Photocatalytic degradation of methyl methacrylate copolymers

The photolytic and photocatalytic degradation of the copolymers poly(methyl methacrylate-co-butyl methacrylate) (MMA-BMA), poly(methyl methacrylate-co-ethyl acrylate) (MMA-EA) and poly(methyl methacrylate-co-methacrylic acid) (MMA-MAA) have been carried out in solution in the presence of solution combustion synthesized TiO₂ (CS TiO₂) and commercial Degussa P-25 TiO₂ (DP 25). The degradation rates of the copolymers were compared with the respective homopolymers. The copolymers and the homopolymers degraded randomly along the chain. The degradation rate was determined using continuous distribution kinetics. For all the polymers, CS TiO₂ exhibited superior photo-activity compared to the uncatalysed and DP 25 systems, owing to its high surface hydroxyl content and high specific surface area. The time evolution of the hydroxyl and hydroperoxide stretching vibration in the Fourier transform-infrared (FT-IR) spectra of the copolymers indicated that the degradation rate follows the order MMA-MAA > MMA-EA > MMA-BMA. The same order is observed for the rate coefficients of photocatalytic degradation. The photodegradation rate coefficients were compared with the activation energy of pyrolytic degradation. In degradation by pyrolysis, it was observed that MMA-BMA was the least stable followed by MMA-EA and MMA-MAA. The observed contrast in the order of thermal stability compared to the photo-stability of these copolymers was attributed to the two different mechanisms governing the scission of the polymer and the evolution of the products.     

Role of crystallite size on the photoluminescence properties of SrIn2O4:Eu phosphor synthesized by different methods

Photoluminescence (PL) of Eu³⁺ was studied in SrIn₂O₄ host lattice. A complete solid solubility of Eu³⁺ has been found in the series SrIn_2−xEu_xO₄ [x=0-2.0]. The phase formation at a relatively low temperature and in a very short duration was achieved by combustion synthesis (CS). Concentration quenching of luminescence has been observed in SrIn_2−xEu_xO₄ [x=0.1-2.0] and the critical concentration for maximum emission was found to be with x=0.3. In order to find the role of crystallite size on the PL properties of SrIn₂O₄:Eu³⁺, the results obtained with phosphors synthesized by solid state reaction (SSR) and CS methods were compared.     

Multi-diagnostic approach to characterize the onset of formation of nanoparticles in a premixed laminar ethylene/air flame

The onset of formation of nanoparticles in a premixed laminar ethylene/air flame was studied using optical and non-optical diagnostic techniques. The optical techniques (Visible Imaging, Spectroscopic analysis of optical emission, Laser Induced Incandescence and Optical Extinction) were checked against the direct measurement of particles size distribution done with a commercial sampler. The diagnostic techniques were set up on a standard burner (McKenna). The combustion conditions were varied by tuning two experimental parameters: the equivalent ratio Φ and the cold gases velocity v. Values of Φ were investigated in the range 1.3 to 2.2, in combination with cold unburned gas velocities of 5, 7 and 10 cm/s. By varying the combustion conditions, a transition in the signal detected by the different techniques was observed. The transition was put in correspondence with the sensitivity of the given technique to the onset of the nanoparticles formation. A comparison of the sensitivity of the different techniques was performed.     

Synthesis of Nano‐Sized Zinc Oxide Photocatalyst by Combustion Method

The objective of this research was to use combustion synthesis to create a nano‐sized ZnO photocatalyst using citric acid as the fuel and zinc nitrate as the oxidant. The starting materials were mixed in a stoichiometric ratio, and a slurry precursor with high homogeneity was formed. The precursor was ignited at room temperature, resulting in dry, loose, and voluminous ZnO powders. The powders, characterized by SEM, TEM and XRD, showed a particle size range of 40 to 80 nm with a wurtzite structure. The ZnO powders were introduced as a photocatalyst for the degradation of methyl orange, which was adopted as a model compound. UV light (6W) was used as the irradiation source to induce synthesized ZnO powders to perform catalytic activity. The photocatalytic reaction was executed in 40 mL of a 10 ppm methyl orange aqueous solution under 254 nm UV illumination. In this work, it was observed that both UV light and ZnO powders are needed for the photocatalytic reaction. In addition, it was found that increasing the amount of ZnO powder present in the MO (methyl orange‐C₁₄H₁₄N₃NaO₃S) solution did not correlate directly with an increase in photocatalytic ability. It was found that the scattering problem of UV light also needs to be considered. The optimized photocatalytic degradation ratio in this work reached 92.7%.     

锂掺杂ZnO陶瓷靶材制备及其掺杂引起的缺陷

采用燃烧合成和放电等离子烧结方法制备锂掺杂ZnO陶瓷靶材. 利用XRD, SEM, TEM和激光粒径分析等手段分析合成粉体与陶瓷的显微结构. 结果表明, 锂掺杂ZnO粉体与陶瓷均为纤锌矿结构, 无其他相存在; 粉体的粒径分布为0.18-1.7 μm, 烧结体致密度较高, 晶粒尺寸为1-3 μm. 此外, 分析锂元素在烧结过程中引起掺杂缺陷变化, 锂元素由ZnO晶格的间隙位置转移为替代锌晶格位置, 实现受主掺杂, 为实现p型ZnO薄膜的制备奠定基础.     

A new approach to treating pressure oscillations in combustion instability phenomena

Developing exact models of combustion instabilities is not an easy task to carry out and requires a great deal of time prior to obtaining success. The present study proposes a low-order model for pressure oscillations that does not require any knowledge of the systems, any new physical findings nor intricate details regarding its operating condition. This new approach is obtained using a Modified Van der Pol’s equation (MVDP) which is tuned by use of a Dual Extended Kalman Filter (DKEF) as a recursive estimator with perspectives in control by computer. This phenomenological model is used to predict the pressure signal from a variety of different combustors. Input data were taken from experimental cases such as a Rijke tube, a gas turbine and a liquid-fuel aero-engine combustor. Furthermore, a simulation considering high frequency oscillations to show the capability of the new approach is presented. In all cases, the results demonstrated the feasibility of applying the tractable model MVDP and DKEF running together to investigate pressure oscillations in practical cases.     

Opinion strength influences the spatial dynamics of opinion formation

Opinions are rarely binary; they can be held with different degrees of conviction, and this expanded attitude spectrum can affect the influence one opinion has on others. Our goal is to understand how different aspects of influence lead to recognizable spatio-temporal patterns of opinions and their strengths. To do this, we introduce a stochastic spatial agent-based model of opinion dynamics that includes a spectrum of opinion strengths and various possible rules for how the opinion strength of one individual affects the influence that this individual has on others. Through simulations, we find that even a small amount of amplification of opinion strength through interaction with like-minded neighbors can tip the scales in favor of polarization and deadlock.     

A different approach to fabricate nanocrystalline LTB:Cu pellets with thermoluminescence response

In this study, lithium-tetraborate (LTB) was synthesized by three methods of high-temperature solid state, wet and combustion reactions. Copper was added to pure LTB by solution assisted method, to improve the thermoluminescence (TL) properties. The pellets of LTB were produced using pressing and sintering operations at 850 °C. The synthesized LTB pellets, exposed to the gamma radiation of ⁶⁰Co source in the dose range of 5–20Gy and glow curves as well as dose–response diagrams were obtained. Ultimately, the effects of different factors on TL behaviors like dopant, crystallite size and particle morphologies were studied. The results show that between pure samples, LTB which synthesized by combustion method has higher TL sensitivity than those of other methods. However, it was seen a weak glow peak for 5Gy, due to the nanocrystalline structure of LTB. This property led to decrease TL intensity at low-doses and postponed saturation at high-doses. Fading of this sample was also less than others and has relatively better reproducibility. Among LTB:Cu pellets which synthesized by the wet reaction showed the higher TL response than others due to the creation of more traps and luminescence centers and had promising properties in the case of dose response linearity and fading.     

Laboratory simulation of Hg<Superscript>0</Superscript> emissions from a snowpack

Snow surfaces play an important role in the biogeochemical cycle of mercury in high-latitude regions. Snowpacks act both as sources and sinks for gaseous compounds. Surprisingly, the roles of each environmental parameter that can govern the air–surface exchange over snow are not well understood owing to the lack of systematic studies. A laboratory system called the laboratory flux measurement system was used to study the emission of gaseous elemental mercury from a natural snowpack under controlled conditions. The first results from three snowpacks originating from alpine, urban and polar areas are presented. Consistent with observations in the field, we were able to reproduce gaseous mercury emissions and showed that they are mainly driven by solar radiation and especially UV-B radiation. From these laboratory experiments, we derived kinetic constants which show that divalent mercury can have a short natural lifetime of about 4–6 h in snow.     

负载型La0.8Sr0.2MnO3燃烧催化剂的载体效应

Combustion catalysts La0.8Sr0.2MnO3 supported on γ-Al2O3, α-Al2O3, cordierite (2MgO•2Al2O3•5SiO2) and ZrO2 were compared. Further investigation was focused on LSM/ γ-Al2O3 catalyst. It was observed that LSM/γ－Al2O3 catalyst loaded with 20% (mass fraction) LSM (La0.8Sr0.2MnO3 or corresponding oxides), heated at 750℃ or above, perovskite-type oxides were found by XRD examination, whereas, the same catalyst loaded with 10% or less LSM, perovskite oxides were absent, calcination temperature about 750℃ is necessary for the formation of perovskite structure in LSM/γ-Al2O3 catalysts. High activity of complete oxidation of xylen will be obtained when perovskite-type oxides.
Investigation of TPR showed that neat LSM or LSM/γ-Al2O3(20%) was reduced by H2-N2 mixed gas. Two degradation processes took place. In the first, reduced temperature peak was about 350 - 450℃. If reduction ended at 400℃, perovskite structure was retained, which may be due to the reduction of Mn3+to Mn2+ on the surface of LSM only. In the second process, perovskite structure was destroied, and La2O3, Mn2O3, Mn - Sr - O oxides could be obtained, which took place in the temperature range 685 - 750℃ and ended at 800℃. This was proved by TPR experiments (Fig. 3, 5) and XRD patterns (Fig. 4)
Catalysts LSM/γ-Al2O3(10% or 20%) heated at 500℃ have only one TPR peak, i. e. lower temperature peak. This is due to the absence of perovskite-type oxides in the catalysts. However, neat LSM or LSM/γ-Al2O3(20%) heated 750℃ or above, not only the first low temperature TPR peak but also the second peak, which is contributed by the perovskite-type oxides in these catalysts appeared. Therefore, the second TPR peak, i. e. the higher temperatue peak is a characteristic peak for perovskite-type oxides in the reduced process. When LSM/ γ-Al2O3 (10%) catalys is heated at 750℃, no perovskite-type oxides were detected by XRD, and the second reduction peak was absent also in TPR process. \
The order of the second reduction peak temperature(characteristic peak of perovskite - type ox- ides) is: neat LSM(750℃）> LSM/γ-Al2O3 20% (685-698℃) -deposited LSM/γ-Al2O3 (698℃) > LSM/γ-Al2O3 15% (677 - 680℃) >(LSM/γ-AL2O3 10% 620 - 630℃, for Mn - Al - O medium oxides on surface). It is correleted with the increasing of the effect of support sequentially.
When LSM/γ-Al2O3 catalysts were heated at 900℃, more stable phase, spinel MnAl2O4 appeared, which could be proved by TPR of model catalyst MnAl2O4/γ-Al2O3.