Current Nanoscience - Volume 13, Issue 6, 2017

Background: Enhancement of heat transfer rate is one of the most important aims in industrial applications. The conventional fluids including oil, water and ethylene glycol have poor thermal properties compared to those of most solids. With this information, it leads to the idea that, if we disperse very small particles and let them suspend stably in base fluids, thermal conductivities of that base fluids should be higher. In previous study of the authors, the effects of different thermal conductivity models on heat transfer and pressure drop of nanofluids were not carried out. In view of that consequence, this article is aimed at reporting the effect of different thermal conductivity models on the prediction of convective heat transfer coefficient and thermal performance factor of nanofluids experimentally. Method: An experimental study was performed for TiO2 -water nanofluid with a volume fraction between 0.002 and 0.02 and Reynolds number (Re) from 8,000 to 51,000. The experimental apparatus is a horizontal double tube counter-flow heat exchanger. Results: It shows that by growing the Re or nanoparticle volume fraction value, the Nusselt number enhances for all models studied. All equations used to calculate the thermal conductivity of nanofluid show same trends regarding the Nusselt number when Re or nanoparticle volume concentration changes. Some models could show more variation or low changes in the Nusselt number when the Re or nanoparticle volume concentration changes, however. Meanwhile, all nanofluids have a higher Nusselt number compared to distilled water. Conclusion: The nanofluid Nusselt number significantly enhances with growing Re and volume concentration for all thermal conductivity models studied in this work. By applying the nanofluid at a 0.02 nanoparticle volume fraction and Re equal to 47,000, the maximum thermal performance factor of 1.86 is found, based on Yu and Choi's and Jang and Choi's models. At low Re, all models show approximately same Nusselt numbers for all nanoparticle volume concentration. For moderate and high Re, the difference between the Nusselt numbers calculated by different models enhances. The thermal performance factor is higher than the unity for all Re and all volume concentration in this study, based on every thermal conductivity model.

Background: Although pristine and modified manganese oxides were used as adsorbent for dyes removal from aqueous solutions, their applications were limited to the removal of single dye components. From the practical viewpoint, it is necessary to investigate the adsorption behavior of dyes on manganese oxide adsorbents in multi-component systems. Herein, the present work investigated the performance of core-shell magnetic manganese dioxide (Fe3O4/C/MnO2) nanocomposites as an adsorbent to remove methylene blue (MB) and rhodamine B (RhB) in single and binary dye solutions. Method: Fe3O4/C/MnO2 microspheres were prepared using the redox reaction of KMnO4 to MnO2 in alkaline solution on the surface of carbon-coated magnetite (Fe3O4/C). The effect of pH and adsorbent amount on adsorption was examined, and the adsorption isotherms and kinetics of MB and RhB in single and binary dye solutions were studied. Results: In single dye solutions, the adsorption isotherms of both MB and RhB fitted well with the Langmuir model. In binary dye solution, the adsorption amount of MB increased because of the synergetic effect, while the adsorption amount of RhB decreased due to competitive effect. The adsorption isotherms of MB and RhB in binary dye solution followed the Sheindorf-Rehbun-Sheintuch (SRS) and extended Langmuir model, respectively. Both MB and RhB adsorption could be expressed by the pseudo-second-order kinetic model in single or binary dye solutions. Conclusion: Fe3O4/C/MnO2 nanocomposites exhibited an excellent adsorption property to MB and RhB and high magnetic separability.

Background: Quantum-dot (QD) superlattice solar cells can attain quite high energy conversion efficiencies. The formation of epitaxial QD superlattice is very difficult since extremely delicate control is required for the QD stacking during the growth to avoid QD deformation and dislocation generation. It is well known that CQDs are self-assembled to form superlattice in electron microscope area after sedimentation in a solvent. To apply the colloidal QD superlattice to solar cell, superlattice size must be expanded from electron microscope order to centimeters or more. Method: Long-periodic packing was done by slowly depositing PbS QDs with short-chain butylamine ligands in a solvent into a pyramidal-hole array processed by anisotropic KOH etching of a (001)Si substrate. Results: QDs' ground state energy reduced by 116 meV together with 1.5-time increase in luminescence lifetime after the film formation. Conclusion: We demonstrate that the film prepared by close packing of colloidal QDs with shortchain ligands exhibited the large red shift of emission wavelength with the increase in emission lifetime. The results suggest that the carrier wavefunction was well delocalized in the long-periodic superlattice film on the template.

Background: Arsenic considered as one of the most frequent and most toxic heavy metals. The WHO guideline value for arsenic in drinking water was lowered to 10 ppm. But nevertheless, surface water with arsenic concentrations 200 ppm has also been reported. The presence of arsenic in water resources causes various diseases including cancer, blood pressure, symptoms of skin and etc… several methods have been considered for remove the heavy metals from aqueous media such as: ion exchange, coagulation, adsorption on active alumina and using of iron salts and sulphide as arsenic adsorbent. Method: In this study, evaluate attempt to remove of arsenic from water resources. To limit the spread of the arsenic within water sources, NiO/CNT nanocomposite adsorbents were synthesized and characterized with the aim of removal of one of the aggressive arsenic ions. Affinity and efficiency adsorption parameters of NiO/CNT nanocomposite, such as; contact time, mass of adsorbent, initial concentration of arsenic ions, sizes of existing NiO nanoparticle at adsorbent and adsorption isotherm behaviors were studied. Results: the efficiency of arsenic adsorption enhanced with increasing of contact time, mass of adsorbent and sizes of existing NiO nanoparticle on the surface of CNTs. With increasing the initial concentration up to 5 ppm, the removal efficiency is reduced and it reaches to 90%. Then, with further increase at initial concentration, removal efficiency enhanced and reaches to about 94% at 20 ppm. Thus, the optimal concentration of removal efficiency was not observed. The value of RL for both Freundlich and Langmuir models are between zero and one, so adsorption isotherm of these two models are desirable for adsorption of arsenic on NiO/CNT nanocomposite. Due to the higher regression coefficient (R2) of Freundlich model, the fit is better with Freundlich model than with Langmuir model. Conclusion: The present study shows that NiO-nanoparticles prepared by polyol method is a good adsorbent for removal of As ions from aqueous media and smaller nanoparticle have more activity than larger own. The adsorption process is a function of the adsorbent mass and concentrations and contact time. Optimal adsorptions were for 0.2 g adsorbent and 30 min contact time. Freundlich model is found to be in a good agreement with experimental data on adaptive behavior of As ions on NiO/CNT. NiO/CNT nanocomposite is then considered as a useful catalyst for the treatment of arsenic contaminated water.

Background: Nanofluids have huge applications in many areas wherever heat transfer is concerned. The most profits of nanofluids exhibit superior heat transfer characteristics and great energy saving. The nanofluid thermal conductivity depends on several factors like particle size, particle material type, particle volume fraction, particle shape, operating temperature, base fluid material and type of additives. Method: In the present study, Titanium dioxide (TiO2) nanoparticles were prepared by sol-gel technique. The synthesized TiO2 was characterized using Transmission electron microscopy (TEM) and X-ray powder diffraction (XRD). The nanofluids were prepared by dispersing TiO2 nanoparticles in distilled water base fluid. The thermal conductivity of nanofluids was measured using a modified transient hot-wire method and was measured at different nanofluids volume fractions (0.03%, 0.06%, 0.12%, 0.23%, 0.35% and 0.47%) and temperature ranges from 10°C to 90°C. Results: The results showed that the thermal conductivity increased with increasing the nanoparticle concentrations and temperature. The maximum enhancement of thermal conductivity is 37.35 % at a nanofluid temperature of 90°C and volume fraction of 0.47% while it is 24.11% at a nanofluid temperature of 20°C for the same volume fraction. Conclusion: The results show that the thermal conductivity of the nanofluid remarkably increases with increasing the volume fraction. The thermal conductivity enhancement ratio increases with increasing the nanofluid temperature.

Background: Porous carbon materials are promising candidate supports for various applications. Different approaches have been applied for preparation of various types of porous carbon materials which in the most of them; disordered structures as well as relatively broad pore size distribution are obtained. The most reliable method for preparing of the ordered carbon mesoporous is nano-casting using mesoporous silicas as a hard template. However one of the challenges in the nano-casting preparation is the mother silica template usually produced from expensive initial ingredients, complicated and consuming process. Therefore, in the present work, the synthesis of the ordered silica mesoporous using commercial water glass as the silica source is reported in which the silicic acid has been prepared using cation-exchange resin. Furthermore, the adsorption properties and phenolic compounds removal capability of the templated carbon mesoporous were compared with the mesoporous carbon prepared by SBA-15 and activated carbon. Method: The structural order and textural properties of the materials have been evaluated by SAXRD (Small Angle X-Ray Diffraction), SEM (Scanning Electron Microscopy), TEM (Transmission Electron Microscopy) and nitrogen adsorption–desorption analysis. Finally, the adsorption of phenolic compounds on the carbon mesoporous has been studied. Results: From SAXRD patterns it was deduced that the silicic acid amount has a considerable effect on the final order of the mesostructure. Also, the nitrogen adsorption-desorption isotherms of different silica samples represent Type IV isotherms. The formation of well-oredered hexagonal (P6mm) arrays of mesopores could be clearly observed from SEM and TEM micrographs. Moreover, the carbon templated from the optimized mesoporous silica revealed the well-ordered mesostructure along with type IV adsorption isotherm confirming the nanoporous carbon has been successfully templated. The microstructural images show the almost similar structure of the mother silica template. In addition, EDS analysis of the silica and carbon templated sample confirms the almost elimination of sodium. Finally, the performance the nanoporous carbon materials for phenolic compounds removal was investigated. It is noteworthy that the adsorption capacity and equilibrium point in the case of the prepared nanoporous carbon materials is very close to that of obtained for carbon prepared by SBA-15. Furthermore the results showed the mesoporous carbon samples exhibit considerably much higher adsorption capability in comparison to commercial activated carbon. Finally the kinetic evaluation indicates that the phenolic compounds adsorption is accordance to the pseudosecond- order kinetic model over the entire adsorption time. Conclusion: The impurity-free and well-ordered hexagonal mesoporous silica particles have been successfully synthesized by commercial water-glass using cation exchange resin. The resultant silica has high surface area (778.3 m2/g), pore volume (1.1 cm3 /g) and pore size (6.1 nm), completely comparable to mesoporous silica (SBA-15) produced by TEOS as a silica source. Moreover, the carbon nanoporous templated by the prepared mesoporous silica has a well ordered structure, high surface area (1033.9m2/g) and pore volume (1.08 cm3/g). Finally the results showed the prepared mesoporous carbon could be considered as a suitable candidate for phenolic compounds removal from water and waste water, as well. Furthermore, the experimental results also showed that the adsorption process and equilibrium data were well fitted by pseudo second-order kinetic.

Background: Despite the progress realized in low-dimensional semiconductors, significant researches are still required for them before they can be used at a large scale mainly with the recent emergence of the surface states and the engineering of two dimensional nanomaterials. The ultra-thin quantum dots are characterized by thickness on the atomic scale, possess high flexibility and multi-functionality in optoelectronic applications. Recent studies demonstrated the possibility to drive the commonly used low-dimensional semiconductors into topological insulators states by using electrical or strain engineering instead of searching new chemical materials. Hydrostatic pressure is one of the most useful tools with the purpose to modify the optical properties of low dimensional systems. Method: Our approach is performed in the framework of the effective mass theory and adiabatic approximation. The Schrödinger equation is established in Hylleraas coordinates and solved numerically by using the variational method with a robust ten terms-trial wave function. The excitonic binding and photoluminescence energies are determined and discussed as function of hydrostatic pressure and size. Results: In this work we present the exciton binding energy for a confined electron-hole pair in a cylindrical shaped ultra-thin GaN quantum disk under the effects of hydrostatic pressure. Calculations also include the in-plane electron-hole distance, the hydrostatic pressure coefficient of exciton binding energy as a function of the quantum disk-radius, and the effective band gap. Conclusion: The simultaneous effects of hydrostatic pressure and lateral size on both the excitonic binding energy and photoluminescence show that the strain effect can transform a thin quantum disk into a large-gap material like 2D systems. This approach, constitutes an interesting practical interest, it offers an alternative way to the tuning all energy transitions, instead of modifying the size of the quantum dots or searching for new materials.

Background: Gold nano-clusters (Au-NCs) are non-toxic bio-markers, with higher potentials as compared to quantum dots, and hence the present work was focused on the synthesis of Au- NCs using Cysteine (Cys) as the reducing and protecting agent. Method: The properties of the resulting Cys-Au-NCs were evaluated through scanning electron microscopy (SEM), as well as FT-IR, fluorescence and UV–Vis spectroscopy. Synthesis of the gold nano-clusters was conducted by adding chloroauric acid solution to fresh Cys solutions under stirring. The resultant was kept under stirring in a water bath at 37 °C overnight. Objectives: Considering the low stability of Cys-CuNCs, we decided to study a new approach for determination of Cys through the synthesis of size-selected Au-NCs in the presence of cysteine as a reducing and stabilizing agent, to acquire nanoclusters with higher stability. Results: The spectroscopic results showed various intensities which were attributed to the size of the Cys-Au-NCs. It was also considered that the enhanced fluorescence intensity of Au-NCs observed parallel to increasing the concentration of cysteine could be used for developing proper detection systems for cysteine in aqueous and blood serum samples. This was achieved in the course of the formation of different Cys-Au-NCs with various sizes. Under optimal conditions, the nano-clusters was used as a nano-biosensor and showed excellent selectivity for Cysteine as opposed to the other amino acids tested and produced linear response in the range of 20 to 200 μM. The detection limit of the system was evaluated to reach as low as 8.4 μM. Conclusion: Cysteine-stabilized Au-NCs were successfully synthesized and were found to be stable in aqueous media even after 6 months. Results of the fluorescence emission of the Cys-Au-NCs was found to be selective towards Cys. The nano-biosensor was also successfully used in serum samples for Cys detection.

Background: Mercury pollution has become a serious and enduring threat to the environment. It has affected the organisms along the food chain, including humans. Thus, it is necessary to design an effective mercury removal system to overcome the huge threat of mercury pollution. Our study aim is to optimize the anodization duration of as-prepared WO3-loaded TiO2 nanotubes for improving their photocatalytic mercury (II) reduction performance. Method: Hybrid WO3-TiO2 nanotubes film were successfully formed via electrochemical anodization at applied potential of 40 V in ethylene glycol organic electrolyte containing 1 vol% of hydrogen peroxide (H2O2) and 0.3 wt% ammonium fluoride (NH4F) by varying the anodization time from 15 up to 120 minutes. A tungsten electrode was chosen as the cathode as an innovative and convenient approach to hybridize WO3 with TiO2 nanotubes film. Results: During electrochemical anodization, W6+ ions dissolve from the cathode into the electrolyte solution, migrate towards the titanium foil and are deposited evenly on the Ti foil. This study recorded a maximum photocatalytic mercury (II) reduction performance of 91% (with exposure to 96 W UV-B Germicidal light irradiation for 120 minutes) in the presence of WO3-TiO2 nanotubes film with the highest aspect ratio (53.04) and geometric surface area factor (345.68). Conclusion: The main reason might be attributed to the high specific surface area nanotubes architecture performed strong light scattering effects as well as better incident light absorption from any direction to trigger more charge carriers for photocatalytic reduction of mercury(II) into elemental mercury. WO3 acted as an effective mediator to trap the photo-induced electrons from the TiO2, by contributing intermediate energy band levels below the conduction band of TiO2.

Background: The combination of anticancer drugs in nanoparticles has great potential as a promising strategy to maximize drug efficacies. Gemcitabine (GEM), a nucleoside analogue, and atorvastatin (ATV), a cholesterol lowering agent, have shown anticancer effect with some limitations. Objective: The study aimed to evaluate antitumor activity of the combination therapy of GEM and ATV encapsulated in nanodroplets of microemulsion (ME) formulation in MCF-7 breast cancer cells and healthy HFS human foreskin cells. Method: The physical characterization of drug formulas has been studied by the transmission electron microscope (TEM). The cytotoxicity and efficacy of the formulation were examined by 3(4,5-dimethylthiazole-2-yl)-2,5-diphyneltetrazolium bromide (MTT) assay, light microscopy, and ApopNexin apoptosis detection kit. Results: It has been found that the IC50, inhibitory concentration at which 50 percent of the cells inhibited, for the combination of GEM and ATV at 1:2 ratio, respectively, in the ME (GEM/2ATVME) with a droplet diameter of 4.81±0.86 nm, subjected into the MCF-7 cells for 24h, was similar to the combination of GEM and ATV at 1:1 ratio, respectively, in water (GEM/ATV). According to the FITC/PI assay, 5 μM of GEM/2ATV-ME was less toxic on the HFS cells as higher percentages of viable cells (85.15%) were detected when compared to the GEM/ATV that caused reduction in the percentages of the viable cells (66.45%). Conclusion: Formulating GEM with ATV in ME has improved the therapeutic anticancer potential of both drugs while reducing their side effects on the normal cells.

Background: The research on use of nanofluids for machining applications has gained more attention for over the past two decades. However there is limited review/data, available on the basis of individual nanoparticles performance, when added as an additive to coolant (cutting fluids)/ lubricant used for machining applications. Hence, this article meticulously attempts to come up with an individual nanoparticle wise review, on a wide range of past and present ongoing research and focuses on affirmative aspects of using nanoparticle added coolants/lubricants (nanofluids) used for metal machining. Method: Investigations by researchers all around the globe reveal that addition of nanoparticles to coolants/lubricants has shown better heat dissipation ability at the machining zone. In the present work an attempt is made by conducting a study of 102 research papers, to come up with a report on individual nanoparticle wise comprehensive review, on the effect of suspending 11 different nanoparticles in various coolants/lubricants used for machining applications. The article is structured in a cogent way, starting with a brief introduction to nanofluids, followed by an individual nanoparticle wise review. Each review section comprises of introduction to the individual nanoparticle, its distinct properties, its method of synthesis and unique advantage upon addition to coolant/lubricant used for various machining related applications. Results: Addition of nanometer sized particles in suitable proportions to servo cut oil, canola oil, deionized water, coconut oil, vegetable oil, colza oil and soyabean oil used as coolants for machining of different materials like aerospace alloys, steel(of different grades), nickel based alloys etc. have proved to enhance the machining performance. Out of the 11 different nanoparticles, Al2O3, Gr, MoS2, SiO2 and TiO2 find themselves suitable for maximum machining applications. Use of new coolant supply systems like MQL attempt to promote eco-friendly machining with reduced use of coolants and hence the costs associated with machining. Conclusion: The present review covers most of the important works done by researchers in the area of nanofluids. Effective applications of MQL techniques for machining, call for high thermal conductivity fluids. Hence, from the past two decades the concept of nanofluids has been a revolutionary and appealing area for the researchers. To summarize nanoparticles as additives to coolants/ lubricants combined with Minimum Quantity Lubrication systems could be useful in performing the machining operations with reduction in cost and pollution.