Effects of thermal annealing on structural and magnetic properties of thin Pt/Cr/Co multilayers

Thermal stability of thin Pt/Cr/Co multilayers and the subsequent changes in their structural, magnetic, and magneto-optical properties are reported. We observe CoCrPt ternary alloy phase formation due to annealing at temperatures about 773 K, which is accompanied by enhancement in the coercivity value. In addition, 360° domain wall superimposed on a monodomain like background has been observed in the pristine multilayer, which changes into a multidomain upon annealing at 873 K.     

Light-induced cis/trans isomerization of cis-[Pd(L-S,O)2] and cis-[Pt(L-S,O)2] complexes of chelating N,N-dialkyl-N′-acylthioureas: key to the formation and isolation of trans isomers

Irradiation cis-[M(Lⁿ-S,O)₂] complexes (M = Pt^II, Pd^II) derived from N,N-dialkyl-N′-benzoylthioureas (HLⁿ) with various sources of intense visible polychromatic or monochromatic light with λ < 500 nm leads to light-induced cis?→?trans isomerization in organic solvents. In all cases, white light derived from several sources or monochromatic blue-violet laser 405 nm light, efficiently results in substantial amounts of the trans isomer appearing in solution, as shown by ¹H NMR and/or reversed-phase HPLC separation in dilute solutions at room temperature. The extent and relative rates of cis/trans isomerization induced by in situ laser light (λ = 405 nm) of cis-[Pd(L²-S,O)₂] was directly monitored by ¹H NMR and ¹⁹⁵Pt NMR spectroscopy of selected cis-[Pt(L-S,O)₂] compounds in chloroform-d; both with and without light irradiation allows the δ(¹⁹⁵Pt) chemical shifts cis/trans isomer pairs to be recorded. The cis/trans isomers appear to be in a photo-thermal equilibrium between the thermodynamically favored cis isomer and its trans counterpart. In the dark, the trans isomer reverts back to the cis complex in what is probably a thermal process. The light-induced cis/trans process is the key to preparing and isolating the rare trans complexes which cannot be prepared by conventional synthesis as confirmed by the first example of trans-[Pd(L-S,O)₂] characterized by single-crystal X-ray diffraction, deliberately prepared after photo-induced isomerization in acetonitrile solution.     

Effect of Oxide Coverage on the Growth of Amorphous Al2Pt Phase on an Al Surface

 In the present experiments the high temperature successive deposition (HTSD) of Al and Pt and the half shadowing technique producing wedge shaped area with increasing quantity of deposited Pt are applied for studying the initial stages of solid phase reaction producing amorphous Al₂Pt phase. The nucleation of Al₂Pt phase results in a decoration pattern which could be related to the characteristic local oxide coverage of the Al crystal surface developing by kinetic segregation of oxygen species during the Al film deposition. In the area of larger amount of deposited Pt, where the Al₂Pt phase is continuous Kirkendall voids are present. The samples were investigated in plane by transmission electron microscopy (TEM) and selected area electron diffraction (SAED) and analysed by energy dispersive X-ray spectroscopy (EDX).     

铂电极上自组装铁原卟啉单分子层的表面增强振动光谱初探

应用现场表面增强拉曼光谱和衰减全反射表面增强红外光谱初步研究了0.1mol·L-1HClO4溶液中Pt电极表面铁原卟啉(FePP)自组装单层的电化学和结构特性.以514nm波长为激发线,得到了增强因子约为40的粗糙Pt电极上FePP在不同电位下的表面增强拉曼光谱.分析0.5～-0.3V(SCE)区间内谱峰变化,得到近似的吸附等温式,由此可估算出Fe3+/Fe2+的式量电位大约为-0.2V.原位表面增强红外光谱的测试结果表明,FePP分子主要以斜立方式吸附在Pt膜电极表面,其中一个环外羧酸根与电极表面相接触,而另一羧酸基团以氢键与相邻的FePP分子相连.这样的吸附结构在-0.1～0.9V(SCE)的电位区间内并没有显著的变化.     

高分散还原态Pt基催化剂的制备及其NO氧化的催化性能

Pt⁰被认为是NO氧化的活性物种,而催化剂的制备方法对活性物种的含量起着决定性作用。本文采用非惰性气氛保护的改性醇还原-浸渍法(MARI)合成了高分散高Pt⁰含量的1% (w, 质量分数) Pt/SiO₂-Al₂O₃催化剂(MA-Pt/SA)。X射线粉末衍射(XRD)、CO-漫反射傅里叶变换红外吸收光谱(CO-DRIFTS)和透射电镜(TEM)表征证实在550 ℃焙烧3 h后催化剂的Pt颗粒仅有3.8 nm。同时,X射线光电子能谱(XPS)和H₂-程序升温还原(H₂-TPR)结果表明催化剂具有高Pt⁰含量(60.3%)。模拟柴油车尾气气氛进行活性测试,并与传统浸渍法制备的1% (w) Pt/SiO₂-Al₂O₃催化剂(C-Pt/SA)对比,结果显示MA-Pt/SA具有优异的催化氧化性能,其NO最大转化率高达74%,比C-Pt/SA的NO转化率高了23%。经670 ℃高温老化15 h后,老化的MA-Pt/SA的NO转化率仍然高达69%。此外NO + O₂共吸附原位漫反射傅里叶变换红外吸收光谱(in situ DRIFTS of NO + O₂ co-adsorption)表明高的Pt分散度和高Pt⁰含量能够促进中间物种桥式硝酸盐的生成及分解,进而导致了优异的NO氧化活性。最后,利用同样方法将Pt的负载量降低至0.5% (w)制备催化剂,NO转化率仍达64%。这种制备方法能够获得低贵金属高性能的Pt基催化剂。     

A Ti3C2TX/Pt–Pd based amperometric biosensor for sensitive cancer biomarker detection

The detection of cancer biomarkers is of great significance for the early screening of cancer. Detecting the content of sarcosine in blood or urine has been considered to provide a basis for the diagnosis of prostate cancer. However, it still lacks simple, high-precision and wide-ranging sarcosine detection methods. In this work, a Ti₃C₂T_X/Pt–Pd nanocomposite with high stability and excellent electrochemical performance has been synthesized by a facile one-step alcohol reduction and then used on a glassy carbon electrode (GCE) with sarcosine oxidase (SO_x) to form a sarcosine biosensor (GCE/Ti₃C₂T_X/Pt–Pd/SO_x). The prominent electrocatalytic activity and biocompatibility of Ti₃C₂T_X/Pt–Pd enable the SO_x to be highly active and sensitive to sarcosine. Under the optimized conditions, the prepared biosensor has a wide linear detection range to sarcosine from 1 to 1000 µM with a low limit of detection of 0.16 µM (S/N = 3) and a sensitivity of 84.1 µA/mM cm². Besides, the reliable response in serum samples shows its potential in the early diagnosis of prostate cancer. More importantly, the successful construction and application of the amperometric biosensor based on Ti₃C₂T_X/Pt–Pd will provide a meaningful reference for detecting other cancer biomarkers.     

Aromatization of methane over different Mo-supported catalysts in the absence of oxygen

Both acidity and structure of the support are important factors in converting methane to aromatics. Lower SiO₂/Al₂O₃ ratio seems to favor the aromatization of methane over the Mo/HZSM-5 catalyst. When Pt is added as a modifier the activity of Mo/HZSM-5 catalyst will decrease slightly, but coke formation will enhanced.     

Study of silica supported PtxNi1-x catalysts by ion scattering spectroscopy

As supported Pt_xNi_1–x catalysts are used for hydrogenation reactions, it seemed necessary to assess the surface composition of the reduced samples. To approach the usual reduction conditions we applied in situ reduction in a reaction chamber (1 mbar H₂ up to 500 °C) placed in ultra high vacuum recipient (UHV: 10^–9 to 2.10^–10mbar). All ion scattering spectroscopy measurements were performed in UHV. Charging of the samples was avoided by electron bombardment (5 eV). The variation of the surface composition was determined after subsequent sputtering, thermal treatment at 500 °C and during oxygen adsorption. A comparison with previous results of surface compositions of binary alloys (polycrystalline foils [1, 2] and single crystals Pt_xNi_1–x [3]) is given.Dedicated to Professor Dr. rer. nat. Dr. h. c. Hubertus Nickel on the occasion of his 65th birthday     

Comparison ofn-decane hydroconversion with Pt/SAPO-5 and Pt/SAPO-11 catalysts

The product distributions from bifunctional conversion ofn-decane over Pt/SAPO-5 and Pt/SAPO-11 catalysts are compared in detail. Selectivities in decane reaction vary largely with the catalyst employed: Pt/SAPO-11 produces high yields of feed isomers, whereas Pt/SAPO-5 gives high yields of cracked products and only under mild reaction conditions are isodecanes the main products obtained. These selectivities seem to be determined by the structure of the catalyst.