Journal of nanoscience and nanotechnology最新文献

In this work, UV light activated multi-cycle photoelectric properties of TiO₂ and CdS/TiO₂ films in formaldehyde were researched. TiO₂ film was prepared by screen printing, CdS/TiO₂ compounded film was synthesized by SILAR method. XRD and FE-SEM was used to characterize the TiO₂ and CdS/TiO₂ samples. Multi-cycle photoelectric properties of TiO₂ and CdS/TiO₂ with uv light on and off were evaluated by testing the photocurrent. On one hand, under the same bias voltage, CdS/TiO ₂showed a higher photocurrent than that by TiO₂. The reason for this result should be ascribed to the compounded structure in CdS/TiO₂, with which the separation and transfer of photogenerated electron-hole pairs could be improved. On the other hand, with the testing cycle number increased, the photocurrent amplitudes of TiO₂ and CdS/TiO₂ increased. These results suggested that the time to reach a stable photocurrent value for TiO₂ and CdS/TiO₂ is much longer than one cycle time (300 S). To illustrate the increased photocurrent amplitude value cycle by cycle, the photocurrent of CdS/TiO₂ to a much longer time (more than 4000 seconds) was also tested. To explain these results, corresponding possible illustrations were presented.

This paper discusses the structure, particle morphology, and optical properties of un-doped ZnO and ZnO doped with Er³⁺ and Yb³⁺ lanthanide ion nanoparticles (NPs) through a process denominated sol-gel-hydrothermal. According to the pattern of X-ray diffraction, ZnO:Er and ZnO:Yb is formed by a single-phase wurtzite structure with crystallites sized ~65 nm on average, and Er or Yb dopant ions in the hexagonal structure of ZnO, specifically in its distorted lattice sites. The results also suggest the possible role of oxygen vacancies or O^x- (defects) in the energy transfer from ZnO to the Er or Yb ions with a decrease of 3.18 eV and 3.19 eV in bandgap values to a red shift.

The presence of microcapacitors near percolatrion threshold determines dielectric permittivity of a material. Motivated by this concept, we focused our work by preferentially allocating functionalized reduced graphene oxide (FRGO) in hard segment (disperse phase) of Thermoplastic polyurethane (TPU) by solution blending method and characterized. Morphological studies of TPU/FRGO nanocomposites established homogeneous dispersion of FRGO throughout the TPU matrix. It is noted that TPU/FRGO (1 phr) nanocomposites exhibit maximum increase in tensile strength (33%) and elongation at break (10%). Thermogravimetric analysis (TGA) showed maximum enhancement in onset of decomposition temperature (~6 °C) in 2 phr FRGO loaded TPU. Differential scanning calorimetry (DSC) analysis showed maximum reduction (~2 °C) in glass transition temperature (T_g) of soft segment of TPU followed by maximum improvements in melting temperature (~4 °C) as well as crystallization temperature (~22 °C) of hard segment compared to neat TPU. Further, a significantly high value of dielectric permittivity (401) is achieved in 1.5 phr loaded FRGO at 100 Hz due to the formation of significantly higher number of microcapacitors near the percolation threshold. It is anticipated that such thermally stable and mechanically strong high dielectric TPU/FRGO nanocomposites can find applications in the field of electronic devices.

Polyelectrolyte multilayers are promising drug carriers with potential applications in the delivery of poorly soluble drugs. Furthermore, the polyelectrolyte multilayer contributes towards electrostatic interactions, which enhances the physical and chemical stability of colloids when compared to those prepared by other approaches. The aim of this work was to generate a polyelectrolyte multilayer on well characterised nanoparticles of the poorly water-soluble drug, griseofulvin. Griseofulvin (GF) nanoparticles (300 nm) were produced by wet bead milling, bearing a negative surface charge due to the use of poly(sodium 4-styrenesulfonate) (PSS) as a stabiliser. Six further layers of alternating chitosan and PSS polyelectrolyte multilayer were successfully generated at the particle surface either via use of: (1) the conventional method of adding excess coating polymer followed by centrifugation, or (2) the continuous in situ approach of adding sufficient amount of coating polymer. The continuous in situ method was designed de novo by the consecutive addition of polymers under high shear rate mixing. In comparison to the continuous in situ method, the conventional method yielded nanoparticles of smaller size (282 ±9 nm vs. 497 ±34 nm) and higher stability by maintaining its size for 6 months. In conclusion, the parent griseofulvin nanosuspension proved to be a suitable candidate for the polyelectrolyte multilayer fabrication providing an avenue for a bespoke formulation with versatile and potentially enhanced drug delivery properties.

Nanomaterials, such as magnetic nanoparticles have attracted significant attention of medical area due to their capacity to improve the performance of immunoassays. Therefore the aim of this work was to study the bovine serum albumin (BSA) conjugation in superparamagnetic (MNPs)/poly(methyl methacrylate) (PMMA) nanoparticles with further characterization and application in enzyme-linked immunosorbent (ELISA) assay. The successful conjugation of BSA in MNPs- PMMA nanoparticles was confirmed by several techniques, including light scattering, zeta potential, transmission electron microscopy (TEM) and Lowry protein quantification assay. The superparamagnetic properties were confirmed by vibrating sample magnetometer. BSA conjugated MNPs-PMMA nanoparticles presented higher interactions with antibody than free BSA. The BSA + MNPs-PMMA nanoparticles (magnetic ELISA assay) reduced the time and increased the sensibility of traditional ELISA assay, reinforcing the idea that the use these nanomaterials are an excellent alternative for the immunoassays field.

A newly synthesized free fatty acids from waste palm oil functionalized magnetic nanoparticles immobilized on the surface of graphene oxide (FFA@MNP-GO) was successfully synthesized and characterized in this research. The combinations of long alkyl chain of free fatty acid with graphene oxide that consists of large delocalized 77-electron systems and abundant of hydrophilic groups with hydroxyl, epoxide and carboxylic groups offer the determination of simultaneous wide range of polarities of organic pollutants in real matrices through hydrogen bonding, hydrophobic and 77-77 interactions. The fabricated adsorbent was successfully applied as a magnetic solid phase extraction (MSPE) adsorbent for the simultaneous separation of selected phthalate esters (PAEs) and polycyclic aromatic hydrocarbons (PAHs) in apple and cabbage extracts prior to their high performance liquid chromatography with diode-array detector (HPLC-DAD) determination. Factors affecting the extraction efficiency such as amount of adsorbent, desorption solvent, volume of desorption solvent, extraction time, desorption time, pH and sample volume were investigated and optimized. The results revealed that under optimal conditions, the detection limit of selected PAEs and PAHs were in the range of 0.56-0.97 ng mL^-1 and 0.02-0.93 ng mL^-1, respectively. The spiked recoveries of real apple and cabbage extracts for PAEs and PAHs were in the range of 81.5-117.6% with good relative standard deviation (RSD) (n = 5) less than 10% and 86.7-118.2% with acceptable RSDs (n = 5) ranging from 1.5 to 11.0%, respectively. This study reported for the first time the use of MSPE procedure for simultaneous determination of chosen PAHs and PAEs in real samples including apple and cabbage extracts by using new adsorbent, FFA@MNP-GO.

In order to combat antibiotic resistance, the development of new antibacterial agents is essential. In this study, we prepared four types of amino acid modified chitosan (CS-AA). Compared with chitosan modified with hydrophobic amino acids, the chitosan modified with positively charged amino acids showed higher antibacterial efficiency against Escherichia coli (E. coli) under similar grafting rate. CS-AA achieves antibacterial properties mainly by destroying the integrity of bacterial cell membranes. All the four types of CS-AA show low toxicity towards red blood cells. This work indicates that positively charged groups are more important than hydrophobic groups in the design of chitosan-based antibacterial agents, and provides helpful information for the molecular design of effective antibacterial agents.

THIS ARTICLE WAS WITHDRAWN BY THE PUBLISHER IN MAY 2021

This study is focused on a simple and fast synthesis of nonstoichiometric magnetite nanoparticles with the chemical formula Fe_3-XO₄ and magnesium ferrite nanoparticles (Mg_1-XFe_2+XO₄). The nanoparticles were prepared with Fe²⁺ ions (FeSO₄ · H₂O) alkalised by KOH under oxidative conditions and in a microwave field. X-ray powder diffraction (XRD) and ⁵⁷Fe transmission Mössbauer spectroscopy were used to determine the phase composition and crystal structure in detail. The presence of synthetic magnetite, maghemite, goethite, and magnesium ferrite was observed. Room temperature Mössbauer spectroscopy revealed the existence of ferromagnetic sublattices and superparamagnetic fraction. The superparamagnetic component corresponds to magnesium ferrite nanoparticles. Low temperature Mössbauer spectroscopy was used to locate the blocking temperature of superparamagnetic nanoparticles and to separate the sublattices. The presumed spherical morphology of nanoparticles and their size under 100 nm have been confirmed by transmission electron microscopy (TEM). The obtained results were used to provide possible reaction scheme, which serves to tailor the synthesis to a desired application.

A small aliquot (10-14 μL) of ZnO nanoparticles dispersed in deionized water was deposited by evaporation to produce a dry residue on the working area of a screen-printed electrode. An electrochemical test solution containing K₃Fe(CN)₆ and KCl was added to the electrode surface for analysis by electrochemical impendence spectroscopy (EIS). Using this deposition analysis technique, a new relationship between the charge transfer resistance (R_ct) and the amount of ZnO nanoparticles has been explored. Based on the trend of increasing R_ct value with an increase of ZnO nanoparticles, a quantitative analysis method can be established to determine the mass of nanoparticles (0.01-1.00 μg) deposited from an unknown dispersion. To study the matrix effect, addition of Nafion solution to the aqueous dispersion resulted in a change of the linear range to 0.3-0.5 μg nanoparticles. Addition of methanol (10% by volume) to the aqueous dispersion changes the analysis range to 0.2-0.6 μg nanoparticles, while additional methanol (50% by volume) changes the analysis range to 0.06-1.00 μg nanoparticles. The analytical sensitivity, as indicated by the slope of each standard calibration curve, ranked as: aqueous dispersion > Nafion/aqueous dispersion > 10% methanol/aqueous dispersion > 50% methanol/aqueous dispersion. Altogether these results verify that deionized water is the best dispersion medium for EIS analysis of ZnO nanoparticles.