Two-step diffusion in cellular hygroscopic (vascular plant-like) materials.

Vascular plants, a vast group including conifers, flowering plants, etc., are made of a cellular hygroscopic structure containing water in the form of either free (i.e., in a standard liquid state) or bound (i.e., absorbed in the cell walls) water. From nuclear magnetic resonance techniques, we distinguish the dynamics of bound water and free water in a typical material (softwood) with such a structure, under convective drying. We show that water extraction relies on two mechanisms of diffusion in two contiguous regions of the sample, in which respectively the material still contains free water or only contains bound water. However, in any case, the transport is ensured by bound water. This makes it possible to prolong free water storage despite dry external conditions and shows that it is possible to extract free water in depth (or from large heights) without continuity of the free water network.

Analysis of water content in wood material through 1D and 2D 1 H NMR relaxometry: Application to the determination of the dry mass of wood.

There is an increasing interest on wood as it is an environmentally sustainable product (e.g., biodegradable and renewable). Thus, an accurate characterisation of wood properties is of extreme importance as they define the kind of application for which each type of wood can be used. For instance, dry mass of wood is a key parameter itself and is needed to calculate Moisture Content (MC) of wood, which is correlated to its physical properties. Due to the limitations of commonly used drying methods, preliminary work has shown the potential of 1 H NMR to measure dry mass of wood, but it has never been validated. Here, we performed a critical analysis of 1D and 2D 1 H NMR relaxometry methods for obtaining the dry mass of wood, and we compared their performance to three commonly used drying methods. This showed that commonly used drying methods do not remove all water from wood. Moreover, we are able to classify them accordingly to their performance. In addition, we showed that MC values obtained by 1 H NMR relaxometry methods are higher (up to 20%) than values from commonly used drying methods. This empathises the importance of accurate values of dry mass of wood and the utility of 1 H NMR relaxometry on wood sciences. When comparing both NMR relaxometry methods, 2D should provide the more accurate results, but 1D measurements would also be a recommended choice as they are faster than 2D and their results clearly overcome commonly used drying methods in a noninvasive and nondestructive manner.

Improving the sustainability of granular iron/pumice systems for water treatment.

Metallic iron (Fe(0)) is currently used in subsurface and above-ground water filtration systems on a pragmatic basis. Recent theoretical studies have indicated that, to be sustainable, such systems should not contain more than 60% Fe(0) (vol/vol). The prediction was already validated in a Fe(0)/sand system using methylene blue as an operational tracer. The present work is the first attempt to experimentally verify the new concept using pumice particles. A well-characterized pumice sample is used as operational supporting material and is mixed with 200 g of a granular Fe(0), in volumetric proportions, varying from 0 to 100%. The resulting column systems are characterized (i) by the time dependent evolution of their hydraulic conductivity and (ii) for their efficiency for the removal of Cu(II), Ni(II), and Zn(II) from a three-contaminants-solution (about 0.3 mM of each metal). Test results showed a clear sustainability of the long term hydraulic conductivity with decreasing Fe(0)/pumice ratio. In fact, the pure Fe(0) system clogged after 17 days, while the 25% Fe(0) system could operate for 36 days. The experimental data confirmed the view that well-designed Fe(0) PRBs may be successful at removing both reducible and non-reducible metal species.

Nanoscale Metallic Iron for Environmental Remediation: Prospects and Limitations.

The amendment of the subsurface with nanoscale metallic iron particles (nano-Fe(0)) has been discussed in the literature as an efficient in situ technology for groundwater remediation. However, the introduction of this technology was controversial and its efficiency has never been univocally established. This unsatisfying situation has motivated this communication whose objective was a comprehensive discussion of the intrinsic reactivity of nano-Fe(0) based on the contemporary knowledge on the mechanism of contaminant removal by Fe(0) and a mathematical model. It is showed that due to limitations of the mass transfer of nano-Fe(0) to contaminants, available concepts cannot explain the success of nano-Fe(0) injection for in situ groundwater remediation. It is recommended to test the possibility of introducing nano-Fe(0) to initiate the formation of roll-fronts which propagation would induce the reductive transformation of both dissolved and adsorbed contaminants. Within a roll-front, Fe(II) from nano-Fe(0) is the reducing agent for contaminants. Fe(II) is recycled by biotic or abiotic Fe(III) reduction. While the roll-front concept could explain the success of already implemented reaction zones, more research is needed for a science-based recommendation of nano-Fe(0) for subsurface treatment by roll-fronts.

An MRI-SPI and NMR relaxation study of drying-hydration coupling effect on microstructure of cement-based materials at early age.

Hydration and drying coupling effect monitoring with single point imaging profiles allowed us to evaluate "free" pore and "bounded" chemical water quantity. White cement pastes inverse Laplace analysis of T1 measurements shown original results with two components during setting. After hardening, we found three components. Single point imaging measures were also used to study the evolution of transition zone in repaired concrete. MRI results demonstrated its interest compared with destructive method for longitudinal study and phenomena kinetic monitoring.