97 research outputs found
Optical spectroscopy of nanoporous membranes based on anodic alumina in an ammonia gas flow
Background and Objectives: Membranes in the form of highly ordered nanostructures of porous anodic aluminum oxide (PAAO) with adjustable pore properties were obtained by electrochemical anodizing. PAAO nanostructures were prepared in an oxalic acid electrolyte at a direct current electrochemical potential of 30–60 V. The ready-made nanoporous membranes were modified with thin silver films 1.8, 3.6 and 5.4 nm thick. The study of the membrane surface by scanning electron microscopy has shown that nanoporous membranes have hexagonally arranged and highly ordered arrays of pores with a diameter of (30±4) nm and a packing density of about 1.8 · 10¹⁰ cm–2. Optical interference spectra of PAAO were recorded in the wavelength range of 300–900 nm. The optical properties of nanoporous membranes with a free and silver-modified surface changed depending on the time of interaction of the membrane surface with the ammonia gas flow, which led to changes in the interference pattern and, in turn, to changes in the effective optical thickness (EOT) of the membranes. Features of the influence of the membrane surfacemodified with silver onthe shape and sensitivity ofthe optical signal ofthe sensor have been revealed. The aim ofthis work was to experimentally study the temporal characteristics of the optical spectral response of nanoporous anodic alumina membranes with a free pore surface and modified with thin silver films in an ammonia gas flow. Materials and Methods: The thickness of the PAAO membrane, determined profilometrically, did not exceed 1.0 µm. The average inner diameter of Al2O3 nanopores is (30±4) nm. The silver films were deposited by magnetron sputtering at direct current. Changes in the effective optical thickness are used to quantify changes in the optical properties of the membrane. Changes in the effective optical thickness will be mainly determined by the effective refractive index of the PAAO-Ag molecular film of the adsorbed gas structure. The effective refractive index of the membrane was determined from the measured position of the interference maxima and the given membrane thickness. Results: Association processes have been considered, i.e. binding of analyte molecules to the surface of the PAAO nanoporous membrane. A stream of gaseous ammonia was chosen as the analyte. According to the Langmuir isotherm model, the sensor response during real-time measurements should follow a negative exponential trend. It has been shown that the shape of the sensor’s optical signal qualitatively repeats the shape of the theoretical curve of real-time optical probing in the regions of molecular binding and equilibrium. The molecular association time of the free surface of the PAAO nanoporous membrane was 7 ± 1 minutes. The deposition of thin silver films on the surface of a nanoporous PAAO membrane leads to a change in the shape of the optical signal and a decrease in its magnitude. Conclusion: On the basis of the synthesized nanoporous PAAO membranes with a free surface and modified with ultrathin silver films, experimental studies of the effect of ammonia flow on multibeam light interference in such membranes have been carried out. It has been found that the surface roughness and size effect of the silver film thickness have a significant effect on the transmission spectra and sensory sensitivity of the membranes. It has been shown that the largest relative change in the refractive index of the membrane in an ammonia flow is observed for the thinnest silver film 1.8 nm thick. It has been noted that there is a threshold value of the thickness of a silver film deposited on the surface of a nanoporous PAAО membrane, above which the use of such films in optical sensors with the mechanism of multipath light interference is not advisable, and the use of a different mechanism is required, for example, the mechanism of localized surface plasmon resonance
Electrophysical Characteristics of a Polymer Composite Based on Ultrahigh Molecular Weight Polyethylene with CuO Nanoparticles
Методом импедансной спектроскопии исследованы электрофизические свойства
композитного материала на основе сверхвысокомолекулярного полиэтилена с ограниченной
массовой концентрацией 0,5 мас.% оксида меди CuO в диапазоне частот от 102 до 108
Гц. Предполагается, что введение в состав полимера малых концентраций наночастиц
способствует более равномерному их осаждению на поверхностях полимерных гранул. Это
позволяет в процессе тестирования таких образцов выявить наиболее вероятные механизмы их
поляризации и протекания электрического тока в относительно однородном ансамбле наночастиц
в полимерной матрице. Установлено, что внедряемые в полимерную матрицу наночастицы
незначительно влияют на процессы электрической поляризации, но приводят к появлению
частотно-зависимой
проводимости в широком диапазоне частот. Этот процесс сопровождается
существенным возрастанием диэлектрических потерь. Электрофизические характеристики
полученных композитов обсуждаются с учётом переноса электрических зарядов (ионов или
электронов) как по внутренней, так и по поверхностной структуре наночастиц CuOThe electrophysical properties of a composite material based on ultrahigh molecular weight polyethylene with a limited mass concentration of 0.5 wt% copper oxide CuO in the frequency range from 102 to 108 Hz were studied by impedance spectroscopy. It is assumed that the introduction of low concentrations of nanoparticles into the polymer composition contributes to their more uniform deposition on the surfaces of polymer granules. This makes it possible to reveal the most probable mechanisms of their polarization and the flow of electric current in a relatively homogeneous ensemble of nanoparticles in a polymer matrix during testing of such samples. It has been established that nanoparticles introduced into the polymer matrix have little effect on the processes of electric polarization, but lead to the appearance of frequency-dependent conductivity in a wide frequency range. This process is accompanied by a significant increase in dielectric losses. The electrophysical characteristics of the resulting composites are discussed taking into account the transfer of electric charges (ions or electrons) both along the internal and surface structures of CuO nanoparticle
Kinetics of Аdsorption of nickel(II) Ions by Zeolite with Immobilized Thiosemicarbazide
Исследовано влияние температуры на кинетику адсорбции ионов никеля(II)
цеолитом с иммобилизованным тиосемикарбазидом. В рамках диффузионных моделей Бойда
и Морриса-Вебера
использован количественный подход для первичного разграничения внешне
и внутри диффузионного лимитирования адсорбции. Показано, что диффузия ионов через
пленку раствора и диффузия в зерне цеолита вносят свой вклад в общую скорость процесса,
и адсорбция протекает в смешанно-диффузионном
режиме. Вклад химической стадии в кинетику
гетерогенного процесса адсорбции был охарактеризован в рамках кинетических моделей
Лагергрена, Хо и Маккея и Еловича. Наиболее применимой для описания исследуемых процессов
является модель псевдо-второго
порядка. Модель предполагает, что скорость процесса адсорбции
ионов никеля(II) лимитирует химическая реакция, которая в случае рассматриваемых цеолитов
сопровождается образованием хелатных комплексов (состава 1:1) за счет донорно-акцепторного
взаимодействия ионов металла с атомами азота и серы тиосемикарбазидного фрагмента. Такой
тип взаимодействия характерен как для материалов функционализированных тиосемикарбазидом,
так и в целом для органических адсорбентов, содержащих N- и S‑активные группировкиThe effect of temperature on the adsorption kinetics of nickel(II) ions by zeolite with immobilized thiosemicarbazide has been studied. Within the framework of the diffusion models of Boyd and Morris-Weber, a quantitative approach was used for the primary distinction between external and internal diffusion limitation of adsorption. It is shown that the diffusion of ions through the solution membrane and diffusion in the zeolite grain contribute to the overall rate of the process, and adsorption proceeds in a mixed diffusion mode. The contribution of the chemical stage to the kinetics of the heterogeneous adsorption process was characterized in terms of the kinetic models of Lagergren, Ho, and McKay and Elovich. The most applicable for describing explored the processes is the pseudo-second order model. The model assumes that the rate of adsorption of nickel(II) ions is limited by a chemical reaction, which, in the case of the zeolites under consideration, is accompanied by the formation of chelate complexes (composition 1:1) due to the donor-acceptor interaction of metal ions with nitrogen and sulfur atoms of the thiosemicarbazide fragment. This type of interaction is typical both for materials functionalized with thiosemicarbazide and, in general, for organic adsorbents containing N- and S‑active group
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Research and Design of a Routing Protocol in Large-Scale Wireless Sensor Networks
无线传感器网络,作为全球未来十大技术之一,集成了传感器技术、嵌入式计算技术、分布式信息处理和自组织网技术,可实时感知、采集、处理、传输网络分布区域内的各种信息数据,在军事国防、生物医疗、环境监测、抢险救灾、防恐反恐、危险区域远程控制等领域具有十分广阔的应用前景。 本文研究分析了无线传感器网络的已有路由协议,并针对大规模的无线传感器网络设计了一种树状路由协议,它根据节点地址信息来形成路由,从而简化了复杂繁冗的路由表查找和维护,节省了不必要的开销,提高了路由效率,实现了快速有效的数据传输。 为支持此路由协议本文提出了一种自适应动态地址分配算——ADAR(AdaptiveDynamicAddre...As one of the ten high technologies in the future, wireless sensor network, which is the integration of micro-sensors, embedded computing, modern network and Ad Hoc technologies, can apperceive, collect, process and transmit various information data within the region. It can be used in military defense, biomedical, environmental monitoring, disaster relief, counter-terrorism, remote control of haz...学位:工学硕士院系专业:信息科学与技术学院通信工程系_通信与信息系统学号:2332007115216
New Functional Alkoxysilanes and Silatranes: Synthesis, Structure, Properties, and Possible Applications
The aza-Michael reaction of 3-aminopropyltriethoxysilane (1) and -silatrane (2) with acrylates affords functionalized silyl-(3–8) and silatranyl-(9–14) mono- and diadducts with up to a 99% yield. Their structure has been proved with IR and NMR spectroscopies, mass spectrometry and XRD analysis. The hydrolytic homo-condensation of triethoxysilanes 3–5 gives siloxanes 3a–5a, which form complexes with Ag, Cu, and Ni salts. They are also able to adsorb these metals from solutions. The hetero-condensation reaction of silanes 4–8 with OH groups of zeolite (Z), silica gel (S) and glass (G) delivers the modified materials (Z4, S7, G4, G5, G7, G8, etc.), which can adsorb ions of noble metal (Au, Rh, Pd: G4 + Au, G5 + Pd, G7 + Rh). Thus, the synthesized Si-organic polymers and materials turned out to be promising sorbents (enterosorbents) of noble, heavy, toxic metal ions and can be applied in industry, environment, and medicine
Functionalized 2,3′-Bipyrroles and Pyrrolo[1,2-<i>c</i>]imidazoles from Acylethynylpyrroles and Tosylmethylisocyanide
An efficient method for the synthesis of pharmaceutically prospective but still rare functionalized 2,3′-bipyrroles (in up to 80% yield) by the cycloaddition of easily available acylethynylpyrroles with tosylmethylisocyanide (TosMIC) has been developed. The reaction proceeds under reflux (1 h) in the KOH/THF system. In the t-BuONa/THF system, TosMIC acts in two directions: along with 2,3′-bipyrroles, the unexpected formation of pyrrolo[1,2-c]imidazoles is also observed (products ratio~1:1)
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