Growth kinetic study of ionic liquid mediated synthesis of gold nanoparticles using Elaeis guineensis (oil palm) kernels extract under microwave irradiation

Gold nanoparticles (AuNPs) are the most studied nanomaterials due to their promising applications. However, surface capping of AuNPs is essential to protect aggregation for enhanced colloidal stability. In this study, a single step method was established to synthesize stable AuNPs using oil palm kernel (OPK) extract prepared in IL[EMIM][OAc] (1-ethyl-3-methylimidazolium acetate). Ionic liquids were used for phytochemicals extraction along with capping and stabilizing of AuNPs after their synthesis. The OPK extract reduced the gold precursor, and UV–vis spectroscopy revealed a sharp surface plasmon (SPR) peaks in the region of 524–529 nm, which confirmed the formation of AuNPs. UV–vis and TEM analysis indicated that microwave assisted synthesis was rapid to synthesize well dispersed and small sized AuNPs in comparison with conventional heating. FTIR analysis of kernels extract before and after its reaction with gold precursor identified the involvement of CH aromatic groups, polyphenolic OH groups, and carbonyl amide groups that are responsible for reduction of trivalent gold ions to AuNPs. EDAX and XPS analysis were performed to identify the elemental gold and its surface interaction with ILs and other organic moieties. Colloidal AuNPs kept at room temperature for periods of six months were remained stable. The change of pristine nanostructure arises due to involvement of different driving forces during growth of nanoparticles. Thermodynamically instability of nanomaterials may leads to Ostwald Repining (OR) or adopt complex pattern of growth and undergo coalesce and orientation attachment (OA). These models were fitted to compare the theoretically growth of particles along with actual increase of particles size. Experimental results suggested that OA growth was originated in early phase, however, it substituted and mainly controlled by OR growth pattern over time.     

Efficient synthesis of magnetic nanoparticle-Musa acuminata peel composite for the adsorption of anionic dye

The impregnation of magnetite (Mt) nanoparticle (NPs) onto Musa acuminata peel (MApe), to form a novel magnetic combo (MApe-Mt) for the adsorption of anionic bromophenol blue (BPB) was studied. The SEM, EDX, BET, XRD, FTIR and TGA were used to characterize the adsorbents. The FTIR showed that the OH and CO groups were the major sites for BPB uptake onto the adsorbent materials. The average Mt crystalline size on MApe-Mt was 21.13 nm. SEM analysis revealed that Mt NPs were agglomerated on the surface of the MApe biosorbent, with an average Mt diameter of 25.97 nm. After Mt impregnation, a decrease in BET surface area (14.89 to 3.80 m²/g) and an increase in pore diameter (2.25–3.11 nm), pore volume (0.0052–0.01418 cm³/g) and pH point of zero charge (6.4–7.2) was obtained. The presence of Pb(II) ions in solution significantly decreased the uptake of BPB onto both MApe (66.1–43.8%) and MApe-Mt (80.3–59.1%), compared to other competing ions (Zn(II), Cd(II), Ni(II)) in the solution. Isotherm modeling showed that the Freundlich model best fitted the adsorption data (R² > 0.994 and SSE < 0.0013). In addition, maximum monolayer uptake was enhanced from 6.04 to 8.12 mg/g after Mt impregnation. Kinetics were well described by the pseudo-first order and liquid film diffusion models. Thermodynamics revealed a physical, endothermic adsorption of BPB onto the adsorbents, with ΔH^o values of 15.87–16.49 kJ/mol, corroborated by high desorption (over 90%) of BPB from the loaded materials. The viability of the prepared adsorbents was also revealed in its reusability for BPB uptake.     

线性响应和两种态特定方法模拟AF350电子跃迁的溶剂效应

在极化连续模型框架下比较了线性响应与两种不同态特定方法计算的溶液中Alexa Fluor 350(AF350)分子激发能和光谱移动值的差异. AF350的第一激发态S0→S1电子跃迁属于π→π^*跃迁, 主要对应于最高占据分子轨道(HOMO)到最低空轨道(LUMO)的跃迁. 该分子激发态偶极矩大于基态偶极矩, 激发态时溶质溶剂相互作用比基态时更强, 随着溶剂极性增大, 会发生光谱红移的现象. 与实验值相比, 线性响应和两种态特定方法均高估了激发能, 其中以IBSF(Improta-Barone-Scalmani-Frisch)方法得到的激发能最小, 矫正的基态反应场方法(cGSRF)得到的激发能最大. 对于光谱移动值, 3种方法与实验值相比都偏小, 线性响应方法(LR)计算出的误差最大, 而IBSF方法得到的结果与实验值最吻合, 是预测溶液中AF350分子激发能和光谱移动值最准确的方法. 对比了Marcus传统理论和基于约束平衡的非平衡溶剂化理论的结果, 发现后者得到的激发能和光谱移动值更接近于实验值.     

铂合金氧还原催化剂:合成、结构和性能

质子交换膜燃料电池是一种将燃料中的化学能直接转化为电能的装置,它具有转化效率高、能量密度高、低温启动、易于操作等优点,因而被认为是最具发展前景的新能源利用方式,在电动汽车、便携电源及分散式电站有着广泛应用.但是,目前质子交换膜燃料电池技术的发展面临着巨大挑战,主要问题包括高成本、低功率密度和低寿命.众所周知,质子交换膜燃料电池中的阴极氧还原反应在酸性条件下是一个复杂的四电子过程,动力学速度缓慢,限制了电池的最终性能.目前大量使用的阴极氧还原催化剂是细小的铂或铂合金纳米颗粒负载在碳载体上,其成本占燃料电池总成本的比例最大.制约燃料电池商业化发展的另一个重要问题是电池寿命低,其中氧还原催化剂的稳定性是决定电池寿命的主要因素.在这样的研究背景下,如何降低催化剂中铂的用量、提高催化剂活性和稳定性显得尤为重要,这也是近年来国内外学者研究的热点.在铂基合金催化剂中,通常采用过渡金属元素作为掺杂元素,由于原子半径不匹配(几何效应)以及电子结构不同(电子效应),合金催化剂表现出优于纯铂催化剂的催化性能.近几年,对于铂基合金催化剂的研究已取得重大进展,以合金组成和结构研究为基础,通过精确控制原子结构、调控表面电子状态以及制备工艺,获得了各种特殊形貌的催化剂,大大提高了催化活性.本文深入综述了近年来铂基合金氧还原催化剂制备、形貌和性能,特别关注了催化剂形貌和催化活性之间的关系.值得注意的是,具有有序原子排列的铂合金催化剂不仅在半电池中表现出优异活性,在实际质子交换膜燃料电池中也显示了很好的活性和稳定性.另一方面,碳载体的形貌及微观结构也对提高催化活性和稳定性起到决定性作用,通过化学手段加强金属纳米颗粒与碳载体之间的相互作用也是提高催化剂稳定性的重要途径.尽管铂基氧还原催化剂在近几年取得了重要进展,但在实际商业化过程中还存在诸多挑战,本文在综述进展的基础上,对铂基催化剂的发展提出了展望.首先,对于氧还原反应机理仍需要深入研究,采用更加精确的理论模型模拟氧还原动力学过程,以获得影响催化活性的关键因素.其次,提高催化剂在膜电极中的催化活性和利用率.目前,氧还原催化剂在半电池测试中性能优异,但是实际燃料电池操作条件下其性能远不能达到要求,这与膜电极、催化剂层及扩散层结构相关.因此,基于不同铂基催化剂的特性,合理设计膜电极组件的结构是将催化剂进行实际应用的基础.最后,催化剂的稳定性仍需进一步提高,尽管目前大部分催化剂在实验室半电池研究中表现了很好的稳定性,但在实际燃料电池中的稳定性研究还不足,而且对催化剂在膜电极中性能衰退机理的研究也非常有限.因此,对于铂基氧还原催化剂的研发仍需要国内外科研工作者不懈的努力.     

钯铂核壳纳米催化剂颗粒中的原子扩散

铂原子单层的核壳结构催化剂因其高效的铂原子利用率和优异铂质量活性而广泛应用于燃料电池领域.在该系列材料中,钯@铂核壳催化剂具有更优于纯铂的氧还原(ORR)催化活性,因而拥有较好的应用前景.但由于钯原子在热力学上更倾向于富集到材料表面,钯@铂核壳催化剂的催化稳定性及原子扩散的途径需要更深入的研究.本文探究了热处理条件对钯@铂核壳结构稳定性的破坏,并确定了原子扩散对催化活性的影响.原位扫描透射电子显微镜-电子能量损失谱(STEM-EELS)证明了在250 oC的氩气氛围中,钯@铂纳米颗粒中原本清晰可见的1–2原子铂壳层已经消失,并伴随着颗粒表面钯铂合金化的形成.因钯金属可以吸收氢气而导致晶格间距的展宽,钯@铂核壳结构的破坏也可以通过氢气氛围中的原位X射线衍射谱中(111)衍射峰的展宽和位移进行判断.对钯@铂核壳纳米催化剂进行一系列温度的热处理结果显示,核壳结构的破坏在200 oC左右开始,并于200–300 oC之间急剧发生.一氧化碳电化学氧化脱附实验表明,热处理之后的核壳催化剂表面的一氧化碳氧化峰位置发生了明显的正移,也证明了热处理之后催化剂表面电子结构的变化.核壳结构改变对催化活性的影响也通过旋转圆盘电极进行了测量.相比于未经处理的样品, 200 oC处理之后的钯@铂核壳催化剂在0.9 V电位处的质量活性损失了约37%.进一步提高热处理温度至300 oC之后,钯@铂核壳催化剂的质量活性只有初始状态的44%.本文揭示核壳结构中因热处理而导致的原子扩散现象,并为燃料电池中核壳催化剂的应用及膜电极的制备工艺条件提供了参考.     

Stability of Copper(II), Nickel(II) and Zinc(II) Binary and Ternary Complexes of Histidine,Histamine and Glycine in Aqueous Solution

The binary and mixed-ligand complexes formed between ligands (histidine (His), histamine (Him) and glycine (Gly)) and some transition metals (Cu(II), Ni(II) and Zn(II)) were studied potentiometrically in aqueous solution at (25.0 ± 0.1) C and I = 0.10 M KCl in order to determine the protonation constants of the free ligands and stability constants of binary and ternary complexes. The complexation model for each system has been established by the software program BEST from the potentiometric data. The most probable binding mode for each binary species of histidine and for all mixed species was also discussed based upon derived equilibrium constants and stability constants related to the binary species. The ambidentate nature of the histidine ligand, i.e. the ability to coordinate histamine-like, imidazolepropionic acid-like and glycine-like modes was indicated from the results obtained. The stability of ternary complexes was quantitatively compared with their corresponding binary complexes in terms of the parameters, log K, log X and ₁₁₁₀. The concentration distributions of various species formed in solution were also evaluated. In terms of the nature of metal ion, the complex stability follows the trend Cu(II) > Ni(II) > Zn(II), which is in agreement with the Irving-Williams order of metal ions. Thus, the results obtained were compared and evaluated with those in the literature.     

Structural changes in β-lactoglobulin by conjugation with three different kinds of carboxymethyl cyclodextrins

β-Lactoglobulin-carboxymethyl cyclodextrin (β-LG-CMCyD) conjugates were prepared by using water soluble carbodiimide. Three kinds of CMCyDs differing in molecular mass were used to investigate the effects of different CMCyD contents, net charge and hydrophobicity on the structural changes in β-lactoglobulin. The effect of CMCyDs on the structure of β-lactoglobulin was utilized to investigate the contribution of hydrophobic interactions to the stability of the protein. Spectroscopic studies suggested that the conformation around had not changed in either conjugate but the α-helix content of β-LG-CMCyD conjugates had markedly increased as compared with that of β-lactoglobulin. The differential scanning calorimetry technique confirmed that the addition of one glucose unit in β-LG-CMCyD conjugates, enthalpy change of calorimetry decreased and the denaturation temperature of each conjugate was higher than that of native β-lactoglobulin. The heat contents agreed well with the conformational transition measured by molar ellipticity at 222 nm ([θ]₂₂₂) and Stoke's radius (R_S) values. Therefore, hydrophobic forces play an important role in stabilizing and shielding of the β-LG-CMCyD conjugates.     

Iridium mediated methyl and phenyl C-H activation of 2-(arylazo)phenols. Synthesis, structure, and spectral and electrochemical properties of some organoiridium complexes

Reaction of 2-(2′,6′-dimethylphenylazo)-4-methylphenol with [Ir(PPh₃)₃Cl] in refluxing ethanol in the presence of a base (NEt₃) affords an organoiridium complex 5, where the 2-(2′,6′-dimethylphenylazo)-4-methylphenol is coordinated to iridium, via C-H activation of a methyl group, as a dianionic tridentate C,N,O-donor. Two triphenylphosphines and a hydride are also coordinated to the metal center. A similar reaction carried out in toluene affords complex 5 along with a similar complex 7, where a chloride is coordinated to iridium instead of the hydride. Reaction of 2-(2′-methylphenylazo)-4-methylphenol with [Ir(PPh₃)₃Cl] in refluxing ethanol in the presence of a base (NEt₃) affords an organoiridium complex 12, where the 2-(2′-methylphenylazo)-4-methylphenol is coordinated to iridium, via C-H activation at the ortho position of the phenyl group in the 2′-methylphenylazo fragment, as a dianionic tridentate C,N,O-donor. Two triphenylphosphines and a hydride are also coordinated to the metal center. A similar reaction carried out in toluene affords a complex 12 along with a similar complex 13, where a chloride is coordinated to iridium instead of the hydride. Structures of complexes 5, 12 and 13 have been determined by X-ray crystallography. In all these complexes, the two triphenylphosphines are trans. All these complexes show intense MLCT transitions in the visible region. Cyclic voltammetry on all the complexes shows an Ir(III)-Ir(IV) oxidation within 0.60-0.73 V vs. SCE, followed by an oxidation of the coordinated 2-(arylazo)phenolate ligand within 1.08-1.39 V vs. SCE. A reduction of the coordinated 2-(arylazo)phenolate ligand is observed within −1.10 to −1.26 V vs. SCE.     

Effect of Nano-anatase TiO2 on Spectral Characterization of Photosystem Ⅱ Particles from Spinach

The photosystem I (PS Ⅱ) particles were purified by means of nano-anatase TiO2 treatment of spinach and studied by spectroscopy. The results show that the electron transport and the oxygen-evolving rate of PS I are accelerated after it has been treated with nano-anatase TiO2; the UV-Vis absorption spectrum of PS I particles is increased; the red shift of fluorescence emission peak of PS I is 2 nm; the peak intensity is decreased; the PS Ⅱ signal I s of low temperature electron paramagnetic resonanace(EPR) spectrum is intensified under light, and the PS I circular dichroism(CD) spectrum is similar to that of control. It is suggested that nano-anatase TiO2 might bind to the PS I reaction center complex and intensify the function of the PS I electron donor, however, nano-anatase TiO2 treatment does not change the configuration of the PS Ⅱ reaction center complex.     

Preparation and Crystal Structure of 3-（2-Hydroxyphenyl） -6- （4-nitrophenyl）-7H- 1,2,4-triazolo[3,4-b][1, 3,4]thiadiazine

Introduction3,6- Disubstituted- 7H- 1 ,2 ,4- triazolo[3,4- b][1 ,3,4]thiadiazines are amongst the various hete-rocycles that received considerable attention duringthe last two decades as potential biologically activeagents.This kind of N- bridged heterocycles hasbeen reported to possess the wide spectrum of bio-logical properties,such as antimicrobial[1] ,an-tibacterial,antifungal[2 ] ,antiinflammatory[3 ] ,di-uretic[4] ,anthelmintic,and analgesic properties[5] .They can be also used as plant…