烷基聚葡糖苷微乳液中脂肪酶催化的酯合成反应动力学

在烷基聚葡糖苷C10G1．54／正丁醇／环己烷／磷酸盐缓冲液体系形成的油包水微乳液中,研究了在较高底物浓度下,脂肪酶催化正己酸和正丁醇的酯合成反应动力学及其影响因素。结果表明,在正己酸的初始浓度CHA^0较小时,反应初速率V0随正己酸浓度增大而增大,但随正丁醇表观浓度增大而减小;在CHA^0较大时,反应初速率V0随正丁醇表观浓度增大而增大,但随正己酸浓度增大而减小．在正己酸和正丁醇摩尔浓度之比为3．0左右反应速率最大．这些实验结果与传统的米氏反应不符,为此,从界面膜的构成,尤其是两种底物在界面膜上的分布情况人手进行了探讨．考察了C10G1.54浓度、正丁醇浓度和两者总浓度等对反应初速率V0的影响．     

粒度对多相反应动力学参数的影响

以纳米氧化锌与硫酸氢钠溶液为反应体系, 研究反应物粒度对动力学参数的影响规律. 讨论了表观活化能降低的原因. 结果表明：当反应物粒径、反应温度和搅拌速率一定时, 纳米氧化锌与硫酸氢钠溶液的反应速率仅与反应物的浓度有关；反应物粒度对多相反应的反应级数、速率常数、表观活化能和指前因子均有较大的影响；随着反应物粒径的减小, 表观活化能和指前因子减小, 而反应级数和速率常数增大, 并且速率常数和表观活化能与反应物粒径的倒数呈线性关系；反应物粒度是通过摩尔表面积、摩尔表面能和摩尔表面熵三个方面影响多相反应的动力学参数的.     

氨基酸在氯乙醇水溶液中的体积性质

利用精密数字密度计测定了甘氨酸、L-丙氨酸和L-丝氨酸在不同质量分数的氯乙醇水溶液中的密度，计算了这些氨基酸在氯乙醇水溶液中的表观摩尔体积、极限偏摩尔体积、迁移偏摩尔体积、理论水化数和体积作用系数，讨论了迁移偏摩尔体积和理论水化数的变化规律. 结果表明，三种氨基酸在氯乙醇水溶液中的迁移偏摩尔体积均为正值, 且随氯乙醇浓度的增大而增大. 氨基酸侧链对迁移偏摩尔体积的贡献与侧链性质密切相关. 三种氨基酸在氯乙醇水溶液中的理论水化数均随溶液中氯乙醇浓度的增加而减小. 甘氨酸与氯乙醇分子间的相互作用主要以1 : 1和1 : 2形式为主， L-丙氨酸和L-丝氨酸与氯乙醇分子间的相互作用主要以1 : 1形式为主.     

重稀土与偶氮氯膦Ⅲβ型反应动力学研究及机理的探讨

一定条件下,偶氮氯膦Ⅲ的重稀土螯合物可由α型转化成β型。连续扫描的谱图表明:α型是瞬时形成的。随着反应进行,α峰下降而β峰上升。在恒溫、Yb:R=1:1和pH=3.2时,测得非缓冲体系和缓冲体系(NaAc—HCl)的反应级数分别为2和1,表观活化能分别为71.1KJ/mol和49.8KJ/mol。对于许多缓冲体系,具有亲核基团的缓冲介质能够加速此转化过程。在此缓冲体系中,β型螯合物的生成速率随氢离子浓度的增大而减小,随缓冲介质浓度增大而增大。实验还表明:两个α型分子形成一个β型分子并释放出一个质子。据此,对缓冲体系和非缓冲体系分别拟出了合理的机理,稳态处理后的动力学速率方程满意地解释了所有实验事实。最后讨论了反应机理的可能模式。     

ACPMA/BPO引发甲基丙烯酸甲酯聚合及其动力学

以4,4′-偶氮二[4-氰基戊酰(对-二甲氨基)苯胺](ACPMA)/过氧化二苯甲酰(BPO)为氧化还原引发体系,研究了甲基丙烯酸甲酯(MMA)在N,N-二甲基甲酰胺(DMF)中的聚合及其动力学行为.考察了聚合反应温度、单体浓度、ACPMA浓度和BPO浓度对聚合反应速率和聚合物分子量的影响,测定了反应级数和聚合反应的活化能.结果表明,在一定范围内,聚合反应速率随单体浓度增大、ACPMA浓度增大、BPO浓度增大和反应温度的升高而增大;聚合物分子量随单体浓度的增大而增大,随ACPMA浓度的增大、BPO浓度增大和反应温度的升高而降低.该体系具有氧化还原引发体系的特征,其引发MMA的聚合速率方程为Rp=K[ACPMA]0.57     

孤岛减压渣油窄馏分的热反应动力学：——反应级数的计算

用超临界流体萃取精密分馏技术将孤岛减压渣油分成１５个窄馏分，选取其中８个在热重装置上进行了反应动力学研究。所得数据用（经本文作者改进）Ｚｓａｋｏ法进行动力学处理，计算了各窄馏分的热反应级数。结果发现，升温速率的改变对各窄馏分在同一转化率范围的反应级数影响不大，而在每一升温速率下，反应级数随反应温度和转化深度不同而改变。同时，不同升温速率下，随着转化深度的增加，各窄馏分的表观活化能升高。     

278.15-313.15 K下糖-水二元体系的介电常数

测定了D-(-)-果糖、D-(+)-葡萄糖、D-(+)-半乳糖、D-(+)-木糖和D-(-)-核糖五种糖的水溶液在不同质量摩尔浓度和不同温度下的介电常数(D). 结果表明, 在一定温度下, 这些糖的水溶液介电常数对数值都随糖浓度的增大而减小; 在一定糖浓度时, 介电常数值随温度升高而减小. 果糖、葡萄糖、半乳糖和木糖水溶液的介电常数(D)随温度的变化均满足关系式: lgD=A1-B1(T-298.15), 而核糖水溶液则符合: lgD=A2-B2(T-298.15)+C2(T-298.15)2. 此外, 这五种糖的水溶液的介电常数与摩尔分数(x)满足关系式: lg(D/D0)=-B3x. 在相同温度和浓度时, 介电常数的大小顺序通常为: 水>半乳糖-水>果糖-水>葡萄糖-水≥木糖-水(而核糖较特殊).     

不同温度下水溶液中树胶醛糖与HCl相互作用的体积性质

采用密度法研究了在278.15—318.15 K(间隔10 K)下树胶醛糖+HCl+水三元溶液的密度、树胶醛糖在盐酸(0.2—2.1087 mol/kg)中的表观摩尔体积VΦ,A、标准表观摩尔体积VΦ,A0和树胶醛糖与HCl的体积相互作用参数. 研究结果表明, 树胶醛糖在盐酸中的VΦ,A和VΦ,A0均随HCl浓度的增加而线性增大. 在一定温度下, 树胶醛糖从纯水到盐酸水溶液的标准转移表观摩尔体积均为正值, 且随盐酸浓度的增加而增大. 在所测温度范围内, 树胶醛糖在盐酸中的VΦ,A0随温度T的变化关系可表示为VΦ,A0=b0+b1(T-273.15)0.84. 树胶醛糖与HCl对体积相互作用参数VEN大于零, 但数值很小且对温度变化不甚敏感.     

重金属盐溶解-沉淀反应的吉布斯自由能变的定量估算

对重金属盐溶解-沉淀反应的吉布斯自由能变(ΔG)进行了定量估算;在不加缓冲剂和pH调节剂的纯水体系中,观测了重金属离子Pb2+、Ni 2+及Zn2+的沉淀-溶解反应,计算了反应的表观平衡常数Kf及表观溶度积常数K′sp;与此同时,对相关计算结果进行了实验验证.结果表明,重金属盐溶解-沉淀反应的ΔG只与反应物的初始浓度和平衡浓度有关,通过测定反应物的平衡浓度即可求得反应的ΔG;重金属离子Pb2+、Ni 2+及Zn2+的沉淀-溶解反应表观平衡常数Kf及表观溶度积常数K′sp皆随重金属盐的起始表观浓度Q0的增大而发生规律性变化:Kf先增大后减小,K′sp趋于最大恒定值,并接近于Ksp;而三种体系的ΔG均为负值,ΔG的绝对值先随Q0的增大而增大,然后趋于相对恒定.实验结果表明,不能用Kf而只能用Ksp描述重金属盐的沉淀-溶解平衡,ΔG绝对值与真正参与反应的反应物的量呈正相关;ΔG<0说明纯水中重金属盐的溶解反应是自发进行的.类似地,通过计算溶解-沉淀反应的ΔG,可以判断沉淀法处理重金属污染废水在热力学上的可行性.     

氨基酸-醇-水体系的密度与表观摩尔体积

用DMA602/60型震动管数字密度计测定了298.15 K下甘氨酸、丙氨酸分别在纯水和四个不同浓度甲醇、乙醇和丙醇水溶液中的密度, 计算了相应的表观摩尔体积, 用最小二乘法拟合了氨基酸在醇水溶液中的标准偏摩尔体积. 根据McMillan-Mayer理论拟合了水溶液中氨基酸分别与醇相互作用的对相互作用参数Vab和三相互作用参数Vabb, Vaab. 结果表明甘氨酸、丙氨酸在醇水溶液中的表观摩尔体积都随醇浓度的增加而增加, 都属亲水破坏性溶质; 其自相互作用参数和三相互作用参数均为正值, 对相互作用参数Vab均为负值且随烃基链的延长, 负值依次增大. 分别根据极性分子的相互作用模型、结构水化模型和溶剂分离缔合模型进行了讨论.     

Frequency-domain measurement of the photodegradation process of fluorescein

The frequency-domain technique is applied to measure the photodegradation rate of fluorescein in aqueous solutions. The illuminating light is modulated, and the changes in fluorescence from the illuminated region are detected synchronously. A constant flow rate is imposed on the fluorescein solution to control the mass transport of fluorescein into the illuminated region. The fluorescence response is described by a model that assumes that photodegradation occurs from the triplet excited state. The predictions of the model are consistent with the observed variations in the fluorescence response with flow rate, modulation frequency and incident power. We discuss in this article how the dependence of the model parameters on experimental conditions can be used to infer the photodegradation rate as well as some of the details of the photodegradation mechanism. The results are consistent with the known mechanism of photodegradation of fluorescein. The frequency-domain technique gives a photodegradation rate of 53 s(-1) in an air-saturated solution and 37 s(-1) in solutions purged with argon gas.     

水溶液中苯乙酮及其降解产物的紫外光光解

在紫外光作用下,水中苯乙酮(10^-^4mol.dm^-^3,pH=6)能发生直接光降解,生成邻羟基和间羟基苯乙酮等中间产物,并且这些产物又可进一步光解生成二羟基苯乙酮。在相同条件下,它们的相对光降解速率大小为:苯乙酮>间羟基苯乙酮>对羟基苯乙酮>邻羟基苯乙酮。     

Method of kinetic analysis of photodegradation: nifedipine in solutions

A rate equation for photodegradation was derived from Lambert-Beer's law and Grotthus-Draper's law: -dc/dt=k1(1-exp(-(k2c+k3(c0-c))))k2c/(k2c+k3(c0-c)) where c is the concentration of reactant, c0 is the initial concentration of reactant, t is time, k1 is the rate constant, and k2 and k3 are the absorption coefficient of reactant and its photodegradation product, respectively. In a case where the photodegradation products have no photoabsorption, k3 assumes the value of zero in the above general equation. In a case where the photodegradation products have the same spectrum and molar absorptivity as that of the reactant, k3 assumes the value of k2, and hence the photodegradation is not a first-order reaction; however, the equation itself gives the pseudo-first-order reaction rate equation. In a case where the concentration of reactant is high enough, the equation approaches a zero-order reaction rate equation. The photodegradation rate of nifedipine in solutions under a germicidal lamp, near an ultraviolet fluorescent lamp and a fluorescent lamp was analyzed using the above equation. The photodegradation rate was directly proportional to the amount of light absorbed, and fitted well with the equation. The above theoretical equation was substantiated by the photodegradation of nifedipine, and hence is expected to apply to other photosensitive drugs.     

Adsorption and Photodegradation of Methylene Blue by Using PAni/TiO2 Nanocomposite

In this study, polyaniline-titanium dioxide (PAni-TiO₂) nanocomposite has been prepared and was utilized as an effective catalyst for photodegradation of methylene blue (MB) dyes from aqueous solution. Adsorption characteristic on the PAni-TiO₂ surface and the aqueous solubility of the dyes also play an important role in the photodegradation of dye. Adsorption and photodegradation process occurs simultaneously on the surface of the catalyst at first adsorption occurs (21.5%) on the outer surface of the catalyst and then photodegrade the material up to (66.5%). In reaction mechanism OH^· makes the vital role to the degradation of methylene blue and its intermediates. To know the surface and stability of the photocatalyst, it was characterized by FTIR, TEM, TGA–DTA, XRD, UV-vis spectrophotometer, and SEM analysis. Kinetic data indicate that up to 20 minutes photodegradation rates usually follows the pseudo-first-order reaction. After 20 minutes, it follows the Langmuir-Hinshelwood (LH) kinetics. Photo reactivity of PAni-TiO₂ was studied with pH of solution, dosage of photocatalyst and concentration of dye. The reaction rate constant (r) and equilibrium binding constant (K) values were incredibly significant than other catalyst.     

Effect of operational parameters on photodegradation of methylene blue on ZnS nanoparticles prepared in presence of an ionic liquid as a highly efficient photocatalyst

In the present study, photocatalytic degradation of methylene blue (MB) on ZnS nanoparticles, prepared in aqueous solution of a room-temperature ionic liquid (RTIL), was studied and the results were compared with commercial ZnS. Influence of various operational parameters such as calcination temperature, catalyst weight, pH of solution, and initial concentration of MB on the photodegradation reaction was investigated to achieve maximum degradation efficiency. The optimum value of pH and catalyst dose was found to be 9.5 and 0.6 g l^-1. It was demonstrated that the photodegradation of MB follows a pseudo first-order kinetic. At optimized conditions, the rate constant of the reaction on ZnS nanoparticles prepared in aqueous solution of the RTIL is about five and four times greater than the prepared sample in water and commercial ZnS, respectively.     

可见光驱动Ag@AgCl催化反应的原位微量热研究

室温下用葡萄糖还原前驱体AgCl制备了可见光驱动的表面负载Ag纳米颗粒(NPs)催化剂Ag@AgCl,并采用X射线衍射(XRD)、场发射扫描电镜(FE-SEM)对其形貌、组成和结构进行了表征.首次运用自主设计的新型光化学-微量热系统,获取了三个功率光催化降解甲基橙的原位特征热谱曲线和原位热动力学精细信息,并与紫外-可见光谱获得的动力学信息关联,结合甲基橙逐步被氧化降解的特征,讨论了光催化降解机理.结果表明:光催化降解过程首先是偶氮双键在光的作用下迅速吸热断裂,再进入氧化降解中间产物的放热阶段,最后以恒定的速率长时间放热.光催化反应主要受光功率大小、粒子的传质以及活性氧化物种产生的速率等共同影响.随着光功率减小,光催化反应速率减缓,体系热效应的特征变化出现滞后现象,达到最大吸、放热峰及甲基橙完全降解所需时间延长.     

Viscoelastic properties of polyacrylonitrile gels: dependence of sol-gel transition on concentration and aging time

Dynamic viscoelasticity was observed for polyacrylonitrile solution in dimethylacetamide in the process of sol-gel transition. The gel was prepared by the freezing and thawing method, i.e., the solution was frozen at −50°C and then kept at 25°C so as to undergo gelation. The longer the freezing time, the shorter was the gelation time. Also the higher the concentration, the shorter the gelation time. The strength of the network, S and critical exponent n at the transition point were evaluated. The S value increased with increasing concentration and was constant in value in spite of the variation of freezing time when the concentration of the solution was constant.     

Photo-oxidation of phenol over titania pillared zirconium phosphate and titanium phosphate

The photodegradation of phenol was studied in the aqueous solutions over titania pillared zirconium phosphate and titanium phosphate under solar radiation and compared with that of the UV-radiation (6 W low pressure Hg vapor lamp). This reaction was studied by varying different parameters such as catalyst dose, initial phenol concentration, pH of solution and irradiation time. The degradation rate of phenol was favourable under neutral pH condition. The degradation process approximately obeyed first-order kinetics with apparent rate of degradation constant increasing with decreasing the initial phenol concentration.     

Degradation of polymer coating systems studied by positron annihilation spectroscopy. IV. Oxygen effect of UV irradiation

The effect of oxygen on the photodegradation of a polyurethane coating induced by accelerated UV irradiation was studied with two different light sources: 313‐nm UVB and Xe lamps. Doppler‐broadened energy spectra (DBES) and positron annihilation lifetimes were measured as a function of incident positron energy (0–30 keV) and irradiation time (0–100 h). The photodegradation of the coating was characterized in terms of subnanometer defect changes. Significant variations of the S parameter (a defect parameter from DBES) and the ortho‐positronium lifetime and intensity were observed as a function of oxygen concentration during exposure to UV irradiation. These results showed a significant enhancement in photodegradation due to the presence of oxygen, as indicated by a decrease in free volume and holes at the atomic level. Enhanced degradation in the presence of oxygen, as indicated by increased free‐radical production (observed with electron spin resonance spectroscopy), was also observed. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2035–2047, 2001     

Degradation of carbofuran in aqueous solution by Fe(III) aquacomplexes as effective photocatalysts

The photodegradation of carbofuran by excitation of iron(III) aquacomplexes was investigated under UV irradiation. The degradation rate was strongly influenced by the pH, and initial concentration of Fe(III). The degradation efficiency of carbofuran at the difference pH was in good agreement with the initial concentration of Fe(OH)²⁺ in the solution. An initial carbofuran concentration of 10 mg L⁻¹ was completely degraded within 50 min at pH 2.8 with original Fe(III) concentration of 8 × 10⁻⁴ mol L⁻¹. This degradation reaction was found to follow the first order kinetics law and the rate constant of 1.60 × 10⁻³ s⁻¹ was observed. The decrease of TOC content was observed during the photocatalytic process and the removal percentage obtained was about 70% after 25 h. Furthermore, ammonium ion as an end-product was detected in the solution. Therefore, this process based on the catalytic reaction of Fe(II, III) is responsible for the continuous production of hydroxyl radicals in such system. A gas chromatography-mass spectrometry analysis showed the formation of four photoproducts, such as 2,2-dimethyl-2,3-dihydro-benzofuran-7-ol, etc., revealing that the carbamate branch, C-3 and C-2 positions in furan ring were attack targets of hydroxyl radicals. Based on these results, the photocatalytic system could be useful technology for the treatment and the mineralization of compounds like carbofuran.