Table of Content

20 August 2001, Volume 19 Issue 3

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A PRACTICAL METHOD TO SYNTHESIZE 2,2’,7,7’-TETRAIODO-9,9’-SPIROBIFLUORENE

WU Xiao-ming, CHEN Xiao-chuan, CAO Xiao-ping, PAN Xin-fu

2001, 19(3):  161-164.  DOI: 10.7517/j.issn.1674-0475.2001.03.161

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2,2’,7,7’-tetraiodo 9,9’-spirobifluorene (2) is the key intermediate of hole transport media and conducting polymers. We developed a practical method by which 2 was highly selective synthesized in good yield.

THE EFFECT OF ACTIVE CARBON SUPPORT ON PHOTOCATALYTIC DEGRADATION OF DICHLOROACETIC ACID FOR TiO₂

LI Xue-ping, ZHANG Jing-bo, YIN Feng, LIN Yuan, XIAO Xu-rui

2001, 19(3):  165-168.  DOI: 10.7517/j.issn.1674-0475.2001.03.165

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The photocatalytic degradation of dichloroacetic acid in the aqueous solution was studied using pure TiO₂ and TiO₂ supported on active carbon as photocatalysts. It was found that the photocatalytic reaction rate of TiO₂ was increased by the presence of active carbon support, but the TiO₂/AC prepared by adding active carbon during the formation of TiO₂ sol exhibited much higher photocatalytic activity than TiO₂+AC formed by mechanical mixture of TiO₂ particles and active carbon in the suspension. The apparent rate constants, KCl^- for Cl^- production were 6.72×10^-3,3.72×10^-3 and 3.45×10^-3 min^-1 for TiO₂/AC, TiO₂+AC and TiO₂ respectively. The photocatalytic activity of TiO₂/AC having various AC content was also compared. With AC mass fraction of 5%-20% the KCl^- for TiO₂/AC was obviously larger than that for TiO₂, but the result was contrary to this for higher AC mass fraction(≥30%). The present results have clearly demonstrated that because as TiO₂ was supported on active carbon, the effective surface area of the photocatalysts and their adsorbability for organic molecules can be increased, providing high concentration environments of organic molecules around TiO₂ particles and resulting to the enhancement of photocatalytic activity of TiO₂.

STUDY ON THE PHOTODEGRADATION MECHANISM OF CYANINE DYES AND MEROCYANINE DYES SOLUTION

YANG Song-jie, MENG Fan-shun, TIAN He, YAO Si-de

2001, 19(3):  169-176.  DOI: 10.7517/j.issn.1674-0475.2001.03.169

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The photodegradation kinetics of cyanine dyes and merocyanine dyes were studied by UV-Vis absorption spectroscopy. The results show that the rate of the photofading reactions of the dyes follow quasi-first-order or zero order kinetics in acetonitrile. The main photodegradation products of the dyes were identified by GC/MS spectrometry. Those cyanine dyes holding a positive charge have relative good photostability comparing with merocyanines. The experimental results imply that the photodegradation intermediates for the cyanine dyes may be the semi-oxide-state of dye, Dye⁺. The transient absorption spectra of Dye⁺ were measured by nanosecond laser flash photolysis.

THE INTRAMOLECULAR EXCIMER FORMATION AND THE pH EFFECT ON THE FLUORESCENCE OF MULTI-PEDAL COMPOUNDS

XIE Hong-zhi, SUN Zhao-yong, AI Xi-cheng, ZHANG Xin-kang, WU Shi-kang

2001, 19(3):  177-184.  DOI: 10.7517/j.issn.1674-0475.2001.03.177

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The steady and transient state photo physical behaviors of multi pedal naphthyl urea derivatives were studied in this work. It is due to the fact that the interaction between urea groups perturbs the π-π overlap of naphthyl groups resulting in a negative effect on the excimer formation of naphthalene. Experiments show that because the electronic donating group, tertiary amine, exists in the molecule 1, the fluorescence of excited naphthyl group can be quenched via the intra molecular electron transfer process. In this case, although the fluorescence of excimer can be observed by method of spectrum normalization from the steady state spectra of tri podal compound, but the intensity is quite weak. In addition, the pico second single photon counting method is used to measure the fluorescence life time of these compounds. It is found that the decay process of transient species is an tri exponential one. The emission species with the longest life time is attributed to the formation and decomposition of naphthalene excimer. The quantity of the largest life time component in total excited species is just only 4%. This corresponds to the results obtained from the steady state study. The results indicate that for the compound 1, used as a fluorescence chemical sensor, the change of fluorescence of the excimer used as a sensing part for the detection of foreign species is not suitable. On the contrary, if the foreign species introduced is able to affect the degree of intra molecular electron transfer of this compound, and furthermore to affect the fluorescence intensity of naphthalene, it should be a very sensitive way to indicate whether the complexation of guest molecule with host occurs.

SYNTHESIS AND PHOTOSTABILITY OF CYANINE AND MEROCYANINE DYES SOLUTION

YANG Song-jie, MENG Fan-shun, CHEN Kong-chang, TIAN He, WANG Wen-wei

2001, 19(3):  185-192.  DOI: 10.7517/j.issn.1674-0475.2001.03.185

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The photodegradation kinetics of cyanine dyes and merocyanine dyes were studied by UV-Vis absorption spectroscopy. The results show that the rate of the photofading reactions of the dyes follows quasi-first-order or zero-order kinetics in acetonitrile. Those cyanine dyes holding a positive charge have relative good photostability comparing with merocyanines.

PHOTO AND THERMAL DECOMPOSITION OF DIFFERENT DIPHENYLAMINE-4-DIAZONIUM SALTS AND THEIR RESINS

SUN Feng, YANG Bo-xuan, WANG Ren-xiang, CAO Wei-xiao

2001, 19(3):  193-197.  DOI: 10.7517/j.issn.1674-0475.2001.03.193

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The photo and thermal decomposition of three diphenylamine-4-diazonium salts: DS, MDS, NDS and the corresponding diazoresins DR, MDR, and NDR were investigated in water and in solid films. It was found that the photo-decomposition is no obvious difference in aqueous solution for various salts and resins, but the thermal decomposition is different remarkably. The methoxy substituted diazonium salt(MDS) and resin(MDR) possess higher thermal stability than that of DS, NDS and their resins. In the case of solid films the NDR exhibits superior thermal stability due to its high hydrophobic characteristic.

PREPARATION OF NANOMETER Al₂O₃ PARTICLES

TANG Fang-qiong, GUO Guang-sheng, HOU Li-ping

2001, 19(3):  198-201.  DOI: 10.7517/j.issn.1674-0475.2001.03.198

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Dispersed nano-Al₂O₃ particles were prepared by the hydrolysis of metal alkoxides in isopropanol solution with the method of two step. The effect of reactive condition on particle size and distribution was investigated systematically. The size of prepared particles varies from 20 nm to 100 nm along with the change of reactive condition.

A STUDY ON PHOTOCATALYTIC OXIDATION OF I^-OVER A TiO₂ THIN FILM

CUI Yu-min, SHAN De-jie, ZHU Yi-ren

2001, 19(3):  202-207.  DOI: 10.7517/j.issn.1674-0475.2001.03.202

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Photocatalytic oxidation of I^- in aqueous solution was studied in a photocatalytic reactor, in which the surface of the glass beads was covered with evenly transparent TiO₂ thin film by sol gel process. It is observed that the yield of I₂ formation is dependent on the crystal structure of the catalyst, the illumination time, the initial concentrations of I^- and H⁺. The results show that the yield of I₂ can reach 41.26% over anatase TiO₂ coated film, with photocatalyst (4.0 g) in the solution of KI (3 L), of 0.3 mol/L, of 3.0 mol/L and illumination time of 8 h.

THE MECHANISM AND APPLICATION OF HYBRID UV CURING SYSTEM

CHEN Ming, CHEN Qi-dao, XIAO Shan-qiang, HONG Xiao-yin

2001, 19(3):  208-216.  DOI: 10.7517/j.issn.1674-0475.2001.03.208

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Hybrid UV curing or dual curing consists of two or more kinds of polymerization or crosslinking reactions that take place in the same system, which is a novel approach to modify polymer materials in-situ. Hybrid UV curing system includes free radical-cationic hybrid UV curing system, Free radical-condensation polymerization system and free radical-free radical system. The mechanism and application of hybrid UV curing are reviewed in this paper.

THE ADVANCEMENT ON FLUORESCENT SENSORS AND SWITCHES FOR METAL CATIONS IN PET SYSTEM

XU Feng-bo, LI Qing-shan, ZHANG Zheng-zhi, WU Li-zhu

2001, 19(3):  217-228.  DOI: 10.7517/j.issn.1674-0475.2001.03.217

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Molecular recognition is a core concept of supramolecular chemistry, in which fluorescent sensors and switches system is one of the most important part. In this work, we summarized the recent achievements and advancement in this field.

A REVIEW ABOUT MECHANISM OF THE STABILIZERS AND ANTIFOGGANTS FOR SILVER HALIDE EMULSION

LIU Xiao-hui, LI Yuan, HUANG De-yin, ZOU Jing

2001, 19(3):  229-236.  DOI: 10.7517/j.issn.1674-0475.2001.03.229

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A review about mechanism of the stabilizers and antifoggants for silver halide emulsion was presented in this paper with reference to a survey of publications which were published on this subject in three decades. Three different mechanisms of adsorption effect, salt effect and oxidation effect were summarized.