Growth mechanism of 2D heterostructures of polypyrrole grown on TiO2 nanoribbons for high-performance supercapacitors

The patterning of functional structures is crucial in the field of materials science. Despite the enticing nature of two-dimensional surfaces, the task of directly modeling them with regular structures remains a significant challenge. Here we present a novel method to pattern a two-dimensional polymer in a controlled way assisted by chemical polymerization, which is confirmed through discernible observation. The fabrication process involves in situ polymerization to create 2D layers of polypyrrole (PPy) on extended 2D TiO2 nanoribbons, resulting in oriented arrays known as 2D PPy/TiO2. These arrays exhibit enhanced electrochemical performance, making them ideal for supercapacitor applications. The skeleton structure of this material is distinctive, characterized by a homogeneous distribution of layers containing various elements. Additionally, it possesses a large contact surface, which effectively reduces the distance for ion transport and electron transfer. The 2D PPy/TiO2 electrode has a maximum specific capacitance of 280 F g-1 at an applied current density of 0.5 A g-1. Moreover, it demonstrates excellent rate capability and cycling stability. Therefore, this approach will open an avenue for improving polymerization-based patterning toward recommended applications.

Determination of Ascorbic Acid in Pharmaceuticals and Food Supplements with the New Potassium Ferrocyanide-Doped Polypyrrole-Modified Platinum Electrode Sensor

This paper reports the results obtained from the determination of ascorbic acid with platinum-based voltammetric sensors modified with potassium hexacyanoferrate-doped polypyrrole. The preparation of the modified electrodes was carried out by electrochemical polymerization of pyrrole from aqueous solutions, using chronoamperometry. Polypyrrole films were deposited on the surface of the platinum electrode, by applying a constant potential of 0.8 V for 30 s. The thickness of the polymer film was calculated from the chronoamperometric data, and the value was 0.163 μm. Cyclic voltammetry was the method used for the Pt/PPy-FeCN electrode electrochemical characterization in several types of solution, including KCl, potassium ferrocyanide, and ascorbic acid. The thin doped polymer layer showed excellent sensitivity for ascorbic acid detection. From the voltammetric studies carried out in solutions of different concentrations of ascorbic acid, ranging from 1 to 100 × 10−6 M, a detection limit of 2.5 × 10−7 M was obtained. Validation of the analyses was performed using pharmaceutical products with different concentrations of ascorbic acid, from different manufacturers and presented in various pharmaceutical forms, i.e., intravascular administration ampoules, chewable tablets, and powder for oral suspension.

An Overview of Functionalized Graphene Nanomaterials for Advanced Applications

Interest in the development of graphene-based materials for advanced applications is growing, because of the unique features of such nanomaterials and, above all, of their outstanding versatility, which enables several functionalization pathways that lead to materials with extremely tunable properties and architectures. This review is focused on the careful examination of relationships between synthetic approaches currently used to derivatize graphene, main properties achieved, and target applications proposed. Use of functionalized graphene nanomaterials in six engineering areas (materials with enhanced mechanical and thermal performance, energy, sensors, biomedical, water treatment, and catalysis) was critically reviewed, pointing out the latest advances and potential challenges associated with the application of such materials, with a major focus on the effect that the physicochemical features imparted by functionalization routes exert on the achievement of ultimate properties capable of satisfying or even improving the current demand in each field. Finally, current limitations in terms of basic scientific knowledge and nanotechnology were highlighted, along with the potential future directions towards the full exploitation of such fascinating nanomaterials.

Design and Characterization of a Novel ZnO-Ag/Polypyrrole Core-Shell Nanocomposite for Water Bioremediation

Incorporating nanostructured metal and metal oxide in a polymer matrix is a strategic way to develop a novel candidate for water bioremediation. In this study, under microwave irradiation, a ZnO–Ag/polypyrrole (PPy) nanocomposite with a core/shell structure was prepared by interfacial polymerization of pyrrole in the presence of ZnO nanoparticles and AgNO₃ as an oxidant. The antimicrobial behavior of the ZnO–Ag core combined with the electrical properties of the conducting PPy shell created a special ZnO–Ag/PPy nanocomposite with inherent adsorption behavior and antimicrobial properties. More impressively, the as-prepared ZnO–Ag/PPy displayed enhanced adsorption of Cd²⁺ and PO₄³⁻ ions in the mixed solution. At pH 8, it had overall removal efficiencies of 95% and 75% for Cd²⁺and PO₄³⁻ ions, respectively. The Freundlich adsorption model, rather than the Langmuir adsorption model, better fits the adsorption isotherm results. The adsorption kinetics also followed the pseudo-second-order kinetic model. Additionally, the engineered nanocomposite demonstrated antifungal activity against different fungi, as well as remarkable antibacterial activity against Gram-negative and Gram-positive bacteria. The synergistic combination of crystallinity, coherence of the ZnO–Ag core in the PPy matrix, and the negative zeta potential all contribute to this nanocomposite’s high efficiency. Our results have significant consequences in the wastewater bioremediation field using a simple operation process.

Enhanced removal of toxic hexavalent chromium from aqueous solution by magnetic Zr-MOF@polypyrrole: performance and mechanism

Magnetic Zr-based metal organic framework (UiO-66) @Polypyrrole (magnetic UiO-66@Ppy) was prepared to eliminate Cr(VI) from water. SEM and TEM results clearly revealed that the magnetic UiO-66@Ppy was a core-double-shell structure with the core of Fe₃O₄, inner shell UiO-66, and outer shell Ppy. The introduction of zirconium MOFs UiO-66 effectively prevented the agglomeration of polypyrrole and provided more available adsorption sites, the surface area increased from 9.57 m²/g (Ppy) to 10.57 m²/g (Fe₃O₄@Ppy) and 52.49 m²/g (magnetic UiO-66@Ppy). The magnetic UiO-66@Ppy possessed a high adsorption capacity of 259.1 mg/g in removing Cr(VI) from water. Adsorption kinetics followed the pseudo-second-order model. The removal of Cr(VI) involved the following mechanisms: (1) electrostatic attraction and ions exchange, the HCrO₄^- was adsorbed on the surface of magnetic UiO-66@Ppy by the protonated N(PpyN⁺) and Cl^-; (2) reduction, Cr(VI) was reduced to Cr(III) by the reductive functional group(-NH-); (3) chelation, Cr(III) was immobilized on adsorbent by amine groups.

Novel electrochemical sensors from poly[N-(ferrocenyl formacyl) pyrrole]@multi-walled carbon nanotubes nanocomposites for simultaneous determination of ascorbic acid, dopamine and uric acid

Novel multi-walled carbon nanotubes coated with poly[N-(ferrocenyl formacyl) pyrrole] (MWCNTs@PFFP) nanocomposites were prepared through the in situ oxidation polymerization reaction of N-(ferrocenyl formacyl) pyrrole in the presence of MWCNTs. The MWCNTs@PFFP nanocomposites were characterized by FT-IR, Raman, TGA, XRD, XPS, SEM and TEM techniques. The MWCNTs@PFFP nanocomposites were fabricated into novel electrochemical sensors for simultaneous determination of ascorbic acid (AA), dopamine (DA) and uric acid (UA). The electrochemical behavior of the MWCNTs@PFFP/GCE sensors was examined, and the parameters that influence electrochemical signals were optimized. The experimental results showed that the fabricated modified electrode sensors exhibited good sensitivity, selectivity, specificity, repeatability and a long lifetime, remaining the initial current of at least 92.5% after 15 days storage in air. The sensors possessed a linear response concentration range over 200-400 μM for AA, 2-16 μM for both DA and UA, and a limit of detection as low as 40.0, 1.1 and 7.3 × 10-1 μM for AA, DA and UA, respectively. They are expected to be used as a potential tool for the simultaneous detection of DA, AA and UA in the human body.

Ultrathin NiS/Ni(OH)2 Nanosheets Filled within Ammonium Polyacrylate-Functionalized Polypyrrole Nanotubes as an Unique Nanoconfined System for Nonenzymatic Glucose Sensors

Ultrathin two-dimensional NiS/Ni(OH)₂ nanosheets (NiS/Ni(OH)₂ NSs) were successfully filled within the hollow interiors of ammonium polyacrylate-functionalized polypyrrole nanotubes (NH₄PA/PPyNTs) by a simple solvothermal method. This kind of novel hierarchical nanostructures with typical structural features of a nanoconfined system, denoted by NiS/Ni(OH)₂/NH₄PA/PPyNTs, were prepared by two main sections: polyacrylic acid (PAA) was first polymerized on PPyNTs containing vinyl groups, and the obtained PAA/PPyNTs exhibited a typical Janus structure, whose external surface was covered with carboxyl groups and the internal surface was still covered with PPy chains; second, Ni²⁺ ions as a precursor were facilely combined with -NH- segments in PPy chains by the coordination interaction under the solvothermal environment; therefore, NiS/Ni(OH)₂ NSs (<1 nm) were well distributed on the internal surface of NH₄PA/PPyNTs by the in situ growth. Because of the synergistic effects of ionizable NH₄PA, PPy with good conductivity, NiS and Ni(OH)₂ with electrocatalytical activity, as well as the nanoconfinement effect, the obtained NiS/Ni(OH)₂@NH₄PA/PPyNTs exhibited excellent electrocatalytic performance for detecting glucose. Sufficiently thin shells composed of ionizable NH₄PA and good conductive PPyNTs can not only promote the electronic transmission effectively during the electrochemical detection of glucose but also hardly limit the transport of glucose and products. In addition, ultrathin NiS/Ni(OH)₂ NSs may further enhance the electrocatalytic performance for glucose because of the more exposed active sites with the large surface area. Therefore, NiS/Ni(OH)₂@NH₄PA/PPyNTs can be applied as a good electrode material with stability and sensitivity for building a nonenzymatic glucose sensor.

A review on graphene-based nanocomposites for electrochemical and fluorescent biosensors

Biosensors with high sensitivity, selectivity and a low limit of detection, reaching nano/picomolar concentrations of biomolecules, are important to the medical sciences and healthcare industry for evaluating physiological and metabolic parameters.

Removal of safranin dye from water using polypyrrole nanofiber/Zn-Fe layered double hydroxide nanocomposite (Ppy NF/Zn-Fe LDH) of enhanced adsorption and photocatalytic properties

Polypyrrole nanofiber/Zn-Fe layered double hydroxide (Ppy NF/Zn-Fe LDH) was synthesized as nanocomposite of enhanced adsorption and photocatalytic properties. The formation of the composite was confirmed by XRD, FT-IR, HSEM, HRTEM, BET surface area and UV-vis spectrophotometer. Ppy NF/Zn-Fe LDH composite exhibits clear enhancing in the specific surface area and obvious reducing in the band gap energy (from 2.8 eV for Zn-Fe LDH to 2.31 eV for the composite). This was reflected in a considerable improvement in the adsorption capacity and photocatalytic removal of safranin dye. The adsorption capacity was enhanced by about 22% higher than Ppy NF and by 31% higher than Zn-Fe LDH. The photocatalytic removal was improved by 41.6% higher than Ppy NF and by about 54% higher than Zn-Fe LDH. The adsorption of safranin dye by the composite is chemisorption adsorption and occurs in a multilayer form. The complete photocatalytic removal of 5 mg/L of safranin dye can be achieved after 120 min illumination time using 0.05 g of the composite as photocatalyst and the best results can be obtained at neutral to alkaline conditions. Realistic application of the composite for the removal of dye from raw water samples revealed the applicability of the product for the purification of tap water, groundwater, and sewage water. Moreover, it can be used for six cycles of safranin dye removal from water. The photocatalytic degradation process appears to be controlled by the created hydroxyl radicals and formed photogenerated holes as the dominant active oxidizing radicals.

Progress in utilisation of graphene for electrochemical biosensors

This review discusses recent graphene (GR) electrochemical biosensor for accurate detection of biomolecules, including glucose, hydrogen peroxide, dopamine, ascorbic acid, uric acid, nicotinamide adenine dinucleotide, DNA, metals and immunosensor through effective immobilization of enzymes, including glucose oxidase, horseradish peroxidase, and haemoglobin. GR-based biosensors exhibited remarkable performance with high sensitivities, wide linear detection ranges, low detection limits, and long-term stabilities. Future challenges for the field include miniaturising biosensors and simplifying mass production are discussed.