High Density Single Fe Atoms on Mesoporous N-Doped Carbons: Noble Metal-Free Electrocatalysts for Oxygen Reduction Reaction in Acidic and Alkaline Media.

It remains a challenge to develop efficient noble metal-free electrocatalysts for the oxygen reduction reaction (ORR) in various renewable energy systems. Single atom catalysts have recently drawn great attention as promising candidates both due to their high activity and their utmost atom utilization for electrocatalytic ORR. Herein, the synthesis of an efficient ORR electrocatalyst that is composed of N-doped mesoporous carbon and a high density (4.05 wt%) of single Fe atoms via pyrolysis Fe-conjugated polymer is reported. Benefiting from the abundant atomic Fe-N4 sites on its conductive, mesoporous carbon structures, this material exhibits an excellent electrocatalytic activity for ORR, with positive onset potentials of 0.93 and 0.98 V in acidic and alkaline media, respectively. Its electrocatalytic performance for ORR is also comparable to that of Pt/C (20 wt%) in both media. Furthermore, it electrocatalyzes the reaction almost fully to H2 O (or barely to H2 O2 ). Additionally, it is durable and tolerates the methanol crossover reaction well. Furthermore, a proton exchange membrane fuel cell and a zinc-air battery assembled using it on their cathode deliver high maximum power densities (320 and 91 mW cm-2 , respectively). Density functional theory calculation reveals that the material's decent electrocatalytic performance for ORR is due to its atomically dispersed Fe-N4 sites.

Nitrogen-doped mesoporous carbon single crystal-based Ag nanoparticles for boosting mild CO2 conversion with terminal alkynes.

Fabrication of efficient heterogeneous catalysts with high turnover frequency (TOF) is intriguing for rapid and scalable CO2 conversion under mild conditions, but it still faces some challenges due to use of some bulky and irregular supports causing inaccessible inner pores and insufficient utilization of active sites. Herein, using a unique nitrogen-doped mesoporous single-crystal carbon (named IRFC) as a host for loading Ag nanoparticles for the first time, a series of Ag/IRFC catalysts with high TOF (8.7-22.3 h-1) were facilely prepared by a novel "impregnation and in-situ reduction" strategy. The neat morphology and high porosity of IRFC with abundant N species, providing homogeneous surface, adequate space and anchoring sites for Ag immobilization, greatly facilitated the formation of highly-distributed ultrasmall Ag nanoparticles (2.3 nm). Meanwhile, smooth and short diffusion pathways were inherited from the ordered mesopores and small particle sizes of IRFC. Owing to these unparalleled structural features, the Ag/IRFC catalysts exhibited excellent catalytic activity, stability, and generality for mild CO2 conversion even under diluted conditions. This work not only presents a novel catalyst for mild CO2 conversion, but also brings some inspirations to designing highly efficient catalysts using well-shaped supporting nanomaterials for direct utilization of low-concentration CO2, such as flue gas.

Mechanical Insights into the Electrochemical Properties of Thornlike Micro-/Nanostructures of PDA@MnO2@NMC Composites in Aqueous Zn Ion Batteries.

As emerging energy storage devices, aqueous zinc ion batteries (AZIBs) with outstanding advantages of high safety, high energy density, and environmental friendliness have attracted much research interest. Herein, the favorable thornlike MnO2 micro-/nanostructures (PDA@MnO2@NMC) are rationally constructed by the incorporation of both carbon substrates (NMC) and polydopamine (PDA) surface modifications. Ex situ X-ray diffraction and Raman characteristics show the formation of MnOOH and ZnMn2O4 products, corresponding to H+ and Zn2+ insertions in two discharge platforms. Density functional theory (DFT) calculations also demonstrate that PDA can firmly anchor onto MnO2 surfaces and prevent the dissolution of MnOOH. In addition, PDA with more hydrophilic groups can capture more H+ together with the increased surface capacitance and the extension of the first discharge platform, while the NMC carbon substrate can provide abundant active sites for the overgrown MnO2 nanowires, improve the conductivity, and promote fast ion and electron transportations. Further, electrochemical impedance spectroscopy (EIS) and GITT results show that the ohmic resistance of PDA@MnO2@NMC decreases to almost half and, in particular, the ion diffusion coefficient increases more than 30 times of pure MnO2. As such, PDA@MnO2@NMC in the AZIB cathode exhibits excellent electrochemical performance compared to the pure MnO2, which is expected to have favorable competitiveness in energy storage devices.

One-step elimination of Cr(VI) by catalytic hydrogenation of Cr(VI) and simultaneous Cr(OH)3 recovery on Pt catalysts encapsulated in N-doped mesoporous carbon.

Hexavalent chromium Cr(VI) is a highly toxic heavy metal, which is commonly eliminated by stepwise reduction at acidic pH and precipitation of Cr(OH)3 at alkaline pH. A unique Pt catalyst with Pt particles embedded in the framework of N-doped mesoporous carbon CMK-3 (denoted as Pt@NCMK-3) was designed and fabricated to one-step eliminate Cr(VI) pollution at near neutral pH via simultaneous Cr(VI) reduction by catalytic hydrogenation and Cr(OH)3 recovery. Structural characterization showed that Pt particles of Pt@NCMK-3 were effectively embedded in the carbon rods of NCMK-3. Batch experiments revealed that Pt@NCMK-3 exhibited a higher catalytic activity and stability than other test catalysts. Fixed-bed column reaction results indicated that under the experimental conditions Pt@NCMK-3 had better breakthrough performances than other catalysts. Additionally, after 4 treatment-recovery cycles Pt@NCMK-3 maintained nearly identical breakthrough performance, whereas other catalysts displayed markedly decreased breakthrough bed volumes, reflecting a substantially higher stability of Pt@NCMK-3.

DSPE-PEG-Coated Uniform Nitrogen-Doped Carbon Capsules for NIR-Mediated Synergistic Chemophototherapy of Skin Cancer.

Uniform monodispersed nitrogen-doped carbon spheres have been emerging as an exciting platform for multipurpose medical applications like photothermal therapy and photoacoustic imaging and as carriers for aromatic anticancer drugs. However, synthesis of uniform N-doped mesoporous carbon of size less than 100 nm with reasonable photothermal and photodynamic activities is a challenging task. In this connection, the present paper reports synthesis of nitrogen-doped mesoporous carbon spheres (NMCSs) from five different copolymers of pyrrole and substituted aniline (-H, o-NH2, m-NH2, p-NH2, and m-NO2) using a soft template approach. It has been found that NMCSs synthesized from poly(pyrrole-co-m-nitroaniline) show uniform mesoporous particles of size 80 nm, a photothermal conversion efficiency η of 52.7%, and an average 1O2 quantum yield of 20% under exposure of a 980 nm NIR laser. With a high η of 52%, a multifunctional nanodrug has been formulated by loading 5-Fu in NMCS. The overall drug-loaded NMC was encapsulated by thermosensitive DSPE-PEG to improve translocation of the particle in the cell and thermosensitive drug release. A reliable release of anticancer drug 5-Fu (78%) has been achieved in 50 h in lysosomal conditions under 980 nm laser exposure. This NMC-5-Fu-DSPE-PEG nanodrug produces reactive oxygen species and enhances the therapeutic effect in comparison with free drug under an NIR laser as verified in B16F0 melanoma cells.

Direct synthesis of nitrogen-doped mesoporous carbons from triazine-functionalized resol for CO2 uptake and highly efficient removal of dyes.

In this study we synthesized a triazine-formaldehyde phenolic resin as a nitrogen-containing resol (N-resol) through the condensation of 2,4,6-tris(4-hydroxyphenyl)triazine and formaldehyde. We then used this N-resol as a carbon and nitrogen atom source, mixing it with a diblock copolymer of PEO-b-PCL as the soft template, for the direct synthesis of N-doped mesoporous carbons. Interestingly, the self-assembled N-resol/PEO-b-PCL blends underwent a mesophase transition from cylinder to gyroid and back again to cylinder structures upon increasing the N-resol concentration (i.e., cylinder at 50/50; gyroid at 60/40; cylinder at 70/30). After removing the soft template at 700 °C, the resultant N-doped mesoporous carbons possessed high N atom contents (up to 13 wt%) and displayed gyroid and cylinder nanostructures. The synthesized N-doped mesoporous carbons exhibited excellent CO2 uptake capacities (up to 72 and 150 mg g-1 at 298 and 273 K, respectively). Furthermore, the N-doped mesoporous gyroid carbon structure displayed high adsorption capacities toward organic dyes in water. The maximum adsorption capacities of rhodamine B and methylene blue in water reached as high as 204.08 and 308.64 mg g-1, respectively; furthermore, these N-doped mesoporous carbons also maintained up to 98 % of their maximum adsorption capacities within 45 min.

N-doped mesoporous carbon as a new sorbent for ultrasonic-assisted dispersive micro-solid-phase extraction of 1-naphthol and 2-naphthol, the biomarkers of exposure to naphthalene, from urine samples.

This study aimed to optimize a new sample preparation method using N-doped mesoporous carbon sorbent for simultaneous measurement of 1-naphthol and 2-naphthol, the biomarkers of exposure to naphthalene. The samples were analyzed using high-performance liquid chromatography supplied with ultraviolet detector (HPLC-UV). N-doped mesoporous carbon sorbent was obtained via the hard template procedure. The synthesized nanosorbent was then characterized by transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET), and elemental analysis (CHN). The effective factors in the extraction of the studied biomarkers were examined by the Box-Behnken (BBD) methodology. Regarding the optimum conditions, the sketched calibration curve for naphthols was linear in the concentration levels of 1-600 µg L-1 for human urine samples. The accuracy and reproducibility of the introduced method were determined using the relative recovery (RR %) and relative standard deviation (RSD %) tests on the fortified urine samples. RR% and RSD% were found to be 97.0-101.2% and 3.1-9.0%, respectively. The calculated method detection limit of the optimized procedure was 0.3 µg L-1 and 0.5 µg L-1 for 1-naphthol and 2-naphthol, respectively.

Facile synthesis of nitrogen-enriched nanoporous carbon materials for high performance supercapacitors.

Mesoporous carbons with ultrahigh nitrogen content were prepared for supercapacitors through the hard template method. Silica nanoparticles were used as the hard template, and ethylenediamine and CCl4 served as precursor. Large amount of mesopores were generated through removing the silica nanoparticles with HF. The effect of carbonization temperature on the pore structure and nitrogen content and thus on the capacitive performance of supercapacitors were investigated. It was found that the higher carbonization temperature leads to an initial increase and then decrease of specific surface area and a continuous decrease in N content. The sample carbonized at 700 °C (NC700) shows the highest capacitance (306 F g-1) due to the higher surface area (533 m2 g-1) and ultrahigh N content (18.06%). The increase in specific surface area results in improvement of double-layer capacitance, while the N element increases the pseudocapacitance and the wettability of the carbons. In addition, NC700 shows excellent stability with 96.6% capacitance retention even after 10,000 cycles at a current density of 3 A g-1.

Highly effective catalytic peroxymonosulfate activation on N-doped mesoporous carbon for o-phenylphenol degradation.

As a broad-spectrum preservative, toxic o-phenylphenol (OPP) was frequently detected in aquatic environments. In this study, N-doped mesoporous carbon was prepared by a hard template method using different nitrogen precursors and carbonization temperatures (i.e., 700, 850 and 1000 °C), and was used to activate peroxymonosulfate (PMS) for OPP degradation. For comparison, mesoporous carbon (CMK-3) was also prepared. Characterization results showed that the N-doped mesoporous carbon samples prepared under different conditions were perfect replica of their template. In comparison with ethylenediamine (EDA) and dicyandiamide (DCDA) as the precursors, N-doped mesoporous carbon prepared using EDA and carbon tetrachloride as the precursors displayed a higher catalytic activity for OPP degradation. Increasing carbonization temperature of N-doped mesoporous carbon led to decreased N content and increased graphitic N content at the expense of pyridinic and pyrrolic N. Electron paramagnetic resonance (EPR) analysis showed that PMS activation on N-doped mesoporous carbon resulted in highly active species and singlet oxygen, and catalytic PMS activation for OPP degradation followed a combined radical and nonradical reaction mechanism. Increasing PMS concentration enhanced OPP degradation, while OPP degradation rate was independent on initial OPP concentration. Furthermore, the dependency of OPP degradation on PMS concentration followed the Langmuir-Hinshelwood model, reflecting that the activation of adsorbed PMS was the rate controlling step. Based on the analysis by time-of-flight mass spectrometry, the degradation pathway of OPP was proposed.

Co-entrapped, N-doped mesoporous carbons prepared from melamine formaldehyde resins with CoCl2 as template for hydrogen evolution.

Cobalt-entrapped, nitrogen-doped mesoporous carbon materials have been prepared using melamine formaldehyde resin (MF resin) as precursor and CoCl2 as template. A fraction of CoCl2 can be reduced to Co nanoparticles and wrapped by the nitrogen doped carbon. Meanwhile, the ratio of MF resin to CoCl2 is an important parameter determining the mesoporous structures of the final products. The surface area of the obtained material decreases with the increase in the ratio of MF resin to CoCl2. Electrocatalytic tests show that the obtained catalysts are highly active for hydrogen evolution reaction in both acidic and basic media, achieving a current density of 10 mA cm-2 at 171 and 186 mV under acidic and alkaline conditions, respectively. Additionally, these catalysts also show good long-term stabilities.

Cobalt nanoparticles supported on N-doped mesoporous carbon as a highly efficient catalyst for the synthesis of aromatic amines.

Inexpensive and reusable transition metal heterogeneous catalysts exhibiting excellent catalytic performance represent an attractive alternative to noble metal and homogeneous catalysts. In this work, we fabricated a novel nanocatalyst comprised of Co nanoparticles (NPs) supported on a N-doped mesoporous carbon (Co/mCN-900) by simple one-pot pyrolysis of a homogeneous mixture of melamine, polyacrylonitrile, and Co(NO3)2·6H2O under a N2 atmosphere at 900°C. The as-obtained Co/mCN-900 catalyst displayed a fluffy mesoporous structure with highly dispersed and accessible Co NPs acting as catalytic active sites. The Co/mCN-900 catalyst was effective in hydrogenating nitroarenes at milder conditions (i.e., 1MPa H2 and 120°C) as compared to previously reported Co- and Ni-based catalysts. The Co/mCN-900 catalyst also catalyzed the reductive N-alkylation of nitroarenes with carbonyl compounds to form the corresponding aromatic secondary amines under very mild reaction conditions. In addition, the Co/mCN-900 catalyst showed good reusability since its morphology and activity were maintained after several reaction cycles. Therefore, this work provides a facile and promising method for fabricating non-precious transition metal-based catalysts with excellent performance and great potential for sustainable chemistry applications.