October 21, 2022
Release Subtitle:
Researchers demonstrate that the process of anion nanoconfinement is enhanced by an acidic adsorption layer in carbon nanotubes
Release Summary Text:
Carbon materials separate anion impurities and purify water but the
underlying mechanism remains unknown. Recently, researchers from Okayama
University, Japan investigated the anion adsorption mechanism in
single-walled carbon nanotubes (SWCNT). They found that an acidic
adsorbed layer is formed in the SWCNT pore even when the aqueous
environment has a neutral pH. The layer in the pore adsorbs nitrate
anions due to strong confinement by the pore and strong interaction
between the layer and anion.
Full text of release:
Efficient purification processes that separate impurities from air and
water are necessary to sustain life on earth. To this end, carbon
materials have long been used for deodorizing, separating, and removing
harmful anion impurities by adsorption. So far, the detailed mechanism
by which carbon purifies water has remained a mystery. Additionally, it
is not known if the aqueous solution adsorbed on the carbon material is
acidic, alkaline, or neutral. To address these gaps, researchers led by
Dr. Takahiro Ohkubo, Associate Professor in the Department of Chemistry,
Faculty of Natural Science and Technology, Okayama University, Japan
investigated the fundamental mechanism by which anions are adsorbed by
carbon nanopores.
In a recent article made available online on 16 September 2022 and published in volume 629 Part B of the Journal of Colloid and Interface Science,
the researchers report employing Raman spectroscopic tools to examine
the adsorption of nitrate ions by the cylindrical pore of single-walled
carbon nanotubes (SWCNT). Dr. Ohkubo and his colleagues succeeded in
deciphering the mechanism of acidic layer formation near the pore walls.
It turns out that, when an aqueous solution containing ions penetrates
the carbon material, even if the aqueous solution is neutral, an acidic
aqueous layer containing protons is formed that maintains a stable
state. Commenting on the novelty and fundamental nature of their work,
Dr. Ohkubo states, “To date, there have
been no reports demonstrating the existence of acidic adsorption layers
formed within nanotubes of carbon materials.”
The research team, which also included Dr. Nobuyuki Takeyasu, Associate
Professor in the same faculty in Okayama University, found that the
acidic layer facilitates efficient adsorption of the negatively charged
nitrate anion impurities, where the adsorbed amount of nitrate ions is
much larger than that of the cations, or the positively charged groups.
In addition, hydroxide ions are generated as counter-ions. The anions
present in the bulk solution are exchanged with the hydroxide ions in
the SWCNT, making the aqueous solution alkaline. The team examined anion
adsorption using several alkali metal nitrates including lithium
nitrate, sodium nitrate, rubidium nitrate, and cesium nitrate solutions.
They found that more nitrate ions are adsorbed than metal ions. The
amount of proton adsorption was almost the same regardless of the type
of alkali metal ion used. Dr. Ohkubo observes, “The
acidic layer in the pore can strongly adsorb the nitrate anion species
because of both strong confinement by the pore and the strong
interaction between the layer and the anion.”
The findings are indeed important steps towards designing and developing
carbon nanotubes suitable for ion adsorption and purification of water
and air. The mechanism of purification set forth in this research is a
novel model that explains the alkalinity of the aqueous solution medium,
which has hitherto been a mystery. The researchers observe that the
findings of their study strongly point to the need of neutralizing water
before use when ionic impurities are trapped by carbon materials.
Another remarkable contribution of this study is the demonstration that
the nanomaterial interface is a novel chemical reaction field, which
could guide further experiments. Taken together, this work takes our
understanding of the mechanism of anion adsorption by carbon to the next
level, making way for novel carbon nanotubes as efficient purifiers.
Release URL:
https://www.eurekalert.org/news-releases/968455
Reference:
Acidic layer-enhanced nanoconfinement of anions in cylindrical pore of single-walled carbon nanotube
Journal: Journal of Colloid and Interface Science
DOI:10.1016/j.jcis.2022.09.070
Contact Person:Takahiro Ohkubo
Dr. Takahiro Ohkubo is an Associate Professor in the Department of
Chemistry, Graduate School of Natural Science and Technology, Okayama
University. He is involved in active research on topics including
structure and property of nano-confined systems, nanostructures
(clusters and small particles), porous materials, surface science, and
carbon-based materials. Dr. Ohkubo has won several awards in his
academic career including ‘Best contribution award in education, Faculty
of Science, Okayama University’ (2017) and ‘Young researcher award 2012
from Colloid and Interface Chemistry Division of Chemical Society of
Japan (2012)’. He has authored over 100 articles that have contributed
significantly to his research field.
https://www.okayama-u.ac.jp/eng/research_highlights/index_id173.html
0 件のコメント:
コメントを投稿