Preliminary study on the photoproduction of hydroxyl radicals in aqueous solution with Aldrich humic acid, algae and Fe(III) under high-pressure mercury lamp irradiation

Under a high-pressure mercury lamp (HPML) and using an exposure time of 4 h, the photoproduction of hydroxyl radicals ((OH)-O-.) could be induced in an aqueous solution containing humic acid (HA). Hydroxyl radicals were determined by high-performance liquid chromatography using benzene as a probe. The results showed that (OH)-O-. photoproduction increased from 1.80 to 2.74 muM by increasing the HA concentration from 10 to 40 mg L-1 at an exposure time of 4 h (pH 6.5). Hydroxyl radical photoproduction in aqueous solutions of HA containing algae was greater than that in the aqueous solutions of HA without algae. The photoproduction of (OH)-O-. in the HA solution with Fe(111) was greater than that of the solution without Fe(III) at pH ranging from 4.0 to 8.0. The photoproduction of (OH)-O-. in HA solution with algae with or without Fe(111) under a 250 W HPML was greater than that under a 125 W HPML. The photoproduction of (OH)-O-. in irradiated samples was influenced by the pH. The results showed that HPML exposure for 4 h in the 4-8 pH range led to the highest (OH)-O-. photoproduction at pH 4.0.

Chemisorption and reaction characteristics of methyl radicals on Cu(110)

Methyl radicals are generated by pyrolysis of azomethane, and the condition for achieving neat adsorption on Cu(110) is described for studying their chemisorption and reaction characteristics. The radical-surface system is examined by X-ray photoemission spectroscopy, ultraviolet photoemission spectroscopy, temperature-programmed desorption, low-energy electron diffraction (LEED), and high-resolution electron energy loss spectroscopy under ultrahigh vacuum conditions. It is observed that a small fraction of impinging CH3 radicals decompose into methylene possibly on surface defect sites. This type of CH2 radical has no apparent effect on CH3(ads) surface chemistry initiated by dehydrogenation to form active CH2(ads) followed by chain reactions to yield high-mass alkyl products. All thermal desorption products, such as H-2, CH4, C2H4, C2H6, and C3H6, are detected with a single desorption peak near 475 K. The product yields increase with surface coverage until saturation corresponding to 0.50 monolayer of CH3(ads). The mass distribution is, however, invariant with initial CH3(ads) coverage, and all desorbed species exhibit first-order reaction kinetics. LEED measurement reveals a c(2 x 2) adsorbate structure independent of the amount of gaseous exposure. This strongly suggests that the radicals aggregate into close-packed two-dimensional islands at any exposure. The islanding behavior can be correlated with the reaction kinetics and is deemed to be essential for the chain propagation reactions. Some relevant aspects of the CH3/Cu(111) system are also presented. The new results are compared with those of prior studies employing methyl halides as radical sources. Major differences are found in the product distribution and desorption kinetics, and these are attributed to the influence of surface halogen atoms present in those earlier investigations.

Determination of photochemically produced hydroxyl radicals in seawater and freshwater

A variety of short-lived, reactive chemical species (i.e. free radicals and excited state species) are known to be photochemically produced in natural waters. Some of these transients may strongly affect chemical and biological processes, and they have been implicated in the degradation of organic pollutants and natural organic compounds in aqueous environments. Previous studies demonstrated that the highly reactive hydroxyl radical (OH) is photochemically formed in seawater. However, the quantitative importance of this key species in the sea has not been previously studied because of past analytical limitations. By using a highly sensitive probe based on α-H atom abstraction from methanol, we were able to measure production rates and steady-state concentrations of photochemically produced OH radicals in coastal and open ocean seawater and freshwaters. The validity of the method was tested by intercalibrating with an independent, OH-specific reaction, hydroxylation of benzoic acid, and also by competition kinetics experiments. Our OH production rates and steady-state concentrations for freshwaters are in excellent agreement with those measured by previous investigators for similar waters. In contrast, for seawater, the values we measured are 1–3 orders of magnitude higher than previously predicted by models, indicating that there is a major unknown photochemical OH source (s) in seawater.

Photo-sensitized oxidation in natural water via .OH radicals

A method is presented for determining production and consumption rates of .OH radicals produced photochemically in natural surface waters. It is based on the determination of the kinetics by which the concentration of a specified trace compound decreases during irradiation. In samples from Lake Greifensee (Switzerland) low production rates for .OH limit its possible effects. In addition, fast consumptions by the natural dissolved organic solutes and by the bicarbonate protect organic micropollutants from oxidation by .OH. Neither direct nor indirect H2O2 photolysis was a significant source of .OH in the lakewater studied lacking iron, whereas nitrate photolysis could have been a source. Comparison with reaction kinetic formulations allows generalizations for other types of waters.

Styrene polymerization catalyzed by metal porphyrin complex/MAO for in situ synthesizing polystyrene containing air stable pi cation radicals

A novel catalyst system based on nickel(II) tetraphenylporphyrin (Ni(II)TPP) and methylaluminoxane for styrene polymerization was developed. This catalyst system has a high thermal stability and show fairly good activity. The obtained polystyrene (PS) was isotactic-rich atactic polymer by C-13 NMR analysis, and its molecular weight distribution was rather narrow (M-w/M-n approximate to 1.6, by GPC analysis). ESR revealed that Ni(II)TPP pi cation radicals were formed in the polymerization and could remain in the resulting PS stably. The mechanism of the polymerization was discussed and a special coordination mechanism was proposed. The PS product containing Ni(II)TPP pi cation radicals can be used as a potential functional material.

A monometallic tri-spin single-molecule magnet based on rare earth radicals

A mononuclear tri-spin single-molecule magnet based on the rare earth radical [Tb(hfac)(3)(NITPhOEt)(2)] (NITPhOEt = 4'-ethoxy-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) has been synthesized, structurally characterized and the alternating current signals show a slow relaxation of magnetization and frequency-dependent signals.

Effect of the fold surface of the lamellae on the behavior of the trapped radicals in irradiated polyamide-1010

Two types of macromolecular free radicals -CH2CONHCHCH2- (a) and -CH2C=O (b) trapped in irradiated Polyamide-1010 (PA1010) and PA1010 filled with neodymium oxide (Nd2O3) were characterized by an ESR approach. It was found out that a was mainly trapped in the fold surface of the lamellae and b in the amorphous phase. This result suggested that trapped radicals mainly existed in the noncrystalline phases. The effect of the fold surface area of the lamellae on the behavior of the trapped radicals are discussed in this article. Whether for the specimens with similar crystallinities but different crystallite sizes or for those with the same concentration of neodymium oxide but different crystallinities, radical a exists dominantly in a specimen with a larger fold surface area of the lamellae. Under a certain circumstance, radical a can transform into radical b for a specimen with a larger fold surface area of the lamellae. It means that the fold surface area of the lamellae plays an important role in the transformation of radical a to b. (C) 1998 John Wiley & Sons, Inc.

ESR approach to free radicals trapped in irradiated polyamide-1010

Two types of macromolecular free radicals similar to CH2CONH(C) over dotHCH(2) similar to (a) and similar to CH2(C) over dot = O (b) trapped in irradiated polyamide-1010 (PA1010) and PA1010 filled with neodymium oxide (Nd2O3) were characterized by an ESR approach. It is found that (a) is prevailingly trapped in the fold surface of the lamellae and (b) in the amorphous phase. This result suggests that trapped radicals mainly exist in the non-crystalline phases. The effect of the fold surface area of the lamellae on the behavior of the trapped radicals is discussed in this paper. Whether for the specimens with similar crystallinities, but different crystallite sizes, or for those with the same concentration of neodymium oxide, but different crystallinities, radical (a) exists dominantly in the specimen with a larger fold surface area of the lamellae. Under certain circumstances, radical (a) can transform into radical (b), obviously for a specimen with a larger fold surface area of the lamellae. It means that the fold surface area of the lamellae plays an important role in the transformation of radical (a) to (b). (C) 1997 Elsevier Science Ltd.

Dependence of decaying of trapped radicals on aggregates on polyamide 1010

The decaying of free radicals in the course of heating, trapped in irradiated polyamide 1010 with different crystallinities, were investigated using an ESR technique. The decaying temperature, at which all radicals decay completely, depends on the aggregation of polyamide 1010 prior to radiation. The higher the crystallinity, the higher the temperature at which the radicals disappear. Dynamically speaking, radicals in specimens with higher crystallinity take longer to decay. (C) 1997 Elsevier Science Ltd.

Synthesis and hydroxyl radicals scavenging activity of quaternized carboxymethyl chitosan

In order to determine the effect of the forms of the amido groups of chitosan on antioxidant activity, quaternized carboxymethyl chitosan (QCMC) derivatives were prepared with a degree of quaternization ranging from 34.3% to 59.5%. The antioxidant activity of QCMCs against hydroxyl radicals was assessed. The results indicated that QCMCs have better hydroxyl radicals scavenging activity than that of carboxymethyl chitosan, as a result of the positive charge of the quaternized chitosan. (C) 2007 Elsevier Ltd. All rights reserved.

Hydroxyl radicals scavenging activity of N-substituted chitosan and quaternized chitosan

N-substituted chitosan and quaternized chitosan were synthesized and their antioxidant activity against hydroxyl radicals was assessed, respectively. Compared with the antioxidant activity of chitosan, the results indicated that the two kinds of chitosan derivatives had different scavenging ability on hydroxyl radicals, which should be related to the form of amido in the two kinds of chitosan derivatives. (c) 2006 Elsevier Ltd. All rights reserved.