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“Soft” Chemical Synthesis and Manipulation of Semiconductor Nanocrystals
Published in Victor I. Klimov, Nanocrystal Quantum Dots, 2017
Jennifer A. Hollingsworth, Victor I. Klimov
The two stages of growth (the relatively rapid first stage and Ostwald ripening) differ in their impact on size dispersity. During the first stage of growth, size distributions remain relatively narrow (dependent on the nucleation event) or can become more focused, whereas during Ostwald ripening, size tends to defocus as smaller particles begin to shrink and, eventually, dissolve in favor of growth of larger particles.19 The benchmark preparation for CdS, CdSe, and CdTe NQDs,20 which dramatically improved the total quality of the nanoparticles prepared until that point, relied on Ostwald ripening to generate size series of II-VI NQDs. For example, CdSe NQDs from 1.2 to 11.5 nm in diameter were prepared.20 Size dispersions of 10%–15% were achieved for the larger-size particles and had to be subsequently narrowed by size-selective precipitation. The size-selective process simply involves first titrating the NQDs with a polar “nonsolvent,” typically methanol, to the first sign of precipitation plus a small excess, resulting in precipitation of a small fraction of the NQDs. Such controlled precipitation preferentially removes the largest NQDs from the starting solution, as these become unstable to solvation before the smaller particles do. The precipitate is then collected by centrifugation, separated from the liquids, redissolved, and precipitated again. This iterative process separates larger from smaller NQDs and can generate the desired size dispersion of ≤5%.
Biomanufacture
Published in John M. Centanni, Michael J. Roy, Biotechnology Operations, 2016
John M. Centanni, Michael J. Roy
Early in downstream processing, and often at other stages in biomanufacture, the liquid fraction must be clarified, without significant loss of the desired protein, using combinations of precipitation, centrifugation, and filtration. Precipitation is a simple and inexpensive application; however, many methods for precipitation, such as changing the pH or adding simple salts, may either degrade the protein of interest or add contaminants to the product. Precipitation is based on the knowledge that a desirable protein or an undesirable impurity becomes insoluble under certain conditions such as low pH or high salt concentrations. Once a precipitate is formed, it is separated from the undesirable materials by centrifugation or filtration. Desirable molecules in the precipitate are recovered by diluting the precipitate with physiologic buffer. Undesirable proteins in the precipitate can then be discarded. An example of precipitation is purification of an immunoglobulin on addition of buffer with a high salt concentration. Immunoglobulin precipitates in this environment, leaving impurities in the supernatant. This is centrifuged, and the pellet is recovered and diluted with normal saline to again solubilize the immunoglobulin protein. Another example is the application of a polycationic agent, such as polyethyleneimine, which precipitates undesirable nucleic acids; however, the desired recombinant protein remains in the solution. After centrifugation, the pellet with impurities is discarded and the supernatant is retained or vice versa, depending on which fraction holds the desired product.
Wind action and arid regions
Published in F.G. Bell, Geological Hazards, 1999
The most commonly precipitated material is calcium carbonate. These caliche deposits are referred to as ‘calcrete’ (Braithwaite, 1983; Netterberg, 1980). Calcrete occurs where soil drainage is reduced due to long and frequent periods of deficient precipitation and high evapotranspiration. Nevertheless, the development of calcrete is inhibited beyond a certain aridity, since the low precipitation is unable to dissolve and drain calcium carbonate towards the water table. Consequently, in arid climates gypcrete may take the place of calcrete. Climatic fluctuations that, for example, took place in North Africa during Pleistocene times, therefore led to alternating calcification and gypsification of soils. Certain calcretes were partially gypsified and elsewhere gypsum formations were covered with calcrete hardpans (Horta, 1980). Similarly, the cemented sands, known as gatch, in Kuwait also owe their origin to past conditions. These occur at depth and bear little relationship to present-day groundwater levels, their cementation having occurred sometime in the past. They are probably being continually modified by dissolution and cementation (Al Sanad et al., 1990). Cementation provides a high proportion of the shear strength of many of these soils. However, only small amounts (around 2%) of such salts as calcite and gypsum are required to give this enhanced strength. In the case of cementation with halite, which is frequently on a seasonal basis, the strength of soils close to the surface may be increased by three to four times. Nonetheless, soaking and prolonged throughflow of fresh water can lead to a loss of soil strength. This can be brought about by over-irrigation or leaking drains.
Effects of precipitated size of water-soluble amide-containing polymers and pore size of filters on recovery of Pd nanoparticles dispersed in acetone solution including colloidal polymer
Published in Solvent Extraction and Ion Exchange, 2021
Wataru Kasaishi, Juzo Oyamada, Shintaro Morisada, Keisuke Ohto, Hidetaka Kawakita
Nitrile butadiene rubber (NBR) is catalyzed by Pd NP in acetone to control the mechanical strength.[7] Pd NP have been used to effect chemical changes in NBR.[8] The recovery of leaked Pd NP without changing the chemical properties of NBR is difficult. Kajiwara et al. proposed a novel method to recover Pd NP in NBR acetone solution[9,10:] 1) water-soluble polymer solution is dropped into Pd NP-containing NBR acetone solution; 2) the water-soluble polymer forms a complex with Pd NP during shrinking via dehydration; 3) the polymer precipitates with Pd NP; and 4) the precipitate is recovered by filtration. They have discussed the novel recovery method of Pd NP dispersed in viscous polymer solution by adding water-soluble polymer[9] and evaluated the mass-transfer coefficient in the presence of fluid flow in the reactor.[10] In this method, the size of the dispersed precipitate and the interaction of Pd NP with the water-soluble polymer influence the recovery efficiency of Pd NP.
Properties and potential application of efficient biosurfactant produced by Pseudomonas sp. KZ1 strain
Published in Journal of Environmental Science and Health, Part A, 2018
Agata Zdarta, Wojciech Smułek, Anna Trzcińska, Zefiryn Cybulski, Ewa Kaczorek
Cell growth and the accumulation of the metabolite products were strongly influenced by medium composition and type of carbon source. For the optimization of culture conditions, the studies were performed using three different media: Wei, Siśkinea-Trocenko[17] and mineral salt medium (MSM)[18] and two carbon sources (glucose or glycerol) at different concentrations (1%–4%). The conditions were optimized to ensure the highest yield of biosurfactant production. The process of biosurfactant production was carried out in a bioreactor (working volume 1.5 L). To 1.5 L of Wei medium, 2% of glucose and 50 mL of bacterial suspension were added. The pH value was set at 7. The experiment was conducted for 21 days at 25°C. After bioreactor batch culture termination (Fig. 1), the biomass was centrifuged. The supernatant was acidified with hydrochloric acid to pH of 2 and left at 4°C for 24 h. Thereafter, the precipitate was separated by centrifugation. The obtained supernatant was suspended in 0.05 M sodium bicarbonate and centrifuged again. The substance obtained after centrifugation was dissolved in ethyl acetate and left at 4°C for 24 h. After that, the solution was filtrated and the solvent was removed in a rotary evaporator to gain crude extract. Biosurfactant crude extract samples were placed in a freezer overnight and freeze dried on the next day. The samples were lyophilized on a freeze dryer.
Decontamination of corrosion oxides in the heat transport system of a pressurized heavy water reactor using chelate-free inorganic acid
Published in Journal of Nuclear Science and Technology, 2022
Naon Chang, Heechul Eun, Seonbyeong Kim, Bumkyung Seo, Yongsoo Kim
In order to reduce the purified solution to the initial condition of process solution, the chemical compositions, consumed during decontamination or removed during precipitation and filtration, are necessary to be re-injected. Therefore, the make-up test of the chemical composition was carried out. The amounts of chemical compositions injected were calculated by comparing the compositions in the purified solution with that in the initial process solution as indicated in Tables 1 and 2. The results of the calculation are shown in Table 3. The purified solutions in which the Fe(OH)2 particles were completely removed were used in this step (R = 0.55 − 0.70). Table 3 shows the injected amount of decontamination reagents for reducing the purified process solution to the initial condition of process solution. 600 ppm of N2H4, which was consumed during dissolving the 350 ppm of Fe2+ ions in the Fe3O4, is needed to be injected into the purified process solution. The injection amounts of H2SO4 were in proportion to the R. Additionally, 31.8 ppm of Cu2+, which was removed during the precipitation, should be injected into the purified process solution. After the make-up test, the pH range of the reduced solution was 2.68 to 2.76. These pH values of the reduced solution were similar to those of the initial condition of process solution, 2.75. Based on this result, it was verified that the spent process solution was perfectly reduced to the initial condition when the R ranged from 0.55 to 0.70. When the spent process solution is recycled, the lowest possible amount of Ba(OH)2 needs to be injected considering the amount of radioactive waste generation. For this reason, the R was determined to be 0.6 for the effective removal of Fe2+ ions and the reduction of radioactive waste. Based on these results, the recycling process of the spent process solution for decontamination of the carbon steel HTS in the PHWR was designed, and it is shown in Figure 4. The recycling process is performed after finishing the decontamination step. The recycling process is composed with the precipitation, filtration, and make-up steps. When the decontamination performance of the process solution reached to limitation, Ba(OH)2 is injected into the spent process solution in proportion to the concentration of SO4− ions to convert the Fe2+ ions into Fe(OH)2 in the precipitation step. In the filtration step, the precipitates are removed from the solution using filter. In the make-up step, the consumed composition and removed compositions are re-injected into the purified solution for reducing the spent process solution to the initial condition of process solution.