Journal of Nano Research Vol. 74

Abstract: Semiconducting single-wall carbon nanotubes (SWCNTs) have already emerged as a promising candidate for molecular electronics and photovoltaic applications including solar cells. Any application of semiconducting SWCNTs is primarily related to proper information about its bandgap. In this work, the impact of the chirality indices and diameters of a series of armchair and zigzag SWCNTs on the electronic properties (band gap, electronic band structure and density of states (DOS)) are investigated using semi-empirical π orbitals tight-binding (TB) method. The results indicate that the electronic behaviour of the nanotubes changes according to chirality, the total number of electronic sub-bands gets increased when the chirality increases and Van Hove singularities (VHs) appear in its electronic DOS. We have found that for small diameter tubes (less than 0.8 nm), the calculated band gaps don’t agree with DFT calculations based on ab-initio (LDA and GGA) methods, which shows that the semi-empirical TB method including π orbitals only is not sufficient to give a reasonable description of small nanotubes. All Obtained results are in good agreement with previous studies. Semiconducting SWCNTs used in this study are particularly well-suited for the nanoelectronic devices and optoelectronic applications with their direct bandgap and optical transitions, while metallic SWCNTs are considered to be ideal candidates for variety of future nanoelectronic applications such as nanocircuit interconnects and power transmission cables.

Abstract: Various filling fractions of silver silica nanocomposites (Ag-SiO₂ NC) were successfully synthesized via sol-gel technique and deposited onto indium tin oxide via electrophoretic deposition (EPD). Ag-SiO₂ NC was investigated using X-ray diffraction, FTIR spectroscopy, Uv-vis and transmission electron microscopy. The XRD and Uv-vis results revealed that Ag-SiO₂ NC is stable with a filling fraction of 0.6 in the dielectric medium with excellent absorption peak. Spectroscopy Ellipsometry shows that the effective permittivity and refractive index obtained from this filling fraction are -0.88 and 0.90, respectively. We discovered a ragged of metamaterial properties at negative permittivity.

Abstract: This work presents the fabrication and testing of a cost-effective, low power consuming, high sensitivity aluminum nitride nanowire-film-based ultraviolet photodetector. Time-dependent dynamics of photocurrent rise and decay have been investigated with varying applied bias ranging from 1 V to 20 V by periodical exposures to 254 nm ultraviolet light. The device shows stable and repeatable photocurrent cycles at low bias voltage of 1V indicating the sensitivity and low power operating capability. Furthermore, the photocurrent increases as the bias voltage increases such that the photocurrent at 20 V is approximately seventeen times larger than that of at 1 V. Despite the relatively long device length, the device reveals a quick response with a rise time of 270 ms. Moreover, the responsivity of the photodetector has been determined as 3.78 mA/W and 0.201 mA/W at 20 V and 1 V, respectively. This study demonstrates the potential of aluminum nitride nanowires for applications in next generation, low power consumption nanoscale optoelectronic devices in advanced communication, flame detection, air purification, ozone sensing, leak detection and other space monitoring.

Abstract: Hexavalent Chromium (Cr (VI)) and Reactive Blue (RB) removal efficiencies of halotolerant Citricoccus sp. were examined for different parameters such as initial pH, contact time, temperature static/shaking, NaCl concentration, and different pollutant concentrations. In this research, Citricoccus sp. attached cellulose acetate (CA) nanofiber webs (NfW) were produced by electrospinning method to improve the removal yield even further. The Cr (VI) removal yield was calculated as 11.39 ± 0.002% for the pristine CA-NfW, whereas it was 39.19 ± 0.43% for bacteria attached CA-NfW. Therefore, the Cr (VI) removal capacities of bacteria attached CA-NfW were significantly higher than that of pristine CA-NfW. In addition, reusability tests revealed that bacteria attached CA-NfW can be used at least three successive times in decolorization and Cr (VI) removal steps. The decolorization rate of the RB and Cr (VI) removal yield was found to be 31.5 ± 0.2% and 5.63 ± 0.30%, respectively. These results are promising and therefore suggest that bacteria attached CA-NfW could be applicable for the removal of wastewater containing Cr (VI) and reactive dye due to their versatility and reusability.

Abstract: Photocatalytic reduction of 4-nitrophenol is one of the most promising methods to remove this hazardous pollutant from wastewaters and generated a raw compound widely use in industrial processes. In the present work, three Bi₂S₃/TiO₂ catalysts with different Bi₂S₃ content, were synthesized by a hydrothermal method. The materials were characterized by XRD, X-ray fluorescence, physisorption of N₂, HRTEM, UV-Vis reflectance spectroscopy and zeta potential measurements. The catalytic activity of the synthesized materials was tested in the photoreduction of 4-nitrophenol in aqueous medium. Although the results indicate the formation of heterojunction for all the samples, the physicochemical properties of each material depend on the Bi₂S₃ content. The material with 6%wt of Bi₂S₃ exhibit the major catalytic activity, reducing 80% of the target molecule within 60 minutes of reaction.

Abstract: There are many methods for synthesizing magnetite nanoparticles. Most methods take a long time, and the result is undesirable. In this paper a green method was used to synthesize nanoparticles because it takes a short time and is both straightforward and eco-friendly. It is done by adding : =1:2 molar ratio solution with different amounts of extract and different amounts of NaOH solution for 20 min at different temperatures, in hotplate stirrers, to control their relative size. UV-Vis spectroscopy, vibrating sample magnetometer technique (VSM), transmission electron microscopy (TEM), and X-ray diffraction (XRD) were used to characterize the magnetite nanoparticles. The result confirms that the changes in amounts of NaOH and extract led to a change in the pH of a solution and that the increase in amounts of the extract caused the low addition of NaOH. These changes influenced the process of synthesis and characterization. The Uv-vis analysis confirms that the surface plasmon resonance had a highly visible brad peak in the 290–460 nm range, as well as a peak shift to shorter wavelengths (blue shift) with a pH change and a peak shift to longer wavelengths (red shift) with a temperature change. TEM imaging confirms that all the synthesized had a spherical shape with size changed according to a parameter change of within 40–9 nm. Magnetic analysis showed the magnetite nanoparticles synthesized have smaller sizes and are superparamagnetic with the influence of particle size on the magnetic properties, including Hc, Ms, and Mr.

Abstract: The feasibility of graphene oxide (GO) obtained by both Hummers and Tour method to prepare reduced graphene oxide (rGO) as well as chemically reduction under different experimental conditions were evaluated with the objective of establishing the key items that should be considered when performing the synthesis of GO and rGO. This key items can be supportive to select the most feasible methodology to synthesize GO and rGO depending on the future application. Reduced graphene oxide was prepared by combining chemical and solvothermal as well as combined reduction adding a final thermal annealing step. Obtained GO and rGO were characterized by XRD, Raman spectroscopy, XPS and BET analysis. A higher oxidation degree was achieved for samples from Tour method than those oxidized by Hummers method. On the contrary, lower oxidation degree from Hummers graphene oxide (GO-H) facilitates the subsequent reduction process, leading to a higher reduced rGO. Hence, rGO samples obtained from the Hummers method in the different reduction treatments presented higher C/O atomic ratios than the corresponding Tour method. In addition, the combination of a solvothermal treatment and chemical reduction, including a final annealing stage, increases significantly the value of the C/O ratio as well as it contributes to decrease the defect density and the restoration of π-conjugated structure. Besides, rGO samples obtained from Tour method presented higher SSA and pore volume than those samples obtained from Hummers method. Results from this study suggest the suitability of Tour graphene oxide (GO-T) for chemical functionalization which is very useful for several applications. In addition, GO and rGO coming from Tour method are more appropriate to applications in which high surface area is required. Taking into account the vast possible applications for chemically-exfoliated graphene the findings of this study could help to select the best method for oxidising graphite depending on the intended application.

Abstract: Yttria stabilized tetragonal zirconia (Y_0.08Zr_0.94O₂, YSZ) nanopowders were successfully synthesized by microwave solvothermal method (MSM). The synthesizing temperature, holding time and mineralizer concentration were optimized. The crystallization and particle distribution of as-prepared YSZ nanopowders were identified by DSC/TG, XRD, FESEM, TEM, FTIR, DLS, and BET. The dispersion of YSZ nanopowders dried by different methods and modified by polyethyleneimine (PEI) was analyzed and discussed. The results show that the PEI modified samples have the best dispersion, and the dispersion of freeze-dried samples is better than that of traditional dried ones. The particle size of the PEI modified samples calculated from the surface area determined by BET is 15.7 nm, which is consistent with that determined by TEM (16.5 nm), but slightly smaller than that calculated by the Scherrer formula according to XRD (22.3 nm). This may be attributed to the different testing principles in these methods.

Abstract: According to the motion style, a nanomotor can be classified into linear nanomotor and rotary nanomotor. Nanomotors, as the core components of nanomachine, have broad research prospects and applications. Here, a molecular dynamics method is used to simulate the linear nanomotor on a stretched carbon nanotube substrate. The results show that the nanomotor speed is well controlled by the temperature gradient, the axial strain of the substrate and the nanomotor size. When the nanomotor moves stably on the substrate carbon nanotube with a temperature difference of 200 K at both ends, the time required for the nanomotor to travel the same distance on the substrate carbon nanotube with 15% strain is about 62% longer than that without strain. The mechanism for the nanomotor movement and speed control is attributed to the thermophoretic force acting on the nanomotor. Specifically, the thermophoretic force increases with increasing substrate temperature gradient and decreases with increasing substrate strain. These results provide a novel method for controlling the speed of a nanomotor and inform nanomotor design and manufacture, as well as presenting a deeper understanding of the mechanism and movement law of the nanomotor.

Abstract: MXene is a recently emerged two dimensional (2D) layered materials, a novel series of transition metal carbides, nitrides and carbonitrides were established by a group of scientists from Drexel University in 2011. Multi-layered MXene nanomaterials have been synthesized using different wet chemistry etching approaches. To date, around twenty different types of MXenes are synthesized using different wet chemistry etching techniques. To ensure reproducibility of the MXene, advanced characterizations in terms of morphology, structure as well as elemental compositions of the MXene flakes are conducted. MXenes nanosheets possess a significant thermo-electrical conductivity, reasonable band gap and high intrinsic carrier mobilities. The family materials of the MXenes have high potential for making energy storage devices such as batteries and supercapacitors as well as several many other implications such as electromagnetic interference shielding and capacitive desalination. MXenes are the potential candidates for hydrogen storage due to the interactive nature of hydrogen and these layered-structure materials. MXenes in biomedical applications were proven as valuable materials due to the tunable physiochemical properties into new distinct structures which is difficult to be manipulated in bulk materials. Besides, MXenes possess suitability of functionalization for tuning the various required properties for the specific properties. The many potential properties of MXene have disclosed new possibility to address the current need of higher efficiency materials for different applications.