Bottom-up synthesis of nitrogen-doped nanocarbons by a combination of metal catalysis and a solution plasma process

We aimed to develop the bottom-up synthesis of nanocarbons with specific functions from molecules without any leaving group, halogen atom and boronic acid, by employing a metal catalyst under solution plasma irradiation. Pyridine was used as a source of carbon. In the presence of a Pd catalyst, the plasma treatment enabled the synthesis of N-doped carbons with a pyridinic configuration, which worked as an active catalytic site for the oxygen reduction reaction

Carbon Nanodots as Electrocatalysts towards the Oxygen Reduction Reaction

© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Electrocatalysts perform a key role in increasing efficiency of the oxygen reduction reaction (ORR) and as a result, efforts have been made by the scientific community to develop novel and cheap materials that have the capability to exhibit low ORR overpotentials and allow the reaction to occur via a 4 electron pathway, thereby mimicking as close as possible to traditionally utilised platinum. In that context, two different types of carbon nanodots (CNDs) with amide (CND-CONH 2 ) and carboxylic (CND-COOH) surface groups, have herein been fabricated and shown to exhibit excellent electrocatalytic activity towards the ORR in acid and basic media (0.1 M H 2 SO 4 and 0.1 M KOH). CND surface modified carbon screen-printed electrodes allow for a facile electrode modification and enabling the study of the CNDs electrocatalytic activity towards the ORR. CND-COOH modified SPEs are found to exhibit improved ORR peak current and reduced overpotential by 21.9 % and 26.3 %, respectively compared to bare/unmodified SPEs. Additionally, 424 μg cm −2 CND-COOH modified SPEs in oxygenated 0.1 M KOH are found to facilitate the ORR via a near optimal 4 (3.8) electron ORR pathway. The CNDs also exhibited excellent long-term stability and tolerance with no degradation being observed in the achievable current with the ORR current returning to the baseline level within 100 seconds of exposure to a 1.5 M solution of methanol. In summary, the CND-COOH could be utilised as a cathodic electrode for PEMFCs offering greater stability than a commercial Pt electrode

Effect of Oxygen Partial Pressure on Crystal Structure, Oxygen Vacancy, and Surface Morphology of Epitaxial SrTiO3 Thin Films Grown by Ion Beam Sputter Deposition

Epitaxial SrTiO3 (STO) thin films were grown on (001)-oriented LaAlO3 (LAO) substrates at 800 °C by an ion beam sputter deposition (IBSD). Oxygen partial pressure (PO2) was varied at 1.5 × 10−5, 1.5 × 10−4, and 1.5 × 10−3 Torr during the growth. The effects of PO2 on crystal structure, oxygen vacancy, and surface morphology of the STO films were investigated and are discussed to understand their correlation. It was found that PO2 played a significant role in influencing the crystal structure, oxygen vacancy, and surface morphology of the STO films. All STO films grew on the LAO substrates under a compressive strain along an in-plane direction (a- and b-axes) and a tensile strain along the growth direction (c-axis). The crystalline quality of STO films was slightly improved at higher PO2. Oxygen vacancy was favorably created in the STO lattice grown at low PO2 due to a lack of oxygen during growth and became suppressed at high PO2. The existence of oxygen vacancy could result in a lattice expansion in both out-of-plane and in-plane directions due to the presence of Ti3+ instead of Ti4+ ions. The surface roughness of the STO films gradually decreased and was nearly close to that of the bare LAO substrate at high PO2, indicating a two-dimensional (2D) growth mode. The results presented in this work provide a correlation among crystal structure, oxygen vacancy, and surface morphology of the epitaxial STO films grown by IBSD, which form a useful guideline for further study

Enhanced Electrocatalytic Activity of Cobalt-Doped Ceria Embedded on Nitrogen, Sulfur-Doped Reduced Graphene Oxide as an Electrocatalyst for Oxygen Reduction Reaction

N, S-doped rGO was successfully synthesized and embedded Co-doped CeO2 via hydrothermal synthesis. The crystal structure, surface morphology and elemental composition of the prepared catalyst were studied by XRD, Raman spectra, SEM, TEM and XPS analyses. The synthesized electrocatalyst exhibits high onset and halfwave potential during the ORR. This result shows that a combination of N- and S-doped rGO and Co-doped CeO2 leads to a synergistic effect in catalyzing the ORR in alkaline media. Co–CeO2/N, S–rGO displays enhanced ORR performance compared to bare CeO2. The superior stability of the prepared catalyst implies its potential applications beyond fuel cells and metal–air batteries

Conversion of industrial carpet waste into adsorbent materials for organic dye removal from water

The vast amount of carpet waste produced from the manufacturing processes is dumped in landfills, causing environmental issues and problems. In addition to recycling and reuse processes, the conversion of carpet waste into a higher value-added product is an interesting option to manage carpet waste with the most benefits and values. This work highlights the conversion of industrial carpet waste into alternative adsorbents for dye removal. The pre-consumer carpet waste was pyrolyzed at different temperatures ranging from 500 to 900 °C under argon flow. Due to the high fraction of calcium carbonate (CaCO3) filled in the adhesive layer in carpet, CaCO3 was acquired at 500 and 600 °C, while the calcium hydroxide (Ca(OH)2) with a hexagonal platelet-shaped crystal began to form at 700 °C. In addition to CaCO3 and Ca(OH)2, carbon was also found in the samples due to the carbonization of the polymeric fibers and backings. The specific surface area increased with increasing pyrolysis temperature ranging from 15 to 26 m2 g−1 with a predominance of mesopores. Potential utilization as dye adsorbents was evaluated using methylene blue (cationic dye) and methyl orange (anionic dye) at concentrations of 10, 15, and 20 mg L−1. Among all samples, the carpet waste pyrolyzed at 900 °C showed the highest adsorption efficiency of about 100% for methylene blue and 93–99% for methyl orange at the dye concentration of 10–20 mg L−1. The lower adsorption efficiency of methyl orange was due to the effect of electrostatic interaction between the dye molecules and adsorbent surface. The results in this work offer useful information for converting carpet waste into alternative dye adsorbents towards sustainable water management

Electrocatalytic Properties of a BaTiO₃/MWCNT Composite for Citric Acid Detection

Although barium titanate (BaTiO3) shows prominent dielectric properties for fabricating electronic devices, its utilization in electrochemical applications is limited. Thus, this study examined the potential of a BaTiO3-based composite in the detection of a food additive, i.e., citric acid. First, a submicron-scale BaTiO3 powder was synthesized using the solution combustion method. Then, a BaTiO3/multiwalled carbon nanotube (MWCNT) composite was hydrothermally synthesized at BaTiO3:MWCNT mass ratios of 1:1 and 2:1. This composite was used as a working electrode in a nonenzymatic sensor to evaluate its electrocatalytic activity. Cyclic voltammetric measurements revealed that the BaTiO3/MWCNT composite (2:1) exhibited the highest electrocatalytic activity. Reduction reactions were observed at applied voltages of approximately 0.02 and −0.67 V, whereas oxidation reactions were detected at −0.65 and 0.47 V. With acceptable sensitivity, decent selectivity, and fair stability, the BaTiO3/MWCNT composite (2:1) showed good potential for citric acid detection