Sínteses e caracterizações de TiO2 puro, dopado e co-dopado pelo método sol-gel e suas atividades fotocatalíticas

Nanopartículas de dióxido de titânio vêm sendo extensamente empregadas como fotocatalisa-dores, já que são eficientes na degradação de diversos poluentes. Visando a obtenção de titâ-nias com diferentes propriedades, realizaram-se sínteses através do método sol-gel, a partir da hidrólise do tetraisopropóxido de titânio (IV) TIPP e seguindo-se os princípios da Química Verde, dispensando-se temperaturas e pressões elevadas. Foi estudada a influência de dife-rentes parâmetros, como: pH, solvente, razão molar álcool/TIPP e ordem de adição dos rea-gentes. Foram obtidas titânias na forma cristalina anatásio, nanométricas, com elevadas áreas superficiais específicas e predominantemente mesoporosas. Visando-se obter titânias com melhores propriedades óticas, isto é, capazes de sofrer a fotoativação pela luz visível, foram sintetizadas titânias dopadas e co-dopadas com os metais ferro e rutênio (Fe3+ e Ru3+) e o a-metal N (N3). A síntese desses materiais também foi realizada através do método sol-gel, sendo a dopagem realizada durante o processo de hidrólise. As amostras foram caracterizadas na forma de pó por difração de raios-X, adsorção-dessorção de nitrogênio, microscopia ele-trônica de varredura e espectroscopia de refletância difusa no UV-Visível. A titânia pura a-presentou como única fase cristalina o anatásio, quando calcinada até 400 C, com a presença de traços de brookita. A partir de 600 C, observou-se o aparecimento da fase rutilo, que em 900C foi a única fase encontrada na titânia. A dopagem com Ru3+dificultou a transformação de fase anatásio para rutilo, ao contrário da dopagem com Fe3+. O processo de co-dopagem acelerou a formação de rutilo, que se apresentou como única fase nas amostras calcinadas a 600 C. As titânias dopadas apresentaram uma leve diminuição na energia de bandgap, sendo os dopantes capazes de deslocar a absorção para o vermelho. Foram realizados testes fotoca-talíticos visando à degradação do azocorante Reactive Yellow 145 com lâmpada de vapor de mercúrio de 125 W a fim de se comparar as atividades fotocatalíticas das titânias puras, dopa-das e co-dopadas, calcinadas a 300C. De todas as titânias sintetizadas, a titânia pura foi a que melhor degradou o corante, tendo um desempenho semelhante ao do TiO2 P25, da Evo-nik

Avaliação do potencial fotoprotetor de extratos de musgos e investigação de seus riscos toxicológicos

A radiação ultravioleta (UV) induz diversos efeitos nocivos nos organismos e a quantidade desta radiação que atinge a biosfera é afetada pela concentração de ozônio, latitude, altitude, clima e reflexão especular. As respostas de briófitas em relação aos efeitos da radiação UV e a presença de compostos que absorvem esta radiação têm sido estudadas. Sanionia uncinata, Holomitriopsis laevifolia e Leucobryum laevifolium são espécies de musgos encontrados em locais expostos a alta incidência de radiação UV e com habitats distintos. Considerando que as respostas de musgos contra os efeitos da radiação UV e seus mecanismos de proteção ainda são pouco caracterizados, o objetivo deste estudo foi investigar o potencial fotoprotetor e possíveis riscos toxicológicos associados aos extratos dos musgos S. uncinata, proveniente da Antártica e H. laevifolia e L. laevifolium, proveniente do Amazonas. Seus extratos metanólico (EM), aquoso (EA), hidroalcoólico (EH) e etanólico (EE) foram estudados com a caracterização química por absorção ao UV e visível e pela cromatografia líquida de alta eficiência; quantificação do índice total de compostos fenólicos; determinação da capacidade captadora do radical 2,2-difenil-1-picril-hidrazila a fim de avaliar as atividades antioxidantes; avaliação do potencial de fotoproteção cutânea pela determinação do fator de proteção solar; avaliações do potencial mutagênico e citototóxico, através do ensaio de Salmonella/microssoma, utilizando as cepas TA97, TA98, TA100, TA102 e TA104; do potencial fotomutagênico através do ensaio de fotomutagenicidade, usando as cepas TA102 e TA104; e investigação dos efeitos genotóxicos e fotogenotóxicos, pelo ensaio de micronúcleo e fotomicronúcleo, respectivamente, usando diferentes linhagens celulares estabelecidas. Foram encontradas atividades fotoprotetoras e antioxidantes e observou-se que os extratos se apresentaram singulares devido a sua composição química. Os resultados fotoprotetores, além dos mutagênicos/fotomutagênicos, genotóxicos/fotogenotóxicos e suas respectivas avaliações citotóxicas também permitiram selecionar extratos e suas concentrações, como promissores candidatos em fotoproteção Assim, os EA e EH de H. laevifolia e L. laevifolium apresentam, no geral, os resultados mais significativos, tornando-se potenciais para avaliações refinadas em fotoproteção e na separação de componentes que possam levar a futuras aplicações como antioxidantes e protetores solares ou como adjuvantes.

Optical properties of aluminum-, gallium-, and indium-doped Bi4Ti3O12 thin films

Undoped and Al-, Ga-, and In-doped Bi4Ti3O12 thin films were prepared on fused quartz substrates by chemical solution deposition. Their microstructures and optical properties were investigated by x-ray diffraction and UV-visible-NIR spectrophotometer, respectively. The optical band-gap energies, Urbach energies, and linear refractive indices of all the films are derived from the transmittance spectrum. Following the single oscillator model, the dispersion parameters such as the average oscillator energy (E-0) and dispersion energy (E-d) are achieved. The energy band gap and refractive indices are found to decrease with introducing the dopants of Al, Ga, and In, which is useful for the band-gap engineering and optical waveguide devices. The refractive index dispersion parameter (E-0/S-0) increases and the chemical bonding quantity (beta) decreases in all the films compared with those of bulk. It is supposed to be caused by the nanosize grains in films. (c) 2009 American Institute of Physics. [DOI 10.1063/1.3138813]

Effect of incorporating nonlanthanoidal indium on optical properties of ferroelectric Bi4Ti3O12 thin films

Bi4Ti3O12 (BTO) and Bi3.25In0.75Ti3O12 (BTO:In) thin films were prepared on fused quartz and LaNiO3/Si (LNO) substrates by chemical solution deposition (CSD). Their microstructures, ferroelectric and optical properties were investigated by X-ray diffraction, scanning electron microscope, ferroelectric tester and UV-visible-NIR spectrophotometer, respectively. The optical band-gaps of the films were found to be 3.64 and 3.45 eV for the BTO and BTO:In films, respectively. Optical constants (refractive indexes and extinction coefficients) were determined from the optical transmittance spectra using the envelope method. Following the single electronic oscillator model, the single oscillator energy E-0, the dispersion energy E-d, the average interband oscillator wavelength lambda(0), the average oscillator strength S-0, the refractive index dispersion parameter (E-0/S-0), the chemical bonding quantity beta, and the long wavelength refractive index n(infinity) were obtained and analyzed. Both the refractive index and extinction coefficient of the BTO:In films are smaller than those of the BTO films. Furthermore, the refractive index dispersion parameter (E-0/S-0) increases and the chemical bonding quantity beta decreases in the BTO and BTO:In films compared with those of bulk. (C) 2007 Published by Elsevier B.V.

Determination of the absorption for incident light propagating parallel through the guest-host polymer film waveguide

Guest host polymer thin films of polymethyl methacrylate (PMMA) incorporated with (4'-nitrobenzene)-3-azo-9-ethylcarbazole (NAEC) were fabricated by spin coating and then poled by the method of corona-onset poling at elevated temperature. The absorption mechanism of the polymeric film, which is very important for the optical transmission losses and directly relates to the orientation of chromophore NAEC in polymer PMMA, was investigated in detail. From the UV-visible absorption spectra for NAEC/PMMA film before and after being poled, we determined the change of absorption coefficient kappa with the wavelength and approximately calculated the maximum absorption A(parallel tomax) as 3.46 for incident light propagating parallel through the film, i.e. the ordinary polarized light, which cannot be directly measured in the spectro photometer. (C) 2002 Elsevier Science Ltd. All rights reserved.

Optical properties of NAEC-PMMA nonlinear polymeric thin film

Novel guest nonlinear optical (NLO) chromophore molecules (4-nitrobenzene)-3-azo-9-ethylcarbazole (NAEC) were doped in poly (methyl methacrylate) (PMMA) host with a concentration of approximately 15% by weight. For a useful macroscopic electro-optic (EO) effect, these NLO molecules NAEC were arranged in a noncentrosymmetric structure in the host polymer by corona-onset poling at elevated temperature (COPET). For applying NAEC-PMMA polymer in optical devices such as EO switch, its optical properties have been investigated. The UV/Visible absorption spectra for the unpoled and poled polymer film were determined. The refractive index of the film was also determined from measurements of the coupling angles with the reflective intensity at 632.8 nm wavelength. Using the simple reflection technique, the EO coefficient 33 value was measured as 60 pm/V at 632.8 nm wavelength. The second-order nonlinear coefficient d(33) was characterized by the second-harmonic-generation (SHG) experimental setup and the calculated d(33) value reached 18.4 pm/V at 1064 nm wavelength. The relation between the second-order nonlinear coefficients d(33) and d(13) for the poled polymer film was also discussed in detail and the ratio d(33)/d(13) value was obtained as 3.3. (C) 2002 Kluwer Academic Publishers.

Polarization multiplexing holographic optical recording of a new photochromic diarylethene

A new unsymmetrical photochromic diarylethene 1a is synthesized, and the photochromic properties of it are also investigated. The compound exhibits good photochromism with UV/ visible light irradiation. Compound 1a in polymethyl methacrylate ( PMMA ) film changes color upon 313- nm light irradiation from colorless to blue, in which the absorption maximum is observed at 587 nm. Photon- mode polarization multiplexing holographic optical recording is performed successfully using this compound as a recording medium. In the diarylethene 1b/ PMMA film, polarization multiplexing hologram recording and retrieval, and a combination with the angular multiplexing scheme, are demonstrated systematically. The results indicate that recording capacity can be significantly improved with the combined method of polarization and angular multiplexing holographic recording. (C) 2008 Society of Photo- Optical Instrumentation Engineers.

二维纳米粒子阵列的制备及其拉曼光谱研究

随着纳米科学的迅速发展，金属纳米粒子以其独特的性能己被广泛应用于各学科的研究，由此发展起来的纳米物理、纳米化学、纳米材料和纳米电子学等新兴领域已经成为十分活跃的前沿研究方向。在纳米粒子的许多应用中，如：作为电子和光学器件中的结构组分，表面增强光谱中的基底，生物和化学传感器，都需要把纳米粒子固定在一个基底上构筑成一维，二维或三维有序的结构。本论文通过合成不同性质的金、银纳米粒子，采用自组装技术，在金属，玻璃和导电玻璃的表面成功构筑了有序的纳米结构，并研究由此带来的一系列新颖的光学性质及其作为新型的增强基底在表面增强拉曼光谱中的应用。本论文主要研究内容和结论如下：1、通过合成粒度分布均匀，性能稳定的金属银溶胶，利用自组装技术在玻璃表面成功构筑银纳米粒子的二维亚单层结构，利用UV一visible技术，发现在组装结构中银纳米粒子之间的相互作用对偶极子表面等离子体共振有较大的影响，这也可能意味着相邻银粒子间电磁场的增强与银粒子的偶极子模式间的偶合密切相关。2、利用自组装方法，分别在工T0电极和光滑银基底表面构筑了银纳米粒子有序结构，通过与分子吸附在粗糙银电极表面得到的增强拉曼光谱比较，在有序银纳米粒子组装体中藕联分子的拉曼散射得到很大增强，其特征谱峰的峰位置和强度都有变化。组装体中祸联分子对琉基苯胺（PATP）拉曼散射的增强归因于银粒子和银表面之间的电磁祸合，并且电磁场主要集中在银粒子和银基底表面之间的这一区域，即银粒子的局域等离子体（LSP）与银基底的表面等离子激元（SPP）的祸合作用。3、合成具有不同化学性质的银纳米粒子，利用对琉基苯胺作为祸联分子在光滑银基底表面构筑了Ag/PATP／Ag银纳米粒子二维组装阵列。利用表面增强拉曼光谱技术发现银溶胶中不同性质的银纳米粒子，即银溶胶纳米粒子表面吸附的阴离子对藕联分子与银基底之间的电荷传递有着重要的影响。4、利用表面增强拉曼光谱技术，发现苯功能衍生物：苯硫酚，对琉基苯胺和对苯硫酚在粗糙银电极上有着不同的吸附取向：苯硫酚是直立吸附，对琉基苯胺则是垂直吸附在银表面，而对苯硫酚采取平躺的吸附构像。5、利用电化学沉积法，在对琉基苯胺修饰的光滑的银电极表面构筑了银纳米粒子的有序二维结构，通过与利用自组装方法构筑的银粒子阵列中祸联分子表面增强拉曼光谱的研究比较，发现银离子在吸附层修饰的银电极表面进行电化学沉积可能采取两种机理：在双电层附近，溶液中的阴离子参予了整个过程，银粒子与基底之间存在静电吸引作用；银离子直接在吸附分子的氨基表面还原并成键，然后进一步的生长。6、利用电化学沉积法，在金纳米粒子表面沉积了一层汞，SEM，UV－vis及电化学实验证明在具有修饰层的导电玻璃（PVP一ITO）电极上成功合成了汞包金纳米粒子阵列，将汞电极表面的研究拓展到了分子水平。利用金纳米粒子产生的增强电磁场可以研究吸附在汞包金纳米粒子上的分子的表面增强拉曼光谱，简单分子对琉基苯胺在金纳米粒子阵列及汞包金纳米粒子阵列上采取同样的吸附方式，而复杂分子结晶紫在汞包金纳米粒子上采取一种接近平躺的方式吸附，而在金纳米粒子表面则是倾斜吸附的方式。进一步将汞包金纳米粒子阵列电极应用到分子的现场谱学中，从而为更好的理解汞电极上的电化学过程打下了基础。

MeV离子辐照聚酰亚胺的化学结构及电性能转变

在室温真空条件下,用北京大学离子注入机提供的3 MeV Si~+对厚度大约25μm的电绝缘聚酰亚胺(PI/Kapton)进行了表面改性,通过紫外可见光谱分析(UV/Visible)、傅立叶转换红外光谱分析(FTIR)及电性能测量,研究了不同离子注量(1×10~(12)—1×10~(15)cm~(-2))下注入层中聚酰亚胺各官能团的化学降解及石墨化结构转变机制。红外结果表明,官能团随离子注入量的增加指数降解,并通过实验点的拟合给出了典型分子键的损伤截面。辐照后聚合物的导电性发生了巨大变化,在我们的实验中,聚酰亚胺的面电阻与未辐照样相比下降了近10个数量级,呈现出半导体的电特性。紫外光谱中吸收边缘从紫外到可见区的红移表明了光能隙的逐渐减小,这是由于芳香团尺寸的增加而引起的。

Simultaneous determination of methylene blue and new methylene blue by slab optical waveguide spectroscopy and artificial neural networks

A slab optical waveguide (SOWG) has been used for study of adsorption of both methylene blue (MB) and new methylene blue (NMB) in liquid-solid interface. Adsorption characteristics of MB and NMB on both bare SOWG and silanized SOWG by octadecyltrichlorosilane (ODS) were compared. The simultaneous determinations of both MB and NMB were explored by flow injection SOWG spectrophotometric analysis and artificial neural networks (ANNs) for the first time. Concentrations of MB and NMB were estimated simultaneously with the ANNs. Results obtained with SOWG were compared with those got by conventional UV-visible spectrophotometry. (C) 2003 Elsevier Science B.V All rights reserved.

Synthesis and Metal-ion Binding Properties of New N2S4O2- and N2S5O2-Donor Macrocycles

Synthetic procedures for new mixed-donor macrocycle compounds were reported. The macrocyclic compounds were used in solvent extraction metal picrates such as Ag+, Hg2+, Cd2+, Zn2+, Cu2+, Ni2+, Mn2+, Pb2+, and Co2+. The metal picrate extractions were investigated at 25±0.1°C with the aid of UV-visible spectrometry. It was found that 6,7,9,10,12,13,23,24-octahydro-19H,26Hdibenzo[h,t](1,4,7,13,16,22,10,19) dioxatetrathiadiazasiclotetracosine-20,27(21H,28H)-dione showed selectivity towards Ag+, Hg2+, and Cd2+ among the other metals. The extraction constants (Log Kex) and complex compositions were determined for the Ag+ and Hg2+ complexes for this compound and 9,10,12,13,23,24,26,27,29,30-decahydro-5H,15H-dibenzo-[h,w][1,4,7,13,16,19,25-,10,22] dioxapentathiadiazacycloheptacosine-6,16(7H,17H)-dione.

Two novel molybdenum complexes containing [Mo2O2S2](2+) fragment: synthesis, crystal structures and catalytic studies

Mo2O2S2(HGly)(GlY)(2) 1 and K-6[Mo2O2S2(nta)(2)][Mo2O2S2(ntaH)(2)]center dot 4H(2)O 2 were synthesized by the reactions of (NH4)(2)MoS4 and amino acids L (L = glycine, nitrilotriacetic acid) in ethanol-water medium at ambient temperature. The two complexes were characterized by elemental analysis, infrared spectra, UV-visible spectra, TG-DTA and XPS.

Synthesis, characterization and catalytic properties of chiral BINOL functionalized mesoporous silicas for enantioselective Morita-Baylis-Hillman reaction

Several Chiral BINOL functionalized mesoporous silicas were prepared by post grafting of organosilane derivatives of (S)-BINOL (1,1'-bi-2-naphthol) on SBA-15 and characterized by C-13 CP/MAS NMR, FT-IR, UV-visible absorption spectra, elemental analysis, powder XRD, nitrogen adsorption-desorption isotherms and TEM techniques. Their catalytic properties were demonstrated in enantioselective Morita-Baylis-Hillman reaction of 3-phenylpropanal and cyclohexenone.

Monitoring catalytic degradation of dye molecules on silver-coated ZnO nanowire arrays by surface-enhanced Raman spectroscopy

Catalytic degradation of organic dye molecules has attracted extensive attention due to their high toxicity to water resources. In this paper, we propose a novel method for the fabrication of uniform silver-coated ZnO nanowire arrays. The degradation of typical dye molecule rhodamine 6G (R6G), as an example, is investigated in the presence of the as-prepared silver-coated ZnO nanowire arrays. The experimental results show that such composite nanostructures exhibit high catalytic activity, and the reaction follows pseudo-first-order kinetics. Furthermore, these nanowire arrays are desirable SERS substrates for monitoring the catalytic degradation of dye molecules. Compared with traditional UV-visible spectroscopy, SERS technology can reflect more truly the catalytic degradation process occurring on the surface of the catalysts.

Characterization and optimization of AuNPs labeled by Raman reporters on glass based on silver enhancement

In this report, gold nanoparticles (AuNPs) labeled by Raman reporters (AuNPs-R6G) were assembled on glass and used as the seeds to in situ grow silver-coated nanostructures based on silver enhancer solution, forming the nanostructures of AuNPs-R6G@Ag, which were characterized by scanning electron microscopy (SEM) and UV-visible spectroscopy. More importantly, the obtained silver-coated nanostructures can be used as a surface enhancement Raman scattering (SERS) substrate. The different SERS activities can be controlled by the silver deposition time and assembly time of AuNPs-R6G on glass. The results indicate that the maximum SERS activity could be obtained on AuNPs-R6G when these nanostructures were assembled on glass for 2 h with silver deposition for 2 min.