高熵纳米合金在电化学催化中的应用

The implementation of clean energy techniques, including clean hydrogen generation, use of solar-driven photovoltaic hybrid systems, photochemical heat generation as well as thermoelectric conversion, is crucial for the sustainable development of our society. Among these promising techniques, electrocatalysis has received significant attention for its ability to facilitate clean energy conversion because it promotes a higher rate of reaction and efficiency for the associated chemical transformations. Noble-metal-based electrocatalysts typically show high activity for electrochemical conversion processes. However, their scarcity and high cost limit their applications in electrocatalytic devices. To overcome this limitation, binary catalysts prepared by alloying with transition metals can be used. However, optimization of the activity of the binary catalysts is considerably limited because of the presence of the miscibility gap in the phase diagram of binary alloys. The activity of binary electrocatalysts can be attributed to the adsorption energy of molecules and intermediates on the surface. High-entropy alloys (HEAs), which consist of diverse elements in a single NP, typically exhibit better physical and/or chemical properties than their single-element counterparts, because of their tunable composition and inherent surface complexity. Further, HEAs can improve the performance of binary electrocatalysts because they exhibit a near-continuous distribution of adsorption energy. Recently, HEAs have gained considerable attention for their application in electrocatalytic reactions. This review summarizes recent research advances in HEA nanostructures and their application in the field of electrocatalysis. First, we introduce the concept, structure, and four core effects of HEAs. We believe that this part will provide the basic information about HEAs. Next, we discuss the reported top-down and bottom-up synthesis strategies, emphasizing on the carbothermal shock method, nanodroplet-mediated electrodeposition, fast moving bed pyrolysis, polyol process, and dealloying. Other methods such as combinatorial co-sputtering, ultrashort-pulsed laser ablation, ultrasonication-assisted wet chemistry, and scanning-probe block copolymer lithography are also highlighted. Among these methods, wet chemistry has been reported to be effective for the formation of nano-scale HEAs because it facilitates the concurrent reduction of all metal precursors to form solid-solution alloys. Next, we present the theoretical investigation of HEA nanocatalysts, including their thermodynamics, kinetic stability, and adsorption energy tuning for optimizing their catalytic activity and selectivity. To elucidate the structure–property relationship in HEAs, we summarize the research progress related to electrocatalytic reactions promoted by HEA nanocatalysts, including the oxygen reduction reaction, oxygen evolution reaction, hydrogen evolution reaction, methanol oxidation reaction, and CO₂ reduction reaction. Finally, we discuss the challenges and various strategies toward the development of HEAs.     

Melting evolution and diffusion behavior of vanadium nanoparticles

Molecular dynamics calculations have been performed to study the melting evolution, atomic diffusion and vibrational behavior of bcc metal vanadium nanoparticles with the number of atoms ranging from 537 to 28475 (diameters around 2–9 nm). The interactions between atoms are described using an analytic embedded-atom method. The obtained results reveal that the melting temperatures of nanoparticles are inversely proportional to the reciprocal of the nanoparticle size, and are in good agreement with the predictions of the thermodynamic liquid-drop model. The melting process can be described as occurring in two stages, firstly the stepwise premelting of the surface layer with a thickness of 2–3 times the perfect lattice constant, and then the abrupt overall melting of the whole cluster. The heats of fusion of nanoparticles are also inversely proportional to the reciprocal of the nanoparticle size. The diffusion is mainly localized to the surface layer at low temperatures and increases with the reduction of nanoparticle size, with the temperature being held constant. The radial mean square vibration amplitude (RMSVA) is developed to study the anharmonic effect on surface shells.     

Lancifodilactone F: a novel nortriterpenoid possessing a unique skeleton from Schisandra lancifolia and its anti-HIV activity

[structures: see text] Lancifodilactone F (1), possessing an unprecedented rearranged pentanortriterpenoid backbone derived from cycloartane, was isolated from the leaves and stems of Schisandra lancifolia (Rehd. et Wils) A. C. Smith. Its structure was established by comprehensive NMR and MS spectroscopic analysis, coupled with single-crystal X-ray experiment. Compound 1 exerted minimal cytotoxicity against C8166 cells (CC50 > 200 microg/mL) and showed anti-HIV activity with EC50 = 20.69 +/- 3.31 microg/mL and a selectivity index > 6.62.     

Carbon nanotube salts. Arylation of single-wall carbon nanotubes

[reaction: see text] Carbon nanotube salts prepared by treating single-wall carbon nanotubes (SWNTs) with lithium in liquid ammonia react readily with aryl iodides to give SWNTs functionalized by aryl groups.     

Photodegradation catalyst discovery by high-throughput experiment

A high-throughput experimental methodology was developed for photocatalysis reaction. In this work, a CCD imaging analysis system and photocatalytic reactor for UV light was designed and tested. By making use of the technologies, we have screened several catalyst libraries. From the SiO2-supported single component catalyst library, we found that TiO2, ZrO2, Nb2O5, and WO3 were good candidates for highly active catalyst formulation. We designed and screened several triangle catalyst libraries and found that the WO3- and Nb2O5-codoped TiO2 catalyst showed much higher photodegradation activities for the degradation of 1,6-hexamethylenediamine than did the pure TiO2 catalyst. The doping of ZrO2 into TiO2 did not generate apparent positive effects on catalytic activity.     

Preparation of monolithic silica column with strong cation-exchange stationary phase for capillary electrochromatography

A monolithic silica based strong cation-exchange stationary phase was successfully prepared for capillary electrochromatography. The monolithic silica matrix from a sol-gel process was chemically modified by treatment with 3-mercaptopropyltrimethoxysilane followed by a chemical oxidation procedure to produce the desired function. The strong cation-exchange stationary phase was characterized by its substantial and stable electroosmotic flow (EOF), and it was observed that the EOF value of the prepared column remained almost unchanged at different buffer pH values and slowly decreased with increasing phosphate concentration in the mobile phase. The monolithic silica column with strong cation-exchange stationary phase has been successfully employed in the electrochromatographic separation of beta-blockers and alkaloids extracted from traditional Chinese medicines (TCMs). The column efficiencies for the tested beta-blockers varied from 210,000 to 340,000 plates/m. A peak compression effect was observed for atenolol with the mobile phase having a low phosphate concentration.     

Dynamical hysteresis in a three-level atomic system

We have experimentally investigated dynamical hysteresis behavior by changing the sweeping frequency of the cavity input field in the optical bistability of rubidium atoms (in a three-level atomic-type configuration) inside an optical cavity. The shape, width (or area), and direction of the hysteresis cycle are sensitive functions of the sweeping frequency for such an optical bistable system.     

Upconversion from aqueous phase lanthanide chelates

We have prepared and characterized several lanthanide ion complexes of multidentate ligands or chelates in an effort to develop new upconverting luminescent labels that can be immune to autofluorescence and photobleaching. This study has involved the characterization of various chelates of Nd, Er, and Tm with respect to relative luminescent efficiency and excited-state lifetimes and explored various two-photon stepwise excitation mechanisms. Using peak laser powers near 100 kW, the upconversion emissions of Nd in Nd(EDTA)2(5-) at 386 nm, Er in Er(DPA)3(3-) at 550 nm, and Tm in Tm(DPA)3(3-) at 480 nm, at levels of approximately 10(-12) moles can be detected.     

Berry phase correction to electron density of states in solids

Liouville's theorem on the conservation of phase-space volume is violated by Berry phase in the semiclassical dynamics of Bloch electrons. This leads to a modification of the phase-space density of states, whose significance is discussed in a number of examples: field modification of the Fermi-sea volume, connection to the anomalous Hall effect, and a general formula for orbital magnetization. The effective quantum mechanics of Bloch electrons is also sketched, where the modified density of states plays an essential role.