Mechanism and kinetics of hydrothermal replacement of magnetite by hematite

The replacement of magnetite by hematite was studied through a series of experiments under mild hydrothermal conditions(140 -220℃, vapour saturated pressures) to quantify the kinetics of the transformation and the relative effects of redox and non-redox processes on the transformation. The results indicate that oxygen is not an essential factor in the replacement reaction of magnetite by hematite, but the addition of excess oxidant does trigger the oxidation reaction, and increases the kinetics of the transformation. However, even under high O_2(aq) environments, some of the replacement still occurred via Fe^(2+) leaching from magnetite. The kinetics of the replacement reaction depends upon temperature and solution parameters such as pH and the concentrations of ligands, all of which are factors that control the solubility of magnetite and affect the transport of Fe^(2+) (and the oxidant) to and from the reaction front. Reaction rates are fast at ~200℃, and in nature transport properties of Fe and,in the case of the redox-controlled replacement, the oxidant will be the rate-limiting control on the reaction progress. Using an Avrami treatment of the kinetic data and the Arrhenius equation, the activation energy for the transformation under non-redox conditions was calculated to be 26 ± 6 kJ mol^(-1).This value is in agreement with the reported activation energy for the dissolution of magnetite, which is the rate-limiting process for the transformation under non-redox conditions.

Morphology-dependent structures and catalytic performances of Au nanostructures on Cu_2O nanocrystals synthesized by galvanic replacement reaction

Au nanostructures were prepared on uniform Cu2O octahedra and rhombic dodecahedra via the galvanic replacement reaction between HAuCl 4 and Cu2O. The compositions and structures were studied by Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), High-Resolution Transmission Electron Microscope (HRTEM), X-Ray Diffraction (XRD), X-Ray Absorption Spectroscopy (XAS), X-ray Photoelectron Spectroscopy (XPS) and in-situ DRIFTS spectroscopy of CO adsorption. Different from the formation of Au-Cu alloys on Cu2O cubes by the galvanic replacement reaction (ChemNanoMat 2 (2016) 861-865), metallic Au particles and positively-charged Au clusters form on Cu2O octahedra and rhombic dodecahedra at very small Au loadings and only metallic Au particles form at large Au loadings. Metallic Au particles on Cu2O octahedra and rhombic dodecahedra are more active in catalyzing the liquid phase aerobic oxidation reaction of benzyl alcohol than positively-charged Au clusters. These results demonstrate an obvious morphology effect of Cu2O nanocrystals on the liquid-solid interfacial reactions and prove oxide morphology as an effective strategy to tune the surface reactivity and catalytic performance. (C) 2016 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights reserved.

Transformation of Undesired Li_(2)CO_(3)into Lithiophilic Layer Via Double Replacement Reaction for Garnet Electrolyte Engineering

Garnet-type solid-state electrolytes(SSEs)are a remarkable Li-ion electrolyte for the realization of next-generation all-solid-state lithium batteries due to their excellent stability against Li metal as well as high ionic conductivities at room temperature.However,garnet electrolytes always contain undesired and hardly removable Li_(2)CO_(3) contaminations that have persistently large resistance and unstable interface contact with Li metal.This is a critical bottleneck for the practical application of garnet electrolytes.Here,we design a novel strategy to completely root out Li_(2)CO_(3) both inside and on the surface of garnet.This is achieved by a so-called double replacement reaction between Li_(2)CO_(3) and SiO_(2) during one-step hot press process for garnet electrolyte densification.It leads to in-situ transformation of LixSiOy(LSO)mostly locating around the grain boundaries of garnet.Due to the higher ion conductivity and better electrochemistry stability of LSO than Li_(2)CO_(3),the modified garnet electrolyte shows much improved electrochemical performance.Moreover,the wettability between modified garnet electrolyte and lithium metals was significantly enhanced in the absence of surface Li_(2)CO_(3).As a proof of concept,an assembled Li symmetric cell with modified garnet electrolyte displays a high critical current density(CCD)of 0.7 mA cm^(-2)and a low interfacial impedance(5Ωcm^(2))at 25℃.These results indicate that the upcycling of Li_(2)CO_(3)is a promising strategy to well-address the degradation and interfacial issue associated with garnet electrolytes.

Self-supporting and dual-active 3D Co-S nanosheets constructed by ligand replacement reaction from MOF for rechargeable Al battery

Metal sulfides with high theoretical capacities are expected as promising cathode materials of Al batteries(AIBs). However, powdery active materials are mainly synthesized and loaded on current collector by insulating binder without capacity. Meanwhile, S as inert element in metal sulfides can not usually provide capacity. So, powdery metal sulfides only exhibit limiting practical capacity and poor cycling stability due to weak conductivity and low mass utilization. Herein, the novel self-supporting and dual-active Co-S nanosheets on carbon cloth (i.e. Co-S/CC) with hierarchically porous structure are constructed as cathode of AIBs. Co-S nanosheets are derived from ZIF-67 nanosheets on CC by a facile ligand replacement reaction. As a result, the binder-free Co-S/CC cathode with good conductivity delivers excellent initial discharge capacity of 383.4 m Ah g^(-1)(0.211 m Ah cm^(-2)) at current density of 200 m A g^(-1)and maintain reversible capacity of 156.9 m Ah g^(-1)(0.086 m Ah cm^(-2)) with Coulombic efficiency of 95.8% after 500 cycles,which are much higher than those of the traditional slurry-coating cathodes. Both Co and S as active elements in Co-S/CC contribute to capacity, which leads to a high mass utilization. This work provides a significant strategy for the construction of self-supporting metallic cathode for advanced high-energy density Al battery.

Pt-Te alloy nanowires towards formic acid electrooxidation reaction

The high-performance anodic electrocatalysts is pivotal for realizing the commercial application of the direct formic acid fuel cells.In this work,a simple polyethyleneimine-assisted galvanic replacement reaction is applied to synthesize the high-quality PtTe alloy nanowires(PtTe NW)by using Te NW as an efficient sacrificial template.The existence of Te atoms separates the continuous Pt atoms,triggering a direct reaction pathway of formic acid electrooxidation reaction(FAEOR)at PtTe NW.The one-dimensional architecture and highly active sites have enabled PtTe NW to reveal outstanding electrocatalytic activity towards FAEOR with the mass/specific activities of 1091.25 mA mg^(-1)/45.34 A m^(-2)at 0.643 V potential,which are 44.72/23.16 and 20.26/11.75 times bigger than those of the commercial Pt and Pd nanoparticles,respectively.Density functional theory calculations reveal that Te atoms optimize the electronic structure of Pt atoms,which decreases the adsorption capacity of CO intermediate and simultaneously improves the durability of PtTe NW towards FAEOR.This work provides the valuable insights into the synthesis and design of efficient Pt-based alloy FAEOR electrocatalysts.

Deep eutectic solvent-induced synthesis of Ni-Fe catalyst with excellent mass activity and stability for water oxidation

Ni-Fe bimetallic electrodes are currently recognized as a kind of benchmark transition metal-based oxygen evolution reaction(OER)electrocatalysts.Facile synthesis of Ni-Fe bimetallic electrode materials with excellent catalytic activity and satisfied stability by a simple and low-cost route is still a big challenge.Herein,well-defined Ni-Fe nanoparticles in-situ developed on a planar Fe substrate(Ni-Fe NPs/Fe)is fabricated via a facile one-step galvanic replacement reaction(GRR)carried out in an Ethaline-based deep eutectic solvent(DES).The prepared Ni-Fe NPs/Fe exhibits outstanding OER performance,which needs an overpotential of only 319 mV to drive a current density of 10 mA cm^(-2),with a small Tafel slope of 41.2 mV dec^(-1) in 1.0 mol L^(-1) KOH,high mass activity(up to 319.78 A g^(-1) at an overpotential of 300 mV)and robust durability for 200 h.Impressively,the Ni-Fe bimetallic oxygen-evolution electrode obtained from the Ethaline-based DES is catalytically more active and durable than that of its counterpart derived from the 4.2 mol L^(-1) NaCl aqueous solution.The reason for this is mainly related to the different morphology and surface state of the Ni-Fe catalysts obtained from these different solvent environments,particularly for the differences in phy-chemical properties,active species formed and deposition kinetics,offered by the Ethaline-based DES.

A novel PdNi/Al_2O_3 catalyst prepared by galvanic deposition for low temperature methane combustion

Galvanic deposition method was used to prepare the Pd/Ni-Al2O3-GD catalyst for the combustion of methane under lean conditions. The new catalyst and compared catalysts （Pd/Al2O3-IW, Pd-Ni/Al2O3-IW, Pd/Ni-Al2O3-IW） prepared by incipient wetness impregnation were characterized by N2-physisorption, XRD and TEM to clarify particle size and size distribution of palladium species. Combined O2-TPD and XPS results with the catalytic data, it shows that the surface palladium species with low valence exhibits better combustion performance due to their stronger interaction with support. The results indicate that the galvanic deposition method is an effective route to prepare efficient catalyst for methane combustion, and it also provides useful information for improving the present commercial catalyst.

Preparation of a Pt-Ni_(2)P/NF catalyst for highly efficient hydrogen evolution using a magnetic field to promote Ni-Pt galvanic replacement

The noble metal Pt is an ideal catalyst for promoting the hydrogen evolution reaction(HER)during the electrolysis of water.However,Pt is also expensive and suffers from low utilization rates.In this work,a Pt-Ni_(2)P/NF nanorod catalyst with a low Pt loading was synthesized under different magnetic fields,and it was found that the application of a magnetic field can increase the rate of the galvanic replacement reaction.When the magnetic field strength increases from 0 to 600 mT,the chemical reaction rate increases gradually,and the utilization rate of Pt increased by 2.3 times under 600 mT.The mechanism of the magnetic field-induced magnetohydrodynamic(MHD)effect on the galvanic replacement reaction was revealed.In a 1 M KOH solution and at a current density of 10 mA cm^(-2),the overpotential of Pt-Ni_(2)P/NF prepared by applying a 600 mT magnetic field was as low as 15 mV and the Tafel slope was 37 mV dec^(-1),compared with values of 82 mV and 70 mV dec^(-1) for a specimen prepared without a magnetic field.Additionally,at an overpotential of 90 mV,the mass-based Pt activity of the former material was 12 times greater while its turnover frequency was 19 times greater.This work provides theoretical and technical knowledge expected to assist in the controllable preparation of materials in magnetic fields and the efficient utilization of metallic resources.

Nanostage Alloying of Metals in Liquid Phase

Alloying of metals is known from antiquity. Alloy making i.e., homogenizing metals started in a “hit-or-miss” way. The 1st alloy from copper (Cu) and tin (Sn) was produced around 2500 BC and from then Bronze Age began. Subsequently iron (Fe) age started after the Bronze Age. Aluminium (Al) alloying was discovered much later because pure Al could not be recovered easily even though Al is the most abundant metal in the earth’s crust. Refining of Al is a very difficult job because of its strong affinity towards oxygen. To ease alloying, melting points (mp) of the individual constituents and reactivity of metal towards oxygen were the hurdles. Now understanding the thermodynamics of metal mixing has paved alloying. Periodic properties of elements concerning size, electronegativity, crystal structure, valency, lattice spacing, etc. are considered for alloying. In this feature article, more emphasis is given to Hume-Rothery rules in which the necessary parameters for alloying have been illustrated. Importantly standard electrode potential (E0) values, eutectic, phase diagram, size-related strain in metals, etc. have been looked into in the present discussion. One elegant example is Sn-Pb alloy, known as soft solder. Soft solder was in use for many years to connect metals and in electric circuitry. Low melting, flowability, and conductivity of soft solder had placed Sn-Pb alloy a unique position in industries, laboratories and even in cottage industries. However, toxic Pb volatilizes during soldering and hence soft solder is banned almost in all countries. We felt the need for a viable alternative to obtain soldering material and then silver (Ag) based highly conducting, an eco-friendly alloy of Sn resulted in from a high boiling liquid. The discovery engenders not only a new conducting soldering alloy but also a new concept of melting metals together. Furthermore, new ideas of alloying have been generalized at their nanostages from a suitable high boiling solvent.

Mechanism of Suppressing ASR Using Ground Reactive Sandstone Powders instead of Cement

In order to understand the effect of powders ground from reactive sandstone replacing cement on reducing or suppressing alkali-silica reaction（ASR）, and to identify the mechanism of suppressing ASR by this powders, mortar and paste containing reactive sandstone powders of four replacement levels ranging from 10wt% to 40wt% and four specific surfaces areas ranging from 210 m^2/kg to 860 m^2/kg were studied. The experimental results showed that incorporation of 40wt% reactive sandstone powders could suppress ASR effectively except for mortar containing reactive sandstone powders with specific surface area of 610 m^2/kg, which disagreed with the most results reported that the higher reactive powder specific surface area, the smaller ASR expansion. By means of fl ame photometry, Fourier transform infrared spectroscopy（FT-IR） and thermo gravimetric analysis（TG）, the mechanism of reactive sandstone powders on reducing or suppressing ASR was soluble alkalis type of reactive sandstone powders and the competition of liberating and bonding alkali of cement paste containing reactive sandstone powders,when the ability of alkali bonding was greater than the ability of alkali liberation, ASR caused by reactive sandstone was supressed effectively.

Investigation on Molecular Non-covalent Interaction in the Sodium Dodecyl Benzene Sulfonate-polychrome Blue B-protein Replacement Reaction

The molecular non-covalent interaction often originates from the electrostatic attraction and accords with the Langmuir isothermal adsorption. The sodium dodecyl benzene sulfonate (SDBS)-polychrome blue B (PCB)-protein [bovine serum albumin (BSA), ovalbumin (OVA) and myoglobin (MB)] ternary reaction has been investigated at pH 3.88. Protein to replace PCB from the PCB-SDBS binding product was used to characterize the assembly of an invisible-spectral compound, SDBS, on proteins by measuring the variation of PCB light-absorption by the microsurface adsorption-spectral correction (MSASQ technique. The effect of ionic strength and temperature on the aggregation was studied. Results showed that the aggregates SDBS(92)(.)BSA, SDBS(58)(.)OVA and (SDBS15MB)-M-. at 30 degreesC and SDBS(83)(.)BSA, SDBS(39)(.)OVA and (SDBS10MB)-M-. at 50 degreesC are formed.

Galvanic replacement reaction for in situ fabrication of litchi-shaped heterogeneous liquid metal-Au nano-composite for radio-photothermal cancer therapy

With tremendous research advances in biomedical application,liquid metals(LM)also offer fantastic chemistry for synthesis of novel nano-composites.Herein,as a pioneering trial,litchi-shaped heterogeneous eutectic gallium indium-Au nanoparticles(EGaIn-Au NPs),served as effective radiosensitizer and photothermal agent for radio-photothermal cancer therapy,have been successfully prepared using in situ interfacial galvanic replacement reaction.The enhanced photothermal conversion efficiency and boosted radio-sensitization effect could be achieved with the reduction of Au nanodots onto the eutectic gallium indium(EGaIn)NPs surface.Most importantly,the growth of tumor could be effectively inhibited under the combined radio-photothermal therapy mediated by EGaIn-Au NPs.Inspired by this approach,in situ interfacial galvanic replacement reaction may open a novel strategy to fabricate LM-based nano-composite with advanced multi-functionalities.

Chiral AuCu heterostructures with site-specific geometric control and tailored plasmonic chirality

Rational design and construction of chiral-achiral hybrid structures are of great importance to realize the multifunctional complex chiral structures toward emerging technological applications. However, significant challenges remain due to the lack of fine control over the heterostructure. Here, we have developed a general bottom-up synthetic strategy for the site-selective growth of Cu nanodomains on intrinsically chiral Au nanocrystals. Chiral AuCu heterostructures with three distinct architectures were achieved by controlling the overgrowth of Cu nanodomains in a site-specific manner. The geometry-dependent plasmonic chirality of the heterostructures was demonstrated experimentally by circular dichroism spectroscopy and theoretically through finite-difference time-domain simulations. The site-specific geometric control of chiral AuCu heterostructures was also extended to employ anisotropic chiral Au nanoplates and nanorods as the building blocks. By virtue of the galvanic replacement reactions between metal ions and Cu atoms, chiral heterostructures with increasing architectural complexity and compositional diversity can be further achieved. The current work not only opens up a promising strategy to synthesize complex chiral hybrid nanostructures but also provides an important knowledge framework that guides the rational design of multifunctional chiral hybrid nanostructures toward chiroptical applications.

Matryoshka-caged gold nanorods： Synthesis, plasmonic properties, and catalytic activity

Matryoshka-caged gold nanorods （mCGNRs） were successfully synthesized by alternating between a seed-mediated silver-coating method and galvanic replacement reactions （GRRs）. As the number of matryoshka layers of the mCGNRs increased, the plasmon resonance peak broadened and was red-shifted, and the catalytic activity towards the reduction of 4-nitrophenol （4-NTP） increased. When mCGNRs with 6 layers were used as nanocatalysts in the reduction of 4-nitrophenol, the reaction rate coefficient was 5.2- and 3.7-times higher than that of the gold-nanorod- and caged-gold-nanorod-catalyzed reductions of 4-nitrophenol, respectively. In addition, the surface-plasmon-resonance-based absorption of light enhanced the catalytic performance of the mCGNRs. With the support of a polyurethane foam, the mCGNRs synthesized in this study can be applied as recydable heterogeneous catalysts for the reduction of 4-nitrophenol.

Toward dendrite-free and anti-corrosion Zn anodes by regulating a bismuth-based energizer

Aqueous rechargeable zinc metal batteries display high theoretical capacity along with economical effectiveness,environmental benignity and high safety.However,dendritic growth and chemical corrosion at the Zn anodes limit their widespread applications.Here,we construct a Zn/Bi electrode via in-situ growth of a Bi-based energizer upon Zn metal surface using a replacement reaction.Experimental and theoretical calculations reveal that the Bi-based energizer composed of metallic Bi and ZnBi alloy contributes to Zn plating/stripping due to strong adsorption energy and fast ion transport rates.The resultant Zn/Bi electrode not only circumvents Zn dendrite growth but also improves Zn anode anti-corrosion performance.Specifically,the corrosion current of the Zn/Bi electrode is reduced by 90%compared to bare Zn.Impressively,an ultra-low overpotential of 12​mV and stable cycling for 4000​h are achieved in a Zn/Bi symmetric cell.A Zn–Cu/Bi asymmetric cell displays a cycle life of 1000 cycles,with an average Coulombic efficiency as high as 99.6%.In addition,an assembled Zn/Bi-activated carbon hybrid capacitor exhibits a stable life of more than 50,000 cycles,an energy density of 64​Wh kg−1,and a power density of 7​kW​kg−1.The capacity retention rate of a Zn/Bi–MnO_(2)full cell is improved by over 150%compared to a Zn–MnO_(2)cell without the Bi-based energizer.Our findings open a new arena for the industrialization of Zn metal batteries for large-scale energy storage applications.