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Interfaces: Adsorption, Reactions, Films, Forces, Measurement Techniques, Charge Transfer, Electrochemistry, Electrocatalysis, Energy Production and Storage
Fast capture of fluoride by anion-exchange zirconium-graphene hybrid adsorbent Jing Zhang, Yueqi Kong, Yang Yang, Nan Chen, Chuanping Feng, Xiaodan Huang, and Chengzhong Yu Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.9b00589 • Publication Date (Web): 05 May 2019 Downloaded from http://pubs.acs.org on May 13, 2019
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Langmuir
Fast capture of fluoride by anion-exchange zirconium-graphene hybrid adsorbent Jing Zhang†,‡, Yueqi Kong‡, Yang Yang‡, Nan Chen†, Chuanping Feng†, and Xiaodan Huang‡*, Chengzhong Yu‡* †. School of Water Resources and Environment, China University of Geosciences (Beijing), Beijing 100083, China ‡. Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, Brisbane QLD 4072, Australia
ABSTRACT Fluoride contamination is a severe problem affecting the drinking water safety around the world. High-rate adsorbent materials
are
particularly
desirable
for
potable
water
defluoridation. Current research on fluoride adsorbent materials is
primarily
capacities.
focused
But
they
on
metal-based
generally
suffer
adsorbents from
slow
with
high
adsorption
kinetics due to the adsorption mechanism of sluggish exchange between coordinated hydroxyl groups and fluoride ions. Designing metal-based adsorbents to mimic the rapid ion exchange behavior of anion-exchange resins is a promising approach to integrate fast adsorption and high capacity for fluoride removal. Herein,
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a
ZrO(OH)1.33Cl0.66-rGO
chloride
ions
was
hybrid
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adsorbent
synthesized
with
containing the
exchangeable
assist
of
cation-π
interaction. Unlike most adsorbents requiring high surface area, this composite has a negligible surface area (1.45 m2 g-1), but can
deliver
a
fast
fluoride
capture
performance
(reaching
equilibrium in 5 mins) with high adsorption rate constants of 1.05 min-1 and 0.171 mg·g-1·min-1, around 10 times faster than the best result reported in literature. Besides, ZrO(OH)1.33Cl0.66-rGO can also demonstrate a high fluoride uptake (44.14 mg g-1) and high removal efficiency (94.4 %) in 35 mg L-1 fluoride solution, both among the highest performances for fluoride adsorption.
Introduction Fluoride
contamination
in
groundwater
is
one
of
the
most
serious environmental issues on the worldwide basis.1 Consumption of water containing excess fluoride can cause adverse health effects, such as fluorosis and metabolism disorders.1,2 The World Health Organization recommends a maximum fluoride concentration in drinking water of 1.5 mg L-1.3 Adsorption technology has been extensively
investigated
contaminated
water,
cost.4-6
Metal-based
hydroxides11
and
for
because
of
adsorbents
metal-organic
the its
treatment high
including frameworks
of
fluoride
efficiency metal (MOFs)12
and
low
oxides,7-10 have
been
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Langmuir
developed for water defluoridation due to their high binding affinities towards fluoride. It
has
been
recognized
that
the
mechanism
of
metal-based
fluoride adsorbents is the exchange between fluoride ions and surface hydroxyl groups of the adsorbents.9-12 The hydroxyl groups either
exist
on
metal
hydroxides
surface
or
can
be
formed
through the hydroxylation of metal oxides and MOFs in aqueous environments.13 centres,
They
resulting
consequently
oxide
materials
for
usually
in
retarded
zirconium
fluoride
are
stably
sluggish
dissociation
(ZrO2)
is
water
defluoridation.9,10,16-19
adsorbents
such
as
of
the
most
ZrO2-carbon
to
metal
processes
kinetics13-15.
adsorption one
coordinated
and
For
example,
widely
studied
Zirconium-based composite,9
ZrO2
mesoporous fibers10 and Fe-Zr/Fe-Ca-Zr hybrid oxides17 have been recently
developed
and
delivered
high
adsorption
capacities
(e.g. ZrO2 mesoporous fibers: 297.7 mg g-1 at 300 mg L-1 fluoride solution10). However, they usually required around 50 to 100 mins to
reach
the
equilibrium
adsorption,
owing
to
the
sluggish
fluoride to hydroxyl group exchange mechanism.9,10,16-18 Zhang et al.
recently
composite
reported
adsorbent
with
a a
zirconium-chitosan/graphene combined
adsorption
oxide
mechanism
of
fluoride to hydroxyl exchange and a minor fluoride to chloride ion
exchange
to
accelerate
the
adsorption
process,19
but
it
remains suffering from its intrinsic slow adsorption kinetics
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(45
mins
become
equilibrium a
major
time).
The
impediment
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slow to
adsorption develop
process
has
high-throughput
defluoridation systems for either centralized water treatments or point-of-use water filtrations. Other
high
capacity
fluoride
adsorbents,
such
alumina,20
as
layered double hydroxides11,21 and MOFs,12,18 also have the slow adsorption
problem,
due
to
the
same
hydroxyl
group
exchange
mechanism. This problem would grow worse when coping with the real contaminated waters, because the low-concentration fluoride pollutants in them (
