Aggregation of self-assembled Ni(OH)2 nanosheets under hydrothermal conditions

We investigate aggregation process of the Ni(OH)₂ under hydrothermal condition. The samples are characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results show that the self-assembled Ni(OH)₂ nanosheets with the hexagonal structure is about 30 nm in thickness. We investigate the effect of reaction temperature on the morphology of the product. The nanosheets can aggregate together when the temperature and reaction time are suitable. And a possible mechanism is also proposed to explain the growth and aggregation process of Ni(OH)₂ nanosheets.     

MoS2-ZnO多孔纳米片的光催化及其室温气敏传感性能

为开发一种高性能、可回收、低成本的光催化剂,本论文使用水热法制备了多孔结构的ZnO纳米片复合MoS₂ （MoS₂-ZnO）光催化材料。通过XRD、SEM、光致发光光谱（PL）、XPS等手段对样品的形貌、光学性质等进行了测试表征。结果表明,所制备的MoS₂-ZnO样品为多孔片状结构;这种复合结构中MoS₂不仅有助于增强ZnO中光生载流子的分离效率,而且还能增强可见光区的吸收,从而提高光催化和气敏性能。在模拟太阳光下,MoS₂-ZnO纳米复合材料对高浓度（15 mg/L）的亚甲基蓝染液（MB）表现出较高的光催化降解活性。同时,MoS₂-ZnO制备的气敏传感器对低浓度（2.05 mg/m³）NO₂还具有较高的灵敏度。本工作为制备高效太阳能驱动的光催化剂和气体传感器提供了重要参考。     

二硫化钼/石墨烯复合材料的一步水热合成及电催化性能EI北大核心CSCD

为提高催化剂的催化活性及稳定性,采用一步水热法合成二硫化钼/石墨烯(MoS 2/RGO)复合催化剂。利用X射线衍射仪、扫描电子显微镜、透射电子显微镜及旋转圆盘电极等分别对催化剂的物理-化学性能进行表征。结果表明:与石墨烯复合后,MoS 2呈少层花瓣状结构,层间距增加且均匀附着在石墨烯薄层上;二硫化钼催化剂的氧还原过程主要以二电子途径进行,而MoS 2/RGO复合催化剂在氧还原过程中可发挥协同催化作用,其氧还原过程中平均转移电子数为3.58,且复合催化剂在20000 s后的电流密度保持率高达89.7%。     

生物分子辅助水热法合成花状二硫化钼

以钼酸钠和硫代乙酰胺为原料,生物分子L-白氨酸为添加剂水热条件下合成了花状二硫化钼(MoS2),并通过X-射线衍射,X-光电子能谱以及冷场发射扫描电镜对产物的结构和性质进行了表征和分析.通过考察反应温度、氨基酸的种类等对产物形貌的影响,得出只有当用L-白氨酸作添加剂且其用量为lmmol,反应温度为220℃时才能得到形貌...     

Photoluminescence of Diamond Films and Ultrafine Diamond under UV Laser Excitation

Time-resolved photoluminescence spectra of diamond films and synthetic diamond powders are measured under pulsed UV laser excitation at time delays in the range 0–50 ns. The results are compared with the photoluminescence spectra of synthetic and natural diamond single crystals. The luminescence decay time is determined for the diamond films and ultrafine diamond.     

Photocatalytic performance of pure anatase nanocrystallite TiO2 synthesized under low temperature hydrothermal conditions

Photocatalytic performance of a hydrothermally synthesized pure anatase TiO₂ with 8 nm average crystallite size for decomposition of Reactive Red 141 was examined by investigating the effects of UV-light irradiation time, irradiation power, amount of TiO₂ and initial dye concentration. Change in the UV absorbance of the dye during irradiation was monitored. One wt.% TiO₂ in 30 mg/l Reactive Red 141 aqueous solution was found adequate for complete decolorization in 70 min at 770 W/m² irradiation power. It was realized that, compared to Degussa P-25, the synthesized nano-TiO₂ can be repeatedly used as a new catalyst. The results also proved that Reactive Red 141 is decomposed catalytically due to the pseudo first-order reaction kinetics.     

Electrical and photo-electrical properties of MoS2 nanosheets with and without an Al2O3 capping layer under various environmental conditions

The electrical and photo-electrical properties of exfoliated MoS₂ were investigated in the dark and in the presence of deep ultraviolet (DUV) light under various environmental conditions (vacuum, N₂ gas, air, and O₂ gas). We examined the effects of environmental gases on MoS₂ flakes in the dark and after DUV illumination through Raman spectroscopy and found that DUV light induced red and blue shifts of peaks (E¹_2 g and A_1 g) position in the presence of N₂ and O₂ gases, respectively. In the dark, the threshold voltage in the transfer characteristics of few-layer (FL) MoS₂ field-effect transistors (FETs) remained almost the same in vacuum and N₂ gas but shifted toward positive gate voltages in air or O₂ gas because of the adsorption of oxygen atoms/molecules on the MoS₂ surface. We analyzed light detection parameters such as responsivity, detectivity, external quantum efficiency, linear dynamic range, and relaxation time to characterize the photoresponse behavior of FL-MoS₂ FETs under various environmental conditions. All parameters were improved in their performances in N₂ gas, but deteriorated in O₂ gas environment. The photocurrent decayed with a large time constant in N₂ gas, but decayed with a small time constant in O₂ gas. We also investigated the characteristics of the devices after passivating by Al₂O₃ film on the MoS₂ surface. The devices became almost hysteresis-free in the transfer characteristics and stable with improved mobility. Given its outstanding performance under DUV light, the passivated device may be potentially used for applications in MoS₂-based integrated optoelectronic circuits, light sensing devices, and solar cells.     

Study on growth and photoluminescence of zinc telluride crystals synthesized by hydrothermal method

Zinc telluride powders were synthesized in sodium hydroxide solution by hydrothermal method by changing the growth temperature and time. The powders were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy and micro-Raman spectroscopy, respectively. The results indicate that zinc telluride crystallizes in zinc blende structure and their sizes were increased with the increase in temperature and time, and oxygen easily is incorporated into zinc telluride crystals. The photoluminescence of the powders were investigated at room temperature. The photoluminescence spectra exhibit the emission peaks related to complex defects containing zinc vacancies and impurities and excitons bound to isoelectronic oxygen traps at about 556 and 703 nm, respectively. The growth of zinc telluride crystals and the relation of the photoluminescence with the growth conditions were analyzed.     

水热法制备MnO2的电容特性

采用水热法制备了超级电容器MnO2电极材料,以单因素实验确定了最佳的制备条件为:水热处理温度为120℃和反应时间为6h.XRD测试结果表明,所制得的MnO2是α-MnO2和r-MnO2的混合晶型.最佳制备条件下所制得的MnO2的比电容达168.39 F·g-1.为改善MnO2的倍率特性进行Al掺杂,XRD的测试结果表明,Al3 进入到MnO2的晶格中.电化学测试结果表明,掺Al改善了电极材料的倍率特性和循环稳定性.     

Scalable salt-templated directed synthesis of high-quality MoS2 nanosheets powders towards energetic and environmental applications

Two-dimensional (2D) transition metal dichalcogenides (TMDCs) have emerged as perfect platforms for developing applications in nano-electronics, catalysis, energy storage and environmental-related fields due to their superior properties. However, the low-cost, batch production of high-quality 2D TMDCs remains a huge challenge with the existing synthetic strategies. Herein, we present a scalable chemical vapor deposition (CVD) approach for the batch production of high-quality MoS₂ nanosheet powders, by using naturally abundant, water-soluble and recyclable NaCl crystal powders as templates. The high-quality MoS₂ nanosheets powders are achieved by a facile water dissolution-filtration process, by virtue of the excellent dispersibility of the as-grown products in water. The internal mechanism for the scalable synthesis strategy is explored. The applications of the MoS₂ nanosheets powders are also demonstrated as catalysts or adsorbents in hydrogen evolution reaction (HER) and organic dyes adsorption, respectively. This work should hereby pave ways for the mass production and application of powdery TMDCs in energetic and environmental related fields.

     

Magnetic chains of Co spheres synthesized by hydrothermal process under magnetic field

Hydrothermal process under magnetic fields is successfully used to synthesize Co chains using reduction approach by carefully controlling the reaction conditions. The formation of the chain structure might be that magnetic fields drive the nanoscale crystals of Co to form chains. The Co sphere size and chain length are analyzed by X-ray diffraction (XRD) and scan electron microscopy (SEM). The result of the vibrating sample magnetometer (VSM) shows that the magnetic chains possess the saturation magnetization of 102 emu/g. The factors on the magnetic properties of the magnetic nanochains are discussed.     

Scalable synthesis of few-layered MoS2/C sandwiched nanocomposites via ionic crystal (NH4)2MoS4 assisted ball-milling method and their enhanced high-rate lithium storage property

Ball milling has been proven to be an efficient method for exfoliating and reassembling heterogeneous layered nanocomposites on a large scale. This study explores the use of ammonium tetrathiomolybdate (NH₄)₂MoS₄, an ion crystal with an octahedral structure, as both a precursor of layered molybdenum disulfide (MoS₂) and an intermediate during ball milling to assist in the exfoliation and fragilization of expandable graphite (EG). Due to its ion crystal structure and high hardness, (NH₄)₂MoS₄ can efficiently transfer and magnify the impacting and shearing forces generated during the ball milling process, accelerating the exfoliation and fragmentation efficiency of EG. Moreover, (NH₄)₂MoS₄ is nano-crystallized by the ball milling forces and uniformly distributed on the carbon nanosheets. Electrochemical performance tests indicate that the resulting nanocomposites, with a satisfactory heterogeneous structure, exhibit excellent Li-storage capacity, achieving 529 mA h g⁻¹ after 150 cycles at a high current density of 500 mA g⁻¹. The relationship between the microstructure and improved electrochemical performance, as well as the formation mechanism of the product, is discussed in detail. This study provides a new approach for conveniently constructing nanocomposites using two types of layered materials that offer satisfactory rate capability and cyclability, making them potentially suitable for application in Li-ion batteries.     

Spectral and Temporal Characteristics of Photoluminescence in Alpha Alumina Crystals under UV Laser Excitation

The photoluminescence spectra of -Al₂O₃ irradiated with different gamma doses are measured under excitation with the frequency-doubled radiation (255.3 nm) from a copper vapor laser. The effect of the time delay on the shape of the emission spectrum is examined. The 385-nm luminescence decay time is determined to be 19 ns.