Flexomagnetic Effect Enhanced Ferromagnetism and Magnetoelectrochemistry in Freestanding High-Entropy Alloy Films.

Freestanding thin films of functional materials enable the tuning of properties via strain and strain gradients, broadening their applications. Here, a systematic approach is proposed to fabricate freestanding CrMnFeCoNi high-entropy alloy (HEA) thin films by pulsed laser deposition using expansion-contraction of NaCl substrates and weak van der Waals interaction of the interface, which form wrinkles with inhomogeneous strain gradients when transferred to a viscous handle. We demonstrate that the nonuniform gradients of external strain (flexomagnetic effect) can induce the partial structural phase transition from FCC to BCC in the wrinkled HEA film, resulting in a 10-fold increase in its room-temperature saturation magnetization compared with the unstrained flat HEA film. Furthermore, after applying an external magnetic field, due to the different electron transfer behavior caused by the electron scattering in wrinkled and flat HEA films, their electrocatalytic magnetic responses showed a diametrically opposite picture. Our work provides a promising strategy for tuning physical and chemical properties via complex strained geometries.

Giant barocaloric effects with a wide refrigeration temperature range in ethylene vinyl acetate copolymers.

Solid-state cooling technology based on the caloric effects of phase-transition materials has been a research hotspot due to its environmental friendliness and high efficiency, but limited for practical applications due to its narrow working temperature region. Here, we report giant barocaloric effects based on pressure-driven liquid-solid phase transitions in elastic copolymers of ethylene and vinyl acetate. Giant adiabatic temperature changes of up to 29.6/-26.9 K are directly observed under rapid compressions/decompressions of 400 MPa near the liquid-solid phase transition points. Strikingly, since both the solid and the liquid sides can show giant barocaloric effects, a very broad refrigeration temperature region of more than 110 K is achieved in these copolymers. Furthermore, a cooling prototype is designed to demonstrate the potential applications of these liquid/elastic barocaloric materials. Our study sheds light on exploring liquid-solid phase transition materials for the next-generation refrigerators.

Strain Control of Phase Transition and Exchange Bias in Flexible Heusler Alloy Thin Films.

The practical applications for the distinctive functions of metamagnetic Heusler alloys, such as magnetic shape memory effect, various caloric effects, etc., strongly depend on the phase transition temperatures. Here, flexible Heusler alloy Ni-Mn-Sn films have been deposited on mica substrates by pulsed laser deposition with a Ti buffer layer. Clear ferromagnetic (FM) transition followed by the martensitic transformation at around room temperature and exchange bias (EB) with a blocking temperature of 70 K are observed. Under the application of both tensile and compressive strains by bending the mica substrates, all the characteristic temperatures of Ni-Mn-Sn films, including the FM transition temperature, martensitic transformation temperature, and blocking temperature of EB, are significantly increased by about 10 K. Furthermore, EB field and coercivity are both strongly strengthened, which is mainly caused by the simultaneous enhancement of FM and anti-FM Mn-Mn coupling because of their shortened separations by strain and verified by the Monte Carlo simulation results. The strain controlling for structural and magnetic properties provides efficient manipulation for Heusler alloy-based magnetic devices.

Electrocatalytically inactive copper improves the water adsorption/dissociation on Ni3S2 for accelerated alkaline and neutral hydrogen evolution.

Nickel dichalcogenides, especially Ni3S2, present inferior alkaline and neutral hydrogen evolution activity due to their sluggish water dissociation kinetics. Although these materials hold promise as non-noble metal-based electrocatalysts for the hydrogen evolution reaction (HER) in acidic media, developing efficient strategies to enhance the water dissociation processes of nickel dichalcogenides in alkaline and neutral solutions is also an important area of research. The present work discloses an electrocatalytically inactive copper doping strategy to promote the water adsorption and dissociation process of Ni3S2 (Cu-Ni3S2) nanoparticles supported on nickel foam (NF) towards improving the alkaline and neutral hydrogen evolution reactions. Based on combined density functional theory calculations and electrochemical characterizations, the doping of Cu can accelerate the Volmer step and therefore strengthen the water adsorption/dissociation on the respective Ni sites and S sites during the HER process. As a result, the electrocatalyst exhibits superior and stable HER performance in both 1 M KOH and 1 M phosphate-buffered saline (PBS) solutions, with much lower overpotentials of 121 and 228 mV at a current density of 10 mA cm-2, respectively, in comparison to bare Ni3S2. We therefore conclude that the tailored control of the water adsorption/dissociation capability of Ni3S2 will open significant opportunities for the rational design of alkaline and neutral electrocatalysts from earth-abundant and stable materials.

Nanocomposites consisting of nanoporous platinum-silicon and graphene for electrochemical determination of bisphenol A.

Three-dimensional nanoporous PtSi (NP-PtSi) alloy was prepared by dealloying ternary PtSiAl alloy ribbons. By combining the nanoporous morphology of PtSi and graphene (GR), a new composite material was developed, which was used to modify the surface of a glassy carbon electrode (GCE). The resulting modified electrodes showed an excellent electrocatalytic activity towards the electro oxidation of bisphenol A. Based on differential pulse voltammetry measurements, NP-PtSi/GR/GCE showed linear response over the concentration range 0.30 to 85 µM bisphenol A, while the detection limit was found to be 0.11 µM (S/N = 3). NP-PtSi/GR/GCE showed also satisfactory stability and selectivity over various compounds present in real samples, and they were successfully applied to the determination of bisphenol A in inoculated milk samples. Graphical abstract Nanoporous PtSi (NP-PtSi) was fabricated by dealloying PtSiAl alloy ribbons. Based on the NP-PtSi alloy and graphene (GR) composites that modified glassy carbon electrode (GCE), a sensitive and stable electrochemical sensor was developed for the determination of bisphenol A by differential pulse voltammetric (DPV) method.

Electrochemical determination of dopamine using a glassy carbon electrode modified with a nanocomposite consisting of nanoporous platinum-yttrium and graphene.

A nanoporous platinum-yttrium alloy (NP-PtY) was fabricated by dealloying ribbons of a PtYAl alloy. Owing to the high porosity and the synergistic effect of Y in the Pt backbone, the NP-PtY exhibits superior structural stability, reproducibility and electrocatalytic activity. An electrochemical sensor was developed for the highly sensitive and selective detection of dopamine (DA) based on the use of a glassy carbon electrode modified with NP-PtY alloy and graphene. The sensor, best operated at 0.16 V vs. SCE, has a linear range covering the 0.9 to 82 µM concentration range, a 0.36 µM detection limit (at S/N = 3), and good selectivity over tyramine, tryptamine, phenethylamine, uric acid, and ascorbic acid. It gave satisfactory results in the determination of DA in spiked samples of urine. Graphical abstract Nanoporous platinum-yttrium alloy (NP-PtY) was fabricated by means of a one-step dealloying process. A glassy carbon electrode modified with the NP-PtY and graphene nanocomposite exhibits a wide linear range and a low detection limit towards dopamine. The sensor has remarkable reproducibility, stability and selectivity.

Facile Synthesis of Nanoporous Pt-Y alloy with Enhanced Electrocatalytic Activity and Durability.

Recently, Pt-Y alloy has displayed an excellent electrocatalytic activity for oxygen reduction reaction (ORR), and is regarded as a promising cathode catalyst for fuel cells. However, the bulk production of nanoscaled Pt-Y alloy with outstanding catalytic performance remains a great challenge. Here, we address the challenge through a simple dealloying method to synthesize nanoporous Pt-Y alloy (NP-PtY) with a typical ligament size of ~5 nm. By combining the intrinsic superior electrocatalytic activity of Pt-Y alloy with the special nanoporous structure, the NP-PtY bimetallic catalyst presents higher activity for ORR and ethanol oxidation reaction, and better electrocatalytic stability than the commercial Pt/C catalyst and nanoporous Pt alloy. The as-made NP-PtY holds great application potential as a promising electrocatalyst in proton exchange membrane fuel cells due to the advantages of facile preparation and excellent catalytic performance.

Phosphorus-doped helical carbon nanofibers as enhanced sensing platform for electrochemical detection of carbendazim.

A combined chemical vapor deposition with high-pressure annealing has been developed for the production of phosphorus-doped helical carbon nanofibers (P-HCNFs). The resulting P-HCNFs have a large specific surface area, well-defined three-dimensional hierarchical helical structure and rapid apparent heterogeneous electron transfer. Based on the high electrocatalytic activity, the P-HCNFs were used to develop an amperometric sensor for carbendazim detection. The experimental results demonstrated that the sensor is promising for the determination of carbendazim in food samples due to the high sensitivity, wide linear range and low detection limit.

Particle Size Effect on Charge Ordering and Magnetocaloric Effect in Nanosized Nd0.5Sr0.5MnO3.

Nd0.5Sr0.5MnO3 nanoparticles with average sizes of 32-1000 nm in diameter were prepared by sol-gel method. The synthesized nanoparticles were characterized using X-ray diffraction, high- resolution transmission microscopy, scanning electron microscopy, and vibrating sample magnetometer. All samples have the single-phase orthorhombic structure, and the grain size increases with the increase in annealing temperature. A charge ordering (CO) transition at T(CO) and a ferromagnetic-paramagnetic transition at Tc were observed in 1000 nm nanoparticles. With the decrease in particle size, CO transition gradually shifts to lower temperature, becomes increasingly weak, and disappears for 85 nm nanoparticles. An inverse magnetocaloric effect with positive magnetic entropy change was observed around T(CO), and it decreases with the decrease in size due to the suppression of CO phase. The observed negative magnetic entropy change at Tc shows a surprising nonmonotonic behavior with the variation of particles size. All these results may give rise to a new insight into the magnetothermal behaviors in nanosized CO perovskite manganites.

Magnetoelectricity coupled exchange bias in BaMnF4.

Multiferroic BaMnF4 powder was prepared by hydrothermal method. Hysteretic field dependent magnetization curve at 5 K confirms the weak ferromagnetism aroused from the canted antiferromagnetic spins by magnetoelectric coupling. The blocking temperature of 65 K for exchange bias coincides well with the peak at 65 K in the zero-field cooled temperature-dependent magnetization curve, which has been assigned to the onset temperature of two-dimensional antiferromagnetism. An upturn kink of exchange field and coercivity with decreasing temperature was observed from 40 K to 20 K, which is consistent with the two-dimensional to three-dimensional antiferromagnetic transition at Néel temperature (~26 K). In contrast to the conventional mechanism of magnetization pinned by interfacial exchange coupling in multiphases, the exchange bias in BaMnF4 is argued to be a bulk effect in single phase, due to the magnetization pinned by the polarization through magnetoelectric coupling.

Expanded organic building units for the construction of highly porous metal-organic frameworks.

Two new organic building units that contain dicarboxylate sites for their self-assembly with paddlewheel [Cu2(CO2)4] units have been successfully developed to construct two isoreticular porous metal-organic frameworks (MOFs), ZJU-35 and ZJU-36, which have the same tbo topologies (Reticular Chemistry Structure Resource (RCSR) symbol) as HKUST-1. Because the organic linkers in ZJU-35 and ZJU-36 are systematically enlarged, the pores in these two new porous MOFs vary from 10.8 Šin HKUST-1 to 14.4 Šin ZJU-35 and 16.5 Šin ZJU-36, thus leading to their higher porosities with Brunauer-Emmett-Teller (BET) surface areas of 2899 and 4014 m(2) g(-1) for ZJU-35 and ZJU-36, respectively. High-pressure gas-sorption isotherms indicate that both ZJU-35 and ZJU-36 can take up large amounts of CH4 and CO2, and are among the few porous MOFs with the highest volumetric storage of CH4 under 60 bar and CO2 under 30 bar at room temperature. Their potential for high-pressure swing adsorption (PSA) hydrogen purification was also preliminarily examined and compared with several reported MOFs, thus indicating the potential of ZJU-35 and ZJU-36 for this important application. Studies show that most of the highly porous MOFs that can volumetrically take up the greatest amount of CH4 under 60 bar and CO2 under 30 bar at room temperature are those self-assembled from organic tetra- and hexacarboxylates that contain m-benzenedicarboxylate units with the [Cu2(CO2)4] units, because this series of MOFs can have balanced porosities, suitable pores, and framework densities to optimize their volumetric gas storage. The realization of the two new organic building units for their construction of highly porous MOFs through their self-assembly with [Cu2(CO2)4] units has provided great promise for the exploration of a large number of new tetra- and hexacarboxylate organic linkers based on these new organic building units in which different aromatic backbones can be readily incorporated into the frameworks to tune their porosities, pore structures, and framework densities, thus targeting some even better performing MOFs for very high gas storage and efficient gas separation under high pressure and at room temperature in the near future.

Helical carbon nanotubes: intrinsic peroxidase catalytic activity and its application for biocatalysis and biosensing.

A combined hydrothermal/hydrogen reduction method has been developed for the mass production of helical carbon nanotubes (HCNTs) by the pyrolysis of acetylene at 475 °C in the presence of Fe(3)O(4) nanoparticles. The synthesized HCNTs have been characterized by high-resolution transmission electron microscopy, scanning electron microscopy, X-ray diffraction analysis, vibrating sample magnetometry, and contact-angle measurements. The as-prepared helical-structured carbon nanotubes have a large specific surface area and high peroxidase-like activity. Catalysis was found to follow Michaelis-Menten kinetics and the HCNTs showed strong affinity for both H(2)O(2) and 3,3',5,5',-tetramethylbenzidine (TMB). Based on the high activity, the HCNTs were firstly used to develop a biocatalyst and amperometric sensor. At pH 7.0, the constructed amperometric sensor showed a linear range for the detection of H(2)O(2) from 0.5 to 115 µM with a correlation coefficient of 0.999 without the need for an electron-transfer mediator. Because of their low cost and high stability, these novel metallic HCNTs represent a promising candidate as mimetic enzymes and may find a wide range of new applications, such as in biocatalysis, immunoassay, and environmental monitoring.