Ahmad Tayyebi

Magnetite/dextran-functionalized graphene oxide nanosheets for in vivo positive contrast magnetic resonance imaging

Superparamagnetic iron oxide (SPIO) nanomaterials are widely used as magnetic resonance imaging (MRI) contrast agents (CAs). These CAs significantly shorten transverse relaxation time (T2) and so decrease the intensity of the T2-weighted MRI (negative contrast imaging). However, the partial-volume effect is known to be one of the problems in negative contrast MRI. In this work, SPIO nanoparticles were modified by dextran and graphene oxide (GO) nanosheets to achieve a positive contrast MRI with high intensity. This modification resulted in shortening the longitudinal relaxation time (T1) of the SPIO nanoparticles (in addition to the T2 shortening). Using FLASH pulse sequence, T1-weighted positive contrast MRI of Wistar rats revealed that the SPIO/dextran-functionalized GO (SPIO-Dex-FGO) significantly enhanced the contrast to noise ratio (CNR) of the positive contrast MRI as compared to the common clinical positive CA, i.e., Magnevist®. In fact, based on the CNR calculations for in vivo positive contrast images it was found that the SPIO-Dex-FGO could provide the same CNR as Magnevist® at concentrations two orders of magnitudes lower than the concentrations used for Magnevist®. Therefore, SPIO-Dex-FGO can be proposed as a promising substitution for the current CAs such as Magnevist® in T1-weighted positive contrast MRI, at lower and safer concentrations.

Supercritical synthesis of a magnetite-reduced graphene oxide hybrid with enhanced adsorption properties toward cobalt & strontium ions

The current study presents a supercritical synthesis of magnetite-reduced graphene oxide (M-RGO) in methanol media, in which Fe3O4 nanoparticles are simultaneously formed, surface modified and decorated on the surface of the reduced graphene oxide. Simulations using density functional theory, which were performed using the M06-2x/cc-pVDZ level of theory, indicate that upon adsorption of a Fe3O4 cluster on the graphene, the overall charge on the graphene surface becomes about −0.0236e, indicating charge transfer from the Fe3O4 cluster to the graphene surface. Instrumental and chemical analyses exhibited the formation of strong bonds between Fe3O4 and graphene, through C–O–Fe and C–Fe bridges. Based on this data the study puts forward a formation mechanism for M-RGO. The adsorption behavior of the M-RGO towards Co2+ and Sr2+ ions demonstrated an appreciably higher uptake capacity than that of magnetite-graphene oxide (M-GO), a zero zeta potential point at pH ≈ 2, endothermic and spontaneous adsorption, and fast kinetics that was controlled by the chemical reaction between the ions and the surface active sites of the Fe3O4 nanoparticles. The material also showed good reusability, quick elution by 0.5 mol dm−3 HCl, and most importantly, simple separation from the solution using a magnet. Overall, the M-RGO appears to be a promising alternative for the current magnetite-graphene oxide hybrids in the adsorption of heavy metal ions.

Synthesis and characterization of new biopolymeric microcapsules containing DEHPA–TOPO extractants for separation of uranium from phosphoric acid solutions

A novel microcapsule adsorbent for separation of uranium from phosphoric acid solutions was developed by immobilizing the di(2-ethylhexyl) phosphoric acid–trioctyl phosphine oxide extractants in the polymeric matrix of calcium alginate. Physical characterization of the microcapsules was accomplished by scanning electron microscopy and thermogravimetric techniques. Equilibrium experiments revealed that both ion exchange and solvent extraction mechanisms were involved in the adsorption of ions, but the latter prevailed in a wider range of acid concentration. According to the results of kinetics study, at low acidity level, the rate controlling step was slow chemical reaction of ions with the microdroplets of extractant, whereas it changed to intraparticle diffusion at higher acid concentration. The study also attempted identification of the diffusion paths of the ions within the microcapsules, and the mechanism of change of mass transfer rate during the uptake process. The prepared microcapsules preserved their entire capacity after three cycles of adsorption, and their breakthrough behaviour was well fitted by a new formula derived from shrinking core model.

Synthesis and Characterization of a Bentonite-Alginate Microspherical Adsorbent for Removal of Uranyl Ions from Aqueous Solutions

A novel microspherical adsorbent for the removal of uranium from aqueous solutions was developed by immobilizing of natural bentonite in the polymeric matrix of calcium alginate. Different uptake properties of the prepared microspheres were examined using batch, stirred and column methods. The adsorbent showed high affinity toward uranium ions, especially at pHs above 3. Major uptake mechanisms included ion exchange, chelating of the (UO2)2+ ions to the ‒OH groups of alginate, and surface complexation with bentonite. Surprisingly, the capacity of microspheres was higher than both its constituents, revealing that a synergetic effect occurs. Adsorption kinetics was controlled by slow chemical reaction of ions with bentonite, and it obeyed a shrinking core model. Also a pseudo-second order chemical reaction fairly fitted the kinetics data. The synthesized microsphrese, in addition to cost efficiency, showed a relatively good column performance and high durability and reusability.

Synthesis, characterization and biological evaluation of a well dispersed suspension of gallium-68-labeled magnetic nanosheets of graphene oxide for in vivo coincidence imaging

Abstract Graphene oxide (GO) nanosheets were hybridized with Fe3O4 nanoparticles (NPs) to form magnetic GO (MGO) and were further labeled by [68Ga]GaCl3 as a potential drug delivery system. Paper chromatography, Fourier transform infra red (FTIR) spectroscopy, low-angle X-ray diffraction (XRD), CHN and atomic force microscopy (AFM) were utilized to characterize the trinary composite ([68Ga]@MGO). Biological evaluations of the prepared nanocomposite were performed in normal Sprague Dawley rats and it was found to be a possible host for theranostic radiopharmaceuticals. The results showed that the grafting of Fe3O4 NPs on nanocomposite reduced the unwanted liver and spleen uptakes and increased the ratio of kidney/liver uptake from 0.037 to 1.07, leading to the fast removal of radioactive agent and less imposed radiation to patients. The high level of hydrogen bonding caused by the presence of functional groups is responsible for this effect. Considering the accumulation of the tracer in vital organs of rat (especially brain), efficient iron oxide grafting, fast wash-out, the short half-life gallium-68 and less imposed radiation doses to patients, this nanocomposite could be a suitable candidate for positron emission tomography (PET) studies and imaging applications.

Effect of graphene oxide nanosheets on visible light-assisted antibacterial activity of vertically-aligned copper oxide nanowire arrays

In the present work, the effect of graphene oxide (GO) nanosheets on the antibacterial activity of CuO nanowire arrays under visible light irradiation is shown. A combined thermal oxidation/electrophoretic deposition technique was employed to prepare three-dimensional networks of graphene oxide nanosheets hybridized with vertically aligned CuO nanowires. With the help of standard antibacterial assays and X-ray photoelectron spectroscopy, it is shown that the light-activated antibacterial response of the hybrid material against gram-negative Escherichia coli is significantly improved as the oxide functional groups of the GO nanosheets are reduced. In order to explore the physicochemical mechanism behind this behavior, ab-initio simulations based on density functional theory were performed and the effect of surface functional groups and hybridization were elucidated. Supported by the experiments, a three-step photo-antibacterial based mechanism is suggested: (i) injection of an electron from CuO into rGO, (ii) localization of the excess electron on rGO functional groups, and (iii) release of reactive oxygen species lethal to bacteria. Activation of new photoactive and physical mechanisms in the hybrid system makes rGO-modified CuO nanowire coatings as promising nanostructure devices for antimicrobial applications in particular for dry environments.

Evaluation of dosimetric characteristics of graphene oxide/PVC nanocomposite for gamma radiation applications

Abstract Graphene oxide-polyvinyl chloride composite was prepared using tetrahydrofuran solvent-assisted dispersion of characterized nano flakes of graphene oxide in polymer matrix. Electrical percolation threshold of GO/PVC nanocomposite was determined via a finite element simulation method with a 2D model and compared with experimental results. A conductive cell with two silver coated walls was designed and fabricated for exploring dosimetric properties of the composite. Some characteristics of the new nanocomposite such as linearity of dose response, repeatability, sensitivity and angular dependence are investigated. According to 2D proposed method, obtained data associated to electrical conductivity of the GO/polymer composite for PVC matrix plotted in different GO weight percentages and had good compatibility (validity) with experimental data. The dose response is linear in the 17–51 mGy dose range and it can be introduced for gamma radiation dosimetry in diagnostic activities.

Sonochemical-driven ultrafast facile synthesis of WO3 nanoplates with controllable morphology and oxygen vacancies for efficient photoelectrochemical water splitting

Among the various synthetic techniques, the sonochemical method has emerged as an interesting method for fabricating different photocatalysis materials with unique photoelectrochemical (PEC) properties. In comparison with the classical method without sonication, this study examines the promoting effect of ultrasonic irradiation during the synthesis of tungsten oxide (WO3) nanoplates within short reaction times (15 and 30 min). The shorter ultrasonic reaction time (15 min) was sufficient for the uniform growth of thin and compact layers of WO3 nanoparticles (NPs) on the surface of a tungsten foil. In the classical method, however, partial cracks or patches formed when WO3 samples underwent acid treatment for either 15 min or 30 min at 90° C. The WO3 nanoplates fabricated with 15- or 30-min sonication followed by 15- or 30-min deposition (U-15/30-15/30) showed much higher photocurrent density than the WO3 samples fabricated with the classical method without sonication (C-15/30) at 90 °C. The as-prepared monoclinic WO3 with 30-min ultrasonication and 30-min deposition (U-30/30) showed a maximum photocurrent density of ∼6.51 mA/cm2 under simulated solar light at 1.8 V vs. Ag/AgCl, which was 2.12- to 2.93-fold higher than that of the two classical samples. The ultrasonic samples exhibited extraordinarily high stability for water oxidation by maintaining 98% of their initial photoactivity for 2200 sec, as compared to the low stability (66-61%) of both classical samples. The WO3 nanoplates prepared by sonication method had many advantages, such as facile synthetic route, compact, porous and uniform nanoplate morphology, decreased electron-hole pairs recombination rate and controlled oxygen vacancies for greatly enhanced PEC water splitting performance and stability over extended time.

Synthesis of “L-cysteine–graphene oxide” hybrid by new methods and elucidation of its uptake properties for Hg(II) ion

ABSTRACT This study introduces two new, simple, and scalable methods for synthesis of “cysteine–graphene oxide” hybrid, namely nucleophilic and covalent methods. Produced adsorbents could uptake 500 and 600 mg Hg2+/g, respectively, which are larger than capacities of most of the commercial adsorbents. By means of different instrumental techniques, chemical structures of the obtained graphene products were disclosed, and two pertinent mechanisms for their formations were suggested. Time for attaining uptake equilibrium for nucleophilic/covalent samples was 30 min/150 min, and kinetics was controlled by liquid film resistance/chemical reaction mechanisms, respectively. High selectivity and good regenerability are other key features of the prepared adsorbents.

Modification of square root formula for approximate estimation of diffusion coefficient of particulate adsorbents

The well known square root formula for the kinetics of adsorption by spherical particle U(t)={\frac{6}{r_0}}({\frac{Dt}{\pi}})^{1/2} is only valid in the early stage of adsorption (U(t)\le 0.3), where U(t) shows fractional attainment to the equilibrium. Present study shows that with a little manipulation of this formula, its application range can be extended to U(t)\le 0.95. The suggested formula U(t)={\frac{6}{r_0}}({\frac{Dt}{\pi}})^{1/2}-{\frac{3Dt}{r^2_0}} in addition of simplicity, has higher accuracy than both square root and Vermeulens formulas.