Shiqiang Wei

A Robust and Efficient Pd3 Cluster Catalyst for the Suzuki Reaction and Its Odd Mechanism

Co-reporter:Fangyu Fu, Ji Xiang, Hao Cheng, Longjiu Cheng, Hanbao Chong, Shuxin Wang, Peng Li, Shiqiang Wei, Manzhou Zhu, and Yadong Li

ACS Catalysis March 3, 2017 Volume 7(Issue 3) pp:1860-1860

Publication Date(Web):January 24, 2017

DOI:10.1021/acscatal.6b02527

The palladium-catalyzed Suzuki–Miyaura coupling reaction is one of the most versatile and powerful tools for constructing synthetically useful unsymmetrical aryl–aryl bonds. In designing a Pd cluster as a candidate for efficient catalysis and mechanistic investigations, it was envisaged to study a case intermediate between, although very different from, the “classic” Pd(0)Ln and Pd nanoparticle families of catalysts. In this work, the cluster [Pd3Cl(PPh2)2(PPh3)3]+[SbF6]− (abbreviated Pd3Cl) was synthesized and fully characterized as a remarkably robust framework that is stable up to 170 °C and fully air-stable. Pd3Cl was found to catalyze the Suzuki–Miyaura C–C cross-coupling of a variety of aryl bromides and arylboronic acids under ambient aerobic conditions. The reaction proceeds while keeping the integrity of the cluster framework all along the catalytic cycle via the intermediate Pd3Ar, as evidenced by mass spectrometry and quick X-ray absorption fine structure. In the absence of the substrate under the reaction conditions, the Pd3OH species was detected by mass spectrometry, which strongly favors the “oxo-Pd” pathway for the transmetalation step involving substitution of the Cl ligand by OH followed by binding of the OH ligand with the arylboronic acid. The kinetics of the Suzuki–Miyaura reaction shows a lack of an induction period, consistent with the lack of cluster dissociation. This study may provide new perspectives for the catalytic mechanisms of C–C cross-coupling reactions catalyzed by metal clusters.Keywords: catalysis; C−C cross-coupling; mechanism of Pd-catalyzed reaction; metal cluster; Suzuki−Miyaura reaction;

Fast Photoelectron Transfer in (Cring)–C3N4 Plane Heterostructural Nanosheets for Overall Water Splitting

Co-reporter:Wei Che, Weiren Cheng, Tao Yao, Fumin Tang, Wei Liu, Hui Su, Yuanyuan Huang, Qinghua Liu, Jinkun Liu, Fengchun Hu, Zhiyun Pan, Zhihu Sun, and Shiqiang Wei

Journal of the American Chemical Society March 1, 2017 Volume 139(Issue 8) pp:3021-3021

Publication Date(Web):February 13, 2017

DOI:10.1021/jacs.6b11878

Direct and efficient photocatalytic water splitting is critical for sustainable conversion and storage of renewable solar energy. Here, we propose a conceptual design of two-dimensional C3N4-based in-plane heterostructure to achieve fast spatial transfer of photoexcited electrons for realizing highly efficient and spontaneous overall water splitting. This unique plane heterostructural carbon ring (Cring)–C3N4 nanosheet can synchronously expedite electron–hole pair separation and promote photoelectron transport through the local in-plane π-conjugated electric field, synergistically elongating the photocarrier diffusion length and lifetime by 10 times relative to those achieved with pristine g-C3N4. As a result, the in-plane (Cring)–C3N4 heterostructure could efficiently split pure water under light irradiation with prominent H2 production rate up to 371 μmol g–1 h–1 and a notable quantum yield of 5% at 420 nm.

Strong Surface Hydrophilicity in Co-Based Electrocatalysts for Water Oxidation

Co-reporter:Fumin Tang, Weiren Cheng, Yuanyuan Huang, Hui Su, Tao Yao, Qinghua Liu, Jinkun Liu, Fengchun Hu, Yong Jiang, Zhihu Sun, and Shiqiang Wei

ACS Applied Materials & Interfaces August 16, 2017 Volume 9(Issue 32) pp:26867-26867

Publication Date(Web):July 31, 2017

DOI:10.1021/acsami.7b07088

Developing efficient and durable oxygen evolution electrocatalyst is of paramount importance for the large-scale supply of renewable energy sources. Herein, we report the design of significant surface hydrophilicity based on cobalt oxyhydroxide (CoOOH) nanosheets to greatly improve the surface hydroxyl species adsorption and reaction kinetics at the Helmholtz double layer for high-efficiency water oxidation activity. The as-designed CoOOH-graphene nanosheets achieve a small surface water contact angle of ∼23° and a large double-layer capacitance (Cdl) of 8.44 mF/cm2 and thus could evidently strengthen surface species adsorption and trigger electrochemical oxygen evolution reaction (OER) under a quite low onset potential of 200 mV with an excellent Tafel slope of 32 mV/dec. X-ray absorption spectroscopy and first-principles calculations demonstrate that the strong interface electron coupling between CoOOH and graphene extracts partial electrons from the active sties and increases the electron state density around the Fermi level and effectively promotes the surface intermediates formation for efficient OER.Keywords: 3d electron structure; electrochemical water oxidation; proton−electron transfer; surface adsorption; surface hydrophilicity;

Red-emitting Au7 nanoclusters with fluorescence sensitivity to Fe2+ ions

Co-reporter:Lina Yang;Juan Chen;Ting Huang;Li Huang;Zhihu Sun;Yong Jiang;Tao Yao

Journal of Materials Chemistry C 2017 vol. 5(Issue 18) pp:4448-4454

Publication Date(Web):2017/05/11

DOI:10.1039/C7TC00724H

Luminescent gold nanoclusters have recently emerged as an important class of sensing and imaging materials in optical applications. Here we report a red-emitting gold nanocluster with a precise molecular formula of Au7(DHLA)2Cl2, synthesized via the size-focusing strategy using a bidentate ligand of dihydrolipoic acid (DHLA). This Au nanocluster is water-soluble and emits fluorescence at 683 nm with a quantum yield of 3.6% in water. The intense fluorescence of Au7(DHLA)2Cl2 originates from the aggregation of Au(I)–DHLA/Cl motifs on the Au(0) core in a rigid core/shell-like structure. Moreover, we find that trace levels of Fe2+ ions can quench selectively and sensitively the fluorescence of the Au7(DHLA)2Cl2 nanocluster, making it a potential fluorescent sensor for Fe2+ with a limit of detection of 3.8 μM (0.2 ppm). A dissociation-induced fluorescence quenching mechanism is also proposed to describe the fluorescence response of the nanocluster to Fe2+ ions.

Carbon Dioxide Electroreduction into Syngas Boosted by a Partially Delocalized Charge in Molybdenum Sulfide Selenide Alloy Monolayers

Co-reporter:Jiaqi Xu;Xiaodong Li;Wei Liu;Yongfu Sun;Zhengyu Ju;Tao Yao;Chengming Wang;Huanxin Ju;Junfa Zhu;Yi Xie

Angewandte Chemie International Edition 2017 Volume 56(Issue 31) pp:9121-9125

Publication Date(Web):2017/07/24

DOI:10.1002/anie.201704928

AbstractStructural parameters of ternary transition-metal dichalcogenide (TMD) alloy usually obey Vegard law well, while interestingly it often exhibits boosted electrocatalytic performances relative to its two pristine binary TMDs. To unveil the underlying reasons, we propose an ideal model of ternary TMDs alloy monolayer. As a prototype, MoSeS alloy monolayers are successfully synthesized, in which X-ray absorption fine structure spectroscopy manifests their shortened Mo−S and lengthened Mo−Se bonds, helping to tailor the d-band electronic structure of Mo atoms. Density functional theory calculations illustrate an increased density of states near their conduction band edge, which ensures faster electron transfer confirmed by their lower work function and smaller charge-transfer resistance. Energy calculations show the off-center charge around Mo atoms not only benefits for stabilizing COOH* intermediate confirmed by its most negative formation energy, but also facilitates the rate-limiting CO desorption step verified by CO temperature programmed desorption and electro-stripping tests. As a result, MoSeS alloy monolayers attain the highest 45.2 % Faradaic efficiency for CO production, much larger than that of MoS2 monolayers (16.6 %) and MoSe2 monolayers (30.5 %) at −1.15 V vs. RHE. This work discloses how the partially delocalized charge in ternary TMDs alloys accelerates electrocatalytic performances at atomic level, opening new horizons for manipulating CO2 electroreduction properties.

Carbon Dioxide Electroreduction into Syngas Boosted by a Partially Delocalized Charge in Molybdenum Sulfide Selenide Alloy Monolayers

Co-reporter:Jiaqi Xu;Xiaodong Li;Wei Liu;Yongfu Sun;Zhengyu Ju;Tao Yao;Chengming Wang;Huanxin Ju;Junfa Zhu;Yi Xie

Angewandte Chemie 2017 Volume 129(Issue 31) pp:9249-9253

Publication Date(Web):2017/07/24

DOI:10.1002/ange.201704928

AbstractStructural parameters of ternary transition-metal dichalcogenide (TMD) alloy usually obey Vegard law well, while interestingly it often exhibits boosted electrocatalytic performances relative to its two pristine binary TMDs. To unveil the underlying reasons, we propose an ideal model of ternary TMDs alloy monolayer. As a prototype, MoSeS alloy monolayers are successfully synthesized, in which X-ray absorption fine structure spectroscopy manifests their shortened Mo−S and lengthened Mo−Se bonds, helping to tailor the d-band electronic structure of Mo atoms. Density functional theory calculations illustrate an increased density of states near their conduction band edge, which ensures faster electron transfer confirmed by their lower work function and smaller charge-transfer resistance. Energy calculations show the off-center charge around Mo atoms not only benefits for stabilizing COOH* intermediate confirmed by its most negative formation energy, but also facilitates the rate-limiting CO desorption step verified by CO temperature programmed desorption and electro-stripping tests. As a result, MoSeS alloy monolayers attain the highest 45.2 % Faradaic efficiency for CO production, much larger than that of MoS2 monolayers (16.6 %) and MoSe2 monolayers (30.5 %) at −1.15 V vs. RHE. This work discloses how the partially delocalized charge in ternary TMDs alloys accelerates electrocatalytic performances at atomic level, opening new horizons for manipulating CO2 electroreduction properties.

Partial-surface-passivation strategy for transition-metal-based copper–gold nanocage

Co-reporter:Shoujie Liu, Xusheng Zheng, Li Song, Wei Liu, Tao Yao, Zhihu Sun, Yue Lin and Shiqiang Wei

Chemical Communications 2016 vol. 52(Issue 39) pp:6617-6620

Publication Date(Web):12 Apr 2016

DOI:10.1039/C6CC01779G

An effective strategy involving the corrosion of partial-surface-passivated Cu nanoparticles is proposed for synthesizing transition-metal-based Cu–Au alloy nanocages. Time-dependent X-ray absorption spectroscopy demonstrates that the hollow-cage Cu–Au alloy nanostructure is formed by sequential erosion of the partial surface and interior Cu and by the alloying of Au and Cu.

Symmetry-Controlled Structural Phase Transition Temperature in Chromium-Doped Vanadium Dioxide

Co-reporter:Xiaogang Tan, Wei Liu, Ran Long, Xiaodong Zhang, Tao Yao, Qinghua Liu, Zhihu Sun, Yuanjie Cao, and Shiqiang Wei

The Journal of Physical Chemistry C 2016 Volume 120(Issue 49) pp:28163-28168

Publication Date(Web):November 15, 2016

DOI:10.1021/acs.jpcc.6b08586

Understanding the key factor controlling phase transitions of correlated oxides by chemical doping is becoming of fundamental and technological interest. Here, we report vanadium chain symmetry as an effective means of mediating the structural phase transition (SPT) temperature in hydrothermal Cr-doped VO2. In-situ X-ray absorption fine structure spectroscopy unveils that high structural symmetry with equidistant 2.93 Å V–V zigzag chains, along with the dimerized V–V straight chain induced by Cr-doping, can stabilize VO2 at elevated temperature, thus raising the critical temperature of the VO2 phase transition. The Cr-doped VO2 system exhibited a SPT process involving lattice expansion, accompanied by V–V chain reconstruction into the rutile phase. These findings provide novel insights and guidance in chemically tailoring the phase transition of VO2.

Vacancy-Induced Ferromagnetism of MoS2 Nanosheets

Co-reporter:Liang Cai; Jingfu He; Qinghua Liu; Tao Yao; Lin Chen; Wensheng Yan; Fengchun Hu; Yong Jiang; Yidong Zhao; Tiandou Hu; Zhihu Sun

Journal of the American Chemical Society 2015 Volume 137(Issue 7) pp:2622-2627

Publication Date(Web):January 30, 2015

DOI:10.1021/ja5120908

Outstanding magnetic properties are highly desired for two-dimensional ultrathin semiconductor nanosheets. Here, we propose a phase incorporation strategy to induce robust room-temperature ferromagnetism in a nonmagnetic MoS2 semiconductor. A two-step hydrothermal method was used to intentionally introduce sulfur vacancies in a 2H-MoS2 ultrathin nanosheet host, which prompts the transformation of the surrounding 2H-MoS2 local lattice into a trigonal (1T-MoS2) phase. 25% 1T-MoS2 phase incorporation in 2H-MoS2 nanosheets can enhance the electron carrier concentration by an order, introduce a Mo4+ 4d energy state within the bandgap, and create a robust intrinsic ferromagnetic response of 0.25 μB/Mo by the exchange interactions between sulfur vacancy and the Mo4+ 4d bandgap state at room temperature. This design opens up new possibility for effective manipulation of exchange interactions in two-dimensional nanostructures.

Single-Atom Pd1/Graphene Catalyst Achieved by Atomic Layer Deposition: Remarkable Performance in Selective Hydrogenation of 1,3-Butadiene

Co-reporter:Huan Yan; Hao Cheng; Hong Yi; Yue Lin; Tao Yao; Chunlei Wang; Junjie Li; Shiqiang Wei;Junling Lu

Journal of the American Chemical Society 2015 Volume 137(Issue 33) pp:10484-10487

Publication Date(Web):August 13, 2015

DOI:10.1021/jacs.5b06485

We reported that atomically dispersed Pd on graphene can be fabricated using the atomic layer deposition technique. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy and X-ray absorption fine structure spectroscopy both confirmed that isolated Pd single atoms dominantly existed on the graphene support. In selective hydrogenation of 1,3-butadiene, the single-atom Pd1/graphene catalyst showed about 100% butenes selectivity at 95% conversion at a mild reaction condition of about 50 °C, which is likely due to the changes of 1,3-butadiene adsorption mode and enhanced steric effect on the isolated Pd atoms. More importantly, excellent durability against deactivation via either aggregation of metal atoms or carbonaceous deposits during a total 100 h of reaction time on stream was achieved. Therefore, the single-atom catalysts may open up more opportunities to optimize the activity, selectivity, and durability in selective hydrogenation reactions.

In situ studies on controlling an atomically-accurate formation process of gold nanoclusters

Co-reporter:Lina Yang, Hao Cheng, Yong Jiang, Ting Huang, Jie Bao, Zhihu Sun, Zheng Jiang, Jingyuan Ma, Fanfei Sun, Qinghua Liu, Tao Yao, Huijuan Deng, Shuxin Wang, Manzhou Zhu and Shiqiang Wei

Nanoscale 2015 vol. 7(Issue 34) pp:14452-14459

Publication Date(Web):27 Jul 2015

DOI:10.1039/C5NR03711E

Knowledge of the molecular formation mechanism of metal nanoclusters is essential for developing chemistry for accurate control over their synthesis. Herein, the “top-down” synthetic process of monodisperse Au13 nanoclusters via HCl etching of polydisperse Aun clusters (15 ≤ n ≤ 65) is traced by a combination of in situ X-ray/UV-vis absorption spectroscopy and time-dependent mass spectrometry. It is revealed experimentally that the HCl-induced synthesis of Au13 is achieved by accurately controlling the etching process with two distinctive steps, in sharp contrast to the traditional thiol-etching mechanism through release of the Au(I) complex. The first step involves the direct fragmentation of the initial larger Aun clusters into metastable intermediate Au8–Au13 smaller clusters. This is a critical step, which allows for the secondary size-growth step of the intermediates toward the atomically monodisperse Au13 clusters via incorporating the reactive Au(I)–Cl species in the solution. Such a secondary-growth pathway is further confirmed by the successful growth of Au13 through reaction of isolated Au11 clusters with AuClPPh3 in the HCl environment. This work addresses the importance of reaction intermediates in guiding the way towards controllable synthesis of metal nanoclusters.

Homochiral metal phosphonate nanotubes

Co-reporter:Xun-Gao Liu, Song-Song Bao, Jian Huang, Kazuya Otsubo, Jian-Shen Feng, Min Ren, Feng-Chun Hu, Zhihu Sun, Li-Min Zheng, Shiqiang Wei and Hiroshi Kitagawa

Chemical Communications 2015 vol. 51(Issue 82) pp:15141-15144

Publication Date(Web):20 Aug 2015

DOI:10.1039/C5CC05647K

A new type of homochiral metal–organic nanotubular structures based on metal phosphonates are reported, namely, (R)- or (S)-[M(pemp)(H2O)2][M = CoII (1), NiII (2)] [pemp2− = (R)- or (S)-(1-phenylethylamino)methylphosphonate]. In these compounds, the tube-walls are purely inorganic, composed of metal ions and O–P–O bridges. The cavity of the nanotube is hydrophilic with one coordination water pointing towards the center, while the outer periphery of the nanotube is hydrophobic, decorated by the phenylethyl groups of pemp2−. The thermal stabilities, adsorption and proton conductivity properties are investigated.

In situ unravelling structural modulation across the charge-density-wave transition in vanadium disulfide

Co-reporter:Xu Sun, Tao Yao, Zhenpeng Hu, Yuqiao Guo, Qinghua Liu, Shiqiang Wei and Changzheng Wu

Physical Chemistry Chemical Physics 2015 vol. 17(Issue 20) pp:13333-13339

Publication Date(Web):09 Apr 2015

DOI:10.1039/C5CP01326G

A deep understanding of the relationship between electronic and structure ordering across the charge-density-wave (CDW) transition is crucial for both fundamental study and technological applications. Herein, using in situ X-ray absorption fine structure (XAFS) spectroscopy coupled with high-resolution transmission electron microscopy (HRTEM), we have illustrated the atomic-level information on the local structural evolution across the CDW transition and its influence on the intrinsic electrical properties in VS2 system. The structure transformation, which is highlighted by the formation of vanadium trimers with derivation of V–V bond length (ΔR = 0.10 Å), was clearly observed across the CDW process. Moreover, the corresponding influence of lattice variation on the electronic behavior was clearly characterized by experimental results as well as theoretical analysis, which demonstrated that vanadium trimers drive the deformation of space charge density distribution into √3 × √3 periodicity, with the conductivity of a1g band reducing by half. These observations directly unveiled the close connection between lattice evolution and electronic property variation, paving a new avenue for understanding the intrinsic nature of electron-lattice interactions in the VS2 system and other isostructural transition metal dichalcogenides across the CDW transition process.

X-ray absorption fine structure spectroscopy in nanomaterials

Co-reporter:Zhihu Sun;Qinghua Liu;Tao Yao;Wensheng Yan

Science China Materials 2015 Volume 58( Issue 4) pp:313-341

Publication Date(Web):2015 April

DOI:10.1007/s40843-015-0043-4

X-ray absorption fine structure (XAFS) spectroscopy has been widely used for decades in a wide range of scientific fields, including physics, chemistry, biology, materials sciences, environmental sciences, etc. This review article is devoted to the applications of XAFS in nanomaterials. The basic principles of XAFS are briefly described from the view point of practical application, including its theory, data analysis and experiments. Using selected examples from recent literatures, the power of XAFS in determination of local atomic/electronic structures is illustrated for various nanomaterials, covering metal and semiconductor nanoparticles, catalysts, core/shell structures, ultrathin nanosheets, and so on. The utilization of time-resolved XAFS technique is also briefly introduced, for in-situ probing the nucleation/growth processes of nanomaterials and identifying reaction intermediates of nanostructured catalysts under operando conditions.X射线吸收精细结构谱学(XAFS)技术是近40年来同步辐射领域最为重要的实验技术之一, 在物理、化学、生物、材料和能源科学等诸多领域得到了广泛应用. 本文简要综述了XAFS技术在纳米材料科学研究中的应用. 首先介绍了XAFS的基本原理、实验方法及数据分析处理过程, 进一步通过对XAFS技术在应用于纳米材料研究中的一些代表性工作进行概述, 如金属与半导体纳米颗粒、催化剂、核壳结构、二维超薄纳米片, 以及原位XAFS技术在研究纳米材料的原位成核/生长过程和纳米催化剂在工作状态下的中间态表征等, 展示了XAFS技术在纳米材料领域对其原子和电子结构表征的强大能力.

Pt/Fe3O4 Core/Shell Triangular Nanoprisms by Heteroepitaxy: Facet Selectivity at the Pt–Fe3O4 Interface and the Fe3O4 Outer Surface

Co-reporter:Maowei Jiang, Wei Liu, Xiaoli Yang, Zheng Jiang, Tao Yao, Shiqiang Wei, and Xiaogang Peng

ACS Nano 2015 Volume 9(Issue 11) pp:10950

Publication Date(Web):October 4, 2015

DOI:10.1021/acsnano.5b04130

Pt/Fe3O4 core/shell triangular nanoprisms were synthesized using seed-mediated heteroepitaxy. Their well-defined shape, facets, and ordered-assembly allowed detailed analysis of mechanism of the heteroepitaxy. At the Pt–Fe3O4 interface, existence of both lattice and chemical mismatch resulted in facet-selective epitaxy along ⟨111⟩ directions of two lattices. X-ray absorption fine structure measurements demonstrated that the Pt seed nanocrystals were composed of an iron-rich Pt–Fe metallic thin layer sandwiched between the Pt core and a Fe–O outer-surface. The Fe–O outer-surface of the seed nanocrystals presumably offered epitaxial sites for the following deposition of the Fe3O4 shell. Each tip and side of a triangular nanoprism respectively possessed a groove and a ridge, and a (111) plane parallel to the basal planes linked all grooves and ridges. This interesting (111) plane approximately bisected the triangle nanoprisms and located near the Pt-seed. The outer surface of the hybrid nanocrystals was also found to be facet-selective, that is, solely {111} facets of Fe3O4 lattice. These polar {111} facets allowed the surface to be only occupied with high-density iron ions, and thus offered best surface coordination for the electron donating ligands in the solution.Keywords: core/shell; facet-selectivity; heteroepitaxy; interface; nanoprism ; surface;

All-Surface-Atomic-Metal Chalcogenide Sheets for High-Efficiency Visible-Light Photoelectrochemical Water Splitting

Co-reporter:Yongfu Sun;Zhihu Sun;Shan Gao;Hao Cheng;Qinghua Liu;Fengcai Lei;Yi Xie

Advanced Energy Materials 2014 Volume 4( Issue 1) pp:

Publication Date(Web):

DOI:10.1002/aenm.201300611

Artificial all-surface-atomic 2D sheets can trigger breakthroughs in tailoring the physical and chemical properties of advanced functional materials. Here, the conceptually new all-surface-atomic semiconductors of SnS and SnSe freestanding sheets are realized using a scalable strategy. As an example, all-surface-atomic SnS sheets undergo surface atomic elongation and structural disordering, which is revealed by X-ray absorption fine structure spectroscopy and first-principles calculations, endowing them with high structural stability and an increased density of states at the valence band edge. These exotic atomic and electronic structures make the all-surface-atomic SnS sheet-based photoelectrode exhibit an incident photon-to-current conversion efficiency of 67.1% at 490 nm, much higher than the efficiencies of other visible-light-driven water splitting. A photocurrent density of 5.27 mA cm^-2, which is two orders of magnitude higher than that of the bulk counterpart, is also achieved for the all-surface-atomic SnS sheets-based photoelectrode. This will allow the manipulation of the basic properties of advanced materials on the atomic scale, thus paving the way for innovative applications.

Low Overpotential in Vacancy-Rich Ultrathin CoSe2 Nanosheets for Water Oxidation

Co-reporter:Youwen Liu ; Hao Cheng ; Mengjie Lyu ; Shaojuan Fan ; Qinghua Liu ; Wenshuai Zhang ; Yuduo Zhi ; Chengming Wang ; Chong Xiao ; Shiqiang Wei ; Bangjiao Ye ;Yi Xie

Journal of the American Chemical Society 2014 Volume 136(Issue 44) pp:15670-15675

Publication Date(Web):October 13, 2014

DOI:10.1021/ja5085157

According to Yang Shao-Horn’s principle, CoSe2 is a promising candidate as an efficient, affordable, and sustainable alternative electrocatalyst for the oxygen evolution reaction, owing to its well-suited electronic configuration of Co ions. However, the catalytic efficiency of pure CoSe2 is still far below what is expected, because of its poor active site exposure yield. Herein, we successfully overcome the disadvantage of insufficient active sites in bulk CoSe2 by reducing its thickness into the atomic scale rather than any additional modification (such as doping or hybridizing with graphene or noble metals). The positron annihilation spectrometry and XAFS spectra provide clear evidence that a large number of VCo″ vacancies formed in the ultrathin nanosheets. The first-principles calculations reveal that these VCo″ vacancies can serve as active sites to efficiently catalyze the oxygen evolution reaction, manifesting an OER overpotential as low as 0.32 V at 10 mA cm–2 in pH 13 medium, which is superior to the values for its bulk counterparts as well as those for the most reported Co-based electrocatalysts. Considering the outstanding performance of the simple, unmodified ultrathin CoSe2 nanosheets as the only catalyst, further improvement of the catalytic activity is expected when various strategies of doping or hybridizing are used. These results not only demonstrate the potential of a notable, affordable, and earth-abundant water oxidation electrocatalyst based on ultrathin CoSe2 nanosheets but also open up a promising avenue into the exploration of excellent active and durable catalysts toward replacing noble metals for oxygen electrocatalysis.

Half-Unit-Cell α-Fe2O3 Semiconductor Nanosheets with Intrinsic and Robust Ferromagnetism

Co-reporter:Weiren Cheng, Jingfu He, Tao Yao, Zhihu Sun, Yong Jiang, Qinghua Liu, Shan Jiang, Fengchun Hu, Zhi Xie, Bo He, Wensheng Yan, and Shiqiang Wei

Journal of the American Chemical Society 2014 Volume 136(Issue 29) pp:10393-10398

Publication Date(Web):July 8, 2014

DOI:10.1021/ja504088n

The synthesis of atomically thin transition-metal oxide nanosheets as a conceptually new class of materials is significant for the development of next-generation electronic and magnetic nanodevices but remains a fundamental chemical and physical challenge. Here, based on a “template-assisted oriented growth” strategy, we successfully synthesized half-unit-cell nanosheets of a typical transition-metal oxide α-Fe2O3 that show robust intrinsic ferromagnetism of 0.6 μB/atom at 100 K and remain ferromagnetic at room temperature. A unique surface structure distortion, as revealed by X-ray absorption spectroscopy, produces nonidentical Fe ion environments and induces distance fluctuation of Fe ion chains. First-principles calculations reveal that the efficient breaking of the quantum degeneracy of Fe 3d energy states activates ferromagnetic exchange interaction in these Fe5-co–O–Fe6-co ion chains. These results provide a solid design principle for tailoring the spin-exchange interactions and offer promise for future semiconductor spintronics.

Realizing High Water Splitting Activity on Co3O4 Nanowire Arrays under Neutral Environment

Co-reporter:Jingfu He, Yanhua Peng, Zhihu Sun, Weiren Cheng, Qinghua Liu, Yajuan Feng, Yong Jiang, Fengchun Hu, Zhiyun Pan, Qing Bian, Shiqiang Wei

Electrochimica Acta 2014 Volume 119() pp:64-71

Publication Date(Web):10 February 2014

DOI:10.1016/j.electacta.2013.11.138

•We reveal the true determinant of catalytic rate of Co3O4 under near-neutral electrolytes.•The catalysis process of Co3O4 is hindered by a threshold surface H+ concentration.•The catalytic current density is limited by H+ mass transfer rate from electrode surface.•Adding proper buffering agents would ensure the water splitting activity under pH 7-13.Enhancing catalytic water-splitting activity under mild environments is significant to solve the long-standing cost, safety and stability issues in photoelectrochemical cells. Here, we demonstrate the crucial role of improving surface H transfer in achieving efficient water-splitting catalytic activity of Co3O4 nanowire arrays in near-neutral pH working electrolytes. Under weak OH circumstances, the impedance of mass transfer quickly multiplies and the catalytic current declines to a current plateau in the region of 1.7–2.1 V vs. RHE, due to the surface H concentration approaching a threshold value in the range of 10−3–10−4 M. The proper choice of buffering agents to facilitate the mass transfer, with 0.1 M KPi as a prototype, would decrease the overpotential by 500 mV for neutral electrolyte and favors to achieve a catalytic current comparable to that under strong alkali environments (pH > 13). These results also provide a solid guideline for extending the electrocatalytic utility of other transition metal catalysts to near-neutral pH environments.

Graphene Activating Room-Temperature Ferromagnetic Exchange in Cobalt-Doped ZnO Dilute Magnetic Semiconductor Quantum Dots

Co-reporter:Zhihu Sun, Xiaoyu Yang, Chao Wang, Tao Yao, Liang Cai, Wensheng Yan, Yong Jiang, Fengchun Hu, Jingfu He, Zhiyun Pan, Qinghua Liu, and Shiqiang Wei

ACS Nano 2014 Volume 8(Issue 10) pp:10589

Publication Date(Web):September 15, 2014

DOI:10.1021/nn5040845

Control over the magnetic interactions in dilute magnetic semiconductor quantum dots (DMSQDs) is a key issue to future development of nanometer-sized integrated “spintronic” devices. However, manipulating the magnetic coupling between impurity ions in DMSQDs remains a great challenge because of the intrinsic quantum confinement effects and self-purification of the quantum dots. Here, we propose a hybrid structure to achieve room-temperature ferromagnetic interactions in DMSQDs, via engineering the density and nature of the energy states at the Fermi level. This idea has been applied to Co-doped ZnO DMSQDs where the growth of a reduced graphene oxide shell around the Zn0.98Co0.02O core turns the magnetic interactions from paramagnetic to ferromagnetic at room temperature, due to the hybridization of 2pz orbitals of graphene and 3d obitals of Co2+–oxygen-vacancy complexes. This design may open up a kind of possibility for manipulating the magnetism of doped oxide nanostructures.Keywords: Co-doped ZnO QDs; ferromagnetic exchange; RGO; XAFS;

Unidirectional Thermal Diffusion in Bimetallic Cu@Au Nanoparticles

Co-reporter:Shoujie Liu, Zhihu Sun, Qinghua Liu, Lihui Wu, Yuanyuan Huang, Tao Yao, Jing Zhang, Tiandou Hu, Mengran Ge, Fengchun Hu, Zhi Xie, Guoqiang Pan, and Shiqiang Wei

ACS Nano 2014 Volume 8(Issue 2) pp:1886

Publication Date(Web):January 28, 2014

DOI:10.1021/nn4063825

Understanding the atomic diffusions at the nanoscale is important for controlling the synthesis and utilization of nanomaterials. Here, using in situ X-ray absorption spectroscopy coupled with theoretical calculations, we demonstrate a so far unexplored unidirectional diffusion from the Au shell to the Cu core in thermally alloying Cu@Au core@shell architecture of ca. 7.1 nm. The initial diffusion step at 423 K is found to be characterized by the formation of a diffusion layer composed of a Au-dilute substitutional CuAu-like intermetallic compound with short Cu–Au bond length (2.61 Å). The diffusion further happens by the migration of the Au atoms with large disorder into the interior Cu matrix at higher temperatures (453 and 553 K). These results suggest that the structural preference of a CuAu-like compound, along with the nanosized effect, plays a critical role in determining the atomic diffusion dynamics.Keywords: core@shell nanoparticle; Cu@Au; dilute substitutional intermetallic; in situ X-ray absorption spectroscopy; unidirectional atomic diffusion

Realizing Ferromagnetic Coupling in Diluted Magnetic Semiconductor Quantum Dots

Co-reporter:Wensheng Yan ; Qinghua Liu ; Chao Wang ; Xiaoyu Yang ; Tao Yao ; Jingfu He ; Zhihu Sun ; Zhiyun Pan ; Fengchun Hu ; Ziyu Wu ; Zhi Xie

Journal of the American Chemical Society 2013 Volume 136(Issue 3) pp:1150-1155

Publication Date(Web):December 31, 2013

DOI:10.1021/ja411900w

Manipulating the ferromagnetic interactions in diluted magnetic semiconductor quantum dots (DMSQDs) is a central theme to the development of next-generation spin-based information technologies, but this remains a great challenge because of the intrinsic antiferromagnetic coupling between impurity ions therein. Here, we propose an effective approach capable of activating ferromagnetic exchange in ZnO-based DMSQDs, by virtue of a core/shell structure that engineers the energy level of the magnetic impurity 3d levels relative to the band edge. This idea has been successfully applied to Zn0.96Co0.04O DMSQDs covered by a shell of ZnS or Ag2S. First-principles calculations further indicate that covering a ZnS shell around the Co-doped ZnO core drives a transition of antiferromagnetic-to-ferromagnetic interaction, which occurs within an effective depth of 1.2 nm underneath the surface in the core. This design opens up new possibility for effective manipulation of exchange interactions in doped oxide nanostructures for future spintronics applications.

XAFS in dilute magnetic semiconductors

Co-reporter:Zhihu Sun, Wensheng Yan, Tao Yao, Qinghua Liu, Yi Xie and Shiqiang Wei

Dalton Transactions 2013 vol. 42(Issue 38) pp:13779-13801

Publication Date(Web):28 Jun 2013

DOI:10.1039/C3DT50888A

X-Ray absorption fine structure (XAFS) spectroscopy has experienced a rapid development in the last four decades and has proved to be a powerful structure characterization technique in the study of local environments in condensed matter. In this article, we first introduce the XAFS basic principles including theory, data analysis and experiment in some detail. Then we attempt to make a review on the applications of XAFS to the study of atomic and electronic structure in dilute magnetic semiconductor (DMS) systems. The power of XAFS in characterizing this interesting material system, such as determining the occupation sites and distribution of the dopants, detecting the presence of metal clusters or secondary phases, as well as identifying the defect types and dopant valence, will be illuminated by selected examples. This review should be of interest both to newcomers in the DMS field and to an interdisciplinary community of researchers working in synthesis, characterization and utilization of DMS materials.

In-Plane Coassembly Route to Atomically Thick Inorganic–Organic Hybrid Nanosheets

Co-reporter:Xiaodong Zhang, Qinghua Liu, Lingju Meng, Hui Wang, Wentuan Bi, Yanhua Peng, Tao Yao, Shiqiang Wei, and Yi Xie

ACS Nano 2013 Volume 7(Issue 2) pp:1682

Publication Date(Web):January 23, 2013

DOI:10.1021/nn3056719

Control over the anisotropic assembly of small building blocks into organized structures is considered an effective way to design organic nanosheets and atomically thick inorganic nanosheets with nonlayered structure. However, there is still no available route so far to control the assembly of inorganic and organic building blocks into a flattened hybrid nanosheet with atomic thickness. Herein, we highlight for the first time a universal in-plane coassembly process for the design and synthesis of transition-metal chalcogenide–alkylamine inorganic–organic hybrid nanosheets with atomic thickness. The structure, formation mechanism, and stability of the hybrid nanosheets were investigated in detail by taking the Co9S8–oleylamine (Co9S8–OA) hybrid nanosheets as an example. Both experimental data and theoretical simulations demonstrate that the hybrid nanosheets were formed by in-plane connection of small two-dimensional (2D) Co9S8 nanoplates via oleylamine molecules adsorbed at the side surface and corner sites of the nanoplates. X-ray absorption fine structure spectroscopy study reveals the structure distortion of the small 2D Co9S8 nanoplates that endows structural stability of the atomically thick Co9S8–OA hybrid nanosheets. The brand new atomically thick nanosheets with inorganic–organic hybrid network nanostructure will not only enrich the family of atomically thick 2D nanosheets but also inspire more interest in their potential applications.Keywords: atomically thick; coassembly; in-plane; inorganic−organic hybrid; two-dimensional nanosheets

Ultrathin Nanosheets of Half-Metallic Monoclinic Vanadium Dioxide with a Thermally Induced Phase Transition

Co-reporter:Dr. Tao Yao;Dr. Liang Liu;Chong Xiao;Xiaodong Zhang;Dr. Qinghua Liu; Shiqiang Wei; Yi Xie

Angewandte Chemie 2013 Volume 125( Issue 29) pp:7702-7706

Publication Date(Web):

DOI:10.1002/ange.201302891

Ultrathin Nanosheets of Half-Metallic Monoclinic Vanadium Dioxide with a Thermally Induced Phase Transition

Co-reporter:Dr. Tao Yao;Dr. Liang Liu;Chong Xiao;Xiaodong Zhang;Dr. Qinghua Liu; Shiqiang Wei; Yi Xie

Angewandte Chemie International Edition 2013 Volume 52( Issue 29) pp:7554-7558

Publication Date(Web):

DOI:10.1002/anie.201302891

Atomically Thick Bismuth Selenide Freestanding Single Layers Achieving Enhanced Thermoelectric Energy Harvesting

Co-reporter:Yongfu Sun ; Hao Cheng ; Shan Gao ; Qinghua Liu ; Zhihu Sun ; Chong Xiao ; Changzheng Wu ; Shiqiang Wei ;Yi Xie

Journal of the American Chemical Society 2012 Volume 134(Issue 50) pp:20294-20297

Publication Date(Web):December 5, 2012

DOI:10.1021/ja3102049

Thermoelectric materials can realize significant energy savings by generating electricity from untapped waste heat. However, the coupling of the thermoelectric parameters unfortunately limits their efficiency and practical applications. Here, a single-layer-based (SLB) composite fabricated from atomically thick single layers was proposed to optimize the thermoelectric parameters fully. Freestanding five-atom-thick Bi2Se3 single layers were first synthesized via a scalable interaction/exfoliation strategy. As revealed by X-ray absorption fine structure spectroscopy and first-principles calculations, surface distortion gives them excellent structural stability and a much increased density of states, resulting in a 2-fold higher electrical conductivity relative to the bulk material. Also, the surface disorder and numerous interfaces in the Bi2Se3 SLB composite allow for effective phonon scattering and decreased thermal conductivity, while the 2D electron gas and energy filtering effect increase the Seebeck coefficient, resulting in an 8-fold higher figure of merit (ZT) relative to the bulk material. This work develops a facile strategy for synthesizing atomically thick single layers and demonstrates their superior ability to optimize the thermoelectric energy harvesting.

Hexane-Driven Icosahedral to Cuboctahedral Structure Transformation of Gold Nanoclusters

Co-reporter:Yuanyuan Li ; Hao Cheng ; Tao Yao ; Zhihu Sun ; Wensheng Yan ; Yong Jiang ; Yi Xie ; Yongfu Sun ; Yuanyuan Huang ; Shoujie Liu ; Jing Zhang ; Yaning Xie ; Tiandou Hu ; Lina Yang ; Ziyu Wu

Journal of the American Chemical Society 2012 Volume 134(Issue 43) pp:17997-18003

Publication Date(Web):October 10, 2012

DOI:10.1021/ja306923a

Whether and how nanoclusters possessing a rich diversity of possible geometric configurations can transform from one structural type to another are critical issues in cluster science. Here we demonstrate an icosahedral-to-cuboctahedral structural transformation of Au nanoclusters driven by changing the chemical environment. For icosahedral Au13 clusters protected by a mixture of dodecanethiol and triphenylphosphine ligands, solvent exchange of ethanol by hexane leads to quick selective desorption of the thiolate layers from the cluster surface. The surviving Au cores then undergo a much slower energy-minimization process via structural rearrangement, stabilized in the cuboctahedral structure and protected by triphenylphosphine in the hexane environment. In response to the dramatically changed atomic structure, the character of the electronic structure of the Au clusters is converted from semiconducting to metallic. This work addresses the structure–property correlation and its strong dependence on the chemical environment for metal nanoclusters.

Probing Nucleation Pathways for Morphological Manipulation of Platinum Nanocrystals

Co-reporter:Tao Yao ; Shoujie Liu ; Zhihu Sun ; Yuanyuan Li ; Shi He ; Hao Cheng ; Yi Xie ; Qinghua Liu ; Yong Jiang ; Ziyu Wu ; Zhiyun Pan ; Wensheng Yan

Journal of the American Chemical Society 2012 Volume 134(Issue 22) pp:9410-9416

Publication Date(Web):May 14, 2012

DOI:10.1021/ja302642x

Understanding the formation process in the controlled synthesis of nanocrystals will lead to the effective manipulation of the morphologies and properties of nanomaterials. Here, in-situ UV–vis and X-ray absorption spectroscopies are combined to monitor the tracks of the nucleation pathways in the solution synthesis of platinum nanocrystals. We find experimentally that the control over nucleation pathways through changing the strength of reductants can be efficiently used to manipulate the resultant nanocrystal shapes. The in-situ measurements show that two different nucleation events involving the formation of one-dimensional “PtnClx” complexes from the polymerization of linear “Cl3Pt–PtCl3” dimers and spherical “Ptn0” clusters from the aggregation of Pt0 atoms occur for the cases of weak and strong reductants; and the resultant morphologies are nanowires and nanospheres, respectively. This study provides a crucial insight into the correlation between the particle shapes and nucleation pathways of nanomaterials.

Controllable synthesis of gold nanoparticles with ultrasmall size and high monodispersity via continuous supplement of precursor

Co-reporter:Yuanyuan Li, Shoujie Liu, Tao Yao, Zhihu Sun, Zheng Jiang, Yuying Huang, Hao Cheng, Yuanyuan Huang, Yong Jiang, Zhi Xie, Guoqiang Pan, Wensheng Yan and Shiqiang Wei

Dalton Transactions 2012 vol. 41(Issue 38) pp:11725-11730

Publication Date(Web):01 Aug 2012

DOI:10.1039/C2DT31270K

Synthesis of monodisperse small Au nanoparticles in a controllable manner is of great importance for fundamental science and technical applications. Here, we report a “precursor continuous-supply” strategy for controllable synthesis of 0.9–3.3 nm Au nanoparticles with a narrow size distribution of 0.1–0.2 nm, using a weak reductant to slow-down the reducing rate of AuClPPh3 precursor in ethanol. Time-dependent X-ray absorption and UV-Vis absorption measurements revealed that owing to the joint use of AuClPPh3 and ethanol, the remnant AuClPPh3 was self-supplied and the precursor concentration was maintained at a level near to its equilibrium solubility (ca. 1.65 mmol L−1) in ethanol. Hence the nucleation duration was extended that focused the initial size distribution of the Au clusters. With reaction going on for 58 min, most of AuClPPh3 with a nominal Au concentration of 17.86 mmol L−1 was converted to ethanol-soluble Au clusters with a size of about 1.0 nm, resulting in a high-yield synthesis.

In situ study on the electronic structure of graphene grown on 6H–SiC with synchrotron radiation photoelectron spectroscopy

Co-reporter:Chaoyang Kang, Jun Tang, Limin Li, Haibin Pan, Pengshou Xu, Shiqiang Wei, Xiufang Chen, Xiangang Xu

Applied Surface Science 2012 Volume 258(Issue 6) pp:2187-2191

Publication Date(Web):1 January 2012

DOI:10.1016/j.apsusc.2011.02.068

Abstract

Low energy electron diffraction (LEED) and synchrotron radiation photoelectron spectroscopy (SRPES) were used to study the synthesis process and detailed electronic structures of graphene produced by thermal decomposition of 6H–SiC $(0 0 0 \bar{1})$ in ultrahigh vacuum (UHV). The LEED results showed that as annealing temperature increased, different reconstructions of 6H–SiC $(0 0 0 \bar{1})$ appeared and the anisotropic graphene layers were produced finally. The results of C 1s core levels indicated that the component, which was assigned to graphene emerged and the interface interaction between graphene and the substrate was weak. The existence of Si clusters was confirmed by Si 2p core levels and perhaps these clusters led to rough epitaxial graphene surface. The results of valence band spectra showed that at high annealing temperature both of σ and π bonds existed in the grown graphene layers.

Freestanding Tin Disulfide Single-Layers Realizing Efficient Visible-Light Water Splitting

Co-reporter:Dr. Yongfu Sun;Hao Cheng;Shan Gao;Dr. Zhihu Sun;Dr. Qinghua Liu;Qin Liu;Fengcai Lei;Dr. Tao Yao;Dr. Jingfu He; Shiqiang Wei; Yi Xie

Angewandte Chemie 2012 Volume 124( Issue 35) pp:8857-8861

Publication Date(Web):

DOI:10.1002/ange.201204675

Innentitelbild: Freestanding Tin Disulfide Single-Layers Realizing Efficient Visible-Light Water Splitting (Angew. Chem. 35/2012)

Co-reporter:Dr. Yongfu Sun;Hao Cheng;Shan Gao;Dr. Zhihu Sun;Dr. Qinghua Liu;Qin Liu;Fengcai Lei;Dr. Tao Yao;Dr. Jingfu He; Shiqiang Wei; Yi Xie

Angewandte Chemie 2012 Volume 124( Issue 35) pp:

Publication Date(Web):

DOI:10.1002/ange.201205557

Ni-Doped Overlayer Hematite Nanotube: A Highly Photoactive Architecture for Utilization of Visible Light

Co-reporter:Weiren Cheng, Jingfu He, Zhihu Sun, Yanhua Peng, Tao Yao, Qinghua Liu, Yong Jiang, Fengchun Hu, Zhi Xie, Bo He, and Shiqiang Wei

The Journal of Physical Chemistry C 2012 Volume 116(Issue 45) pp:24060-24067

Publication Date(Web):October 29, 2012

DOI:10.1021/jp306738e

To efficiently transform absorbed photons to chemical energy is highly desired for the full utilization of visible light in solar hydrogen generation process. Here, a highly active photoanode consisting of a thin NixFe2–xO3 overlayer on the surface of hematite nanotube has been constructed to raise the utilization of the photoexcited carriers by Fe2O3 in the visible spectrum. We find that the obtained overlayer photoanodes promote the charge migration of photogenerated carriers to the surface, accelerating surface oxygen evolution and avoiding low-energy photoexcited holes recombination at the semiconductor–liquid junction. Relative to the pristine Fe2O3 photoanodes, a sustainably high incident photon to electron conversion efficiency from 40% at 400 nm until 10% at 500 nm is observed for Ni-doped overlayer hematite, yielding ∼280% enhancement of the photoconversion efficiency. Our results provide some guidance for the future design and optimization for the structure of photoanode.

Inside Cover: Freestanding Tin Disulfide Single-Layers Realizing Efficient Visible-Light Water Splitting (Angew. Chem. Int. Ed. 35/2012)

Co-reporter:Dr. Yongfu Sun;Hao Cheng;Shan Gao;Dr. Zhihu Sun;Dr. Qinghua Liu;Qin Liu;Fengcai Lei;Dr. Tao Yao;Dr. Jingfu He; Shiqiang Wei; Yi Xie

Angewandte Chemie International Edition 2012 Volume 51( Issue 35) pp:

Publication Date(Web):

DOI:10.1002/anie.201205557

Freestanding Tin Disulfide Single-Layers Realizing Efficient Visible-Light Water Splitting

Co-reporter:Dr. Yongfu Sun;Hao Cheng;Shan Gao;Dr. Zhihu Sun;Dr. Qinghua Liu;Qin Liu;Fengcai Lei;Dr. Tao Yao;Dr. Jingfu He; Shiqiang Wei; Yi Xie

Angewandte Chemie International Edition 2012 Volume 51( Issue 35) pp:8727-8731

Publication Date(Web):

DOI:10.1002/anie.201204675

Modifying the Atomic and Electronic Structures of Gold Nanocrystals via Changing the Chain Length of n-Alkanethiol Ligands

Co-reporter:Yong Jiang, Peidong Yin, Yuanyuan Li, Zhihu Sun, Qinghua Liu, Tao Yao, Hao Cheng, Fengchun Hu, Zhi Xie, Bo He, Guoqiang Pan, and Shiqiang Wei

The Journal of Physical Chemistry C 2012 Volume 116(Issue 47) pp:24999-25003

Publication Date(Web):November 1, 2012

DOI:10.1021/jp3096117

The interfacial atomic and electronic structures of ligand-protected nanomaterials are vital factors but are inadequately known. Here, we demonstrate that the adsorption geometry, as well as the electronic structures of Au–S interface, can be tailored via varying the hydrocarbon “tail” lengths of n-alkanethiol ligands. Fully n-alkanethiols (n = 3, 8, and 12) capped Au nanocrystals of 3.0 nm were characterized in solution by X-ray absorption fine structure at the Au L3-edge. With increasing alkyl length, it is found that the headgroup S atom occupies the nanocrystals surface sites with gradually higher coordinations, along with the progressively shortened Au–S bond length. As a result, the strongest Au–S interactions coming from the longest n-alkanethiols capping lead to the most significant d charge transfer from the surface Au layer to the S atoms.

Improving Photoelectrochemical Water Splitting Activity of TiO2 Nanotube Arrays by Tuning Geometrical Parameters

Co-reporter:Suzhen Liang, Jingfu He, Zhihu Sun, Qinghua Liu, Yong Jiang, Hao Cheng, Bo He, Zhi Xie, and Shiqiang Wei

The Journal of Physical Chemistry C 2012 Volume 116(Issue 16) pp:9049-9053

Publication Date(Web):April 5, 2012

DOI:10.1021/jp300552s

Here we report a study to improve the solar water splitting activity of TiO2 photoanodes by tuning the porosity of the nanotube arrays. Through modifying the electrochemical anodization conditions, the average wall thickness and inner diameter of the synthesized TiO2 nanotube arrays were controlled in the range of 8–20 nm and 40–145 nm, respectively, corresponding to a variation of the porosity from 47.1% to 75.7%. The photoelectrochemical (PEC) measurements demonstrate that the sample with maximum porosity (75.7%) shows the peak ultraviolet conversion efficiency of 7.02%. Further analysis reveals that the photoconversion efficiency increases monotonously with porosity rather than with wall thickness and/or inner diameter. We suggest that the large porosity can ensure a much shorter hole diffusion path toward wall surface and accelerate ion migration in the tube to overcome the kinetic bottleneck, thus enhancing the PEC water splitting efficiency of the TiO2 nanotube arrays.

From VO2 (B) to VO2 (A) nanobelts: first hydrothermal transformation, spectroscopic study and first principles calculation

Co-reporter:Shudong Zhang, Bo Shang, Jinlong Yang, Wensheng Yan, Shiqiang Wei and Yi Xie

Physical Chemistry Chemical Physics 2011 vol. 13(Issue 35) pp:15873-15881

Publication Date(Web):08 Aug 2011

DOI:10.1039/C1CP20838A

The phase transition process from VO2 (B) to VO2 (A) was first observed through a mild hydrothermal approach, using hybrid density functional theory (DFT) calculations and crystallographic VO2 topology analysis. All theoretical analyses reveal that VO2 (A) is a thermodynamically stable phase and has a lower formation energy compared with the metastable VO2 (B). For the first time, X-ray absorption spectroscopy (XAS) of the V L-edge and O K-edge was performed on different VO2 phases, and the differences in the electronic structure of the two polymorphic forms provide further experimental evidence of the more stable VO2 (A). Consequently, transformation from VO2 (B) to VO2 (A) is much easier to be realized from a dynamical point of view. Notably, the transformation of VO2 (B) into VO2 (A) show the sequence VO2 (B)-high-temperature VO2 (AH) phase-low-temperature VO2 (A) phase, which was achieved by hydrothermal treatment, respectively. Also, an alternative synthesis route was proposed based on the above hydrothermal transformation, and VO2 (A) was successfully prepared via the simple one-step hydrothermal method by hydrolysis of VO(acac)2 (acac = acetylacetonate). Therefore, VO2 nanostructures with controlled phase compositions can be obtained in high yields. Through elucidating the structural evolution in the crystallographic shear mechanism, we can easily guide the design of other metal oxide nanostructures with controllable phases.

Tuning the Spin State of Cobalt in a CoLa Heterometallic Complex through Controllable Coordination Sphere of La

Co-reporter:Dr. Song-Song Bao;Dr. Yi Liao;Dr. Yan-Hui Su;Xu Liang;Dr. Feng-Chun Hu;Dr. Zhihu Sun;Dr. Li-Min Zheng;Dr. Shiqiang Wei;Dr. Roger Alberto;Yi-Zhi Li ;Dr. Jing Ma

Angewandte Chemie International Edition 2011 Volume 50( Issue 24) pp:5504-5508

Publication Date(Web):

DOI:10.1002/anie.201007872

Local structure of Se nanotube investigated by X-ray absorption fine structure spectroscopy

Co-reporter:Yajuan Feng;Zhi Xie;Zhihu Sun;Jing Zhang;Tao Yao;Yuanyuan Li

Rendiconti Lincei 2011 Volume 22( Issue 1 Supplement) pp:17-24

Publication Date(Web):2011 December

DOI:10.1007/s12210-011-0150-4

The structures of selenium nanoparticles and nanotubes synthesized by the dismutation of precursor Na2SeSO3 under acidic condition in micellar solution are studied by transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray absorption fine structure spectroscopy (XAFS). Spherical-like nanoparticles contain both amorphous and crystalline parts while, as shown by XRD patterns, nanotubes have the crystal structure of trigonal selenium (t-Se). They display quite different XANES spectral features indicating different local atomic arrangements. Theoretical XANES calculations show that the local structure around Se atom in the nanotubes is similar to a hexangular cylinder. Quantitative extended XAFS (EXAFS) analysis further shows that the average Se–Se bond length for both nanotubes and nanoparticles is 2.35 Å.

Wavelet-XAFS investigation for Mn:Si diluted magnetic semiconductor thin films

Co-reporter:Zhiyun Pan;Yajuan Feng;Zhi Xie;Qinghua Liu;Yong Jiang;Jian Ye

Rendiconti Lincei 2011 Volume 22( Issue 1 Supplement) pp:25-32

Publication Date(Web):2011/12/01

DOI:10.1007/s12210-011-0146-0

The Morlet wavelet transformation (MT) was used to analyze Mn K-edge extended X-ray absorption fine structure (EXAFS) spectra of Mn-doped Si-based diluted magnetic semiconductor (DMS) thin films grown by the magnetron co-sputtering method. MT of EXAFS data shows that the Mn–Mn scattering path can be distinguished by the Mn–Si scattering path in the spectra of MnxSi1−x DMS thin films. In all DMS thin films Mn atoms fill Si sites without forming Mn–Si compounds while Mn–Si compounds are present in the annealed analogues. From the analysis of experimental data we point out that low-concentration Mn-doped samples are characterized by a more symmetric structure.

Impurity Concentration Dependence of Optical Absorption for Phosphorus-Doped Anatase TiO2

Co-reporter:Yanhua Peng ; Jingfu He ; Qinghua Liu ; Zhihu Sun ; Wensheng Yan ; Zhiyun Pan ; Yanfei Wu ; Suzhen Liang ; Weiren Cheng

The Journal of Physical Chemistry C 2011 Volume 115(Issue 16) pp:8184-8188

Publication Date(Web):April 6, 2011

DOI:10.1021/jp200287n

The efficient absorption of visible light is crucial for improving the photocatalytic activity of foreign species-doped TiO2. With first-principles calculations, we explore the effects of phosphorus doping on mediating the photocatalytic activity of anatase. It is found that the P impurity tends to occupy the cation site in TiO2; more importantly, there exists a critical phosphorus concentration of about 0.7% for maximizing the absorption of solar light. The optical energy gap is narrowed by ∼0.3 eV at the low doping concentration of 0.7%, whereas it increases with P concentration at the higher P concentration region of 0.7−3.1 atm. %. These results suggest that the dopant concentration dependence might be responsible for numerous seeming controversies of optical absorption observed in experiments. This finding points to a possibility of tailoring the optical absorption of TiO2 by varying the dopant content.

Insights into Initial Kinetic Nucleation of Gold Nanocrystals

Co-reporter:Tao Yao ; Zhihu Sun ; Yuanyuan Li ; Zhiyun Pan ; He Wei ; Yi Xie ; Masaharu Nomura ; Yasuhiro Niwa ; Wensheng Yan ; Ziyu Wu ; Yong Jiang ; Qinghua Liu

Journal of the American Chemical Society 2010 Volume 132(Issue 22) pp:7696-7701

Publication Date(Web):May 14, 2010

DOI:10.1021/ja101101d

Understanding the initial nucleation mechanism of monodisperse nanocrystals (NCs) during synthesis process is an important prerequisite to control the desired sizes and to manipulate the properties of nanoscale materials. The acquisition of information for the small nanocluster nucleation process, however, still remains challenging. Here, using a continuous-flow in situ X-ray absorption fine structure (XAFS) spectroscopy for time-resolved studies, we have clarified the initial kinetic nucleation of Au clusters under the grain size of 1 nm for the classical Au NCs synthesis via the reduction of AuCl4− in aqueous solution. The in situ XAFS results present the experimental revelation of the formation of intermediate Cl3−Au−AuCl3− dimer and the subsequent higher complexes ‘AunCln+x’ in the initial nucleation stage. We propose a kinetic three-step mechanism involving the initial nucleation, slow growth, and eventual coalescence for the Au NCs formation, which may be helpful for the synthesis of metallic nanomaterials.

Room-Temperature Ferromagnetic Silver Vanadium Oxide (Ag1.2V3O8): A Magnetic Semiconductor Nanoring Structure

Co-reporter:Changzheng Wu;Haiou Zhu;Jun Dai;Wensheng Yan;Jinlong Yang;Yangchao Tian;Yi Xie

Advanced Functional Materials 2010 Volume 20( Issue 21) pp:3666-3672

Publication Date(Web):

DOI:10.1002/adfm.201001179

Abstract

Magnetic nanoring structures are attractive for spintronic devices due to their unique attributes of well-defined and reproducible magnetic states originating from their characteristic geometry. Almost all previous magnetic nanorings have been exclusively limited to traditional ferromagnetic materials, and a magnetic semiconductor (MSC) nanoring structure has been reported rarely during the past decades. Here, it is demonstrated that room-temperature ferromagnetic Ag_1.2V₃O₈ nanobelts and nanorings may be achieved by controlled oxidation of the V⁴⁺ precursors in an Ag⁺-containing aqueous solution. The polarization-induced self-coiling of in situ formed Ag_1.2V₃O₈ nanobelts is responsible for the formation of the perfectly circular nanoring geometry. The NEXAFS spectra and the density functional calculations clearly reveal that the electron transfer originates from the hybridization of the doped Ag⁺ and V⁴⁺ atoms, causing ordering of the magnetic moments that give rise to the intrinsic ferromagnetism of the Ag_1.2V₃O₈ structure.

Structural Study on Co−Ni Bimetallic Nanoparticles by X-ray Spectroscopy

Co-reporter:Hong Zhang, Tao Yao, Zhihu Sun, Yuanyuan Li, Qinghua Liu, Fengchun Hu, Zhiyun Pan, Bo He, Zhi Xie and Shiqiang Wei

The Journal of Physical Chemistry C 2010 Volume 114(Issue 32) pp:13596-13600

Publication Date(Web):July 27, 2010

DOI:10.1021/jp105080t

The Co100−xNix (x = 0, 30, 50, and 70) bimetallic nanoparticles (NPs) synthesized by a solvothermal method show interesting shape changes from aggregated clusters to ordered nanorings with increasing Ni concentration. A comprehensive structural study of these Co100−xNix NPs is performed with X-ray diffraction and X-ray absorption fine structure spectroscopy. It is shown that the pure Co NPs consist of a majority of the fcc structure and a minority of the hcp phase. When 30% Ni is added, alloyed Co−Ni NPs with an inhomogenous atomic distribution are formed. The further addition of Ni to ≥50% could considerably improve the crystallinity and homogeneity of the alloyed NPs, as suggested by the fact that the disorder degree (σ2) is gradually lowered and the coordination number ratios NCo−Co/NCo−Ni and NNi−Ni/NNi−Co gradually approach the stoichiometry of the NPs. The ordered and homogeneous fcc structure helps to strengthen the magnetocrystalline anisotropic interactions, which may facilitate the head-to-tail assembly of the Co−Ni NPs.

High Photocatalytic Activity of Rutile TiO2 Induced by Iodine Doping

Co-reporter:Jingfu He, Qinghua Liu, Zhihu Sun, Wensheng Yan, Guobin Zhang, Zeming Qi, Pengshou Xu, Ziyu Wu and Shiqiang Wei

The Journal of Physical Chemistry C 2010 Volume 114(Issue 13) pp:6035-6038

Publication Date(Web):March 15, 2010

DOI:10.1021/jp911267m

To improve the energy conversion of solar irradiation, a photocatalyst with high reactivity under visible light is required. Using density functional theory, the structural and electronic properties of iodine cation-doped rutile TiO2 are studied. The total energy calculations show that iodine substituting for titanium sites in TiO2 matrix is energetically favorable. The electronic structure calculations reveal that iodine doping induces a delocalized band consisting of I 5s states and O 2p states at the top of the valence band of TiO2. Due to this delocalized state, the band gap is markedly narrowed by about 0.4 eV, the optical absorption is extended to the visible light region, and the excited electron−hole pairs are expected to have better mobility. Moreover, the conduction band edge is raised above the reduction level of H2/H2O by I-doping, which enables the achievement of high photocatalytic efficiency of I-doped rutile TiO2.

Structural evolution in the nanoscale diffusion process: a Au–Sn bimetallic system

Co-reporter:Kuai Yu, Tao Yao, Zhiyun Pan, Shiqiang Wei and Yi Xie

Dalton Transactions 2009 (Issue 46) pp:10353-10358

Publication Date(Web):19 Oct 2009

DOI:10.1039/B916215A

This work shows the structural evolution of a Au–Sn bimetallic system during the nanoscale diffusion process. Based on X-ray absorption fine structure (XAFS) spectroscopy, X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray spectrometry (EDX), insights were obtained into the detailed composition and structure of the Au–Sn bimetallic system, demonstrating the sequential formation of stable Au/AuSn, AuSn, AuSn/AuSn2 and AuSn2 nanocrystals (Au/AuSn and AuSn/AuSn2 refer to core/shell structures) rather than disordered alloys or alloys with an equal Sn atomic distribution. Furthermore, the formation mechanism of Au–Sn intermetallic compounds and their core/shell structures are discussed. Through elucidating the structural evolution in the diffusion process, we can easily guide the design of other novel bimetallic phases and their core/shell structures which could be predicted between the noble metals (Cu, Ag, Au) and the IIIA or IVA (In, Sn, Pb) metallic elements owing to the rapid diffusion mechanism.

Magnetic Property and Spatial Occupation of Co Dopants in Zn0.98Co0.02O Nanowires

Co-reporter:Tao Yao, Wensheng Yan, Zhihu Sun, Zhiyun Pan, Yi Xie, Yong Jiang, Jian Ye, Fengchun Hu and Shiqiang Wei

The Journal of Physical Chemistry C 2009 Volume 113(Issue 32) pp:14114-14118

Publication Date(Web):July 17, 2009

DOI:10.1021/jp902685k

Single phase Co-doped ZnO dilute magnetic semiconductor nanowire was synthesized by a chemical solution method and characterized by X-ray absorption fine structure (XAFS). The Co K-edge XAFS spectroscopy reveals that the doped Co ions are substantially incorporated into the ZnO host lattice. Moreover, the spatial occupation of Co dopants in Zn0.98Co0.02O nanowire is resolved further by the detailed O K-edge XANES analysis. We suggest that the Co ions are randomly doped into the ZnO matrix and located at the Zn sites. The magnetization measurement of the Co-doped ZnO nanowire shows the room temperature ferromagnetic characteristic with a relatively larger saturation magnetization. Furthermore, we suggest that the enhanced ferromagnetism can be ascribed to the coeffect of the size effect and the homogeneity of Co dopants for Zn0.98Co0.02O nanowire, which will make it useful in nanometer spintronic devices.

High-Temperature Ferromagnetism of Hybrid Nanostructure Ag−Zn0.92Co0.08O Dilute Magnetic Semiconductor

Co-reporter:Tao Yao, Wensheng Yan, Zhihu Sun, Zhiyun Pan, Bo He, Yong Jiang, He Wei, Masaharu Nomura, Yi Xie, Yaning Xie, Tiandou Hu and Shiqiang Wei

The Journal of Physical Chemistry C 2009 Volume 113(Issue 9) pp:3581-3585

Publication Date(Web):2017-2-22

DOI:10.1021/jp809560s

Hybrid-nanostructure Ag−Zn0.92Co0.08O dilute magnetic semiconductors synthesized by a solvothermal method show that the magnetic property of the nanorods is changed from paramagnetism to room-temperature ferromagnetism when 2% Ag is codoped into Zn0.92Co0.08O nanorods. The detailed analysis of the X-ray absorption fine structure spectra at both Co and Ag K-edge reveals that a substantial part of Ag atoms exists in the tetrahedral interstitial sites of (Zn, Co)O matrix in the Ag(2%)−Zn0.92Co0.08O. We suggest that the interstitial Ag atoms, together with Ag nanoparticles, play a most important role in mediating the high-temperature ferromagnetism of Ag(2%)−Zn0.92Co0.08O, due to the strong hybridization between the Co 3d states and the spin-split impurity band at the Fermi level.

Formation of AlCuFe icosahedral quasicrystal by mechanical alloying: XAFS and XRD studies

Co-reporter:Shilong Yin, Zhi Xie, Qing Bian, Bo He, Zhiyun Pan, Zhihu Sun, Zheng Wei, Liying Qian, Shiqiang Wei

Journal of Alloys and Compounds 2008 Volume 455(1–2) pp:314-321

Publication Date(Web):8 May 2008

DOI:10.1016/j.jallcom.2007.01.058

The structural evolutions of the mechanically alloyed ternary Al70Cu20Fe10 powders with the milling times and the annealing treatment were studied by X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS). It was found that during the milling process, only Cu can incorporate into the lattice of Al to form an Al2Cu compound or an AlCu solid solution, depending on the milling times. However, Fe remains the original structure of bcc α-Fe. Annealing treatment at 700 °C for 4 h can drive the α-Fe to react with the Al2Cu compounds and AlCu solid solution, and the main products of the annealed Al70Cu20Fe10 (10 h) and the annealed Al70Cu20Fe10 (40 h) are the icosahedral Al65Cu20Fe15 quasicrystal and the Al(Cu, Fe) solid solution, respectively. The local structural disorders around Fe and Cu atoms in the icosahedral QC phase is about 50% larger than those of the Al(Cu, Fe) solid solution.

Structural evolutions of CdSe nanocrystals in ripening process

Co-reporter:Xinfeng Zhang, Zhihu Sun, Wensheng Yan, Feng Wei, Shiqiang Q. Wei

Materials Chemistry and Physics 2008 Volume 111(2–3) pp:513-516

Publication Date(Web):15 October 2008

DOI:10.1016/j.matchemphys.2008.05.001

A size-selective separation method is used to synthesize CdSe nanocrystals (NCs) with different grain sizes. The structural evolutions of CdSe NCs in the ripening process are investigated by high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), and X-ray absorption fine structure (XAFS) spectroscopy. The results indicate that the structural disorder σS2 of the Se–Cd bond in CdSe NCs rises from 0.0005, 0.0012 and 0.0034 Å2 as the size of NCs increases from 1.9 to 2.7 and 3.1 nm. The small σS2 of the 1.9 nm NCs unambiguously reveals that at this stage the CdSe NCs are well crystallized and almost free of interior defects. The unusual increase of σS2 with size can only be interpreted by the interior defects rather than surface defects of NCs. The interior defects produced in the core of the CdSe NCs through the ripening process are accumulated. This leads to a rapid increase in their structural disorders for the large CdSe NCs.

Local structure of liquid gallium studied by X-ray absorption fine structure

Co-reporter:Shiqiang Wei, Hiroyuki Oyanagi, Wenhan Liu, Tiandou Hu, Shilong Yin, Guozhu Bian

Journal of Non-Crystalline Solids 2000 Volume 275(Issue 3) pp:160-168

Publication Date(Web):October 2000

DOI:10.1016/S0022-3093(00)00251-9

X-ray absorption fine structure (XAFS) has been used to study the local structures of Ga in the temperature region between 78 and 373 K. The three model atomic pair distribution functions, i.e. Gaussian function, convolution of Gaussian and exponent function, and cumulant expansion, are used to analyze EXAFS data of the liquid Ga. Assuming an asymmetric atom pair distribution function made from the convolution of Gaussian, PG, and exponent function, PE, we have obtained the structure parameters for liquid Ga (305 K): average bond length, , coordination number, N=9.8, thermal disorder parameter, and static disorder parameter, . Although the short Ga–Ga covalent bond is not observed for liquid Ga, the Ga atoms in the first coordination shell are distributed in a wide R region centered at . Based on these results, we propose that the coordination geometry changes from the distorted body centered cubic (N=7) to the distorted body centered tetragonal (N=10) associated with a solid–liquid phase transition.

From VO2 (B) to VO2 (A) nanobelts: first hydrothermal transformation, spectroscopic study and first principles calculation

Co-reporter:Shudong Zhang, Bo Shang, Jinlong Yang, Wensheng Yan, Shiqiang Wei and Yi Xie

Physical Chemistry Chemical Physics 2011 - vol. 13(Issue 35) pp:NaN15881-15881

Publication Date(Web):2011/08/08

DOI:10.1039/C1CP20838A

The phase transition process from VO2 (B) to VO2 (A) was first observed through a mild hydrothermal approach, using hybrid density functional theory (DFT) calculations and crystallographic VO2 topology analysis. All theoretical analyses reveal that VO2 (A) is a thermodynamically stable phase and has a lower formation energy compared with the metastable VO2 (B). For the first time, X-ray absorption spectroscopy (XAS) of the V L-edge and O K-edge was performed on different VO2 phases, and the differences in the electronic structure of the two polymorphic forms provide further experimental evidence of the more stable VO2 (A). Consequently, transformation from VO2 (B) to VO2 (A) is much easier to be realized from a dynamical point of view. Notably, the transformation of VO2 (B) into VO2 (A) show the sequence VO2 (B)-high-temperature VO2 (AH) phase-low-temperature VO2 (A) phase, which was achieved by hydrothermal treatment, respectively. Also, an alternative synthesis route was proposed based on the above hydrothermal transformation, and VO2 (A) was successfully prepared via the simple one-step hydrothermal method by hydrolysis of VO(acac)2 (acac = acetylacetonate). Therefore, VO2 nanostructures with controlled phase compositions can be obtained in high yields. Through elucidating the structural evolution in the crystallographic shear mechanism, we can easily guide the design of other metal oxide nanostructures with controllable phases.

Homochiral metal phosphonate nanotubes

Co-reporter:Xun-Gao Liu, Song-Song Bao, Jian Huang, Kazuya Otsubo, Jian-Shen Feng, Min Ren, Feng-Chun Hu, Zhihu Sun, Li-Min Zheng, Shiqiang Wei and Hiroshi Kitagawa

Chemical Communications 2015 - vol. 51(Issue 82) pp:NaN15144-15144

Publication Date(Web):2015/08/20

DOI:10.1039/C5CC05647K

A new type of homochiral metal–organic nanotubular structures based on metal phosphonates are reported, namely, (R)- or (S)-[M(pemp)(H2O)2][M = CoII (1), NiII (2)] [pemp2− = (R)- or (S)-(1-phenylethylamino)methylphosphonate]. In these compounds, the tube-walls are purely inorganic, composed of metal ions and O–P–O bridges. The cavity of the nanotube is hydrophilic with one coordination water pointing towards the center, while the outer periphery of the nanotube is hydrophobic, decorated by the phenylethyl groups of pemp2−. The thermal stabilities, adsorption and proton conductivity properties are investigated.

Structural evolution in the nanoscale diffusion process: a Au–Sn bimetallic system

Co-reporter:Kuai Yu, Tao Yao, Zhiyun Pan, Shiqiang Wei and Yi Xie

Dalton Transactions 2009(Issue 46) pp:NaN10358-10358

Publication Date(Web):2009/10/19

DOI:10.1039/B916215A

This work shows the structural evolution of a Au–Sn bimetallic system during the nanoscale diffusion process. Based on X-ray absorption fine structure (XAFS) spectroscopy, X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray spectrometry (EDX), insights were obtained into the detailed composition and structure of the Au–Sn bimetallic system, demonstrating the sequential formation of stable Au/AuSn, AuSn, AuSn/AuSn2 and AuSn2 nanocrystals (Au/AuSn and AuSn/AuSn2 refer to core/shell structures) rather than disordered alloys or alloys with an equal Sn atomic distribution. Furthermore, the formation mechanism of Au–Sn intermetallic compounds and their core/shell structures are discussed. Through elucidating the structural evolution in the diffusion process, we can easily guide the design of other novel bimetallic phases and their core/shell structures which could be predicted between the noble metals (Cu, Ag, Au) and the IIIA or IVA (In, Sn, Pb) metallic elements owing to the rapid diffusion mechanism.

Red-emitting Au7 nanoclusters with fluorescence sensitivity to Fe2+ ions

Co-reporter:Lina Yang, Juan Chen, Ting Huang, Li Huang, Zhihu Sun, Yong Jiang, Tao Yao and Shiqiang Wei

Journal of Materials Chemistry A 2017 - vol. 5(Issue 18) pp:NaN4454-4454

Publication Date(Web):2017/04/03

DOI:10.1039/C7TC00724H

Luminescent gold nanoclusters have recently emerged as an important class of sensing and imaging materials in optical applications. Here we report a red-emitting gold nanocluster with a precise molecular formula of Au7(DHLA)2Cl2, synthesized via the size-focusing strategy using a bidentate ligand of dihydrolipoic acid (DHLA). This Au nanocluster is water-soluble and emits fluorescence at 683 nm with a quantum yield of 3.6% in water. The intense fluorescence of Au7(DHLA)2Cl2 originates from the aggregation of Au(I)–DHLA/Cl motifs on the Au(0) core in a rigid core/shell-like structure. Moreover, we find that trace levels of Fe2+ ions can quench selectively and sensitively the fluorescence of the Au7(DHLA)2Cl2 nanocluster, making it a potential fluorescent sensor for Fe2+ with a limit of detection of 3.8 μM (0.2 ppm). A dissociation-induced fluorescence quenching mechanism is also proposed to describe the fluorescence response of the nanocluster to Fe2+ ions.

In situ unravelling structural modulation across the charge-density-wave transition in vanadium disulfide

Co-reporter:Xu Sun, Tao Yao, Zhenpeng Hu, Yuqiao Guo, Qinghua Liu, Shiqiang Wei and Changzheng Wu

Physical Chemistry Chemical Physics 2015 - vol. 17(Issue 20) pp:NaN13339-13339

Publication Date(Web):2015/04/09

DOI:10.1039/C5CP01326G

A deep understanding of the relationship between electronic and structure ordering across the charge-density-wave (CDW) transition is crucial for both fundamental study and technological applications. Herein, using in situ X-ray absorption fine structure (XAFS) spectroscopy coupled with high-resolution transmission electron microscopy (HRTEM), we have illustrated the atomic-level information on the local structural evolution across the CDW transition and its influence on the intrinsic electrical properties in VS2 system. The structure transformation, which is highlighted by the formation of vanadium trimers with derivation of V–V bond length (ΔR = 0.10 Å), was clearly observed across the CDW process. Moreover, the corresponding influence of lattice variation on the electronic behavior was clearly characterized by experimental results as well as theoretical analysis, which demonstrated that vanadium trimers drive the deformation of space charge density distribution into √3 × √3 periodicity, with the conductivity of a1g band reducing by half. These observations directly unveiled the close connection between lattice evolution and electronic property variation, paving a new avenue for understanding the intrinsic nature of electron-lattice interactions in the VS2 system and other isostructural transition metal dichalcogenides across the CDW transition process.

Partial-surface-passivation strategy for transition-metal-based copper–gold nanocage

Co-reporter:Shoujie Liu, Xusheng Zheng, Li Song, Wei Liu, Tao Yao, Zhihu Sun, Yue Lin and Shiqiang Wei

Chemical Communications 2016 - vol. 52(Issue 39) pp:NaN6620-6620

Publication Date(Web):2016/04/12

DOI:10.1039/C6CC01779G

An effective strategy involving the corrosion of partial-surface-passivated Cu nanoparticles is proposed for synthesizing transition-metal-based Cu–Au alloy nanocages. Time-dependent X-ray absorption spectroscopy demonstrates that the hollow-cage Cu–Au alloy nanostructure is formed by sequential erosion of the partial surface and interior Cu and by the alloying of Au and Cu.

XAFS in dilute magnetic semiconductors

Co-reporter:Zhihu Sun, Wensheng Yan, Tao Yao, Qinghua Liu, Yi Xie and Shiqiang Wei

Dalton Transactions 2013 - vol. 42(Issue 38) pp:NaN13801-13801

Publication Date(Web):2013/06/28

DOI:10.1039/C3DT50888A

X-Ray absorption fine structure (XAFS) spectroscopy has experienced a rapid development in the last four decades and has proved to be a powerful structure characterization technique in the study of local environments in condensed matter. In this article, we first introduce the XAFS basic principles including theory, data analysis and experiment in some detail. Then we attempt to make a review on the applications of XAFS to the study of atomic and electronic structure in dilute magnetic semiconductor (DMS) systems. The power of XAFS in characterizing this interesting material system, such as determining the occupation sites and distribution of the dopants, detecting the presence of metal clusters or secondary phases, as well as identifying the defect types and dopant valence, will be illuminated by selected examples. This review should be of interest both to newcomers in the DMS field and to an interdisciplinary community of researchers working in synthesis, characterization and utilization of DMS materials.

Controllable synthesis of gold nanoparticles with ultrasmall size and high monodispersity via continuous supplement of precursor

Co-reporter:Yuanyuan Li, Shoujie Liu, Tao Yao, Zhihu Sun, Zheng Jiang, Yuying Huang, Hao Cheng, Yuanyuan Huang, Yong Jiang, Zhi Xie, Guoqiang Pan, Wensheng Yan and Shiqiang Wei

Dalton Transactions 2012 - vol. 41(Issue 38) pp:NaN11730-11730

Publication Date(Web):2012/08/01

DOI:10.1039/C2DT31270K

Synthesis of monodisperse small Au nanoparticles in a controllable manner is of great importance for fundamental science and technical applications. Here, we report a “precursor continuous-supply” strategy for controllable synthesis of 0.9–3.3 nm Au nanoparticles with a narrow size distribution of 0.1–0.2 nm, using a weak reductant to slow-down the reducing rate of AuClPPh3 precursor in ethanol. Time-dependent X-ray absorption and UV-Vis absorption measurements revealed that owing to the joint use of AuClPPh3 and ethanol, the remnant AuClPPh3 was self-supplied and the precursor concentration was maintained at a level near to its equilibrium solubility (ca. 1.65 mmol L−1) in ethanol. Hence the nucleation duration was extended that focused the initial size distribution of the Au clusters. With reaction going on for 58 min, most of AuClPPh3 with a nominal Au concentration of 17.86 mmol L−1 was converted to ethanol-soluble Au clusters with a size of about 1.0 nm, resulting in a high-yield synthesis.

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Abstract

Abstract