Photofragmentation of a benzophenone derivative having benzylic C–O bond studied by laser flash photolysis in solution

Photochemical profiles of p-(4-phenylphenoxy)methylbenzophenone (PPMeBP) in solution were investigated by means of emission and transient absorption measurements. PPMeBP showed that fluorescence originating from the corresponding p-phenylphenoxy (PP) moiety at 295 K, and dual phosphorescence originating from the corresponding p-benzoylbenzyl (BB) and PP moieties at 77 K was observed. These observations indicated that the BB and PP moieties of PPMeBP have very little electronic conjugation. 266- and 308-nm laser flash photolyses of PPMeBP showed the formation of the p-phenylphenoxy radical, indicating that photoexcited PPMeBP undergoes C–O bond cleavage. Upon 355-nm laser photolysis of PPMeBP, the C–O bond did not dissociate, and formation of the triplet state of the PP moiety was observed. The apparent quantum yields of fragmentation of PPMeBP were found to depend on the excitation wavelength. Triplet sensitization of PPMeBP using benzophenone revealed that the C–O bond does not cleave in the triplet state of the PP moiety. Based on the schematic energy diagram for excited PPMeBP, the mechanism of the C–O bond was discussed.     

Selective Cleavage of β-Keto and Vinylogous β-Keto Esters by 3-Quinuclidinol

As a result of a continuing study utilizing nitrogenous bases^2–6, we now wish to report that the base 3-quinuclidinol (13) is useful for the cleavage of β-keto and vinylogous β-keto esters.     

Selective electrochemical CO bond cleavage of β-O-4 lignin model compounds mediated by iodide ion

The electrochemically oxidative cleavage of lignin β-O-4 model compounds mediated by iodide ion has been studied. The results indicate that electrolytic conditions play a predominant role in determining the distribution of cleavage products. The preparative-scale electrolysis proceeds in a simple undivided cell, employing a catalytic amount of NaI as the redox mediator and supporting electrolyte in methanol. Under these conditions, the C_βO bond is selectively cleaved with 2,2-dimethoxy-2-arylacetaldehyde being the main product. In some cases, the reaction gives a good yield of cleavaged products. The results further demonstrate that the indirect electrolysis mediated by halide is a versatile approach for chemical transformation.     

Reaction intermediates of a dihydropyridine derivative of 2′,3′-dideoxycytidine related to AIDS dementia studied by laser flash photolysis

A derivative of 2′,3′-dideoxycytidine (ddC), carrying one 1,4-dihydro-1-methyl-3-pyridinyl-carbonyl group at the cytidine exocyclic amino group and one at the ribose 5-hydroxyl group, was exposed in water-ethanol solution to high-power pulsed laser emission at a wavelength of 354.7 nm. Measurement of the transient absorption spectra with nanosecond time resolution shows that the photoejection of an electron occurs due to stepwise two-photon absorption by the dihydropyridine via its fluorescent state. The spectrum of the cation radical formed in this reaction was determined, together with that of the neutral radical appearing following deprotonation of the cation. The electron is apparently abstracted only from the pyridine group attached to the ribose, since a comparative study on ddC carrying a dihydropyridine only at the exocyclic amino group showed no evidence for photoionization in the same experimental conditions.     

The degradation of polyacrylamide in aqueous solution induced by chemically generated hydroxyl radicals: Part II—Autoxidation of Fe2+

Hydroxyl radicals, generated by the autoxidation of Fe²⁺, have been shown to attack polyacrylamide molecules in solution and cause chain scission. In acid solution the extent of degradation is determined by the rate of autoxidation which is very dependent on pH and the chelation of the iron. In alkaline solution degradation is negligible.     

The degradation of polyacrylamide in aqueous solution induced by chemically generated hydroxyl radicals—Part III: Xanthine/xanthine oxidase

Hydroxyl radicals generated via the iron catalysed Haber-Weiss reaction from the superoxide radical formed by the reduction of dissolved oxygen during the xanthine oxidase catalysed oxidation of xanthine have been shown to degrade polyacrylamide.     

Fast and Selective Semihydrogenation of Alkynes by Palladium Nanoparticles Sandwiched in Metal–Organic Frameworks

The semihydrogenation of alkynes into alkenes rather than alkanes is of great importance in the chemical industry. Unfortunately, state-of-the-art heterogeneous catalysts hardly achieve high turnover frequencies (TOFs) simultaneously with almost full conversion, excellent selectivity, and good stability. Here, we used metal–organic frameworks (MOFs) containing Zr metal nodes (“UiO”) with tunable wettability and electron-withdrawing ability as activity accelerators for the semihydrogenation of alkynes catalyzed by sandwiched palladium nanoparticles (Pd NPs). Impressively, the porous hydrophobic UiO support not only leads to an enrichment of phenylacetylene around the Pd NPs but also renders the Pd surfaces more electron-deficient, which leads to a remarkable catalysis performance, including an exceptionally high TOF of 13835 h⁻¹, 100 % phenylacetylene conversion 93.1 % selectivity towards styrene, and no activity decay after successive catalytic cycles. The strategy of using molecularly tailored supports is universal for boosting the selective semihydrogenation of various terminal and internal alkynes.     

Analysis of neem oils by LC–MS and degradation kinetics of azadirachtin-A in a controlled environment

Since it was first isolated, the oil extracted from seeds of neem (Azadirachtin indica A juss) has been extensively studied in terms of its efficacy as an insecticide. Several industrial formulations are produced as emulsifiable solutions containing a stated titer of the active ingredient azadirachtin-A (AZ-A). The work reported here is the characterization of a formulation of this insecticide marketed under the name of Neem-azal T/S and kinetic studies of the major active ingredient of this formulation. We initially performed liquid–liquid extraction to isolate the neem oil from other ingredients in the commercial mixture. This was followed by a purification using flash chromatography and semi-preparative chromatography, leading to ¹³C NMR identification of structures such as azadirachtin-A, azadirachtin-B, and azadirachtin-H. The neem extract was also characterized by HPLC–MS using two ionization sources, APCI (atmospheric pressure chemical ionization) and ESI (electrospray ionization) in positive and negative ion modes of detection. This led to the identification of other compounds present in the extract—azadirachtin-D, azadirachtin-I, deacetylnimbin, deacetylsalannin, nimbin, and salannin. The comparative study of data gathered by use of the two ionization sources is discussed and shows that the ESI source enables the largest number of structures to be identified. In a second part, kinetic changes in the main product (AZ-A) were studied under precise conditions of pH (2, 4, 6, and 8), temperature (40 to 70 °C), and light (UV, dark room and in daylight). This enabled us to determine the degradation kinetics of the product (AZ-A) over time. The activation energy of the molecule (75±9 kJ mol^–1) was determined by examining thermal stability in the range 40 to 70 °C. The degradation products of this compound were identified by use of HPLC–MS and HPLC–MS–MS. The results enabled proposal of a chemical degradation reaction route for AZ-A under different conditions of pH and temperature. The data show that at room temperature and pH between 4 and 5 the product degrades into two preferential forms that are hydrolyzed to a single product over time and as a function of pH change.     

Photocatalytic behavior of α-Bi2Mo3O12 prepared by the Pechini method: degradation of organic dyes under visible-light irradiation

Nanoparticles of α-Bi₂Mo₃O₁₂ were prepared by the Pechini method. The process of formation of the bismuth molybdate was followed by simultaneous thermogravimetric and differential thermal analysis (TGA/DTA). Different samples of α-Bi₂Mo₃O₁₂ were obtained at 400, 450, and 500 °C, and characterized by X-ray powder diffraction (XRD), nitrogen physisorption (BET), and scanning electron microscopy (SEM). When observed by SEM, the morphology of the sample obtained at the lowest temperature consisted of semi-spherical particles with an average diameter of 150 nm. On the other hand, the highest calcination temperature led to the formation of sintered particles of 500–600 nm. The photocatalytic activity of α-Bi₂Mo₃O₁₂ was tested by photodegradation of the organic dyes rhodamine B (rhB) and indigo carmine (IC) under visible-light irradiation. The bismuth molybdate nanoparticles were able to bleach aqueous solutions of both organic dyes. The sample obtained at 400 °C was the best photocatalyst with half-lives, t _1/2, of 108 and 154 min for rhB and IC, respectively.     

Selective degradation of lignin and elimination of HO radicals in pulps by O<Subscript>3</Subscript> and UV laser flash irradiation

HO^. radical is an aggressive reagent to abstract hydrogen from diverse substitutes and lead them to degradation, however, in reaction of active oxygen species with lignins, complex phenolic polymers, in dispersed lignocellulose such as pulp for environment-benign delignification, HO^. radicals should be eliminated as more as possible to prevent cellulose from unfavorably concomitant degradation. A reaction system of O₃ is constructed under UV laser flash irradiation, and HO^. radicals are controlled efficiently by it. A new mechanism is proposed, for the first time, that O^. radicals generated from reaction of O₃ with UV laser flash irradiation might be the contributor to scavenge HO^. radicals.     

4-n-壬基酚的激光闪光光解和紫外光降解

采用266nm激光闪光光解瞬态吸收光谱和254nm紫外光降解,研究了乙腈及乙腈-水混合溶液中4-n-壬基酚（4-n-NP）的各种光解行为,考察了不同物理化学体系对4-n-NP光解行为的影响规律.实验发现,在266nm激光闪光光解下,4-n-NP既发生光电离又发生光激发,获得了4-n-NP光电离生成的阳离子自由基,以及光激发生成的激发三重态的瞬态特征吸收谱.由S2O82-光分解产生的SO4·-可快速氧化4-n-NP,测得反应速率常数为2.85×109M-1s-1,判定4-n-NP阳离子自由基在pH高于2.2条件下会转变成脱质子中性自由基.研究发现,使用254nm紫外光直接降解4-n-NP比较困难,UV结合添加H2O2可提高其降解效率,UV结合添加K2S2O8可极大提高4-n-NP降解效率,3.5min的光照即可使1×10-4M的4-n-NP完全降解.本文就4-n-NP在各种条件下的光解机理进行了探讨,为此类具有生物激素效应的非离子表面活性剂光降解奠定了基础.     

Atrazine and Parathion-Methyl Removal by UV And UV/O3 in Drinking Water Treatment

Abstract

The degradation of atrazine and parathion-methyl by UV-light in the presence of O₂(UV/O₂) and by a combination of UV-light and ozone in the presence of O₂(UV/O₂/O₃) was studied at a pilot plant for drinking water treatment. The photolysis rate of parathion-methyl increased with UV/O₂/O₃ compared to the treatment with UV/O₂ only, while the photodecomposition rate of atrazine was not enhanced by the UV/O₂/O₃ combination under the working conditions applied.

In field experiments with a large-scale plant the degradation of atrazine and desethylatrazine was studied at a drinking water supply. The applied ozone dose rates were smaller and the residence time of the liquid phase in the UV-reaction unit was shorter than in the pilot plant. The degradation rate of both atrazine and desethylatrazine increased with increasing ozone dose rates and increasing radiant power. At a continuous flow rate of 70 m³/h of contaminated raw water atrazine could be degraded below the threshold limit for pesticides (0.1[ugrave]g/L) at optimum operation conditions, whereas the resulting desethylatrazine concentration exceeded this limit. At a continuous flow rate of 30 m³/h desethylatrazine could be degraded below the threshold limit, too.     

Degradation of Microcystin-RR by Combination of UV/H2O2 Technique

The experiments were performed to investigate the degradation of microcystins in order to assess the effectiveness and feasibility of UV/H2O2 system for the disinfection of water polluted by microcystins. The influence factors such as H2O2, pH and UV light intensities were investigated respectively. Degradation of microcystin-RR （MC-RR） could be fitted by either the pseudo-first-order or second-order rate equations. This homogenous system could significantly enhance the degradation rate due to the synergetic effect between UV and H2O2. The degradation mainly followed the mechanism of direct photolysis and .OH oxidation reactions. Experimental results showed that 94.83% of MC-RR was removed under optimal experimental conditions and the UV/H2O2 system provided an alternative to promote the removal of microcystins in drinking water supplies.     

Co/Al2O3催化剂上3-甲基-2-丁烯醛选择性加氢反应

3-甲基-2-丁烯醛(3-MeCal)是一种典型的α,β-不饱和醛,其C=O加氢产物3-甲基-2-丁烯醇(3-MeCol)作为重要的有机中间体,在医药、香料、农药等生产领域有着广泛的应用.我们采用沉积沉淀法制备了Co/Al2O3催化剂,将其应用于3-MeCal液相选择性加氢反应中,考察了反应温度、H2初始压力、催化剂焙烧温度和还原温度对3-MeCal选择性加氢反应的影响.发现反应温度为80℃,H2初始压力为1×106Pa下,加氢反应效果良好.通过H2-TPR与XRD表征了焙烧温度对催化剂的影响,发现适当焙烧温度能增强Co物种与载体Al2O3间作用力.焙烧温度为600℃,还原温度为550℃下制备的催化剂反应48 min后转化率为23.0%,3-MeCol选择性达到88.6%.制备的Co/Al2O3催化剂具有良好的磁性,在外磁场作用下可与液相反应体系实现高效分离,循环使用3次后,催化性能没有明显下降,表现出良好的循环使用性能.     

Pt/Al2O3催化剂用于丙烯选择性还原NO

分别采用浸渍法(IM)和溶胶-凝胶法(SG)制备了一系列不同铂负载量的催化剂,在固定床反应器上用C3H6作还原剂,测试了选择性还原NO_x的活性,结果发现,在IM法和SG法制备的催化剂中,活性组分铂最佳负载质量分数分别为0.5%和2%.针对两种催化剂,分别考察了氧浓度、丙烯浓度及反应气流量对选择性催化还原NO_x性能的影响,催化活性随丙烯浓度的增大而上升.2%Pt/Al₂O₃(SG)催化剂的抗SO₂性能好于0.5%Pt/Al₂O₃(IM)催化剂,H₂O的存在可明显拓宽活性温度范围,并向高温区间移动,在200～400℃范围内可有效净化NO_x.     

Photocatalytic degradation of azo dyes in aqueous solutions under UV irradiation using nano-strontium titanate as the nanophotocatalyst

Research on photocatalytic degradation rate of azo dyes using nano-strontium titanate in photocatalysis process was the main goal of present study. In this regard, the influence of the main operating parameters such a photocatalyst concentration, dye concentration, temperature, pH and the presence of hydrogen peroxide upon dye removal rate under UV irradiation was studied. The absorbance of samples was measured by a UV–Vis spectrophotometer. The structure and morphology of nano-powder were investigated using scanning electron microscopy and crystalline structure by X-ray diffraction spectroscopy. The results reveal that nano-strontium titanate has high and significant photocatalytic activity and in comparison with nano-titanium dioxide was superior photocatalyst.     

Euphorbia polygonifolia extract assisted biosynthesis of Fe3O4@CuO nanoparticles: Applications in the removal of metronidazole,ciprofloxacin and cephalexin antibiotics from aqueous solutions under UV irradiation

In this study, a new, economical and green method was reported for synthesizing Fe₃O₄@CuO nanoparticles without adding any surfactants using Euphorbia polygonifolia extract as a renewable, mild and safe reducing agent and effective stabilizer. The green synthesized NPs were analyzed by various methods such as XRD, FESEM, FT-IR, EDS, VSM, UV–visible, DRS, BET and TGA-DTA. Based on the BET analysis, the Fe₃O₄@CuO NP had a surface area of 69.20 m²/g. The FTIR analysis verified the existence of different functional groups of phytochemicals from Euphorbia polygonifolia extract which were accountable for the NPs formation. The catalytic performance of the catalyst for the degradation of metronidazole, ciprofloxacin and cephalexin antibiotics was examined in aqueous mediums at room temperature. The results showed an extraordinary catalytic performance, easy reusability and long-term stability of the composite for reducing antibiotic pollution. In this process, the effects of environmental conditions such as initial pH of the environment, initial concentration of antibiotics, the concentration of modified photocatalyst and reaction time were studied. According to the results, at the optimal conditions, the highest removal efficiency for metronidazole, ciprofloxacin and cephalexin antibiotics using Fe₃O₄@CuO nanoparticles, were 89%, 94%, and 96%, respectively. Also, it was observed that even after recycling, the NPs presents good nanocatalytic stability for the degradation of antibiotics. Using the NPs for five cycles did not significantly alter the photocatalyst efficiency, showing that the photocatalytic stability of the NPs was excellent.     

Praseodymium Oxide Modified CeO2/Al2O3 Catalyst for Selective Catalytic Reduction of NO by NH3

A series of CeO₂/Al₂O₃ catalysts was modified with praseodymium oxide using an extrusion method. The catalytic activities of the obtained catalysts were measured for the selective catalytic reduction of NO with NH₃ to screen suitable addition of praseodymium oxide. These samples were characterized by XRD, N₂‐BET, NH₃‐TPD, NO‐TPD, Py‐IR, H₂‐TPR, Raman spectra and XPS, respectively. Results showed the optimal catalyst with the Pr/Ce molar ratio of 0.10 exhibited more than 90% NO conversion in a wide temperature range of 290–425°C under GHSV of 5000 h^?1. The number of Lewis acid sites and the chemisorbed oxygen concentration of the catalysts would increase with the Pr incorporation, which was favorable for the excellent catalytic performance. In addition, the Pr incorporation inhibited growth of the Al₂O₃ crystal particles and led to the lattice expansion of CeO₂, which increased catalytic activity. The results implied that the higher chemisorbed oxygen concentrations and the more Lewis acid sites were conductive to obtain the excellent SCR activity.     

Kinetics and mechanism of dissolved organic phosphorus (DOP) digestion by the UV/O3 process

In this study, the kinetics and mechanism of UV/O₃ synergistic oxidative digestion of dissolved organic phosphorus (DOP) were investigated, focusing on the ozone direct oxidation and hydroxyl radical oxidation parts of glufosinate and triphenyl phosphate (TPhP). The p-chlorobenzoic acid (p-CBA) was selected as the probe compound, and two kinds of reaction kinetic models were proposed by competitive kinetic method with R_ct according to the different scale of rate constants of hydroxyl radical oxidation. Under the condition of weakly alkaline (pH = 9.0) and weakly acidic environment (pH = 5.0), the second-order rate constants of glufosinate and TPhP was determined indirectly to be ko_{3/glufosinate} = (2.903 ± 0.247)M⁻¹s⁻¹ and ko_3/TPhP = (3.307 ± 0.204) M⁻¹s⁻¹ by ozone direct oxidation, and k_{·OH/glufosinate} = (1.257 ± 1.031) × 10⁹ M⁻¹s⁻¹ and k_·OH/TPhP = (7.120 × 10⁸ ± 0.963) M⁻¹s⁻¹ by hydroxyl radical oxidation, respectively. The comparison of the contribution levels of the two parts to the digestion process showed that the contribution levels in the digestion of glufosinate and TPhP processes both the contribution of ·OH were higher than those of ozone, 86.3% and 72.6%, respectively.