Effect of vinyl acetate on aging mechanism of polyacrylate under UV light

Diversity of aging behaviors of polyacrylate and poly(vinyl acetate‐acrylate) with the ultraviolet light radiation was studied. The aging degree was evaluated and the mechanism dominated the behaviors was investigated by color aberration, the degree of cross‐linking, molecular weight and its distribution by gel permeation chromatography (GPC), ultraviolet absorption spectroscopy (UV–vis), and fourier transform infrared spectrometer (FTIR). These studies found that although photodegradation mechanism of poly(vinyl acetate‐acrylate) still preserves three main steps of the scission of main chain, formation of double bond and the generation of cross‐linking reaction, introducing structural units of vinyl acetate to polyacrylate cause the rules various. The structural units can aggravate the aging of polyacrylate, through increasing formation of double bonds and generating cross‐linking reaction. However, what is interesting is that the structural units can strikingly restrain main chain from scission. It is significant for modifying the photodegradation behaviors of polyacrylate coatings. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Hydrothermal synthesis of hierarchical rose-like Bi2WO6 microspheres with high photocatalytic activities under visible-light irradiation

Hierarchical rose-like Bi₂WO₆ photocatalyst was successfully synthesized through a simple hydrothermal route using thiourea and acetic acid as complexing agents. The as-synthesized product was determined as pure orthorhombic Bi₂WO₆ based on the results of X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) measurements. The photocatalyst had an average diameter of 2–3 μm and it was constructed by many nanoflakes. The surfaces of these nanoflakes were coarse and had many nanocrystals on them. The hierarchical rose-like structure was formed through a typical hierarchical assembly process with the synergistic action of acetic acid and thiourea. The photocatalyst showed excellent visible-light-driven photocatalytic performance, it could decompose rhodamine B(RhB) within 50 min. This excellent performance resulted from its special microstructure and the relatively large surface area.     

Modeling of Photochemical Reactions in a Focused Laser Beam,II

A method is described for obtaining the rate constant of the photodegradation process of fluorophores illuminated by a focused laser beam. The explicit kinetic equations, describing the population dynamics of excited singlet and triplet states, are averaged over the illuminated volume to describe the resulting fluorescence signal. The illumination is modulated at frequencies from 1 Hz to 100 Hz. Synchronous detection of the resulting fluorescence yields in-phase and quadrature components. The measurement of the ratio of quadrature to in-phase components at several power levels yields information on the photodegradation rate. Specifically it is shown that the data can be interpreted in a manner which yields the value of the photodegradation rate independently of other parameters entering the model. Experiments are performed with erythrosine B which has a large intersystem crossing rate to the triplet state. Measurements in solutions with different viscosities show that the photodegradation rate depends on the viscosity. This is interpreted as evidence for an intermolecular interaction mechanism. We explore the uncertainty of the estimated photodegradation constant taking into account the uncertainties of the measurements used in the synchronous detection technique.     

Part 3. Copolymers of 1H,1H,2H,2H‐perfluorodecyl acrylate and 2,2,2‐trifluoroethyl methacrylate with butyl methacrylate

Copolymers of 2,2,2‐trifluoroethyl methacrylate, or 1H,1H,2H,2H‐perfluorodecyl acrylate (XFDA) and butyl methacrylate (BMA) have been irradiated in air under artificial solar light and their photo‐oxidative stability has been investigated. Molecular and chemical changes occurring during the treatments have been monitored by weight loss and gel content determination, size exclusion chromatography and FTIR spectroscopy. It has been determined that the overall behaviour of both copolymers is controlled by the BMA units, independently of the total fluorine content. The photo‐ageing takes place mainly via the mechanism of oxidation of methacrylic polymers containing long side ester groups, whose flexibility favours macroradical coupling reactions. The tendency to crosslink is balanced only in the case of the initial stages of degradation of XFDA/BMA by the scission reactions derived from the direct attack of oxygen on the fluorinated acrylic units. © 2001 Society of Chemical Industry     

膨润土负载红磷复合材料的吸附富集-定位光降解性能

为了提高红磷催化剂的光催化性能, 选择剥离膨润土(EB)为载体, 将水热处理后的红磷(HRP)负载在EB上, 制得EB/HRP复合光催化剂, 并通过不同手段对催化剂进行表征。选择罗丹明B为模型污染物, 考察了EB/HRP复合光催化剂的光降解性能。结果表明, 随着EB含量的增加, EB/HRP复合光催化剂的光降解效率呈现先增加后减小的趋势, 当EB的质量分数为9%时, 复合光催化剂(EB₉/HRP)表现出最强的吸附性能和光降解性能, 其降解速率常数k值为0.0641 min^-1, 是HRP的2倍。另外, 经过五次循环光降解实验, EB₉/HRP仍具有较高的光催化活性(96.8%)。因此, EB₉/HRP复合催化剂具有较好的光催化活性和稳定性, 有望成为一种降解污染物的高效而稳定的光催化剂。     

Photocatalytic degradation of formaldehyde by nanostructured TiO2 composite films

Interest in the photocatalytic oxidation of formaldehyde from contaminated wastewater is growing rapidly. The photocatalytic activity of the nanocrystalline Fe³⁺/F^? co-doped TiO₂–SiO₂ composite film for the degradation of formaldehyde solution under visible light was discussed in this study. The films were characterised by field emission scanning electron microscopy (FE-SEM) equipped with energy-dispersive spectroscopy, X-ray diffraction (XRD), BET surface area, UV–Vis absorption spectroscopy, and photoluminescence spectroscopy. The FE-SEM results revealed that the Fe³⁺/F^? co-doped TiO₂–SiO₂ film was composed of uniform round-like nanoparticles or aggregates with the size range of 5–10 nm. The XRD results indicated that only the anatase phase was observed in the film. Compared with a pure TiO₂ film and a singly modified TiO₂ film, the Fe³⁺/F^? co-doped TiO₂–SiO₂ composite film showed the best photocatalytic properties due to its strong visible light adsorption and diminished electrons-holes recombination.     

Solar photocatalytic degradation of Aldrin

Photocatalytic degradation of the pesticide Aldrin dissolved in water was carried out, in one case, using concentrated solar radiation and, in another case, using non-concentrated solar radiation. In these experiments, the effects of catalyst concentration, oxidant agent concentration, and solar irradiation were tested. In experiments without irradiation, strong adsorption of the pesticide over titanium dioxide was observed in the first few minutes of contact in the presence of titanium dioxide (TiO₂). These results can be explained by means of Coulombic interactions between the catalyst surface and the pesticide molecules. During the photodegradation process, results show a residual degradation (photolysis) in both the cases, when no catalyst was added. In the case of the non-concentrated solar system, the achieved results suggest that the use of H₂O₂ increased the degradation rate. For concentrated sunlight, an increase of the Aldrin concentration was observed during the first few minutes of irradiation. This can be explained as a desorption process that is triggered by a change in surface charge of the catalyst in the presence of hydrogen peroxide (H₂O₂) during irradiation. When photocatalysis was performed with TiO₂ alone, no Aldrin was detected in the water solutions throughout the entire experiment. This result was unexpected; however, it might be explained by the adsorption of the pesticide on the catalyst surface and by the absence of the oxidant’s effect. Three transformation products (TPs) of the degradation process were identified: dieldrin, chlordene and 12-hydroxy-dieldrin. The results presented here are in agreement with previously reported results for photocatalytic degradation of other chlorinated pesticides using lamps as radiation sources.     

菲在TiO2催化下的光降解研究

以汞灯为光源，TiO2为催化剂，对菲的光催化降解途径进行了研究。将水溶性极小的菲预先吸附到TiO2上之后，菲可以在紫外线的照射下发生快速、完全的矿化。通过GC－MS手段检测到一些中间产物，给出了菲光催化降解的详细途径。另外，研究了菲在表面活性剂十六烷基三甲基溴化铵（HTAB）的助溶下TiO2催化的光降解过程，探讨了表面活性剂的浓度和溶液pH值对反应速率的影响。     

Photodegradation of Lipofuscin in Suspension and in ARPE-19 Cells and the Similarity of Fluorescence of the Photodegradation Product with Oxidized Docosahexaenoate

Retinal lipofuscin accumulates with age in the retinal pigment epithelium (RPE), where its fluorescence properties are used to assess retinal health. It was observed that there is a decrease in lipofuscin fluorescence above the age of 75 years and in the early stages of age-related macular degeneration (AMD). The purpose of this study was to investigate the response of lipofuscin isolated from human RPE and lipofuscin-laden cells to visible light, and to determine whether an abundant component of lipofuscin, docosahexaenoate (DHA), can contribute to lipofuscin fluorescence upon oxidation. Exposure of lipofuscin to visible light leads to a decrease in its long-wavelength fluorescence at about 610 nm, with a concomitant increase in the short-wavelength fluorescence. The emission spectrum of photodegraded lipofuscin exhibits similarity with that of oxidized DHA. Exposure of lipofuscin-laden cells to light leads to a loss of lipofuscin granules from cells, while retaining cell viability. The spectral changes in fluorescence in lipofuscin-laden cells resemble those seen during photodegradation of isolated lipofuscin. Our results demonstrate that fluorescence emission spectra, together with quantitation of the intensity of long-wavelength fluorescence, can serve as a marker useful for lipofuscin quantification and for monitoring its oxidation, and hence useful for screening the retina for increased oxidative damage and early AMD-related changes.     

射频等离子体修饰二氧化钛氧空位的光降解机理

用溶胶-凝胶法在石英基材上制备了纳米二氧化钛(TiO2)薄膜.用射频等离子体修饰TiO2薄膜.提出了射频等离子体使TiO2对光谱响应红移的修饰方法.X射线衍射分析结果表明:TiO2被等离子体修饰后仍然保持锐钛矿晶型.紫外-可见光谱分析结果表明:放电功率为400W时,TiO2薄膜的吸收边向可见光红移.Fourier变换红外光谱表明:等离子体修饰使TiO2薄膜的亲水性增强.电子自旋共振的结果表明:被修饰薄膜中Lande因子g=2.000 3处氧空位俘获的电子的信号明显增强.放电功率为400W时,结晶紫溶液的光降解实验表明:等离子体修饰的TiO2的光催化活性较好.