhanced Photocatalytic Dye Degradation

We report the fabrication and proficient photocatalytic application of a series of heterojunction nanocomposites with cauliflower-like architecture synthesized out of copper oxide (CuO) and single-walled carbon nanotubes (SWCNTs). The photocatalysts with such a unique design were synthesized via facile recrystallization followed by calcination and were abbreviated as CuO-SWCNT-1, CuO-SWCNT-2, and CuO-SWCNT-3, representing the components and calcination time in hours. The photocatalytic efficiency of the fabricated nanocomposites was scanned by evaluating the decomposition of methylene blue (MB) dye under visible light irradiation. All samples of the as-synthesized nanocomposites were substantially effective photocatalysts for the photo-deterioration of MB solution. Moreover, CuO-SWCNT-3 revealed the best photocatalytic capability with 96% degradation of MB solution in 2 h under visible light irradiation. Pristine CuO nanocrystals generated through the same route and the SWCNTs were employed as controls, where the photocatalytic action of the nanocomposites was remarkably better than that of pristine CuO as well as SWCNTs. The recyclability of the photocatalysts was also explored, and the results asserted that the samples could be reused for three cycles without being altered in photocatalytic performance or morphology.

  • Open access
  • 18 Reads
Environmentally-friendly anticorrosive layered zirconia/titania/low-carbon steel structures
Irina Stambolova, Nikolay Boshkov, Nelly Boshkova, Daniela Stoyanova, Maria Shipochka, Silviya Simeonova, Nikolay Grozev

Improved corrosion protection of low carbon steel was achieved by barrier non-toxic sol gel multilayered structures, composed by ZrO2 top coating and TiO2 underlayers. Zirconium precursor solution was maintained constant, whereas, the content of TiO2 solutions was varied. The phase composition, morphology and corrosion protective properties were analyzed by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), X-ray diffraction spectroscopy (XRD) and atomic force microscopy (AFM). Hydrophobicity properties were evaluated by the measuring of the contact angle with Ramé-Hart automated goniometer. Potentiodynamic polarization technique was used to determine the corrosion resistance and protective ability of the coatings in a 5% NaCl solution. Two different types of polymers were added to titanium solution in order to study the effect of TiO2 surface on the corrosion behaviour of multilayered structures. The polymer modification as compared to the non-modified titania layer has positive effect on the corrosion properties of the structures. Due to relatively dense surface morphology, amorphous structure of zirconia layer and low crystallized TiO2 coating, all of the samples extend service life of low carbon steel in model corrosion medium. The feasibility of the sol gel deposition method make possible to prepare oxide coatings with appropriate dense surface, which ensure high corrosion resistance.

  • Open access
  • 15 Reads
Fluorinated and platinized Titania for Glycerol oxidation
Julie J. Murcia, Edgar Bautista, Elsa Ávila Martínez, Reyna Rangel, Rubi Romero, Jairo Cubillos Lobo, Hugo Rojas Sarmiento, Jhon Hernández, Oswaldo Cárdenas, María Hidalgo, José Navío, Ramiro Baeza

In this research, photocatalysts based on TiO2 modified by fluorination and platinum addition were evaluated in the glycerol oxidation. These materials were characterized by different instrumental analysis techniques to determine the physicochemical properties. It was found that the surface modification lead to improve the materials absorption in the Visible region of the electromagnetic spectra and to increase the surface area of TiO2. By HPLC analysis was possible to observed that the photocatalysts 0.5% Pt-F-TiO2 showed the highest yield and selectivity towards glyceraldehyde (GAL). It was also observed that the increase in the platinum content until values of 2% had a negative effect in the effectiveness of fluorinated Titania in the glycerol photo-oxidation. The fluorination and platinum addition modify some physicochemical properties of TiO2, leading also to modify the reaction mechanism and selectivity during glycerol partial photo-oxidation and the dose of photocatalysts is an important reaction condition to obtain GAL and Dyhidroxyacetone (DHA) with yields above to 70%.

  • Open access
  • 37 Reads
Synthesis and characterization of a fullerenol derivative for the development of cell penetration vehicles

Several biological barriers are generally responsible for the limited delivery of cargoes at the cellular level. These barriers include overpassing the plasma membrane, escaping from the endosomes after cellular uptake, and eventually, crossing the nuclear envelope. Fullerenols have unique structural features and possess suitable properties for interaction with the cells. This study aimed to synthesize and characterize a fullerenol derivative with desirable characteristics (size, surface charge, surface functionality, hydrophilicity) to develop cell penetration vehicles. Fullerenol was synthesized from fullerene C60 solubilized in toluene followed by hydroxylation with aqueous hydrogen peroxide in the presence of tetra-n-butylammonium hydroxide (TBAH) as a phase transfer catalyst. The obtained product was purified by a Florisil chromatography column (water as the eluent) followed by dialysis (cellulose membrane dialysis tubing) and freeze-drying (yield 66 %). Subsequently, a silane coupling agent was conjugated on the fullerenol surface to render free amine functional groups for further covalent functionalization with other molecules. Characterization via Scanning Electron Microscopy (SEM), Dynamic light scattering (DLS), FTIR-ATR, Raman, and UV–visible spectroscopies was conducted to evaluate composition, size, morphology, surface functionality, and structural properties. We are currently working on the conjugation of the potent cell-penetrating agents Buforin II (BUFII) and the Outer membrane protein A (OmpA) on the surface of the fullerenol to estimate whether cell penetration and endosome escape are improved with respect to conventional polymeric vehicles and our own previous developments with Iron Oxide Nanoparticles.