Multifunctional mixed valence N-doped CNT@MFe2O4 hybrid nanomaterials: from engineered one-pot coprecipitation to application in energy storage paper supercapacitors

Voltammetric immunosensor based on oxidized carbon nanotubes/MnFe2O4 hybrid nanoplatform for amplified detection of celery (Apium graveolens)

Celery is a food allergen that must be included in the ingredient list of commercial food products in the European Union. This is a challenge for the food industry because of potential cross-contamination and undeclared ingredients because of their low concentrations. So, the food industry requires expedited high-performance analytical methods. The development, validation and application of a magnetic nanomaterial-based voltammetric immunosensor is reported to quantify a major celery allergen (Api g 1), achieving a low limit of detection (32 pg·mL-1, in a 40-μL sample). The applicability of the biosensor was evaluated by analysing twenty food products and the lowest Api g 1 content (1.1 ± 0.9 mg·kg-1) was quantified in a cooked sample. The selectivity of the method and the interference of similar fresh products (e.g., parsley, basil) were evaluated. This portable and easy-to-use biosensor can be a fit-for-purpose solution to tackle a major problem for the food industry.

Fabrication of CNT-N@Manganese Oxide Hybrid Nanomaterials through a Versatile One-Pot Eco-Friendly Route toward Engineered Textile Supercapacitors

The expansion of the Internet of Things market and the proliferation of wearable technologies have generated a significant demand for textile-based energy storage systems. This work reports the engineered design of hybrid electrode nanomaterials of N-doped carbon nanotubes (CNT-N) functionalized with two types of manganese oxides (MOs)-birnessite (MnO2) and hausmannite (Mn3O4)-and their application in solid-state textile-based hybrid supercapacitors (SCs). A versatile citric acid-mediated eco-friendly one-pot aqueous precipitation process is proposed for the fabrication of the hybrids. Remarkably, different types of MOs were obtained by simply changing the reaction temperature from room temperature to 100 °C, without any post-thermal treatment. Asymmetric textile SCs were developed using cotton fabrics coated with CNT-N and the hybrids as textile electrodes, and poly(vinyl) alcohol/orthophosphoric acid as the solid-gel electrolyte. The asymmetric devices presented enhanced energy storage performance relative to the symmetric device based on CNT-N and excellent cycling stability (>96%) after 8000 charge/discharge cycles owing to synergistic effects between CNT-N and the MOs, which endowed nonfaradaic and pseudocapacitive features to the SCs. The asymmetric SC based on CNT-N@MnO2 featured 47% higher energy density and comparable power density to the symmetric CNT-N-based device (8.70 W h cm-2 at 309.01 μW cm-2 vs. 5.93 W h cm-2 at 346.58 μW cm-2). The engineered hybrid CNT-N@MO nanomaterials and the eco-friendly citric acid-assisted one-pot precipitation route open promising prospects not only for energy storage, but also for (photo)(electro)catalysis, wastewater treatment, and (bio)sensing.

Schiff Base Complex of Copper Immobilized on Core-Shell Magnetic Nanoparticles Catalyzed One-Pot Syntheses of Polyhydroquinoline Derivatives under Mild Conditions Supported by a DFT Study

We synthesized a stable and reusable Schiff base complex of copper immobilized on core-shell magnetic nanoparticles [Cu(II)-SB/GPTMS@SiO2@Fe3O4] with simple, efficient, and available materials. A variety of characterization analyses including Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET), thermogravimetric analysis (TGA), X-ray diffraction (XRD), vibrating-sample magnetometry (VSM), energy-dispersive X-ray spectrometry (EDX), and inductively coupled plasma (ICP) confirm that our synthesized nanocatalyst was obtained. The particle size distribution from the TEM image was obtained in the range of 42-55 nm. The existence of cupric species (Cu2+) in the catalyst was determined with XPS analysis and clearly indicated two peaks at 933.7 and 953.7 eV for Cu 2p3/2 and Cu 2p1/2, respectively. BET results showed that our catalyst synthesized with a mesoporous structure and with a specific area of 48.82 m2 g-1. After detailed characterization, the resulting nanocatalyst exhibited excellent catalytic performance for the explored catalytic reactions in the one-pot synthesis of polyhydroquinoline derivatives by the Hantzsch reaction of dimedone, ethyl acetoacetate, ammonium acetate, and various aldehydes under sustainable and mild conditions. The corresponding products 5a-l are achieved in yields of 88-97%. Additionally, density functional theory (DFT) calculations were carried out to investigate the electrostatic potential root (ESP), natural bond orbital (NBO), and molecular orbitals (MOs), drawing the reaction mechanism using the total energy of the reactant and product and the study of structural parameters.

S-Doping Promotes Pyridine Nitrogen Conversion and Lattice Defects of Carbon Nitride to Enhance the Performance of Zn-Air Batteries

The efficient operation of Zn-air batteries (ZABs) requires highly active and stable reversible air catalysts. Studies have shown that heteroatom-doped carbonaceous nanomaterials are effective metal-free electrocatalysts for the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR). Herein, we design a facile and scalable catalyst doping scheme to manufacture S-doped carbon nitride (S-C₃N₄). Surprisingly, this metal-free catalyst exhibits excellent OER and ORR electrocatalytic activities in alkaline electrolytes, being comparable to those of commercial Pt/C. For the first time, it is proved by experiments that S doping can not only effectively increase the lattice defects of C₃N₄ but also promote the conversion of pyrrolic nitrogen to pyridine nitrogen, thereby enhancing the bifunctional catalytic activity (OER and ORR). When the catalyst is used as an air electrode for rechargeable ZABs, its performance is obviously better than that provided by commercial Pt/C. Our findings and material design strategies are expected to provide new ideas for the synthesis of various high-performance carbon-based electrocatalysts.

A Comprehensive Study of Pristine and Calcined f-MWCNTs Functionalized by Nitrogen-Containing Functional Groups

We present the study of pristine and calcined f-MWCNTs functionalized by nitrogen-containing functional groups. We focus on the structural and microstructural modification tuned by the previous annealing. However, our primary goal was to analyze the electronic structure and magnetic properties in relation to the structural properties using a multi-technique approach. The studies carried out by X-ray diffraction, XPS, and ⁵⁷Fe Mössbauer spectrometry revealed the presence of γ-Fe nanoparticles, Fe₃C, and α-FeOOH as catalyst residues. XPS analysis based on the deconvolution of core level lines confirmed the presence of various nitrogen-based functional groups due to the purification and functionalization process of the nanotubes. The annealing procedure leads to a structural modification mainly associated with removing surface impurities as purification residues. Magnetic studies confirmed a significant contribution of Fe₃C as evidenced by a Curie temperature estimated at T_C = 452 ± 15 K. A slight change in magnetic properties upon annealing was revealed. The detailed studies performed on nanotubes are extremely important for the further synthesis of composite materials based on f-MWCNTs.

Conductive Electrospun Nanofiber Mats

Conductive nanofiber mats can be used in a broad variety of applications, such as electromagnetic shielding, sensors, multifunctional textile surfaces, organic photovoltaics, or biomedicine. While nanofibers or nanofiber from pure or blended polymers can in many cases unambiguously be prepared by electrospinning, creating conductive nanofibers is often more challenging. Integration of conductive nano-fillers often needs a calcination step to evaporate the non-conductive polymer matrix which is necessary for the electrospinning process, while conductive polymers have often relatively low molecular weights and are hard to dissolve in common solvents, both factors impeding spinning them solely and making a spinning agent necessary. On the other hand, conductive coatings may disturb the desired porous structure and possibly cause problems with biocompatibility or other necessary properties of the original nanofiber mats. Here we give an overview of the most recent developments in the growing field of conductive electrospun nanofiber mats, based on electrospinning blends of spinning agents with conductive polymers or nanoparticles, alternatively applying conductive coatings, and the possible applications of such conductive electrospun nanofiber mats.