UV-B辐射增强对长白山五种藓类植物生长的影响

对生长在中国长白山的5种藓类植物——垂枝藓、拟垂枝藓、塔藓、星塔藓和高山金发藓分别以辐射强度为0.2(自然光照,对照)、3.0(紫外线中等辐射强度)和6.0kJ.m-2.d-1(高剂量辐射强度)的UV-B照射40d后,测定其株高、生物量及叶绿素含量.结果表明:中等和高强度的UV-B辐射使拟垂枝藓和塔藓的株高、生物量和叶绿素含量分别下降了32.3%、62.4%、81.3%和21.4%、59.4%、62.8%,其相对生长速率均为负值;高剂量UV-B辐射处理下垂枝藓的生物量稍有上升,而高山金发藓地下部分的生物量增加1倍,但叶绿素含量变化不明显.高山金发藓和垂枝藓抵抗UV-B辐射的能力较强,拟垂枝藓和塔藓对UV-B辐射较敏感.

UV-B增强对番茄的伤害及H_2O_2的防护作用

UVB辐射使番茄叶片的叶绿素a,叶绿素b及总叶绿素含量先升高后降低,同样使叶片的抗氧化酶过氧化氢酶(CAT)和过氧化物酶(POD)活性先升高随后降低,而使超氧化物歧化酶(SOD)活性升高,膜脂过氧化产物MDA的含量增加;中等剂量(5mmol·l-1)的H2O2预处理能提高叶绿素b的含量,明显提高抗氧化酶的活性,并延缓CAT活性的降低,抑制膜质过氧化产物MDA的产生.中等浓度H2O2预处理能提高番茄对UVB增强的抗性.

不同UV-C辐射时间对豌豆幼苗光合特性及抗氧化酶活性的影响

研究了不同UV-C辐射时间对豌豆幼苗光合特性及抗氧化酶活性的影响。结果表明,UV-C辐射增强使叶片光合速率减弱,气孔导度、胞间CO2浓度、蒸腾速率和羧化效率明显降低,CO2补偿点升高。随着UV-C辐射时间的延长,POD和CAT活性先升高随后降低,SOD活性、叶绿素含量则逐渐降低,但丙二醛含量逐渐增加。这说明UV-C辐射增强引起抗氧化酶活性降低,使膜脂过氧化,导致光合作用减弱。

Identifying the isolated transition metal ions/oxides in molecular sieves and on oxide supports by UV resonance Raman spectroscopy

Isolated transition metal ions/oxides in molecular sieves and on surfaces are a class of active sites for selective oxidation of hydrocarbons. Identifying the active sites and their coordination structure is vital to understanding their essential role played in catalysis and designing and synthesizing more active and selective catalysts. The isolated transition metal ions in the framework of molecular sieves (e.g., TS-1, Fe-ZSM-5, and V-MCM-41) or on the surface of oxides (e.g., MoO3/Al2O3 and TiO2/SiO2) were successfully identified by UV resonance Raman spectroscopy. The charge transfer transitions between the transition metal ions and the oxygen anions are excited by a UV laser and consequently the UV resonance Raman effect greatly enhances the Raman signals of the isolated transition metal ions. The local coordination of these ions in the rigid framework of molecular sieves or in the relatively flexible structure on the surface can also be differentiated by the shifts of the resonance Raman bands. The relative concentration of the isolated transition metal ion/oxides could be estimated by the intensity ratio of Raman bands. This study demonstrates that the UV resonance Raman spectroscopy is a general technique that can be widely applied to the in-situ characterization of catalyst synthesis and catalytic reactions. (C) 2003 Elsevier Science (USA). All rights reserved.

Phase transformation in the surface region of zirconia and doped zirconia detected by UV Raman spectroscopy

The phase evolution of yttrium oxide and lanthanum oxide doped zirconia (Y2O3-ZrO2 and La2O3-ZrO2, respectively) from their tetragonal to monoclinic phase has been studied using UV Raman spectroscopy, visible Raman spectroscopy and XRD. UV Raman spectroscopy is found to be more sensitive at the surface region while visible Raman spectroscopy and XRD mainly give the bulk information. For Y2O3-ZrO2 and La2O3-ZrO2, the transformation of the bulk phase from the tetragonal to the monoclinic is significantly retarded by the presence of yttrium oxide and lanthanum oxide. However, the tetragonal phase in the surface region is difficult to stabilize, particularly when the stabilizer's content is low. The phase in the surface region can be more effectively stabilized by lanthanum oxide than yttrium oxide even though zirconia seemed to provide more enrichment in the surface region of the La2O3-ZrO2 sample than the Y2O3-ZrO2 sample, based on XPS analysis. The surface structural tension and the enrichment of the ZrO2, component in the surface region of ZrO2-Y2O3 and ZrO2-La2O3 might be the reasons for the striking difference between the phase change in the surface region and the bulk. Accordingly, the stabilized tetragonal surface region can significantly prevent the phase transition from developing into the bulk when the stabilizer's content is high.

ZnO clusters encapsulated inside micropores of zeolites studied by UV Raman and laser-induced luminescence spectroscopies

Using microporous zeolites as host, sub-nanometric ZnO clusters were prepared in the micropores of the host by the incipient wetness impregnation method. A small amount of sub-nanometric ZnO clusters were introduced into the channels of HZSM-5 zeolite, whereas a large quantity of sub-nanometric ZnO clusters can be accommodated in the supercages of HY zeolite and no macrocrystalline ZnO exists on the extra surface of the HY material. The vibrations of the zeolite framework and ZnO were characterized by UV Raman spectroscopy. The optical properties of these ZnO clusters were studied by UV-visible absorption spectroscopy and laser-induced luminescence spectroscopy. It is found that there are strong host-guest interactions between the framework oxygen atoms of zeolite and ZnO clusters influencing the motions of the framework oxygen atoms. The interaction may be the reason why ZnO clusters are stabilized in the pores of zeolites. Different from bulk ZnO materials, these sub-nanometric ZnO clusters exhibit their absorption onset below 265 nm and show a purple luminescence band (centered at 410-445 nm) that possesses high quantum efficiency and quantum size effect. This purple luminescence band most likely originates from the coordinatively unsaturated Zn sites in sub-nanometric ZnO clusters. On the other hand, the differences in the pore structure between HZSM-5 and HY zeolites cause the absorption edge and the purple luminescence band of ZnO clusters in ZnO/HZSM-5 show a red shift in comparison with those of ZnO clusters in ZnO/HY.

Direct determination of sialic acids in serum by capillary electrophoresis with UV detection

A novel method for the determination of N-acetylneuraminic acid (NANA) and N-glycolylneuraminic acid (NGNA) has been developed using high-performance capillary electrophoresis with UV detection at 195 nm, without pre or post-column derivatisation. The acids were separated in a 50-cm, fused-silica capillary (50 mu m i.d, 45.5-cm effective length) with Na2B4O7-Na2HPO4 buffer. The detection limit for NANA is a concentration of 9.6 x 10(-6) M or, in terms of mass: 3.879 x 10(-14) mol (39 fmol). This method is applicable to determination of NANA in normal human serum. The results were also compared with those of the colorimetrie method.

Degradation products formed during UV-irradiation of humic waters

Natural humic lake water and aqueous solutions of humic substances were treated with ultraviolet (UV) radiation (λ = 254 nm). The effects on the dissolved organic carbon content (DOC) and the absorbance at 254 nm (Abs254) and 460 nm (Abs460) were monitored and the identity and concentrations of gas chromatographable organic degradation products were determined. The DOC content and the (Abs254) of the humic solutions decreased continuously with increasing UV-dose. Several aromatic and aliphatic degradation products were identified and roughly quantified The concentrations of aromatic hydroxy carboxylic acids and hydroxy aldehydes increased when relatively low UV-doses were used, but declined following further irradiation. The concentrations of aliphatic dibasic acids increased over the full range of UV-doses

UV-photooxidation as pretreatment step in inorganic analysis of environmental samples

Many laboratories deal with the determination of heavy metals, carbon, nitrogen and phosphorus. The first step in chemical analysis is a proper preparation of the investigated samples. The presence of organic substances can cause problems in many analytical methods. This paper describes the application of UV irradiation as a method of destruction of organic matter in the investigated samples.

水质对UV/H_2O_2降解邻苯二甲酸二甲酯反应动力学的影响

研究了不同初始pH值、浊度与常见阴离子浓度等水质条件对UV/H2O2工艺降解邻苯二甲酸二甲酯(DMP)反应速率的影响,并进一步比较了去离子水和自来水中DMP的降解速率。结果表明,UV/H2O2对DMP的光降解过程符合一级反应动力学模型,不同水质条件对降解速率有不同程度的影响。酸性条件较碱性条件更有利于DMP降解;水的浊度大于7NTU时,光降解速率常数迅速下降;NO3-、Cl-、HCO3-等阴离子对DMP降解有抑制作用,且随离子浓度增大,抑制作用增强,3种离子对DMP光降解的抑制程度顺序为HCO3->NO3->Cl-。在5个30W低压汞灯照射下,当H2O2的浓度为20mg.L-1时,DMP在去离子水和自来水中光降解速率常数分别为0.0428min-1和0.0315min-1,自来水中的光降解速率常数较去离子水中的低,这可能是水中多种离子影响的结果。

水中无机阴离子对UV/H_2O_2降解LAS的影响及机理

研究了UV/H2O2工艺对直链烷基苯磺酸钠(LAS)的去除效果以及水中常见无机阴离子对LAS降解的影响和机理.结果表明,UV/H2O2工艺可以有效的去除水中LAS,光降解过程符合一级反应动力学模型.在H2O2投加量为8 mg.L-1,14 W低压汞灯照射下,LAS在蒸馏水和自来水中光降解速率常数分别为0.0180 min-1和0.0122 min-1;NO3-、Cl-、SO42-和HCO3-对LAS光降解有抑制作用,4种离子在浓度分别为5、10、15 mmol.L-1时,对LAS光降解的抑制程度均为HCO3->NO3->Cl->SO42-;随着离子浓度增大,抑制作用增强;自来水中的光降解速率常数低于蒸馏水中的光降解速率常数是由于水中多种离子影响的结果.

脱落酸对UV-C胁迫下小麦幼苗光合特性及抗氧化酶活性的影响

研究了UV-C辐射下短期和长期脱落酸(ABA)处理对小麦幼苗CO2同化作用、羧化效率、光合CO2响应以及抗氧化酶活性等的影响.结果表明,在无UV-C辐射情况下,短期和长期ABA处理能提高光合速率,比对照增加14·69%和20·46%,降低气孔导度,比对照降低14·74%和17·31%,但对胞间CO2浓度和羧化效率影响不大.当受到UV-C辐射时,光合速率、羧化效率、气孔导度和胞间CO2浓度逐渐降低.长期ABA处理变化最小,其次为ABA短期处理,对照降低最大.ABA处理能够提高小麦光合对CO2的响应,UV-C辐射抑制光合对CO2的响应.ABA处理能够提高小麦抗氧化酶(CAT、SOD、POD)活性而降低MDA含量.在UV-C辐射下,CAT活性先升高随后降低,在辐射处理1h时活性达最大值,ABA处理的SOD和POD活性先升高后降低,且ABA长期处理比短期处理增加明显,对照则逐渐降低.ABA处理可能通过提高小麦CO2同化作用和抗氧化酶活性增强对UV-C胁迫的抗性,且ABA长期处理比短期处理效果更明显.