Engineering of 3D graphene hydrogel-supported MnO2-FeOOH nanoparticles with synergistic effect of oxidation and adsorption toward highly efficient removal of arsenic

Iron-manganese-based adsorbent has been regarded as a promising candidate for arsenic purification from water, especially the inorganic As(III), due to its inherent advantage of low cost and large-scale producibility. However, the nanoparticle aggregation, metal leaching and insufficient removal efficiency remain the main challenges in the practical applications of the granular adsorbents. In this work, we develop a universal strategy for the fabrication of an active Fe(III) oxyhydroxide-Mn(IV) oxide/3D graphene oxide (GO) gel composite via a simple hydrothermal reaction. The successful immobilization of Fe-Mn oxyhydroxide/oxides on the interconnected GO gels was intuitively confirmed by the transmission electron microscopy and atomic force microscopy. The combinative characterizations of the X-ray absorption near edge structure and X-ray photoelectron spectroscopy clearly reveal the electron transfer from Fe atoms to Mn atoms. The optimized Fe-Mn/GO composites possess the superior performance with the removal efficiency of over 90% for As(III) at pH 7.0 and ∼97% for As(V) at pH 5.0 and the As(III, V) levels (100 μg l^-1) are reduced to below the WHO guideline of 10 μg l^-1. The sorption isotherm and kinetic experiments on the As removal were also carried out. The post characterizations are employed to better unveil the oxidation-adsorption mechanism. Notably, the application of Fe-Mn/GO composites in the treatment of As-simulated natural water demonstrated a stable and continuous operation for over 20 days and an effluent concentration of arsenic as low as the 10 μg l^-1 in a specially designed flow reactor.

Powder hybrid nanomaterial: Detonation nanodiamonds - Carbon nanotubes and its stable reversible water nanofluids

A hybrid nanomaterial composed of detonation nanodiamonds-multi-walled carbon nanotubes (DND-CNT) in powdered form and the form of stable recoverable water nanofluid was obtained. The ability to obtain a hybrid material in the form of powder, as well as in the form of an aqueous suspension opens the way for the creation of new composite materials based on metals and polymers, as well as new types of nanofluids. Particle size in water suspension was investigated by dynamic light scattering (DLS) method and has been shown that while the original DND was agglomerates with the particle size about one μm, the particles size of a hybrid material in water suspension was 40-60 nm. Such result was achieved by growing multi-walled carbon nanotubes on the surface of nanodiamonds aggregates coated with a metal catalyst using catalyst chemical vapor deposition (CCVD) method for nanotubes growth. The resulting nanomaterial is a powdered hybrid material obtained based on a scalable technology. The measured electrical conductivity of the water suspension amounted to 35 μS/cm what is 6 times higher than the electrical conductivity of the pure distilled water.

Liquid-Phase Hydrodeoxygenation of Guaiacol over Mo2C Supported on Commercial CNF. Effects of Operating Conditions on Conversion and Product Selectivity

In this work, a Mo2C catalyst that was supported on commercial carbon nanofibers (CNF) was synthetized and tested in the hydrodeoxygenation (HDO) of guaiacol. The effects of operating conditions (temperature and pressure) and reaction time (2 and 4 h) on the conversion of guaiacol and products selectivity were studied. The major reaction products were cresol and phenol, followed by xylenols and toluene. The use of more severe operating conditions during the HDO of guaiacol caused a diversification in the reaction pathways, and consequently in the selectivity to products. The formation of phenol may have occurred by demethylation of guaiacol, followed by dehydroxylation of catechol, together with other reaction pathways, including direct guaiacol demethoxylation, and demethylation of cresols. X-ray diffraction (XRD) analysis of spent catalysts did not reveal any significant changes as compared to the fresh catalyst.

Implication of iron nitride species to enhance the catalytic activity and stability of carbon nanotubes supported Fe catalysts for carbon-free hydrogen production via low-temperature ammonia decomposition

This study prepared the Fe₂N/CNTs catalysts by using wet-impregnation and followed by nitrogenization, for carbon-free hydrogen production from NH₃ decomposition.

Single-Atomic Ruthenium Catalytic Sites on Nitrogen-Doped Graphene for Oxygen Reduction Reaction in Acidic Medium

The cathodic oxygen reduction reaction (ORR) is essential in the electrochemical energy conversion of fuel cells. Here, through the NH₃ atmosphere annealing of a graphene oxide (GO) precursor containing trace amounts of Ru, we have synthesized atomically dispersed Ru on nitrogen-doped graphene that performs as an electrocatalyst for the ORR in acidic medium. The Ru/nitrogen-doped GO catalyst exhibits excellent four-electron ORR activity, offering onset and half-wave potentials of 0.89 and 0.75 V, respectively, vs a reversible hydrogen electrode (RHE) in 0.1 M HClO₄, together with better durability and tolerance toward methanol and carbon monoxide poisoning than seen in commercial Pt/C catalysts. X-ray adsorption fine structure analysis and aberration-corrected high-angle annular dark-field scanning transmission electron microscopy are performed and indicate that the chemical structure of Ru is predominantly composed of isolated Ru atoms coordinated with nitrogen atoms on the graphene substrate. Furthermore, a density function theory study of the ORR mechanism suggests that a Ru-oxo-N₄ structure appears to be responsible for the ORR catalytic activity in the acidic medium. These findings provide a route for the design of efficient ORR single-atom catalysts.

Catalytic etching of monolayer graphene at low temperature via carbon oxidation

In this work, an easy method to etch monolayer graphene is shown by catalytic oxidation in the presence of ZnO nanoparticles (NPs). The catalytic etching of monolayer graphene, which was transferred to the channel of field-effect transistors (FETs), was performed at low temperature by heating the FETs several times under an inert gas atmosphere (ZnO + C → Zn + CO or CO2). As the etching process proceeded, diverse etched structures in the shape of nano-channels and pits were observed under microscopic observation. To confirm the evolution of etching, current-voltage characteristics of monolayer graphene were measured after every step of etching by catalytic oxidation. As a result, the conductance of monolayer graphene decreased with the development of etched structures. This decrease in conductance was analyzed by percolation theory in a honeycomb structure. Finally, well-patterned graphene was obtained by oxidizing graphene under air in the presence of NPs, where Al was deposited on graphene as a mask for designed patterns. This method can substitute graphene etching via carbon hydrogenation using H2 at high temperature.

New insights into the role of lattice oxygen in the catalytic carbonization of polypropylene into high value-added carbon nanomaterials

Lattice oxygen in catalysts played an important role in the carbonization of PP into CNMs including PL-CFs, CNFs and CS-CNTs.

Iron carbide and nitride via a flexible route: synthesis, structure and magnetic properties

Fe₄N and Fe₃C have been controllably synthesized by adjusting the molar ratio of hexamethylenetetramine to ferric chloride hexahydrate.

The structure and magnetic properties of Fe3N as a photocatalyst applied in hydrogen generation induced by visible light

Fe₃N can be efficiently synthesized from an iron-ethanediamine precursor, whose diameter can be controlled by the synergistic effect of acetone and ethanediamine.