非晶纳米过氧聚钨酸的Raman谱、热稳定性及UV-Vis光吸收特性

过氧聚钨酸是通过化学途径合成各种纳米结构氧化钨的重要前驱物之一。本文以双氧水(H₂O₂)、钨粉(W)和无水乙醇为原料合成了过氧聚钨酸溶胶,随后在常温下长时间放置,直至自然凝固,并在120 ℃干燥3 h后得到最终的深黄色胶状固体。利用XRD、SEM、Raman谱、TG/DSC分析和UV-Vis谱等分别考察了样品的成分结构、热稳定性和UV-Vis光吸收特性。宽的XRD峰表明样品是非晶结构,明显峰位的高斯型拟合表明样品是氧化钨与水合氧化钨的复合物。SEM表明样品呈纳米颗粒状(50～100 nm)和片层状形貌(厚约50 nm)。宽而明显的Raman峰的高斯型拟合进一步表明样品是非晶氧化钨和水合氧化钨的复合物,不仅拥有非常明显的O—W—O对称伸缩、非对称伸缩和WO振动,而且伴有O—W—O对称弯曲、非对称弯曲及吸附水的振动模式。TG/DSC分析表明过氧聚钨酸凝胶固体在120～500 ℃范围内存在四个不同的热力学过程：(Ⅰ)过氧聚钨酸凝胶固体的缓慢晶化(120～165 ℃);(Ⅱ)H₂O₂的分解和H₂O的去吸附(165～236 ℃);(Ⅲ)水合氧化钨的快速分解(236～287 ℃);(Ⅳ)最终产物WO₃的晶化和相变(287～500 ℃)。UV-Vis谱表明样品在350～600 nm范围存在一个明显的带边吸收,其光学带隙约2.25 eV,明显低于当前已报道的WO₃和H₂WO₄的带隙值(2.45～3.50 eV)。存留在复合物中的水分子、氧缺陷以及结构性畸变应该是导致其拥有较窄带隙的关键因素。     

基于二维红外技术研究氧化羧甲基纤维素钠/胶原的相互作用及热稳定性

采用氧化羧甲基纤维素钠(OCMC)作为交联剂,对胶原溶液进行改性并采用二维红外技术分析OCMC与胶原之间的相互作用及其对胶原热稳定性的影响。一维红外图谱显示OCMC交联改性对胶原的主要特征吸收峰即酰胺Ⅰ,Ⅱ和Ⅲ带的峰位与强度无明显影响;改性前后胶原的酰胺Ⅲ带与1 455 cm-1处吸光度的比值A_Ⅲ/A_{1 455}均接近于1.000,以上结果显示交联键的引入不会破坏胶原的三股螺旋结构,但无法获知胶原与OCMC之间的相互作用及胶原结构的变化。以OCMC用量为外扰条件建立二维红外相关图谱,进一步分析两者间相互作用。结合胶原结构与OCMC中基团的响应强度及顺序可知：OCMC首先通过羧基与胶原中精氨酸的胍基或赖氨酸的氨基发生静电作用,随后醛基与胶原氨基之间发生希夫碱反应;两者之间相互作用以希夫碱反应为主。由于静电作用与交联键的引入,改性后胶原的热稳定性得到提升。随着温度的升高,纯胶原与改性胶原的特征吸收峰均发生红移且A_Ⅲ/A_{1 455}值不断降低,说明两者在升温过程中其氢键不断减弱,导致三股螺旋发生解旋,但与纯胶原相比,改性胶原特征吸收峰的红移程度与A_Ⅲ/A_{1 455}值降低幅度较小,证实了改性后胶原的热稳定性有所提高。胶原与改性胶原在升温过程中结构变化的分析结果表明：改性前后胶原二级结构的崩塌均表现为三股螺旋结构被破坏转变成无规卷曲结构;然而在测试温度范围内,三股螺旋结构对温度的敏感度及响应顺序发生明显变化：（1）对于纯胶原,对温度最为敏感的结构是胶原的螺旋结构,而改性胶原的无规卷曲结构是最为敏感的、最不敏感的结构是胶原螺旋结构,反映出改性后胶原的螺旋结构得到稳定;（2）改性后胶原螺旋结构对温度的响应发生滞后,进一步证实胶原的稳定作用主要归功于三股螺旋结构的加固。     

Probing the Conformational Stability of Two Different Copper Proteins: A Dynamic Fluorescence Study on Azurin and Ascorbate Oxidase

Tryptophan fluorescence is extremely useful to monitor structural conformational transitions in proteins. Denaturant-induced unfolding of azurin and ascorbate oxidase has been studied by dynamic fluorescence measurements in the frequency domain and the results have been interpreted in terms of continuous distribution of lifetimes. The data add new information on the unfolding mechanism that was previously analyzed by steady-state emission spectroscopy. In particular, the existence of multiple, parallel unfolding pathways may be envisaged and correlated, in both cases, to the two protein structures. The effect of metal depletion has been also characterized by fluorescence lifetime measurements. In the case of azurin, a monomeric protein, the data demonstrate that copper removal yields a totally different unfolding pathways with respect to the holo protein, indicating that metal ion plays a fundamental structural role in the wild type, native protein. In the case of ascorbate oxidase a dimer of 140 kDa, only minor effects have been detected by copper removal. However, the analysis of the fluorescence decay in presence of different amounts of guanidinium hydrochloride gives new important insights on the unfolding intermediates. In particular the data support the hypothesis of a partial exposure of an outer layer of dimer at intermediate denaturant concentration. This ability of dynamic fluorescence to pinpoint the presence of structural micro-heterogeneity in the unfolding pathways of proteins demonstrates the greater power of this technique compared to the most commonly used steady-state measurements.     

非平衡磁控溅射法制备的Cr-DLC薄膜真空退火的Raman光谱研究

利用非平衡磁控溅射法制得厚度达到2.23 μm的掺铬含氢类金刚石(Cr-DLC)碳膜。采用Raman光谱和XPS对制得的薄膜进行了结构和热稳定性等表征。结果表明：室温时,薄膜在1 544 cm-1附近的Raman“G”峰归属于石墨结构中C—C键的伸缩振动,即E_2g 模式;而1 367 cm-1附近的“D”峰归属于sp2碳环的“呼吸”振动模式,即A_1g模式;计算得到薄膜sp3键的相对含量约为48at.%。加热至300 ℃,薄膜的Raman谱图与室温时相似,表明此温度段薄膜的结构稳定,未发生明显改变;至400 ℃时,I_D/I_G值迅速增大,sp2键含量升高, 表明此时DLC膜发生了明显的结构变化,开始发生石墨化。继续升温,膜中I_D/I_G比率增加,“G”峰位向高波数方向位移,表明 sp2/sp3比率逐渐增大,薄膜石墨化程度加强,sp2键的无序度逐渐降低,最终导致薄膜的摩擦系数和磨损率等逐渐增大, 热稳定性逐渐降低。退火600 ℃时,I_D/I_G值以及sp2键含量达到最大值,DLC薄膜失效。     

射频溅射功率对AZO薄膜结构及光电特性和热稳定性的影响

采用射频磁控溅射法,在玻璃基片上制备了ZnO:Al(AZO)透明导电薄膜。用X射线衍射(XRD)仪、紫外-可见分光光度计、方块电阻测试仪和台阶仪对不同溅射功率下Al掺杂ZnO薄膜的结晶、光学、电学性能、沉积速率以及热稳定性进行了研究。研究结果表明:不同溅射功率下沉积的AZO薄膜具有六角纤锌矿结构,均呈c轴择优取向;(002)衍射峰强和薄膜的结晶度随溅射功率的提高逐渐增强;随溅射功率的提高,AZO薄膜的透射率有所下降,但在可见光(380～780nm)范围内平均透射率仍80%;薄膜的方块电阻随溅射功率的增加逐渐减小;功率为160～200W时,薄膜的热稳定性最好,升温前后方块电阻变化率为13%。     

基于光谱分析技术的肉桂醛与玉米醇溶蛋白作用机理的研究

通过荧光光谱、紫外光谱、圆二色谱、红外光谱、核磁共振光谱研究肉桂醛与玉米醇溶蛋白间的作用机理,为改善玉米醇溶蛋白膜的机械性能及抗菌性和抗氧化性提供研究依据。通过三维荧光光谱检测,发现肉桂醛对玉米醇溶蛋白有明显的荧光猝灭作用,而且溶剂乙醇对猝灭现象有影响。用紫外差谱观察到玉米醇溶蛋白在紫外区278 nm的吸收强度随肉桂醛浓度增大而加大,但增加的幅度与浓度改变不成比例,氨基酸残基的特征吸收峰的位置没有变化。加入肉桂醛前后,圆二色谱显示的两条曲线近乎重合。利用全反射ATR附件测定傅里叶变换红外光谱,发现加入肉桂醛之后,1 650和1 538 cm-1的吸收峰峰位没有发生明显的变化,但1 625 cm-1处出现了明显的肩峰,体现了肉桂醛碳碳双键的吸收,指纹区879.44 cm-1处的峰消失,973.46 cm-1处出现新峰,显示出肉桂醛反式双键的吸收,说明玉米醇溶蛋白与肉桂醛发生了非键合作用。对酰胺Ⅰ带进行自去卷积计算,发现玉米醇溶蛋白的二级结构中α螺旋结构变化甚微,β转角发生显著改变。通过核磁共振氢谱,分析4个位置的质子H的化学位移,仅改变了0.01,而且加入肉桂醛1和4 h之后,化学位移改变量相等,证明肉桂醛与玉米醇溶蛋白的结合反应发生在蛋白表面。对体系的热力学参数进行计算,可知肉桂醛与玉米醇溶蛋白之间发生的是结合比为1∶1的自发结合反应;在肉桂醛低浓度时,猝灭常数随温度的升高而降低,但变化不显著;结合常数很大,数量级达到105,且随温度的升高而降低。在有无肉桂醛的条件下,对玉米醇溶蛋白荧光寿命的测定,进一步确认二者之间发生的是静态猝灭。综合多种光谱分析结果,说明肉桂醛与玉米醇溶蛋白主要在芳香区的外部发生π-π堆积,以静电力结合,是静态猝灭机制,与作用时间的长短无关。结果表明玉米醇溶蛋白中加入肉桂醛,对其二级结构不会造成明显的影响。     

Optimization of Thermal Stability of High-Density Polyethylene Composite Using Antioxidant,Carbon Black and Nanoclay Addition by a Central Composite Design Method: X-ray Diffraction and Rheological Characterization

The thermal stability of high-density polyethylene, as characterized by an Oxidation Induction Time (OIT) test in the presence of the three additives, antioxidant, carbon black and nanoclay, was investigated. The twenty experiments used were designed by using the Central Composite Design (CCD) method, and the effects of the main parameters and their interactions were analyzed. The results of Analysis of Variance (ANOVA) showed that the antioxidant, nanoclay and carbon black contents, the antioxidant-nanoclay interaction and the antioxidant-carbon black interaction, had significant effects on the thermal stability. By optimization of the percent compositions used, the best composition was obtained, 0.26%, 2.21% and 4.69% for antioxidant, carbon black and nanoclay, respectively, to achieve thermal stability equal to the targeted value of 60?minutes. X-ray diffraction confirmed a weak polymer-nanocaly interaction in the optimal sample structure. The rheology frequency sweep test showed an increase in the elastic and viscous modulus in the optimal sample relative to the control samples. The Melt Flow Index (MFI) test for an optimum sample showed a pseudo-plastic structure with the lowest melt flow index of 0.2614 g/10 min, which was consistent with the results of the complex viscosity, with the optimal sample having the highest value (128500?Pa.s). The density test indicated the most crystalline structure for the optimized sample, with the highest value (0.976?g/cm³) compared to the control samples (0.962 and 0.957?g/cm³ for the polyethylene/nanoclay and the polyethylene/carbon black sample, respectively).     

基于可见-近红外和热红外光谱联合分析的煤和矸石分类方法研究

煤与矸石是矿山采煤过程中主要固体堆放物,对其进行遥感动态监测是矿山环境保护的重要需求。由于煤与部分矸石存在“异物同谱”现象,在使用传统的可见-近红外遥感分类时,往往将部分矸石划分为煤,导致遥感分类精度降低。首先对铁法矿区的12个煤样本和115个矸石样本进行可见-近红外光谱测试,发现绝大部分矸石样品的光谱与煤差异很大,二者易于区分,但有部分矸石与煤样本存在“异物同谱”现象。为进一步对矸石与煤区分,测试了混分样本的热红外光谱,发现二者存在明显的光谱差异,利用热红外光谱特征可以将其区分开来。在此基础上,提出了基于可见-近红外和热红外光谱联合分析的煤与矸石区分方法。该方法首先对所有样本进行可见-近红外光谱测试,利用Mao模型进行第一步分类识别;其次对煤与矸石混分的样品进行热红外光谱测试,利用光谱吸收比率SAR作为判别指标进行第二步分类,两步的分类结果为最终分类结果。该方法在铁法、兖州、神东和木里矿区的验证结果表明,其具有很高的分类准确率,效果远好于单独基于可见-近红外光谱特征的分类方法。研究结果表明,利用多种光谱联合分析的方法可以解决单波段存在的“异物同谱”现象,对于地物遥感分类具有重要的借鉴意义。     

An FTIR study of the bonding of methoxy on Ni(100): effects of coadsorbed sulfur, carbon monoxide and hydrogen

The vibrational spectra of CH₃O_(a), CD₃O_(a), CDH₂O_(a) and CD₂HO_(a) on Ni(100) are analyzed and interpreted in terms of resonances between fundamental modes and either combinations or overtones. Analysis of the symmetry of the modes observed suggests that methoxy binds normal to the surface with C_s symmetry, at least at low coverages. Two distinct vibrational bands emerge in the vibrational spectrum of methoxy in the v(CO) region as the coverage increases which are attributed to bonding in four-fold hollow sites and bridging sites. These bands exhibit blue shifts of about 25 cm⁻¹ with increasing coverage up to the saturation coverage. The vibrational bands in the v(CH) region appear concomitantly at all coverages and shift down 12 cm⁻¹ as the coverage is increased. These shifts are attributed to changes in the metal-oxygen bond which are reflected in changes in the strength of the C---O and C---H bonds. Affects on the bonding also appear to occur with the coadsorption of hydrogen or CO with methoxy. Coadsorption of 0.36 ML hydrogen with 0.04 ML methoxy induces blue shifts of 15 and 7 cm⁻¹ for the v(CO) bands at 949 and 984 cm⁻¹, respectively. Adsorbing 0.43 ML of CO with 0.04 ML methoxy (and 0.04 ML hydrogen) causes a red shift of 20 and 12 cm⁻¹ for these bands. A drastic drop in mode intensities for methoxy when CO is coadsorbed suggests that the methoxy tilts away from the surface normal. Pre-adsorbing sulfur on the Ni(100) surface reduces the amount of methoxy formed from methanol, but the v(CO) methoxy bands are unshifted in frequencies relative to their position for the same methoxy coverage on the clean surface.