The Roles of Impurities and Surface Area on Thermal Stability and Oxidation Resistance of BN Nanoplatelets.

This study considers the influence of purity and surface area on the thermal and oxidation properties of hexagonal boron nitride (h-BN) nanoplatelets, which represent crucial factors in high-temperature oxidizing environments. Three h-BN nanoplatelet-based materials, synthesized with different purity levels and surface areas (~3, ~56, and ~140 m2/g), were compared, including a commercial BN reference. All materials were systematically analyzed by various characterization techniques, including gas pycnometry, scanning electron microscopy, X-ray diffraction, Fourier-transform infrared radiation, X-ray photoelectron spectroscopy, gas sorption analysis, and thermal gravimetric analysis coupled with differential scanning calorimetry. Results indicated that the thermal stability and oxidation resistance of the synthesized materials were improved by up to ~13.5% (or by 120 °C) with an increase in purity. Furthermore, the reference material with its high purity and low surface area (~4 m2/g) showed superior performance, which was attributed to the minimized reactive sites for oxygen diffusion due to lower surface area availability and fewer possible defects, highlighting the critical roles of both sample purity and accessible surface area in h-BN thermo-oxidative stability. These findings highlight the importance of focusing on purity and surface area control in developing BN-based nanomaterials, offering a path to enhance their performance in extreme thermal and oxidative conditions.

Short-Time Magnetron Sputtering for the Development of Carbon-Palladium Nanocomposites.

In recent nanomaterials research, combining nanoporous carbons with metallic nanoparticles, like palladium (Pd), has emerged as a focus due to their potential in energy, environmental and biomedical fields. This study presents a novel approach for synthesizing Pd-decorated carbons using magnetron sputter deposition. This method allows for the functionalization of nanoporous carbon surfaces with Pd nano-sized islands, creating metal-carbon nanocomposites through brief deposition times of up to 15 s. The present research utilized direct current magnetron sputtering to deposit Pd islands on a flexible activated carbon cloth substrate. The surface chemistry, microstructure, morphology and pore structure were analyzed using a variety of material characterization techniques, including X-ray photoelectron spectroscopy, X-ray diffraction, Raman spectroscopy, gas sorption analysis and scanning electron microscopy. The results showed Pd islands of varying sizes distributed across the cloth's carbon fibers, achieving high-purity surface modifications without the use of chemicals. The synthesis method preserves the nanoporous structure of the carbon cloth substrate while adding functional Pd islands, which could be potentially useful in emerging fields like hydrogen storage, fuel cells and biosensors. This approach demonstrates the possibility of creating high-quality metal-carbon composites using a simple, clean and economical method, expanding the possibilities for future nanomaterial-based applications.

Radionuclide Removal from Aqueous Solutions Using Oxidized Carbon Fabrics.

The adsorption of actinide ions (Am(III) and U(VI)) from aqueous solutions using pristine and oxidized carbon fabrics was investigated by means of batch experiments at different pH values (pH 4, 7 and 9) and temperatures (25, 35 and 45 °C) under ambient atmospheric conditions. The experimental results indicated that both the pH and the fabric texture affected the adsorption rate and the relative removal efficiency, which was 70% and 100% for Am(III) and U(VI), respectively. The Kd (L/kg) values for U(VI) were generally found to be higher (2 < log10(Kd)< 3) than the corresponding values for Am(III) adsorption (1.5 < log10(Kd) < 2). The data obtained from the experiments regarding the temperature effect implied that the relative adsorption for both actinides increases with temperature and that adsorption is an endothermic and entropy-driven reaction. The application of the fabrics to remove the two actinides from contaminated seawater samples showed that both the relative removal efficiency and the Kd values decreased significantly due to the presence of competitive cations (e.g., Ca2+ and Fe3+) and complexing anions (CO32-) in the respective waters. Nevertheless, the removal efficiency was still remarkable (50% and 90% for Am(III) and U(VI), respectively), demonstrating that these materials could be attractive candidates for the treatment of radionuclide/actinide-contaminated waters.

Nanoporous Carbon Electrodes Derived from Coffee Side Streams for Supercapacitors in Aqueous Electrolytes.

Coffee, as one of the most traded resources, generates a vast amount of biogenic by-products. Coffee silver skins (CSS), a side stream from the roasting process, account for about 4 wt.%. Despite the abundancy of CSS, possible routes to generate added value for broad applications are limited. Herein, we present an approach to use CSS as a precursor material for supercapacitor electrodes. KOH activated carbon (AC) was produced from CSS. The resulting AC-CSS was characterized by X-ray diffraction, gas sorption analysis, scanning electron microscopy, and Raman spectroscopy. The highly porous AC-CSS exposes a specific surface area of more than 2500 m2 g-1. Electrodes formed with AC-CSS were electrochemically characterized by performing cyclic voltammetry and galvanostatic cycling. The electrodes were further assembled into a supercapacitor device and operated using 1 M sulfuric acid as electrolyte. In addition, various quinones were added to the electrolyte and their impact on the capacitance of AC-CSS electrodes was analyzed. In this work, we were able to show that CSS are a valuable source for supercapacitor applications and that coffee-waste-derived quinones can act as capacitance enhancers. Thus, the findings of this research show a valuable path towards sustainable and green energy storage solutions.

Flexible nanoporous activated carbon for adsorption of organics from industrial effluents.

This paper reports a study involving the formation of a self-assembled polymeric monolayer on the surface of a high surface area activated carbon to engineer its affinity towards organic contaminants. A nanoporous activated carbon cloth with a surface area of ∼1220 m2 g-1 and a pore volume of ∼0.42 cm3 g-1 was produced by chemical impregnation, carbonisation and high-temperature CO2 activation of a commercially available viscose rayon cloth. The subsequent modification with a silane polymer resulted in a nanoscale self-assembled monolayer that made it selective towards organic solvents (contact angle <10°) and repellant towards water (contact angle >145°). The adsorbent showed more than 95% efficiency in the separation of various types of oil/water mixtures under neutral, basic and acidic conditions. Benefiting from inherent nanoscale features, a robust hierarchical structure and a thermally stable monolayer (∼300 °C), this nanoporous adsorbent maintained high efficiency for more than 20 cycles and separated surfactant stabilised emulsion with >92% oil removal efficiency. The adsorbent was studied extensively with a series of advanced characterisation techniques to establish the formation mechanism and performance in emulsion separation. Findings from this work provide crucial insights towards large-scale implementation of surface engineered activated carbon-based materials for a wide range of industrial separation applications.

Boron Nitride Nanotubes Versus Carbon Nanotubes: A Thermal Stability and Oxidation Behavior Study.

Nanotubes made of boron nitride (BN) and carbon have attracted considerable attention within the literature due to their unique mechanical, electrical and thermal properties. In this work, BN and carbon nanotubes, exhibiting high purity (>99%) and similar surface areas (~200 m2/g), were systematically investigated for their thermal stability and oxidation behavior by combining thermal gravimetric analysis and differential scanning calorimetry methods at temperatures of up to ~1300 °C under a synthetic air flow environment. The BN nanotubes showed a good resistance to oxidation up to ~900 °C and fully transformed to boron oxide up to ~1100 °C, while the carbon nanotubes were stable up to ~450 °C and almost completely combusted up to ~800 °C. The different oxidation mechanisms are attributed to the different chemical nature of the two types of nanotubes.