24 Interaction of Co(II) and Co(III) Complexes on Synthetic Birnessite: Surface Characterization John G. Dillard and Catherine V. Schenck
Downloaded by UNIV OF ARIZONA on December 20, 2012 | http://pubs.acs.org Publication Date: November 13, 1987 | doi: 10.1021/bk-1987-0323.ch024
Department of Chemistry, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061 2+
The interaction of Co(HO) and Co(III) complexes;Co(NH ) Co(en) ,(en= NHCHCHNH)withsynthetic birnessite has been studied as a function of pH. The chemical nature of the birnessite sample surface was characterized using X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS). Sorption of Co(HO) on birnessite in the pH range 4-7 2
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2
2
2
6
3+
3
2
2+
2
6
results in the oxidation of Co(II) to Co(III) as shown by XPS results. Interaction of the Co(III) complexes with the birnessite surface occurs by loss of coordinated ligand, yielding Co(II) and Co(III) species from Co(NH ) , while Co(III) is the dominant cobalt state following the reaction of Co(en) with birnessite. 3+
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6
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3
The i n t e r a c t i o n and sorption of metal ions with metal oxide and clay surfaces has occupied the attention of chemists, s o i l s c i e n t i s t s , and geochemists for decades ( 1 - 4 ) . T r a n s i t i o n metal oxides receiving particular emphasis have included various oxides of manganese and iron (5). Interest i n sorption phenomena i s promoted by the desire to better understand incorporation of metals into minerals, especially marine deposits (5), the removal of trace metal pollutants and radionuclides from r i v e r s and streams, v i a sorption and/or p r e c i p i t a t i o n phenomena (1,6), and the deposition of metals on s o l i d substrates i n the preparation of catalysts (7,8). An important and s i g n i f i c a n t task i n sorption studies i s the e f f o r t to i d e n t i f y the chemical form(s) of the sorbed metal ion. 0097-6156/86/0323-0503S06.00/0 © 1986 American Chemical Society
In Geochemical Processes at Mineral Surfaces; Davis, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
504
G E O C H E M I C A L PROCESSES AT M I N E R A L SURFACES
Among the
the
questions
metal
present
conditions
of
was
present, to
what
importance
that
(13).
published
(14,15).
formed
that
of
with
that
at
of
at
the
of
a
of
similar
it
was
the
about
reasoned oxide
studied
result
by
that
attributed
of
of
cobalt that
studied
cobalt(II)
surface
and of
thermodynamic In
the
(19).
was
the
for
study
birnessite
following
of
cobalt(II)
and
pH
has
spectroscopic
techniques,
and
i o n mass
secondary
contribution
that
such
information
obtained
metal
and
within
oxide about
the
surface
of
two
X-ray
an
metal
50 Â
of
the
all
methyl
dioxide
of
the of
indicated
anoxic
the
birnessite
illustrate the
rates
of as
the
state
the
or
importance.
birnessite
aqueous
complexes
In
birnessite
under
with
a
and
solutions
function
of
sensitive
(SIMS). can
chemical
material
the
was
geochemical
oxide/metal the
of
in
methyl
was
results
chemistry
investigation
the
been
form
nature
on
surface
on
has
oxidation
photoelectron
spectrometry
regarding
the
top
amine
using
the
of
yield
Fe(III)
ions
on
studies
interaction
cobalt(III)
investigated
ions
influencing
reactions
the the
These
to
dioxide
yield
Co(II)
present
the The
intermediates.
cobalt(III)
in
on
on manganese
and
by
(17).
process
these
tin
it by
thermodynamically,
Sn(IV)
analysis
was
surfaces
of
been
to
found
importance the
the
sheets.
Mn(II)
the
of
In (16),
sites.
manganese
surface
Surface
Mn(III)
stability
present
of
the
was
to
and
methyl
solution on
active
tin(IV)
Sn(II)
reaction.
mineral
of
diminished
oxidized
surface
following
importance
in
chemistry
pH
controlled
oxidized
of
Sn(II)
of
of
presumably
favored
role
adsorption
dissolved
surface
were
the
not
is
state
(hausmanite)
processes
was
oxide
reduced
particular
of
solid
0 ^
3
function
rate
production
formation
n
experiments.
surface
was
that
M
been
MnO^ o c t a h e d r a l
methyl
Of
adsorption
oxygen
conditions
found
the
of
the
kinetics
and
decreased
investigation
role
tin(II)
the
a
slower
The
The
prevented
manganese
the
slow.
initial
the
of
have
oxidation
of
on
concentrating
strategic
was
oxidation
in a
As(III)
manganese d i o x i d e to
of
oxidation
that
was
from
processes
the
as
Mn(IV)
transfer.
3
of
compound
of
in
and
Mn(II)
manganese(IV)
an
too
It CH
species.
which an
(17)
are
(18).
ions
tin
such
is
complex?
part
variety role
further
at
the
conditions
methylation
tin
with
19% o f
Although
Fe(III)
that
FeOOH p r e c i p i t a t e
As(III)
Under
or
vacancies
formation with
sorbed in
conditions
of
rate
pH>4 p r o c e e d e d
reaction
a
formation of
birnessite
at
oxide.
the
conditions
Reactions
As(V)
the
economic
noted
pH
