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Assemblies of β-iron oxyhydroxide (β-FeOOH) nanostructures were synthesized by a facile, mild, and non-toxic ultrasonication method. Quasi-rectangular, chrysanthemum-like, and silk-like architectures, respectively, were obtained by introducing a urea surfactant, synthesized Fe 3 O 4 template, and natural kapok seed template. This versatile and efficient synthetic method can be extended to the fabrication of a series of novel, multifunctional assembled architectures. Hierarchical structures with identical morphologies were constructed from porous β-FeOOH nanorods with high surface areas. The effects of the assembly mode on the nonlinear optical (NLO) properties of the β-FeOOH nanorod assemblies were explored using the open-aperture Z-scan technique. Individual β-FeOOH nanorods and their analogous nanoassemblies exhibited excellent NLO performances upon excitation at 532 and 1064 nm in the nanosecond laser pulse regime, both in liquid and sol–gel solid-state matrices. These nanomaterials are promising candidates for broadband optical limiters; however, their abilities to attenuate intense and potentially dangerous laser beams differ. Our results confirm that nanoassembly formation can be used to effectively tailor the NLO activities of β-FeOOH nanorods, and the possible mechanisms for these behaviors are discussed. The observed NLO effects originate from nonlinear scattering and free-carrier absorption at 532 and 1064 nm, respectively. This study provides new insights into the assembly of one-dimensional building blocks, which will be useful in the rational design and preparation of hierarchical materials and enable tailoring and improvement of the NLO properties of materials. [ABSTRACT FROM AUTHOR]

N-doped carbons (NCs) have attracted considerable attention for their outstanding physicochemical properties, including tunable porosity, electronic features and modified surface. Here, we report the preparation of hierarchically porous NCs derived from the direct pyrolysis of ZIFs (ZIF-7 and ZIF-8) and poly– m –phenylenediamine-covered carbon black (P m PDA-C) for the stabilization of Cu nanoparticles (NPs). The configuration of N species can be effectively regulated by changing the ligand of ZIFs and pyrolysis atmosphere. A remarkable N configuration synergistic effect is observed in the oxy-carbonylation of methanol to dimethyl carbonate with molecular oxygen. The results indicate that the Cu NPs on pristine carbon have a turn over frequency (TOF) of 4.4 h−1 for the reaction, while those on NCs from ZIF-8 and ZIF-7 present TOF values as high as 17.9 h−1 and 28.5 h−1, respectively. The extensive characterizations reveal that NCs with a nitrogen content of 2–5 wt% and a pyrrolic-/pyridinic-N molar ratio of 2–3 are vital for the performance enhancement of Cu NPs. This work shows that the stabilization and enhanced performance of active Cu NPs on NCs are realized by the rational design of precursors to generate the proper N configurations. Image 1 • A series of NCs are prepared from ZIFs with N content in the range of 0–20 wt%. • The N configuration is regulated by ligand of ZIFs and varying pyrolysis conditions. • The performance of supported Cu catalysts is correlated with N configurations. • NCs with 2–5 wt% N and pyrrolic-/pyridinic-N ratio at 2–3 are vital for Cu catalysis. [ABSTRACT FROM AUTHOR]

Understanding of molecular diffusion mechanisms in zeolite plays a crucial role in the processes of adsorption and separations and can greatly facilitate the design of zeolite at molecular level. However, compared with the case of free gas phase, the diffusion behaviors in channel of zeolite are much more complicated due to the confined pore environments. To dig more detailed information about the diffusivity mechanism of gas molecules in the zeolite pore, diffusion behaviors of H 2 , He, N 2 , CH 4 and CO 2 molecules in the one-dimensional (1-D) channel of AlPO 4 -5 (AFI) zeolite-like materials were investigated using a combined classic molecular dynamics (MD) simulations and density functional theory (DFT) calculations. It is found that the diffusion behavior for light molecules (H 2 and He) at low loading in AlPO 4 -5 channel is more freedom because of their small molecular diameter and low energy variation (ΔE) in the longitudinal direction of the pore. Then, transport of light gas molecules can be described as Knudsen diffusion and the molecular mass plays a key role in this case. Transports of N 2 , CH 4 or CO 2 , with larger molecular diameter and higher ΔE value, were proposed to compete with surface diffusion and their diffusivity should be controlled by the adsorption energy between gas molecule and pore wall. Therefore, the diffusion degree of gas molecules at low loading is decreased as follows: H 2 > He > N 2 > CH 4 > CO 2. When the gas molecule loading increases, the gas diffusion freedom will be limited due to the increased gas-gas and gas-porous media collisions. Thus, the diffusion of these gas molecules with higher concentration is dominated by the gas-gas and the gas-AFI interactions. DFT calculation results demonstrate that both gas-gas and the gas-AFI interaction energies depend on their van der Waals diameter. As a result, the diffusion of these gas molecules at higher loading in AlPO 4 -5 channel is decreased as: He > H 2 > N 2 > CH 4 > CO 2. Our results confirmed that the diffusivity of gas molecules within the 1-D channel of AlPO 4 -5 is controlled by the molecular mass or gas-wall interactions at low loading, while is dominated by the gas-gas/gas-wall interactions at high loading. [Display omitted] • DFT calculation results confirmed that AlPO 4 -5 unit cell with P 1 symmetry is much more stable than that with P 6 cc symmetry. • Transport of light gas molecules (H 2 and He) with small d m and low ΔE at low loading in AlPO 4 -5 channel can be described as Knudsen diffusion and the molecular mass plays a key role in this case. • Transports of N 2 , CH 4 and CO 2 , with larger molecular diameter and higher ΔE value, at low loading in AlPO 4 -5 channel were considered as surface diffusion and their diffusivity should be controlled by the gas-AFI interactions. • The diffusion of these gas molecules in AlPO 4 -5 channel with higher concentration is dominated by the gas-gas and the gas-AFI interactions. [ABSTRACT FROM AUTHOR]

• The inert tungsten carbides are activated by C-etching in the presence of Pt. • Pt–WC with C-defects shows efficient activity for cleavage of aryl ether C O bond. • The catalytic promotion is ascribed to the synergy effects of Pt species and C-defects. • Pt–WC displays a different reaction pathway compared with WC and Pt alone. • The synergy effects of other transition metals and C-defects are also manifested. Transition-metal carbides are attractive heterogeneous catalysts for the transformation of lignin-derived compounds. However, the effects of the surface carbon defect (C-defect) remain unclear due to coke deposition and exposed C terminations. Herein, we transform inert tungsten carbides (WC) into active catalysts via surficial C-etching using transition metals in the presence of H 2. An optimized 1% Pt–WC catalyst with synergy of Pt and C-defects can perform a 78.6% conversion in the selective hydrogenolysis of guaiacol to phenol with 89.0% selectivity at 300 °C, while the intact WC only gives a 7.1% guaiacol conversion with 51.0% phenol selectivity under the same conditions. As a result, the 1% Pt–WC catalyst exhibits 19-fold higher reaction rate and 12.6-fold higher turnover frequency than those of WC. Moreover, no substantial loss of catalytic performance has been observed with 1% Pt–WC for 50 h on stream. A rational reaction pathway is accordingly proposed through in-depth characterizations. [ABSTRACT FROM AUTHOR]

Most of multi-component high entropy alloys (HEAs) are only based on metal elements and rarely added with nonmetallic elements. In present paper, CoCrFeNiMn HEA added with 0.1 at.% N has been successfully synthesized by mechanical alloying (MA) followed by vacuum hot pressing sintering (VHPS). During the MA process, the alloying elements were gradually alloyed and formed as face-center (FCC) solid solutions. Subsequently, σ phases, Cr 2 N phases, FCC matrix phases with traces of Cr 23 C 6 carbides were observed after VHPS. In comparison with CoCrFeNiMn HEA produced by the same method, the Vickers hardness increased up to 468HV, while the yield stress, ultimate compressive strength increased by 203 MPa and 115 MPa respectively, accompanied by a small decrease in plasticity. This demonstrates that adding N element is a viable approach for properties enhancement of HEAs. [ABSTRACT FROM AUTHOR]

• LaCo 1- x Mn x O 3 perovskites with different substitutions of Co by Mn are prepared. • Substitution of Mn promotes Co 2 C formation and elevates Co 2 C/Co0 ratio. • TPR-MS and XPS are employed to quantitatively define the Co 2 C content. • The yield of alcohols can be attributed to the dual sites of Co0–Co 2 C. LaCo 1- x Mn x O 3 perovskites with different substitutions of Co by Mn were investigated as precursors of catalysts for the CO hydrogenation to produce higher alcohols. Characterization of LaCo 1- x Mn x O 3 perovskites revealed modifications in their structure with the incorporation of Mn into the perovskite lattice affected the structure of the catalysts by reduction prior the reaction. The presence of Mn facilitated the production of alcohols and suppressed the formation of undesirable products, i.e., methane and methanol. Quantitative analysis showed that the catalysts derived from Mn-containing perovskites favored the formation of Co 2 C under the reaction conditions. Thereby the enhanced alcohol selectivity could be explained by the increment of Co 2 C/Co0 ratio. The results demonstrate that the catalysts originated from LaCo 1- x Mn x O 3 perovskites are stable and effective for the synthesis of alcohols by CO hydrogenation. [ABSTRACT FROM AUTHOR]