Agnès Grandjean

Extraction of radioactive cesium using innovative functionalized porous materials

A new approach to an efficient and selective extraction of Cs+ ions from water, sea water enriched with Cs+ and a radioactive solution simulating the effluents of the Fukushima reactors (137Cs, 29 kBq L−1) was developed by using porous silica- or glass-based nanocomposites containing Prussian blue type nanoparticles, Co2+/[Fe(CN)6]3−, with sizes below 10 nm. A particular emphasis is given on the kinetics of cesium sorption fitted by using the classical reaction order model as well as a diffusion model in order to better understand the sorption mechanism. Compared to the amount of Co2+/[Fe(CN)6]3− nanoparticles, the sorption capacities of studied nanocomposites are more than three times higher than the ones observed for the respective bulk materials. These nanocomposites present a high selectivity to Cs+ and extract it in trace amounts.

Mesoporous materials in the field of nuclear industry: applications and perspectives

In the context of increasing global energy demand associated with high prices for classical fossil fuels and rising concerns about CO2 emissions, nuclear power is attracting renewed interest. Despite the recent accident in the Fukushima power plant, numerous countries maintain very ambitious nuclear programmes. The Generation IV International Forum [A Technology Roadmap for Generation IV Nuclear Energy Systems, Generation IV International Forum, 2002] (an initiative launched by the US Department of Energy in 2000 to coordinate and promote efforts to design the next generation of nuclear power plants) supports works to develop new power plant designs and innovative concepts in the nuclear fuel cycle. These new concepts aim at achieving higher levels of security and resource efficiency as well as a higher resistance towards nuclear proliferation. Because of this blossoming of new ideas, mesoporous materials, which are already widely found in applications such as catalysis, sensing and optics, are expected to make their way in the field of nuclear power production. Up to now, some (hybrid) mesoporous solids have already been investigated as solid ligands to remove actinides and fission product contaminants from liquid effluents, but also as model materials to investigate radiation defects, as possible nuclear waste disposal form and as functional materials to be placed in or close to new forms of nuclear waste matrices. This contribution aims at reviewing the applications of mesoporous materials already described in the field of nuclear industry, and to underline some promising research directions in this area.

Stability of mesoporous silica under acidic conditions

The stability of various structured mesoporous materials (SBA-1, SBA-3, SBA-15, MCM-41, MCM-48) was tested under acidic stress in order to understand the mechanism of their alteration. The native materials and the materials resulting from acidic attack under various conditions were analysed by small angle X-ray scattering coupled with nitrogen adsorption and solid 29Si NMR. Among three acid media (HCl, H2SO4, H3PO4) at similar ionic strength, we focused particularly on phosphoric acid, which proved to have the strongest impact on the starting materials. The results are discussed by correlating the wall thickness and pore diameter values with regard to stability. In particular, the alteration kinetics were interpreted for the case of SBA-15 in the following scenario: the micropores were first damaged by the acidic stress, and then the mesopores were partially collapsed or partially blocked. We show that a materials resistance against acidic media is linked to a critical wall thickness–pore diameter threshold.

Facile one-pot synthesis of copper hexacyanoferrate nanoparticle functionalised silica monoliths for the selective entrapment of 137Cs

In this study, hexacyanoferrate nanoparticle (NP) functionalised silica monoliths were used to selectively remove Cs+ from aqueous solutions which also contained large concentrations of Na+. Various NP loading levels were examined from 0.2 wt% up to 5.1 wt% producing different 133Cs and 137Cs sorption results.

Iodine Capture by Hofmann-Type Clathrate NiII(pz)[NiII(CN)4]

The thermally stable Hofmann-type clathrate framework Ni(II)(pz)[Ni(II)(CN)4] (pz = pyrazine) was investigated for the efficient and reversible sorption of iodine (I2) in the gaseous phase and in solution with a maximum adsorption capacity of 1 mol of I2 per 1 mol of Ni(II)(pz)[Ni(II)(CN)4] in solution.

Electrical conductivity measurements of oxides from molten state to glassy state

This article describes an experimental setup designed to measure the electrical conductivity of molten and viscous oxides from 1200 to 400 °C. The “4-electrode” method was adapted to perform impedance measurements over wide temperature and frequency ranges. High-frequency electrode effects were calculated and eliminated. Low-frequency electrode polarization was avoided with the 4-electrode configuration. The ac impedance was measured at one immersion depth. Calibration and complex impedance analysis were necessary to obtain the electrical conductivity of the melt. The results of this technique for a borosilicate melt are presented and compared with those of high-temperature calibration-free solid-state measurements, and their accuracy is evaluated.

Incorporation of iodates into hydroxyapatites: a new approach for the confinement of radioactive iodine

A new strategy for the confinement of iodine has been developed: it consists in incorporating iodate anions (IO3−) into hydroxyapatite (Ca10(PO4)6(OH)2, HA). The iodate-substituted HA was synthesized by precipitation, and characterized in detail. Its thermal stability and resistance to leaching were then evaluated, revealing promising properties in view of radioactive iodine confinement applications.

From phosphate rocks to uranium raw materials: hybrid materials designed for selective separation of uranium from phosphoric acid

Innovative hybrid materials with high capacities to selectively extract uranium ions from phosphoric acid media were developed by grafting phosphorous-based ligands within the pores of mesoporous silica (SBA15) or mesoporous carbon (CMK3).

Surface Diels-Alder reactions as an effective method to synthesize functional carbon materials.

The post-synthesis chemical modification of various porous carbon materials with unsaturated organic compounds is reported. By this method, amine, alcohol, carboxylate, and sulfonic acid functional groups can be easily incorporated into the materials. Different carbonaceous materials with surface areas ranging from 240 to 1500 m(2)g(-1) and pore sizes between 3.0 and 7.0 nm have been studied. The resulting materials were analyzed by elemental analysis, nitrogen sorption, FTIR spectroscopy, zeta-potential measurements, thermogravimetric analysis, photoelectron spectroscopy, and small-angle X-ray scattering. These analyses indicated that the degree of functionalization is dependent on the nature of the dienophile (reactivity, steric hindrance) and the porosity of the carbon material. As possible applications, the functionalized carbonaceous materials were studied as catalysts in the Knoevenagel reaction and as adsorbents for Pb(2+) from aqueous solution.

Immobilization of iodine into a hydroxyapatite structure prepared by cementation

In order to manage radioactive iodine-129 coming from nuclear spent fuel, robust host matrices with durable long term behaviour need to be developed. In this work, a new process of synthesis of an iodate-substituted hydroxyapatite by means of a cementation route is described. This material was obtained from a mixture of tetracalcium phosphate (TTCP), tricalcium phosphate (αTCP) and sodium iodate (NaIO3), taken in a molar ratio of 1/2/0.5. The progress of the reaction leading to the setting and hardening of cement paste was monitored by combined measurements of electrical conductivity and heat flux release, together with XRD characterization of materials at definite times of hydration. Sodium iodate acts as a set retarder, by leading to the precipitation of non-cohesive transient phases, which are then destabilized when the massive precipitation of hydroxyapatite occurs. These delays can however be limited by adding hydroxyapatite seeds to the cement paste, which means that it is possible to control the setting time in view of an industrial application. This novel cementitious system leads to a porous material composed of iodine-substituted hydroxyapatite needles covering residual TTCP and αTCP particles. Iodine has entered the hydroxyapatite structure in the form of iodate anions only. An iodine incorporation rate of 6.5 wt% has been obtained by this cementitious system, which is a promising value in view of using these materials for the conditioning of radioactive iodine.