Photochemical reduction of molecular weight and number of double bonds in natural rubber film

Natural rubber (NR) can be degraded depending on various factors such as heat, mechanical force, chemical reaction, and light. Light is a very interesting factor because it can cause the NR to degrade under low temperature and pressure. The photo-degradation of NR films was carried out to investigate the effects of the light and the temperature on the reduction of the weight-average molecular weight (Mw) and the double bonds in the NR films. The NR films, with and without catalysts, titanium dioxide (TiO₂), and potassium persulfate (K₂S₂O₈), were exposed to light from a mercury light bulb at 7,000 and 36,000 lux, and at the temperature of 25 °C and 80 °C for 192 hrs. After exposure, the Mw of the NR films was analyzed by gel permeation chromatography (GPC). Changes in the Mw were used to construct a kinetic model for the process, (1/Mw)=(1/Mw₀)+(kt/2M₀) where k is the rate constant, and M₀ is the Mw of the monomer unit. The linear relationship between 1/Mw and time suggested pseudo first-order processes with random scission. The Mw distribution information from the GPC was used to calculate the number of double bonds in the NR films. The trend of the double bonds reduction curves was quite similar to the result obtained from the calculation from the FTIR spectra. This indicated that this calculation method might possibly be another alternative way to obtain the number of double bonds in the NR.     

Synthesis,characterization and photo-catalytic studies of mixed metal oxides of nano ZnO and SnOx

Novel mixed metal oxides of Zinc and Tin (MZOTO) were synthesized by a simple co-precipitation method. The effect of blending varying compositions of SnO_x (x=1, 2) to ZnO has been evaluated, and it was found that the crystal structure, morphology, optical properties and photo-catalytic behavior were dependent on the percentage of SnO_x. The obtained samples were characterized using XRD, EDAX, FESEM, UV–vis spectroscopy, Photoluminescence, etc. XRD data revealed that the ZnO and SnO_x co-exist as mixture and their structures were found as hexagonal and cubic/orthorhombic respectively. FESEM image intricate about the morphology of the MZOTO prepared in 1:0.5 ratio providing nano flower structures that resemble like Chrysanthemum species. The band gaps of all the obtained MZOTOs were determined from UV–vis reflectance spectra using Kubelka-Munk relation. Photoluminescence emission studies revealed that the recombination of excited e⁻ with the h⁺ of ZnO is greatly influenced by SnO_x nanoparticles. Visible light photo-catalytic activities of MZOTOs were followed spectrophotometrically against the degradation of crystal violet solution. MZOTO2 obtained in the ratio of 1:0.5 shows better catalytic efficiency compared to other samples, degrading crystal violet completely within 40 min. The reusability and free radical trapping experiments were performed to study the performance and mechanism of MZOTO2 as the photo-catalyst. The photo catalytic efficiency of 1:0.5 MZOTO was higher due to the presence of flower-like structures that effectively captivated more photons from the sunlight.     

均相亚甲基蓝光敏氧化法处理造纸废水研究

本文探讨了利用均相亚甲基蓝光敏氧化法替代高浓度H2O2强化氧化法处理造纸废水的可行性与影响光敏氧化过程的因素。结果显示，在相同的光强下，复合光比紫外光效果好；在反应体系溶解氧高于2．0mg／L，光照4h时，光敏剂对造纸废水COD的去除量与其本身的体积质量比可达到333．5，具有较高的效率。     

Photo-stability and performance of CdSe/ZnS quantum dots in luminescent solar concentrators

The performances of luminescent solar concentrators (LSCs) made with two versions of quantum dots (QDs) with CdSe cores and ZnS shells are compared to LSCs containing the organic dye, Lumogen^® F Red 300 (LR), to assess the viability of QD LSCs. In addition to spectroscopic and light collection measurements, the photo-degradation response of the version I (vI) QD LSC is compared to the LR LSC. The measured fluorescence quantum yield of the version II (vII) QDs (57%) is about half that of LR (>90%) and twice that of the vI QDs (31%). Though the quantum yield for vII QDs is lower than LR, the vII QD LSC has nearly twice the short-circuit current of the LR LSCs or the vI QD LSCs when their respective red-peak optical densities are the same in 6.2 × 6.2 × 0.6 cm LSCs. This is a reflection of the main advantage of QDs for use in LSCs, that QDs collect considerably more sunlight than LR due to their broad absorption spectrum. Despite the fact that the QD LSCs absorbs more photons than the LR LSCs, the slow phase of the photo-degradation rate of the QD LSC is approximately five times slower than the LR LSC under nearly constant light exposure. Most surprising is the observation that the photo-degradation of the QD LSC’s absorption completely recovers during a prolonged dark cycle. In a normal day/night cycle, this will benefit the performance of the QD LSC.     

高能紫外光降解硫化天然橡胶降解能力及降解机理的研究

采用高能紫外光反应容器,研究了硫化天然橡胶的光降解过程。通过溶胶凝胶含量、GPC、核磁共振氢谱,表征硫化天然橡胶降解程度以及溶胶分子结构,通过红外光谱、接触角、元素分析表征硫化天然橡胶紫外光降解机理。结果表明,硫化天然橡胶在高能紫外光照射下能够快速降解,溶胶含量随照射时间增加而增加,溶胶分子量随照射时间增大而减小。紫外光照射过程中氧气参与紫外光降解过程,使得硫化天然胶主链发生断裂,导致降解产物含有含氧基团,亲水性及氧原子数目增加,但随着照射时间的增加含氧基团继续在紫外光作用下发生反应,导致含氧基团减少,亲水性下降。     

Preparation and characterization of α-Fe2O3 nanorod-thin film by metal-organic chemical vapor deposition

Alpha iron oxide (α-Fe₂O₃) films were grown on catalyst-free silicon substrate using a vertical type metal-organic chemical vapor deposition process. X-ray powder diffraction and field-emission transmission electron microscopy measurements showed that these α-Fe₂O₃ films consisted of bundles of one dimensional (1D) nanorods and the nanorods in these α-Fe₂O₃ films were single crystalline with a well-ordered rhombohedral structure. The nanorods showed a preferred growth orientation in the [104] direction. Magnetic force microscopy image suggests that spin domains were formed in the α-Fe₂O₃ nanorods. Photo-catalytic property of these nanorod films was confirmed through the photo-degradation of Rhodamine B by UV irradiation. These α-Fe₂O₃ film/nanorod materials could be used as building blocks for nanodevice applications.     

玻璃纤维布负载TiO2光催化剂及其催化性能

用SEM分析了采用浸渍法制备的玻璃纤维布负载TiO2光催化剂的负载情况,又以紫外线高压汞灯为光源,研究了TiO2光催化剂对甲基橙的光降解作用,同时分析了负载次数与pH值对甲基橙降解的影响。结果表明,在试验条件下采用浸渍法制备玻璃纤维布负载TiO2光催化剂的最佳涂覆次数为6次,在酸性条件下降解效果较好。     

Preparation of cerium oxide nanoparticles in Salvia Macrosiphon Boiss seeds extract and investigation of their photo-catalytic activities

Cerium oxide nanoparticles (CNPs) with desired particle size and spherical morphology were prepared from cerium nitrate in bio media of Salvia macrosiphon Boiss seeds extract, as a green synthesis route. Then they were characterized by XRD, UV–Vis and FTIR spectroscopies, FESEM and TGA. Band gap energy of the prepared powders was also determined which was found in the range of 2.5–3.5?eV. Determination of DLS and zeta potential were showed that CNPs had the small size and unique colloidal stability, respectively. Then the photo-catalytic activity of them was investigated by degradation of Rhodamine B (RhB) dye as a model of waste water pollutants, under UV-irradiation and optimum conditions were evaluated. Results showed that decreasing the particle size increased the rate of photo-catalytic reaction remarkably but ascending the band gap energy, in contrast. The photo-catalytic mechanism was also studied by using different scavengers.     

Self-cleaning behaviour of alkyd coating impregnated with mixed metal oxides of Zn and Sn

Earlier, we reported the photocatalytic behaviour of mixed metal oxides of zinc and tin (MZOTO) and concluded that the composition prepared in the ratio 1:0.5 displays excellent results. Present study details about the formulation of alkyd resin based coating using MZOTO as the pigment in suitable proportion; the contents were homogeneously mixed by high energy ball milling technique. On exposing the coated specimen contaminated by artificial pollutant like crystal violet to sunlight, the pollutant was bleached within 4 h showing its excellent self-cleaning property. Thus the prepared coating provides a new vision to next generation self-cleaning coating to degrade organic pollutants.     

Ce-doped ZnO nanoparticles for efficient photocatalytic degradation of direct red-23 dye

This paper reports the simple, rapid and high-yield synthesis of Ce-doped ZnO nanoparticles using solution combustion method and its application for photocatalytic degradation. Several concentrations of Ce (0.5%, 1.39%, 2.55%, 3.28%, 3.71% and 4.14%) were doped into ZnO and the prepared nanoparticles were characterized by several techniques in terms of their morphological, structural, compositional, optical and photocatalytic properties. The detailed characterization studies revealed that the prepared Ce-doped ZnO nanoparticles are well-crystalline and possessing good optical properties. Further, the prepared Ce-doped ZnO nanoparticles were used as efficient photocatalyst for the photocatalytic degradation of harmful organic dye, i.e. direct red-23 (DR-23). From the detailed photocatalytic experiments, it was observed that Ce-doped ZnO nanoparticles are exhibiting appreciable photocatalytic activity and the degradation percentage was increased with increasing the concentration of Ce up to 3.28%; however, when the Ce concentration was further increased, the photocatalytic degradation was decreased. Thus, at optimum Ce concentration (3.28%), the prepared Ce-doped ZnO nanoparticles are exhibiting appreciable photocatalytic degradation (~99.5%) only in 70 min.