In-situ fabrication of ZnO nanoparticles sensors based on gas-sensing electrode for ppb-level H_2S detection at room temperature

The zinc oxide(ZnO)nanoparticles(NPs)sensors were prepared in-situ on the gas-sensing electrodes by a one-step simple sol-gel method for the detection of hydrogen sulfide(H₂S)gas.The sphere-like ZnO NPs were characterized by scanning electron microscopy(SEM),transmission electron microscopy(TEM),x-ray diffraction(XRD),energy dispersive x-ray analysis(EDX),and their H₂S sensing performance were measured at room temperature.Testing results indicate that the ZnO NPs exhibit excellent response to H₂S gas at room temperature.The response value of the optimal sample to750 ppb H₂S is 73.3%,the detection limit reaches to 30 ppb,and the response value is 7.5%.Furthermore,the effects of the calcining time and thickness of the film on the gas-sensing performance were investigated.Both calcining time and film thickness show a negative correlation with the H₂S sensing performance.The corresponding reaction mechanism of H₂S detection was also discussed.     

不同维度Co3O4纳米材料的水热合成研究进展

过渡金属氧化物Co_3O_4的晶体结构及表面特性与其形貌、尺寸和微观结构密切相关。本文将不同形貌Co_3O_4纳米材料按尺寸分为:纳米球、立方块、多面体等零维材料,纳米线、纳米棒、纳米管、纳米柱等1D材料,纳米片、纳米薄膜等2D材料,海胆状、微米球等由纳米单元构成的微米尺寸3D超结构。探讨了对形貌形成的影响因素,重点研究其水热合成过程,总结了可能的形成机理,以利于对不同维度材料的形成规律有较深入的理解,进而能在理论上指导特定维度、特定形貌材料的可控合成。     

Rheological properties of nanocellulose suspensions: effects of fibril/particle dimensions and surface characteristics

The rheological properties of aqueous suspensions based on three different nanocelluloses were compared. One system was obtained via acid hydrolysis (thus yielding crystalline nanocellulose, CNC) and the other two from mechanical shearing, but from different origins and subjected to different pretreatments. Of the latter two, one was considered to be a rather typical cellulose nanofibril (CNF) suspension whereas the other was a kind of intermediate between CNF and CNC. All three nanocellulose elements differed in dimensions as evident from transmission electron microscopy and atomic force microscopy. With regard to the length of the fibrils/particles, the three nanocelluloses formed three distinct groups with lengths between 200 and slightly more than 800 nm. The three cellulosic elements were also subjected to a TEMPO-mediated oxidation yielding a similar carboxylate content in the three systems. Furthermore, the TEMPO-oxidized elements were grafted with poly(ethylene glycol) (PEG). The amount of grafted PEG was about 35 wt%. The shear viscosity, the storage modulus and the loss modulus of suspensions of the unmodified, the TEMPO-oxidized and the grafted nanocelluloses were determined at room temperature and the solids content of the suspensions was varied between 0.7 and 2.0 wt%. It was concluded that the rheological properties varied significantly between the suspensions depending on the dimensions of the cellulosic elements and their surface characteristics. In this context, the length (or the aspect ratio) of the particles played a very important role.     

有机物化学检验法的分析、讨论与应用

随着仪器分析的发展和广泛应用,针对有机化合物的化学鉴别方法研究近年来逐渐淡出化学学科前沿。然而化学鉴别方法由于其广泛的实用性和较低的成本,仍在有机定性与定量分析中占有一席之地。从典型有机物的化学鉴定分析方法入手,根据机理分类阐述了各类有机物的化学检验,并详细地讨论了几种机理较为复杂或易存在认识误区的化学检验手段,如茚三酮定性定量测试、双缩脲定性定量测试、Fehling与Benedict定性测试等。     

Acetone Formation from Photolysis of 2-Propanol on Anatase-TiO2(101)

Photocatalysis of 2-propanol on A-TiO₂(101) has been investigated using a temperature programed desorption method with 266 nm laser light. A clear mechanism is proposed for photodissociation of 2-propanol on A-TiO₂(101). Acetone product on five coordinate Ti⁴⁺ sites is formed in a stepwise manner in which the O-H dissociation proceeds first and then followed by secondary C-H dissociation of 2-propanol while H atoms are transferred to the adjacent bridge bond oxygen (BBO) sites. Low temperature water is formed in a thermally driven process via H-atom on BBO in exchange with isopropyl groups of molecule 2-propanol, while isopropyl radical desorbs at high temperature during the TPD process. The observation demonstrates the prospect of TiO₂ as a photocatalyst for degradation of organics.     

Finite dimensional characteristic functions of Brownian rough path

The Brownian rough path is the canonical lifting of Brownian motion to the free nilpotent Lie group of order 2: Equivalently, it is a process taking values in the algebra of Lie polynomials of degree 2, which is described explicitly by the Brownian motion coupled with its area process. The aim of this article is to compute the finite dimensional characteristic functions of the Brownian rough path in ?^d and obtain an explicit formula for the case when d = 2     

Determination of cobalt(II) using β-cyclodextrin-capped ZnO quantum dots as a fluorescent probe

The authors describe a method for the determination of cobalt(II) ions based on the use of luminescent and water-soluble ZnO quantum dots capped with β-cyclodextrin (β-CD@ZnO QDs). The modified QDs display strong yellow-green fluorescence with a peak at 537 nm under 360 nm excitation. High-resolution transmission electron microscopy, Fourier transform infrared spectroscopy, luminescence, and UV-visible absorption spectroscopy were used to characterize the β-CD@ZnO QDs. The fluorescence of the QDs is quenched by Co(II) ions. This finding was exploited to design a quenchometric assay designed for the detection of Co(II) in water solution. The detection limit is 0.34 μM (based on the 3σ/slope criterion), and the linear range extends from 1.0 to 10 μM. The method was applied to quantify Co(II) in spiked real samples. The quenching mechanism was studied, and this showed that aggregation-induced quenching causes the main effect.

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Graphical abstract The fluorescence of β-cyclodextrin-capped ZnO quantum dots (β-CD@ZnO QDs) is quenched by cobalt ions, and this finding is exploited in a fluorescence assay for cobalt ions in aqueous solutions.

     

Silver-catalyzed efficient synthesis of enaminones from propargyl alcohols and amines

Enaminones are used as the key intermediates to construct heterocyclic compounds with various bioactivities. In this study, a simple and efficient approach for the synthesis of enaminones via amination of propargyl alcohols was developed. Under the catalysis of Ag₂CO₃, the reaction proceeded smoothly to afford the desired products in good yields. Preliminary mechanism experiments showed that Ag₂CO₃ played an essential role in the procedure of the reaction.     

Synthesis and Structure of Low‐valent η4‐Cinnamaldehyde Cobalt Complexes

Three η⁴‐(C=C–C=O) coordination cobalt(I) complexes 1 – 3 were synthesized by the reactions of cinnamaldehyde, p‐fluorocinnamaldehyde, and p‐chlorocinnamaldehyde with CoMe(PMe₃)₄. Complex 4 as η²‐(C=C) coordination was prepared by the reaction of chalcone with Co(PMe₃)₄. The structures of complexes 1 – 4 were confirmed by single‐crystal X‐ray diffraction. Although the reactions didn't undergo C–H bond activation and decarbonylation, the formation of complexes 1 – 4 deepens our understanding of the reactions between α,β‐unsaturated aldehyde or ketone with low‐valent central cobalt atom.     

KOH direct treatment of kombucha and in situ activation to prepare hierarchical porous carbon for high-performance supercapacitor electrodes

Kombucha, a renewable biomass, has been successfully utilized as an accessible carbon source to fabricate kombucha-derived hierarchical porous carbon (KHPC) by KOH direct treatment and in situ activation. The prepared KHPC shows an interconnected hierarchical porous structure, a pore volume of 0.41 cm³ g^?1, and a specific surface area of 917 m² g^?1. Due to the multiple synergistic effects of these advantages, the KHPC-3 exhibits a high specific capacitance of 326 F g^?1 at a current density of 1 A g^?1 in 6 M KOH, good rate capability of 82% retention from 1 to 20 A g^?1, and cycling performance with 91.3% retention over 5000 cycles. Moreover, the KHPC-3 symmetric supercapacitor reveals a good energy density of 20.97 Wh kg^?1 at a power density of 871.2 W kg^?1 and retains 8.08 Wh kg^?1 at 6330 W kg^?1 in 1 M Na₂SO₄ electrolyte. Therefore, the KHPC obtained via the simple synthesis process shows great promise as an electrode material in energy storage devices.