Current Nanoscience - Volume 16, Issue 2, 2020

Both mono and hybrid nanofluids, the engineered colloidal mixture made of the base fluid and nanoparticles, have shown many interesting properties and become a high potential nextgeneration heat transfer fluids in various heat exchangers for engineering applications. The present review focuses on improving the performance of tubular heat exchangers by using nanofluids. For this, the present review briefly summarizes the preparation, characterization and thermophysical properties (thermal conductivity, viscosity, specific heat capacity and density) of mono and hybrid nanofluids. Research works on heat transfer and pressure drop characteristics of nanofluids in the double tube and shell-tube heat exchangers with both straight and coiled tubes, and various engineering applications (power generation, refrigeration and air-conditioning, renewable energy, domestic cooling or heating, etc.) are well-grouped and thoroughly discussed. Physical mechanisms for the heat transfer enhancement using nanofluids are explored as well. Most of the studies reveal that there are significant enhancements in the heat transfer process and in the effectiveness of both straight and coiled tube heat exchangers with a slight increase in pressure drop using nanofluids. Hence, there is an excellent opportunity to use nanofluids in tubular heat exchangers; however, high cost (high payback period) and stability are the main challenges for practical implementation. Finally, some useful recommendations are also provided.

Electron beam lithography (EBL) and ion beam lithography (IBL) are extremely promising nanofabrication techniques for building nano-electronic devices due to their outstanding physical and electronic properties. In this review, an overview of EBL and IBL and a comparison of nanoelectronics fabricated based on four types of materials, namely graphene, ZnO, TiO2 and Ge, are presented. In each type of material, numerous practical examples are also provided in the illustration. Later, the strengths and weaknesses of EBL and IBL are presented in details. Finally, the similarities and differences between the two techniques are discussed and concluded.

Background: In recent times, CNTs have been much explored, and a topic of interest in science and technology and not limited to any specific field. The diverse application area included field emission, energy storage, atomic electronics, nuclear force microscopy, and imaging. In biology, CNTs engaged in developing novel tools for the delivery of biologically important molecules as well as in diverse biomedical arenas. However, despite their promise, studies of the interaction of CNTs with biological systems most often resulted in cytotoxicity at an early stage, and problems relevant to the safety and biological compatibility of CNTs are of greatest importance. The toxic effects of carbon nanotubes (CNTs) are required to be either evaded, diminished, or decreased up-to clinical acceptance level. However, rich surface chemistry that CNTs possess can be employed to functionalize them as per the specific biomedical requirements which may be useful to overcome toxicity issues. Objective: To explore the recent reports on the functionalized CNTs for a variety of biomedical applications such as biosensing, electrochemical detection of drug, bone tissue engineering, and vitamin detection. Results: Most of the cited articles reveal that the functionalization of CNTs may reduce its toxicity and enhance its utilization in different biological applications. Conclusion: The review successfully frames to provide novel applications of functionalized CNTs in the biomedical arena including detection of vitamins, bone tissue engineering, electrochemical determination of drugs, and development of biosensors along with a discussion on current patent and clinical trial status of functionalized CNTs.

Background: A sensing material of zinc oxide (ZnO) was investigated for its use in the electrospun nanofibers for gas sensing. The metal oxide semiconductor gas sensor response is caused by the oxygen that undergoes a chemical reaction on the surface of an oxide, resulting in a change in the measured resistance. Objective: One-dimensional nanofibers gas sensor have high sensitivity and diverse selectivity. Methods: One-dimensional nanofiber by an electrospinning method was collected and a sensing membrane was formed. In addition, the gas sensing mechanism was discussed and verified by X-ray photoelectron spectroscopy (XPS). Results: The ZnO nanofiber membrane had an optimum crystalline phase with a lattice spacing of 0.245 nm and a non-woven fabric structure at a calcination temperature of 500°C, whereas the nanofiber diameter and membrane thickness were about 100 nm and 8 μm, respectively. At an operating temperature of 200°C, the sensing material exhibited good recovery and reproducibility in response to Carbon monoxide (CO), and the concentration was also highly discernible. In addition, the reduction in the peak of OIII at 531.5 to 532.5 eV according to the analysis of XPS was consistent with the description of the sensing mechanism. Conclusion: The gas sensor of ZnO nanofiber membranes has high sensitivity and diverse selectivity, which can be widely applied in potential applications in various sensors and devices.

Background: Biosynthesis of gold nanoparticles from medicinal plants has become an interesting strategy in biomedical research due to its exclusive properties including less toxic cellular level through its ecofriendly biological function. Objective: To examine the anti-lipid accumulation effect of spherical gold nanoparticles (size 10-20 nm) synthesized from Dendropanax morbifera Léveille (D-AuNPs) in both 3T3-L1 and HepG2 cells. Methods: 3T3-L1 preadipocytes and HepG2 hepatocytes were stimulated with cocktail media to generate obese and fatty liver disease models. Cell cytotoxicity and cell proliferation assays were performed in adipocytes at different stages of growth. An anti-lipid accumulation assay was performed in 3T3-L1 obese and HepG2 fatty liver models using different doses of D-AuNPs. Expression of adipogenic genes of PPARγ, CEBPα, Jak2, STAT3, and ap2 and hepatogenic genes PPARα, FAS, and ACC was measured by real-time PCR. In addition, protein expression of PPARγ and CEBPα was evaluated by immunoblotting assay. Results: We found that D-AuNPs (size 10–20 nm) at concentrations up to 100 μg/ml were nontoxic to 3T3-L1 and HepG2 at post-confluent and mature stages. In addition, pretreatment of D-AuNPs at post-confluent stage reduced triglyceride content. In addition, the adipogenesis process was negatively controlled by D-AuNPs, with downregulated PPARγ, CEBPα, Jak2, STAT3, and ap2 expression in 3T3-L1 cells and FAS and ACC levels in HepG2 cells. Conclusion: These data indicated that D-AuNPs exert antiadipogenic properties. We hypothesize that Dendropanax contains a large amount of phenolic compound that coats the surface of gold nanoparticles and has the ability to reduce the excess amount of lipid in both cell lines.

Background: Endotoxin-free engineered nanoparticle suspensions are imperative for their successful applications in the field of nanomedicine as well as in the investigations in their toxicity. Gold nanoparticles are known to interfere with various in vitro assays due to their optical properties and potential for surface reactivity. In vitro endotoxin testing assays are known to be susceptible to interference caused by the sample being tested. Objective: This study aimed to identify a preferred assay for the testing of endotoxin contamination in gold nanoparticle suspensions. Methods: The interference by gold nanoparticles on three assays namely, the commonly used limulus amebocyte lysate chromogenic assay, the limulus amebocyte lysate gel-clot method, and the less common recombinant Factor C (rFC) assay, was tested. Results: Possible interference could be observed with all three assays. The interference with the absorbance- based chromogenic assay could not be overcome by dilution; whilst the qualitative nature of the gel-clot assay excluded the possibility of distinguishing between a false positive result due to enhancement of the sensitivity of the assay, and genuine endotoxin contamination. However, interference with the rFC assay was easily overcome through dilution. Conclusion: The rFC assay is recommended as an option for endotoxin contamination detection in gold nanoparticle suspensions.

Background: Based on various distinguished physical and chemical properties of gold nanoparticles, they have far wide applications in several areas of industry and medicine, such as catalysis, bio-sensor and drug delivery. Compared to a chemical method, biological synthesis is an economical and less toxic process, thus it is a better alternative for nanoparticle synthesis. In this study, an environmentally friendly method was chosen to produce AuNPs using Curcuma xanthorrhiza. Methods: Alkaline aqueous extract of C. xanthorrhiza rhizomes, which acts as a reducing and stabilizing agent was used to produce AuNPs by bio-reduction of HAuCl4. The formation of AuNPs was periodically monitored by UV-visible spectroscopy. The obtained AuNPs were characterized by Xray diffraction, energy dispersive spectroscopy, scanning electron microscopy, transmission electron microscopy, and Fourier transform infrared (FTIR) spectroscopy. Catalytic activity and toxicity of the AuNPs were evaluated. Results: The AuNPs obtained from this study mostly were spherical in shape with approximately 15 nm in size. The presence of functional groups derived from C. xanthorrhiza rhizome extract involved in the gold bio-reduction process was confirmed by the spectrum of FTIR spectroscopy. The biosynthesized AuNPs at the concentration of 0.5 μg/ml had catalytic activity in dye degradation of Congo red. The results showed that this biogenic AuNPs did not cause any toxicity to zebrafish embryos and all tested cell lines. Conclusion: The biocompatible AuNPs with catalytic activity were successfully fabricated with C. xanthorrhiza rhizome extract by simple eco-friendly and inexpensive method. This catalytic activity of the obtained AuNPs is potentially useful for industrial applications as well as nanoscience and nanotechnology.

Background: Removal of sulfur-containing compounds from the aqueous environment is necessary as these compounds pose potential risks to human health, hygienic management and bring great economic losses due to fouling of resin bed and corrosion of process equipment. Objective: This work aims to study the H2S removal efficiency using high surface area mesoporous silica (MCM–41). Methods: In this study, mesoporous silica (MCM–41) with a high surface area of 1270 m2/g and high porosity of 69% was prepared by sol-gel technique. Results: The obtained MCM–41 has exhibited a superior performance in adsorbing H2S from wastewater with a maximum adsorption capacity of 52.14 mg/g. The adsorption isotherm and kinetics of the current adsorption process are best represented by Freundlich isotherm and pseudo-secondorder models, respectively. Conclusion: Therefore, MCM–41 is an excellent adsorbent for wastewater treatment applications.

Background: Liquid C8-C15 long-chain alkanes, as the main components of jet fuels or diesel, can be synthetized from abundant and renewable biomass derivatives by extending the carbon- chain length through cascade C-C coupling over acidic catalysts and hydrodeoxygenation over metal particles. Objective: This research aims to develop a carbon-increasing catalytic process through the dimerization of 5-methylfurfuryl alcohol to produce the C11 oxygenate bis(5-methylfuran-2-yl) methane. Methods: In this work, 5-methylfurfural, derivable from sugars, could be reduced to the expensive 5- methylfurfuryl alcohol over Cs2CO3 using an eco-friendly hydride polymethylhydrosiloxane. In the subsequent carbon-increasing process, a solid acidic nanocatalyst 3-chlorpyridine phosphotungstic acid (3-ClPYPW) was developed to be efficient for the conversion of 5-methylfurfuryl alcohol to bis(5-methylfuran-2-yl) methane under mild reaction conditions. Results: A good bis(5-methylfuran-2-yl) methane yield of 51.6% was obtained using dichloromethane as a solvent at a low temperature of 70°C in 11 h. The solid nanocatalyst was able to be reused for at least four cycles without a remarkable loss of catalytic activity. The kinetic study proved that the reaction is a first-order reaction with apparent activation energy (Ea) of 41.10 kJ mol-1, while the thermodynamic study certified that the reaction is non-spontaneous and endothermic. Conclusion: A novel catalytic pathway for the synthesis of BMFM (C11 oxygenate) by the one-pot process was successfully developed over solid acidic nanocatalysts 3-ClPYPW.

Background: Copper is an important micronutrient required for the growth of the plants. It activates enzymes and helps in protein synthesis in plants. Nanoparticles in the size range from 1 to 100 nm possess unique properties, such as the high surface area to volume ratio, size-dependent capabilities and unique optical properties, and hence, copper nanoparticles (CuNPs) were evaluated for growth promotion of mung bean (Vigna radiata L.). Objective: The main aim of the study was to synthesize CuNPs using neem extracts, and evaluate their activity on viability of seeds and growth of seedlings in V. radiata. Methods: Here, we synthesized CuNPs by the neem (Azadirachta indica) leaf extract, which was treated with copper sulphate and ascorbic acid. The reduction of copper sulphate to CuNPs was confirmed by the UV-Visible spectrophotometer and was further characterized by XRD, FTIR, NTA, and Zeta potential measurement. The efficacy of biogenic CuNPs (size <50 nm) was evaluated on germination and growth promotion of V. radiata seeds. The copper content was confirmed in CuNPs treated plants after analysis by Atomic Absorption Spectroscopy (AAS). Results: CuNPs were synthesized by the neem (A. indica) leaf extract as brown precipitation. Preliminary detection was performed by UV-Visible spectrophotometer, which showed a peak at 619 nm. Further characterization by X-ray diffraction confirmed the Face Centered Cubic crystal structure. Fourier Transform Infra Red spectroscopy analysis revealed the presence of amino acids as functional groups in the leaf extract. Nanoparticle tracking and analysis (NTA) demonstrated an average size of 41±21 nm with the concentration of 3.3x109 particles/ml. Zeta potential value was found to be -18.2 mV. The growth promotion effect showed the maximum germination recorded at 100 ppm of CuNPs; while copper ions showed an adverse effect on root growth. The AAS analysis demonstrated the increased copper content in the CuNPs treated seedlings than that of the control. Conclusion: It is a first report to demonstrate the positive effect of biogenic CuNPs on growth, nutrition and enhanced seed germination, and hence, CuNPs could be used as a nano-fertilizer after further extensive nursery trials.

Background: Due to temperature-insensitive and limited tribochemical reaction, nanolubricants have received tremendous focus over the past few years. The addition of nanoparticles in lubricant has been demonstrated to reduce the coefficient of friction and increase the loadcarrying capability of lubricant in coupled surfaces. Much attention has been paid to copper nanoparticles for their perfect friction reduction and wear resistance performances. However, it is difficult to maintain stable dispersion in lubricant oil for the aggregation of copper nanoparticles. Methods: A novel macromolecular coupling agent copolymer, styrene-butyl methacrylate-3- methoxyacryloyl-propyltrimethoxyl silicon was successfully prepared by free radical polymerization. The structure and composition of the copolymer were characterized through X-ray diffractometer, Fourier-transform infrared spectrometer, and nuclear magnetic resonance spectrometer. The loadcarrying capacities and anti-wear properties of the base oil were evaluated on four-ball tester. Results: The average size of the nano-Cu particle was around 40 nm. The modifier, St-MMA-(KH- 570) macromolecular copolymer could improve the dispersibility of nano-Cu particles. The introduction of the nano-Cu particles helped to improve the tribological properties of base oil. Conclusion: The macromolecular coupling agent was synthesized by free radical solution polymerization method. The modifier was able to bond to the nano-Cu via chemical interaction. The modified Cu nanoparticles as the additive were able to greatly improve the anti-wear and extreme pressure properties of base oil. The optimum concentration of modified Cu nanoparticles in base oil was 0.25 wt.%.

Background: World energy crisis has triggered more attention to energy developing of clean energy carrier. To find simple, economical and effective hydrogen evolution reaction catalysts is one of the major challenges. Rational design and modification of electrocatalysts materials are of great importance for the development of low-cost and effective catalysts. Methods: Herein, we report a Ni-CNTs-HG/NF electrode catalyst, which is fabricated on the surface of Ni foam by electrodeposition technique. The fabrication strategy allows the construction of a composite architecture with the Ni foam morphology at the macro level, and the Ni nanoparticles supported by carbon nanotubes and Hydrophilic graphene nanosheets at the nanoscopic level. Results: Compared to NF electrocatalyst, the Ni-CNTs-HG/NF, the CNTs and HG sheets possess the largest electrocatalytic active surface area, providing Ni nanoparticles with catalytically active sites. The Ni-CNTs-HG/NF electrocatalyst exhibits better HER performance in alkaline electrolytes. Conclusion: The Ni-CNTs-HG cathode performs its activity under alkaline conditions with an overpotential i.e 56 and 227 mV at a current density of 10 and 100mAcm-2, which is much lower than that of Ni foam electrode (423 and 278 mV). The secret of the enhanced electrochemical activity lies in its interior structure by coupling metal nanoparticles with carbon materials.

Background: Titanium dioxide (TiO2) is currently one of the most widely known nanomaterials produced for different purposes. The adverse effects of nano-dispersed TiO2 cause a serious concern about human health problems related to the intake of TiO2 nanoparticles (TiO2 NPs). The investigation of TiO2 NPs’ penetration through the gut epithelium into secondary organs and the relevant biological effects has an undoubted importance when assessing the potential risk of using TiO2 NPs. Objective: In the current study, we investigated the effect of rutile TiO2 NPs on tissues of the small intestine, liver, and spleen. For this purpose, we used a physiological model that simulates the single administration of TiO2 NPs directly into the intestinal lumen of an experimental animal. Methods: Suspensions TiO2 NPs were administered via an isolated loop of the small intestine at a single dose of 250 mg/kg of body weight. TiO2 NPs were detected in rats’ tissues by transmission electron microscopy. Results: TiO2 NPs were found in tissues of the small intestine mucosa, liver, and spleen. The administration of TiO2 NPs resulted in different changes in the cellular ultrastructures: hyperplasia of the smooth endoplasmic reticulum, an increase in the size of the mitochondria, the emergence of local extensions into the perinuclear space, and the appearance of myelin-like structures. Conclusion: The ultrastructural changes found in the individual cells of the small intestine, liver, and spleen indicated intracellular pathology, induced by the high doses of the TiO2 NPs. The spleen tissue appeared to be the most sensitive to the effect of TiO2 NPs.

Background: The architecture and sequential learning rule-based underlying ARFIS (adaptive-receiver-based fuzzy inference system) are proposed to estimate and predict the adaptive threshold-based detection scheme for diffusion-based molecular communication (DMC). Methods: The proposed system forwards an estimate of the received bits based on the current molecular cumulative concentration, which is derived using sequential training-based principle with weight and bias and an input-output mapping based on both human knowledge in the form of fuzzy IFTHEN rules. The ARFIS architecture is employed to model nonlinear molecular communication to predict the received bits over time series. Results: This procedure is suitable for binary On-OFF-Keying (Book signaling), where the receiver bio-nanomachine (Rx Bio-NM) adapts the 1/0-bit detection threshold based on all previous received molecular cumulative concentrations to alleviate the inter-symbol interference (ISI) problem and reception noise. Conclusion: Theoretical and simulation results show the improvement in diffusion-based molecular throughput and the optimal number of molecules in transmission. Furthermore, the performance evaluation in various noisy channel sources shows promising improvement in the un-coded bit error rate (BER) compared with other threshold-based detection schemes in the literature.