Malgorzata Aleksandrzak

Adsorption of anionic azo-dyes from aqueous solutions onto graphene oxide: Equilibrium, kinetic and thermodynamic studies

In the present study, graphene oxide (GO) was used for the adsorption of anionic azo-dyes such as Acid Orange 8 (AO8) and Direct Red 23 (DR23) from aqueous solutions. GO was characterized by Fourier Transform-Infrared Spectroscopy (FTIR), X-ray Photoelectron Spectroscopy (XPS), Thermogravimetric Analysis (TGA), Atomic Force Microscopy (AFM), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), High-Resolution Transmission Electron Microscopy (HRTEM) and zeta potential measurements. The influence of dye initial concentration, temperature and pH on AO8 and DR23 adsorption onto GO was investigated. Equilibrium data were analyzed by model equations such as Langmuir Freundlich, Temkin, Dubinin-Radushkevich and Redlich-Peterson isotherms and were best represented by Langmuir and Redlich-Peterson isotherm model. Kinetic adsorption data were analyzed using the pseudo-first-order kinetic model, the pseudo-second-order kinetic model and the intraparticle diffusion model. The adsorption kinetics well fitted using a pseudo-second-order kinetic model. Thermodynamics parameters, ΔG°, ΔH° and ΔS°, were calculated, indicating that the adsorption of AO8 and DR23 onto GO was spontaneous process. The adsorption process of AO8 onto GO was exothermic, while the adsorption of DR23 onto GO was endothermic in nature.

Reduced graphene oxide and inorganic nanoparticles composites – synthesis and characterization

Abstract Graphene – novel 2D material, which possesses variety of fascinating properties, can be considered as a convenient support material for the nanoparticles. In this work various methods of synthesis of reduced graphene oxide with metal or metal oxide nanoparticles will be presented. The hydrothermal approach for deposition of platinum, palladium and zirconium dioxide nanoparticles in ethylene glycol/water solution was applied. Here, platinum/reduced graphene oxide (Pt/RGO), palladium/reduced graphene oxide (Pd/RGO) and zirconium dioxide/reduced graphene oxide (ZrO2/RGO) nanocomposites were prepared. Additionally, manganese dioxide/reduced graphene oxide nanocomposite (MnO2/RGO) was synthesized in an oleic-water interface. The obtained nanocomposites were investigated by transmission electron microscopy (TEM), X-ray diffraction analysis (XRD), Raman spectroscopy and thermogravimetric analysis (TGA). The results shows that GO can be successfully used as a template for direct synthesis of metal or metal oxide nanoparticles on its surface with a homogenous distribution.

Reduced graphene oxide nanocomposites with different diameters and crystallinity of TiO2 nanoparticles – synthesis, characterization and photocatalytic activity

Abstract TiO2-reduced graphene oxide nanocomposites with different diameters and crystallinity of titania nanoparticles were synthesized via the sol-gel method followed by calcination in air or treatment under vacuum. The materials were characterized with transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, photoluminescence spectroscopy and diffuse-reflectance UV–vis spectroscopy. The photocatalytic activity of the resulting materials was examined in the process of phenol decomposition under UV–vis light irradiation. The influences of TiO2 loading and calcination treatment on photocatalytic activity of the composites were investigated. It was found that higher TiO2 concentrations resulted in higher photocatalytic activity. This is in agreement with the band gap energy values, as lower visible light absorption and higher Eg values were obtained for the samples prepared with higher TiO2 loading. Furthermore, photoactivity was affected by the calcination treatment. Higher activity under UV–vis was shown by the samples calcinated under vacuum, which was attributed to the better crystallinity compared to the samples treated with air.

Equilibrium and kinetics studies for the adsorption of Ni2+ and Fe3+ ions from aqueous solution by graphene oxide

Abstract In this study, the adsorption of Ni2+ and Fe3+ metal ions from aqueous solutions onto graphene oxide (GO) have been explored. The effects of various experimental factors such as pH of the solution, initial metal ion concentration and temperature were evaluated. The kinetic, equilibrium and thermodynamic studies were also investigated. The adsorption rate data were analyzed using the pseudo-first-order kinetic model, the pseudo-second-order kinetic model and the intraparticle diffusion model. Kinetic studies indicate that the adsorption of both ions follows the pseudo-second-order kinetics. The isotherms of adsorption data were analyzed by adsorption isotherm models such as Langmuir and Freundlich. Equilibrium data fitted well with the Langmuir model. The maximum adsorption capacities of Ni2+ and Fe3+ onto GO were 35.6 and 27.3 mg g−1, respectively. In addition, various thermodynamic parameters, such as enthalpy (ΔHO), entropy (ΔSO) and Gibbs free energy (ΔGO), were calculated.

A biofunctionalizable ink platform composed of catechol-modified chitosan and reduced graphene oxide/platinum nanocomposite

We present an ink platform for a printable polymer–graphene nanocomposite that is intended for the development of modular biosensors. The ink consists of catechol-modified chitosan and reduced graphene oxide decorated with platinum nanoparticles (rGO–Pt). We modified the chitosan with catechol groups, in order to obtain adhesive properties and improve solubility. Dispersions of rGO–Pt in ethylene glycol were admixed with an aqueous solution of modified chitosan to yield an ink that is suitable for non-contact piezoelectric printing using a commercial microplotter (Sonoplot GIX Microplotter Desktop). As a proof of concept, printed patterns were biofunctionalized with DNA oligonucleotide probes for Streptococcus agalactiae (Group B streptococcus) using glutaraldehyde as a linker. Confocal microscopy revealed the successful hybridization of complementary polymerase chain reaction (PCR) products and low non-specific binding. Our results demonstrate that catechol-modified chitosan/rGO–Pt nanocomposites can be used as inks for piezoelectric printing and facilitate the attachment of biorecognition elements for biosensor applications.

Graphene-based electrochemical biosensing system for medical diagnostics

In this contribution the results on the development of a novel measurement system for electrochemical biosensing are presented. It covers the most important work on innovative graphene-based nanocomposites used in preparation of biosensing electrodes, design of different electrode types and a specialized flow chamber, specialized hardware and software for two versions (mobile and laboratory) of the electronic control and read-out system. The results of lab tests performed with the prototype system GruntMaster 6001 are shown in comparison to the measurements obtained by means of commercially available professional platforms used as a reference. The prototype is currently in the process of commercialization.