Surface oxidation of commercial activated carbon with enriching carboxyl groups for high-yield electrocatalytic H2O2production.

Two-electron oxygen reduction reaction (2e-ORR) for H2O2production is regarded as a more ecologically friendly substitute to the anthraquinone method. However, the search of selective and cheap catalysts is still challenging. Herein, we developed a neutral-selective and efficient nonprecious electrocatalyst that was prepared from a commercial activated carbon (AC) by simply microwave-assisted ash impurity elimination and hydrogen peroxide oxidation for surface functional sites optimization. The oxygen configuration can be tuned with enriching carboxyl group up to 6.65 at.% by the dosage of hydrogen peroxide (mass ratio of H2O2/C = ∼0-8.3). Chemical titration experiments identified the carbonyl groups as the most potential active sites, with selectivity boosted by the additional carboxyl groups. The microwave-assisted moderate-oxidized activated carbon (MW-AC5.0) demonstrated optimal 2e-ORR activity and selectivity in neutral electrolyte (0.1 M K2SO4), with H2O2selectivity reaching ∼75%-97%, a maximum H2O2production rate (1.90 mol·gcatal-1·h-1@0.1 V) and satisfying faradaic efficiency (∼85%) in gas-diffusion-electrode. When coupled with Fenton reaction, it can degrade a model organic pollutant (methylene blue [MB], 50 ppm) to colorless in a short time of 20 min, indicating the potential applications in the environmental remediation.

Surface-confinement assisted synthesis of nitrogen-rich single atom Fe-N/C electrocatalyst with dual nitrogen sources for enhanced oxygen reduction reaction.

The utilization of earth abundant iron and nitrogen doped carbon as a precious-metal-free electrocatalyst for oxygen reduction reaction (ORR) significantly depends on the rational design and construction of desired Fe-Nxmoieties on carbon substrates, which however remains an enormous challenge. Herein a typical nanoporous nitrogen-rich single atom Fe-N/C electrocatalyst on carbon nanotube (NR-CNT@FeN-PC) was successfully prepared by using CNT as carbon substrate, polyaniline (PANI) and dicyandiamine (DCD) as binary nitrogen sources and silica-confinement-assisted pyrolysis, which not only facilitate rich N-doping for the inhibition of the Fe agglomeration and the formation of single atom Fe-Nxsites in carbon matrix, but also generate more micropores for enlarging BET specific surface area (up to 1500 m2·g-1). Benefiting from the advanced composition, nanoporous structure and surface hydrophilicity to guarantee the sufficient accessible active sites for ORR, the NR-CNT@FeN-PC catalyst under optimized conditions delivers prominent ORR performance with a half-wave potential (0.88 V versus RHE) surpass commercial Pt/C catalyst by 20 mV in alkaline electrolyte. When assembled in a home-made Zn-air battery device as cathodic catalyst, it achieved a maximum output power density of 246 mW·cm-2and a specific capacity of 719 mA·h·g-1Znoutperformed commercial Pt/C catalyst, holding encouraging promise for the application in metal-air batteries.

Highly coordinative molecular cobalt-phthalocyanine electrocatalyst on an oxidized single-walled carbon nanotube for efficient hydrogen peroxide production.

H2O2 production via the two-electron oxygen reduction reaction (2e- ORR) offers a potential alternative to the current anthraquinone method owing to its efficiency and environmental friendliness. However, it is necessary to determine the structures of electrocatalysts with cost-effectiveness and high efficiency for future industrialization demand. Herein, a supramolecular catalyst composed of cobalt-phthalocyanine on a near-monodispersed and oxidized single-walled carbon nanotube (CoPc/o-SWCNT) was synthesized via a solution self-assembly method for catalyzing the 2e- ORR for H2O2 electrosynthesis. Benefiting from the enhanced intermolecular interaction by introducing oxygen functional groups on o-SWCNTs, the oxidation states of single-atom Co sites were tuned via the formation of two extra Co-O bonds. Coupled with structural characterizations, density-functional theory (DFT) calculations reveal that the depressed d-band center of the Co site regulated by two axially-bridged O atoms gives rise to a suitable binding strength of oxygen intermediates (*OOH) to favor the 2e- ORR. Thus, the CoPc-6wt%/o-SWCNT-2 catalyst with optimized synthetic parameters delivers competitive 2e- ORR performance for H2O2 electrosynthesis in a neutral electrolyte (pH = 7), including enhanced H2O2 generation, satisfactory molar selectivity of ∼83-95% and long-period stability (75 h) in H-cell measurement. Moreover, it could also be boosted to show a high current of 45 mA cm-2, recorded turnover frequency of 25.3 ± 0.5 s-1 and maximum H2O2 production rate of 5.85 mol g-1 h-1 with a continuous H2O2 accumulation of 1.2 wt% in a flow-cell device, which outperformed most of the reported neutral-selective nonprecious metal single-atom catalysts.

Insights into the roles of organic coating in tuning the defect chemistry of monodisperse TiO(2) nanocrystals for tailored properties.

This work initiated a systematic study on the chemical nature of organic coating for monodispersed nanoparticles and its impact on the defect chemistry and the relevant properties. Monodispersed TiO(2) nanoparticles were prepared by a nonhydrolytic sol-gel reaction, which showed features of uniform diameter distribution around 5.2 nm, high crystallinity, and single anatase structure. These nanoparticles were terminated by oleate-related molecules, which stabilized the surface oxygen vacancies and further generated intense photoluminescence and co-existence of ferromagnetism and diamagnetism. After removal of organic coating, the nanoparticles became highly aggregated with no apparent changes in particle size, while the oxygen vacancy concentration was significantly reduced, as followed by energy position shift towards the deeper-levels which promoted the separation of photogenerated electrons and holes for improved photocatalytic activity. The results reported here are fundamentally important, which may be extended to comprehend the size-dependent defects and structure-property correlations of monodispersed nanoparticles for applications.

Nature of catalytic activities of CoO nanocrystals in thermal decomposition of ammonium perchlorate.

This work addresses the chemical nature of the catalytic activity of X-ray "pure" CoO nanocrystals. All samples were prepared by a solvothermal reaction route. X-ray diffraction indicates the formation of CoO in a cubic rock-salt structure, while infrared spectra and magnetic measurements demonstrate the coexistence of CoO and Co 3O 4. Therefore, X-ray "pure" CoO nanocrystals are a unique composite structure with a CoO core surrounded by an extremely thin Co 3O 4 surface layer, which is likely a consequence of the surface passivation of CoO nanocrystals from the air oxidation at room temperature. The CoO core shows a particle size of 22 or 280 nm, depending on the types of the precursors used. This composite nanostructure was initiated as a catalytic additive to promote the thermal decomposition of ammonium perchlorate (AP). Our preliminary investigations indicate that the maximum decomposition temperature of AP is significantly reduced in the presence of CoO/Co 3O 4 composite nanocrystals and that the maximum decomposition peak shifts toward lower temperatures as the loading amount of the composite nanocrystals increases. These findings are different from the literature reports when using many nanoscale oxide additives. Finally, the decomposition heat for the low-temperature decomposition stages of AP was calculated and correlated to the chemical nature of the CoO/Co 3O 4 composite nanostructures.

Synthesis and photoluminescence of well-dispersible anatase TiO2 nanoparticles.

High-purity anatase TiO(2) nanoparticles were prepared using a low-temperature sol-gel route. The as-prepared sample was characterized by X-ray diffraction, transmission electron microscopy, infrared spectroscopy, thermogravimetric analysis, UV-vis spectroscopy, and photoluminescence. It is shown that the as-prepared sample crystallized in a pure anatase phase with an average crystallite size of about 7 nm, and the surfaces were highly hydrated. These nanoparticles were stabilized as a water suspension via the cooperation of DLVO force and surface hydration force. These suspensions showed characteristic band-gap emission at 397+/-1.5 nm, which is a little red-shifted compared with the band-gap energy of indirect electronic transition measured in the UV-vis absorption spectrum. These observations were explained by the light-induced relaxation of polar water molecules in the surface hydration layer.

A visible and colorimetric aptasensor based on DNA-capped single-walled carbon nanotubes for detection of exosomes.

Recently, many studies have shown the potential use of circulating exosomes as novel biomarkers for monitoring and predicting a number of complex diseases, including cancer. However, reliable and cost-effective detection of exosomes in routine clinical settings, still remain a difficult task, mainly due to the lack of adequately easy and fast assay platforms. Therefore, we demonstrate here the development of a visible and simple method for the detection of exosomes by integrating single-walled carbon nanotubes that being excellent water solubility (s-SWCNTs) and aptamer. Aptamers, specific to exosomes transmembrane protein CD63, are absorbed onto the surface of s-SWCNTs and improve the minic peroxidase activity of s-SWCNTs, which can efficiently catalyze H2O2-mediated oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) and lead to a change from colorless to blue in solution. However, after adding exosomes, the aptamers are bound with CD63, leaving from the surface of s-SWCNTs through conformational changes, which results the color of solution from deep to moderate, and this can be observed by the naked eye and monitored by UV-vis spectrometry. Under optimal conditions, the linear range of exosomes is estimated to be 1.84×106 to 2.21×107 particles/µL with a detection of limit (LOD) of 5.2×105 particles/µL. Consequently, a visible and simple approach detecting exosomes is successfully constructed. Moreover, this proposed colorimetric aptasensor can be universally applicable for the detection of other targets by simple change the aptamer.

MnO2 Nanofilms on Nitrogen-Doped Hollow Graphene Spheres as a High-Performance Electrocatalyst for Oxygen Reduction Reaction.

Platinum is commonly chosen as an electrocatalyst used for oxygen reduction reaction (ORR). In this study, we report an active catalyst composed of MnO2 nanofilms grown directly on nitrogen-doped hollow graphene spheres, which exhibits high activity toward ORR with positive onset potential (0.94 V vs RHE), large current density (5.2 mA cm-2), and perfect stability. Significantly, when it was used as catalyst for air electrode, a zinc-air battery exhibited a high power density (82 mW cm-2) and specific capacities (744 mA h g-1) comparable to that with Pt/C (20 wt %) as air cathode. The enhanced activity is ascribed to the synergistic interaction between MnO2 and the doped hollow carbon nanomaterials. This easy and cheap method paves a way of synthesizing high-performance electrocatalysts for ORR.

Sulfur- and nitrogen-doped, ferrocene-derived mesoporous carbons with efficient electrochemical reduction of oxygen.

Development of inexpensive and sustainable cathode catalysts that can efficiently catalyze the oxygen reduction reaction (ORR) is of significance in practical application of fuel cells. Herein we report the synthesis of sulfur and nitrogen dual-doped, ordered mesoporous carbon (SN-OMCs), which shows outstanding ORR electrocatalytic properties. The material was synthesized from a surface-templating process of ferrocene within the channel walls of SBA-15 mesoporous silica by carbonization, followed by in situ heteroatomic doping with sulfur- and nitrogen-containing vapors. After etching away the metal and silica template, the resulting material features distinctive bimodal mesoporous carbon frameworks with high nitrogen Brunauer-Emmett-Teller specific surface area (of up to ∼1100 m(2)/g) and uniform distribution of sulfur and nitrogen dopants. When employed as a noble-metal-free electrocatalyst for the ORR, such SN-OMC shows a remarkable electrocatalytic activity; improved durability and better resistance toward methanol crossover in oxygen reduction can be observed. More importantly, it performs a low onset voltage and an efficient nearly complete four-electron ORR process very similar to the observations in commercial 20 wt % Pt/C catalyst. In addition, we also found that the textural mesostructure of the catalyst has superseded the chemically bonded dopants to be the key factor in controlling the ORR performance.

Sulfur and nitrogen co-doped, few-layered graphene oxide as a highly efficient electrocatalyst for the oxygen-reduction reaction.

S and N co-doped, few-layered graphene oxide is synthesized by using pyrimidine and thiophene as precursors for the application of the oxygen reduction reaction (ORR). The dual-doped catalyst with pyrrolic/graphitic N-dominant structures exhibits competitive catalytic activity (10.0 mA cm(-2) kinetic-limiting current density at -0.25 V) that is superior to that for mono N-doped carbon nanomaterials. This is because of a synergetic effect of N and S co-doping. Furthermore, the dual-doped catalyst also shows an efficient four-electron-dominant ORR process, which has excellent methanol tolerance and improved durability in comparison to commercial Pt/C catalysts.