Table of Content

15 November 2021, Volume 50 Issue 11

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Invited

Research Progress of Ultra-Wide Bandgap Semiconductor β-Ga₂O₃

WANG Xinyue, ZHANG Shengnan, HUO Xiaoqing, ZHOU Jinjie, WANG Jian, CHENG Hongjuan

2021, 50(11):  1995-2012. 

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At the beginning of the 21st century, β-Ga₂O₃, an ultra-wide bandgap semiconductor, was researched initially in Japan. β-Ga₂O₃ wafers with different orientations were prepared by Tohoku University using floating zone technique. High-quality homoepitaxial wafers was obtained by Kyoto University which was engaged in β-Ga₂O₃ epitaxy research. Based on this substrate, the first Ga₂O₃-based MESFET device was successfully constructed by Japan National Institute of Information and Communications Technology in 2012. This work demonstrated the great potential of β-Ga₂O₃ in power devices and opened a new era of β-Ga₂O₃ research. Since then, β-Ga₂O₃ single crystals, epi-wafers and devices have attracted a lot of research institutions' attention. Recent years, with the technological progress, the upper limit of breakdown voltage of β-Ga₂O₃ power devices was repeatedly refreshed. The time line of the development of β-Ga₂O₃ single crystal, epi-wafers, devices and the research status of power devices are summarized and analyzed in this article. This paper points out the existing problems and possible solutions in the application of β-Ga₂O₃, and looks forward to its future development, and provides a reference for the future technological development of β-Ga₂O₃.

Research Articles

Growth and Properties of Gd³⁺/Yb³⁺ Co-Doped Yttrium Aluminate Crystals

TAN Huiyu, WANG Rui, ZHANG Peixiong, YIN Hao, LI Zhen, CHEN Zhenqiang

2021, 50(11):  2013-2018. 

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High-quality Gd³⁺/Yb³⁺ co-doped yttrium aluminate crystal was successfully grown by the Czochralski method. The crystal structure, segregation coefficient, spectrum and laser performance were characterized. The results show that the grown crystal space group is Pnma, which belongs to the orthorhombic system, and the segregation coefficient of Yb³⁺ is 1.13. According to the polarization absorption and fluorescence spectra, it is found that the absorption cross section of the crystal at 980 nm is 2.14×10^-20 cm² in the b polarization direction, which is suitable for InGaAs laser diode pumping. At the same time, the emission cross section at 1 044 nm is 0.39×10^-20 cm²and the fluorescence lifetime is 1.638 ms. In addition, a laser experiment was performed on the Gd/Yb∶YAP crystal in the b tangential direction, and the continuous laser output achieves at 1 μm, the slope efficiency is 23.5%, and the maximum output power reaches 0.51 W.

Electronic Structures and Optical Properties of Ru, Rh, Pd Doped GaSb

YANG Weixia, ZHANG Hexiang, PAN Fengchun, LIN Xueling

2021, 50(11):  2019-2026. 

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Electronic structures and optical properties of transition metal (TM, TM refers to Ru, Rh and Pd, respectively) doped GaSb were studied by first-principles calculations. The results show that the three TMs are more likely to substitute for Ga to form TM@Ga defect and enhance the response of GaSb semiconductor to infrared photons, making the optical absorption edge of the system red shift. The doped TM@Ga introduce impurity levels distributed around the Fermi level in the band gap, which greatly strengthens the dielectric properties of the system. The enhancement of the photoelectric field intensity can promote the generation and migration of electron-hole pairs, thus improving the photoelectric conversion efficiency of GaSb semiconductor. The optical properties of TM@Ga doped GaSb are all superior to that of undoped system, but Ru is the best choice among the three dopants. Moreover, the molar concentration and location of Ru also have an impact on optical properties of GaSb semiconductor. The absorption amplitude of Ru-GaSb is the biggest when the concentration is 6.25% (atomic fraction), which can improve the photoelectric conversion efficiency and photocatalytic performance effectively.

First-Principles Study on the Effects of Ag Doping and Defect Coexistence on the Photocatalytic Properties of ZnO

ZHANG Haifeng, WANG Bin, CHENG Caiping, YI Sijing

2021, 50(11):  2027-2035. 

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The effects of Ag doping and defect coexistence on the photoelectric properties of ZnO were studied by first-principles method. The calculation results indicate that O-rich condition is beneficial to Ag doping, while O-poor condition has an inhibitory effect. When Ag doping concentration is lower, Ag_Zn is dominant doping model under O-rich or O-poor conditions, and the model is more stable. When Ag doping concentration is higher, Ag_Zn-Ag_Zn is dominant doping model under O-rich condition, and that is Ag_Zn-Ag_i under O-poor condition. Under O-rich condition, it is difficult to introduce the coexistence defect of V_Zn and O_i by Ag doping. V_O is a preferred model under O-poor condition, and it can promote Ag doping to a certain extent. Ag doping reduces the band gap of ZnO. The higher of doping concentration is, the narrower of band gap will be. The defect coexistence of V_Zn, V_O and O_i increase the band gap of Ag doped models. Ag doping and the defect coexistence of V_Zn, O_i all red shift the absorption edge of ZnO to the visible region, which expands the absorption range of ZnO to sunlight. Ag_Zn-V_O is transparent in the visible region. In the low energy region, Ag_Zn-Ag_Zn shows higher optical absorptivity, but the corresponding formation energy is also higher than that of Ag_Zn. V_Zn improves the optical absorptivity of Ag_Zn-V_Zn and Ag_Zn-Ag_Zn-V_Zn in the low energy region. V_O is beneficial to the adsorption of O₂ by ZnO and can produce more H₂O₂ and ·HO. The defect coexistence of V_Zn and V_O both improve the photocatalytic performance of ZnO.

First-Principles Study on Electronic Structure and Optical Properties of (La, Y)-Doped AlN

ZOU Jiang, LI Ping, XIE Quan

2021, 50(11):  2036-2044. 

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The geometry of pure AlN, (La, Y) single-doped and La-Y co-doped AlN superlattices was optimized by the plane wave ultrasoft pseudopotential method based on density functional theory. The band structure, density of states and optical properties of the system before and after rare earth elements (La, Y) doping were calculated. The results show that the undoped AlN is a direct band gap semiconductor, and the band gap value is E_g=4.237 eV. The density of state is mainly contributed by electron orbitals of Al-3p and N-2s.After doping, the band structure property is changed, the band gap value reduces, the band curve is denser, and the total density of states moves down as a whole.In terms of optical properties, the doping of rare earth elements improves the static dielectric constant and light absorption performance, enhances the refractive index and reflectivity, and reduces the probability of electron absorption photon and energy loss.Among them, La-Y co-doped system changes obviously.

Effect of Nitrogen Doping on the Perfomances of the Hydrogen Terminated Diamond RF Transistors

LIU Xiaochen, YU Xinxin, GE Xingang, JIANG Long, LI Yifeng, AN Xiaoming, GUO Hui

2021, 50(11):  2045-2052. 

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The microwave plasma chemical vapor deposition technology was employed to grow the single crystal diamond substrates with different crystalline qualities by changing the nitrogen content in the gas source. The sample size was controlled at 5 mm×5 mm×0.5 mm by laser cutting and polishing. The surfaces of diamond substrates were hydrogenated and the diamond RF transistors were fabricated on them. The influence of the nitrogen content on the crystalline quality of the diamond and the performance of the device has been systematically studied. With the increase of the nitrogen content, although the growth rate of the single crystal diamond increases, the FWHM of Raman and XRD rocking curves, as well as the corresponding NV defects in the photoluminescence spectra also gradually increases, indicating that the crystalline quality became worse, which not only degrade the carrier mobility of the channels, but also make the diamond RF transistor suffer from the problems of current collapse and performance degradations. By reducing the nitrogen content and improving the crystalline quality of the diamond, the carrier mobility significantly increases, the current gain cutoff frequency f_T and power gain cutoff frequency f_max significantly increases from 17 GHz and 22 GHz to 32 GHz and 53 GHz, respectively.

Effect of CaCO₃ Doping on Growth Behavior of Type Ⅰb Diamond along Different Crystal Faces

CHEN Jiaxi, ZHANG Xiyun, LI Shangsheng, GUO Mingming, HU Meihua, SU Taichao, HUANG Guofeng, LI Zhanchang, ZHOU Zhenxiang, NIE Yuan, WANG Mengzhao, ZHOU Xubiao

2021, 50(11):  2053-2059. 

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It is of great academic value to study the influence of carbonate doping on the growth behavior of synthetic diamond crystals. In this paper, CaCO₃ was doped into the carbon source in the diamond synthesis cavity at different ratios using the temperature gradient method at high pressure and high temperature (HPHT). The purpose of the study is to investigate the effect of CaCO₃ doping on the growth behavior of diamond along the (100) or (111) crystal plane, respectively. The crystal morphology of doped synthetic diamonds was studied by optical microscopy. The results show that with the increase of the CaCO₃ content, the crystal shape of diamond growing along the (100) plane change from tower to plate accompanied by crack crystal or crystals stock. The color of the crystal becomes lighter and then darker, and the inclusions appear in diamond. Besides, the crystal shape of diamond growing along (111) surface gradually changes from plate to tower accompanied by crack and twin crystals phenomena. With the increase of the CaCO₃ content, the color of diamond crystals gradually becomes darker, and more inclusions appear in diamond. The Raman spectroscopy results show that with the increase of CaCO₃ content, the Raman peak position shifts of doped diamond growing along (100) or (111) plane increase, and the full width at half maximum (FWHM) becomes larger. This indicates that the doping of CaCO₃ increases crystal lattice distortion and internal stress of diamond. In this paper, the causes for the effect of CaCO₃ doping on the crystal shape, color, internal quality and other behaviors of the diamond growing along the two different faces were analyzed, which lays the foundation for the subsequent study of this topic.

Growth Characteristics of Type Ⅰb Diamonds in FeNi, NiMnCo and Their Composite Catalysts

WANG Mengzhao, XU Antao, LI Shangsheng, GAO Guangjin, HU Meihua, SU Taichao, HUANG Guofeng, LI Zhanchang, ZHOU Zhenxiang, NIE Yuan, CHEN Jiaxi, ZHOU Xubiao

2021, 50(11):  2060-2066. 

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In this paper, Ni₇₀Mn₂₅Co₅ and Fe₆₄Ni₃₆ alloys and their composite alloys were used as catalysts to study the growth characteristics of typeⅠb diamonds grown along (100) crystal plane at different temperatures under 5.6 GPa pressure by high temperature and high pressure temperature gradient method. The results show that the diamond synthesized with Fe₆₄Ni₃₆ catalyst has a cracking growth zone of about 50 K in the high temperature growth range of (111) crystal plane. The diamond synthesized with Ni₇₀Mn₂₅C_o5 catalyst is prone to crystal stock defects in the growth range, especially in the high temperature crystal growth range of (111) crystal plane. The excessive melting of Fe₆₄Ni₃₆ catalyst at high temperature may be the cause of crystal cracking, and the low viscosity of Ni₇₀Mn₂₅Co₅catalyst melt may be the reason for easy formation of crystal stock. The combination of two kinds of catalysts can effectively avoid the formation of cracking and crystal stock. Raman spectroscopic characterization shows that the internal quality of crystal stock is similar to that of single crystals. There are more lattice distortion and impurities in the cracky crystals and the stress in the crystal is larger.The diamond crystal synthesized by compound catalyst system has low internal stress and good quality.

Tribological Properties of SiC-Based Diamond Films Synthesized with Different Methane Concentrations

WANG He, SHEN Jianhui, YAN Guangyu, WU Yuhou, ZHANG Huisen

2021, 50(11):  2067-2074. 

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Diamond films with different methane concentrations were deposited on silicon carbide substrate by hot filament chemical vapor deposition (HFCVD). The morphology and phase of the diamond films were analyzed using field emission scanning electron microscope, Raman spectrometer, and atomic force microscope. The friction coefficient and wear rate of all the diamond films were calculated in dry sliding condition by the reciprocating friction experiment. Phase analysis and friction experiment results were used to analyze the influence of methane concentration on diamond film tribological properties. Results show that the quality of diamond crystals deteriorates with the increase of methane concentration, and the film changes from microcrystalline to nanocrystalline. The diamond film with 3% methane concentration has better wear resistance and the wear rate is 2.2×10^-7 mm³/mN; the friction coefficient of diamond films prepared at 5% methane concentration is lower (0.032), and the wear rate is 5.7×10^-7 mm³/mN. Compared with the silicon carbide substrate (9.89×10^-5 mm³/mN), the wear rate of the diamond film is improved by two orders of magnitude, which significantly improves the wear resistance of the silicon carbide substrate.

Optoelectronic Properties of Two-Dimensional MoS₂/WSe₂ Heterojunction

HUANGFU Luyao, DAI Mengde, NAN Haiyan, GU Xiaofeng, XIAO Shaoqing

2021, 50(11):  2075-2080. 

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In recent years, phototransistors based on two-dimensional semiconductors like transition metal di-chalcogenides including MoS₂ have been studied extensively. Although the phototransistor based on monolayer MoS₂ exhibits a high responsivity, its low carrier mobility also limits the response time of the photodetector to order of seconds. The stacking of two-dimensional semiconductors can form uniform van der Waals heterostructures with low trap defect states, and this is an effective way to improve the performance of two-dimensional photodetectors. In this work, MoS₂/WSe₂ vertical heterostructures were constructed via mechanical exfoliation and transferring method. The strong space charge region originating from the heterojunction can effectively separate the photo-generated carriers, therefore, the as-fabricated photodetectors have good photoelectric detection ability in self-powered mode. The responsivity and detectivity reach 2.12×10³ A/W and 2.33×10¹¹ Jones, respectively. Meanwhile, the response time of the heterojunction device greatly reduces to 40 ms. Such two dimensional heterojunction devices possess the advantages of simple fabrication method and good performance, and has a broad application prospect in the field of optoelectronics.

Synthesis, Structure and Photoluminescent Properties of Ca_1.8Li_0.6La_0.6-x(PO₄)₂∶xEu³⁺Phosphor with Whitlockite Structure

TANG Wanjuan, GUO Qingfeng, SU Ke, MEI Lefu, LIAO Libing

2021, 50(11):  2081-2085. 

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Whitlockite is an excellent luminescent material. It has lower synthesis temperature and an abundance of adjustable crystal lattice.Ca_1.8Li_0.6La_0.6-x(PO₄)₂∶xEu³⁺ (x=0,0.01,0.03,0.06,0.09,0.15) was synthesized by high temperature solid state reaction at 1 250 ℃, and its structure and luminescent properties were characterized by X-ray powder diffraction (XRD) and fluorescence spectrometer. The results show that the phosphors belongs to whitlockite structure, and the doping of Eu³⁺ does not change the structure to a great extent. The phosphor in the system emits red light, and the characteristic emission of Eu³⁺ appears in the emission spectrum. The strongest emission peak locates at 617 nm and comes from ⁵D₀→⁷F₂ transition of Eu³⁺. As the concentration of Eu³⁺ increases, the fluorescence lifetime decreases, which proves the existence of energy transfer between Eu³⁺.

Preparation and Photocatalytic Performance of TiO₂/Ni₃[Ge₂O₅](OH)₄ Composite Material

MIN Tao, MA Guohua, LIU Guijun, ZHENG Yuting

2021, 50(11):  2086-2092. 

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Using Ni₃[Ge₂O₅](OH)₄ as the carrier and ammonium fluorotitanate as the raw material, the nano-TiO₂/Ni₃[Ge₂O₅](OH)₄ composite material was prepared by the hydrothermal-assisted liquid phase deposition method. The phase composition, structural characteristics and microscopic morphology were tested and analyzed through X-ray diffraction (XRD), Raman spectroscopy (RM), field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HTEM), ultraviolet-visible absorption spectroscopy (UV-Vis) and other characterization methods, and the effect of different loadings of titanium dioxide on the photodegradability of methylene blue of the nano-TiO₂/Ni₃[Ge₂O₅](OH)₄ composite material was explored. The results show that the experiment has realized the close combination and effective dispersion of nano-TiO₂ and Ni₃[Ge₂O₅](OH)₄. The TiO₂ has an anatase structure with an average particle size of 20 nm. The composite material can effectively inhibit the recombination of photo-generated carriers, improve the adsorption performance of the material, and increase the photocatalytic efficiency of the material. When the molar ratio of TiO₂ to Ni₃[Ge₂O₅](OH)₄ in the composite material is 3.1∶1, the material has the highest photocatalytic efficiency for methylene blue, and the photodegradation rate of methylene blue in 90 min is 99.81%.

Synthesis of Potato-Based Carbon Quantum Dots, Mn Doping and Their Application in Ag⁺ Detection

LI Jiayao, HAN Weijie, YANG Zhouping, SHI Yangfan, LU Shiping, LIU Xinmei

2021, 50(11):  2093-2102. 

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In this study, carbon quantum dots (CQDs) were prepared using potato as carbon source via hydrothermal method, and then Mn-doped CQDs (Mn-CQDs) were prepared by the addition of manganese carbonate as dopant in the reaction system. CQDs and Mn-CQDs were characterized by transmission electron microscopy (TEM), X-ray diffraction spectroscopy (XRD), X-ray photoelectron spectroscopy (XPS), UV-Vis absorption spectroscopy, photoluminescence (PL) spectroscopy, and infrared spectrometer. The results show that CQDs and Mn-CQDs are spherical with an average particle size of 3 nm to 5 nm. Mn doping enhanced the intensity and stability of photoluminescence of CQDs. The maximum excitation wavelengths of CQDs and Mn-CQDs are 435 nm and 395 nm, and the corresponding emission wavelengths are 525 nm and 465 nm, respectively. In the application of the detection of metal ions, both CQDs and Mn-CQDs exhibit good selectivity to Ag⁺, and the low detection limits of CQDs and Mn-CQDs to Ag⁺ are 0.064 μmol/L and 0.027 μmol/L, respectively, indicating the relatively high sensitivity of Mn-CQDs in the trace detection of Ag⁺compared to CQDs.

Synthesis, Structure and DNA Photocleavage of a Polypyridine Copper(Ⅰ) Complex

ZHANG Qin, HUANG Yu, LI Zhimin, HU Mai, LIAO Xiangwen, WANG Jintao

2021, 50(11):  2103-2108. 

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In this paper, a copper complex [CuL₂](PF₆)₃·H₂O(complex 1) was synthesized using 1-methyl-4′-(p-tolyl)-2,2′,6′,2″-terpyridine hexafluorophosphate (L) as the ligand. The structure of the synthesized complex was characterized by X-ray single crystal diffraction technique, thermogravimetric analysis and X-ray photoelectron spectroscopy (XPS). The results of single crystal diffraction analysis show that the complex belongs to the monoclinic crystal system, the P_1/c space group, and the unit cell parameters were a=1.273 15(10) nm, b=1.902 01(13) nm, c=2.109 55(17) nm, β=101.269(2)° and V=5.009 9(7) nm³. The XPS analysis result shows that the copper ions in complex 1 exists in the form of +1 valence. Thermogravimetric analysis shows that the complex has good thermal stability. DNA photocleavage studies monitored by agarose gel electrophoresis shows that the complex cleaved DNA efficiently, which indicates that the complex has obvious potential biological activity.

Green Synthesis and Characterization of Lead(Ⅱ) Coordination Polymer of Pyridine-2,6-Dicarboxylate

SUN Dawei, TAN Sihui, LUO Huan, CHEN Zhaohui, ZHONG Guoqing

2021, 50(11):  2109-2115. 

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The coordination polymer [Pb(μ-pda)]_n (1) was synthesized with pyridine-2,6-dicarboxylic acid (H₂pda) and lead acetate as raw materials by room temperature solid state reaction. The composition and structure of 1 were characterized by elemental analysis, X-ray powder diffraction, X-ray single crystal diffraction and infrared spectroscopy. Its thermal stability and fluorescence properties were also studied. The single crystal structure shows that 1 belongs to monoclinic system with space group P2₁/n, and the cell parameters are a=0.980 84(11) nm, b=0.554 73(7) nm, c=1.433 62(16) nm and β=105.093(3)°. The molecular structure of 1 is composed of two Pb²⁺ and two pda^2-. It contains two [Pb(μ-pda)] units, each Pb²⁺ center is coordinated with six oxygen atoms and one nitrogen atom from pda^2- to form a seven coordinated single-cap triangular prism configuration. The thermal stability study shows that the thermal decomposition reaction of 1 in nitrogen atmosphere include the collapse of complex framework and the oxidative decomposition of ligand, and the final residue is PbO. The fluorescence property of 1 indicates that the coordination polymer has fluorescence, which may come from the fluorescence inside the ligand π^*→π charge transition.

Crystal Structure and Density Functional Theory of 5-Bromo-2-(4-Methylpiperidin-1-yl)Pyrimidine

YE Wenjun, CHEN Yumei, CHEN Dongmei, GUO Qian, ZHOU Zhixu

2021, 50(11):  2116-2122. 

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Pyrimidine derivatives have important applications in the fields of medicine, chemical industry and functional materials. In drug discovery, especially in the research and development of anticancer drugs, 5-bromo-2-(4-methylpiperidin-1-yl)pyrimidine is a significant intermediate containing a pyrimidine ring. In this paper, 5-bromo-2-(4-methylpiperidin-1-yl)pyrimidine was prepared by one-step aromatic nucleophilic substitution reaction, and its single crystal was obtained by solution crystallization, and crystallographic analysis was carried out (crystal system: orthorhombic, space group: P2₁2₁2₁, unit cell: a=10.181 42(6) nm, b=17.620 0(8) nm, c=10.179 02(5) nm, Z=4, ρ_c=1.478 g·cm^-3, R=0.056 6, wR=0.168 8). By the way, the crystal structure shows that the intramolecular hydrogen bonds and the van der Waals forces jointly maintain the stable arrangement of molecules space, and hydrogen bonds are one of the key factors for crystal stability. In B3LYP/6-311G(d, p) mode, density functional theory (DFT) was used to calculate the optimal structure and frontier orbit energy, and the result of DFT optimization is similar to the experimentally determined data. The structure and the results are basically the same. In addition, in order to further reveal the physicochemical properties of the title compound, the molecular electrostatic formula and frontier molecular orbital were further investigated by DFT.

Structure and Electrocatalytic Performance of a Keggin-Type Polyoxometalate-Based Supramolecular Complex H₃[{H(4-AP)}₆(PMo^V₆Mo^VI₆O₄₀)]

XU Na, WANG Jinling, ZHANG Zhong, LI Xiaohui, CHANG Zhihan

2021, 50(11):  2123-2128. 

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A Keggin-type polyoxometalate-based supramolecular complex H₃[{H(4-AP)}₆(PMo^V₆Mo^VI₆O₄₀)] (4-AP=4-aminopyridine) was successfully synthesized from ammonium molybdate, nickel chloride, and 4-aminopyridine by hydrothermal method. The structural unit of the complex contains a [PMo^V₆Mo^VI₆O₄₀]^9- anion and six protonated ligands. [PMo^V₆Mo^VI₆O₄₀]^9- anion and ligands are connected to each other by N(1)—H(1)…O(3), N(2)—H(2A)…O(5), and N(2)—H(2B)…O(1) hydrogen bonds, which further form a two-dimensional supramolecular layer. It was characterized by X-ray single crystal diffraction, IR spectra, and powder X-ray diffraction. The crystal structure analysis shows that the complex belongs to the trigonal crystal system, R-3 space group, a=2.191 2 (10) nm, b=2.191 2 (10) nm, c=1.042 3 (5) nm, α=β=90°, γ=120°, V=4.333 8 (4) nm³, Z=3, R₁=0.036 2, wR₂=0.095 6. The electrocatalytic performance shows that the complex has a good electrocatalytic reduction effect on H₂O₂ and K₂Cr₂O₇. It also has a good effect of electrocatalytic oxidation on ascorbic acid.

Synthesis, Structure and Characterization of Co(Ⅲ)/Cu(Ⅱ) Complexes Based on Organic Carboxylic Acid Ligands

BAO Yuting, LI Haichao, MA Qin, SUN Zan

2021, 50(11):  2129-2137. 

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Two novel complexes, namely [Co(L′)₃] (1) and [Cu(L′)₂]_n (2) (HL′=5-bromopyridine-2-carboxylic acid), were obtained under solvothermal conditions by the assembly process of organic carboxylate ligand containing halogen (3-bromopyridine-2,6-dicarboxylic acid, H₂L) and Co(NO₃)₂·6H₂O or Cu(NO₃)₂·3H₂O respectively, and characterized by element analysis (EA), X-ray single diffraction (SXRD), X-ray powder diffraction (PXRD), infrared spectroscopy (IR) and thermogravimetric analysis (TGA). The single crystal X-ray diffraction reveals that ligand H₂L transform to HL′ during a decarboxylation process. In the asymmetric unit of 1, there are two mononuclear units. In each unit, central Co(Ⅲ) ion is in a slightly distorted octahedron. Complex 1 shows mononuclear structure, forming a three-dimensional (3D) supramolecular structure via C—H…O hydrogen bonding interactions. The asymmetric unit of 2 contains one central Cu atom and two L′^- ligands. In each unit, central Cu(Ⅱ) ion is in a slightly distorted octahedron. Complex 2 exhibits 1D chain structure, forming a three-dimensional (3D) supramolecular structure via C—H…O hydrogen bonding interactions. Furthermore, the stability property of complexes 1 and 2 was also investigated.

Charge Transport Properties of Spirofluorene-Based Hole Transport Materials

HU Weixia, YANG Jixin, HUANG Kai, HE Rongxing

2021, 50(11):  2138-2143. 

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Spirofluorene-based hole transport materials have attracted much attention because of their excellent photoelectric properties. In order to explore the charge transport mechanism, the electronic structure, recombination energy and electron coupling of three spirofluorene-based small molecular hole transport materials were studied by density functional theory. Combined with Marcus charge transfer theory, the carrier mobility of all small molecules is accurately calculated and compared with the experimental data. The results show that the hole mobilities of X60 and HT2 molecules are in good agreement with the experimental data, which is in the same order of magnitude, indicating that the theoretical model is feasible to accurately calculate the hole mobility of molecules. In addition, the hole mobility of ST2 is 1.82×10^-4 cm²·V^-1·s^-1, and it displays good stability, which indicates that the modification of heteroatoms in spiro-rings can further improve the performance of hole transport materials. This work provides an important strategy for the development of efficient hole transport materials.

Synthesis of Lithium Titanium Ion Sieve by Sol-Gel Soft Template Method

SUN Jianke, CHEN Jin, ZHAO Kun, LIU Lu, LIU Yingying, YI Dawei

2021, 50(11):  2144-2149. 

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With lithium acetate and butyl titanate as lithium and titanium sources, and cetyltrimethylammonium bromide (CTAB) as the soft template, the sol-gel method is used to obtain CTAB-added lithium titanium by roasting. The compound (Li₄Ti₅O₁₂) was pickled with hydrochloric acid to prepare a lithium titanium ion sieve (H₄Ti₅O₁₂, HTO). The effects of crystal phase, morphology and time on the adsorption capacity of lithium titanium ion sieve were investigated by thermogravimetric analysis (TG-DTG), X-ray diffraction (XRD), scanning electron microscopy (SEM), contact angle and performance tests. Compared with the addition amount of CTAB, 0.1 g CTAB ionic sieve precursor has fewer impurities and pure crystal phase. The quasi-second-order kinetic correlation coefficient R²(0.997 24) of HTO is greater than that of first-order kinetic correlation coefficient R²(0.984 35), indicating that the adsorption process is consistent with chemisorption. The adsorption capacity of HTO in Li⁺ solution for 24 h reaches 24.44 mg/g, and after 8 times of adsorption and desorption, the adsorption capacity remains at 23.68 mg/g, only reduces by 3.1%. Therefore, HTO has good cyclic adsorption performance and stability, and has a broad market prospect.

CoO Porous Nanosheets Array/Carbon Cloth as Flexible Anode Material for Lithium-Ion Batteries

WANG Jun, ZHAO Yu, FAN Baoyan, ZHANG Jun, XING An, LIU Xiaoyan

2021, 50(11):  2150-2155. 

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In recent years, flexible electronics is an emerging and promising technology for next generation of optoelectronic devices. The study of new inexpensive, flexible and lightweight electrode materials has triggered a gold rush. Herein, hierarchical porous CoO nanosheets arrays/carbon cloth composites successfully synthesized were using a hydrothermal reaction followed by calcination. The three-dimensional network structure can accommodate large mechanical strains by providing the gaps to alleviate volume change. The porous structure can improve the specific surface area of the active substance CoO, which is conducive to the improvement of lithium storage capacity of electrode materials. When investigated as flexible anode for lithium-ion batteries, the CoO porous nanosheets array/carbon cloth materials achieve an initial charge capacity of 1 862.8 mAh·cm^-2 with coulombic efficiency of 87.8% at constant current of 100 mA·cm^-2. The reversible capacity is 1 428.9 mAh·cm^-2 after 100 cycles at current density of 700 mA·cm^-2. And it is capable to retain a capacity of 1 353.8 mAh·cm^-2 even at current density of 1 000 mA·cm^-2. The excellent electrochemical performance of the composites could be attributed to the unique morphology, structure of the CoO porous nanosheets, as well as directly grown on current collector. Thus, this work introduces an easy and economic method for fabrication CoO porous nanosheets array/carbon cloth materials for high-performance flexible lithium ion battery.

Synthesis and Photocatalytic Performance of Catalytic Graphitization of g-C₃N₄ Carbonaceous Materials

LI Yue, WANG Bo, ZHU Xiaoli, LIU Kun

2021, 50(11):  2156-2163. 

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The preparation methods for porous graphitic carbon materials have mostly employed a conventional two-step strategy, in which hydroxides act as the pore-forming agent and transition metal nitrates or chlorides as the graphitization catalyst. However, most of the reagents mentioned above are toxic and corrosive, and multi-step processes are time-consuming. In this work, a one-step strategy to synthesize porous graphitic g-C₃N₄-derived carbon materials was established, and its photocatalytic performance was studied. The g-C₃N₄ bulks were prepared by conventional thermal polycondensation approach from dicyandiamide. Potassium ferrate (K₂FeO₄) was utilized as both activating agent and catalyst to fulfil the synchronous carbonization and graphitization of g-C₃N₄, this method is less time-demanding, highly efficient and pollution-free, when compared with a conventional two-step strategy. The g-C₃N₄-derived carbon materials delivers not only significantly improved visible-light absorption but also greatly enhanced photocatalytic activity compared to pristine g-C₃N₄. The effect of g-C₃N₄-derived carbon materials with different graphitization temperature on the degradation of methyl orange (MO) solution under visible light was studied. The results indicate that the degradation rate of g-C₃N₄-derived carbon materials prepared at 700 ℃ is 12.4 mg/g. Photoelectrochemical measurements reveal that the porous graphitic samples exhibit improved carrier densities, charge separation, and photocurrent (a 5.4-fold increase) compared to that of the original g-C₃N₄. Consequently, this facile and versatile method could provide a promising and cost-effective approach to improve the absorption and photocatalysis performance of g-C₃N₄-derived carbonaceous materials.

Reviews

Construction and Application of Structural Color Contact Lenses Based on Photonic Crystals

WANG Xiaomei, WANG Zhao, HAO Lingyun, ZHANG Xiaojuan, LIU Chu

2021, 50(11):  2164-2172. 

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Photonic crystals (PCs), consisting of periodic arrays with different refractive indices, have been widely used in the fields of energy conversion, sensing, display and anti-counterfeiting due to their attributes of regulating the transmission of lightwaves. Contact lenses (CLs), traditionally used for vision correction, show long-term wearing safety, thus providing a wearable platform for continuous ocular physiological parameters (glucose, intraocular pressure (IOP), corneal temperature, and pH value etc.) monitoring and drug delivery. In this review, PCs and CLs are introduced, and an overview of recent advances of construction strategy of structural color CLs based on PCs and their applications as ophthalmic sensors and UV protection are illustrated. Finally, the existing problems and development trends are forecasted.

Research Progress of WO₃ Crystal Facet Tuning by Organic Structure Inducers

CUI Jiameizi, ZHENG Jinyou, ZHANG Kaidi, ZHAI Zihao, MA Wei, ZHANG Lili, YU Xiaomei

2021, 50(11):  2173-2182. 

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Solar semiconductor photocatalysis technology has been widely studied by researchers all over the world because of its green pollution-free, renewable and beneficial solution to global warming. Since the catalytic activities of semiconductor photocatalysts depend on their surface electron structures and atomic structures, which are strongly dependent on the crystal face, the catalytic activities of photocatalysts are significantly affected by the crystal surface exposed in the reaction process. In recent years, crystal facet tuning engineering has become a very important method of fine-tuning the physical and chemical properties of semiconductors. Tungsten trioxide (WO₃) semiconductor catalyst is often used for photoanode in photoelectrochemical systems because of its good photocatalytic properties. In this paper, the recent progress of organic substances (organic small molecules and organic macromolecules) as structural inducers for the WO₃ crystal structure regulation is reviewed, the mechanism and principle of the regulation of organic substances on crystal surface are introduced, looking for new experimental direction and breakthrough points, summarizing the current applications of WO₃ photoelectrocatalysis in real life, such as solar water splitting, electrochromism, gas sensors, degradation of organic pollutants, etc. Finally, perspectives are given on the interesting research direction that may guide future studies.

Research Progress on Preparation of Ti₃C₂T_x MXene and Its Application in Supercapacitors

NIU Lili, WANG Pei, ZHANG Li, LIU Yanbin, FU Fengyan

2021, 50(11):  2183-2191. 

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Two dimensional (2D) material Mxenes has attracted extensive attention as supercapacitor electrode materials because of its high specific surface area, high conductivity and solution processability. Several preparation methods of Ti₃C₂T_x MXene such as HF and fluoride based etching, alkali based etching, electrochemical etching and Lewis acid molten salt etching are summarized. The assembly strategies of Ti₃C₂T_x MXene electrode materials such as vacuum assisted filtration, cationic self-assembly, layer by layer assembly, printing process, assembly of MXene aerogels, hydrogels, and their applications in supercapacitors are reviewed. Many studies have shown that the structure and the electrochemical performance of MXene electrodes is considerably affected by different preparation methods and electrode assembly strategies. The preparation methods and electrode assembly strategies of Ti₃C₂T_x MXene are compared and summarized, the existing problems in the research are pointed out, and the future research direction of MXene is prospected.

Review on Echelon Utilization and Recovery Methods of Cathode Materials from Retired Lithium Iron Phosphate Battery

LIU Mengning, LI Xiaoqiang

2021, 50(11):  2192-2203. 

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With the rapid development of electric vehicles, the consumption of lithium-ion batteries (LIBs) is increasing fast. Lithium iron phosphate batteries (LFPBs) have a large stock in the market due to their superior safety performance, long service life, low price of raw materials, environmental friendliness and mature technology. Therefore, the scrap volume of retired lithium iron phosphate batteries is also increasing, and research of its recycling methods is imminent. This article summarizes the current status of the echelon utilization of lithium batteries, including multiple methods for determining the performance of retired lithium iron phosphate batteries, applications for different residual energy, analysis of return on investment, and the recovery of metals in lithium iron phosphate batteries. Several processes were compared including physical methods such as crushing, pneumatic separation, eddy current, and cold-shocking, chemical methods such as leaching, precipitation, activation, and biological leaching methods. Related technologies for repairing and regenerating lithium iron phosphate (LFP) are introduced, in order to achieve retiring maximize the utilization of lithium iron phosphate battery resources, and provide technical reference for subsequent research on recycling retired lithium iron phosphate batteries.