Preparation of acid–base bi-functional hydrotalcite based catalyst for converting Vietnamese coconut oil to green hydrocarbons

Acid–base bi-functional hydrotalcite like compounds based on partial incorporation of Al³⁺ into brucite structure of Mg(OH)₂ with various molar ratios were prepared through co-precipitation method. The co-precipitation of the precursors produced precipitations followed by drying at 120 °C for 12 h and calcination in air flow at 500 °C for 6 h to obtain the catalysts (Mg–Al HLCs). Many techniques including XRD, TG–DTA, EDX, NH₃-TPD, CO₂-TPD, GC–MS and XANES were used to characterize and optimize Mg/Al molar ratio based on the thermal stability of the Mg–Al HLCs and their activities in decarboxylation process of coconut oil. The results showed that the best molar ratio of Mg/Al was 3/1 providing a stable hydrotalcite like structure, and the catalyst possessed both acid and base sites on its surface enhancing its activity and selectivity in the decarboxylation process. The catalysts revealed high performance in the decarboxylation process of coconut oil established at 400 °C for 4 h for green hydrocarbons belonging to kerosene fractions.     

Photo retro-Diels-Alder reactions

Photo-retro-Diels-Alder (PrDA) reactions of a variety of Diels-Alder (DA) adducts were studied. Experimental results showed that the photoreactivity (quantum yield) depends on the electron-donating ability of the diene component and the electron-withdrawing ability of the dienophile component. The mechanism was studied by trapping the reaction intermediate, O(2) quenching, time-resolved absorption, and fluorescence spectroscopy. All the results support a mechanism that involves a charge-separated intermediate generated from a singlet excited state. The PrDA reaction may find applications in photoresponsive materials, photolithography, drug delivery, and mechanistic research.     

Crosslinked nanofibrillated cellulose: poly(acrylic acid) nanocomposite films; enhanced mechanical performance in aqueous environments

Nanofibrillated cellulose (NFC) was compounded with poly(acrylic acid) (PAA) via solvent casting. Nanocomposite films were thermally-crosslinked to allow the formation of ester bonds between NFC and PAA, as confirmed by ¹³CNMR and infrared spectroscopy. The network morphology of the cellulose nanofibrils was left intact by the introduction of PAA and crosslinking. Water absorption and swelling was diminished by the introduction of crosslinking, due to the reduced number of vacant hydroxyl and carboxyl groups available to interact with water molecules. Crosslinking with PAA increased the activation energy required for thermal degradation. PAA effectively reinforced NFC, increasing Young’s modulus, tensile strength and glass transition temperature. Crosslinking imparted restraints on segmental motion of polymer chains, further enhancing the thermomechanical properties and retaining elasticity. Wet-strength properties were enhanced due to the reduced hydrophilicity of crosslinked nanocomposite films.     

Separation and simultaneous determination of the active ingredients in theophylline tablets by micellar electrokinetic capillary chromatography

The separation and determination of seven active ingredients in theophylline tablets by micellar electrokinetic capillary chromatography is described. On a 35 cm × 50 μm I.D. capillary, baseline separation is possible with a carrier solution containing 0.05 M sodium dodecyl sulphate (SDS) in 0.02 M borate buffer (pH 9.2) solution. The migration time of solutes increased markedly with increasing SDS concentration and slightly with increasing pH. With consecutive injections of samples, slight decreases in the migration times of the solutes occurred, but they were in parallel, owing to the temperature rise of the capillary with time. The column efficiency was influenced by the micellar concentration and applied voltage, and optimum values at which the highest theoretical plate number was achieved were established. The determination of the active ingredients was performed using hydrochlorothiazide and levamisole hydrochyloride (for ephedrine hydrochloride only) as internal standards, with good linearity with correlation coefficients from 0.9965 to 0.9999 and recoveries from 94.1 % to 101.1%. For quantitative information, measurements of peak height were better than peak area.     

Flavonoid glycosides from Chromolaena odorata leaves and their in vitro cytotoxic activity

Two new flavonoid glycosides, (1, 2), and eleven known compounds, (3-13), were isolated from from a 70% EtOH extract of the leaves of Chromolaena odorata (Asteraceae). Their structures were elucidated by 1D and 2D NMR spectroscopic interpretation as well as by chemical studies. The newly isolated compounds were tested in vitro for their cytotoxic activities against the LLC and HL-60 cancer cell lines. Compound 1 showed cytotoxicity against LLC and HL-60 cancer cell lines with IC(50) values of 28.2 and 11.6 μM, respectively. Compound 2 exhibited significant cytotoxic activity in the inhibition of HL-60 cancer cell lines with IC(50) value of 10.8 μM.     

酯化型环氧化合物摩擦成膜对润滑油摩擦学性能影响之研究

用油酸和环氧树脂合成了一种能够形成摩擦聚合膜的酯化型环氧化合物润滑油添加剂——DE成膜剂。以液体石蜡或二线油为基础油,在栓-盘式试验机和四球试验机上就DE成膜剂对润滑油摩擦学性能的影响进行了研究。结果表明,添加DE成膜剂明显地改善了润滑油的摩擦学性能;在基础油中加入DE成膜剂比加环氧树脂、脂肪酸酯或油酸时的摩擦系数低、表面擦伤少、承载能力高、磨损量小。文章还对DE成膜剂在摩擦表面上形成的摩擦聚合膜的作用机制进行了分析和探讨。     

Angle- and time-resolved mass spectrometric study on pulsed laser ablation of an La-Ca-Mn-O target

Pulsed laser ablation (PLA) of an La₂O₃-CaO-MnO₂ target at 532 nm has been investigated by angle- and time-resolved quadrupole mass spectrometry. The results show that different kinds of metal oxides as well as metal ions and atoms are produced during the ablation at high laser fluence. The measured TOF spectra are fitted by multicomponent Maxwell-Boltzmann distribution with a stream velocity, which gives the translational energy of 6.34 and 0.43 eV for Mn⁺ ions and Mn atoms, respectively. It implies that ablated ions are mainly formed via a nonthermal process, while the neutral atoms mainly via a thermal one. The angular distributions of Mn + ions and Mn atoms can be described by a cos ⁿ θ and a bicosine function a cosθ+ (1-a)cos ⁿ θ, respectively. Possible mechanisms of laser ablation of La-Ca-Mn-0 are discussed. Project supported by the National Natural Science Foundation of China (Grant No. 29683001).     

Study on the New Fluorescence Enhancement System of Tb –N-(2 - Pyridinyl) Ketoacetamide-Et<Subscript>3</Subscript>N-Zn and its Application

A sensitive fluorescence enhancement system was developed for the determination of zinc (II). The fluorescence intensity of the Tb- N- (2 - Pyridinyl) ketoacetamide (PKA) system was greatly enhanced by the addition of triethylamine (Et₃N) and zinc nitrate in the methanol solution. The excitation and emission wavelengths were 329 nm and 546 nm, respectively. Under optimal conditions, the fluorescence intensities varied linearly with the concentration of Zn²⁺ in the range of 8.0×10⁻⁷−5.0×10⁻⁶ M with a detection limit of 9.9×10⁻⁸ M. The interferences of some substances were described. This method was applied to the determination of amounts of Zn²⁺ in soybean, rice, and wheat, respectively. The results showed that the proposed procedure is a high selective, simple, and rapid method to the determination of Zn²⁺ ion. The mechanism of fluorescence enhancement was also studied.     

The influence of TiO2 nanoparticle incorporation on surface potential decay of corona-resistant polyimide nanocomposite films

PI nanocomposite films containing surface modified nanoparticles by employing silane coupling agent were prepared using in-situ dispersion polymerization process. The surface potential decay measurements on films were investigated over the different negative corona-charged voltages and times in a controlled environment where temperature and relative humidity were kept at 21 °C and 45%, respectively. There is a significant change in the surface potential decay characteristics after nano-fillers were introduced into polyimide. The surface potential decay pattern depends also on the amount of nano-fillers. The possible surface potential decay and corona resistance mechanisms responsible for the observed phenomena were discussed.     

铝质材料的摩擦学表面改性

在工程应用中，铝质材料是一类重要性仅次于钢铁的金属材料。但是，铝质材料作为摩擦学材料，却存在着质软、摩擦系数高、磨损大、容易拉伤且难以润滑等严重弱点。为了总结科学工作者在铝质材料的摩擦学表面改性方面的研究成果，借以推动有关工作的深入开展，对这类材料的各种摩擦学表面改性技术的研究进展及其发展现状作了概述，其中，重点综合介绍的是本世纪八十年代新发展起来的自润滑阳极氧化铝处理技术的基本原理、处理方法和应用等，同时，根据有关的测试和分析结果，对自润滑阳极氧化铝在研究和开发工作中所存在的一些问题，以及产生这些问题的原因等进行了分析与讨论，并就其今后的发展方向和应当进行改进研究的几个重点课题作了预测与评述。