A general route via formamide condensation to prepare atomically dispersed metal-nitrogen-carbon electrocatalysts for energy technologies

Single-atom electrocatalysts (SAECs) have gained tremendous attention due to their unique active sites and strong metal–substrate interactions. However, the current synthesis of SAECs mostly relies on costly precursors and rigid synthetic conditions and often results in very low content of single-site metal atoms. Herein, we report an efficient synthesis method to prepare metal–nitrogen–carbon SAECs based on formamide condensation and carbonization, featuring a cost-effective general methodology for the mass production of SAECs with high loading of atomically dispersed metal sites. The products with metal inclusion were termed as formamide-converted metal–nitrogen–carbon (shortened as f-MNC) materials. Seven types of single-metallic f-MNC (Fe, Co, Ni, Mn, Zn, Mo and Ir), two bi-metallic (ZnFe and ZnCo) and one tri-metallic (ZnFeCo) SAECs were synthesized to demonstrate the generality of the methodology developed. Remarkably, these f-MNC SAECs can be coated onto various supports with an ultrathin layer as pyrolysis-free electrocatalysts, among which the carbon nanotube-supported f-FeNC and f-NiNC SAECs showed high performance for the O2 reduction reaction (ORR) and the CO2 reduction reaction (CO2RR), respectively. Furthermore, the pyrolysis products of supported f-MNC can still render isolated metallic sites with excellent activity, as exemplified by the bi-metallic f-FeCoNC SAEC, which exhibited outstanding ORR performance in both alkaline and acid electrolytes by delivering ∼70 and ∼20 mV higher half-wave potentials than that of commercial 20 wt% Pt/C, respectively. This work offers a feasible approach to design and manufacture SAECs with tuneable atomic metal components and high density of single-site metal loading, and thus may accelerate the deployment of SAECs for various energy technology applications

Ordered-Mesoporous-Carbon-Bonded Cobalt Phthalocyanine: A Bioinspired Catalytic System for Controllable Hydrogen Peroxide Activation

The chemistry of enzymes presents a key to understanding the catalysis in the world. In the pursuit of controllable catalytic oxidation, researchers make extensive efforts to discover and develop functional materials that exhibit various properties intrinsic to enzymes. Here we describe a bioinspired catalytic system using ordered-mesoporous-carbon (OMC)-bonded cobalt tetraaminophthalocyanine (CoTAPc-OMC) as a catalyst that could mimic the space environment and reactive processes of metalloporphyrin-based heme enzymes and employing linear dodecylbenzenesulfonate as the fifth ligands to control the activation of H₂O₂ toward the peroxidase-like oxidation. The generation of nonselective free hydroxyl radicals was obviously inhibited. In addition, functional modification of OMC has been achieved by a moderate method, which can reduce excessive damage to the structure of OMC. Because of its favorable and tunable pore texture, CoTAPc-OMC provides a suitable interface and environment for the accessibility and oxidation of C.I. Acid Red 1, the model compound, and exhibits significantly enhanced catalytic activity and sufficient stability for H₂O₂ activation. The high-valent cobalt oxo intermediates with high oxidizing ability have been predicted as the acceptable active species, which have been corroborated by the results from the semiempirical quantum-chemical PM6 calculations

Anchored Iron Ligands as an Efficient Fenton-Like Catalyst for Removal of Dye Pollutants at Neutral pH

The development of a pH-tolerant Fenton-like catalyst is an active and challenging research front in the area of environmental engineering. In the present work, a novel catalyst iron−γ-aminopyridine ligand (FeAPy) was prepared and immobilized on activated carbon fibers (ACFs) by a covalent bond to obtain a heterogeneous FeAPy-ACFs. FeAPy-ACFs present a pH-tolerant microenvironment for the Fenton-like oxidation process, which exhibits remarkable catalytic ability across a wide pH range from acidic to alkaline. At neutral pH, employing hydrogen peroxide as an oxidant, the FeAPy-ACFs showed enhanced catalytic ability to degrade hazardous environmental pollutants Acid Red 1 (AR1) dyes and avoid secondary pollution with regard to FeAPy. FeAPy-ACFs are stable and remain efficient in repetitive test cycles with no obvious decrease of catalytic activity. Moreover, in comparison to most reported supports for Fenton-like catalyst, the introduction of ACFs contributed specifically to the activity improvement of FeAPy. Probe studies combined with electron paramagnetic resonance experiments were conducted to ascertain the role of several reactive species (•OH, HO₂•, and Fe^IVO) on dye decolorization

Waste-to-Energy Conversion on Graphitic Carbon Nitride: Utilizing the Transformation of Macrolide Antibiotics To Enhance Photoinduced Hydrogen Production

Photocatalytic H₂ evolution is usually from pure water or water with sacrificial agents. Surprisingly, it has been found that the presence of poisonous macrolide antibiotics in an aqueous medium for catalytic H₂ evolution enhances the H₂ yield while itself being degraded, using Pt/graphitic carbon nitride (Pt/g-C₃N₄) under visible light (λ > 420 nm). Hence, a promising method that addresses the issues of energy shortage and environmental pollution is proposed. Among macrolide antibiotics, Roxithromycin (Rox) is so effective in facilitating the decomposition of water that it can be acted as a model in this paper to explain phenomenon as mentioned above. Furthermore, the mechanism of the reaction is also explored and 13 intermediates of Rox are identified by ultraperformance liquid chromatography and high-resolution mass spectrometry. The degradation pathway of Rox is proposed on the basis of the identified intermediates. In the whole process, both energy generation and pollutant control can be achieved simultaneously. Thereby, this represents a surprising waste-to-energy conversion process

Hydroxyl Radical-Dominated Catalytic Oxidation in Neutral Condition by Axially Coordinated Iron Phthalocyanine on Mercapto-Functionalized Carbon Nanotubes

The ligands and protein surroundings are important in peroxidase processes with iron porphyrins as catalysts. Similarly, two bioinspired composite catalysts made from iron phthalocyanine with axial ligands, 4-aminopyridine and 2-aminoethanethiol, were anchored on multiwalled carbon nanotubes to degrade some pollutants to the water environment, such as 4-chlorophenol, dyes, and so on. The effect of pH and sustained catalytic stability were investigated in the presence of two catalysts. Different axial ligands and carbon nanotubes that synergistically donated electrons to the central iron of iron phthalocyanine significantly improved the catalytic activity and stability during hydrogen peroxide activation. Electron paramagnetic resonance spin-trapping experiments indicated that catalytic oxidation is dominated by hydroxyl radicals in both catalytic systems, which is different from the high-valent metal-oxo generated in common biomimetic catalytic systems with iron porphyrins in the presence of the fifth ligands. The high catalytic activity and strong durability are distinct from traditional peroxide-activating catalysts of metal complexes dominated by hydroxyl radicals, where catalysts have poor stability and are self-destructive in repetitive cyclic oxidation. In our catalytic system, the axial ligand and carbon nanotubes together affect the electronic structure of the central iron in which electron-donor substituents shift the Fe^III/II potential to more negative values, which make the activation process of hydrogen peroxide occur at neutral pH, and increase the rate of the step from Fe^III to Fe^II. However, the reaction takes place under acidic conditions, and Fe^III/Fe^II cycling occurs slowly in the traditional Fenton system with hydrogen peroxide

Inhibition of PP2A with okadaic acid confers resistance to rapamycin inhibition of IGF-1-induced phosphorylation of Erk1/2 and cell motility.

<p>(A) Serum-starved Rh1 cells were pretreated treated with or without OA (100 nM) for 1 h, and then treated with or without rapamycin (Rapa, 100 ng/ml) for 2 h, followed by stimulation with or without IGF-1 (10 ng/ml) for 15 min. Cell lysates were analyzed by Western blotting using indicated antibodies. β-tubulin served as loading control. (B) Motility of Rh1 cells was determined by the wound healing assay, as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0010578#s2" target="_blank"><i>Materials and Methods</i></a>. Following wounding, serum-starved Rh1 cells were pretreated treated with or without OA (100 nM) for 1 h, and then treated with or without rapamycin (Rapa, 100 ng/ml) for 2 h, followed by stimulation with or without IGF-1 (10 ng/ml) for 22 h. Cells migrated over the denuded area were observed and photographed with an Olympus inverted phase-contrast microscope equipped with Quick Imaging system. The number of cells migrating per millimeter of scratch was counted. Results are means ± SE of 3–4 independent experiments. ^a<i>P</i><0.05, difference <i>vs.</i> control group; ^b<i>P</i><0.05, difference <i>vs.</i> IGF-1 group.</p

Rapamycin activates PP2A in an mTOR-dependent manner.

<p>Serum-starved Rh30 cells were exposed to rapamycin (Rapa, 100 ng/ml) for the indicated time (A), or pretreated with or without rapamycin (Rapa, 100 ng/ml) or okadaic acid (OA, 100 nM) for 2 h, and then stimulated with or without IGF-1 (10 ng/ml) for 1 h (B), or the indicated serum-starved Rh30 cells were exposed to rapamycin (Rapa, 100 ng/ml) for 2 h (C, D). PP2A in cell lysates was immunoprecipitated with antibodies to PP2A catalytic subunit (PP2Ac) plus protein A/G agarose beads, followed by <i>in vitro</i> phosphatase assay using Ser/Thr Phosphatase Assay Kit 1 (Millipore). Data represent mean ± SE from 3–4 independent experiments. ^a<i>P</i><0.05 <i>vs.</i> controls, ^b<i>P</i><0.05 <i>vs.</i> Rapa group.</p

Inhibition of Erk1/2 with PD98059 blocks IGF-1-stimulated cell motility.

<p>(A) Serum-starved Rh1 cells were exposed to increasing concentrations of PD98059 (0–50 µM) for 2 h, and then to IGF-1 for 15 min, followed by Western blotting using the indicated antibodies. (B) Motility of Rh1 cells was determined by the wound healing assay. Serum-starved cells were pretreated for 2 h with rapamycin (Rapa) (100 ng/ml) or PD98059 (PD) (10 µM) alone, or in combination as indicated, followed by stimulation with or without IGF-1 (10 ng/ml) for 22 h. Results are means ± SE of 3–4 independent experiments. ^a<i>P</i><0.05, difference <i>vs.</i> control group; ^b<i>P</i><0.05, difference <i>vs.</i> IGF-1 group.</p

Expression of dominant negative PP2A confers resistance to rapamycin inhibition of cell motility.

<p>(A) Rh1 cells were stably transfected with vector alone (Rh1/pcDNA) or with a vector expressing HA-tagged dn-PP2Ac (L199P), serum-starved for 24 h, and then treated with or without rapamycin (Rapa, 100 ng/ml), followed by <i>in vitro</i> phosphatase assay using Ser/Thr Phosphatase Assay Kit 1 (Millipore). Data represent mean ± SE from 3–4 independent experiments. ^a<i>P</i><0.05 <i>vs.</i> Rh1/pcDNA control, ^b<i>P</i><0.05 <i>vs.</i> Rh1/pcDNA Rapa group. (B) Serum-starved Rh1/pcDNA and Rh1/dn-PP2A cells were stimulated with or without IGF-1 (10 ng/ml) for 15 min, followed by Western blotting using the indicated antibodies. (C) Motility of Rh1/pcDNA and Rh1/dn-PP2A cells was determined by the wound healing assay, as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0010578#s2" target="_blank"><i>Materials and Methods</i></a>. Serum-starved cells were pretreated with or without rapamycin (Rapa, 100 ng/ml) or PD98059 (PD, 10 µM) for 2 h, and then stimulated with or without IGF-1 (10 ng/ml) for 22 h. Results are means ± SE of 3–4 independent experiments. ^a<i>P</i><0.05, difference <i>vs.</i> control group; ^b<i>P</i><0.05, difference <i>vs.</i> IGF-1 group.</p

Cd-induced neuronal apoptosis is associated with induction of [Ca^2<b>+</b>]_i elevation.

<p>(A and B) PC12 cells were treated with 0–20 µM Cd for 24 h, or with 0, 10 and 20 µM Cd for 0–24 h, and then loaded with 5 µM Fluo-3/AM for 30 min at 37°C in the dark, followed by measurement of [Ca²⁺]_i fluorescence intensity, as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0019052#s2" target="_blank">Materials and Methods</a>. (C and D) SH-SY5Y cells were exposed to 0–20 µM Cd for 24 h, or 10 µM Cd for 0–24 h, and then loaded with 2.5 µM Fluo-4/AM for 60 min at 37°C in the dark, followed by recording of the images under a fluorescence microscope. (E and F) Cell viability of PC12 cells, treated with 0–20 µM Cd for 24 h or with 20 µM Cd for 0–24 h, was evaluated by one solution assay. Results are presented as mean ± SE; <i>n</i> = 6. ^**<i>P</i><0.01 difference vs. control group.</p