Synthesis and characterization of water-soluble carbon nanotubes from mustard soot

Carbon nanotubes (CNT) has been synthesized by pyrolysing mustard oil using an oil lamp. It was made water-soluble (wsCNT) through oxidative treatment by dilute nitric acid and was characterized by SEM, AFM, XRD, Raman and FTIR spectroscopy. The synthesized wsCNT showed the presence of several junctions and defects in it. The presence of curved graphene structure (sp²) with frequent sp³ hybridized carbon is found to be responsible for the observed defects. These defects along with the presence of di- and tri-podal junctions showed interesting magnetic properties of carbon radicals formed by spin frustration. This trapped carbon radical showed ESR signal in aqueous solution and was very stable even under drastic treatment by strong oxidizing or reducing agents. Oxidative acid treatment of CNT introduced several carboxylic acid group functionalities in wsCNT along with the nicking of the CNT at different lengths with varied molecular weight. To evaluate molecular weights of these wsCNTs, an innovative method like gel electrophoresis using high molecular weight DNA as marker was introduced.     

Conductivity and dielectric properties of sol–gel derived porous zirconia

The 8-mol percentage Y₂O₃-stabilized Porous Zirconia was prepared using sol–gel method. Zirconium oxalate gel was prepared by the addition of appropriate amount of oxalic acid solution into the 1 M aqueous solution of zirconium-oxy chloride. A cubic phase zirconia powder was obtained by calcination and milling of the zirconium oxalate gel. Crystallization temperature was found about 450 °C from the Differential thermal analysis. The phase analysis by X-ray diffraction shows the presence of cubic phase. Pellets sintered at 1,350 °C were highly porous, and the electrical conductivity was found with lower value due to the porosity, and the hardness was about 8.0 GPa. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7–9, 2006.     

Effects of paramagnetic cations on the nonexponential spin-lattice relaxation of rare spin nuclei in solids

Nonexponential spin-lattice relaxation is often observed for rare spin nuclei in the solid state. Deviation from single-component decay may be amplified by the coupling of rare spin nuclei to paramagnetic centers. Nonexponential spin-lattice relaxation was observed in derivatized silica gels resins. This phenomenon was localized and enhanced when paramagnetic transition metal cations were bound to surface functional groups. A stretched exponential analysis method was determined to be robust in fitting nonexponential relaxation curves for silica gels both with and without bound paramagnetic ions. Spin-lattice relaxation rates (T₁⁻¹) for functional group nuclei increased as a function of percent surface coverage with metal ion. The magnitude of the relaxation rate increase was dependent upon internuclear distances from the paramagnetic center. At low surface coverages, a semi-random distribution of paramagnetic centers increased the degree of stretching of spin-lattice relaxation decays, as measured by decreases in the calculated stretching parameter β. At higher surface coverages, calculated β values reached a limiting value, indicating that while the spin-diffusion mechanism in metal-ex-changed silica gels is restricted, it is not completely diminished.     

四磺酸基酞菁氯化铝复合二氧化硅干凝胶的制备及光学性能研究

采用溶胶凝胶法将不同掺杂浓度的四磺酸基酞菁氯化铝(AlClPcTS)植入二氧化硅凝胶基质,制备了均匀掺杂的复合干凝胶通过对二氧化硅凝胶基质和掺杂AlClPcTS后复合干凝胶孔结构的测定和对复合体系紫外可见吸收光谱的表征,证实了AlClPcTS在基质中的成功掺杂,并发现AlClPcTS同时以单体和二聚体的形式存在于复合体系中,且AlClPcTS二聚体所占比例随着凝胶化过程的进行而增大对不同AlClPcTS掺杂浓度复合干凝胶的光限幅性能进行了测试,并讨论了掺杂浓度对复合体系光限幅性能的影响,证明复合体系的光限幅性能随掺杂浓度的提高而增强.     

Effect of fluorine in Li1.27Cr0.2Mn0.53O2 cathode for secondary lithium batteries

Fluorine substituted Li_1.27Cr_0.2Mn_0.53O₂ electrode, prepared by sol–gel method, was investigated in the present work. Thermal analysis was done on this cathode material and found to be thermally stable with a loss of weight near 300 °C. Influence of fluorine substitution on the structural and electrochemical properties of the Li_1.27Cr_0.2Mn_0.53O₂ electrode was studied by X-ray diffraction (XRD) and field emission scanning electron microscope. XRD pattern of the fluorine-doped Li_1.27Cr_0.2Mn_0.53O₂ cathode material quenched at 900 °C indicates a phase pure material. The charge–discharge profile of the prepared cathode material showed that the fluorine substitution for oxygen in the cathode material resulted in improved capacity retention. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, December 7–9, 2006.     

Spectroscopic and photoluminescence studies on optically transparent magnetic nanocomposites based on sol–gel glass: Fe3O4

Sol–gel glasses with Fe₃O₄ nanoparticles having particle sizes laying in the range 10–20 nm were encapsulated in the porous network of silica resulting in nanocomposites having both optical and magnetic properties. Spectroscopic and photoluminescence studies indicated that Fe₃O₄ nanocrystals are embedded in the silica matrix with no strong Si–O–Fe bonding. The composites exhibited a blue luminescence. The optical absorption edge of the composites red shifted with increasing concentration of Fe₃O₄ in the silica matrix. There is no obvious shift in the position of the luminescence peak with the concentration of Fe₃O₄ except that the intensity of the peak is decreased. The unique combinations of magnetic and optical properties are appealing for magneto–optical applications.     

PNIPAM线性链与凝胶在二元溶剂中相变的变温NMR研究

通过对聚N-异丙基丙烯酰胺（PNIPAM）水溶液和凝胶在水和甲醇混合溶剂中的¹H NMR谱图以及弛豫时间(T₁与T₂)等多种NMR参数随温度变化的研究,发现PNIPAM大分子的基团质子NMR信号、溶剂的弛豫时间都可以用来灵敏表征PNIPAM在二元溶剂中的相变行为. 在PNIPAM凝胶中,温度升到LSCT以上,溶剂峰由单峰变为双峰,分别对应于受限在大分子网络内的受限溶剂和排除到大分子网络外的自由溶剂,两者的弛豫时间存在明显差异. 在PNIPAM溶液中,溶剂峰在相变前后并没有显著变化. 通过PNIPAM溶胀在water/alcohol混合溶剂中的相变研究进一步证实了PNIPAM与不同溶剂之间的相互作用强弱.      

Probing the ferroelectric phase transition in sol–gel‐derived polycrystalline bismuth ferrite thin films

Polycrystalline BiFeO₃ (BFO) thin films were successfully grown on Pt/Ti/SiO₂/Si(100) and SrTiO₃ (STO) (100) substrates using the chemical solution deposition (CSD) technique. X‐ray diffraction (XRD) patterns indicate the polycrystalline nature of the films with rhombohedrally distorted perovskite crystal structure. Differential thermal analysis (DTA) was performed on the sol–gel‐derived powder to countercheck the crystal structure, ferroelectric (FE) to paraelectric (PE) phase transition, and melting point of bismuth ferrite. We observed a significant exothermic peak at 840 °C in DTA graphs, which corresponds to an FE–PE phase transition. Raman spectroscopy studies were carried out on BFO thin films prepared on both the substrates over a wide range of temperature. The room‐temperature unpolarized Raman spectra of BFO thin films indicate the presence of 13 Raman active modes, of which five strong modes were in the low‐wavenumber region and eight weak Raman active modes above 250 cm⁻¹. We observed slight shifts in the lower wavenumbers towards lower values with increase in temperature. The temperature‐dependent Raman spectra indicate a complete disappearance of all Raman active modes at 840 °C corresponding to the FE–PE phase transitions. There is no evidence of soft mode phonons. Copyright © 2008 John Wiley & Sons, Ltd.     

Crystallization behavior and origin of c-axis orientation in sol–gel-derived ZnO:Li thin films on glass substrates

Preferentially, c-axis-oriented lithium-doped zinc oxide (ZnO:Li) thin films were prepared on Pyrex borosilicate glass substrates by a sol–gel method starting from zinc acetate dihydrate, lithium chloride, 2-methoxyethanol and monoethanolamine. Decomposition and crystallization behavior of dip-coated amorphous precursor films during post-annealing treatments were investigated by thermogravimetry–differential thermal analysis (TG–DTA), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), optical transmittance measurements, field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). It was revealed that the films contained the organic compounds at temperatures up to 300°C, which was the key to the transformation from the amorphous to the crystalline state. Thermodynamical consideration of nucleation and crystal growth was made taking account of surface energies of the film and the glass substrate and an interfacial energy between them. Mechanisms underlying the c-axis orientation were proposed based upon the initial orientation due to nucleation and final growth orientation.     

温度对涂有溶胶-凝胶多层干涉膜的卤钨灯光谱的影响

本文叙述了两个问题.首先,采用溶胶-凝胶浸渍水解法在H4汽车灯上制备了多层干涉膜.该膜层温度升高使这种灯透过膜层的光谱有所移动,于是引起灯发射光谱的变化.其次,我们研究了温度对膜材料光学性质的影响.