Browsing by Author "Liu, C"
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- ItemControlled one‐pot synthesis of nickel single atoms embedded in carbon nanotube and graphene supports with high loading(Wiley, 2020-04-09) Zhao, S; Wang, T; Zhou, G; Zhang, L; Lin, C; Veder, JP; Johannessen, B; Saunders, M; Yin, L; Liu, C; De Marco, R; Yang, SZ; Zhang, Q; Jiang, SPSingle‐atom catalysts (SACs) have attracted much attentions due to the advantages of high catalysis efficiency and selectivity. However, the controllable and efficient synthesis of SACs remains a significant challenge. Herein, we report a controlled one‐pot synthesis of nickel single atoms embedded on nitrogen‐doped carbon nanotubes (NiSA−N−CNT) and nitrogen‐doped graphene (NiSA−N−G). The formation of NiSA−N−CNT is due to the solid‐to‐solid rolling up mechanism during the high temperature pyrolysis at 800 °C from the stacked and layered Ni‐doped g‐C3N4, g‐C3N4−Ni structure to a tubular CNT structure. Addition of citric acid introduces an amorphous carbon source on the layered g‐C3N4−Ni and after annealing at the same temperature of 800 °C, instead of formation of NiSA−N−CNT, Ni single atoms embedded in planar graphene type supports, NiSA−N−G were obtained. The density functional theory (DFT) calculation indicates the introduction of amorphous carbon source substantially reduces the structure fluctuation or curvature of layered g‐C3N4‐Ni intermediate products, thus interrupting the solid‐to‐solid rolling process and leading to the formation of planar graphene type supports for Ni single atoms. The as‐synthesized NiSA−N−G with Ni atomic loading of ∼6 wt% catalysts shows a better activity and stability for the CO2 reduction reaction (CO2RR) than NiSA−N−CNT with Ni atomic loading of ∼15 wt% due to the open and exposed Ni single atom active sites in NiSA−N−G. This study demonstrates for the first time the feasibility in the control of the microstructure of carbon supports in the synthesis of SACs. © 1999-2024 John Wiley & Sons, Inc or related companies. All rights reserved.
- ItemEffect of silicon on the distribution and speciation of uranium in sunflower (Helianthus annuus)(Elsevier, 2024-10) Wang, LL; Laing, Y; Liu, S; Chen, F; Wang, JG; Chen, YL; Paterson, DJ; Kopittke, PM; Wang, YH; Liu, C; Ye, YSunflower (Helianthus annuus) can potentially be used for uranium (U) phytoremediation. However, the factors influencing the absorption of U and its subsequent distribution within plant tissues remain unclear, including the effect of silicon (Si) which is known to increase metal tolerance. Here, using hydroponics, the effect of Si on the distribution and speciation of U in sunflower was examined using synchrotron-based X–ray fluorescence and fluorescence-X-ray absorption near-edge spectroscopy. It was found that ∼88 % of U accumulates within the root regardless of treatments. Without the addition of Si, most of the U appeared to bind to epidermis within the roots, whereas in the leaves, U primarily accumulated in the veins. The addition of Si alleviated U phytotoxicity and decreased U concentration in sunflower by an average of 60 %. In the roots, Si enhanced U distribution in cell walls and impeded its entry into cells, likely due to increased callose deposition. In the leaves, Si induced the sequestration of U in trichomes. However, Si did not alter U speciation and U remained in the hexavalent form. These results provide information on U accumulation and distribution within sunflower, and suggest that Si could enhance plant growth under high U stress. © 2024 Elsevier B.V.
- ItemIncreased phase coherence length in a porous topological insulator(American Physical Society (APS), 2023-06-15) Nguyen, A; Akhgar, G; Cortie, DL; Bake, A; Pastuovic, Z; Zhao, W; Liu, C; Chen, YH; Suzuki, K; Fuhrer, MS; Culcer, D; Hamilton, AR; Edmonds, MT; Karel, JThe surface area of Bi2Te3 thin films was increased by introducing nanoscale porosity. Temperature dependent resistivity and magnetotransport measurements were conducted both on as-grown and porous samples (23 and 70 nm). The longitudinal resistivity of the porous samples became more metallic, indicating the increased surface area resulted in transport that was more surfacelike. Weak antilocalization was present in all samples, and remarkably the phase coherence length doubled in the porous samples. This increase is likely due to the large Fermi velocity of the Dirac surface states. Our results show that the introduction of nanoporosity does not destroy the topological surface states but rather enhances them, making these nanostructured materials promising for low energy electronics, spintronics and thermoelectrics. ©2023 American Physical Society
- ItemPreferred spin excitations in the bilayer iron-based superconductor CaKðFe0.96Ni0.04Þ4As4 with spin-vortex crystal order(American Physical Society, 2022-03-31) Liu, C; Bourges, P; Sidis, Y; He, GH; Bourdarot, F; Danilkin, SA; Ghosh, H; Ghosh, S; Ma, XY; Li, SL; Li, Y; Luo, HQ; Xie, TSpin-orbit coupling (SOC) is a key to understand the magnetically driven superconductivity in iron-based superconductors, where both local and itinerant electrons are present and the orbital angular momentum is not completely quenched. Here, we report a neutron scattering study on the bilayer compound CaK(Fe0.96Ni0.04)4As4 with superconductivity coexisting with a noncollinear spin-vortex crystal magnetic order that preserves the tetragonal symmetry of the Fe-Fe plane. In the superconducting state, two spin resonance modes with odd and even L symmetries due to the bilayer coupling are found similar to the undoped compound CaKFe4As4 but at lower energies. Polarization analysis reveals that the odd mode is c-axis polarized, and the low-energy spin anisotropy can persist to the paramagnetic phase at high temperature, which closely resembles other systems with in-plane collinear and c-axis biaxial magnetic orders. These results provide the missing piece of the puzzle on the SOC effect in iron-pnictide superconductors, and also establish a common picture of c-axis preferred magnetic excitations below Tc regardless of the details of magnetic pattern or lattice symmetry. © 2022 American Physical Society
- ItemTransport measurements in porous Bi2Te3 thin films(American Physical Society, 2022-03-16) Akhgar, G; Nguyen, A; Cortie, DL; Bake, A; Zhao, WY; Liu, C; Fuhrer, MS; Culcer, D; Hamilton, AR; Edmonds, MT; Karel, JRecent theoretical work has predicted the existence of disordered topological insulators , however, minimal experimental work has been conducted on disordered TIs. Here we used molecular-beam epitaxy (MBE) to grow Bi2Te3 thin films that were comprised of nanocrystals embedded in an amorphous matrix. Further disorder was introduced through Ne ion irradiation which produced porosity in the films. In this talk we will present magnetoresistance measurements on porous Bi2Te3, where weak anti-localisation (WAL) was observed. The magnetoresistance curves were fitted using a Dirac Fermion model specifically derived to model weak antilocalization in TIs. Our results also show that the temperature dependence of the phase coherence length in porous Bi2Te3, with an increased surface to volume ratio, exhibits 2D-like transport.
- ItemUnsaturated edge-anchored Ni single atoms on porous microwave exfoliated graphene oxide for electrochemical CO2(Elsevier, 2019-04) Cheng, Y; Zhao, S; Li, H; He, S; Veder, JP; Johannessen, B; Xiao, J; Lu, S; Pan, J; Chisholm, MF; Yang, SZ; Liu, C; Chen, JG; Jiang, SPSupported single atom catalysts (SACs), emerging as a new class of catalytic materials, have been attracting increasing interests. Here we developed a Ni SAC on microwave exfoliated graphene oxide (Ni-N-MEGO) to achieve single atom loading of ∼6.9 wt%, significantly higher than previously reported SACs. The atomically dispersed Ni atoms, stabilized by coordination with nitrogen, were found to be predominantly anchored along the edges of nanopores (< 6 nm) using a combination of X-ray absorption spectroscopy (XAS) and aberration-corrected scanning transmission electron microscopy (AC-STEM). The Ni-N-MEGO exhibits an onset overpotential of 0.18 V, and a current density of 53.6 mA mg−1 at overpotential of 0.59 V for CO2 reduction reaction (CO2RR), representing one of the best non-precious metal SACs reported so far in the literature. Density functional theory (DFT) calculations suggest that the electrochemical CO2-to-CO conversion occurs more readily on the edge-anchored unsaturated nitrogen coordinated Ni single atoms that lead to enhanced activity toward CO2RR. © 2018 Elsevier B.V. All rights reserved.