CP MAS Kinetics Study of Ionic Liquids Confined in Mesoporous Silica: Convergence of Non-Classical and Classical Spin Coupling Models

The high data point density measurements of ¹H→¹¹B cross-polarization (CP) kinetics upon magic-angle spinning (MAS) of [bmim][BF₄] confined in mesoporous SBA-15 and MCM-41 were carried out. The complex shaped ¹¹B CP MAS signals were observed in both silica and decomposed into two Lorentz components. This points towards the possibility of bimodal distribution of [bmim][BF₄] in the studied confinements. The convergence of classical and non-classical spin coupling models was deduced processing CP kinetic curves. A good fit of the theoretical curves to the experimental data was achieved using both models without any non-random deviations between theory and experiment to appear. The convergence of spin coupling models was discussed in terms of relatively high mobility of BF₄ ^? anion respect to the cation and the dynamics of anions in pores. These factors delete the borders between spin clusters. The spin diffusion along the pore surfaces in MCM-41 is more than twice faster than in SBA-15.     

Preparation, characterization, and luminescence properties of novel hybrid material containing europium(III) complex covalently bonded to MCM-41

In this paper, a novel luminescent organic-inorganic hybrid material containing covalently bonded ternary europium complex in mesoporous silica MCM-41 has been successfully prepared by co-condensation of tetrethoxysilane (TEOS) and the modified ligand 2-phenyl-1H-imidazo[4,5-f][1,10]phen-3-(triethoxysilyl)propylcarbamate (PIP-Si) in the presence of cetyltrimethylammonium bromide (CTAB) surfactant as template. PIP-Si containing 1,10-phenanthroline covalently grafted to 3-(triethoxysilyl)propyl isocyanate is used not only as a precursor but also as the second ligand for Eu(TTA)₃·2H₂O (TTA: 2-thenoyltrifluoroacetate) complex to prepare a novel functionalized mesoporous material. The resulted mesoporous composite materials, which demonstrate strong characteristic emission lines of Eu³⁺⁵D₀-⁷F_J (J=0, 1, 2, 3, 4), were characterized by Fourier transform infrared (FT-IR), small-angle X-ray diffraction, excited-state decay analysis. Emission intensity of the Eu(III) complex covalently linked to MCM-41 (Eu-MCM-41) increases with the increasing irradiation time, demonstrating better photostability compared with both pure Eu(III) complex and physically incorporated sample.     

Key factor affecting the structural and textural properties of ZSM-5/MCM-41 composite

ZSM-5/MCM-41 micro/mesoporous composite materials were synthesized by the hydrothermal technique with alkali-treated ZSM-5 zeolite as source of silica and aluminum and characterized by various physico-chemical techniques such as X-ray diffraction (XRD), nitrogen sorption at 77 K, transmission electronic microscopy (TEM), FTIR spectroscopy and NH₃ temperature programmed desorption (TPD) techniques. The effect of concentration of CTAB in the synthesis of these solids has been investigated, the mesopore volume, surface area and surface acidity decrease with increasing the concentration of CTAB. Increasing the CTAB concentration causes the recrystallization of zeolite ZSM-5 and it disadvantage the formation of mesoporous materials MCM-41. The catalytic activity of ZSM-5/MCM-41 materials has been evaluated in the Friedel–Crafts acylation of anisole with benzoyl chloride as alkylating agent. The results revealed the reaction to be influenced by surface area, pore volume and surface acidity.     

Tuning the morphology of mesoporous silica by using various template combinations

By using different dual-template combinations, four types of mesoporous silica materials with different morphologies were successfully synthesized. A solid-sphere mesoporous (SSM) silica was obtained using a combination of tri-block copolymer (F127) and 1,12-diaminododecane (DADD), but when F127 was substituted with poly(vinylpyrrolidone) (PVP), a leaf-shaped mesoporous (LSM) silica was obtained. In addition, a hollow-sphere mesoporous (HSM) silica was obtained by using a combination of PVP and dodecylamine (DDA), but a cotton-like mesoporous (CLM) silica was obtained using F127 instead of PVP. All four types of synthesized materials were characterized by SEM, TEM, XRD, and N₂ adsorption–desorption isotherms, and the results showed that all of them exhibited high surface area, large pore volume, worm-like pore structure, and beautiful shapes. The results of storage experiments revealed that the HSM and CLM showed good adsorption and storage properties. The HSM (the largest pore volume) seemed to have the larger storage capacity when compared to the CLM, albeit CLM had the highest surface area among all.     

ZnO nanoparticles embedded in UVM-7-like mesoporous silica materials: Synthesis and characterization

ZnO nanodomains embedded in bimodal mesoporous silica (UVM-7) materials with high Zn content (4≤Si/Zn≤30) have been synthesized by an one-pot surfactant-assisted procedure from a hydro alcoholic medium using a cationic surfactant (CTMABr=cetyltrimethylammonium bromide) as structural directing agent, and starting from molecular atrane complexes of Zn and Si as hydrolytic inorganic precursors. This chemical procedure allows optimizing the dispersion of the ZnO particles in the silica walls. The bimodal mesoporous nature of the final high surface area nano-sized materials is confirmed by XRD, TEM, and N₂ adsorption–desorption isotherms. The small intra-particle mesopore system is due to the supramolecular templating effect of the surfactant, while the large pores have their origin in the packing voids generated by aggregation of the primary nanometric mesoporous particles. A limited pore blocking and a high accessibility to the ZnO active nanoparticles have been achieved. The effects induced by the progressive incorporation of ZnO nanoparticles into the mesostructure have been examined, including a careful optical spectroscopic study (PL and UV–visible).     

温度对吡啶离子液体性质影响的分子动力学模拟研究

运用分子动力学模拟方法研究了温度对三种吡啶离子液体[BPy][BF4]、[HPy][BF4]、[OPy][BF4]热力学性质的影响, 得到了每个体系的密度、自扩散系数、电导率和黏度等. 研究结果表明: 随着温度升高, 同一种离子液体的密度减小, 阴阳离子的自扩散系数明显增大, 电导率升高, 而黏度降低. 在同一温度下, 随着阳离子上烷基链的增长, 离子液体的密度减小, 但热力学性质的变化规律并不完全同步. 烷基链长最短的[BPy][BF4]的自扩散系数和电导率在每个温度下均为最大, 而黏度最小; 但烷基碳链更长的[OPy][BF4]和[HPy][BF4]的各种性质相差不大,甚至当温度大于323K时, 烷基链较长的[OPy][BF4]的自扩散系数比[HPy][BF4]的大.     

温度对吡啶离子液体性质影响的分子动力学模拟研究

运用分子动力学模拟方法研究了温度对三种吡啶离子液体[BPy][BF_4]、[HPy][BF_4]、[OPy][BF_4]热力学性质的影响,得到了每个体系的密度、自扩散系数、电导率和黏度等.研究结果表明:随着温度升高,同一种离子液体的密度减小,阴阳离子的自扩散系数明显增大,电导率升高,而黏度降低.在同一温度下,随着阳离子上烷基链的增长,离子液体的密度减小,但热力学性质的变化规律并不完全同步.烷基链长最短的[BPy][BF_4]的自扩散系数和电导率在每个温度下均为最大,而黏度最小;但烷基碳链更长的[OPy][BF_4]和[HPy][BF_4]的各种性质相差不大,甚至当温度大于323 K时,烷基链较长的[OPy][BF_4]的自扩散系数比[HPy][BF_4]的大.     

离子液体存在下铜的电沉积及其表面增强拉曼散射效应研究

离子液体作为一种绿色介质,在电化学领域中的研究正在兴起,引起了研究者的浓厚兴趣。文章运用循环伏安法研究了离子液体(1-丁基-3-甲基咪唑四氟硼酸盐,[bmim]BF4)存在时,酸性硫酸铜溶液中铜在铜电极上的电化学沉积行为。研究表明,[bmim]BF4的加入使铜的沉积峰电位负移,沉积电流增加。采用扫描电镜(SEM)和X射线衍射(XRD)对铜镀层的形貌及结构进行表征,结果显示离子液体的存在可使铜镀层的层状晶粒尺寸减小,镀层出现(220)高择优取向。以甲基橙(MO)为探针分子,研究了所得铜镀层的表面增强拉曼散射(SERS)效应,发现离子液体存在下得到的铜镀层是较好的SERS基底,具有良好的增强效果及稳定性。对MO分子的增强因子可达4.7×105,而且保存了60天后,其检测灵敏度没有显著的降低。     

The instant-direct-templating synthesis of phenyl-functionalized HOM-type mesoporous silica materials

Two kinds of novel phenyl-functionalized mesoporous silica materials have fabricated for the first time by an instant-direct-templating method using poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) and tetraethyl orthosilicate as surfactant template and precursor, respectively. Samples were characterized by Fourier transform infrared spectroscopy, small-angle X-ray diffraction, thermogravimetric analysis, N₂ adsorption-desorption, scanning electron micrography and transmission electron micrography. The results show that phenyl groups are attached covalently to the pore wall of mesoporous materials after modification. The functionalized materials still preserve a desirable ordered hexagonal P6mm and cubic Ia3d mesophase structure, respectively, have high specific surface area, large pore volume and narrow pore size distribution.     

Ionic liquid; possibility of protein-preserving solvent under high pressure

We have investigated the pressure-induced phase transition behavior (～3.0 GPa) of aqueous 1-butyl-3-methylimidazolium chloride ([bmim][Cl]) solutions with N-methylacetamide (NMA), which is a simple protein model compound, using Raman spectroscopy. From Raman spectral changes and optical observation in the sequence of elevated pressure, we found that the aqueous [bmim][Cl] solution with NMA in the water-rich condition induces the high pressure crystallization at 2.6 GPa. On the other hand, in the [bmim][Cl]-rich condition, high pressure crystalline phase was not observed even up to 3.0 GPa. Our results show that the aqueous [bmim][Cl] solution in the ionic liquid-rich condition along with the use of pressure has a potential for protein-preserving solvent.     

Quantitative characterization of nanoparticle agglomeration within biological media

The electronics industry is one of the world??s fastest growing manufacturing industries. However, e-waste has become a serious pollution problem. This study reports the recovery of e-waste for preparing valuable MCM-48 and ordered mesoporous carbon for the first time. Specifically, this study adopts an alkali-extracted method to obtain sodium silicate precursors from electronic packaging resin ash. The influence of synthesis variables such as gelation pH, neutral/cationic surfactant ratio, hydrothermal treatment temperature, and calcination temperature on the mesophase of MCM-48 materials is investigated. Experimental results confirm that well-ordered cubic MCM-48 materials were synthesized in strongly acidic and strongly basic media. The resulting mesoporous silica had a high surface area of 1,317?m²/g, mean pore size of about 3.0?nm, and a high purity of 99.87?wt%. Ordered mesoporous carbon with high surface area (1,715?m²/g) and uniform pore size of CMK-1 type was successfully prepared by impregnating MCM-48 template using the resin waste. The carbon structure was sensitive to the sulfuric acid concentration and carbonization temperature. Converting e-waste into MCM-48 materials not only eliminates the disposal problem of e-waste, but also transforms industrial waste into a useful nanomaterial.     

STUDY OF MESOPOROUS SILICA MATERIALS BY SMALL ANGLE X-RAY SCATTERING

Small angle X-ray scattering experiments have been performed to study the microstructure of mesoporous silica materials prepared by condensation of tetraethylorthosilicate using non-ionic alkylpolyethyleneoxide (AEO₉) and ionic cetyltrimethylammonium bromide (CTAB) surfactant as templates. It is the pores within the nanometre range that produce the main scattering. The scattering of the pure silica systems obey Porod's law. The scattering of the systems with templates remaining in the pores show positive deviations from Porod's law. This may be because the templates produce some additional scattering background and then make the scattering of pores distorted. The results show that the full removal of templates from the pores of the materials by Soxhlet extraction is very easy for AEO₉, but it is difficult for CTAB. The positive deviation correction is also performed.     

Molecular ordering of mixed surfactants in mesoporous silicas: a solid-state NMR study

The use of mixed surfactants in the synthesis of mesoporous silica nanoparticles (MSNs) is of importance in the context of adjusting pore structures, sizes and morphologies. In the present study, the arrangement of molecules in micelles produced from a mixture of two surfactants, cetyltrimethylammonium bromide (CTAB) and cetylpyridinium bromide (CPB) was detailed by solid-state NMR spectroscopy. Proximities of methyl protons in the trimethylammonium headgroup of CTAB and protons in the pyridinium headgroup of CPB were observed under fast magic angle spinning (MAS) by (1)H-(1)H double quantum (DQ) MAS NMR and NOESY. This result suggested that CTAB and CPB co-exist in the pores without forming significant monocomponent domain structures. (1)H-(29)Si heteronuclear correlation (HETCOR) NMR showed that protons in the headgroups of CTAB are in closer proximity to the silica surface than those in the CPB headgroups. The structural information obtained in this investigation leads to better understanding of the mechanisms of self-assembly and their role in determining the structure and morphology of mesoporous materials.     

Ultrasonic-assisted ultra-rapid synthesis of monodisperse meso-SiO2@Fe3O4 microspheres with enhanced mesoporous structure

A core–shell-type of meso-SiO₂@Fe₃O₄ microsphere was synthesized via an ultrasonic-assisted surfactant-templating process using solvothermal synthesized Fe₃O₄ as core, tetraethoxysilane (TEOS) as silica source, and cetyltrimethyl ammonium bromide (CTAB) as templates. The samples were characterized by FT-IR, XRD, TEM, N₂ adsorption–desorption technology, and vibrating sample magnetometer (VSM). The results show that as-prepared meso-SiO₂@Fe₃O₄(E) and meso-SiO₂@Fe₃O₄(C) microspheres, treated by acetone extraction and high temperature calcination, respectively, still maintain uniform core–shell structure with desirable mesoporous silica shell. Therein, the meso-SiO₂@Fe₃O₄(E) microspheres possess a distinct pore size distribution in 1.8–3.0 nm with large specific surface area (468.6 m²/g) and pore volume (0.35 cm³/g). Noteworthily, the coating period of this ultrasonic-assisted method (40 min) is much shorter than that of the conventional method (12–24 h). The morphology of microspheres and the mesoporous structure of silica shell are significantly influenced by initial concentration of CTAB (C_CTAB), ultrasonic irradiation power (P) and ultrasonic irradiation time (t). The acceleration roles of ultrasonic irradiation take effect during the whole coating process of mesoporous silica shell, including hydrolysis-condensation process of TEOS, co-assembly of hydrolyzed precursors and CTAB, and deposition of silica oligomers. In addition, the use of ultrasonic irradiation is favorable for improving the homogeneity of silica shell and the monodispersity of meso-SiO₂@Fe₃O₄ microspheres.     

Stability and characterization of mesoporous molecular sieve using natural clay as a raw material obtained by microwave irradiation

Mesoporous molecular sieve was synthesized via microwave irradiation method, and using natural clay, sodium silicate and aluminum chloride as raw materials and cetyl trimethyl ammonium bromide (CTAB) as a template agent under alkaline condition. The samples were characterized by various analytic and spectroscopic tools such as XRD, FT-IR, TEM, TG-DSC and N₂ physical adsorption, respectively. The results show that the synthesized sample has typical mesoporous structure and exhibits good mesoporous ordering. On the other hand, the as synthesized sample after calcination at 550 °C for 10 h has a surface area of 576.0 m²/g and an average pore size of 4.83 nm. Furthermore, the synthesized mesoporous molecular sieve still exhibits good mesoporous ordering after calcination at 750 °C for 3 h or hydrothermal treatment at 100 °C for 10 days.     

芘在离子液体及常规溶剂中的激光闪光光解研究

利用纳秒级时间分辨激光光解装置,以Nd:YAG激光器三倍频后的355 nm激光作为激发光源,研究了芘在常规溶剂乙腈、丙酮、环己烷、1-丁基-3-甲基咪唑六氟磷酸离子液体([Bmim][PF6])、N-丁基吡啶四氟硼酸离子液体([BuPy][BF4])以及三乙基庚基铵双三氟甲磺酰亚胺(R4NNTf2)的瞬态光解行为,比较...     

Novel room temperature ionic liquid for fluorescence enhancement of Eu and Tb

The newly prepared ionic liquid, 1-butyl-3-methylimidazolium benzoate, ([bmim][BA]), was found to enhance the fluorescence of Eu³⁺ and Tb³⁺. The fluorescence enhancement resulted from a sensitization of the lanthanide fluorescence by the benzoate anion of the ionic liquid, [bmim][BA], and a reduction in the non-radiative channels in the non-aqueous environment provided by the ionic liquid. However, the fluorescence enhancement of the lanthanides in the ionic liquid was limited due to the operation of the inner filter effect, which resulted from the strong absorption of the benzoate. The inner filter effect was minimized by observing the Eu³⁺ fluorescence using a front face geometry and also by diluting the lanthanide-[bmim][BA] system, using another ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim][Tf₂N]), as a solvent. In the case of Tb³⁺, the emission from the lanthanide was masked by the strong emission from the ionic liquid in the region 450-580 nm. The long lived Tb³⁺ emission was therefore observed using delayed gated detection, where an appropriate delay was used to discriminate against the short lived emission from the ionic liquid. The large fluorescence enhancement due to ligand sensitized fluorescence observed with [bmim][BA] diluted in [bmim][Tf₂N], leads to nanomolar detection of the lanthanides. This is, to the best of our knowledge, the first report of an ionic liquid being employed for ligand sensitized fluorescence enhancement of lanthanides.     

Synthesis, characterization, and oxygen sensing properties of Ru(II) complex covalently grafted to mesoporous MCM-41

Novel oxygen sensing materials consisting of [Ru(Bphen)₂bpy]²⁺ (Bphen=4,7-diphenyl-1,10-phenanthroline, bpy=2,2′-bipyridyl) portion covalently grafted to the backbones of the ordered functionalized mesoporous MCM-41 are synthesized by co-condensation of tetraethoxysilane (TEOS) and the functionalized Ru(II) complex [Ru(Bphen)₂Bpy-Si]²⁺ using surfactant cetyltrimethylammoniumbromide (CTAB) as template. The Bpy-Si was used as not only one of the precursors of the sol-gel process but also the second ligand of Ru(Bphen)₂Cl₂·2H₂O complex to prepare the functionalized mesoporous materials for oxygen sensors. Dye leaching shortcoming is overcome due to the Si-C bonds. The derivative mesoporous oxygen sensing materials are characterized by Fourier transform infrared (FT-IR), small angle X-ray diffraction (SAXRD), luminescence intensity quenching Stern-Volmer plots, and excited-state decay analysis. The mesoporous materials show higher sensitivity to the O₂ concentration in N₂ (I₀/I₁₀₀=23.2) and shorter response time (1.2 s) in comparison with those based on sol-gel method. When the concentration of oxygen is 10%, the luminescence intensity of the oxygen sensor can be quenched by 89.9%, suggesting that it is highly sensing at low concentration of oxygen.     

Synthesis and characterization of double –SO3H functionalized Brönsted acidic hydrogensulfate ionic liquid confined with silica through sol-gel method

Imidazolium-based metal and halogen-free Brönsted acidic ionic liquid (BAIL) (3,3′-(hexane-1,6-diyl)bis(2-methyl-1-(3-sulfopropyl)-1H-benzimidazolium) hydrogensulfate [HbMBIM-PS][HSO₄] was synthesized. The physicochemical properties of this BAIL were investigated using a variety of different analytical and spectroscopic techniques such as ¹H and¹³C-NMR, FT-IR, mass, UV–vis and TGA spectra. A porous silica matrix has been synthesized using BAIL and tetraethoxysilane (TEOS) as silica source by nonhydrolytic sol–gel method. The properties of IL confined silica gel matrix have been studied using FTIR, TGA, SEM, N₂-sorption measurement (BET characterization for determining pore parameters), and NH₃-TPD techniques. From the N₂-sorption measurement, it has been found that BET surface area decreased while pore volume, average pore size and porosity decreased. The thermal stability of the IL has been found to increase upon confinement in silica gel matrix. The results suggested that IL had been successfully confined on silica gel. This IL confined silica gel catalyst is environment friendly and useful for alkane isomerization and esterification reactions.     

离子液体中聚氧化乙烯(PEO)相变过程中的氢键效应

我们把Flory-Huggins模型推广应用到聚合物/离子液体体系,研究聚氧化乙烯(PEO)在离子液体[EMIM][BF_4]中相变过程中的氢键效应,理论模型考虑了三种类型氢键(Ⅰ型:PEO-[EMIM]~+氢键,Ⅱ型:PEO-[BF_4]~-氢键和Ⅲ型:[EMIM]~+-[BF_4]~-氢键)的形成,分析了三种类型的氢键分数随温度、 PEO体积分数的变化.研究发现,三种类型的氢键分数随温度的升高而减少.在较小PEO体积分数条件下,增加PEO体积分数,Ⅰ型、Ⅱ型氢键分数轻微地减小;在较大PEO体积分数条件下,增加PEO体积分数,Ⅰ型、Ⅱ型氢键分数急剧减少.Ⅲ型氢键分数随着PEO体积分数的增加而急剧降低.由于三种氢键效应,第二维里系数A_2随温度的增加而减小.通过计算分析不同分子量的PEO在[EMIM][BF_4]中的相图发现,在PEO体积分数较低的条件下,Ⅰ型、Ⅱ型和Ⅲ型氢键是PEO相变的主要驱动力;在PEO体积分数较高的条件下,Ⅰ型和Ⅱ型氢键在PEO相变过程中起到主导作用.