Surface Phase Engineering Modulated Iron-Nickel Nitrides/Alloy Nanospheres with Tailored d-Band Center for Efficient Oxygen Evolution Reaction.

The oxygen evolution reaction (OER) plays a key role in many electrochemical energy conversion systems, but it is a kinetically sluggish reaction and requires a large overpotential to deliver appreciable current, especially for the non-noble metal electrocatalysts. In this study, the authors report a surface phase engineering strategy to improve the OER performance of transition metal nitrides (TMNs). The iron-nickel nitrides/alloy nanospheres (FeNi3 -N) wrapped in carbon are synthesized, and the optimized FeNi3 -N catalyst displays dual-phase nitrides on the surface induced by atom migration phenomenon, resulting from the different migration rates of metal atoms during the nitridation process. It shows excellent OER performance in alkaline media with an overpotential of 222 mV at 10 mA cm-2 , a small Tafel slope of 41.53 mV dec-1 , and long-term durability under high current density (>0.5 A cm-2 ) for at least 36 h. Density functional theory (DFT) calculations further reveal that the dual-phase nitrides are favorable to decrease the energy barrier, modulate the d-band center to balance the absorption and desorption of the intermediates, and thus promote the OER electrochemical performance. This strategy may shed light on designing OER and other catalysts based on surface phase engineering.

Facile synthesis of iron oxide supported on porous nitrogen doped carbon for catalytic oxidation.

Iron oxide (FexOy) supported on porous nitrogen doped carbon is synthesized by a facile pyrolysis method. SiO2 and NaNO3 are used as the template and activation agent respectively for porous structure generation and large specific surface area (SSA) creation. The obtained materials show superior catalytic oxidation ability and can activate peroxymonosulfate (PMS) in a wide pH range (3-9) to degrade organic pollutants. The degradation process is a two-stage reaction, including a rapid initial decay and a following slow reaction stage. According to the free radical quenching experiments, electron paramagnetic resonance (EPR) spectroscopy analysis, and electrochemical tests, the superoxide radical (O2-) and singlet oxygen (1O2) are proved to play crucial roles in organics degradation. The high SSA (773 m2 g-1), abundant of structural defects, and synergistic effect between FexOy and the nitrogen doped carbon are the key factors for the enhanced activity. The catalysts in this study can be synthesized easily and contain no toxic metals, thus should have great potential in the wastewater remediation.

Preparation of Hollow Cobalt-Iron Phosphides Nanospheres by Controllable Atom Migration for Enhanced Water Oxidation and Splitting.

Transition metal phosphides (TMPs), especially the dual-metal TMPs, are highly active non-precious metal oxygen evolution reaction (OER) electrocatalysts. Herein, an interesting atom migration phenomenon induced by Kirkendall effect is reported for the preparation of cobalt-iron (Co-Fe) phosphides by the direct phosphorization of Co-Fe alloys. The compositions and distributions of the Co and Fe phosphides phases on the surfaces of the electrocatalysts can be readily controlled by Cox Fey alloys precursors and the phosphorization process with interesting atom migration phenomenon. The optimized Co7 Fe3 phosphides exhibit a low overpotential of 225 mV at 10 mA cm-2 in 1 m KOH alkaline media, with a small Tafel slope of 37.88 mV dec-1 and excellent durability. It only requires a voltage of 1.56 V to drive the current density of 10 mA cm-2 when used as both anode and cathode for overall water splitting. This work opens a new strategy to controllable preparation of dual-metal TMPs with designed phosphides active sites for enhanced OER and overall water splitting.

Bamboo-like nitrogen-doped carbon nanotubes on iron mesh for electrochemically-assisted catalytic oxidation.

In this study, bamboo-like nitrogen-doped carbon nanotubes (BN-CNTs) are successfully deposited on etched iron mesh (d-Fe) using chemical vapor deposition (CVD) method with acetonitrile as precursor. The acidic etching process is necessary for the special BN-CNTs structure formation by exposing more Fe0 sites. The BN-CNTs/d-Fe is then evaluated for the electrochemically-assisted PMS activation to degrade phenol. Under cyclic voltammetry (CV, 0-1 V vs. RHE) assistant, 20 ppm phenol can be degraded in 30 min with a rate constant of 0.2837 min-1, ~78 times more than that without CV. Some Fe3+ species in the catalyst will be reduced at the initial stage, a two-step pseudo-first-order kinetic is thus used for the degradation curves fitting. Both the structure defects and doped nitrogen atoms are responsible for the high catalytic activity of BN-CNTs. According to the quenching tests, both radical and non-radical processes are present for PMS activation, thus obtaining enhanced organics removal efficiency. The electrochemically assistant could enhance the PMS adsorption on the electrode as well as electrons transfer between Fen+ and PMS, thus increasing the PMS activation efficiency. The utilization of earth-abundant Fe mesh for the fabricating free-standing electrodes provide a potential low-cost and effective strategy of waste water remediation.

Surfactant-Free Synthesis of Ultrafine Pt Nanoparticles on MoS2 Nanosheets as Bifunctional Catalysts for the Hydrodeoxygenation of Bio-Oil.

Hydrodeoxygenation (HDO) of bio-oil is a crucial step for improving the bio-fuel quality, but developing highly dispersed Pt-based catalysts with high selectivity for target alkanes remains a great challenge. This study presents a fast surfactant-free method to prepare the MoS2-supported Pt catalyst for HDO. Ultrafine Pt nanoparticles with sizes of <5 nm can be readily grown on chemically exfoliated MoS2 nanosheets (NSs) via the direct microwave-assisted thermal reduction. The obtained Pt NPs/MoS2 composites show excellent catalytic performance in the conversion of palmitic acid, and the best selectivity (also the yield) of hexadecane and pentadecane is 80.56 and 19.43%, respectively.

Decorated nickel phosphide nanoparticles with nitrogen and phosphorus co-doped porous carbon for enhanced electrochemical water splitting.

A novel free-standing electrode consisting of nickel phosphide (Ni2P) nanoparticles on nitrogen and phosphorus co-doped porous carbon (NPC) are synthesized on carbon cloth (CC). Polyaniline (PANI) and nickel (Ni) are sequentially electro-deposited on the surface of CC, which are then transformed into NPC and Ni2P by an in-situ carbonization-phosphorization combined process. The electrode surface is distributed with large amounts of uniform macropores, which could expose more active sites and enhance the interfacial exchange with the electrolyte. The Ni2P@NPC@CC electrode delivers early overpotentials of 92 and 280 mV vs. Reversible Hydrogen Electrode (RHE) at 10 mA cm-2 for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline condition, respectively. The electrolytic cell with Ni2P@NPC@CC electrode both as anode and cathode can achieve 10 mA cm-2 at a small bias of 1.54 V for the overall water splitting. Density functional theory (DFT) calculation indicates that combination with Ni2P and NPC can decrease Gibbs free energy for H* adsorption (ΔGH*) and increase charge density on the interface, thus could lead to the enhanced activity for water splitting. The free-standing and noble-metal free Ni2P@NPC@CC electrode is stable, highly active and cost effective, thus have great potential for the hydrogen production.

3D self-supported Ni(PO3)2-MoO3 nanorods anchored on nickel foam for highly efficient overall water splitting.

Electrolyzing water as a sustainable energy source is a promising and appealing method to resolve the environmental crisis. Developing efficient and stable bifunctional electrocatalysts for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) is crucial and challenging in the overall water splitting process. Herein, we report the synthesis of Ni(PO3)2-MoO3 nanorods anchored on nickel foam (Ni(PO3)2-MoO3/NF) within a two-step strategy and their application as a bifunctional water splitting electrocatalyst. The results show that the optimal Ni(PO3)2-MoO3/NF electrodes exhibit superior catalytic activity with robust durability and ultralow overpotentials of 86 mV for HER and 234 mV for OER to achieve 10 mA cm-2 (η10) in alkaline solution. The favorable performance of the obtained catalyst is attributed mainly to the synergetic effect between Ni(PO3)2 and MoO3, as well as the self-supporting porous conductive substrate. As a result, the integrated Ni(PO3)2-MoO3/NF electrodes deliver η10 at a small potential of 1.47 V for overall water splitting, highlighting a promising application as a bifunctional electrocatalyst.

Beryllium-7 in vegetation, soil, sediment and runoff on the northern Loess Plateau.

Beryllium-7 (7Be), as a potentially powerful tracer, was widely used to document soil redistribution and identify sediment sources in recent decades, but the quantity and distribution of 7Be in vegetation, soil, sediment and runoff on the Loess Plateau have not been fully described. In this study, we measured 7Be in vegetation, soil, sediment and runoff on the northern Loess Plateau of China and analyzed its variations during the rainy season to assess the potential of the 7Be method for documenting soil redistribution and identifying sediment sources in a wide range of environments. The results indicated that vegetation, soil, and sediment samples showed higher levels and larger variations of 7Be activities during the rainy season. The drying plants showed 7Be mass activity that was more than three times higher than that of living and semi-decomposed plants. 7Be mass activity in plants and sediment was much higher than in the soil. 7Be activity in runoff water with a few submicron suspended particles varied slightly and was far lower than in plant, soil and sediment samples. The cumulative precipitation generally determined 7Be inventory held by plants and soil. An inverse relationship was found between the 7Be mass activity in sediment and the sediment amount. Globally, approximate 30% of the total 7Be was held by plants in both the herbaceous and subshrub plots. Approximate 10% of the total 7Be was lost with sediment from the bare plot. A very small proportion of 7Be (1.18%-3.20%) was lost with runoff, and the vast majority of 7Be was retained in the slope soil at the end of rainy season. Vegetation cover and soil erosion significantly affected the spatial distribution and variations of the 7Be inventory in soil, providing a necessary condition for the development of a 7Be method to document soil erosion on slopes with vegetation.

Beryllium-7 measurements of wind erosion on sloping fields in the wind-water erosion crisscross region on the Chinese Loess Plateau.

Soil erosion is complex in the wind-water erosion crisscross region of the Chinese Loess Plateau, as interleaving of wind and water erosion occurs on both temporal and spatial scales. It is difficult to distinguish wind erosion from the total erosion in previous studies due to the untraceable of aeolian particles and the limitation of feasible methods and techniques. This study used beryllium-7 measurements to study wind erosion in the wind-water erosion crisscross region on the Chinese Loess Plateau arms to delineate wind erosion distribution, to analyze its implication to erosive winds and surface microrelief, and to determine correlations between erosion rates and slope gradients. Results obtained using beryllium-7 measurements based on observation plots were verified with saltating particle collection method, and were also verified on a field scale. Results indicated that the effective resultant erosion wind was from northward, which was proved by the eight-directional distributed saltating particles. The microrelief of the ground surface contributed to the formation of high or low erosion centers. Wind erosion rates increased with a linear (R2≥0.95) or exponential (R2≥0.83) fitting increase in the slope gradients as reported in previous studies. Compared to wind erosion on field scale, both the plots and fields exhibited similar distribution patterns in wind erosion isolines. We also determined that the wind erosion rate for two fields estimated, based on equations developed from plot scale was acceptable. This study validates the feasibility of beryllium-7 measurements for soil-wind erosion field experiments and the potential to expand this approach to real field conditions.

Quadruple-responsive nanocomposite based on dextran-PMAA-PNIPAM, iron oxide nanoparticles, and gold nanorods.

A quadruple-responsive nanocomposite that responds to temperature, pH, magnetic field, and NIR is obtained by incorporating superparamagnetic iron oxide nanoparticles (SPIONs) and gold nanorods (AuNRs) into a dextran-based smart copolymer network. The dual-sensitive copolymer is prepared by sequential RAFT polymerization of methacrylic acid and N-isopropylacrylamide from trithiocarbonate groups linked to dextran in one pot. These functionalized nanocomposites with superior stability can respond to the four stimuli mentioned above well. As evidenced by UV-vis and TEM measurements, the temperature-induced unusual blue-shift in the longitudinal plasmon band is possibly due to the side-to-side assembly of AuNRs.