Investigation of Hg sorption and diffusion behavior on ultra-thin films of gold using QCM response analysis and SIMS depth profiling
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Using the quartz crystal microbalance (QCM) technique, we demonstrate that the contribution of Hg adsorption and absorption on the sensor response profile can be distinguished by studying the dynamic response curve of QCM based Hg vapor sensors that employ an ultra-thin film of Au in the range of 10 to 40 nm thickness as the sensitive layer. The response magnitudes of the QCMs were extrapolated to zero thickness (ETZT) in an attempt to determine the contribution of adsorbed Hg on the sensor response magnitude and response profile. In general, the ratio of adsorbed to absorbed Hg on Au films is found to decrease with increased Hg vapor concentration. Furthermore, the same ratio was observed to decrease with increasing Au film thickness. The 10 nm and 40 nm Au films for example were found to contain adsorbed Hg content of 43.8% and 16.4%, respectively, with the balance attributed to absorption/amalgamation, when exposed to Hg vapor concentration of 10.55 mg m−3 for a period of 14 hours and an operating temperature of 28 °C. In addition, the QCMs were characterized using secondary ion mass spectroscopy depth profiling in order to study the diffusion behaviour of Hg in the Au surfaces. It is deduced that in order to reduce Hg accumulation in Au thin films, a non-continuous type film (similar to the 10 nm ultra-thin Au sensitive layer morphology) would be more functional as a Hg sensitive layer where quick absorption and desorption processes are required.Keywords:
Quartz Crystal Microbalance
The sorption and desorption behavior of naphthalene on geosorbents were studied through the surged equilibrium experiment methods. The results showed that the sorption and desorption of naphthalene on geosorbents exhibited obviously nonlinear and sorption-desorption hysteretic, the sorption and desorption characteristics might correlate with the structure of geosorbents. The sorption and desorption of naphthalene on the more rigi-dity, more reductive and more aromatic geosorbents exhibited more nonlinear and more sorption-desorption hysteretic.
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A piezoelelctric quartz-crystal plate can be used as a microbalance (a quartz-crystal microbalance, QCM). When substances adsorbed on a gold electrode, a fundamental frequency of a QCM is decreased linearly with increasing mass on the electrode. The host molecule-immobilized QCM is used as a biosensor responding to the addition of guest molecules in aqueous solution in nanogram level.
Quartz Crystal Microbalance
Crystal (programming language)
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The sorption/desorption of DDTs to surface coatings were investigated using the bath equilibration technique. Freundlich isotherm was applied to describe the sorption/desorption of DDTs to surface coatings. The results showed that desorption of DDTs from surface coatings presented hysteresis which was described by hysteresis index (HI). Influences of pH values of solutions and the coexistence of Cu and Pb on sorption and desorption were also studied in the same method. The results indicated that the sorption of DDTs decreased and desorption increased when the values of pH increased from 5 to 9. The coexistence of Cu and Pb inhibited the sorption of DDTs, meanwhile had facility to desorption of DDTs.
Hysteresis
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Lignin was used as a model compound for soil organic matter to gain insight into the mechanisms that control the kinetics of pesticide sorption and desorption. Hydrolytic lignin was immobilized in a matrix of alginate gel, and sorption−desorption experiments were undertaken with isoproturon. Sorption increased with time and was close to equilibrium after 14 days. Desorption was measured after sorption for different time intervals and for a number of successive desorption steps of different lengths. The results showed strong differences between the sorption and desorption isotherms. The ratio of sorbed to dissolved pesticide approached and even exceeded the equilibrium ratio, depending on the number of desorption steps and the length of each equilibration period. A numerical diffusion model was developed to describe radial diffusion into the lignin particles in combination with Freundlich sorption inside the particles. Key model parameters were adjusted to fit the sorption data, and the same parameters were then used to predict stepwise desorption. Desorption was well described by the model, which suggests that sorption and desorption were driven by the same mechanism and occurred at the same rate. The observed difference between the sorption and desorption isotherms could be fully explained by the nonattainment of equilibrium due to slow diffusion into and out of the lignin particles.
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The rates at which methacrylic acid is sorbed and desorbed from aqueous solution by drawn nylon 6.6 fibres have been measured at 30°, 45°, and 60°C. Desorption is faster than the first sorption, and the second sorption proceeds initially at the same rate as desorption. On first sorption only, there is a very short induction period, and supersorption occurs, the amount sorbed passing through a maximum before falling to the equilibrium value. The rates of change of fibre length on sorption and desorption have been correlated with the sorption and desorption rates themselves. They are roughly proportional for desorption (decrease in length) and for sorptions beyond the second (increase in length) On first sorption, there is a relatively long induction period before the irreversible decrease in length begins. It is considered that the first sorption produces an irreversible relaxation in the fibres, allowing greater diffusion rates subsequently. This process is completed on second sorption. The sorption rates are initially dependent on the square root of the time. Diffusion coefficients have been calculated and are found to increase exponentially with concentration and to have activation energies of 13 and 10 kcal/ mole-1 on first sorption and desorption, respectively.
Nylon 6
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In this paper,the container wall sorption percentage and the sorption ratio of Am betweensolution and such sorption materials as bentonite are studied with the HPGe detector connected-with S-85 multichannel system,the influence of container wall sorption on sorption ratio also isdiscussed.The results show that the container wall sorption with solid sorptive materials is lowerthan that without solid sorptive materials. The container wall sorption should be considered forthe sorptive materials with low sorption ratio values and can be neglected for those with highsorption ratio values.
Bentonite
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In this paper we study the possibility to develop an alternative Analytical Method for Investigation in Real‐Time of Liquid Properties, the layout and the operation with Quartz Crystal Microbalance (QCM) Systems. The quartz crystal microbalance (QCM) can be accepted as a powerful technique to monitor adsorption and desorption processes at interfaces in different chemical and biological areas. In our paper, Quartz Crystal Microbalance is used to monitor in real‐time the polymer adsorption followed by azoic dye adsorption and then copolymer adsorption as well as optimization of interaction processes and determination of solution effects on the analytical signal. The solutions of azoic dye (5⋅10−4 g/L, 5⋅10−5 g/L and 5⋅10−6 g/L in DMF) are adsorbed at gold electrodes of QCM and the sensor responses are estimated through decrease and increase of QCM frequency. Also, the response of the sensor at maleic anhydride (MA) copolymer with styrene St (MA‐St copolymer concentration of solution: 5⋅10−4 g/L; 5⋅10−5 g/L and 5⋅10−6 g/L in DMF) is fast, large, and reversible. The detailed investigation showed the fact that the Quartz Crystal Microbalance is a modern method to study a wider number of physical and chemical properties related to the surface and interfacial processes of synthesized copolymer leading to a higher reliability of the research results.
Quartz Crystal Microbalance
Maleic anhydride
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Quartz Crystal Microbalance
Crystal (programming language)
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膜を用いた浄水処理には従来の処理と比較して様々な利点がある一方で,膜ファウリングが大きな問題となる.近年の研究においてバイオポリマーと総称される高分子量親水性有機物が膜ファウリングの発生に強く関与することが示唆されている.本研究では特徴の異なる複数の原水よりバイオポリマーを回収・精製し,これらが発生させる膜ファウリングの差異について検討した.バイオポリマー濃度を統一して実施した膜ろ過試験では原水毎に膜ファウリング発生速度が明らかに異なっており,原水が異なるとバイオポリマーの特性が変化することが示された.バイオポリマー特性の差異はLC-OCDを用いた分子量分布測定,赤外スペクトル分析においても明白であり,バイオポリマーの大半が多糖類より構成される場合には不可逆的ファウリングの発生をより深刻にする可能性が示された.消散監視機能付き水晶振動子マイクロバランス(QCM-D)による分析では興味深い結果が得られた.QCM-D分析において膜材質ポリマーであるPVDFとの高い親和性が示されたバイオポリマーが高い膜ファウリングポテンシャルを有していた.また,バイオポリマーの粘弾性がファウリングの可逆性を説明する可能性が示唆された.今後QCM-Dを用いた分析データを充実させていくことで,膜ファウリングが発生しにくい膜材質を適切に選定できる可能性がある.
Quartz Crystal Microbalance
Biofouling
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