Kx[Bi4- xMnxS6], Design of a Highly Selective Ion Exchange Material and Direct Gap 2D Semiconductor

Article abstract of DOI:10.1021/jacs.9b08674

Layered sulfides with high selectivity for binding heavy metal ions and radionuclide ions are promising materials in effluent treatment and water purification. Here we present a rationally designed layered sulfide K_x[Bi_4-xMn_xS₆] (x = 1.28) deriving from the Bi₂Se₃-structure type by targeted substitution to generate quintuple [Bi_4-xMn_xS₆]^x- layers and K⁺ cations between them. The material has dual functionality: it is an attractive semiconductor with a bandgap of 1.40 eV and also an environmental remediation ion-exchange material. The compound is paramagnetic, and optical adsorption spectroscopy and DFT electronic structure calculations reveal that it possesses a direct band gap and a work function of 5.26 eV. The K⁺ ions exchange readily with alkali or alkaline-earth ions (Rb⁺, Cs⁺, and Sr²⁺) or soft ions (Pb²⁺, Cd²⁺, Cr³⁺, and Zn²⁺). Furthermore, when the K⁺ ions are depleted the Mn²⁺ ions in the Bi₂Se₃-type slabs can also be replaced by soft ions, achieving large adsorption capacities. The ion exchange reactions of K_x[Bi_4-xMn_xS₆] can be used to create new materials of the type M_x[Bi_4-xMn_xS₆] in a low temperature kinetically controlled manner with significantly different electronic structures. The K_x[Bi_4-xMn_xS₆] (x = 1.28) exhibits efficient capture of Cd²⁺ and Pb²⁺ ions with high distribution coefficient, K_d (10⁷ mL/g), and exchange capacities of 221.2 and 342.4 mg/g, respectively. The material exhibits excellent capacities even in high concentration of competitive ions and over a broad pH range (2.5-11.0). The results highlight the promise of the K_x[Bi_4-xMn_xS₆] (x = 1.28) phase to serve not only as a highly selective adsorbent for industrial and nuclear wastewater but also as a magnetic 2D semiconductor for optoelectronic applications.

Full text of DOI:10.1021/jacs.9b08674

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Article
Kx[Bi4-xMnxS6], Design of a Highly Selective Ion
Exchange Material and Direct Gap 2D Semiconductor
Ruiqi Wang, Haijie Chen, Yi Xiao, Ido Hadar, Kejun Bu, Xian Zhang, Jie Pan,
Yuhao Gu, Zhongnan Guo, Fuqiang Huang, and Mercouri G. Kanatzidis
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.9b08674 • Publication Date (Web): 30 Sep 2019
Downloaded from pubs.acs.org on October 5, 2019
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Kx[Bi4-xMnxS6], Design of a Highly Selective Ion
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Exchange Material and Direct Gap 2D Semiconductor
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Ruiqi Wang,a Haijie Chen,b Yi Xiao,a Ido Hadar,b Kejun Bu,c Xian Zhang,d Jie Pan,c Yuhao Gu,a
Zhongnan Guo,b Fuqiang Huang,*,a,c Mercouri G. Kanatzidis*,b
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Beijing National Laboratory for Molecular Sciences and State Key Laboratory of Rare Earth
Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking
University, Beijing 100871, China
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b Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208,
United States
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CAS Key Laboratory of Materials for Energy Conversion and State Key Laboratory of
High-Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese
Academy of Sciences, Shanghai 200050, P. R. China
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Qian Xuesen Laboratory of Space Technology, China Academy of Space Technology, Beijing
100094, P. R. China
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ABSTRACT. Layered sulfides with high selectivity for binding heavy metal ions and radionuclide
ions are promising materials in effluent treatment and water purification. Here we present a
rationally designed layered sulfide Kx[Bi4-xMnxS6] (x = 1.28) deriving from the Bi2Se3-strucutre type
by targeted substitution to generate quintuple [Bi4-xMnxS6]x layers and K+ cations between them.
The material has dual functionality: it is an attractive semiconductor with a bandgap of 1.40 eV and
also an environmental remediation ion-exchange material. The compound is paramagnetic and
optical adsorption spectroscopy and DFT electronic structure calculations reveal that it possesses a
direct band gap and a work function of 5.26 eV. The K+ ions exchange readily with alkali or
alkaline-earth ions (Rb+, Cs+ and Sr2+) or soft ions (Pb2+, Cd2+, Cr3+ and Zn2+). Furthermore, when the
K+ ions are depleted the Mn2+ atoms in the Bi2Se3-type slabs can also be replaced by soft ions,
achieving large adsorption capacities. The ion exchange reactions of Kx[Bi4-xMnxS6] can be used to
create new materials of the type Mx[Bi4-xMnxS6] in a low temperature kinetically controlled manner
with significantly different electronic structures. The Kx[Bi4-xMnxS6] (x = 1.28) exhibits efficient
capture of Cd2+ and Pb2+ ions with high distribution coefficient, Kd (107 mL/g), and exchange
capacities of 221.2 and 342.4 mg/g, respectively. The material exhibits excellent capacities even in
high concentration of competitive ions and over a broad pH range (2.5-11.0). The results highlight
the promise of the Kx[Bi4-xMnxS6] (x = 1.28) phase to serve not only as a highly selective adsorbent
for industrial and nuclear wastewater but also as a magnetic 2D semiconductor for optoelectronic
applications.
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KEYWORDS: Water purification, work function, ion exchange, toxic metal removal, nuclear
remediation, spintronics, topological properties
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INTRODUCTION
Effluent treatment of industrial and nuclear wastes has been a major concern around the world.1-3
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Several heavy metal ions (Pb2+, Cd2+, Hg2+, etc.) and radionuclides (137Cs and Sr, etc.) are major
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pollutants in these effluents and threaten human health and the environment.4-5 Traditional
commonly used and inexpensive adsorbents are clays, zeolites and activated carbon.6-9 However,
because of their weak binding affinity towards these hazardous metal ions, they suffer from
relatively low selectivity and capacity, often cannot reduce the concentrations to desirable levels and
tend to perform poorly in acidic conditions or in solutions with high salt concentration.10-18
Recently, layered chalcogenides with ion-exchange properties have been demonstrated as
promising adsorbents in a wide pH range.19-35 The ability of the layered structure to expand along the
stacking axis contributes to the fast ion exchange kinetics. One example is the KMS series
compounds which are based on SnS2-type layers with mix-occupied Sn/M (M = Mn, Mg, In) sites
and K+ intercalated between the layers. Their efficient adsorption properties have been confirmed on
many heavy metal ions and radionuclides. 19-25, 27, 29, 34-38 The high selectivity of these ion exchangers
arises from their Lewis soft S2 ligands in the anionic slabs, as the pollutant metal ions are soft Lewis
acid. Hard ions such as H+, Na+ and Ca2+ only interact weakly with S2, thus the pollutant metal
adsorption can be effective over a broad pH range and in the present of high salt concentration.10-11
From this point of view, softer Lewis basicity in the chalcogenide slabs will benefit efficiency and
selectivity in the heavy metal adsorption.
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The Lewis basicity of the chalcogenide slab is determined mainly by the metal ion in the
framework. Compared with Sn4+ in the KMS series, Bi3+ is less positively-charged and possesses
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larger ion radii, thus we can expect that the Bi3+-based slabs are more Lewis basic and should
possess stronger binding affinity towards heavy metal ions. The five-atom-thick Bi2Se3-type layers
are an ideal kind of matrix for the rational design of new ion exchangers. This is done by replacing a
fraction of Bi3+ ions in the structure with other metals ions of lower positive charge. This creates a
negatively charged layer whose exact charge depends on the M metal such as [Bi2-xMxSe3]δ. The
compounds AxCdxBi4-xQ6 (A = K, Rb, Cs; Q = S, Se), are examples of this process,39-40 however,
these materials contain heavy and toxic Cd2+ which limits their application in effluent treatment.
In this work, we targeted the Kx[Bi4-xMnxS6] with several considerations in mind. First, the
presence of Mn makes the system suitable for environmental remediation investigations. Second, the
relatively weak Mn-S bonds imply that Mn2+ can also contribute to the adsorption capacity of heavy
metal ions. The solubility constant ksp of MnS (4.6510-14) is more than 10 orders of magnitude
higher than those of heavy metal sulfides such as CdS (8.010-27) and PbS (7.010-29).41-43 The Mn
contribution of adsorption capacity has been demonstrated in KMS-1 (K2xMnxSn3-xS6 (x = 0.50.95)
and K2xMn1-xPS3, as Mn2+ of MnS6 octahedral units inside the layers can be exchanged by Cd2+ and
Pb2+.21, 34 Third, the variable valence states Mn can adopt in the structure can provide an additional
knob to further tune the ion-exchange function as well as the magnetic properties. We hypothesized
that the five-atom-thick octahedral Bi2Se3-type slab could be a better host for achieving this function
than the three-atom-thick SnS2-type KMS-1 slabs because Mn2+ can be better protected from
oxidation inside the thicker slabs.
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Guided by the abovementioned concepts, we synthesized Kx[Bi4-xMnxS6] (x = 1.28) (i.e.
K1.28Mn1.28Bi2.72S6) with quintuple Bi2Se3-type [Bi4-xMnxS6]x layers and K+ cations between them.
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Optical adsorption and DFT calculations reveal that it is a new semiconductor with a direct band gap
of 1.40 eV, potentially promising for optoelectronic applications. This compound is paramagnetic
and exhibits anisotropic and thermally activated charge transport behavior. Various M ions such as
Rb+, Cs+, Sr2+, Pb2+, Cd2+, Cr3+, and Zn2+ replace the K+ ions rapidly and topotactically, and even the
Mn2+ ions held in the slabs can be exchanged totally or partially by soft ions (M2+ = Pb2+、Cd2+、Cr3+
and Zn2+). These ion exchange reactions create new materials of the type My[Bi4-xMnxS6] in a low
temperature kinetically controlled manner with significantly different electronic structures as verified
by optical absorption and work function measurements. With Cs+ exchange a remarkable topotactic
oxidation of Mn2+ to Mn3+ was observed, and confirmed with single-crystal X-ray diffraction and
X-ray photoelectron spectroscopy (XPS). We show highly selective absorption of Cd2+ and Pb2+ by
Kx[Bi4-xMnxS6] (x = 1.28) over a broad pH range that follows the Langmuir model with high
exchange capacities of 221.2 and 342.4 mg/g and particularly high distribution coefficient Kd of 107
mL/g. The selectivity for heavy metal ion remediation, high pH resistance and discrimination against
hard Lewis acid ions make the Kx[Bi4-xMnxS6] system promising for future industrial and nuclear
waste applications.
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EXPERIMENTAL SECTION
Reagents. The following reagents were used as purchased: Mn (Alfa Aesar, 99.9%), Bi (Alfa
Aesar, 99.9%) and S (Alfa Aesar, 99.9%). K2S5 was prepared by the stoichiometric reaction of
elements in liquid NH3 as described previously.44-45
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Synthesis of Kx[Bi4-xMnxS6] (x = 1.28). All operations were carried out in an Ar-filled glovebox.
0.0592 g K2S5 (0.25 mmol), 0.0275 g Mn (0.5 mmol), 0.2299 g Bi (1.1 mmol) and 0.0368 g S (1.15
mmol) were mixed and loaded in a carbon coated silica tube with an inner diameter of 10 mm. The
tube was flame-sealed under vacuum (103 mbar), heated to 700 °C in 10 h, held for 48 h, and
followed by slow cooling to 450 °C in 3 days. Black single crystals were obtained with a yield of ~
99% based on the Bi element. Large plate-like single crystals (1 mm  2 mm  0.2 mm) of
Kx[Bi4-xMnxS6] (x = 1.28) used for electrical resistivity measurement were synthesized by adding
extra 0.0592 g K2S5 (0.25 mmol) into the combination of reactants (to act as a flux) and following
the same heating procedure mentioned above. The product was washed with deionized water twice to
remove the extra K2S5.
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Single Crystal X-ray Crystallography. Single crystals were selected from the products and
mounted on the tips of glass fiber loops with glue for X-ray diffraction. X-ray diffraction data were
collected at 180 K on a Rigaku XtaALB PRO 007HF single crystal X-ray diffractometer equipped
with mirror-monochromatized Mo-K radiation ( = 0.71073
Å) and Oxford Cryo stream (80-500
K). The crystal structures were solved via direct methods and refined by full-matrix least-squares on
F2 using the SHELXTL program package.46 Multi-scan absorption corrections were performed. The
crystallographic data and structure refinement results of Kx[Bi4-xMnxS6] (x = 1.28) are shown in
Table 1 and the selected bond lengths and angles are shown in Table 2. Atomic coordinates,
equivalent isotropic displacement parameters and anisotropic displacement parameters are shown in
Table S1-S2.
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Physical Properties Measurements. Direct-current magnetization measurements as a function of
temperature and magnetic field were performed using a Physical Properties Measurement System
(PPMS) from Quantum Design. Zero-field-cooled (ZFC) and field-cooled (FC) susceptibility data
were collected from 300 to 2 K in an applied magnetic field of 1 T. Magnetic hysteresis, M(H), were
collected with applied magnetic field from 1 to 1 T at 2, 10, 50, 100, 150, 200 and 300 K,
respectively. Electrical resistivity measurements on single crystals were done using the standard
two-probe method on the PPMS.
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Work Function. The work function data was collected by photoemission yield spectroscopy in air
(PYSA). In PYSA, the sample is scanned with monochromatic UV light (3.46.2 eV) and the
generated photoelectrons are measured at each energy, the work function is defined by the onset in
the PYSA spectrum.47 PYSA measurements were performed using an AC-2 spectrometer (Riken
Keiki).
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Electronic Structure Calculations. First-principles calculations were performed by using the
Projected Augmented Wave Method (PAW)48 within the density functional theory (DFT) as
implemented in the Vienna Ab Initio Simulation Package (VASP).49-51 The exchange correlation
functional was treated within the spin-polarized generalized gradient approximation (GGA) and
parameterized by Perdew-Burke-Ernzerhof (PBE) version.52 The cutoff energy of plane wave basis
was set to 380 eV and the Monkhorst-Pack k-point grid of 463 was used for Brillouin zone (BZ)
sampling. The crystal structure and the lattice parameters were fixed as the values observed in
experiments during the structural optimization, while the positions of atoms were relaxed until the
atomic forces on each atom were less than 0.01 eV/Å.
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ICP-AES and ICP-MS Analysis. The concentration of K+, Cs+, Mn2+, Cd2+, and Pb2+ in the range
of 1-100 ppm were determined using a Leeman Prodigy 7 ICP-AES spectrometer. Standards of these
ions were prepared by diluting the commercial ~1000 ppm ICP standards, and the calibration was
liner with maximum errors of 5%. The solutions were diluted to appropriate concentrations using 1
wt % HNO3. The intensity was obtained using a 35 sec exposure and the result was the average of
three readings. The residual concentrations of Cd2+ and Pb2+ in the solutions after ion exchange were
at ppb levels and were determined by ICP-MS using a PerkinElmer NexION 350X ICP-MS
spectrometer.
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Ion-Exchange Experiments. The ion-exchange properties of Kx[Bi4-xMnxS6] (x = 1.28) were
studied as follows: the crystals of the material (~10.0 mg) were added into 0.2 mol/L aqueous
solutions (10 mL) of RbCl, CsCl, SrCl26H2O, CrCl36H2O, ZnCl2, CdCl22.5H2O, or Pb(NO3)2,
respectively. After three days, the products were collected by filtration, washed with water and
acetone and then dried in air. Ion-exchange crystals were selected for SEM imaging and EDS
analysis. Rb+, Cs+ and Zn2+-exchanged single crystals were picked out for detailed crystallographic
analysis. Ground powder of Kx[Bi4-xMnxS6] (x = 1.28) (100 mg) were add in 0.2 mol/L aqueous
solutions (20 mL) of the ions mentioned above. The mixture was stirred for 24 h and the solid
products collected by filtration and characterized with PXRD and UV-Vis spectroscopy.
Sorption studies of Kx[Bi4-xMnxS6] (x = 1.28) with Cs+, Cd2+ and Pb2+ were carried out by the
batch method at V:m = 1000 mL/g at RT. An amount of 10.0 mg ground powder of Kx[Bi4-xMnxS6] (x
= 1.28) was added into 10 mL aqueous solutions containing gradient concentration of Cs+, Cd2+ or
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Pb2+. The mixture was stirred for 24 h and then filtered. The concentration of ions was determined by
ICP-AES or ICP-MS. The obtained data was used for the determination of the sorption isotherms.
Kinetic studies were carried out to estimate the rate and pathways of sorption. Typically, amounts
of 10.0 mg of ground powder of Kx[Bi4-xMnxS6] (x = 1.28) were added into 10 mL of Cs+ (100 ppm),
Pb2+ (350 ppm) or Cd2+ (200 ppm) aqueous solutions in individual tubes and stirred. After certain
time intervals, the solutions were filtered, and the concentrations were determined by ICP-AES.
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RESULTS AND DISCUSSION
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Synthesis and Thermal Behavior. Kx[Bi4-xMnxS6] (x = 1.28) was synthesized via solid state
reactions of K2S5, Mn, Bi and S at 700 °C. The phase purity of the as-synthesized product was
validated by comparing the experimental PXRD pattern with the simulated one, as shown in Figure
1a. Energy dispersive X-ray spectroscopy (EDS) confirmed that all the elements distribute uniformly
in the crystals, as shown in Figure S1. The accurate molar ratio of K/Mn/Bi as determined by
ICP-AES is 1.32/1.28/2.72 is consistent with the single crystal X-ray crystallographic refinement. By
adding extra reactant K2S5 to serve as flux, we succeeded in obtaining large flaky crystals (1 mm  2
mm  0.2 mm) suitable for the resistivity measurements. The thermal behavior of Kx[Bi4-xMnxS6] (x
= 1.28) was investigated using DSC analysis. In the first heating cycle of the DSC a single
endothermic peak was observed at 693.8 C, and on cooling a single exothermic peak at 255.5 C
corresponding to the crystallization of Bi metal, Figure 1b. In the second cycle the endothermic peak
at 693.8 C disappeared, while a new peak appeared at 269.5 C on heating, indicating the melting of
Bi. The product obtained after DSC analysis was examined by PXRD, and the pattern can be well
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matched with the patterns of KBiS2 (PDF#08-0441), MnS (PDF#06-0518) and Bi (PDF#44-1246),
as shown in Figure S2. Therefore, Kx[Bi4-xMnxS6] (x = 1.28) melts incongruently.
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Crystal Structure. The structure and stoichiometry of Kx[Bi4-xMnxS6] (x = 1.28) was determined
from the single crystal X-ray crystallographic refinements. The crystallographic data and structure
refinements are summarized in Table 1. The structure derives from the layered quintuple hexagonal
Bi2Se3 structure, with some Bi3+ sites in the slabs are replaced by Mn2+ ions which requires
disordered alkali cations between the interlayers to balance charge (Figure S3). This compound
crystallizes in space group P63/mmc and is isostructural with the compounds Cs1.2Ag0.6Bi3.4Q6 (Q = S,
Se) and AxCdxBi4-xQ6 (A = K, Rb, Cs; Q = S, Se).39-40
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Kx[Bi4-xMnxS6] (x = 1.28) is composed of anionic Bi2Se3-type quintuple [Bi2.72Mn1.28S6]1.28 layers
of edge-sharing distorted (Mn/Bi)S6 octahedra intercalated by K+ cations, Figure 2a, 2b. There are
two independent K sites (2b, 2c Wyckoff position), one independent Bi/Mn site (4f, occupancy: Bi
68.0% and Mn 32.0%) and two independent S sites (2a, 4f). The coordination environment of
(Mn/Bi)S6 octahedral is shown in Figure 2b. The Mn2+ ion in the (Mn/Bi)S6 octahedra of
Kx[Bi4-xMnxS6] (x = 1.28) is in a relatively loose coordination environment originally intended for the
Bi3+ atoms. The two K sites are partly occupied with refined occupancies 21% and 43%. A
graphene-like layered arrangement of K+ is obtained after omitting the partial occupation of K sites,
as shown in Figure 2c. The open interlayer space of Kx[Bi4-xMnxS6] and relatively large thermal
factors of K+ atoms (Table S1-S2) imply a strong tendency to engage in facile ion-exchange.
Optical Absorption and Electronic Structure Calculations. The optical absorption properties of
Kx[Bi4-xMnxS6] (x = 1.28) were investigated by UV-Vis diffuse reflectance spectroscopy, which
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shows a well-defined band gap of 1.40 eV (Figure 1c). In order to gain insight into the nature of the
electronic structure we performed DFT calculations using an ordered structure model with the space
group Cmcm (Figure S4a) to represent the mixed-occupied Mn/Bi sites that is a periodic array of
fully occupied Mn and Bi sites. The [Bi2.72Mn1.28S6]1.28 layers were approximated as [Bi4Mn2S9]2
layers with the Mn:Bi ratio of 1:2. In each of the sublayers, every MnS6 octahedron is surrounded by
six BiS6 octahedra, as shown in Figure S4b. The disordered K+ layers were modified by removing
all 4c K sites and fully occupying the 8g K sites (Figure S4c). Charge neutrality was satisfied with a
general formula of K2Bi4Mn2S9. Because of the presence of magnetic Mn2+ ions spin-polarized
calculations were carried out. The electronic structures and density of states (DOS) of K2Bi4Mn2S9
are depicted in Figure 3. The valence band maximum (VBM) and the conduction band minimum
(CBM) are both located at  point (Figure 3a), which indicates the direct-band-gap character. The
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*
effective masses of the CBM (me*) and VBM (mh ) for a and c directions were calculated by fitting
―1
∂2퐸
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the E-k bands around the CBM and VBM with m* =
, where
is Plank’s constant, E is
ℏ
ℏ (∂푘2)
the band energy, and k is the wave vector. The calculated electron effective mass (me*) and hole
*
effective mass (mh ) along the a direction (  Y) is 0.36m0 and 1.17m0 (m0 is the effective mass of
*
free electron), respectively, while both me* and mh along the c direction (  Z) are essentially
infinite. This points to the two-dimensional nature of the material and explains its highly anisotropic
conductivity.
For K2Bi4Mn2S9 the DOS of two different spin directions are shown in Figure 3b and Figure S5.
The VBM is mainly contributed by S 3p states and Mn 3d states in the spin-up direction, while the
VBM of the spin-down direction locates at 0.5 eV. The Bi 6s lone-pair states mainly locate between
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1.5 eV and the VBM in both spin directions. The Bi 6p and S 3p states make similar contribution to
the CBM in both spin directions, while the spin-down Mn 3d states also significantly contribute to
the CBM. The spin-up Mn 3d states are fully occupied and mainly locate between 4 and 1.3 eV,
while the spin-down states are empty in the range of 1.2 – 2.7 eV. These results indicate that the
Mn2+ ions in MnS6 octahedra are in high spin (HS) state, which implies the presence of magnetic
properties presented below.
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Magnetic Properties. The magnetic properties, and specifically the magnetization (M) and
inverse molar magnetic susceptibility (1/) of Kx[Bi4-xMnxS6] (x = 1.28) from 2 to 300 K are shown
in Figure 4a. No magnetic transition was observed which indicates paramagnetic behavior of
Kx[Bi4-xMnxS6] (x = 1.28). The 1/ –T curve can be well fitted by the Curie-Weiss law with Curie
constant C = 5.590 K emu/mol and Curie-Weiss temperature  = –58.32 K. The negative  indicates
relatively strong antiferromagnetic interactions between the Mn2+ ions. The effective magnetic
moments of Mn2+ calculated from the Curie constants are eff = 5.22 B, which is close to but
somewhat smaller than the calculated 5.92 B of HS Mn2+ (d5, S =5/2). The data suggests that the
Mn2+ ions in MnS6 octahedra are in a high-spin state. The magnetization (M) as a function of the
applied magnetic field (H) was measured between 2 K and 300 K (Figure 4b), and the linear
dependence of M-H curves also reveals the antiferromagnetic character of Kx[Bi4-xMnxS6] (x = 1.28).
Electrical Resistivity. The electrical resistivity measurements on single crystals are depicted in
Figure 4c. The resistivity versus temperature data exhibit thermally activated charge transport
behavior where the resistivity increases rapidly with falling temperature. This confirms the
semiconducting nature of the material. The Arrhenius dependence (T) = 0 exp(Ea/kBT) (0 is a
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pre-exponential factor, Ea is the activation energy, kB is the Boltzmann constant.) was used to
describe the temperature dependence of resistivity (Insert in Figure 4c). The Ea value was estimated
to be 0.35 eV in the temperature range of 267-297 K. Two other classical models for semiconducting
transport, the small polaron hopping (SPH) model (expressed as (T)/T  exp(Ep/kBT), Ep is
activation energy)53 and variable range hopping (VRH) (expressed as (T)  exp(T0/T)1/4, T0 is
characteristic temperature)54 were also used to fit the curve. These gave Ep = 0.37 eV in the SPH
model and T0 = 235 K in the VRH model (Figure S6), values of activation energy that likely
represent defect states lying in the middle of the energy gap.
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Ion-exchange properties of Kx[Bi4-xMnxS6] (x = 1.28) and the creation of new materials. The
ion-exchange properties of Kx[Bi4-xMnxS6] (x = 1.28) for Rb+, Cs+, Sr2+, Cr3+, Zn2+, Cd2+, and Pb2+ in
aqueous solution are excellent. SEM and EDS analysis of the exchanged materials confirmed that all
K+ ions can be replaced by these ions, as depicted in Figure 5 and Figure S7. Moreover, the Mn2+
ions in the semiconducting slabs can also be exchanged by the soft ions such as Cr3+, Zn2+, Cd2+ and
Pb2+. Although the intralayer Mn2+ ion exchange has been reported in K2xMnxSn3-xS6 (x = 0.5-0.95)
(KMS-1), and K2xMn1-xPS3, the fact that we see again in Kx[Bi4-xMnxS6] (x = 1.28) suggests this
process is more general. The average Mn/BiS bond length (2.750 Å) in Kx[Bi4-xMnxS6] (x = 1.28) is
obviously longer than the Mn/SnS bond length (2.572 Å) in KMS-1, indicating a weaker MnS
bond strength. Thus, we can expect that Mn2+ in Kx[Bi4-xMnxS6] (x = 1.28) can be easily exchanged
with various soft ions.
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For example, we observe that Cr3+ and Cd2+ can completely replace Mn2+ in the slabs, while in the
case of Pb2+ some Mn2+ ions (~16%) remain and distribute uniformly in the Pb2+-exchanged crystals
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(Figure S7df). Interestingly, a complete Mn2+ replacement by Zn2+ is observed on the edge of
plate-like Zn2+-exchanged crystals, while away from the edges the Zn/Mn molar ratio is close to 1:2,
indicating that Zn2+ ions enter from the edge of anionic slabs. The precise contents of metal ions in
the pristine potassium compound and Zn2+, Cd2+ and Pb2+-exchanged products were determined by
ICP-AES (Table 3) and correspond well to the EDS analysis.
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The PXRD patterns of the exchanged products confirm the topotactic character of the process and
the formation of new isostructural compounds. A slight shift of the basal (002), (004) and (006)
Bragg peaks to lower 2 is observed in the patterns of Cs+ and Rb+ exchanged products suggesting a
small expansion of the interlayer space compared to Kx[Bi4-xMnxS6] (x = 1.28) (Figure 6a). The
c-axis lengths calculated by the position of (002) reflection follow the order: Cs+ (23.94 Å) > Rb+
(23.56 Å) > pristine (22.87 Å), which is consistent with the size of the intercalated cations. After Sr2+
exchange, the three (00l) peaks broaden slightly and shift to lower 2, suggesting interlayer
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2+
expansion (Figure 6b) and the insertion of hydrated species such as Sr(H2O)6 . For Zn2+ exchange,
although its size (0.88 Å) is smaller than K+ (1.52 Å), the positions of (00l) peaks do not shift
appreciably after Zn2+ exchange, which also indicates the hydrated nature of intercalated Zn2+. The
heavily broadened Bragg peaks after Cr3+, Pb2+ and Cd2+ exchange indicate a decrease of crystal size
and increase in lattice disorder. The shift of the basal (00l) peaks to higher 2 implies the contraction
of the interlayer space caused by the smaller ionic sizes and strong covalent MS bonding of the
intercalated ions. This also indicates that these ions enter the structure in unhydrated form and are
able to directly bind to the host layers.
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The band gaps of Cs+ and Rb+ exchanged products are almost the same with that of the pristine
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suggesting a weak ionic interaction with the layers (Figure 6c). This is expected since the alkali ions
do not contribute the energy levels of the CBM and VBM. The smaller band gaps of the Sr2+(1.26
eV), Zn2+(1.30 eV), Cd2+(1.26 eV), Pb2+(1.10 eV), and Cr3+(1.02 eV) exchanged products, however,
indicate the stronger interaction between the intercalated ions and sulfur ligands in the slab in the
form of direct MS bonding (Figure 6d). Therefore, these ions significantly modify the electronic
structure of the pristine material. These additional bonds can increase the electronic bandwidths as
they tend to make the compounds more three-dimensional and lead to the narrower band gaps.
Work Functions. The work functions of Kx[Bi4-xMnxS6] (x = 1.28) and Zn2+, Cd2+ and Pb2+
exchanged products were measured using photoelectron spectroscopy in air to assess the energy
levels of the VBM and CBM (Figure S8). Because the materials are semiconductors, these values
are essentially the energy positions of the valence band maxima and are given in Table 3. Compared
to Kx[Bi4-xMnxS6] (x = 1.28), whose work function was measured at 5.26 eV, the work functions of
Zn2+, Cd2+ and Pb2+-exchanged products increase to 5.80 eV, 5.73 eV and 5.41 eV, respectively.
Therefore, the new strong MS bonds further stabilize the highest occupied states in the valence
band as the weak K···S ionic interactions in the pristine material are replaced by stronger covalent
bonding interactions between S2 ions and these metal ions, which significantly modify the electronic
structures. This is consistent with the drastic narrowing of the electronic bandgap described above.
Ion exchange of Rb+, Cs+ and Zn2+ with Kx[Bi4-xMnxS6] single crystals Because the PXRD
patterns reveal that the Rb+, Cs+ and Zn2+ exchanged products are highly crystalline, we were able to
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perform successful “single crystal to single crystal” ion-exchange reactions and precisely determine
the structures of these products.
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Diffraction-quality Rb+ and Cs+ exchanged crystals were picked out for detailed crystallographic
analysis. The crystallographic data and details of the structure refinements are given in Table 4. The
selected bond lengths and angles, atomic coordinates and anisotropic displacement parameters are
given in Table S3-S8. X-ray diffraction refinement reveals that the exchanged products are
isostructural with the pristine potassium compound. The representation of crystal structures of
Kx[Bi4-xMnxS6] and its Rb+ and Cs+-exchanged analogues are shown in Figure S9, along with the
interlayer distances and Mn/BiS bond lengths. The interlayer space extends from 5.19 Å to 5.40 Å
and 5.67 Å after Rb+ and Cs+ exchange, respectively, while the Mn/BiS bond lengths remain almost
the same (Figure S9e-g). The refinement gave the formulas Rb0.88Mn1.28Bi2.72S6 and
Cs1.03Mn1.28Bi2.72S6, which are somewhat lower in alkali metal content. EDS analysis of the
ion-exchange products also show lower Rb/Mn (0.69) and Cs/Mn (0.81) ratios (Figure S7a and
S7b), compared with the K/Mn ratio 1:1 in the pristine compound. Based on charge balanced
arguments these formulas indicate that the average Mn oxidation states in the Rb+ and
Cs+-exchanged products have changed from +2 to +2.31 and +2.2, respectively. The XPS spectrum
of the pristine compound Kx[Bi4-xMnxS6] (x = 1.28), the peak fitted as 639.6 eV and 640.9 eV can be
assigned to Mn2+ 2p3/2, while the peak at 644.8 eV is Mn(II) satellite, Figure 7.55 This result is
consistent with the reported data of the binding energy of Mn2+ in MnS20, 56 and indicates a Mn2+
oxidation state. After Cs+ exchange, however, the peaks of Mn 2p3/2 shift to higher binding energy
(640.8 eV and 641.9 eV) indicating the oxidation of Mn2+. The Mn 2p3/2 peak at 641.9 eV is assigned
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to Mn3+. The strongly electropositive nature of Cs+ makes the [Bi2.72Mn1.28S6]1.28 slabs more
negatively charged which is relieved by the higher oxidation state of Mn as has been previously
explained for KMS-1.20
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Compared with monovalent alkali ion exchange, the bivalent ion exchange especially with soft
metal ions that can strongly bind to the [Bi2.72Mn1.28S6]1.28 layers, causes serious lattice disorder
which leads to poor crystal quality. However, in the case of Zn2+ exchange, the ions exists as
[Zn(H2O)6]2+ and the product exhibits good crystallization allowing for diffraction-quality crystals to
be selected. EDS analysis of the Zn2+-exchanged single crystal reveals that most Mn2+ ions are not
replaced by Zn2+ ions. The crystallographic data and details of the structure refinements are given in
Table S9. The selected bond lengths and angles, atomic coordinates and anisotropic displacement
parameters are given in Table S10-S12. The crystal possessed good crystallinity after Zn2+
exchange, and our refinement resulted in good residual factors (R1=0.0326 and wR2=0.0772) and
goodness of fit (S = 1.392). The electron density peaks at 2b and 2d sites between the layers were
labeled as Zn1 and Zn2 with occupancies of 19% and 13%, respectively (Figure S9d). The interlayer
space extends from 5.19 Å to 5.34 Å after Zn2+ exchange, which indicates the hydrated nature of
intercalated Zn2+ ions. The Mn/BiS bond lengths remain almost unchanged after Zn2+ exchange
(Figure S9h).
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Isotherm and Kinetic Studies of Cs+, Cd2+ and Pb2+ Ion Exchange.
The adsorption performance of Kx[Bi4-xMnxS6] (x = 1.28) towards heavy metal ions was assessed
with detailed studies using the so-called batch method. Specifically, we performed isotherm, kinetics,
competitive and pH-dependent ion exchange reactions of Cs+, Cd2+ and Pb2+ ions.
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Cd2+, Pb2+. The ion-exchange studies of Cd2+ and Pb2+ were performed using the batch method
(V:m = 1000:1 mL/g, pH5.5 for Cd2+, 5.0 for Pb2+, room temperature). The Cd2+, Pb2+ sorption
isotherm curves are graphed in Figure 8a and 8b. Excellent fits of the curves (correlation coefficient
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R2 > 99%) were obtained with the Langmuir isotherm model (1) expressed as
푏퐶푒
5
(1)
푞m
q =
1 + 푏퐶푒
6
where q (mg/g) is the sorption amount at the equilibrium concentration Ce (ppm), qm is the
maximum sorption capacity, b is a constant. The maximum Cd2+ and Pb2+ sorption capacities
calculated by the Langmuir model are 221(3) mg/g and 342(5) mg/g, respectively. The Cd2+
sorption capacity matches well with the theoretical maximum capacity (245 mg/g) with the
exchanged product formula Cd1.91Bi2.72S6 obtained by ICP-AES analysis. The Pb2+ sorption
capacity is also close to the theoretical maximum capacity (360 mg/g) with the exchanged product
formula Pb1.52Mn0.20Bi2.72S6. The distribution coefficient Kd (2) expressed as
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(퐶0 ― 퐶푒)
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d
(푚)
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is an indicator of the sorption capacity and selectivity of a material, where C0 (ppm) is the initial
concentration. The Kd of Cd2+ and Pb2+ were found to be greater than 107 mL/g with low initial
concentrations (Figure S10). The adsorption capacities of Kx[Bi4-xMnxS6] (x = 1.28) towards Cd2+
and Pb2+ are comparable for those of the leading absorbents listed in Table S13. Especially,
Kx[Bi4-xMnxS6] possesses particularly high Kd among these adsorbents, indicating tremendous
affinity of this material for Cd2+ and Pb2+.
The kinetics of Cd2+ and Pb2+ ion exchange were studied with the initial concentration of 200
ppm for Cd2+ and 350 ppm for Pb2+. In both cases equilibrium was reached within 10 h, and the
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removal rates were > 96% and >99%, respectively (Figure 9a and 9b). We also monitored the
release rates of K+ and Mn2+ during the exchange (Figure S11). The results reveal that the K+ ions
in the interlayer space exchanged faster than the Mn2+ ions in the slabs as expected. The plots of
Mn/(Mn+M) (M = Cd, Pb) (Figure 9c and 9d) based on elemental analysis acquired using
ICP-AES show decreasing fraction of Mn as the ion exchange products. The process can be
monitored by PXRD, as shown in Figure 9e and 9f. In both reactions, a new Bragg peak with
higher 2 value than that of the original basal (002) peak appears within 10 min, indicating the fast
intercalation dynamics of Cd2+ or Pb2+ ions. As the ion exchange proceeds, the new Bragg peak
shifts to higher 2 position, as the original basal (002) peak diminishes. Further Cd2+ exchange (>6
h) causes poor crystallinity of the products as revealed by the extensive broadening of Bragg peaks.
In comparison, the Pb2+-exchanged product retains the structural features of the pristine compound
with broader but still strong Bragg peaks after 24 h exchange.
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Cs+. Because of the change in the Mn2+ oxidation in the Cs+ exchange process (which uses
atmospheric oxygen as the oxidant), isotherm and kinetic studies were carried out in both air and in
Ar atmosphere. The Cs+ sorption capacities in Ar are higher than those in air, Figure S12. The
difference in capacities results from the Mn2+ oxidation by O2 in air which reduces the demand of Cs+
to balance charge. An interesting adsorption and release behavior was observed when we conducted
the kinetic study in air, which indicates that the dynamics of Mn2+ oxidation in Kx[Bi4-xMnxS6] (x =
1.28) is slower than that in KMS-1. Detailed discussion about the Cs+ exchange is given in the
supporting information.
Competitive and pH-dependent ion exchange experiments
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The competitive sorption of Cs+ in concentrated solutions of Na+ or Ca2+ was studied under Ar gas.
The removal of Cs+ decreased slightly in the presence of 530 fold excess of Na+, but dropped to
50% in the presence of 17 fold excess of Ca2+, see Figure S13. Thus, Ca2+ is a stronger competitor
than Na+ for Cs+ exchange and can be rationalized by the double positive charge of this ion. We also
checked the ability to remove Cd2+ and Pb2+ from solutions containing a high excess of Na+ or Ca2+.
The high concentration of Na+ or Ca2+ did not affect the absorption towards these heavy metal ions.
Remarkably, the Cd2+ and Pb2+ concentrations can be reduced below 1 ppb (V:m =1000 mL/g, initial
concentration: 6 ppm) with the existence of high concentration of Na+ and Ca2+, see Figure 10a.
To check the relative selectivity of Kx[Bi4-xMnxS6] (x = 1.28) towards Cd2+ and Pb2+, competitive
ion-exchange (containing both ions) were performed with solutions containing 20, 150, 200, 250,
300 ppm of each ion, Figure 10b. At the very large concentration of 300 ppm the Pb2+ removal is
around 85.0% and increases to 99.6% at 150 ppm. In comparison, the Cd2+ removal is only 28.6% at
300 ppm, and it increases to 75.9% at 150 ppm. Both Pb2+ and Cd2+ removal rates can exceeded 99.9%
at 20 ppm. The competitive experiments clearly indicate that the material prefers Pb2+ over Cd2+
which is opposite to the trend observed in KMS-1.
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The acid and base stability of Kx[Bi4-xMnxS6] (x = 1.28) was investigated in a wide range of pH
values (1.7-11.5). The compound retained the layered structure and high crystallinity in pH between
2.5 and 11.0 after stirring for 2 days (Figure 10c). Higher concentration of hydrochloric acid (pH<
2.5) can react with Kx[Bi4-xMnxS6] (x = 1.28) to produce BiOCl(PDF#06-0249). At pH = 11.5, some
unidentified phases with low K content and high O content were observed by SEM and EDS analysis
(Figure S14). Cs+ exchange experiments of Kx[Bi4-xMnxS6] in solutions of various pH (2.611) were
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conducted in Ar gas with initial Cs+ concentration of 10 ppm (Figure S15). The results indicated that
Kx[Bi4-xMnxS6] can remove over 80% of Cs+ in the pH range of 3.611. Even at pH = 2.6 the
removal of Cs+ still retains near 70%. This remarkable capture of Cs+ in acidic conditions should
origin from the relatively “softer” nature of Cs+ ion compared with the hard proton ion. The effect of
pH on the Cd2+ and Pb2+ exchange was also studied in the range of 2.711.0 with initial
concentration of 20 ppm (Figure 10d). Kx[Bi4-xMnxS6] (x = 1.28) displays a maximum Kd (2.1107
mL/g) for Cd2+ at pH  2.7, while Kd values at pH>3.1 are all in the range of 5.0  1055.0  106
mL/g. The Kd The Pb2+ uptake increases in lower pH with the maximum Kd = 8.3107 at pH = 2.7.
Pb2+ Kd values at pH 3.16.6 are all in the range of 2.07.4  107 mL/g, while the Kd values decrease
to 1.75.0  106 mL/g at higher pH (>6.6). Such high Kd values validate the strong uptake of
Kx[Bi4-xMnxS6] (x = 1.28) towards Cd2+ and Pb2+ in the pH range tested.
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CONCLUSION
Kx[Bi4-xMnxS6] (x = 1.28) was designed to possess powerful ion-exchange properties starting from
the Bi2Se3-type layer and making it anionic via the replacement of some Bi3+ atoms with Mn2+ atoms.
However, the material possesses dual characteristics as the paramagnetic compound exhibits
interesting semiconducting characteristics with a direct band gap of 1.40 eV and low effective carrier
masses. Topotactic ion exchange can be performed rapidly by Kx[Bi4-xMnxS6] (x = 1.28) with a
variety of ions such as Rb+, Cs+, Sr2+, Pb2+, Cd2+, Cr3+, and Zn2+. The structures of Rb+, and Cs+
exchanged crystals were solved by single-crystal X-ray diffraction and confirmed an unusual
topotactic oxidation of Mn2+ after Rb+ and Cs+ exchange in air. The formation of Mn3+ lowers the
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absorption capacity for Rb+ and Cs+ but facilitates the kinetics of their subsequent release. The
Kx[Bi4-xMnxS6] (x = 1.28) system exhibits efficient adsorption of Cd2+ and Pb2+ with high exchange
capacities of 221.2 and 342.4 mg/g and particularly high Kd of 107 mL/g, and can efficiently remove
these ions in a wide pH range (2.5-11.0) and with competitive cations present in large excess. All of
these highlight the Kx[Bi4-xMnxS6] (x = 1.28) as a highly selective adsorbent for the quantitative
removal of heavy metals and radioactive ions from industrial and nuclear waste waters. Finally, the
ion exchange reactions of Kx[Bi4-xMnxS6] are a gateway to new materials of the type Mx[Bi4-xMnxS6]
with kinetic control as afforded by the low temperatures.
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ASSOCIATED CONTENT
Supporting Information. Experimental section of XRD, SEM, UV-vis, DSC and XPS. Results and
discussion about Cs+ adsorption. Figures of SEM, EDS, electronic structures, electrical conductivity,
work functions. Tables of atomic coordinates and displacement parameters.
X-ray crystallographic information (CIF).
AUTHOR INFORMATION
Corresponding Author
*E-mail: huangfq@pku.edu.cn
*E-mail: m-kanatzidis@northwestenrn.edu
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
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Work at Northwestern was supported partly by the National Science Foundation (Grant
DMR-1708254). This work also was partially supported by the Innovation Program of the CAS
(Grant KJCX2-EW-W11), “Strategic Priority Research Program (B)” of the Chinese Academy of
Sciences (Grants XDB04040200), NSF of China (Grants 91122034, 51125006, 51202279,
61376056, and 21201012), and Science and Technology Commission of Shanghai (Grant
12XD1406800). PYSA measurements were carried out with equipment acquired by ONR DURIP
grant N00014-18-1-2102.
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References
5
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2
3
1. Shannon, M. A.; Bohn, P. W.; Elimelech, M.; Georgiadis, J. G.; Mariñas, B. J.; Mayes, A. M., Science
and technology for water purification in the coming decades. Nature 2008, 452, 301-311.
2. Schwarzenbach, R. P.; Escher, B. I.; Fenner, K.; Hofstetter, T. B.; Johnson, C. A.; Von Gunten, U.;
Wehrli, B., The challenge of micropollutants in aquatic systems. Science 2006, 313, 1072-1077.
3. Sharma, S. K., Heavy metals in water: presence, removal and safety. RSC: 2014.
4. Sarkar, B., Heavy metals in the environment. CRC Press: 2002.
4
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
5
6
7
8
5. Naja, G. M.; Volesky, B., Toxicity and sources of Pb, Cd, Hg, Cr, As, and radionuclides in the
environment. Heavy metals in the environment 2009, 8, 16-18.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
6. Sarı, A.; Tuzen, M.; Citak, D.; Soylak, M., Equilibrium, kinetic and thermodynamic studies of adsorption
of Pb (II) from aqueous solution onto Turkish kaolinite clay. J. Hazard. Mater. 2007, 149, 283-291.
7. Sarı, A.; Tuzen, M.; Soylak, M., Adsorption of Pb (II) and Cr (III) from aqueous solution on Celtek clay.
J. Hazard. Mater. 2007, 144, 41-46.
8. Benhammou, A.; Yaacoubi, A.; Nibou, L.; Tanouti, B., Adsorption of metal ions onto Moroccan
stevensite: kinetic and isotherm studies. J. Colloid Interface Sci. 2005, 282, 320-326.
9. Bansal, R. C.; Goyal, M., Activated carbon adsorption. CRC press: 2005.
10. Manos, M. J.; Kanatzidis, M. G., Metal sulfide ion exchangers: superior sorbents for the capture of toxic
and nuclear waste-related metal ions. Chem. Sci. 2016, 7, 4804-4824.
11. He, W.; Ai, K.; Ren, X.; Wang, S.; Lu, L., Inorganic layered ion-exchangers for decontamination of toxic
metal ions in aquatic systems. J. Mater. Chem. A 2017, 5, 19593-19606.
12. Barakat, M., New trends in removing heavy metals from industrial wastewater. Arab. J. Chem. 2011, 4,
361-377.
13. Fan, Q.; Li, Z.; Zhao, H.; Jia, Z.; Xu, J.; Wu, W., Adsorption of Pb (II) on palygorskite from aqueous
solution: effects of pH, ionic strength and temperature. Appl. Clay Sci. 2009, 45, 111-116.
14. Fu, F.; Wang, Q., Removal of heavy metal ions from wastewaters: a review. J. Environ. Manage. 2011,
92, 407-418.
15. Hui, K.; Chao, C. Y. H.; Kot, S., Removal of mixed heavy metal ions in wastewater by zeolite 4A and
residual products from recycled coal fly ash. J. Hazard. Mater. 2005, 127, 89-101.
16. Jiang, M. Q.; Jin, X. Y.; Lu, X. Q.; Chen, Z. L., Adsorption of Pb (II), Cd (II), Ni (II) and Cu (II) onto
natural kaolinite clay. Desalination 2010, 252, 33-39.
17. Kobya, M.; Demirbas, E.; Senturk, E.; Ince, M., Adsorption of heavy metal ions from aqueous solutions
by activated carbon prepared from apricot stone. Bioresour. Technol. 2005, 96, 1518-1521.
18. Ozdes, D.; Duran, C.; Senturk, H. B., Adsorptive removal of Cd (II) and Pb (II) ions from aqueous
solutions by using Turkish illitic clay. J. Environ. Manage. 2011, 92, 3082-3090.
19. Manos, M. J.; Ding, N.; Kanatzidis, M. G., Layered metal sulfides: exceptionally selective agents for
radioactive strontium removal. Proc. Natl. Acad. Sci. USA 2008, 105, 3696-3699.
20. Manos, M. J.; Kanatzidis, M. G., Highly Efficient and Rapid Cs+ Uptake by the Layered Metal Sulfide
K2xMnxSn3−xS6 (KMS-1). J. Am. Chem. Soc. 2009, 131, 6599-6607.
21. Manos, M. J.; Kanatzidis, M. G., Sequestration of heavy metals from water with layered metal sulfides.
Chem–Eur. J. 2009, 15, 4779-4784.
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5
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7
8
9
1
2
22. Manos, M. J.; Petkov, V. G.; Kanatzidis, M. G., H2xMnxSn3−xS6 (x = 0.11−0.25): A Novel Reusable
Sorbent for Highly Specific Mercury Capture Under Extreme pH Conditions. Adv. Funct. Mater. 2009, 19,
1087-1092.
3
4
23. Manos, M. J.; Kanatzidis, M. G., Layered metal sulfides capture uranium from seawater. J. Am. Chem.
Soc. 2012, 134, 16441-16446.
5
24. Mertz, J. L.; Fard, Z. H.; Malliakas, C. D.; Manos, M. J.; Kanatzidis, M. G., Selective Removal of Cs+,
Sr2+, and Ni2+ by K2xMgxSn3–xS6 (x = 0.5–1)(KMS-2) Relevant to Nuclear Waste Remediation. Chem. Mater.
2013, 25, 2116-2127.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
6
7
8
9
25. Feng, M. L.; Sarma, D.; Qi, X. H.; Du, K. Z.; Huang, X. Y.; Kanatzidis, M. G., Efficient removal and
recovery of uranium by a layered organic–inorganic hybrid thiostannate. J. Am. Chem. Soc. 2016, 138,
12578-12585.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
26. Li, J. R.; Wang, X.; Yuan, B.; Fu, M. L.; Cui, H. J., Robust removal of heavy metals from water by
intercalation chalcogenide [CH3NH3]2xMnxSn3−xS6·0.5H2O. Appl. Surf. Sci. 2014, 320, 112-119.
27. Hassanzadeh Fard, Z.; Malliakas, C. D.; Mertz, J. L.; Kanatzidis, M. G., Direct extraction of Ag+ and
Hg2+ from cyanide complexes and mode of binding by the layered K2MgSn2S6 (KMS-2). Chem. Mater. 2015,
27, 1925-1928.
28. Neeway, J. J.; Asmussen, R. M.; Lawter, A. R.; Bowden, M. E.; Lukens, W. W.; Sarma, D.; Riley, B. J.;
–
Kanatzidis, M. G.; Qafoku, N. P., Removal of TcO4 from representative nuclear waste streams with layered
potassium metal sulfide materials. Chem. Mater. 2016, 28, 3976-3983.
29. Xiao, C.; Hassanzadeh Fard, Z.; Sarma, D.; Song, T. B.; Xu, C.; Kanatzidis, M. G., Highly efficient
separation of trivalent minor actinides by a layered metal sulfide (KInSn2S6) from acidic radioactive waste. J.
Am. Chem. Soc. 2017, 139, 16494-16497.
30. Li, J. R.; Xu, L.; Fu, M. L.; Wang, Y. X.; Xiao, H., Towards magnetic responsive chalcogenides for
efficient separation in water treatment: facile synthesis of magnetically layered chalcogenide Fe3O4/KMS-1
composite adsorbents and their zinc removal application in water. Inorg. Chem. Front. 2018, 5, 403-412.
31. Qi, X. H.; Du, K. Z.; Feng, M. L.; Li, J. R.; Du, C. F.; Zhang, B.; Huang, X. Y., A two-dimensionally
microporous thiostannate with superior Cs+ and Sr2+ ion-exchange property. J. Mater. Chem. A 2015, 3,
5665-5673.
32. Qi, X. H.; Du, K. Z.; Feng, M. L.; Gao, Y. J.; Huang, X. Y.; Kanatzidis, M. G., Layered
A2Sn3S7·1.25H2O (A = Organic Cation) as Efficient Ion-Exchanger for Rare Earth Element Recovery. J. Am.
Chem. Soc. 2017, 139, 4314-4317.
33. Sarma, D.; Islam, S. M.; Subrahmanyam, K.; Kanatzidis, M. G., Efficient and selective heavy metal
sequestration from water by using layered sulfide K2xSn4−xS8−x (x = 0.65–1; KTS-3). J. Mater. Chem. A 2016,
4, 16597-16605.
34. R Rathore, E.; Pal, P.; Biswas, K., Layered Metal Chalcophosphate (K-MPS-1) for Efficient, Selective,
and ppb Level Sequestration of Pb from Water. J. Phys. Chem. C 2017, 121, 7959-7966.
35. Rathore, E.; Pal, P.; Biswas, K., Reversible and Efficient Sequestration of Cesium from Water by the
Layered Metal Thiophosphate K0.48Mn0.76PS3⋅H2O. Chem–Eur. J. 2017, 23, 11085-11092.
36. Gash, A. E.; Spain, A. L.; Dysleski, L. M.; Flaschenriem, C. J.; Kalaveshi, A.; Dorhout, P. K.; Strauss, S.
H., Efficient recovery of elemental mercury from Hg (II)-contaminated aqueous media using a
redox-recyclable ion-exchange material. Environ. Sci. Technol. 1998, 32, 1007-1012.
51 36
52
53
54
55
56
57
58
59
60
37
38
39
40
41
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Page 26 of 42
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2
3
4
5
1
2
37. Schöllhorn, R.; Roer, W.; Wagner, K., Topotactic formation and exchange reactions of hydrated layered
tin sulfides Ax(H2O)ySnS2. Monatsh. Chem. 1979, 110, 1147-1152.
6
7
8
9
3
4
38. Ai, K.; Ruan, C.; Shen, M.; Lu, L., MoS2 nanosheets with widened interlayer spacing for high ‐
efficiency removal of mercury in aquatic systems. Adv. Funct. Mater. 2016, 26, 5542-5549.
39. Zhao, J.; Islam, S. M.; Kontsevoi, O. Y.; Tan, G.; Stoumpos, C. C.; Chen, H.; Li, R.; Kanatzidis, M. G.,
The Two-Dimensional AxCdxBi4–xQ6 (A=K, Rb, Cs; Q= S, Se): Direct Bandgap Semiconductors and
Ion-Exchange Materials. J. Am. Chem. Soc. 2017, 139, 6978-6987.
5
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
6
7
8
40. Zhao, J.; Islam, S. M.; Hao, S.; Tan, G.; Stoumpos, C. C.; Wolverton, C.; Chen, H.; Luo, Z.; Li, R.;
Kanatzidis, M. G., Homologous Series of 2D Chalcogenides Cs–Ag–Bi–Q (Q= S, Se) with Ion-Exchange
Properties. J. Am. Chem. Soc. 2017, 139, 12601-12609.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
41. Ikeue, K.; Shiiba, S.; Machida, M., Novel visible-light-driven photocatalyst based on Mn−Cd−S for
efficient H2 evolution. Chem. Mater. 2009, 22, 743-745.
42. Liu, L.; Qi, Y.; Lu, J.; Lin, S.; An, W.; Liang, Y.; Cui, W., A stable Ag3PO4@ g-C3N4 hybrid core@ shell
composite with enhanced visible light photocatalytic degradation. Appl. Catal. B- Environ. 2016, 183,
133-141.
43. Shao, H. F.; Zhang, Y. B.; Qian, X. F.; Yin, J.; Zhu, Z. K., Preparation of rod-shape PbSO4 nanocrystal
and its phase transition to PbS. Mater. Lett. 2005, 59 , 3507-3513.
44. Chondroudis, K.; Hanko, J. A.; Kanatzidis, M. G., Chemistry of Gold in Molten Alkali Metal
Polychalcophosphate Fluxes. Synthesis and Characterization of the Low-Dimensional Compounds A3AuP2Se8
(A = K, Rb, Cs), A2Au2P2Se6 (A = K, Rb), A2AuPS4 (A = K, Rb, Cs), and AAuP2S7 (A = K, Rb). Inorg. Chem.
1997, 36, 2623-2632.
45. Hanko, J. A.; Sayettat, J.; Jobic, S.; Brec, R.; Kanatzidis, M. G., A2CuP3S9 (A = K, Rb), Cs2Cu2P2S6, and
K3CuP2S7: New phases from the dissolution of copper in molten polythiophosphate fluxes. Chem. Mater.
1998, 10, 3040-3049.
46. Sheldrick, G., SHELX-97, program for the solution and refinement of crystal structures. University of
Göttingen, Germany 1997.
47. Baikie, I. D.; Grain, A.; Sutherland, J.; Law, J., Near ambient pressure photoemission spectroscopy of
metal and semiconductor surfaces. Phys. Status Solidi-C 2015, 12, 259-262.
48. Blöchl, P. E., Projector augmented-wave method. Phys. Rev. B 1994, 50, 17953.
49. Kresse, G.; Hafner, J., Ab initio molecular dynamics for liquid metals. Phys. Rev. B 1993, 47, 558.
50. Kresse, G.; Furthmüller, J., Efficiency of ab-initio total energy calculations for metals and
semiconductors using a plane-wave basis set. Comp. Mater. Sci. 1996, 6, 15-50.
51. Kresse, G.; Furthmüller, J., Efficient iterative schemes for ab initio total-energy calculations using a
plane-wave basis set. Phys. Rev. B 1996, 54, 11169.
52. Perdew, J. P.; Burke, K.; Ernzerhof, M., Generalized gradient approximation made simple. Phys. Rev.
Lett. 1996, 77, 3865.
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52
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54
55
56
57
58
59
60
37
53. Mott, N. F.; Davis, E. A., Electronic processes in non-crystalline materials. OUP Oxford: 2012.
54. Mott, N., Conduction in glasses containing transition metal ions. J. Non-Cryst. Solids 1968, 1, 1-17.
55. Ilton, E. S.; Post, J. E.; Heaney, P. J.; Ling, F. T.; Kerisit, S. N., XPS determination of Mn oxidation
states in Mn (hydr) oxides. Appl. Surf. Sci. 2016, 366, 475-485.
38
39
40
41
42
56. Strohmeier, B. R.; Hercules, D. M., Surface spectroscopic characterization of manganese/aluminum
oxide catalysts. J. Phys. Chem. 1984, 88, 4922-4929.
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Tables
Table 1. Crystallographic data (180 K) and details of the structure refinement of Kx[Bi4-xMnxS6]
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Formula
Space group
Fw(gmol-1)
a (Å)
K1.28Mn1.28Bi2.72S6
P63/mmc
881.18
3.9521(2)
23.094(2)
312.38(3)
Black
c (Å)
V(Å3)
crystal color
c (gcm-3)
 (mm-1)
F(000)
4.684
40.828
378
data/parameters
Rint
224/16
0.0697
0.0238
R1[I>2(I)]
wR2 (all data )
GOF
0.0519
1.269
3
R
=
Σ||Fo||Fc||
/
Σ|Fo|,
wR
=
Σ{[w(|Fo|2|Fc|2)2]/Σ[w(|Fo|4)]}1/2
and
w
=
2
2
44 4
45
1/[σ2(Fo )+(0.0146P)2+3.0862P] where P = (Fo +2Fc2)/3
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Page 29 of 42
Journal of the American Chemical Society
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Table 2. Selected bond lengths and angles for Kx[Bi4-xMnxS6] (x = 1.28)
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bond type distance (
Å)
angle type
S1BiS13
S2BiS23
S2BiS12
S2BiS12
angle ()
2.8963(3)
2.674(2)
3.456(2)
3.456(2)
86.05(2)
95.30(8)
89.14(4)
89.14(4)
BiS13
BiS23
K1S26
K2S26
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