The preparation of subnanoporous covalent-organic-framework (COF) membranes with high performance for ion/molecule sieving still remains a great challenge. In addition to the difficulties in fabricating large-area COF membranes, the main reason is that the pore size of 2D COFs is much larger than that of most gas molecules and/or ions. It is urgently required to further narrow their pore sizes to meet different separation demands. Herein, we report a simple and scalable way to grow large-area, pliable, free-standing COF membranes via a onestep route at organic-organic interface. The pore sizes of the membranes can be adjusted from >1 nm to sub-nm scale by changing the stacking mode of COF layers from AA to AB stacking. The obtained AB stacking COF membrane composed of highly-ordered nanoflakes is demonstrated to have narrow aperture (∼0.6 nm), uniform pore distribution and shows good potential in organic solvent nanofiltration, water treatment and gas separation.
Aerosol radionuclides ( 131 I, 134 Cs, 137 Cs) and gaseous radioactive xenon ( 133 Xe) were monitored at Xi'an, China following the accident at the Fukushima nuclear power plant in March 2011. The additional annual effective dose attributable to the Fukushima emissions was much lower than the public annual effective dose from natural radiation, according to Chinese national standards. The monitoring results were compared with data from other countries as well as with the radionuclide concentrations observed in Xi'an after the Chernobyl nuclear accident in 1986. Possible transport pathways of the released radionuclides from Fukushima to Xi'an were investigated. The occurrence of an anticyclone in the Pacific Ocean region and the extended period over which the radionuclides were released made the determination transport pathways complex, but divergence in the plume and easterly flow evidently brought the initial suite of radionuclides to Xi'an.
Xe-128 in I-127 transmutation targets irradiated by Xi'an pulse reactor was analyzed by using Quadrupole Mass Spectrometer (QMS) to calculate transmutation rate and release rate. Transmutation is an alternative method to transform long-lived toxic radio nuclides to short-lived radio nuclides or stable nuclides. 127 I targets were irradiated in Xi'an Pulse Reactor for the first time to simulate the transmutation behavior of 129 I. After irradiation, 128 Xe in the target was determinate with online isotope dilution method by Quadrupole Mass Spectrometer (QMS), so that the transmutation rate and release rate could be calculated. Release behaviors of 128 Xe were investigated through melting and step-heated modes. The stepwise heating experiment was done by puncturing method. The result shows the release rate in melting mode is 99.9% (RSD ¼ 1%) and increases with the temperature in stepwise heating mode. The technique proposed in this work is suitable for accurate determination of transmutation rate of 129 I.
In this work, plutonium aerosol generated from a plutonium reprocessing facility is filtered by a six-stage High Efficiency Particulate Air (HEPA) filter system and analyzed in laboratory within a week. Through on-line monitoring of number concentration of particles above 10 nm by a commercial condensation particle counter and off-line monitoring of 239 Pu activity concentration by 242 Pu isotope dilution Inductively-Coupled Plasma Mass Spectrometry (ICP-MS), it is confirmed that the HEPA filter system works properly during the field operation. Direct determination of plutonium aerosol by two types of ICP-MS, Finnigan ELEMENT ICP-MS and Nu MC-ICP-MS, has been conducted. The results show that the detection limits of ELEMENT and Nu for plutonium concentration are 5.0 × 10 −3 Bq/m 3 and 5.5 × 10 −4 Bq/m 3 , respectively. Plutonium concentrations in the filtered gas samples are on the order of 2.0 × 10 −2 Bq/m 3 while the blank value is 5.7 × 10 −3 Bq/m 3. It's discovered that some plutonium nanoparticles have penetrated the six-stage HEPA filter system. This phenomenon is also observed in the repeated works of last two years. The size of the penetrated plutonium nanoparticles is investigated by ELEMENT in single particle mode. The preliminary results indicate that the penetrated plutonium nanoparticles are smaller than 10 nm and assume the form of 239 PuO 2 .
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.