Gd_2O_2S∶Yb^(3+),Er^(3+)纳米粉体的水热-还原法制备及其上转换发光性能研究

以Gd_2O_3,Yb_2O_3,Er_2O_3,HNO_3,CO(NH_2)_2和C_(12)H_(25)SO_4Na为实验原料,通过水热-还原法制备了Yb^(3+)和Er^(3+)共掺杂的Gd_2O_2S∶Yb^(3+),Er^(3+)纳米粉体。通过傅里叶变换红外光谱(FT-IR)、X射线衍射(XRD)、透射电子显微镜(TEM)、选区电子衍射(SAED)和上转换发射光谱(UPL)分析手段对合成产物的结构、形貌和上转换发光性能进行了表征。结果表明,Gd^(3+)∶CO(NH_2)_2∶SO_4^(2-)=2∶1∶x的摩尔比对合成产物的结构有显著的影响,当x=1.0时合成的前驱体在90%Ar+10%H_2混合气氛下800℃煅烧2 h可获得单相Gd_2O_2S纳米粉体,该Gd_2O_2S粉体颗粒呈现近球形,平均颗粒尺寸约30 nm,具有一定的团聚特征。上转换发射光谱表明在980 nm红外光激发下,Gd_2O_2S∶Yb^(3+),Er^(3+)纳米粉体的上转换光谱图的主次发射峰分别位于671 nm和548 nm,归属于Er^(3+)的~4F_(9/2)→~4I_(15/2)和~4S_(3/2)→~4I_(15/2)跃迁。Er^(3+)的猝灭浓度为5%,Gd_2O_2S∶Yb^(3+),Er^(3+)的发光机制为双光子模型。

水热-还原法制备Pt@NiO-C催化剂及其全解水性能的研究

以硝酸镍为镍源,通过水热法制成NiO-C载体,随后利用L-抗坏血酸和氢气将铂离子镶嵌入载体中,制备出Pt和NiO共存的Pt@NiO-C催化剂,并对其全解水性能进行测试。首先运用XRD、SEM、XPS等测试手段,对材料组成与结构进行了表征。结果表明,半导体NiO不仅可以作为析氢贵金属载体,同时也可以为析氧提供活性点位。电化学测试结果显示,在浓度为0.5 mol/L的硫酸溶液中,Pt@NiO-C材料的析氢起始电位仅为25 mV(VS.RHE),塔菲尔斜率为31 m V·dec^(-1),经过20个小时的连续工作依旧能保持稳定的催化性能,析氧性能优于商用铂碳(20%),为质子交换膜制氢技术的发展提供一种新的思路。

水热-还原法合成球形Gd_2O_2S:Pr^(3+)闪烁体粉末

采用Gd2O3、Pr6O11、H2SO4和尿素为实验原料,通过水热-还原法合成了Gd2O2S:Pr3+闪烁体粉末。利用X射线衍射(XRD)、红外光谱(FT-IR)、热重分析(DTA-TG)、扫描电子显微镜(SEM)和光致发光(PL)光谱等手段对合成的粉末进行了表征。研究表明尿素与Gd2(SO4)3的摩尔比(m)对前躯体的物相组成和形貌有很大影响,最佳的m值为2.5。最佳的前躯体在流动的90%Ar+10%H2气氛中800℃煅烧1 h能转变成单相的Gd2O2S粉末。所获得的Gd2O2S粉末呈球形,分散性良好,粒径尺寸约为1μm。在307 nm的紫外光激发下,Gd2O2S:Pr3+闪烁体粉末的主发射峰位于516 nm,归属于Pr3+的3P0-3H4跃迁。在Gd2O2S基质中,Pr3+的猝灭浓度为1%(摩尔分数),猝灭机理为电偶极-电四极相互作用引起的。

放电等离子烧结制备W-20%Cu复合材料的组织及性能研究

以水热合成-共还原工艺制备的W-20%Cu(质量分数)复合粉末为原料,用SPS技术成功制备了W-20%Cu复合材料,并对其显微组织和性能进行了分析研究。结果表明:随着烧结温度的升高和保温时间的延长,W、Cu两相微观结构组织分布更为均匀,孔隙也更少,W-20%Cu复合材料的致密度、硬度和电导率也相应提高;在烧结温度950℃、保温时间5min的工艺条件下,W-20%Cu复合材料的致密度、维氏硬度、电导率分别为98.9%、HV222.8、21.7 MS/m。

Growth of Cu/SSZ-13 on SiC for selective catalytic reduction of NO with NH_3

Silicon carbide(SiC)was used as a support for SSZ‐13zeolite in an attempt to improve the high‐temperature stability and activity of Cu/SSZ‐13in the selective catalytic reduction(SCR)of NO with NH3.SSZ‐13was grown via a hydrothermal method using the silicon and silica contained in SiC as the source of silicon,which led to the formation of a chemically bonded SSZ‐13layer on SiC.Characterization using X‐ray diffraction,scanning electron microscopy,and N2adsorption‐desorption isotherms revealed that the alkali content strongly affected the purity of zeolite and the crystallization time affected the coverage and crystallinity of the zeolite layer.Upon ion exchange,the resulting Cu/SSZ‐13@SiC catalyst exhibited enhanced activity in NH3‐SCR in the high‐temperature region compared with the unsupported Cu/SSZ‐13.Thus,the application temperature was extended with the use of SiC as the support.?2018,Dalian Institute of Chemical Physics,Chinese Academy of Sciences.Published by Elsevier B.V.All rights reserved.

Cu-SAPO-17:A novel catalyst for selective catalytic reduction of NOx

The high-temperature(HT) and low-temperature(LT) hydrothermal stabilities of molecular-sieve-based catalysts are important for the selective catalytic reduction of NOx with ammonia(NH3-SCR). In this paper, we report a catalyst, Cu2+ loading SAPO-17, synthesized using cyclohexylamine(CHA), which is commercially available and inexpensive and is utilized in NH3-SCR reduction for the first time. After systematic investigations on the optimization of Si and Cu2+ contents, it was concluded that Cu-SAPO-17-8.0%-0.22 displays favorable catalytic performance, even after being heated at 353 K for 24 h and at 973 K for 16 h. Moreover, the locations of CHAs, host–guest interaction and the Bronsted acid sites were explored by Rietveld refinement against powder X-ray diffraction data of as-made SAPO-17-8.0%. The refinement results showed that two CHAs exist within one eri cage and that the protonated CHA forms a hydrogen bond with O4, which indicates that the proton bonding with O4 will form the Bronsted acid site after the calcination.

Conversion of ferric oxide to magnetite by hydrothermal reduction in Bayer digestion process

Digesting aluminum-bearing minerals and converting ferric oxide to magnetite simultaneously in Bayer digestion process is crucially important to deal with high-iron diasporic bauxite economically for alumina production.The reaction behaviors of hydrothermal reduction of ferric oxide in alkali solution were studied by both thermodynamic calculation and experimental investigation.The thermodynamic calculation indicates that Fe3O4 can be formed by the conversion of Fe2O3 at proper redox potentials in alkaline solution.The experimental results show that the formation ratio of Fe3O4 either through the reaction of Fe and Fe2O3 or through the reaction of Fe and H2O in alkaline aqueous solution increases remarkably with raising the temperature and alkali concentration,suggesting that Fe（OH）3- and Fe（OH）4- form by dissolving Fe and Fe2O3,respectively,in alkaline aqueous solution and further react to form Fe3O4.Moreover,aluminate ions have little influence on the hydrothermal reduction of Fe2O3 in alkaline aqueous solution,and converting iron minerals to magnetite can be realized in the Bayer digestion process of diasporic bauxite.

纳米钨铜复合粉末的制备及其烧结行为研究

以钨酸钠和硝酸铜为原料,采用水热合成-共还原法制备钨铜复合粉末,再通过真空热压烧结法制备钨铜复合材料,并研究了钨铜复合粉末的结构形貌,以及经不同温度热处理后钨铜复合材料的显微形貌、物性特征。结果表明:采用水热合成-共还原法可制得粒度尺寸约为70nm且颗粒分布均匀的纳米级钨铜复合粉末。钨铜复合粉末经加压烧结及热处理后可得到W相和Cu相紧密结合、Cu相均匀分布在W相周围的钨铜复合材料,其在热处理温度为950℃时致密度最高,达到99.2%;在热处理温度为800℃时导电率最高,达到46.5%IACS;在热处理温度为900℃时布氏硬度最高,达到HB285。

A clean process of lead recovery from spent lead paste based on hydrothermal reduction

An innovative process was proposed for recovering lead from spent lead paste, and it produced less pollution and used lessenergy than the traditional process. First, lead dioxide in lead paste was reduced by glucose under hydrothermal conditions. Theeffects of the reaction time, glucose excess coefficient, temperature and pH on the hydrothermal reduction were systematicallyinvestigated. Under the optimized reduction conditions （i.e., temperature of 175 ℃, time of 120 min, glucose excess coefficient of3.0 and pH of 5.5）, 99.9% reduction ratio of lead dioxide is achieved, and only the PbO·PbSO4 and PbSO4 phases are observed in thereducing residue. Subsequently, the reducing residue is desulfurized in a NaOH solution, and approximately 99.40% of the sulfur isremoved. The main lead phase in the desulfurization residue is 3PbO·H2O.

Inactivation of Protein Tyrosine Phosphatase 1B （PTP1B） Activity by the Aqueous Partition of Guava Leaf Extract

Guava leaf tea has been used as a folk medicine for treating hyperglycemic conditions in Asia and Africa. The hypoglycemic efficacy of guava leaf has been documented by many scientists in these regions, but the hypoglycemic mechanism is poorly understood. Guava leaves were extracted with methanol and the crude extract was partitioned against hexane, ethyl acetate, and butanol in sequence. The leftover in water is defined as the aqueous partition. A second smaller batch was extracted with hot water directly. Oral glucose tolerance test was carried out on healthy mice instead of diabetic mice that lack endogenous insulin. Glucose uptake was examined with 3T3-L1 adipocytes. Oxidative effect on PTP1B （protein tyrosine phosphatase 1b） was carried out with real-time PTP1B enzymatic assay. The aqueous partition of guava leaf extract possesses a potent inhibitory effect on PTP1B enzymatic activity and this PTP1B inhibition is through a slow oxidative but reversible inactivation on the enzyme. The reversible inactivation would suggest guava leaf extract may augment PTP1B inhibition alongside the endogenous H2O2 which itself is induced by insulin. In addition, our study confirmed the hypoglycemic efficacy being associated with guava leaf and found the most effective molecules reside in the aqueous partition which is also less cytotoxic to Chinese hamster ovary cells when compared to other less polar partitions. The guava leaf extract can modulate insulin activity through a redox regulation on PP1B enzymatic activity. It is speculated that a compound similar to gallocatechin in the aqueous partition can reduce an oxygen molecule to hydrogen peroxide which in turn oxidizes the catalytic residue Cys in PTP1B. Therefore, the guava leaf tea can serve as a functional hypoglycemic drink that is suitable for either healthy or diabetic subjects.

Shaped Pt-Ni nanocrystals with an ultrathin Pt-enriched shell derived from one-pot hydrothermal synthesis as active electrocatalysts for oxygen reduction

Alloy nanocrystals （NCs） of Pt with 3d transition metals, especially Ni, are excellent catalysts for the oxygen reduction reaction （ORR）. In this work, we, for the first time, demonstrated the water phase colloidal synthesis of Pt-M （M = Ni, Co and Fe） alloy NCs with tunable composition and morphology through a facile hydrothermal method. Pt-Ni alloy NCs synthesized with this method presented better ORR activity than commercial Pt/C catalysts. The X-ray energy dispersive spectra （EDS） mapping technique revealed that Pt-enriched shells existed on the as-synthesized Pt-Ni alloy NCs. About two atom thick layered Pt-enriched shells formed on Pts0Nis0 NCs and the thickness of the Pt-enriched shells increased as the Ni content increased. Furthermore, X-ray photoelectron spectroscopy analysis revealed that the oxidation level of the surface Pt atoms on the Pt-Ni alloy NCs decreased compared with monometallic Pt NCs, implying a decrease in the oxophilicity of the surface Pt atoms. Pt-Ni alloy NCs with lower oxophilicity of the surface Pt atoms give higher ORR activity. The most active alloy sample showed 13 times higher specific activity and six times higher mass activity at 0.9 V vs. a reversible hydrogen electrode when compared with commercial Pt/C. Pt-Ni alloy NCs also showed better durability than commercial Pt/C in long term ORR tests.

Controllable synthesis of two-dimensional tungsten nitride nanosheets as electrocatalysts for oxygen reduction reaction

A facile synthetic strategy was developed for insitu preparation of two-dimensional (2D)highly crystalline tungsten nitride (WN)nanosheets with controllable morphology as oxygen reduction reaction (ORR)catalysts.The dependence of the crystal structure and morphology of WN on K2SO4content,pH,and pyrolysis temperature was thoroughly examined.The electrocatalytic performance of WN toward ORR in an alkaline electrolyte indicated that K+plays an important role in the control of size and shape in the hydrothermal and nitridation process,thereby promoting the formation of plate-like WO3and 2D WN nanosheets.The WN nanosheets,with largely exposed edge sites,provide abundant catalytic active sites and allow fast charge transfer.Furthermore,they exhibit high stability for ORR and methanol tolerance.

Science Letters:Hydrogen transfer reduction of ketones using formic acid as a hydrogen donor under hydrothermal conditions

The hydrothermal experiments with ketones and formic acid showed that the hydrogen transfer reduction of ketones can be conducted using formic acid as a hydride donor in the presence of NaOH at 300 ℃. The yield of alcohols was considerably higher at a much lower ratio of hydrogen source to ketones than the traditional Meerwein-Ponndorf-Verley （MPV） reduction, reaching 60% for isopropanol from acetone and 70% for lactic acid from pyruvic acid. Water molecules may act as a catalyst in the hydrogen transfer reduction of ketones under hydrothermal conditions.