Oxidative Degradation of 2,4‐Dihydroxybenzoic Acid by the Fenton and Photo‐Fenton Processes: Kinetics,Mechanisms, and Evidence for the Substitution of H2O2 by O2

The kinetics and mechanisms of the oxidative degradation of 2,4‐dihydroxybenzoic acid (2,4‐DHBA) by the Fenton and photo‐Fenton processes were investigated in detail by a combination of HPLC, IC, and TOC analyses. The formation of 2,3,4‐trihydroxybenzoic acid (2,3,4‐THBA) at an early oxidation stage shows that hydroxylation of the aromatic ring is the first step of the process. This intermediate was able to reduce Fe^III and to contribute to the recycling of Fe^II. Complete mineralization could only be achieved under irradiation (photo‐Fenton). A detailed study of the dependence of the rate of mineralization on the concentration of H₂O₂ and dissolved O₂ was carried out. It was found that, even at a low initial concentration of H₂O₂, mineralization by the photo‐Fenton process was complete in a relatively short time, provided that the O₂ concentration was high enough, indicating that O₂ may, at least in part, substitute H₂O₂. Channeling reaction pathways toward O₂ rather than H₂O₂ consumption is of particular interest for the technical development of the photo‐Fenton process.     

In vitro Photo‐Oxidation of Pyruvate to Acetyl: A Main Source for the Formation of Acetyl Coenzyme A in the Citric Acid Cycle to Perform Biochemical Reactions

The kinetics of photooxidation of pyruvate was investigated in presence of zinc oxide catalyst under illumination of visible light. The influence of different parameters such as concentrations of reactants, amount of catalyst and irradiation time was studied on the redox reaction under pseudo‐first order conditions. The results indicated that amount of catalyst, presence of electron accepter in solution and irradiation time was the key factors influencing the efficiency of photo‐oxidation of pyruvate to acetyl.     

Magnetic separation of green synthesized Fe3O4 nanoparticles on photocatalytic activity of methyl orange dye removal

The most frequent method of removing malignant growth-causing tones from current effluents before releasing them into water sources such as rivers, lakes, and groundwater has become standard. Traditional waste-water treatment frameworks have trouble getting rid of these contaminants. This is a unique flavonoid that uses Fe₃O₄ nanorods as photocatalytic agents to corrupt material tone in the watery stage utilizing observable light enlightenment. Green technique was used to amalgamate [email protected]₃O₄ nanorod like gems. Disappearance of the bright (UV) maintenance top at 565 nm confirmed the elimination of Methyl orange tone. After 110 min, the sensational shading disposal of Fe₃O₄ nanorod was observed to be 100%. This is due to photochemical redox process and the use of Fe₃O₄ nanorods with a high energy gap of flavonoids. The findings show that Fe₃O₄ rod-like gems manufactured using green technology are extremely valuable in the photocatalytic annihilation of hazardous contaminants.     

The role of surface oxidation on luminescence degradation of porous silicon

This study reports a comparative analysis on time dependent degradation of photoluminescence (PL) spectra of porous silicon (PS) during dark-aging (DA) and photo-aging (PA). Fourier Transform Infrared (FTIR) spectroscopy studies have been performed to get an insight on possible chemical changes in the PS surface. It has been found that SiH_x bonds decrease progressively while SiO_x bonds increase. FTIR and PL measurements revealed presence of blue shifts in the PL spectra during the aging stages (PA and DA). While the PL intensity of dark aged PS shows a decrease during the first 3 weeks and an increase afterwards, the PL intensity decreases continuously for photo-aged PS. The change in the PL spectra has been investigated by overlapping of two different PL bands which are reflective of oxidation of PS surface and size of Si naonocrystallites. A possible bond configuration model about the oxidation of PS surface has also been proposed. The results are interpreted in terms of quantum size effects in PS and the influence of the surface composition.     

Mechanistic Aspects of the Effects of Stress on the Rates of Photochemical Degradation Reactions in Polymers

Abstract

This review examines the mechanistic origins of the effects of stress on the photochemical degradation rates of polymers. Recent studies have shown that tensile and shear stresses accelerate the rate of the photochemical degradation of polymers. Conversely, compressive stress generally retards the rate of photochemical degradation. After an initial discussion of the photochemical auto‐oxidation mechanism, the three primary hypotheses that purport to explain how stress affects photochemical degradation are examined. The first hypothesis is attributed to Plotnikov, who proposed that stress changes the quantum yields of the reactions that lead to bond photolysis. The second hypothesis, attributed to a number of researchers, says that stress affects the ability of the geminate radical pairs, formed in the photochemical bond cleavage reactions, to recombine. The third hypothesis proposes that stress changes the rates of radical reactions subsequent to radical formation. A further attempt to account for the effects of stress on degradation rates is a modification of the so‐called Zhurkov equation that has been used rather successfully to predict the effects of stress on degradation rates in thermal reactions. This empirical equation relates the quantum yield of degradation to a composite activation barrier for the overall photochemical reaction. Following the discussion of these hypotheses, experimental mechanistic studies of stress effects are summarized, and what little data there is is shown to be consistent with the hypothesis that proposes that stress primarily affects the ability of photochemically generated radical pairs to recombine. By decreasing the efficiency of radical–radical recombination, the effect is to increase the relative efficiencies of the radicals' other reactions and hence the rate of degradation. In addition to stress, other factors can affect the rates of polymer photodegradation. These factors include the absorbed light intensity, the polymer morphology, the rate of oxygen diffusion in the polymer, and the chromophore concentration. Each of these parameters must be carefully controlled in mechanistic studies that probe the effects of stress on degradation rates.     

2-(2-取代苯基丙烯基)-5-取代苯并唑的光性质研究

本文测试了２０个标题化合物的紫外光谱和荧光光谱，讨论了它们的取代基效应，研究了１６种溶剂对其中两个化合物的紫外光谱的溶剂效应以及一个化合物的光反应     

红外GaAs液晶光阀一维等效电路模型分析

叙述了红外GaAs液晶光阀的工作原理和主要构成,并由此建立了红外GaAs液晶光阀一维等效电路模型,根据此模型着重分析光电导层GaAs的厚度对红外液晶光阀的红外调制动态范围、驱动频率和分辨率的影响,给出了部分相关曲线,得到最佳GaAs厚度范围。根据此模型计算出液晶光阀的结构参数,重新设计了液晶光阀并给出了部分实验结果。     

用修正的差分进化算法确定光电模型参数

RsRp模型是研究光伏(PhotoVoltaic,PV)器件特性的一种有效的方法,它兼顾了计算复杂性和精度两个方面。在该模型中有5个参数需要确定,它们分别是光电流PVI,二极管饱和电流oI,二极管理想常数a,串联电阻sR和并联电阻pR。为了能找到准确的PV模型参数,该文提出一种修正的差分进化(Modified Differential Evolution,MDE)算法。MDE在变异中使用不同的尺度因子,有助于提高种群的多样性。另外,它在交叉操作中也采用了不同的交叉率,使自身能够轻易地摆脱局部最优点。实验结果表明,MDE算法能够用较少的时间找到准确的RsRp模型参数,使基于MDE算法和RsRp模型的I-V曲线能与实验点相匹配。     

Photo stability enhancement of Poly(3-hexylthiophene)-PCBM nanocomposites by addition of multi walled carbon nanotubes under ambient conditions

Poly(3-hexylthiophene)-Phenyl-C61-butyric acid methyl ester (P3HT–PCBM) composites find wide application in optoelectronic devices, especially bulk-hetero junction (BHJ) solar cells. These composites, even though could give efficient polymer solar cells with ∼4–5% power conversion efficiencies (PCE), a major problem of photo stability is associated with it and remains unsolved. P3HT–PCBM composite was found to be degrading on irradiation with ultraviolet radiation or a solar simulator providing AM1.5G illumination (1000 W m^–2, 72 ± 2 °C or 330 W m⁻², 25 °C), in presence of oxygen and moisture. Here, we have studied the photo stability of P3HT–PCBM under ambient conditions and showed that a new ternary composite, P3HT–PCBM–MWCNT (multi walled carbon nanotube) has superior photo stability even on extended UV–Vis exposure. A total of 7% (w/w) PCBM and 3% (w/w) MWCNT with respect to P3HT resulted in optimum stability. UV–Visible and fluorescence spectral analysis have been used to study the photo stability, both in solution state and solid/film state. Transmission electron micrograph (TEM) along with selected area electron diffraction (SAED) pattern and Field Emission Scanning Electron Microscopy (FE-SEM) micrographs have been used to show the well coating of MWCNT on P3HT–PCBM composite. Since MWCNT is one of the very important carbon based nanomaterial with several supreme characteristics, this new ternary composite has great importance for optoelectronic applications.