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Morphology and photocatalytic performance of nano-sized TiO_2 prepared by simple hydrothermal method with different pH values

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Rare Metals 2018年第9期37卷 750-758页

作者： Hao Xu Shi-Qi Liu Shan Zhou Tang-Zhi-Jiu Yuan Xiang Wang Xia Tang Jian Yin Hui-Jin Tao School of Material Science and Engineering Central South University State Key Laboratory for Powder Metallurgy Central South University Key Lab of Nonferrous Materials Science and Engineering Ministry of EducationCentral South University

pH value is a key factor in the preparation of nano-sized TiO2 with hydrothermal method. Using Ti（SO4）2 as the titanium source, H2O2 as the complexing agent, NaOH and HCl as the pH value regulator, nano- sized TiO2 powder with various morphologies and sizes was synthesized. Changes in morphology, size and phase type with pH values of samples were characterized by X-ray diffraction （XRD） and transmission electron micro- scopy （TEM） measurements. Results show that under the present preparation conditions, TiO2 powder is an anatase phase with pH value less than 11, but is more likely to be a brookite phase with pH value more than 11. With the increase in pH value from 1 to 11 in hydrothermal envi- ronment, nano-sized anatase TiO2 gradually grows up in all directions. {001 }, { 101 } and { 100} groups of crystal plane are the exposed crystal planes of nano-sized anatase TiO2 for the （004）, （101） and （200） facets found in high-reso- lution TEM image. The photocatalytic performance of nano-sized TiO2 with different morphologies was com- pared by measuring their photocatalytic degradation rates for methylene blue under ultraviolet light. Results show that anatase TiO2 prepared under the alkalescenthydrothermal environment （pH = 9, 11） has a better pho- tocatalytic degrading performance. Different sizes and phases of nanoscaled TiO2 powders with different photo- catalytic performances can be prepared by the control of pH value of hydrothermal solutions.

关键词： hydrothermal method pH value Anatase Brookite Nano-sized crystal morphology

Synthesis of potassium hexatitanate whiskers using hydrothermal method

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Rare Metals 2009年第1期28卷 24-32页

作者： WANG Ju LI Chun LIANG Bin WANG Xiaoqing College of Chemical Engineering Siehuan University Chengdu 610065 China Department of Chemistry Tsinghua University Beijing 100084 China

High quality potassium hexatitanate whiskers were hydrothermally synthesized in one step under moderate temperature and pressure conditions. Effects of the titanium source and reaction conditions on the hydrothermal reaction rate, product phase component, and morphology of whiskers were investigated. The results show that the reactivity of hydrated titania, anatase TiO2, and rutile TiO2 with KOH decreases in turn, and with hydrated titania as titanium source, it is difficult to obtain potassium hexatitanate whiskers with good morphology. In contrast, uniform potassium hexatitanate whiskers with a length of 10-20 μm and a diameter of 200-700 nm were obtained using anatase TiO2 as titanium source. The investigation demonstrates that the initial KOH concentration, annealing temperature and time, molar ratio of K2O/TiO2, etc. significantly affect the morphology of the as-synthesized whiskers. The optimized synthesis condition is as follows： anatase as a titanium source 10 wt.% KOH solution; annealing temperature and time of 300℃ and 5 h, respectively; K2O/TiO2 molar ratio of 5, etc. A rhombic potassium hexatitanate was prepared under the optimum condition and the whisker grew along the [110] direction. The reaction mechanism was discussed.

关键词： potassium hexatitanate whiskers hydrothermal method synthesis

Synthesis and electrochemical performance of LiCoPO_4 micron-rods by dispersant-aided hydrothermal method for lithium ion batteries

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Rare Metals 2009年第2期28卷 117-121页

作者： Zhao, Yujuan Wang, Suijun Zhao, Chunsong Xia, Dingguo College of Environmental and Energy Engineering Beijing University of Technology Beijing 100124 China

LiCoPO4 micron-rods with an average diameter of about 500 nm and length of about 5 μm were synthesized by dispersant-aided hydrothermal method. Poly(n-vinylpyrrolidone) (PVP) was used as dispersant in the hydrothermal method. The starting solution and the concentration of dispersant have significant influences on the morphology of LiCoPO4,and the electrochemical performance is improved via controlling the particle size and morphology by the hydrothermal method. The cell using smaller particle LiCoPO4 as cat...

关键词： lithium cobalt phosphate hydrothermal method dispersant morphology

Selective synthesis and growth mechanism of CeVO_4 nanoparticals via hydrothermal method

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Journal of Rare Earths 2011年第2期29卷 97-100页

作者：刘凤珍邵鑫尹贻彬赵利民孙巧珍邵珠伟刘雪华孟宪华 College of Materials Science and Engineering Liaocheng University State Key Laboratory of Solid Lubrication Lanzhou Institute of Chemical PhysicsChinese Academy of Sciences Renewable Energy & Eco-Materials Engineering Center Liaocheng University

Selective-controlled structure and shape of CeVO4 nanocrystals were successfully synthesized via a hydrothermal method from Na3VO4·12H2O and Ce（NO3）3·*** resulting products were characterized by X-ray powder diffraction （XRD）,field emission scanning electron microscopy （FESEM） and energy dispersive spectroscopy （EDS）.The influence of hydrothermal temperature,precursor solution concentration on the crystal and morphology of products were further *** results showed that the as-synthesized products exhibited pure single-crystal CeVO4 nanoparticles with tetragonal *** hydrothermal temperature and precursor solution concentration had important effects on the formation of CeVO4 ***,the growth mechanism of CeVO4 nanoparticles was explained with Ostwald ripening mechanism.

关键词： CeVO4 hydrothermal method temperature precursor solution concentration Ostwald ripening mechanism rare earths

N-doped NaTaO3 synthesized from a hydrothermal method for photocatalytic water splitting under visible light irradiation

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Journal of Energy Chemistry 2017年第3期26卷 515-521页

作者： Che-Chia Hu Hui-Hsin Huang Yu-Chi Huang Department of Chemical Engineering and R&D Center for Membrane Technology Chung Yuan Christian UniversityTaoyuan City 32023TaiwanChina

NaTaONcatalysts were synthesized by a hydrothermal（H） and a solid-state（S） methods in this *** H-and S-NaTaONsamples were characterized by X-ray diffraction（XRD）, scanning electron microscopy（SEM）, transmission electron microscopy（TEM）, UV–visible（UV–vis） diffuse reflectance spectroscopy, and photoluminescence（PL） spectroscopy. The XRD patterns of the H-and S-samples showed peaks indexed to the pure phase of perovskite NaTaOand minor peaks assignable to TaNat various synthesis temperatures. Substitution of oxygen by nitrogen ions causes the light absorption of the H-and S-NaTaONsamples to be extended to the 600–650 nm region, thus making the samples visible-light active. The NaTaONsamples exhibited photocatalytic activity for Hand Oevolution from aqueous methanol and silver nitrate solutions under visible-light irradiation. The UV–vis and PL spectra of the Hand S-catalysts revealed the presence of cationic vacancies and reduced metallic species, which acted as recombination centers. These results demonstrated that the preparation method plays a critical role in the formation of defect states, thereby governing the photocatalytic activity of the NaTaONcatalysts.

关键词： Photocatalysis H2 production N-doped NaTaO3 hydrothermal method Visible light

Growth Mechanism of Different Morphologies of ZnO Crystals Prepared by hydrothermal method

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Journal of Materials Science & Technology 2011年第2期27卷 153-158页

作者： Hu Wang Juan Xie Kangping Yan Ming Duan State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation Southwest Petroleum UniversityChengdu 610500China College of Materials Science and Engineering Southwest Petroleum UniversityChengdu 610500China School of Chemical Engineering Sichuan UniversityChengdu 610000China

Different morphologies of zinc oxide（ZnO）,including microrods,hexagonal pyramid-like rods and flower-like rod aggregates,had been synthesized,respectively,on glass substrates by controlling the reaction conditions（such as precursor concentration,reaction time and pH value） of hydrothermal *** morphologies of the as-obtained ZnO were observed with scanning electron microscopy and transmission electron ***,the crystalline natures of different ZnO crystals were analyzed with X-ray *** possible growth mechanism of ZnO crystals with different morphologies was discussed.

关键词： Zinc oxide Surface morphology Growth mechanism hydrothermal method Crystal structure

Effects of metal ions on the morphology of calcium sulfate hemihydrate whiskers by hydrothermal method

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Frontiers of Chemical Science and Engineering 2017年第4期11卷 545-553页

作者： Tianjie Liu Hao Fan Yanxia Xu Xingfu Song Jianguo Yu National Engineering Research Center for Integrated Utilization of Salt Lake Resources East China University of Science and Technology Shanghai China

The effects of Na＋, concentrations on the crystal Mg2＋, A13＋ and Fe3＋ ion morphology of calcium sulfate hemihydrate whiskers formed via a hydrothermal method have been studied. In the presence of A13＋ concentrations higher than 1x10-3 mol/L the whiskers were significantly shorter and thicker and the presence of Mg2＋ and Fe3＋ resulted in shorter whiskers. The presence of Nan did not affect the morphology of the whiskers. Through elemental analysis, it was determined that Mg2＋ and A13＋ were selectively adsorbed on the surfaces of the crystals, whereas Fe3＋ underwent a hydrolysis reaction to form a brown precipitate which decreased the ion concentration in the solution. These results indicate that in raw materials used for the industrial preparation of calcium sulfate whiskers, AI3＋ and Fe3＋ should be removed and the Mg2＋ concentration should be less than 8 x 10-3 mol/L in order to obtain pure whiskers with high aspect ratios.

关键词： metal ions morphology calcium sulfatehemihydrate whiskers hydrothermal method selectiveadsorption

Upconversion Luminescence Properties of Ho^(3+),Tm^(3+),Yb^(3+) Co-Doped Nanocrystal NaYF_4 Synthesized by hydrothermal method

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Journal of Rare Earths 2006年第6期24卷 757-760页

作者：杨魁胜李岩余朝义卢利平叶灿华张希艳 School of Materials Science and Engineering Changchun University of Science and TechnologyChangchun 130022China

Nanocrystal of upconversion （UC） phosphor Ho^3＋, Tm^3＋ , and Yb^3＋ co-doped NaYF4 was prepared by the hydrothermal method in the presence of the complexing agent EDTA. Under 980 nm diode laser excitation, the impact of different concentrations of Ho^3＋ ion on the UC luminescence intensity was discussed. The law of luminescence intensity versus pump power shows that the 474 nm blue emission, 538 nm green emission, and 642 nm red emission are all due to the two-photon process, while the 450 nm blue emission is a three-photon process. The UC mechanism and processes were also analyzed. The sample was characterized by transmission electron microscopy （TEM） and X-ray diffraction （XRD）. The result shows that Ho^3＋ ,Tm^3＋ , and Yb^3＋ co-doped NaYF4 prepared by the hydrothermal method exhibits a hexagonal nanocrystal.

关键词： hydrothermal method upconversion EDTA Nanocrystal NaYF4 : Ho^3+ , Tm^3+ , Yb^3+ rare earths

Upconversion Luminescence of YLiF_4∶Er^(3+) Synthesized by hydrothermal method

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Journal of Rare Earths 2005年第6期23卷 657-661页

作者：赵谡玲侯延冰裴晓将徐征 Institute of Optoelectronic Technology Beijing Jiaotong University The Laboratory of Materials for Information Storage and Displays Beijing 100044 China Institute

YLiF4： Er^3＋ was synthesized by hydrothermal method. Concentration of Er^3＋ is changed from 0 to 5 %. The absorption of Er^3＋ in all samples from 200 to 1200 nm was measured at room temperature. The J-O parameters calculated from absorption spectrum are Ω2： = 1.05 × 10^-20 cm^2, Ω4 = 1.25 × 10^-20 cm^2 and Ω6 = 1.35 × 10^-20 cm^2 Infrared-to-visible upconversion emission of YLiF4：Er^3＋ was observed when excited by 980 nm. The results show that the Er^3 ＋ content is less than 1.5 %, excite-state absorption is the main mechanism of upconversion emission. When Er^3＋ content is larger than 1.5%, both of the excite-state absorption and energy transfer lead to the upconversion luminescence. The upconversion intensity was enhanced with the increasing of Er^3＋ concentration. At room temperature, the lifetime of ^2H11/2 and ^4S3/2 is 205 μs while that of ^4F9/2 is 188 μs for sample Er-2. The transition rates and quantum efficiency were also calculated. The quantum efficiencies of ^4S3/2 and 4F9/2 are 27.9% and 10.7%, respectively.

关键词： upconversion luminescence YLiF4 hydrothermal method rare earths