Research Group for Sustainable Functional Materials ScienceGroup Leader : ICHITSUBO Tetsu
Members : TANAKA Kazuya, SHIMOYAMA Iwao, AOYAGI Noboru, OKAMURA Hiroyuki,SUZUKI Kazuya, OKAYASU Satoru, Mei HUIYANG, Ibrahim MAAMOUN

Research Group for Sustainable Functional Materials Science
started up from FY2022. This group was launched to conduct
basic and applied research to aim at creating materials thatcombine high resistance (or resistivity) to harsh and/or extreme
conditions (such as irradiation, heat, and corrosion) and specificfunctions (such as magnetism, optical-, mechanical-, andelectrochemical properties). Also, this group covers
fundamental researches on water treatment for removal ofradionuclides and toxic elements.
Prolonging Reactivity of Iron Nanoparticles for Cr(VI)Removal from Aqueous Solutions via Magnesium Hydroxide
Coating
Chromium (Cr) is one of the highly toxic heavy metals withthe potential to cause severe effects on human health, throughexposure to elevated concentrations in aqueous environments. In
this regard, zero-valent iron nanoparticles (nFe0) can reduce
Cr(VI) to Cr(III) and integrate adsorption and/or coprecipitation in Cr(VI)/Cr(III) immobilization. Nevertheless,nFe0 nanoparticles suffer from some drawbacks, such as particle
aggregation, poor mobility, and rapid core consumption,affecting their reactive performance [1]. Hence, in this work, a
non-magnetic magnesium hydroxide (Mg(OH)2) coating wasused to prolong the reactivity of nFe0 nanoparticles towards
Cr(VI) removal from contaminated water. The short- and longterm progressive release of nFe0@Mg(OH)2 reactivity wasevaluated through several batch tests. As shown in Fig. 1, theresults revealed a multifunctional effect of Mg(OH)2 coating inprotecting nFe0-core from rapid consumption (moderately
soluble coating resulted in the progressive release of electrons)
and Cr(VI) removal added-value (involvement of the coatingshell in Cr(VI) adsorption and Cr(III) co-precipitation) [1].
Additionally, nFe0@Mg(OH)2 showed good performance inpreserving nFe0 long-term reactivity within a wide range of pH(3.0 – 9.0) and temperature (15 – 55 oC). The long-term
investigation exhibited 100% removal efficiency of 40 mg/L
initial Cr(VI) concentration, progressively achieved over 50days reaction time (prolonged reactivity of 1.0 g/L material dose
without desorption). Furthermore, nFe0@Mg(OH)2 showed highregeneration abilities (> 5 cycles) with 1.36 times the averageenhancement in Cr(VI) removal efficiency compared to that ofnFe0. In conclusion, Mg(OH)2 showed promising performancein preserving the reactivity of nFe0-core, confirming the highpotential of nFe0@Mg(OH)2 as a nanomaterial candidate forgroundwater treatment applications.
The Effect of Reaction Conditions on As(V) Sorption ontonFe0@Mg(OH)2For several decades, arsenic (As) contamination in water has
been considered an issue of great concern. In this study, theeffect of different reaction conditions (e.g., Mg/Fe coating ratio,material dose, initial pH, etc.) on As(V) removal bynFe0@Mg(OH)2 was investigated. The results indicated thesuperiority of the highest Mg/Fe coating ratio (100%) over theother lower ratios (25, and 50%) in As(V) removal,
corresponding to the adsorption contribution of Mg(OH)2

coating shell. Furthermore, low pH conditions were favorablefor As(V) removal by nFe0@Mg(OH)2, owing to the induced
dissolution of Mg(OH)2 coating shell, exposing nFe0-core toaqueous corrosion [2]. As K-edge X-ray absorption near edge
structure (XANES) spectra of the reacted samples confirmed
As(V) adsorption and the absence of As(III), implying thecomparable role of As(V) sorption to the reduction of As(V) toAs(III) (involvement of electrostatic sorption, and As(V) uptake
by the formed FeOOH) [2]. Moreover, nFe0@Mg(OH)2-100%
showed high preservation ability towards air oxidation, showing
just 19% decrease in removal efficiency after 1.0 day shelf-time,compared with that of the freshly synthesized material storage.
However, the observed visual deformation in the total size of thematerial as well as the material hardness, affected the dispersionof the material in the reaction solution, thus influencing As(V)removal (especially at the early stages of the reaction).

Fig. 1 Multifunctional magnesium hydroxide coating for ironnanoparticles towards prolonged reactivity in Cr(VI) removalfrom aqueous solutions.

References[1] I. Maamoun et al., J. Env. Chem. Eng. 10, 107431 (2022).
[2] I. Maamoun et al., Adv. Mater. Lett. 14(2), 23021721 (2023).