Quantum critical point in SmO1−xFxFeAs and oxygen vacancy induced by high fluorine dopant

The local lattice and electronic structure of the high-T(c) superconductor SmO(1-x)F(x)FeAs as a function of F-doping have been investigated by Sm L(3)-edge X-ray absorption near-edge structure and multiple-scattering calculations. Experiments performed at the L(3)-edge show that the white line (WL) is very sensitive to F-doping. In the under-doped region (x ≤ 0.12) the WL intensity increases with doping and then it suddenly starts decreasing at x = 0.15. Meanwhile, the trend of the WL linewidth versus F-doping levels is just contrary to that of the intensity. The phenomenon is almost coincident with the quantum critical point occurring in SmO(1-x)F(x)FeAs at x ≃ 0.14. In the under-doped region the increase of the intensity is related to the localization of Sm-5d states, while theoretical calculations show that both the decreasing intensity and the consequent broadening of linewidth at high F-doping are associated with the content and distribution of oxygen vacancies

Strong metal oxide-support interaction in MoO₂/N-doped MCNTs heterostructure for boosting lithium storage performance

The low-rate capability and fast capacity decaying of the molybdenum dioxide anode material have been a bottleneck for lithium-ion batteries (LIBs) due to low carrier transport, drastic volume expansion and inferior reversibility. Furthermore, the lithium-storage mechanism is still controversial at present. Herein, we fabricate a new kind of MoO2 nanoparticles with nitrogen-doped multiwalled carbon nanotubes (MoO2/N-MCNTs) as anode for LIBs. The strong chemical bonding (MoOC) endows MoO2/N-MCNTs a strong metal oxide-support interaction (SMSI), rendering electron/ion transfer and facilitate significant Li+ intercalation pseudocapacitance, which is evidenced by both theoretical computation and detailed experiments. Thus, the MoO2/N-MCNTs exhibits high-rate performance (523.7 mAh/g at 3000 mA g-1) and long durability (507.8 mAh/g at 1000 mA g-1 after 500 cycles). Furthermore, pouch-type full cell composed of MoO2/N-MCNTs anodes and commercial LiNi0.6Co0.2Mn0.2O2 (NCM622) cathodes demonstrate impressive rate performance and cyclic life, which displays an unparalleled energy density of 553.0 Wh kg-1. Ex-situ X-ray absorption spectroscopy (XAS) indicates the enhanced lithium-storage mechanism is originated from a partially irreversible phase transition from Li0.98MoO2 to Li2MoO4 via delithiation. This work not only provides fresh insights into the enhanced lithium-storage mechanism but also proposes new design principles toward efficient LIBs.This work is partly supported by the National Natural Science Foundation of China (Grant No. 11705015, U1832147), Natural Science Foundation of the Jiangsu Higher Education Institutions (23KJA430001)

Activation of subnanometric Pt on Cu-modified CeO2 via redox-coupled atomic layer deposition for CO oxidation

Improving low-temperature activity and noble-metal efficiency remains a challenge for next generation exhaust catalysts. Here, the authors achieve the activation of subnanometric Pt on Cu-modified CeO2 for low-temperature CO oxidation with an onset below room temperature

Effects of Mn average oxidation state on the oxidation behaviors of As(III) and Cr(III) by vernadite

Vernadite is a poorly crystalline phyllomanganate that widely distributed in natural environments, and plays a pivotal role in the geochemical transformations of heavy metal and other pollutants. Though many works have done about the reaction mechanisms between vernadite-like minerals and As(III)/Cr(III), the effects of some basic structure characteristics of the mineral, such as Mn average oxidation state (AOS), on the oxidation of As (III)/Cr(III) are not fully understood. In this study, vernadite samples with different Mn AOSs but almost the same particle sizes (Ver and Ver20) were synthesized, characterized, and their reactivities towards As(III)/Cr(III) oxidation and As(V)/Cr(VI) adsorption were compared. It is found that Ver and Ver20 have almost the same point of zero charge (PZC), but ver20 has increased contents of layer Mn(III) at particle edges and interlayer Mn (III) and Mn(II), thus greatly reduced Mn AOS. Decrease in Mn AOS greatly reduces the oxidation capacity and initial reaction rate (K-obs) of this mineral towards As(III) on mineral-water interfaces. The apparent As(III) oxidation amount and K-obs by Ver are 202 +/- 8mmolkg(-1) and 0.3515 min(-1) while that by Ver20 are 162 +/- 7mmolkg(-1) and 0.0139 min(-1). The oxidation capacity and K-obs for Cr(III) by these vernadie samples are also decreased but in a less extent compared to that in As(III) oxidation, e.g. Cr(III) oxidized by Ver and Ver20 are 2895 +/- 47 and 1974 +/- 109 mmol kg(-1) and the K-obs are 0.0439 and 0.0169 min(-1) respectively. Adsorption density of As(V) or Cr(VI) on Ver20 is similar to 15-18% higher than that on Ver. These results suggest the more important role Mn AOS plays in As(III) oxidation than Cr(III) oxidation, and helps understand the geochemical behaviors of these toxic metals in natural environments mediated by Mn oxide minerals

Highly Selective Oxidation of Methane into Methanol over Cu-Promoted Monomeric Fe/ZSM-5

The selective oxidation of methane into methanol is of paramount importance but poses significant challenges in achieving high methanol productivity and selectivity, especially under mild reaction conditions. We show that a Cu-modified monomeric Fe/ZSM-5 catalyst is a highly efficient material for the direct conversion of methane into methanol in the liquid phase using H2O2 as an oxidant at low temperatures, which exhibits an excellent methanol productivity of 431 molMeOH·mol-1Fe·h-1 (with a methanol selectivity of μ80% over the Cu-Fe(2/0.1)/ZSM-5 catalyst). Combining the control experiments and comprehensive characterization results by among others, Mössbauer spectroscopy, and electron paramagnetic resonance as well as density functional theory calculations, we found that Cu species in the Cu-Fe(2/0.1)/ZSM-5 catalyst play a pivotal role in facilitating the formation of •OH radicals, which quickly react with •CH3 radicals to form CH3OH. These findings provide valuable insights into the rational design of metal-zeolite combinations for the selective oxidation of methane into methanol

A new type of noncovalent surface–π stacking interaction occurring on peroxide-modified titania nanosheets driven by vertical π-state polarization

Noncovalent π stacking of aromatic molecules is a universal form of noncovalent interactions normally occurring on planar structures (such as aromatic molecules and graphene) based on sp2-hybridized atoms. Here we reveal a new type of noncovalent surface–π stacking unusually occurring between aromatic groups and peroxide-modified titania (PMT) nanosheets, which can drive versatile aromatic adsorptions. We experimentally explore the underlying electronic-level origin by probing the perturbed changes of unoccupied Ti 3d states with near-edge X-ray absorption fine structures (NEXAFS), and find that aromatic groups can vertically attract π electrons in the surface peroxo-Ti states and increase their delocalization regions. Our discovery updates the concept of noncovalent π-stacking interactions by extending the substrates from carbon-based structures to a transition metal oxide, and presents an approach to exploit the surface chemistry of nanomaterials based on noncovalent interactions

Mechanisms of Synergistic Removal of Low Concentration As(V) by nZVI@Mg(OH)₂ Nanocomposite

In this work, by using Mg­(OH)₂ nanoplatelets as support material for nanoscale zerovalent iron (nZVI), nZVI@Mg­(OH)₂ composite was prepared and found to have super high adsorption ability toward As­(V) at environmentally relevant concentrations. It was revealed that the variation of corrosion products of nZVI in the presence of Mg­(OH)₂ and Mg²⁺ is an important factor for increase in the adsorption ability toward As­(V). X-ray diffraction (XRD) analysis indicated that the weakly basic condition induced by Mg­(OH)₂ decreases the lepidocrocite (γ-FeOOH) and increases the magnetite/maghemite (Fe₃O₄/γ-Fe₂O₃) content in the corrosion products of nZVI, and the latter has better adsorption affinity to As­(V). Moreover, extended X-ray absorption fine structure spectroscopy (EXAFS) indicated that the coordination between arsenic and iron minerals is influenced by dissolved Mg²⁺, leading to probable formation of magnesium ferrite (MgFe₂O₄) which has considerable adsorption affinity to As­(V). This work provides an important reference not only for the design of pollution control materials but also for understanding arsenic immobilization in natural environments with ubiquitous Mg²⁺ ion

One-pot synthesis of porous 1T-phase MoS2 integrated with single-atom Cu doping for enhancing electrocatalytic hydrogen evolution reaction

Molybdenum sulfide (MoS 2 ) has attracted great interest as a promising non-precious-metal catalyst candidate to replace the precious-metal Pt catalysts for the hydrogen evolution reaction (HER). Nevertheless, the catalytic efficiency of MoS 2 is significantly restricted by its density of catalytic active sites and inert basal plane. In this work, we have designed a facile one-pot solvothermal method to synthesize porous 1T-MoS 2 that is integrated with atomic doping of Cu atoms. The as-prepared Cu@MoS 2 sample exhibits enhanced HER performance with a low overpotential of 131 mV at the current density of 10 mA/cm 2 , a small Tafel slope of 51 mV/dec and as well as a good long-term stability. Enhanced HER performance can be ascribed to the synergistic effect of 1T-MoS 2 metallic phase, single atom Cu doping and numerous sulfur vacancies. Theoretical calculations indicates that the adsorption energy of Cu atom on 1T-MoS 2 surface (−3.68 eV) is much higher than that on 2H-MoS 2 surface (−1.94 eV), moreover, the Cu atom adsorbed on the surface of the 1T-MoS 2 has larger charge transfer (−0.38e), which can be contributed to further enhance HER performance of 1T-MoS 2

Highly Selective Oxidation of Methane into Methanol over Cu-Promoted Monomeric Fe/ZSM-5

The selective oxidation of methane into methanol is of paramount importance but poses significant challenges in achieving high methanol productivity and selectivity, especially under mild reaction conditions. We show that a Cu-modified monomeric Fe/ZSM-5 catalyst is a highly efficient material for the direct conversion of methane into methanol in the liquid phase using H2O2 as an oxidant at low temperatures, which exhibits an excellent methanol productivity of 431 molMeOH·mol-1Fe·h-1 (with a methanol selectivity of μ80% over the Cu-Fe(2/0.1)/ZSM-5 catalyst). Combining the control experiments and comprehensive characterization results by among others, Mössbauer spectroscopy, and electron paramagnetic resonance as well as density functional theory calculations, we found that Cu species in the Cu-Fe(2/0.1)/ZSM-5 catalyst play a pivotal role in facilitating the formation of •OH radicals, which quickly react with •CH3 radicals to form CH3OH. These findings provide valuable insights into the rational design of metal-zeolite combinations for the selective oxidation of methane into methanol