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排序方式: 共有218条查询结果,搜索用时 15 毫秒
1.
In the present study, we propose a novel method for the extraction of parabens in personal care products. A new, simple adsorptive material was obtained by combining metal-organic frameworks and melamine sponges using the adhesive property of polyvinylidene fluoride. This new material, metal-organic frameworks/melamine sponges, was found to be particularly suitable for solid-phase extraction. The structural characteristics of metal-organic frameworks/melamine sponges were first analyzed by scanning electron microscopy. Subsequently, solid-phase extraction was performed on sample solutions, and the extracted substances were then analyzed by high-performance liquid chromatography. Following optimization of important experimental conditions, excellent recovery rates were obtained. Our novel method was then applied to the extraction of four parabens (methylparahydroxybenzoates, ethylparahydroxybenzoates, propylparahydroxybenzoates, and butylparahydroxybenzoates) from real samples. The results yielded limits of detection of 0.26–0.41 ng/mL. The inter- and intra-day recoveries were 104.0–109.7% and 91.2–98.1%, respectively (relative standard deviation, <13.8%).  相似文献   
2.
In this work, an electrochemical sensor coupled with an effective flow-injection amperometry (FIA) system is developed, targeting the determination of gallic acid (GA) in a mild neutral condition, in contrast to the existing electrochemical methods. The sensor is based on a thin electroactive poly(melamine) film immobilized on a pre-anodized screen-printed carbon electrode (SPCE*/PME). The characteristics of the sensing surface are well-characterized by field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS) and surface water contact angle experiments. The proposed assay exhibits a wide linear response to GA in both pH 3 and pH 7.0 phosphate buffer solutions (PBS) under the optimized flow-injection amperometry. The detection limit (S/N = 3) is 0.076 μM and 0.21 μM in the pH 3 and pH 7 solutions, respectively. A relative standard deviation (RSD) of 3.9% is obtained for 57 successive measurements of 50 μM GA in pH 7 solutions. Interference studies indicate that some inorganic salts, catechol, caffeine and ascorbic acid do not interfere with the GA assay. The interference effects from some orthodiphenolic compounds are also investigated. The proposed method and a conventional Folin–Ciocalteu method are applied to detect GA in green tea samples using the standard addition method, and satisfactory spiked recoveries are obtained.  相似文献   
3.
To demonstrate the nature of the interaction of optical isomers of propranolol with the surface of the graphitic electrode modified with melamine, uracil, cyanuric, and isocyanuric acids, we have performed molecular dynamics simulations of the four‐component systems with variable modifier's molecules. We have considered the possible formation of complexes between the propranolol and modifier's molecules, covering the electrode approximated as the graphene surface. Our simulations demonstrate that the l ‐isomer in aqueous solutions is bonded to the electrode surface stronger than its d ‐counterpart; hence, the difference in analytical signals arises. Different strengths of bonding of the propranolol enantiomers to the surface modifiers are caused by the different intramolecular interactions taking place in the molecules of d ‐ and l ‐isomers. Thus, we have computationally shown that the modification of the graphite surface with melamine, uracil, cyanuric, and isocyanuric acids allows for increasing the sensitivity of the electrode toward the propranolol enantiomers and using the modified graphitic electrodes for the detection of its d ‐ and l ‐forms.  相似文献   
4.
利用三聚氰胺甲醛预聚物中N原子与Pd2+的相互作用,将Pd2+化学锚定在预聚物中;并以二氧化硅水凝胶为造孔剂、2,4-二氨基苯磺酸为预聚物缩合促进剂,在水溶液中制备出锚定了Pd2+的胶体纳米球;再经摩尔分数5%氢气焙烧、HF腐蚀,得到Pd质量分数为1.37%、平均粒径为(2.4±0.87) nm的碳载高分散Pd纳米粒子催化剂Pd@C。 将其应用于Suzuki反应,在加入Pd与碘苯物质的量比为1:100的催化剂时,反应5 min收率为99.3%,且经8次循环后活性未降低,表现出良好的催化效果和重复使用性。  相似文献   
5.
Melamine salt of pentaerythritol phosphate kaolin (MPPK) was synthesized by the reaction of pentaerythritol phosphate with kaolin (K) and melamine. The structure of MPPK was confirmed by EDXS, 1H NMR, FTIR, and XRD. MPPK was blended with polypropylene (PP) at different loading levels. Thermogravimetric analysis (TGA) results showed that MPPK improved the thermal stability of PP at high temperatures in all PP composites. Vertical burning rate test manifested that PP composites can achieve V0 at 20% and 25% MPPK loading levels. Cone calorimeter data exhibited that addition of 25% MPPK to PP reduced peak of heat release rate (pHRR) and total heat release (THR) by 86% and 76% and increased the char residue after test to 67%. The results of PP/25% MPPK composite were compared with the data obtained from PP containing 25% K and 25% of traditional intumescent flame retardant composed of melamine phosphate (MP), pentaerythritol (PE), and K. The outcomes indicated that MPPK was more efficient in flame retardancy than the other systems. The digital photographs and SEM images for char residue demonstrated that MPPK succeeded in forming cellular and coherent char layer on the PP surface. The main advantage of adding 25% MPPK to PP was its ability to preserve nearly the inner half of the sample without burning after cone calorimeter test.  相似文献   
6.
In this work, a novel sulfur‐based flame retardant (SA‐M) was synthesized by the self‐assembly of melamine and sulfamic acid. The chemical structure of SA‐M was fully characterized. SA‐M, in company with Al2O3, was then introduced into polyamide 11 (PA 11) by melt compounding in order to improve the fire resistance of the polymer substrate. The observation by scanning electron microscopy (SEM) and electron probe microanalysis (EPMA) indicated the well dispersion of SA‐M in PA 11 matrix. The fire performance of PA 11 composites was evaluated by limiting oxygen index (LOI), vertical burning (UL‐94), and cone calorimeter tests, respectively. The results showed that the presence of 17.5% SA‐M and 2.5% Al2O3 increased the LOI value from 22.4% to 30.9%, upgraded the UL‐94 rating from no rating to V‐0, significantly eliminated the melt dripping, and decreased the peak heat release rate from 1024 to 603 kW/m2. The thermal behaviors were investigated by thermogravimeric analysis (TGA) and TGA‐Fourier transform infrared spectroscopy (FTIR). It was suggested that SA‐M took effects mainly in gas phase by diluting the combustible fuel, leading to the improvement of the fire resistance of PA 11.  相似文献   
7.
8.
Miniemulsion polymerization is employed to produce high solid content (50%) acrylic/melamine latexes with varied crosslinking capability, for their potential application as waterborne crosslinkable coatings. This synthesis strategy allows the efficient incorporation of a hydrophobic crosslinker, iso‐butylated melamine (iBMF), into polymer particles, and to obtain latexes with different iBMF concentrations and acrylic polymer with varied content of hydroxylic groups (OH–). The involved crosslinking mechanisms and the physical transformations during film thermosetting of acrylic/iBMF nanocomposite are exhaustively investigated by combining thermal, spectroscopic, and thermo‐mechanical analyses. The influence of reactive groups concentration (iBMF and OH– content in the acrylic polymer) on the rate of curing, the crosslinking degree, and consequently onto the sensitive properties of cured films are discussed here.  相似文献   
9.
李振武 《物理学报》2014,63(10):106101-106101
单壁碳纳米管能够强烈吸收光线,尤其是在近红外区域,并能将光能转换成热能.同时,单壁碳纳米管还具有相当大的将热能转换成电能的能力.通过真空过滤方法,将由化学气相沉积生成的单壁碳纳米管阵列制备成单壁碳纳米管膜.根据研究的需要设计了一个简单的单壁碳纳米管膜光伏性质测试实验装置,并在其两端成功地实现了由红外光转换为电压输出.通过功能化步骤,制备了单壁碳纳米管/三聚氰胺甲醛树脂复合材料膜,实验结果表明该复合材料能产生符号相反的输出电压.这预示着单壁碳纳米管及其三聚氰胺甲醛树脂复合材料在光电领域具有良好的应用前景.  相似文献   
10.
The 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) polymers, melamine polymers, and DOPO‐melamine copolymers have been successfully synthesized, and their flame retarding properties have also been investigated by blending with polypropylene (PP)/styrene‐ethylene‐butylene‐styrene (SEBS) alloys. Experimental results establish that all of them are good polymeric flame retardants. No blooming or color stains occur when they are incorporated into PP/SEBS alloys. Among lab‐made polymeric flame retardants, DOPO‐ melamine copolymers exhibit the best thermal stability and nonflammability. PP/SEBS alloys containing DOPO‐melamine copolymers display comparable thermal resistance and flame retarding behavior (Td = 290°C; char yield: 15.6%, LOI: 23, and flammability: UL‐94 V0) as the alloys containing common commercial flame retardants (i.e., DOPO, melamine, and ammonium polyphosphate). Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   
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