Photoluminescence characteristics of GaAsSbN/GaAs epilayers lattice-matched to GaAs substrates

The photoluminescence (PL) characteristics of GaAsSbN/GaAs epilayers grown by molecular beam epitaxy (MBE) are carefully investigated. The results show that antimony (Sb) incorporation into GaNAs material has less influence on the N-induced localization states. For the same N concentration, GaAsSbN material can reach an emission wavelength near 1.3 mum more easily than GaInNAs material. The rapid thermal annealing (RTA) experiment shows that the annealing induced rearrangement of atoms and related blueshift in GaAsSbN epilayers are smaller than those in GaNAs and GaInNAs epilayers. The GaAsSbN material can keep a longer emission wavelength near 1.3 mum-emission even after the annealing treatment. Raman spectroscopy analysis gives further insight into the structure stability of GaAsSbN material after annealing. (C) 2004 Elsevier Ltd. All rights reserved.

Growth of GaSb layers on GaAs (001) substrate by molecular beam epitaxy

GaSb 1 mu m-thick layers were grown by molecular beam epitaxy on GaAs (001). The effects of the growth conditions on the crystalline quality, surface morphology, electrical properties and optical properties were studied by double crystalline x-ray diffraction, atomic force microscopy, Hall measurement and photoluminescence spectroscopy, respectively. It was found that the surface roughness and hole mobility are highly dependent on the antimony-to-gallium flux ratios and growth temperatures. The crystalline quality, electrical properties and optical properties of GaSb layers were also studied as functions of growth rate, and it was found that a suitably low growth rate is beneficial for the crystalline quality and electrical and optical properties. Better crystal quality GaSb layers with a minimum root mean square surface roughness of 0.1 nm and good optical properties were obtained at a growth rate of 0.25 mu m h(-1).

Dislocation movement in nitrogen-doped Czochralski silicon

Dislocation movement in N-doped Czochralski silicon (Cz-Si) was surveyed by four point bend method. Dislocation movement velocities in Cz-Si doped with nitrogen, with both nitrogen and antimony, and with only antimony were investigated. The order of measured dislocation movement velocities, at 700 degrees C less than or equal to T less than or equal to 800 degrees C and under resolved stress sigma=4.1 kg/mm(2), was V-Sb.O > V-n.Sb.O>V-N.O. The experiments showed that nigtrogen doping could retard the movement of dislocations.

Magnetic and electronic properties of CaCu3Cr4O12 and CaCu3Cr2Sb2O12 by first-principles density functional calculation

The electronic and magnetic properties of CaCu3Cr4O12 and CaCu3Cr2Sb2O12 are investigated by the use of the full-potential linearized augumented plane wave (FPLAPW) method. The calculated results indicate that CaCu3- Cr4O12 is a ferrimagnetic and half-metallic compound, in good agreement with previous theoretical studies. CaCu3- Cr2Sb2O12 is a ferrimagnetic semiconductor with a small gap of 0.136 eV. In both compounds, because Cr4+ 3d (d(2)) and Cr3+ 3d (d(3)) orbitals are less than half filled, the coupling between Cr-Cu is antiferromagnetic, whereas that between Cu-Cu and Cr-Cr is ferromagnetic. The total net spin moment is 5.0 and 3.0 mu(B) for CaCu3Cr4O12 and CaCu3Cr2Sb2O12, respectively. In CaCu3Cr4O12, the 3d electrons of Cr4+ are delocalized, which strengthens the Cr-Cr ferromagnetic coupling. For CaCu3Cr2Sb2O12, the doping of nonmagnetic ion Sb5+ reduces the Cr-Cr ferromagnetic coupling, and the half-filled Cr3+ t(2g) (t(2g)(3)) makes the chromium 3d electrons localized. In addition, the ordering arrangement of the octahedral chromium and antimony ions also prevents the delocalization of electrons. Hence, CaCu3Cr2Sb2O12 shows insulating behavior, in agreement with the experimental observation.

湖北徐家山锑矿床地球化学和成矿机理研究

　　湖北省通山县的徐家山锑矿床赋存于上震旦统灯影组和陡山沱组的海相碳酸盐岩中，该矿床是华南锑矿带内典型代表性锑矿之一，也是湖北最具经济价值的锑矿床。本论文以该矿床为研究对象，在系统整理前人工作的基础上，进行了深入细致的野外地质考察和系统采样，选取有代表性的样品，运用流体地球化学、元素地球化学、同位素地球化学（C、O、Sr、S、Pb、Sm-Nd）等方法手段，对其成矿流体来源、成矿物质来源、成矿时代、矿床成因等主要矿床学问题进行了系统研究，探讨了该矿床的成矿机理，并对华南锑矿带内上震旦统锑资源潜力进行了初步评价。本论文主要取得以下几点认识： 1）通过对该矿床成矿期脉石矿物（石英、重晶石和方解石）中包裹体镜下观察、显微测温和激光拉曼探针分析，表明该矿床为典型的中低温（150～200℃）热液锑矿床，其热液属NaCl + H2O + CO2 ± N2型，具低盐度（3～6% NaCl）和中等密度（0.90～0.96 g/cm3）特征。结合氢、氧、锶、铅同位素等研究结果，进一步推断这种成矿流体主要来源于经深部循环演化的大气降水，不支持其主要来源于岩浆期后热液的观点。 2）该矿床成矿前和成矿期方解石碳、氧同位素研究结果，表明成矿流体中的溶解碳以H2CO3为主，该流体与围岩发生水－岩相互作用是导致成矿期方解石和辉锑矿沉淀的主要机制。结合方解石的稀土元素地球化学研究，可推断该矿床的两期方解石为同源不同期的产物。 3）微量元素、碳、氧、硫同位素研究结果，表明徐家山矿床的成矿物质与赋矿围岩具有亲缘性；其中最主要的矿石矿物—辉锑矿，其硫同位素组成（+11.2‰～+14.4‰）相对较高（平均值可能在华南锑矿带内最高）、极其均一，且塔式效应明显等为特征，指示该矿的赋矿围岩—震旦纪海相地层是硫的唯一来源。 4）对徐家山锑矿床首次利用锶、铅同位素示踪其成矿物质来源。利用铅同位素示踪手段，首次明确提出该锑矿床存在两个矿源层，部分成矿物质来自赋矿围岩，部分成矿物质来自下伏基底地层，突破了前人对成矿物质仅来源于赋矿围岩的传统认识；并从锶同位素角度，进一步论证了下伏的中元古界冷家溪群基底是成矿元素锑的重要提供者。 5）首次对徐家山矿区成矿期方解石的Sm-Nd同位素组成进行了测定，并初步获得三条等时线年龄（323Ma、348Ma和402Ma）。结合该矿辉锑矿的正常铅模式年龄及成矿地质背景，可推断出该矿床应形成于加里东期。该结论否定了前人燕山期成矿的观点，为重新认识该矿的矿床成因和成矿机理提供新的契机。 6）徐家山锑矿床的成矿时代与那些江南古陆中赋存于前寒武系的锑（和/或金）矿床一致，其成矿流体特征与华南锑矿带其它典型锑矿床相似，揭示出华南锑矿带内不同地段、不同层位产出的锑矿床存在某种共性，这有助于揭示我国华南锑矿带不同锑矿床之间的内在联系以及该矿带锑大规模成矿的机制。 7）根据前人和本文的研究成果，重新厘定了徐家山锑矿床的成因类型，明确提出该锑矿为沉积－改造型矿床，层控特征非常明显。 8）初步评估华南地区上震旦统中锑矿的找矿潜力。认为华南锑矿床带中上震旦统，尤其是鄂南、赣西北、湘西等地的该套地层，锑资源潜力巨大。华南锑矿带中的上震旦统有可能成为我国将来找锑矿取得突破的重要层位之一。

矿山环境中锑的表生地球化学研究—以贵州半坡锑矿区为例

锑(antimony，Sb)是一种典型的毒害重金属元素。我国作为世界上最主要的锑生产国，有关锑的表生地球化学及锑污染防治研究还很薄弱。贵州省位于我国西南低温成矿域中心，具有高Sb地球化学背景值，是我国重要的锑工业基地，境内分布着大量Sb矿床，锑矿储量居全国第四位。贵州又地处我国西南喀斯特中心区域，岩溶地貌极其发育，生态环境脆弱。由于大规模锑矿资源的开采利用，锑矿区土壤和水体中Sb污染十分突出，并通过水体或食物链对矿区及流域居民健康形成潜在威胁。因此，研究矿山环境中Sb的表生地球化学对于认识Sb污染的环境效应和寻求Sb污染修复方式具有至关重要的意义。 本文以贵州半坡大型锑矿区为研究对象，系统研究了Sb在矿区岩石、固体废弃物、土壤、水体和植物体等表生环境介质中的分布、迁移、富集规律与赋存机制，阐明了矿区Sb的表生地球化学过程规律，评价了矿区围岩、（废）矿石和尾矿砂等样品的产酸潜力，筛选出新的锑潜在超富集植物和超耐受性植物，并获得以下主要认识： （1） 独山半坡锑矿区是典型高锑地质地球化学背景区，不仅矿石中Sb含量很高，而且围岩中Sb含量也远高于上地壳Sb的平均含量。辉锑矿是锑的主要载体和释放源。 （2） 在固体废弃物中，冶炼废渣中Sb含量最高，其次为废石堆和尾砂库。废石中元素特征基本与围岩一致，继承了围岩的元素特征，而尾矿砂由于破碎、浮选过程的改造，其元素含量特征与围岩存在差异。尾砂砂中Sb以中层最富，底层和表层依次降低，与Fe、Al矿物的分布特征相似，这种分布模式主要受氧化还原条件、雨水淋滤、Fe/Al矿物吸附机制等因素控制。尾矿砂中不同相态的锑含量依次为残渣态>碳酸盐结合态>有机物结合态>可交换态>铁锰氧化物结合态，其中生物易利用态Sb的空间分布特征与总Sb分布特征一致。 （3） 所有的（废）矿石样品都具有潜在产酸能力，需要采取必要的措施抑制酸性矿山排水的产生。尾矿砂没有产酸潜力，这与矿石在选冶过程中加入石灰处理和S含量过低等原因有关，这种碱性环境可能有利于锑的表生地球化学活化和迁移。 （4） 研究区土壤受到严重锑污染，土壤中Sb含量高达51~7369 mg/kg，且随深度增加而逐渐降低，底层含量与对照区相近。这种高含量的Sb可能是与锑矿化有关的裸露岩石和土壤的自然风化淋滤过程和采矿、冶炼活动等造成的。研究区土壤中不同相态的Sb含量依次为残渣态>铁/锰氧化物结合态>碳酸盐结合态>有机物/硫化物结合态>可交换态。土壤中Sb的生物有效性很低。土壤中Sb的迁移与As密切相关。 （5） 研究区水体为SO4/HCO3-Ca型，水体中的Sb以溶解态、悬浮态和沉积物形式存在，并通过吸附-解吸附和水流推移方式进行迁移。洪水期和枯水期水体中Sb的扩散迁移机制存在差异，洪水期研究区内水体对岔河下游水体污染危害更大。在枯水期，岔河水体中溶解态Sb含量和沉积物中Sb含量存在显著正相关关系，表明枯水期沉积物和水体界面间达到物质交换平衡。水体的氧化还原条件和pH值控制着水体中Sb的存在形态。沉积物中不同相态Sb含量依次为残渣态>碳酸盐结合态，铁锰氧化物结合态>可交换态，有机物/硫化物结合态。研究区水体中Sb主要受矿区采矿、选冶活动的强烈影响。水体中硫同位素示踪研究发现，岔河下游水体中59%的S来自于矿山硫源的贡献，表明矿山活动严重影响到岔河下游水体水质。 （6） 植物对土壤中Sb的吸收与植物部位和种类有关。大体上地下部分>地上部分，且根>叶片>茎。在农作物中，白菜>甘蓝>辣椒和稻谷。研究发现，土荆芥(Chenopodium ambrosioides Linn.)是新的Sb潜在超富集植物，鬼针草(Bidens pilosa Linn.)、一年蓬(Erigeron annuus (Linn.) Pers.)、佛甲草(Sedum lineare Thun)、凹叶景天(Sedum emarginatum Migo)、灰灰菜(Chenopodium album Linn.)和鼠麹草(Gnaphalium affine D. Don)也能大量富集Sb，并有很强耐受性。 （7） 研究区这种特殊的高Sb地质环境和人为活动的影响，导致表生环境中Sb的高度富集，造成农作物、水体中Sb含量极高，通过食物链和水体严重影响当地居民的身体健康。

Determinação de cádmio e chumbo em brinquedos para crianças com idade inferior a 3 anos

Projeto de Pós-Graduação/Dissertação apresentado à Universidade Fernando Pessoa como parte dos requisitos para obtenção do grau de Mestre em Ciências Farmacêuticas

Nanostructured ferroelectric materials

Nanostructured materials are central to the evolution of future electronics and information technologies. Ferroelectrics have already been established as a dominant branch in the electronics sector because of their diverse application range such as ferroelectric memories, ferroelectric tunnel junctions, etc. The on-going dimensional downscaling of materials to allow packing of increased numbers of components onto integrated circuits provides the momentum for the evolution of nanostructured ferroelectric materials and devices. Nanoscaling of ferroelectric materials can result in a modification of their functionality, such as phase transition temperature or Curie temperature (TC), domain dynamics, dielectric constant, coercive field, spontaneous polarisation and piezoelectric response. Furthermore, nanoscaling can be used to form high density arrays of monodomain ferroelectric nanostructures, which is desirable for the miniaturisation of memory devices. This thesis details the use of various types of nanostructuring approaches to fabricate arrays of ferroelectric nanostructures, particularly non-oxide based systems. The introductory chapter reviews some exemplary research breakthroughs in the synthesis, characterisation and applications of nanoscale ferroelectric materials over the last decade, with priority given to novel synthetic strategies. Chapter 2 provides an overview of the experimental methods and characterisation tools used to produce and probe the properties of nanostructured antimony sulphide (Sb2S3), antimony sulpho iodide (SbSI) and lead titanate zirconate (PZT). In particular, Chapter 2 details the general principles of piezoresponse microscopy (PFM). Chapter 3 highlights the fabrication of arrays of Sb2S3 nanowires with variable diameters using newly developed solventless template-based approach. A detailed account of domain imaging and polarisation switching of these nanowire arrays is also provided. Chapter 4 details the preparation of vertically aligned arrays of SbSI nanorods and nanowires using a surface-roughness assisted vapour-phase deposition method. The qualitative and quantitative nanoscale ferroelectric properties of these nanostructures are also discussed. Chapter 5 highlights the fabrication of highly ordered arrays of PZT nanodots using block copolymer self-assembled templates and their ferroelectric characterisation using PFM. Chapter 6 summarises the conclusions drawn from the results reported in chapters 3, 4 and 5 and the future work.

Application of CFD in vacuum dezincing process

Most lead bullion is refined by pyrometallurgical methods - this involves a serics of processes that remove the antimony (softening) silver (Parkes process), zinc (vacuum dezincing) and if need be, bismuth (Betterton-Kroll process). The first step, softening, removes the antimony, arsenic and tin by air oxidation in a furnace or by the Harris process. Next, in the Parkes process, zinc is added to the melt to remove the silver and gold. Insoluble zinc, silver and gold compounds are skimmed off from the melt surface. Excess zinc added during desilvering is removed from lead bullion using one of ghree methods: * Vacuum dezincing; * Chlorine dezincing; or * Harris dezincing. The present study concentrates on the Vacuum dezincing process for lead refining. The main aims of the research are to develop mathematical model(s), using Computational Fluid Dyanmics (CFD) a Surface Averaged Model (SAM), to predict the process behaviour under various operating conditions, thus providing detailed information of the process - insight into its reaction to changes of key operating parameters. Finally, the model will be used to optimise the process in terms of initial feed concentration, temperature, vacuum height cooling rate, etc.

Material effects on stress-induced defect generation in trenched silicon-on-insulator structures

We have investigated the influence of the material properties of the silicon device layer on the generation of defects, and in particular slip dislocations, in trenched and refilled fusion-bonded silicon-on-insulator structures. A strong dependence of the ease of slip generation on the type of dopant species was observed, with the samples falling into three basic categories; heavily boron-doped silicon showed ready slip generation, arsenic and antimony-doped material was fairly resistant to slip, while silicon moderately or lightly doped with phosphorous or boron gave intermediate behavior. The observed behavior appears to be controlled by differences in the dislocation generation mechanism rather than by dislocation mobility. The introduction of an implanted buried layer at the bonding interface was found to result in an increase in slip generation in the silicon, again with a variation according to the dopant species. Here, the greatest slip occurred for both boron and antimony-implanted samples. The weakening of the implanted material may be related to the presence of a band of precipitates observed in the silicon near the bonding interface. (C) 2001 The Electrochemical Society.

Physical and electrochemical evaluation of ATO supported IrO2 catalyst for proton exchange membrane water electrolyser

Antimony doped tin oxide (ATO) was studied as a support material for IrO₂ in proton exchange membrane water electrolyser (PEMWE). Adams fusion method was used to prepare the IrO₂-ATO catalysts. The physical and electrochemical characterisation of the catalysts were carried out using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder conductivity, cyclic voltammetry (CV) and membrane electrode assembly (MEA) polarisation. The BET surface area and electronic conductivity of the supported catalysts were found to be predominantly arisen from the IrO₂. Supported catalyst showed higher active surface area than the pristine IrO₂ in CV analysis with 85% H₃PO₄ as electrolyte. The MEA performance using Nafion®−115 membrane at 80 °C and atmospheric pressure showed a better performance for IrO₂ loading ≥60 wt.% than the pristine IrO₂ with a normalised current density of 1625 mA cm⁻² @1.8 V for the 60% IrO₂-ATO compared to 1341 mA cm⁻² for the pristine IrO₂ under the same condition. The higher performance of the supported catalysts was mainly attributed to better dispersion of active IrO₂ on electrochemically inactive ATO support material, forming smaller IrO₂ crystallites. A 40 wt.% reduction in the IrO₂ was achieved by utilising the support material.

Silicon, the silver bullet for mitigating biotic and abiotic stress, and improving grain quality, in rice?

Adequate silicon fertilization greatly boosts rice yield and mitigates biotic and abiotic stress, and improves grain quality through lowering the content of cadmium and inorganic arsenic. This review on silicon dynamics in rice considers recent advances in our understanding of the role of silicon in rice, and the challenges of maintaining adequate silicon fertility within rice paddy systems. Silicon is increasingly considered as an element required for optimal plant performance, particularly in rice. Plants can survive with very low silicon under laboratory/glasshouse conditions, but this is highly artificial and, thus, silicon can be considered as essential for proper plant function in its environment. Silicon is incorporated into structural components of rice cell walls were it increases cell and tissue rigidity in the plant. Structural silicon provides physical protection to plants against microbial infection and insect attack as well as reducing the quality of the tissue to the predating organisms. The abiotic benefits are due to silicon's effect on overall organ strength. This helps protect against lodging, drought stress, high temperature (through efficient maintenance of transpiration), and photosynthesis by protecting against high UV. Furthermore, silicon also protects the plant from saline stress and against a range of toxic metal stresses (arsenic, cadmium, chromium, copper, nickel and zinc). Added to this, silicon application decreases grain concentrations of various human carcinogens, in particular arsenic, antimony and cadmium. As rice is efficient at stripping bioavailable silicon from the soil, recycling of silicon rich rice straw biomass or addition of inorganic silicon fertilizer, primarily obtained from iron and steel slag, needs careful management. Silicon in the soil may be lost if the silicon-cycle, traditionally achieved via composting of rice straw and returning it to the land, is being broken. As composting of rice straw and incorporation of composted or non-composted straw back to land are resource intensive activities, these activities are declining due to population shifts from the countryside to cities. Processes that accelerate rice straw composting, therefore, need to be identified to aid more efficient use of this resource. In addition, rice genetics may help address declining available silicon in paddy soils: for example by selecting for characteristics during breeding that lead to an increased ability of roots to access recalcitrant silicon sources from soil and/or via selection for traits that aid the maintenance of a high silicon status in shoots. Recent advances in understanding the genetic regulation of silicon uptake and transport by rice plants will aid these goals.

Upgrading of suberin from cork and birch outer bark

O trabalho aqui apresentado teve como principal propósito o estudo do potencial da suberina como fonte de produtos de química fina e como precursor de novos materiais macromoleculares de origem renovável. O interesse na suberina reside, não só na sua ubiquidade e nas suas propriedades únicas em termos de composição química e hidrofobicidade, mas também no facto de ser um dos principais componentes macromoleculares dos subprodutos da indústria corticeira de Quercus suber L. no Sul da Europa, e da indústria de pasta de papel do Norte da Europa, que utiliza a Betula pendula Roth como matéria-prima. A primeira parte do presente trabalho consistiu no estudo detalhado da composição química da cortiça de Quercus suber L. e respectivos resíduos industriais bem como da casca de Betula pendula Roth recorrendo a diferentes técnicas de caracterização, nomeadamente GC-MS, IV, RMN de 1H e de 13C, DSC, termomicroscopia, TGA e difracção de raios-X. Os resultados mostraram que os produtos de despolimerização da suberina representam tipicamente uma fracção substancial de todas as amostras. Para além da suberina, foram também identificados nas diversas amostras quantidades variáveis de compostos triterpénicos, lenhina, polissacarídeos e matéria inorgânica. Os principais resultados da análise por GC-MS mostraram que todas as amostras de suberina despolimerizada são fontes abundantes de ω-hidroxiácidos e de ácidos dicarboxílicos, bem como dos correspondentes derivados epóxidados. No entanto, as quantidades relativas de cada componente identificado foram significativamente diferentes entre amostras. Por exemplo, em amostras de suberina da casca de Quercus suber L. isoladas por metanólise alcalina o composto maioritário encontrado foi o ácido 22-hidroxidocosanóico, enquanto que a suberina também proveniente da cortiça, mas isolada por hidrólise alcalina era composta maioritariamente pelo ácido 9,10-dihidroxioctadecanóico. Já no caso da amostra de suberina despolimerizada proveniente da casca externa da bétula o composto identificado como mais abundante foi o ácido 9,10-epoxi-18-hidroxioctadecanóico. A caracterização das diversas amostras de suberina despolimerizada por FTIR e RMN de 1H e de 13C foram concordantes com os resultados de GC-MS, evidenciando a sua natureza predominantemente lipofílica. Foi ainda determinada a razão entre os grupos CO2H/OH e CO2CH3/OH por RMN de 1H das amostras convenientemente derivatizadas com isocianato de tricloroacetilo, verificando-se que a suberina despolimerizada possuía quantidades não-estequiométricas destes grupos funcionais. A investigação do comportamento térmico das amostras de suberina despolimerizada, por DSC e termomicroscopia, bem como a análise por difracção de raios-X, permitiu concluir que algumas amostras de suberina despolimerizada possuíam importantes domínios cristalinos e pontos de fusão bem definidos, tipicamente próximos de 70 oC, enquanto outras amostras eram essencialmente amorfa. Factores como a fonte de suberina ou as condições de despolimerização estiveram na origem destas diferenças. iv Neste trabalho estudaram-se também os extractáveis lipofílicos da cortiça e dos seus resíduos industriais, em particular os do pó industrial de cortiça e dos condensados negros, mostrando que os extractáveis lipofílicos são uma fonte abundante de compostos triterpénicos, em particular de ácido betulínico e de friedelina. Foram ainda identificadas fracções abundantes de ω-hidroxiácidos e de ácidos dicarboxílicos no condensado negro. A segunda parte deste trabalho abordou a síntese e a caracterização de novos poliésteres alifáticos derivados de suberina. Estes materiais foram sintetizados utilizando, quer misturas de suberina despolimerizada, quer monómeros modelo estruturalmente análogos aos existentes na suberina. Recorreu-se para o efeito a duas aproximações distintas de polimerização por passos, a policondensação e a politransesterificação. Procurou-se em simultâneo maximizar a eficiência da polimerização em termos de peso molecular e de extensão da reacção e utilizar condições de reacção de química “verdes”. Neste sentido, utilizou-se a policondensação em emulsão utilizando um tensioactivo como catalisador e a policondensação em massa utilizando a lipase B de Candida antarctica. Adicionalmente foram também testado os catalisadores trifluorometanosulfonato de bismuto(III) no caso da policondensação, e ainda os catalisadores clássicos óxido de antimónio(III) e o carbonato de potássio no caso da politransesterificação. Os poliésteres resultantes foram caracterizados através de várias técnicas, tais como IV, RMN (de 1H e de 13C), DSC, DMA, TGA, difracção de raios-X e medidas dos ângulos de contacto. Verificou-se que os catalisadores trifluorometanosulfonato de bismuto (III), óxido de antimónio(III) e carbonato de potássio conduziram aos rendimentos de isolamento dos polímeros resultantes mais elevados. No caso dos poliésteres derivados da suberina os resultados em termos de rendimentos e pesos moleculares sofreram um incremento substancial quando a estequiometria da reacção de polimerização foi adequadamente balanceada (r=1) com a adição de uma quantidade extra de um comonómero. Verificou-se a predominância de diferentes estruturas consoante a amostra de suberina utilizada e as condições de síntese adoptada, predominando as cadeias lineares ou então quantidades substanciais de estruturas reticuladas. Globalmente, este primeiro estudo sistemático da utilização de suberina como um precursor de novos poliésteres alifáticos confirmou o elevado potencial deste recurso abundante e renovável como precursor para preparar materiais macromoleculares.

Trace Elements in Ambient Air at Porto Metropolitan Area—Checking for Compliance with New European Union (Eu) Air Quality Standards

Because of the scientific evidence showing that arsenic (As), cadmium (Cd), and nickel (Ni) are human genotoxic carcinogens, the European Union (EU) recently set target values for metal concentration in ambient air (As: 6 ng/m3, Cd: 5 ng/m3, Ni: 20 ng/m3). The aim of our study was to determine the concentration levels of these trace elements in Porto Metropolitan Area (PMA) in order to assess whether compliance was occurring with these new EU air quality standards. Fine (PM2.5) and inhalable (PM10) air particles were collected from October 2011 to July 2012 at two different (urban and suburban) locations in PMA. Samples were analyzed for trace elements content by inductively coupled plasma–mass spectrometry (ICP-MS). The study focused on determination of differences in trace elements concentration between the two sites, and between PM2.5 and PM10, in order to gather information regarding emission sources. Except for chromium (Cr), the concentration of all trace elements was higher at the urban site. However, results for As, Cd, Ni, and lead (Pb) were well below the EU limit/target values (As: 1.49 ± 0.71 ng/m3; Cd: 1.67 ± 0.92 ng/m3; Ni: 3.43 ± 3.23 ng/m3; Pb: 17.1 ± 10.1 ng/m3) in the worst-case scenario. Arsenic, Cd, Ni, Pb, antimony (Sb), selenium (Se), vanadium (V), and zinc (Zn) were predominantly associated to PM2.5, indicating that anthropogenic sources such as industry and road traffic are the main source of these elements. High enrichment factors (EF > 100) were obtained for As, Cd, Pb, Sb, Se, and Zn, further confirming their anthropogenic origin.