RESUMO
The syntheses of high-spin organic polymers have been a daunting task due to the highly reactive nature of organic radicals, especially when they are ferromagnetically coupled. In this paper, we report our approach to obtain high-spin organic polymers, in which a reasonably stable fluorenyl radical was employed as the primary radical unit, and s-triazine serves as the connector that facilitates ferromagnetic coupling between them. Initially, the diamagnetic polymer precursor was synthesized by cyclotrimerization of a cyano-monomer. Subsequently, the high-spin polymers were obtained by oxidizing corresponding anionic polymers using O2 (6) or I2 (7). The temperature-dependent magnetic moments, and field-dependent magnetization data obtained from SQUID measurements revealed ferromagnetic couplings between primary radical units, with coupling J = 7.5 cm-1 and 38.6 cm-1. The percentages of primary unit in the radical form are 29%, and 47% for 6 and 7, respectively. Notably, this marks the first reported instance of a high-spin fluorenyl radical polymer exhibiting ferromagnetic coupling.
RESUMO
A new graphene oxide (GO) nanocomposite that contains chitosan, a biological polymer, combined with a magnetic nanoparticle inorganic material (Fe3O4) was successfully prepared and applied for the adsorption of Pb(II) from aqueous solutions. The structural and morphological properties of the GO/Fe3O4/CS (GFC) nanocomposites were characterized by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. Influent factors for Pb(II) adsorption, including the contacting time, pH of the working medium, working temperature, and adsorbent dosage on the adsorption efficiency, have been optimized. Under optimized conditions, the adsorption isotherm results indicated that the Langmuir model provided a better description for the adsorption of Pb(II) onto the GFC nanosorbent than the Freundlich model. The maximum adsorption capacity (qmax) was 63.45 mg g-1. The pseudo-second-order kinetic model (R2 = 0.999) was fitted with the experimental results, implying that the adsorption of Pb(II) onto GFC is a chemical process. The thermodynamic studies demonstrated the exothermic nature of the adsorption process. Another advantage of the GFC nanosorbent for Pb(II) removal is its capability to be easily recovered under the use of an external magnet and subsequently regenerated. Our work demonstrated that the removal efficiency was stable after several regeneration cycles (i.e., approximately 12% reduction after four successive adsorption-desorption cycles), implying that the GFC nanosorbent exhibits satisfactory regeneration performance. Therefore, with high removal efficiency, high adsorption capacity, and stable reusability, the GFC nanocomposite is a remarkable application potential adsorbent for the in situ treatment of Pb(II) ion-containing aqueous solutions.
RESUMO
A novel nanostructured electrode material based on electrochemically reduced graphene oxide/polyaniline nanowires/silver nanoflowers (ERGO/PANi NWs/AgNFs) was fabricated site-specifically onto a Pt microelectrode (0.80 mm2 area) using a three-step electrochemical procedure: electrosynthesis of ERGO, electropolymerization of PANi NWs, and electrodeposition of AgNFs. Synergistic and complementary properties of ERGO, PANi NWs and AgNFs, including high electrochemical activity, large surface area, and high biocompatibility, were obtained. Besides, the electrosynthesis method allowed the direct formation of the desired nanomaterial onto the Pt microelectrode, so the adhesion between the sandwich-structured nanocomposite and the electrode surface was also improved. The optimized ERGO/PANi NWs/AgNFs nanocomposite was used for the first time to develop an electrochemical DNA sensor. As a result, the DNA probe immobilization was facilitated and the electrochemical signals of the DNA sensor were enhanced. The detection limit of the DNA sensor was 2.70 × 10-15 M. Moreover, potential miniaturization for fabrication of a lab-on-a-chip system, direct detection, high sensitivity, and good specificity are the advantages of the fabricated DNA sensor.
