Current Nanoscience - Volume 12, Issue 5, 2016

Although the photocatalytic activity of TiO2 polymorphs and hexagonal ZnO is well studied with artificial UV light sources, however, their efficacy is not well examined in natural sunlight exposure. In the current study, the photocatalytic activity of the polymorphs of TiO2 (rutile and anatase) and hexagonal ZnO was evaluated in sunlight exposure for the removal of resonance stabilized 2-, and 4- derivatives of chloro and nitrophenol isomers and compared with that of P-25. The polymorphs of TiO2 and hexagonal ZnO, after synthesis by sol-gel and hydrogel routes, were subjected to optical, structural and morphological characterization. The hexagonal ZnO exhibited significantly higher as compared to anatase and rutile polymorphs but comparable with that of P-25 in sunlight illumination. For the hexagonal ZnO, the ring opening route of degradation mediated by superoxide anion radicals was confirmed by the absence of non-hydroxylated aromatic intermediates whereas the contribution of both superoxide anion radicals and hydroxyl radicals was evidenced for the TiO2 polymorphs and P-25. The kinetics of the degradation/mineralization of substrates was also compared.

The present study deals with the synthesis of visible light active CdSrGO hybrid composite by UV assisted photoreduction of Graphene Oxide (GO) and its application for the photocatalytic decolorization of dye. The synthesized samples of CdS and CdS-rGO composites were characterized by the scanning electron microscopy (SEM) and X-ray diffraction (XRD) to study the morphology and phase characterization of the samples. The developed hybrid composite of CdS-rGO was studied for both its photocatalytic activity as well as for adsorption behavior using methylene blue (MB) dye as a model pollutant. The photocatalytic response of the composite was also compared with commercial TiO2 (PC500 and TTP) powders and was found to be higher than these photocatalysts. The effect of rGO concentration on adsorption capacity and photocatalytic response of CdS-rGO composite revealed that rGO plays an important role in the enhancement of photocatalytic performance of CdSrGO composite for the photocatalytic decolorization of MB under visible light irradiation.

Background: Effluents from textile industries is considered to be one of the most challenging industrial wastewaters to treat. The utilization of nanomaterials in various waste water treatment processes has gained tremendous attention in the recent past. Graphene is one such promising candidate for wastewater decontamination. Methods: In present study, Graphene/Fe3O4 nanocomposite (G/Fe3O4) as adsorbent has been synthesized using a simple chemical route and characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), x-rays diffraction (XRD), energy dispersive x-ray (EDX) and thermogravimetric analysis (TGA). Batch adsorption experiments were carried out for the removal of two typical textile dyes, i.e. Acid red- 17 (AR-17) and Remazol brilliant blue R (RBBR), from their spiked aqueous solutions. Influence of pH, contact time, dosage of G/Fe3O4 and initial concentration of dyes was studied for maximum adsorption of dyes. To understand interaction and kinetics of dye removal, isotherm and kinetic models were applied to the adsorption data. Results: The extent of adsorption was found to vary with initial pH, contact time, amount of G/Fe3O4 and dye concentration. Kinetic studies revealed that G/Fe3O4 synthesized could well remove high concentrations of both dyes in a short period of time. The results indicate the Freundlich isotherm as best fitting model. Moreover, adsorption accorded well with pseudo-second order kinetic equation. Conclusion: The results present the potential of G/Fe3O4 nanocomposite as a versatile adsorbent for remedying wastewater in terms of hazardous pollutants.

The zinc oxide-indigo dye nano-composite based smart humidity sensors have been fabricated and investigated. A novel instrument-less technique has been used to fabricate these sensors, where the aluminium electrodes are fixed on the glass substrate without involving any chemical or physical process. The size of each electrode is 5x10 mm2 and the gap between two electrodes is 40 μm. To deposit the active films the ZnO-indigo dye nanocomposite has been prepared by using solution method and films of 20 to 60 μm thicknesses are deposited by drop casting. The fabricated sensors have been tested in the range of 10% to 90% relative humidity (RH). It is observed that the capacitive and resistive sensitivities are 5x103pF/%RH and -154.3MΩ/%RH, respectively. This behavior may be attributed to absorption and adsorption of water molecules which absorb to the active film’s surface. The effects of frequency (measuring) and film thickness on the sensor’s performance have been studied and the results show that with rise in frequency and increase in thickness the sensor’s initial resistance decreases. The experimental results are simulated by using an exponential function and simulated results are well matched with experimental results.

Chitosan nanocomposite spheres (CS-NCsphere) and sheets (CS-NCsheet) were prepared by the simple embedding of Ni-Al in chitosan. The characterization of the samples was carried out by FE-SEM, EDS, XRD, and FTIR analysis. CSNCsphere and CS-NCsheet were applied for the removal of acridine orange (AO), cresyl blue (CB) and methyl orange (MO) from their aqueous solutions. All the nanocomposite samples, regardless of the shapes, were found to be good adsorption assisted photocatalyst for all the dyes as compared to virgin chitosan. Amongst the dyes, MO was selectively removed from the aqueous solution. Furthermore, the removal efficiency (R. E) for MO was higher on CS-NCsphere as compared to CS-NCsheet. The CS-NCsphere showed good removal performance for MO dye in light as compared to dark, which suggests that CS-NCsphere eliminated it by adsorption assisted photodegradation. CS-NCsphere also displayed a significant antibacterial activity by inhibiting the growth of bacteria Micrococcus luteus. Thus, the fabricated CS-NCsphere can be used as bio sorbent in the future.

In this study, the potential of limestone based catalyst on microwave assisted closed heating transesterification of Malaysian rubber seed oil (RSO) which is rich in high Free Fatty Acid (FFA) was investigated. The experimental results showed that the conversion of high FFA oil to biodiesel is very efficient compared to various catalysts. The catalytic activity is not negatively affected by the free fatty acids and can be recycled very easily. Brunauer–Emmett–Teller (BET) analysis was also used to find the surface area of the catalyst at each cycle. The highest conversion achieved was 96.80% with catalyst concentration of 6 wt%; methanol to oil molar ratio of 5:1; reaction temperature of 60°C and reaction time of 60 minutes. The biodiesel produced is within the limits being prescribed by ASTM D 6751.

Zinc oxide (ZnO) nanopowder of size 50±10 nm has been synthesized using low temperature synthesis technique. The ZnO and multiwall carbon nanotubes (CNTs) were mixed in equal amounts. Both types of powders (ZnO and ZnO-CNTs) were tested to measure the effect of pressure using a specially designed transducer. Upon rising pressure from zero to 8.15 kN/m2, the change in impedance was found 35% and 17% and change in capacitance was 41% and 10% while the change in impedance was 36% and 38%, respectively for ZnO and ZnOCNTs nanopowders. The observed changes in the electrical parameters may be regarded as the sample’s densification and porosity reduction due to pressure. With respect to ZnO-CNTs the ZnO shows higher change in resistance; that can be credited to displacement currents.

Background: The performance of plasmonic nanostructures is based on optical properties and the intensity of the electric field. The nature of the nearfields around coinage metal nanoparticles has been well-studied. However, how to project the enhanced electric field to several hundred nanometers distance might be more convenient for the real applications. Methods: In this paper, we examine whether an array of gold nano-stars may be used as enhancement of the electric field to the several hundred nanometers distance. Electron beam lithography was used to fabricate gold nano-star arrays. Near-field optical properties of these arrays were then obtained using near-field scanning optical microscopy (NSOM). The near-field optical properties were also explored with finite-difference time-domain (FDTD) simulations. Results: In the model, a scanning electron microscope image of actual nano-stars was used to build the FDTD targets of 40 nm thickness. The incident wavelength was 532 nm in both simulation and experiment. In the simulations the near-field optical intensity distribution was studied with monitors positioned at various distances (0, 1 and 2 μm above the top surface of a nano-star). The FDTD results were found to be consistent with the experimental NSOM results. Conclusion: We found that the field enhancement is not only localized to the individual nanostars but also projected several hundred nanometers into the space. Such an array could be potential used to probe the intracellular environment of an adjacent cell or near-field imaging.

Background: We report the development and characterization of gelcore solid lipid nanoparticles (SLN) for the encapsulation of hydrophilic proteins, taking bovine serum albumin (BSA) as model compound. Methods: SLN were produced by multiple emulsion (w/o/w) method, while hydrogels were produced by dissolving Carbopol 971 in purified water under high-speed stirring. Physicochemical characterization followed the pH determination, fluorescence and scanning electron microscopy analyses, and the quantification of the drugs by spectrophotometric measurements (for the determination of encapsulation efficiency and release profile). Results: The stability of SLN was found to be dependent on the type of nanoparticle core. Gel-core SLN were more stable than aqueous-core SLN, both during production and during shelf life. It has been shown that an increase in the core volume is possible for gel-core SLN during their preparation. The hydrodynamic diameter of gelcore SLN formulated in the absence and presence of Bovine serum albumin was ca. 200 nm. To determine the encapsulation efficiency (EE) and in vitro release profile, two model compounds, i.e. hydrophilic dye (Methylene blue) and fluorescent probe (Rhodamine B) have been used. It has been shown that EE depends on the type of nanoparticles. EE of the Rhodamine B-loaded SLN was recorded between 80-90%, for both gel-core and aqueous-core SLN. The release of Rhodamine D from gel-core SLN was slower than that from aqueous-core SLN. The release profile was shown to be dependent on the swelling of the core of SLN. Conclusion: The optimized SLN formulation proposed in this study (with the internal gel phase composed of 0.2% Carbopol 971) was found to be more stable over time, depicting lower polydispersity index and slower release, than the aqueouscore SLN.

Using photolysis method, Preyssler acid, H14[NaP5W30O110], was employed in the form of composite film as a green reductant and stabilizer for the synthesis of Au nanoparticles. The synthesized Au NPs/Preyssler film was prepared by a simple and fast sol-gel method and characterized by UV-Visible spectroscopy, particle size distribution, Field Emission Scanning Electron Microscopy (FESEM), and Energy Dispersive Spectroscopy (EDS) analysis. Our findings showed that Au nanoparticles were obtained at about 6-11 nm and were readily inserted and monodispersed in the nanocomposite film. The photocatalytic performance of this NPs/Preyssler film was examined in decolorization of methyl orange (MeO) in aqueous media. UV-Visible studies showed that Au NPs/Preyssler film can efficiently catalyze the decolorization of the aforementioned azo dye. The pseudo-first-order rate constants were also calculated for this reaction.

Background: Polymeric solar cells (PSC) are advantageous over silicon-based photovoltaic devices in many ways, such as mechanical flexibility and low cost of production, butthe low power conversion efficiency (PCE) of PSCs and their relatively small lifetimes due to polymer degradation when exposed to UV radiation constitute considerable disadvantages. The aim of this paper is to enhance the PCE of the produced TiO2 nanosponge/spin-coated P3HT solar cells by doping of the PEDOT:PSS buffer layer with the coumarin known as umbelliferone. Methods: Devices were produced by spin-coating a P3HT layer over an electrochemically grown TiO2 nanostructured thin film. The PEDOT:PSS buffer layer having umbelliferone as an additive was deposited over the P3HT layer using air spray technique. Finally, the samples were thermally treated by annealing at 180°C. Result: The buffer layer, where the PEDOT:PSS layer was doped by umbelliferone, was characterized by NMR, MEV and conductivity measurements. It was observed that the conversion efficiency is enhanced for devices containing umbelliferone in the buffer layer, and the best result indicated a conversion efficiency of around 1.65%, with open circuit voltages and short circuit current as high as 320mV and 0.180mA, respectively, for devices with effective area of around 1mm2. Conclusion: It was observed that the conversion efficiencies of the umbelliferone additivate devices were almost twice as large as the non-additivated devices. The physical reason for the PCE enhancement is associated with chemical bond between umbelliferone molecules and PSS ionomers, producing a conductivity increase and morphological effects on the buffer layer.

Background: Nanomaterials are widely synthesized by wet chemical routes. Magnetic nanoparticles with size ranging from 2 to 20 nm are of significant importance, resulting in a unique magnetic property of the nanoparticles. Maghemite nanostructures with partially disordered (Fe3+)[Fe5/31/3]O4 structures, undergo cation-insertion reactions without resorting to a drastic change in the material composition. Tailoring the superparamagnetic properties of nanoparticles by doping with transition metals, such as vanadium could be advantageous, as it would provide control over properties that are important for biological applications, such as magnetization dependent changes in temperature, relaxivity, and hysteresis. Method: We describe the obtention of vanadium doped maghemite (Fe2-xVxO3) from colloidal suspensions of vanadium and iron salts, using a precipitation–annealing method. A single step simpler synthesis scheme has been proposed in this work, with annealing temperature (350 °C), for a short period of time (~ 15 minutes), in order to achieve smaller in size but developed nanocrystals. Results: Superparamagnetic vanadium doped maghemite with particles (~8 nm) size has been synthesized. For the first time, vanadium up to 5 mol% has been doped on maghemite nanocrystals and characterized successfully for the presence of stable V3+. These results open a new era of vanadium applications in industrial Nanosciences; possessing superparamagnetic properties. Conclusion: A wet chemical route to direct the synthesis of vanadium doped γ- Fe2O3 nanocrystals, has been studied. The doping controls the crystallite size by occupying the vacant octahedral spaces available in the cubic system (space group P4332) maghemite crystals. High surface area magnetic particles, with an average size of ~8 nm were obtained.

Background: Many industries such as textiles, clothing, and printing use organic dyes to color products, which produces a large amount of colored wastewater that is generally hazardous and not readily biodegradable. Different physical, chemical, and biological treatment processes have been widely used for elimination of organic dyes from wastewater. Over the past few years, ultrasound has been widely used as an advanced oxidation process (AOP) for treatment of wastewater pollutants. Adding heterogeneous catalysts is a possible way to enhance the sonochemical degradation efficiency. This study examined the effect of adding nanosized bio-silica particles on the sonocatalytic degradation of AR17 in aqueous solution. Methods: Sonocatalytic degradation of AR17 dye pollutant was performed in the presence of biosilica particles using an ultrasonic bath. In a typical procedure, a desired amount of bio-silica was suspended in 100 mL of AR17 solution with a known initial concentration and then sonicated with an ultrasonic bath. At time intervals of 15 min, a 4-mL sample was taken out and the remaining dye concentration in the solution was measured by a UV-Vis spectrophotometer. Results: By using bio-silica particles, the dye removal efficiency after 75 min increased from 25% to 94% compared with sonolysis alone. The decolorization efficiency decreased as the initial dye concentration increased. Adding NaCl and Na2SO4 as competitive anions reduced the degradation efficiency, indicating that free hydroxyl radicals are responsible for the sonocatalytic degradation of AR17. Five intermediates were successfully characterized by GC-Mass analysis. Conclusion: Adding appropriate amounts of heterogeneous catalysts can increase the yield of sonochemical reactions. The heterogeneous catalysts provide additional nuclei that enhance the number of cavitation bubbles, which enhance the yield of the sonochemical reaction. The results of kinetics investigation of sonocatalytic removal of AR17 which was studied with nonlinear regression analysis, are in good agreement with the experimental data (R2 = 0.993).

Background: Thin films produced by the oblique angle deposition (OAD) method are promising nanocolumns’ materials. Their specific properties depend on the self-shadowing effect and formation of columnar grains by OAD. It determines the coating compliance, and consequently its resistance to spallation, as well as its thermal conductivity. The aims of this paper are to introduce readers to discuss how thermal conductivity of thin films varies with inclined angle and temperature. Methods: Alumina thin films are fabricated by electron-beam evaporation with oblique angle deposition method. The thermal conductivity is measured by the 3ω method. The film thicknesses are measured by cross-sectional scanning electron microscopy. Results: The thermal conductivity (λf) of alumina thin films is dependent of film thickness at various inclined angles. While the λf of alumina thin films decreases with the increasing inclined angles at various film thicknesses. The λf of alumina thin films increases with the increasing temperature at various inclined angles. Conclusion: At the various inclined angles, the thermal conductivity of alumina thin films decreases with the increasing porosity. The cross sectional surface of the 1.1 μm thickness alumina thin film deposited at various inclined angles is the cause that the porosity increases with the increasing inclined angles. It increases with the increasing temperature. So the oblique angle deposition method is an effective way to control the thermal conductivity of thin films.

Background: It has been found that the bilayer structure, especially the bilayer graphenes, can markedly weaken the anisotropy of elastic properties. For tri-layer systems, such as a monolayer grapheme sandwiched in bilayer graphenes and boron nitride nanosheets. The BN-G-BN achieves a more stable combined structure than G-G-G. The results further indicated that the high-temperature distortion resistance of interlayer graphene in the tri-layer complex is related to both material type and constrain conditions at the up-down layers. Methods: The structural stability and high temperature tolerance of bilayer complex nanoribbons are analyzed using the molecular dynamics method. By calculating a variety of potential functions between nanosheets and optimal interlayer distances, the differences in structural stability are examined. By simulating structural performance at high temperatures and analyzing the radial distribution function (RDF) and deformation electron density, the hightemperature distortion resistance is researched. Results: The optimal distances between layers are approximately 0.359 nm for bilayer borophene (B/B), 0.340 nm for bilayer graphene (G/G) and 0.348 nm for the hybrid bilayer (B/G). Analyzing of the results of the binding energy, interaction energy and van der Waals energies between nanosheets revealed that the structural stability of the bilayer complexes from high to low in turn are B/G, B/B and G/G. The dominant interaction sustaining complex stability is a typical van der Waals interaction. The structural analyses on the above complexes at high temperature (1500 K) indicated that the hybrid bilayer nanosheet B/G, in the three bilayer complexes, has the highest temperature tolerance, followed by G/G and then B/B. Conclusion: The results indicated that the bilayer borophene, especially for hybrid bilayer nanosheets, can help to improve the structural stability. The results revealed that the excitation of a greater number of local electrons in borophene results in the high temperature deformation resistance of B/B being inferior to that of G/G. The B/G, in three bilayer complexes composited with graphene and borophene, has the best structural stability and the highest temperature tolerance.

A green method for the synthesis of NiFe2O4/Fe2O3/ CeO2 nanocomposite was explored by using a walnut green hull extract. Walnut green hulls are rich cellulose compounds which make it a good candidate to synthesize nanoparticle due to acting as chelating agents. The as prepared samples were characterized by XRD, FE-SEM, EDX, VSM techniques. The nanoparticles show uniform dispersed and the thickness ranges from 60 to 140 nm. The effect of different extract concentrations on the morphology, crystal growth, particle size and magnetic properties of the samples was investigated. The method has the advantages of cost-effective, non-toxic, and use of walnut green hull extract as an environmentally friendly medium.