Robust method for uniform coating of carbon nanotubes with V2O5 for next-generation transparent electrodes and Li-ion batteries.

Composites comprising vanadium-pentoxide (V2O5) and single-walled carbon nanotubes (SWCNTs) are promising components for emerging applications in optoelectronics, solar cells, chemical and electrochemical sensors, etc. We propose a novel, simple, and facile approach for SWCNT covering with V2O5 by spin coating under ambient conditions. With the hydrolysis-polycondensation of the precursor (vanadyl triisopropoxide) directly on the surface of SWCNTs, the nm-thick layer of oxide is amorphous with a work function of 4.8 eV. The material recrystallizes after thermal treatment at 600 °C, achieving the work function of 5.8 eV. The key advantages of the method are that the obtained coating is uniform with a tunable thickness and does not require vacuuming or heating during processing. We demonstrate the groundbreaking results for two V2O5/SWCNT applications: transparent electrode and cathode for Li-ion batteries. As a transparent electrode, the composite shows stable sheet resistance of 160 Ω sq-1 at a 90% transmittance (550 nm) - the best performance reported for SWCNTs doped by metal oxides. As a cathode material, the obtained specific capacity (330 mA h g-1) is the highest among all the other V2O5/SWCNT cathodes reported so far. This approach opens new horizons for the creation of the next generation of metal oxide composites for various applications, including optoelectronics and electrochemistry.

Albumin Stabilized Fe@C Core-Shell Nanoparticles as Candidates for Magnetic Hyperthermia Therapy.

Carbon-encapsulated iron nanoparticles (Fe@C) with a mean diameter of 15 nm have been synthesized using evaporation-condensation flow-levitation method by the direct iron-carbon gas-phase reaction at high temperatures. Further, Fe@C were stabilized with bovine serum albumin (BSA) coating, and their electromagnetic properties were evaluated to test their performance in magnetic hyperthermia therapy (MHT) through a specific absorption rate (SAR). Heat generation was observed at different Fe@C concentrations (1, 2.5, and 5 mg/mL) when applied 331 kHz and 60 kA/m of an alternating magnetic field, resulting in SAR values of 437.64, 129.36, and 50.4 W/g for each concentration, respectively. Having such high SAR values at low concentrations, obtained material is ideal for use in MHT.

Single-step extraction of small-diameter single-walled carbon nanotubes in the presence of riboflavin.

We propose a novel approach to disperse and extract small-diameter single-walled carbon nanotubes (SWCNTs) using an aqueous solution of riboflavin and Sephacryl gel. The extraction of small-diameter semiconducting SWCNTs was observed, regardless of the initial diameter distribution of the SWCNTs. Dispersion of SWCNTs occurs due to the adsorption of π-conjugated isoalloxazine moieties on the surface of small-diameter nanotubes and interactions between hydroxy groups of ribityl chains with water. During the SWCNT extraction, specific adsorption of riboflavin to SWCNTs leads to the minimization of interactions between the SWCNTs and gel media. Our experimental findings are supported by ab initio calculations demonstrating the impact of the riboflavin wrapping pattern around the SWCNTs on their interaction with the allyl dextran gel.

Machine Learning for Tailoring Optoelectronic Properties of Single-Walled Carbon Nanotube Films.

A machine learning technique, namely, support vector regression, is implemented to enhance single-walled carbon nanotube (SWCNT) thin-film performance for transparent and conducting applications. We collected a comprehensive data set describing the influence of synthesis parameters (temperature and CO2 concentration) on the equivalent sheet resistance (at 90% transmittance in the visible light range) for SWCNT films obtained by a semi-industrial aerosol (floating-catalyst) CVD with CO as a carbon source and ferrocene as a catalyst precursor. The predictive model trained on the data set shows principal applicability of the method for refining synthesis conditions toward the advanced optoelectronic performance of multiparameter processes such as nanotube growth. Further doping of the improved carbon nanotube films with HAuCl4 results in the equivalent sheet resistance of 39 Ω/□-one of the lowest values achieved so far for SWCNT films.

Aerosol-Assisted Fine-Tuning of Optoelectrical Properties of SWCNT Films.

We propose a novel, scalable, and simple method for aerosol doping of single-walled carbon nanotube (SWCNT) films. This method is based on aerosolization of a dopant solution (HAuCl4 in ethanol) and time-controlled deposition of uniform aerosol particles on the nanotube film surface. The approach developed allows fine-tuning of the SWCNT work function in the range of 4.45 (for pristine nanotubes) to 5.46 eV, controllably varying the sheet resistance of the films from 79 to 3.2 Ω/□ for the SWCNT films with 50% transmittance (at 550 nm). This opens a new avenue for traditional and flexible optoelectronics, both to replace existing indium-tin oxide electrodes and to develop novel applications of the highly conductive transparent films.

Facile chemical routes to mesoporous silver substrates for SERS analysis.

Mesoporous silver nanoparticles were easily synthesized through the bulk reduction of crystalline silver(I) oxide and used for the preparation of highly porous surface-enhanced Raman scattering (SERS)-active substrates. An analogous procedure was successfully performed for the production of mesoporous silver films by chemical reduction of oxidized silver films. The sponge-like silver blocks with high surface area and the in-situ-prepared mesoporous silver films are efficient as both analyte adsorbents and Raman signal enhancement mediators. The efficiency of silver reduction was characterized by X-ray diffraction and X-ray photoelectron spectroscopy. The developed substrates were applied for SERS detection of rhodamine 6G (enhancement factor of about 1-5 × 105) and an anti-ischemic mildronate drug (meldonium; enhancement factor of ≈102) that is known for its ability to increase the endurance performance of athletes.

Silver Eco-Solvent Ink for Reactive Printing of Polychromatic SERS and SPR Substrates.

A new reactive ink based on a silver citrate complex is proposed for a photochemical route to surface-enhanced Raman spectroscopy active substrates with controllable extinction spectra. The drop-cast test of the ink reveals homogeneous nucleation of silver and colloid particle growth originating directly from photochemical in situ reduction in droplets, while the following evaporation of the deposited ink produces small nano- and micron-size particles. The prepared nanostructures and substrates were accurately characterized by electron microscopy methods and optical extinction spectroscopy. Varying the duration of UV irradiation allows tuning the morphology of individual silver nanoparticles forming hierarchical ring structures with numerous "hot spots" for most efficient Raman enhancement. Raman measurements of probe molecules of rhodamine 6G and methylene blue reached the largest signal enhancement of 106 by the resonance effects.