Nanotechnologies / Materials
Catalyst, Water purification, etc.

Synthesis and function of nanosheets dopedwith multi-elements in equal molarity
Joining and Welding Research Institute

Hiroya Abe					Specially Appointed Researcher Fei LiProfessor

https://researchmap.jp/read0101989?lang=en

Nanotechnologies / Materials

Abstract
Water pollution by dyes is one of the biggest environmental problems. Adsorption technology has been widely used in wastewater
treatment. Here, high-entropy concept is used to design surface
defective hydroxides realizing the rapid removal of dyes from water.
Multi-element hydroxides containing five, i.e., Mn, Fe, Co, Ni, andZn, transition metal cations are successfully synthesized through abottom-up polyol process( Fig.1). Along with the increase in compositional complexity, the thickness of the nanosheets in the hydroxides decreases, while the degree of surface defects increases.
These surface defects are proved to be the active sites for anionicdyes adsorption. These multi-element hydroxide nanosheets arealso promising electrocatalysts for oxygen evolution reaction.

Fig.1 multi-element hydroxides nanosheet▍ Background & Results
High-entropy alloys describe a class of single-phase solid solution
containing five or more elements in relatively high concentrations(5-35 at.%). This high-entropy concept expands to the whole materials field since 2015. The concept of high-entropy design opens
a door to develop novel materials with vast compositional space.
The multi-element feature of high-entropy materials leads to several
advantages, which are the so-called four core effects, namely thehigh-entropy effect in thermodynamics, the lattice distortion effectin crystallography, the sluggish diffusion effect in kinetics, and the“cocktail” effect in material performance. The key issue in synthesizing high-entropy materials is how to mix homogeneously the multipleelements. High-energy ball milling followed by high-temperature
heat treatment are commonly used approaches. However, it is very
difficult to control the formation of low-dimensional nanomaterials,
such as two-dimensional (2D) high-entropy materials.
Here, we report a simple polyol process for the synthesis of 2D
layered multi-element (Mn, Fe, Co, Ni, Zn) hydroxides (MEHs),
involving the hydrolysis and inorganic polymerization of metal-containing species in ethylene glycol. Hydrolysis and reduction ofmetal cations are two competitive reactions in our polyol process.
By optimizing the synthesis conditions, the MEHs nanosheets canbe successfully obtained after solvothermal treatment at ~200 °C(Fig.2). The surface of these MEHs nanosheets are highly defective. These MEHs nanosheets can adsorb anionic dyes (e.g., Congo red) from wastewater, possessing adsorption kinetics that are
two orders of magnitude higher than that of commercial activatedcarbon(Fig.3). These defects can also be active sites for catalyzing
oxygen evolution reactions, giving an overpotential of 298 mV at acurrent density of 10 mA cm-2 in 1.0 M KOH electrolyte.

▍ Significance of the research and Future perspective

Fig.2 elemental maps of multi-element hydroxides nanosheet

Fig.3 Anionic dye removal functionality of multi-element hydroxide nanosheets

The combination of unique surface features of 2D nanomaterials
and advantages of high-entropy materials brings great possibilities
to discover novel multifunctional materials. Our observations revealthat utilizing configurational entropy to modulate the electronicstructures and defects would be an effective approach to obtain
novel materials with charming applications.
P a t e n t
Tr e a t i s e

Li, Fei; Maruyama, Jun; Abe, Hiroya et al. Bottom-up synthesis of 2D layered high-entropy transition metal hydroxides. Nanoscale Advances. 2022, 4,2468-2489. doi: 10.1039/d1na00871d
Li, Fei; Maruyama, Jun; Abe, Hiroya et al. Defective multi-element hydroxides nanosheets for rapid removal of anionic organic dyes from water and oxygen
evolution reaction. J. Hazard. Mater. 2023, 447, 130803. doi: 10.1016/j.jhazmat.2023.130803

URL
K e y w o r d multi-element, compound, environment