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Teija Laukala Dennis Kronlund Isto Heiskanen Kaj Backfolk 《Cellulose (London, England)》2017,24(7):2813-2826
The precipitation of micro- and nanoparticles of calcium carbonate onto lignocellulosic microfibers was investigated at different microfiber concentrations with and without polyacrylic acid (PAA), i.e. a polymer commonly used to form polymer-induced liquid precursors of CaCO3. Concentrations of PAA, Ca(OH)2, CO2 and microfiber were varied in order to study the impact of reaction conditions on PCC formation in a batch reactor operated at ambient temperature. High resolution scanning electron micrographs of the samples show that both microfiber concentration and PAA dosage affected the nucleation and crystal growth of PCC filler on cellulosic fiber. Interestingly, at higher microfiber concentrations, larger amount of nano-sized spherical crystals were formed on the microfibers. A higher dosage of PAA, on the other hand, resulted in less nucleation on the microfiber, suggesting a preferential bulk nucleation mechanism. A higher concentration of PAA during the precipitation also led to the formation and stabilization of amorphous CaCO3, which was supported by SEM images and XRD analysis (lack of characteristic crystal structure). 相似文献
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Risto Koivula 《Central European Journal of Chemistry》2010,8(6):1179-1184
Antimony is perhaps the most frequently used doping element of tin dioxide. Although antimony of different oxidation states
have been used in the synthesis, the effect of dopant’s valence on ion exchange properties has not been investigated critically.
In our study the valence of antimony had clear effects on the metal uptake properties of Sb-doped SnO2 materials. Extremely high Tc uptake (Kd > 100 000 mL g−1) on Sb(III)-doped material was observed in conditions under which Sb(V)-doped material did not show any Tc uptake. However,
the Sb(V)-doped material showed good Ni2+ uptake properties (Kd up to 33 000 mL g−1), even at pH values below the material’s point of zero charge (pzc), while the Sb(III)-doped material showed Ni2+ uptake only at pH above its pzc. The cation uptake of Sb-doped SnO2 resembles typical weakly acidic cation exchanger character but the uptake of TcO4- does not follow a typical anion exchange pattern. Instead, we propose a sorption process related to redox reactions as the
probable Tc uptake process. 相似文献
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Jukka Lehto Risto Koivula Heikki Leinonen Esko Tusa Risto Harjula 《Separation & Purification Reviews》2019,48(2):122-142
This paper describes the processes used at the Fukushima Daiichi plant, Japan, to purify the waste effluents generated in the cooling of damaged reactors. These include primary cesium removal with the Kurion zeolite system and the SARRY system utilizing silicotitanate to remove radiocesium from water recirculated to reactors for cooling. Another process is the ALPS system to purify the retentates of the reverse osmosis plant to further purify the water from radionuclides after primary cesium separation. In ALPS, a major role is played by the transition metal hexacyanoferrate product CsTreat and sodium titanate SrTreat in the removal of radiocesium and radiostrontium, respectively. The performance of these four exchangers (zeolite, silicotitanate, hexacyanoferrate, and sodium titanate) is critically analyzed with respect to processing capacities and the decontamination factors obtained in the processes. Furthermore, general information on preparation, structure and ion exchange of these ion-exchanger categories is given with additional information on their use in nuclear waste effluent treatment processes. Finally, the importance of selectivity and associated factors are discussed. 相似文献
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Spreading of oils and water on porous and pre-saturated model carbonate coating structures was studied with high speed video imaging. The short-time data were complemented with long time absorption and wicking experiments. The results indicate a strong dependence between surface structural features of the pigment tablets and water spreading at short times, both in non-saturated and water pre-saturated cases, while the oil spreading is mainly dependent on the liquid properties. Sodium polyacrylate dispersant on pigment surfaces is shown to contribute to water spreading and absorption. On pre-saturated structures the liquid-liquid interactions are dominant and the majority of results support spreading according to the molecular kinetic model. The evidence supports the hypothesis of S. Rousu, P. Gane, and D. Eklund, ["Influence of coating pigment chemistry and morphology on the chromatographic separation of offset ink constituents," in The Science of Papermaking Transactions of the 12th Fundamental Research Symposium, FRC The Pulp & Paper Fundamental Research Society, Oxford, UK, 2001, p. 1115] that at long times the oils absorb into the porous structure at a rate proportional to the ratio of viscosity and surface tension, provided there is no sorptive action with the binder. A combination of nanosized pores and large surface area is useful for providing sufficient absorption capability for carbonate based coatings. 相似文献
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Mimicking the action of enzymes by simpler and more robust man-made catalysts has long inspired bioorganic chemists. During the past decade, mimics for RNA-cleaving enzymes, ribonucleases, or, more precisely, mimics of ribozymes that cleave RNA in sequence-selective rather than base-selective manner, have received special attention. These artificial ribonucleases are typically oligonucleotides (or their structural analogs) that bear a catalytically active conjugate group and catalyze sequence-selective hydrolysis of RNA phosphodiester bonds. 相似文献
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Teija Koivula Jaana Laine Tiina Lipponen Outi Perhola Eeva-Liisa K?m?r?inen Kim Bergstr?m Olof Solin 《Journal of Radioanalytical and Nuclear Chemistry》2010,286(3):841-846
The serotonin receptor 5-HT1A ligand 4-[18F]fluoro-N-[2-[1-(2-methoxyphenyl)-1-piperazinyl]ethyl-N-2-pyridinyl-benzamide (p-[18F]MPPF) was produced by a simplified method of Le Bars et al. Traditional oil bath heating was compared to microwave heating.
Various radioanalytical methods, radio-Thin Layer Chromatography (TLC), High Pressure Liquid Chromatography (HPLC) and Mass
Spectrometry (MS), were compared in the evaluation of the labelled product(s). The crude reaction mixture consisted of p-[18F]MPPF and 2–4 radioactive by-products eluting after the product fraction, and the reverse-phase HPLC method failed occasionally
to separate p-[18F]MPPF from the radioactive by-product with close retention time. The heating method had no significant effect on the composition
of labelled by-products. In LC-(ESI)-MS analysis of p-[18F]MPPF the labelled product was identified with m/z ratio of 435 ([M + H+]). The other HPLC fractions were measured to have following m/z ratios: (1) 327; 349; (675) (2) 402; 407/408; (791) and (3) 436, suggesting different kind of decomposition of the labelled
product and/or the inactive precursor. The ion trap mass spectrometer was sufficient for the qualitative analysis of p-[18F]MPPF. However, differentiation of by-products arising from the decomposition of p-[18F]MPPF or from its precursor p-MPPNO2 proved to be challenging. 相似文献
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Cellulose - CaCO3-pulp composite was prepared via precipitation of calcium hydroxide in the presence of pulp. In order to investigate the precipitation selectivity and mechanism, the substrate... 相似文献
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Myllykylä E. Lavonen T. Koivula L. Ollila K. Siitari-Kauppi M. 《Journal of Radioanalytical and Nuclear Chemistry》2017,311(1):225-235
Journal of Radioanalytical and Nuclear Chemistry - The sparingly soluble ThO2 dissolution behaviour was studied under conditions that are expected to prevail in bedrock after the closure of the... 相似文献