|Product ageing (nZVI degradation)|
In respect to research and testing of our product, we would like to inform you that NANOFER 25 is extremly reactive dispersion of iron nanoparticles (NPs), which - if in contact with oxygen (contained in water and air) - intensively oxidizes. Fe(0), which is capable to reduce pollutants in contaminated water so effectively, is transforming to non-reactive Fe3O4 (magnetite). For this reason it is necessary to process the material as soon as possible.
NANOFER 25S is stabilized by a surfactant though, but the main purpose of this surfactant consists in keeping the nanoparticles buoyant and decelerating NPs sedimentation, which consequently leads to optimum migration properties in the rock environment. Surfactant unfortunately does not completly prevent nZVI degradation.
Degradation of reactive nanoparticles of Fe0 is presented in following charts showing the degradation of products depending on time and storage conditions.
Degradation rate of product is affected by sample manipulating technique, which is demonstrated on following case (it is relevant to previous graphs - applies to NANOFER 25 and NANOFER 25S):
Sample No. 1: stored at room temperature (20-22°C), opened once a week for reason of slurry taking for measurement.
Sample No. 2: stored at cold premise (2-4°C), opened once a week for reason of slurry taking for measurement.
Sample No. 3: stored at cold premise (2-4°C), opened one month since manufacturing (the 6th measurement; note: sample was stored in small bottle with high overpressure of protecting atmosphere).
All measurements were made through the use of nZVI TESTER, which principle is based on measuring of developing hydrogen volume during the reaction of Fe(0) with acid. This "Hydrogen method" was compared to Mössbauer spectroscopy and X-ray powder diffraction [thanks to Prof. Radek Zbořil, Ph.D.; Regional Centre of Advanced Technologies and Materials (RCPTM)].
Highest quality of NANOFER dispersions is guaranteed 2 months since production date. The product is possible to use beyond 2 months since production date, however NANOFER concentration in your application should be increased as part of Fe(0) may oxidize to magnetite, which decreases the reactivity then. The following chart shows degradation of NANOFER 25S in 67 days period. It is evident that concentration of Fe(0) particles in slurry decreased by 12% in case of cooled sample of NANOFER 25S and by 63% in case of sample of NANOFER 25S stored at room teperature.
Following recommendations and conclusions result from the measurements:
Transformation of ZVI nanoparticles to magnetite is proceeding in presence of oxygen and water environment - hence the quality of product is decreasing. This process is strongly temperature dependent, so if you need to store the material, place it please into cold premises, at best at a temperature slightly above 0°C. Please do not freeze the slurry, otherwise an irrevocable agglomeration occurs. Please open the bottle containing NANOFER slurry just prior to the application and use it at once if possible, there is a reductive atmosphere in the bottle.
NANOFER is a highly efficient aid, designed for degradation of a wide spectrum of pollutants. The product efficiency is achieved just due to its extreme reactivity that, at the same time, has negative impact on its aging. NANO IRON company is ready to supply the fresh made slurries in the “just in time” manner to any place in the world via world wide express shipping. The highest product quality is guaranteed just by using the product within the shortest possible time since it has been manufactured.
In case of large volume industrial application it is recommended an on-site manufacturing of fresh slurry from dry nanopowder and subsequent immediate application of the fresh product (like in-situ groundwater remediation etc.). Slurries are produced from dry nanopowder by dispersing units made by NANO IRON company; nanopowder does not degrade during the storage (it does not contain any water nor oxygen).