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C: Physical Processes in Nanomaterials and Nanostructures

How Intercalated Sodium, Copper, and Iron Cations Influence the Structural Arrangement of Zirconium Sulfophenylphosphonate Layers? Theoretical and Experimental Points of View Jakub Škoda, Miroslav Pospíšil, Petr Ková#, Klara Melanova, Jan Svoboda, Ludvik Benes, and Vitezslav Zima J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.8b08134 • Publication Date (Web): 08 Jan 2019 Downloaded from http://pubs.acs.org on January 9, 2019

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The Journal of Physical Chemistry

How Intercalated Sodium, Copper, and Iron Cations Influence the Structural Arrangement of Zirconium Sulfophenylphosphonate Layers? Theoretical and Experimental Points of View. Jakub Škoda1, Miroslav Pospíšil1*, Petr Kovář1, Klára Melánová2, Jan Svoboda3, Ludvík Beneš4, Vítězslav Zima2

1Charles

University, Faculty of Mathematics and Physics, Ke Karlovu 3, 121 16 Prague 2, Czech

Republic, [email protected], [email protected], [email protected]. 2Institute

of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Heyrovský

Sq. 2, 162 06, Prague 6, Czech Republic, [email protected], [email protected]. 3

Institute of Organic Chemistry and Technology, Faculty of Chemical Technology, University of

Pardubice, Studentská 95, 532 10 Pardubice, Czech Republic, [email protected]. 4 Joint

Laboratory of Solid State Chemistry, Faculty of Chemical Technology, University of

Pardubice, Studentská 95, 532 10 Pardubice, Czech Republic, [email protected].

e-mail*: [email protected], tel. +420221911245, fax. +420221911249

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Abstract A structural arrangement of sodium, copper and iron cations intercalated in zirconium 4-sulfophenylphosphonate (ZrSPhP), as a potential material for ion-exchange applications, was suggested by molecular simulations methods. The calculations were focused on a detail description of the influence of individual cations on mutual positions of the ZrSPhP layers and arrangement of sulfo groups and water molecules. Results of the calculations were compared with experimental measurements (X-ray diffraction, TGA, chemical analysis). A very good agreement between the experimental and calculated basal peaks was achieved and the correspondence for the non-basal peaks was improved by a cell refinement. A model with sodium cations shows that the cations remain immersed between the sulfo groups of the individual sulfo sheets and the water molecules are homogeneously spread in the interlayer. The copper cations are placed in the interlayer more homogeneously and are shifted from the central part of the interlayer space to the positions close to the sulfo sheets. The iron cations are positioned in the middle of the interlayer. The water molecules remain randomly scattered in the interlayer space, the sulfo groups are connected with the intercalated cations and water molecules by non-bond interactions.


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Introduction Chemistry of the layered phosphates and phosphonates is of great interest of research thanks to their high potential in many applications, such as ion exchanging materials1,2, suitable host matrices for the intercalation chemistry3,4, proton conductors4,5, catalysts6,7, etc. Particularly, the alpha modification

of

zirconium

phosphate

(α-zirconium

bis-(monohydrogen

orthophosphate)

monohydrate, α-ZrP) is one of the first widely studied and structurally determined layered phosphates8-10. The layers of zirconium phosphate consist of zirconium octahedra and phosphate tetrahedra, while each zirconium atom is coordinated to six oxygen atoms arising from six phosphate octahedron groups, creating a cell with a space group P21/n with parameters a = 9.060 Å, b = 5.297 Å, c = 15.414 Å and β = 101.71°. Since 1960’s, when its crystal structure was revealed, many scientific groups focused on the preparation of its derivatives as well as on determination of their properties. Replacing of the protonated terminal oxygen of the phosphate layer with an organic functional group is the origin of creation of Zr phosphonates. The common part of both structures (phosphate and phosphonate) is the inorganic sheet of α-ZrP. From the point of the intercalation chemistry, the interesting derivatives are those containing functional groups, which are interacting with the intercalated guest molecules. Such suitable group is the sulfo group, which is able to produce stable intercalation compounds. In addition, a strong acidic nature of the SO3H groups also makes the zirconium phosphonates good proton conductors, which can be used as components of membranes in the fuel cells11. Recently, using classical molecular simulation methods, we provided the detailed structural description of geometrically optimized structures of the pure zirconium sulfophenylphosphonate (ZrSPhP) and its mixed phenylphosphonate derivatives (Zr(HO3SC6H4PO3)x(C6H5PO3)2-x·yH2O 12. Detailed knowledge of the structure allows us to use the resultant model for further calculations.



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Previously, various metal cations have been used in several cases for the intercalation and modification of clays or layered structure of phosphonates in order to achieve or improve specific properties of the resultant material13-17. Similarly, we synthetized intercalated ZSPhP matrix with sodium Na+, copper Cu2+, and iron Fe3+ cations for the first time and studied the structural properties and their behavior in the modified interlayer. For this reason we used molecular simulations methods and available experimental data to calculate how these metal cations can influence mutual arrangement of the sulfo groups and water molecules and mutual positions and orientations of the ZrSPhP layers.

Experimental and modeling methods Preparation and characterization of the samples Zirconium 4-sulfophenylphosphonate (Zr(HO3SC6H4PO3)1.8·(C6H5PO3)0.2·2H2O, ZrSPhP) was prepared according to the previously described procedure18. Shortly, 20 mL of 1 M 4-sulfophenylphosphonic (H3SPhP) acid (20 mmol) and ZrOCl2·8H2O (3.22 g, 10 mmol) were added to a mixture of 1M HF (50 mL) and 1M HCl (50 mL) in a 300-mL PP beaker. The reaction mixture was heated to 80 °C in an oil bath overnight and evaporated to dryness. The solid was suspended in 1 M HCl and then centrifuged. This process was repeated three times and thus obtained slurry was dried in a rotary evaporator at 70 °C to remove hydrochloric acid. The product was dried in a desiccator over NaOH. Na+, Cu2+ and Fe3+ cations were intercalated by shaking 0.25 g of ZrSPhP in an excess of 0.1 M aqueous solution of corresponding metal salt (NaCl, CuSO4·5H2O or Fe(NO3)3·9H2O) at room temperature for one week. The release of the intercalated cations in an acidic environment was investigated by shaking 0.05 g of the corresponding intercalate in 10 mL of 1 M HCl at room temperature for one week. Similarly, the possibility to replace intercalated Cu2+ and Fe3+ for Na+ was tested by shaking 0.05 g of the corresponding intercalate in 10 mL of 1 M NaCl at room 4 ACS Paragon Plus Environment

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temperature for one week. Solid products were separated by centrifugation, three times washed with distilled water and dried in air. Powder X-ray diffraction data were obtained with a D8 Advance diffractometer (Bruker AXS, Germany) with Bragg-Brentano θ–θ geometry (40 kV, 30 mA) using CuK radiation with secondary graphite monochromator. The diffraction angles were measured at room temperature from 2 to 50° (2θ) in 0.02° steps with a counting time of 15 s per step. The thermogravimetric measurements (TGA) were done using a home-made apparatus constructed of a computer controlled oven and a Sartorius BP210 S balance. The measurements were carried in air between 30 and 960 °C at a heating rate of 5 °C min-1. Energy-dispersive X-ray analysis (EDX) was done using an electron scanning microscope JEOL JSM-5500LV equipped with an energy-dispersive X-ray microanalyzer IXRF Systems (detector GRESHAM Sirius 10). The accelerating voltage of the primary electron beam was 20 kV. The elemental analysis of zirconium, phosphorus, sulfur, and intercalated cations (Na+, Cu2+, Fe3+) was carried out with a sequential, radially viewed ICP (Inductively Coupled Plasma) atomic emission spectrometer INTEGRA XL 2 (GBC, Dandenong Australia), equipped with a concentric nebulizer and a glass cyclonic spray chamber (both Glass Expansion, Australia). The samples for the analysis were weighed, dissolved in 3 M HF and diluted with water. The ion exchange capacity of the ZrSPhP sample was determined in the following way: 1.17 g of NaCl was dissolved in a mixture of 10 mL of water and 10 mL of ethanol. To the solution, 0.2 g of ZrSPhP was added and the formed suspension was stirred at room temperature overnight. The suspension was then titrated with 0.096 M NaOH solution, which was added to the mixture in 0.1-mL doses with 500-s intervals between the additions.

Molecular modeling



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Materials Studio modeling environment was used for the molecular calculations19. The initial model of ZrSPhP was used based on the results of our previously performed geometry optimization which were published by Škoda et al.12 In this publication, the final model was based on the presumption of consistency of the inorganic part of ZrSPhP with the known structural model of α-zirconium hydrogen phosphate layer, as determined by Clearfield and Smith9 and later repeatedly refined by Troup and Clearfield10. The following cell parameters of double layered structure of ZrSPhP were used: a = 45.300 Å, b = 26.485 Å, c = 2d002, α = γ = 90° and β = 101.71°. The originally determined space group P21/n was changed to P1 for purposes of calculations. The basal spacing d002 was taken on the base of the experimental X-ray diffraction patterns of ZrSPhP structures with intercalated cations (Na+, Cu2+, Fe3+) and the c axes of the supercells were set to 39.26 Å, 40.07 Å, and 40.51 Å, respectively. On the base of chemical analysis data (ICP and EDX), we built models with corresponding amounts of the metal cations and water molecules present in the real samples. A set of initial models with different positions and mutual arrangements of the intercalated cations and water molecules was prepared. In the case of models with intercalated sodium cations, their amount in the interlayer space is equal to the amount of deleted hydrogen atoms from the fully occupied original sulfo groups in the initial ZrSPhP structural model. In the cases of models with copper and iron cations, the amount of deleted hydrogen atoms in the initial ZrSPhP structure compensates the charge of the intercalated Cu2+ and Fe3+ cations in accordance with their valence, i.e., two hydrogen atoms per one copper cation and three hydrogen atoms per one iron cation were deleted. The hydrogen atoms were evenly deleted across the individual hydrogen sheets. The cell refinement was done in Reflex module of Materials studio software19 and was carried out using various initial Cagliotti peak profile parameters. The final Cagliotti peak profile parameters for all presented models were W = 0.2, U = V = 0, NA = 0.5 and NB = 0 19. The cell refinement was carried out with fixed Cartesian coordinates for all atoms and was performed to fit a and b


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dimension of the crystallographic axes to reach the best agreement between calculated and experimental non-basal peaks. The geometry optimization was performed with variable c cell parameter, whereas all other cell parameters, a, b, α, γ and β, were taken from the cell refinement and kept fixed during the optimization. The α-ZrP layers together with the adjacent phenyl rings and the sulfur atoms were kept as rigid units (rigid fragments of the structure without conformational changes) during the geometry optimization to keep the base structure of ZrSPhP rigid and to minimize computational time. A series of resultant optimized models with the best agreement with the experimental data was selected based on the basal spacing values and minimum of energy. On these models, quench molecular dynamics were applied to generate new series of suitable structural models in given timesteps. The models with calculated diffraction patterns close to experimental one were selected and subsequently optimized. The quench dynamics was performed for 1.5 ns in an NVT (N – constant number of particles, V – constant volume and T – constant temperature) statistical ensemble. Temperature was set to 298 K, the time step was 1 fs. The cell parameters were constrained and the α-ZrP layers and the phenyl rings with the sulfur atoms were kept fixed during the dynamics simulations. Both geometry optimization and quench dynamics calculations were performed in the Compass force field20. All charges were assigned by this force field and evenly adjusted to reach the balance with total charge of the supercell equal to zero. The electrostatic energy was calculated using the Ewald summation method21 and the van der Waals energy was calculated using the atom based method with the cut-off of 13 Å and spline width of 1 Å 19.

Results and discussion 7 ACS Paragon Plus Environment


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The ion exchange capacity of the starting ZrSPhP, as determined by its titration with aqueous NaOH, is 2.85 meq/g (see the titration curve in the ESI, Figure S1). The stoichiometric structural formulas for each type of cation (sodium, copper and iron) were the following: ZrNa1.8(O3SC6H4PO3)1.8(C6H5PO3)0.2·0.65H2O,

ZrH0.4Cu0.7(O3SC6H4PO3)1.8(C6H5PO3)0.2·2.5H2O,

Fe0.23H1.11Zr(O3SC6H4PO3)1.8(C6H5PO3)0.2·2H2O, as found by ICP and EDX (see Table S1 in the ESI). The amount of the intercalated water was calculated from the TG curves (see ESI, Figure S2). The water is released in the first step up to about 250 °C in all cases. The observed weight losses are in accordance with those calculated from the formulas given above (observed/calculated: Na+intercalate 2/1.96 %, Cu2+-intercalate 7/7.08 %, Fe3+-intercalate 6/6.05 %). In the second step the decomposition of the sulfophenylphosphonate anions occurs. Whereas for ZrSPhP and its intercalates with copper and iron this decomposition step starts at around 500 °C, for the sodium intercalate this step is shifted to 640 °C, which indicates higher stability of this intercalate. The end product of the decomposition of parent ZrSPhP is ZrP2O7. In the case of the Cu2+ and Fe3+ intercalates, the decomposition products contain besides ZrP2O7 also mixed zirconium and copper or zirconium and iron phosphates. The sodium intercalate decomposes to a mixture of NaZr2(PO4)3, Na5Zr(PO4)3, baddeleyite and sodium sulfate. Therefore we did not interpret the total weight loss in this case. The experimental X-ray diffraction patterns of ZrSPhP intercalated with cations with different valences differ from each other (see Figures 1–3, and Figure S3). In each pattern, four basal diffraction peaks are evident, which determine the basal spacing of each intercalated structure depending on the type of the cations, see Table 1. One can see a significant difference between the non-basal peaks of the X-ray diffraction patterns.


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Figure 1. Calculated and experimental X-ray diffraction patterns of ZrSPhP with the Na+ cations.

Figure 2. Calculated and experimental X-ray diffraction patterns of ZrSPhP with the Cu2+ cations.

Figure 3. Calculated and experimental X-ray diffraction patterns of ZrSPhP with the Fe3+ cations.



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Molecular calculations allow us to discover and describe these different intercalated structures and explain why these differences appear in the models. Geometry optimizations were applied to three models differing by the type and valence of metal cation and their layered structure was based primarily on the structure of ZrSPhP. As it was mentioned above, a set of initial models was prepared for each intercalated metal cation into ZrSPhP, differing slightly in the arrangement and positions of the cations and water molecules between the layers of the sulfo groups, thus changing the initial calculation conditions. The optimized models calculated by this procedure very well agree with the experimental data regarding the basal peaks and basal spacings. Unfortunately, the positions of the calculated non-basal peaks were different from the experimental data for three tested cations. Nevertheless, the shape of the calculated non-basal peaks roughly agreed with the experimental data but there were differences in positions. To reach better agreement between the experimental and calculated X-ray powder patterns, especially in the region of the non-basal peaks, we used the cell refinement19 procedures. For the calculations purpose, the α-ZrP layers in the models were fixed and only the lengths of the a and b axes were refined. Series of models with various initial conditions for the cell refinement were set and tested to reach optimal fit with the experimental data. These calculations led to almost the same values of the cell parameters a and b, because these cell parameters varied with difference less than 1 % only from initial, see Table 1. Nevertheless, these differences were sufficient to apparently change the diffraction patterns, see Figure S4 showing differences between the X-ray diffraction patterns for the optimized models before and after the cell refinement for the Fe3+ intercalate. In this Figure S4, we can see a shift of the refined pattern to lower 2 values with respect to the original crystal cell parameters (a = 45.300 Å, b = 26.485 Å). A similar shift to lower 2 values can be observed for the copper cations intercalate for b axis. On the other hand, for the sodium cations intercalate a shift to higher diffraction angles was obtained. The optimized calculated models presented and discussed further are those reaching the best agreement between the calculated and experimental X-ray diffraction data regarding both basal and non-basal diffraction peaks. The Figures S5 – S7 show the difference 10 ACS Paragon Plus Environment

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curves between calculated and experimental patterns for each intercalated cation. The refined values of the a and b cell parameters and calculated c cell parameter are listed in Table 1 together with the experimental (d002exp) and calculated (d002calc) basal spacings. Table 1 Experimental and Calculated Basal Spacings and the Refined a, b and Calculated c Cell Parameters for ZrSPhP Intercalated with the Na+, Cu2+, and Fe3+ Cations. cation

d002exp [Å]

d002calc [Å]

a [Å]

b [Å]

c [Å]

Na+

19.55

19.48

44.482

26.451

39.782

Cu2+

19.82

19.86

45.237

27.466

40.564

Fe3+

19.99

20.00

46.714

26.694

40.846

A) Sodium cations The experimental and calculated diffraction patterns show very good agreement in the basal peaks and quite a good agreement in the non-basal peaks regarding the intensity and positions of the peaks, see Figure 1. The calculated peaks are sharper due to better defined periodicity of the calculated model cell with respect to the non-ideal real cell. The dimension of the structure is most likely to be correct in comparison to the real structure as confirmed by almost identically converging values of the cell parameters during the cell refinement with various set of initial parameters. The models obtained by the dynamics calculation showed that the sodium cations, being initially put into the interlayer space between the opposite sulfo group sheets, have tendency to move into small gaps between the individual sulfo groups in each sulfo group sheet, see Figure 4. Based on the set of the results from molecular dynamics and considering the real atomic size of sodium, the smallest of all cations taken into account, the model for the resultant structure contains the Na+ cations in the space between the sulfo groups. In contrast to that, the water molecules remain in the center of the interlayer space and do not show tendency to move between the 11 ACS Paragon Plus Environment


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individual sulfo groups, as it was presented in our previous work12. The water molecules are positioned mainly between the Na+ ions and not directly over the sulfo groups. The model shows that no sheet of water molecules connected through hydrogen bonds is formed. Its calculated basal spacing is a bit lower than the experimental basal spacing.

Figure 4. Side view along the y axis into the interlayer space of ZrSPhP containing the Na+ cations and water molecules.

B) Copper cations The calculated and experimental X-ray diffraction patterns agree very well from the point of view of their basal peaks, see Figure 2. Non-basal experimental peaks are very broad which means that the crystallinity of Cu2+ containing ZrSPhP is very low. This situation can be described by a series of similar models with various arrangements of the sulfo groups in the interlayer space and with the water molecules immersed between the benzene rings and even with several water molecules being in a close contact with the Zr layer. The series of the calculated models from molecular dynamics have similar energies but various positions and arrangement of the water molecules probably cause the observed disorder of the structure. The Cu2+ cations are positioned in one wide layer between the sulfo groups and are not immersed between the benzene rings or the sulfo groups, see Figure 5. 12 ACS Paragon Plus Environment

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The water molecules have tendency to create a coordination sphere around the Cu2+ cations, a part of them is immersed between the sulfo groups and around 20% of them even reach positions between the benzene rings. This disordered arrangement of the Cu2+ cations and a large number of potential water positions, which could be occupied, contribute to the disorder of the resultant material. In comparison with Na+ containing ZrSPhP the copper compound exhibits a completely different X-ray diffraction pattern from the point of view of the non-basal peaks. Regarding the basal peaks, the intensity of the second peak is dominant compared to that of the first one, which almost disappeared. It is caused mainly by the fact that the Cu2+ cations are centered in the interlayer space between the sulfo groups. This is a contradiction to the models containing the Na+ cations in two separate sheets in the interlayer space. The contribution of the higher amount of the water molecules also must be taken into account. A small peak around 2° 2 in the simulated diffraction pattern is caused by a forced periodicity of two disordered layers which are repeated as a basic super cell. This peak diminished when a larger supercell was tested and used for the optimization.

Figure 5. Side view along the y axis into interlayer space of ZrSPhP containing the Cu2+ cations and water molecules. C) Iron cations



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We can see a very good agreement for the basal and non-basal peaks up to 40° 2 between the simulated and experimental data, see Figure 3. The narrow basal and non-basal peaks indicate a well ordered crystal structure of ZrSPhP intercalated with the Fe3+ cations. Therefore, we can conclude that this presented model very well corresponds to the real crystal structure. Molecular dynamic calculations in this case do not reach better result. The second basal peak is not as dominant as in the case of the Cu2+ cations probably due to a lower amount of the Fe3+ cations and also a lower amount of water in the interlayer space. Due to the selection of one optimized crystal structure, not all experimental peak intensities correspond to the calculated ones. Especially the peak around 25° 2 in the calculated pattern is sharper and more intensive. This peak arises from a sum of two diffraction planes (5 5 -8), (5 -5 -8) and is mainly caused by an ideal fixed periodicity of the Zr layer model with regular positions of the Zr and P atoms in contrast to their positions in the real material. Figure 6 represents a “side view” of the structure with a suggested arrangement of the Fe3+ cations. We can see that most of the Fe3+ cations are in the middle of the interlayer space and they are partially coordinated to the water molecules. The water molecules are mainly positioned between two neighboring sulfo groups sheets or among individual sulfo groups within one sheet and are rarely between the phenyl rings (1-2 water molecules per calculated supercell). A higher amount of the water molecules between the benzene rings in the calculated models lead to disagreement with the experimental X-ray diffraction pattern. This is probably caused by a lower amount of water found in the Fe3+ compound by the thermogravimetric measurement. The lower amount of the Fe3+ cations and water and their arrangement in the “thick” sheet positioned in the interlayer space causes a decrease of the intensity of the second peak compared to the X-ray diffraction pattern of the Cu2+ compound, see Figs. 2 and 3. As the amount of the Fe3+ cations is quite small, their distribution within the interlayer plane was also point of our interest. We tested several models with different initial Fe3+ arrangements and in all cases we did not observe any indication of a significant 14 ACS Paragon Plus Environment

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ordering of the cations. This result leads us to a conclusion that the Fe3+ cations and water molecules are randomly arranged in the corresponding samples.

Figure 6. Side view along the y axis into interlayer space of ZrSPhP containing the Fe3+ cations and water molecules.

In summary, we can see sharp and non-overlapping non-basal peaks in the X-ray diffraction patterns of ZrSPhP intercalated with the Na+ and Fe3+ cations, see Figs. 1 and 3. In the case of the Cu2+ cation, see Figure 2, we can see very wide low-intensity non-basal peaks, which are characteristic for the disordered structure of the intercalate regarding the mutual position and orientation of the host layers. Based on this diffraction pattern we obtained a series of structural models with similar values of total minimum energy and with slightly different positions and rotation of the Zr layers and we present one of these optimized models with the minimal energy in this paper. Figure 7 shows a detailed view on the interlayer space of two neighboring sulfo groups with the individual cations. We can see a different arrangement of the cations and an increasing amount of the water molecules going from the Na+ to Cu2+ to Fe3+ intercalates.



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The Na+ cations are mainly placed between the sulfo sheets in one ZrSPhP layer and substitute originally bonded hydrogen atoms. The majority of the sodium cations are coordinated to the oxygen atoms of the sulfo groups within the same sulfo sheet. Some of them, placed in the center of the interlayer, are coordinated also to the oxygen atoms from the opposite sheets that are facing to the cations. The Cu2+ cations are mainly distributed between the sulfo groups of the opposite layers. The oxygen atoms of the sulfo groups are deviated from their original positions to form a direct connection to the coordinated cation. The Fe3+ cations are positioned directly in the center of the interlayer space, surrounded closely by the sulfo groups of the opposite layers and by the water molecules. For all three structures, the water molecules are distributed in the interlayer space facing with the oxygen atoms to the closest cations.

Figure 7. Comparison of different positions of the intercalated cations (Na+ on the left, Cu2+ in the middle, and Fe3+ on the right) between the ZrSPhP layers. Hydrogen bonds are represented by the dashed lines.

Concentration profiles Concentration profiles for ZrSPhP with Na+, Cu2+, and Fe3+ are presented in Figures 8–10, respectively. As we can see, the interlayer water concentration profiles show wide peaks, which characterize their positions in the interlayer space between two neighboring sulfo sheets with one or two slight maxima showing nearly homogeneously filled interlayer space. In the case of Cu2+ we 16 ACS Paragon Plus Environment

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can see small peaks characterizing penetration of the water molecules among phenyl rings, see Figure 9. In contrast to this, we can see two very intensive maxima peaks for the Na+ cations indicating a formation of two dominant sheets of the Na+ cations in the interlayer space together with a lower middle peak characterizing the positions of several Na+ cations between the neighboring sulfo sheets. Both dominant cation sheets are close to the sulfo sheets, which are characterized by dashed lines in the Figure 8. In the case of the Cu2+ cations we can see a partial formation of two wide peaks in one interlayer space between the sulfur sheets and one peak in the second interlayer space. It seems to be an intermediate state between the Na+ and Fe3+ cations arrangement, where the Fe3+ concentration profiles show a preferred central position of these cations in the interlayer.

Figure 8. Concentration profile of the Na+ cations, the water molecules and the sulfur atoms within the structure of Na+ intercalated ZrSPhP along the (001) direction.



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Figure 9. Concentration profile of the Cu2+ cations, the water molecules and the sulfur atoms within the structure of Cu2+ intercalated ZrSPhP along the (001) direction.

Figure 10. Concentration profile of the Fe3+ cations, the water molecules and the sulfur atoms within the structure of Fe3+ intercalated ZrSPhP along the (001) direction.

Connolly surfaces Connolly surfaces help us to determine the stability of the structures. Based on the change of free volume we can deduce ability of the cations to be released from the ZrSPhP structure. We can see that the water molecules can occupy free volume between the benzene rings in the intercalate in the 18 ACS Paragon Plus Environment

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case of Cu2+. This behavior can be described by a free atom volume determination, which can be presented by Connolly surfaces22. The Connolly surfaces are characterized by moving a probe sphere over the van der Waals surfaces, when the Connolly surface is at the boundary between this probe and the atoms represented by their van der Waals radii. In our case the radius of the Connolly probe is 1 Å, see Figures 11, 12, and 13 for the Na+, Cu2+, and Fe3+ cations, respectively. In fact, those surfaces are a part of the van der Waals surfaces of molecule that is accessible to a solvent. For the ZrSPhP intercalates with the Na+, Cu2+, and Fe3+ cations, the occupied volume, free volume and surface area are shown in Table 2. We can see increasing values for all quantities in the following order: Na+, Cu2+, and Fe3+. The only exception is for the occupied volume, which is the highest one for Cu2+, caused by the presence of the water molecules among the phenyl rings. Decreasing amount of the cations causes increasing of the free volume and surface area despite the larger size of the Cu2+ and Fe3+ cations compared to Na+. The lowest interaction energy was calculated for ZrSPhP with the Na+ cations, which shows that this structure is the most stable intercalate. It is in agreement with the values obtained from the Connolly surfaces described by occupied and free volume, see Table 2. Moreover, these calculated energies were confirmed by experimentally determined change of the content of cations in HCl and NaCl solutions, see Table 3. By treatment with HCl, the content of the sodium cations in the sodium intercalate does not change, in the case of the copper and iron intercalates the amount of these cations decreases. The decrease is more pronounced for the iron intercalate. A similar decrease of the amount of the Cu2+ or Fe3+ cations in their respective intercalates was also observed during their treatment with the NaCl solution. In addition, all acidic protons present in the copper and iron intercalates were replaced with the sodium cations. It means that the sodium cation is the strongest intercalant, while the iron cation is the weakest one.



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Table 2 Parameters of Connolly Surfaces for ZrSPhP with Na+, Cu2+, and Fe3+ and Etotal is Total Interaction Energy of All Interlayer Cations per One Supercell with Surrounding. occupied

free volume

surface area

Etotal

number of

volume [Å3]

[Å3]

[Å2]

[kcal/mol]

cations

Na+

41763

4070

9275

-106061

180

Cu2+

43680

5671

11695

-72569

70

Fe3+

43657

6218

12753

-37105

23

Table 3 The Metal/Zr Ratio in the Starting Intercalates and after their Treatment with HCl and NaCl Solutions, as Determined by ICP and EDX. cation

intercalate

treatment with HCl

treatment with NaCl

M/Zr

M/Zr

M/Zr

Na/Zr

Na+

1.8

1.78

-

-

Cu2+

0.7

0.65

0.58

0.64

Fe3+

0.23

0.16

0.17

1.29


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Figure 11. Connolly surfaces showing accessible volume for ZrSPhP with Na+ cations. Connolly surfaces are shown in grey on outer sphere and blue color represents inner surfaces.

Figure 12. Connolly surfaces showing accessible volume for ZrSPhP with Cu2+ cations. Connolly surfaces are shown in grey on outer sphere and blue color represents inner surfaces.



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Figure 13. Connolly surfaces showing accessible volume for ZrSPhP with Fe3+ cations. Connolly surfaces are shown in grey on outer sphere and blue color represents inner surfaces.

Conclusions Structural models of ZrSPhP intercalated with the Na+, Cu2+, and Fe3+ cations were calculated based on the experimental data. It was shown that the diffraction patterns of the basal and non-basal peaks of calculated model after the cell refinement represent very well the experimentally measured diffraction patterns. The cations were intercalated into the interlayer space between two neighboring sulfo sheets together with the water molecules. The models show different intercalation behavior of the cations with different valence. The Na+ cations were immersed among the sulfo sheets and the interlayer space was mainly occupied by the water molecules. In the intercalate with Fe3+, the cations are located in the middle of the interlayer space between sulfo sheets. The intercalate with the Cu2+ cations was characterized by broad peaks, showing a lower crystallinity of the samples, the cations are more distributed in the interlayer space between the sulfo sheets. The water molecules in the resultant models were mostly homogeneously spread in the interlayer space with the exception of the Cu2+ intercalate, where several water molecules have tendency to penetrate between the phenyl rings closer to the Zr layer. Calculated structural models explain very well different behavior of three selected cations with different valence in the interlayer space of ZrSPhP. As follows from the calculated energies, the strongest interaction is between the host structure and the sodium cation, while the weakest is between the host and the iron cation, as was confirmed experimentally by the exchange reactions. Any turbostratic effect occurring during the intercalation of the studied cations can be excluded, as any movement or rotation of ZrSPhP layers in the calculated models lead to simulated powder X-ray diffraction patterns which are not in agreement with the experimental data.


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Electronic supporting information ESI contains: Table S1, the content of elements in the reported compounds, Figure S1, titration curve of ZrSPhP with NaOH solution, Figure S2, the thermogravimetric curves, Figure S3, powder X-ray diffraction patterns of parent ZrSPhP and its intercalates, Figure S4, X-ray diffraction pattern of Fe-ZrSPhP before and after the cell refinement, and Figures S5 to S7, X-ray diffraction patterns of the ZrSPhP intercalates with difference curve.

Acknowledgements The authors thank the Czech Science Foundation (Project No. 17-10639S); J.Š. thanks project SVV206 323 "Studentský výzkum v oboru biofyzika a chemická fyzika" for financial support.

References [1] Bortun, A. I.; Bortun, L. N.; Clearfield, A.; Khainakov, S. A.; García, J. R. Synthesis and Ion Exchange Properties of Novel Inorganic Adsorbent Tin(IV)-Nitrilotris(Methylene)Triphophonates. Solvent Extr. Ion Exch. 1998, 16, 651–667. [2] Clearfield A. Role of Ion Exchange in Solid-State Chemistry. Chem. Rev. 1988, 88, 125–148. [3] Jaimez, E.; Hix, G. B.; Slade, R. C. T. A Phosphate-Phosphonate of Titanium(IV) Prepared from Phosphonomethyliminodiacetic Acid: Characterisation, n-Alkylamine Intercalation and Proton Conductivity. Solid State Ionics 1997, 97, 195–201. [4] Chaudhari, A.; Kumar, C. V. Intercalation of Proteins into -Zirconium Phosphonates: Tuning the Binding Affinities with Phosphonate Functions. Microporous Mesoporous Mater. 2005, 77, 175–187.



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[5] Alberti, G.; Casciola, M.; Donnadio, A.; Piaggio, P.; Pica, M.; Sisani, M. Preparation and Characterisation of -Layered Zirconium Phosphate Sulfophenylenphosphonates with Variable Concentration of Sulfonic Groups. Solid State Ionics 2005, 176, 2893–2898. [6] Zeng, R.; Fu, X.; Gong, C.; Sui, Y. Synthesis and Catalytic Application of ZirconiumSubstituted Aminoethyl Phosphonate. J. Mater. Sci. 2006, 41, 4771–4776. [7] Forster, P. M.; Cheetham, A. K. Hybrid Inorganic-Organic Solids: An Emerging Class of Nanoporous Catalysts. Top. Catal. 2003, 24, 79–86. [8] Clearfield, A.; Smith, S. D. The Crystal Structure of Zirconium Phosphate and the Mechanism of Its Ion Exchange Behavior. J. Colloid. Interf. Sci. 1968, 28, 325-330. [9] Clearfield, A.; Smith, G. D. Crystallography and Structure of -Zirconium Bis(Monohydrogen Orthophosphate) Monohydrate. Inorg. Chem. 1969, 8, 431–436. [10] Troup, J. M.; Clearfield, A. Mechanism of Ion Exchange in Zirconium Phosphates. 20. Refinement of The Crystal Structure of -Zirconium Phosphate. Inorg. Chem. 1977, 16, 3311– 3314. [11] Clearfield, A.; Demadis, K. Metal Phosphonate Chemistry: From Synthesis to Applications, RSC Publishing: Cambridge, U.K., 2012. [12] Škoda, J.; Pospíšil, M.; Kovář, P.; Melánová, K.; Svoboda, J.; Beneš, L.; Zima V. Geometry Optimization of Zirconium Sulfophenylphosphonate Layers by Molecular Simulation Methods. J. Mol. Model. 2018, 24, 10. [13] Terban, M. W.; Shi, C.; Silbernagel, R.; Clearfield, A.; Billinge S. J. L. Local Environment of Terbium(III) Ions in Layered Nanocrystalline Zirconium(IV) Phosphonate-Phosphate Ion Exchange Materials. Inorg. Chem. 2017, 56, 8837–8846.


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[14] Chmielarz, L.; Piwowarska, Z.; Kuśtrowski, P.; Węgrzyn, A.; Gil, B.; Kowalczyk, A.; Dudek, B.; Dziembaj, R.; Michalik, M. Comparison Study of Titania Pillared Interlayered Clays and Porous Clay Heterostructures Modified with Copper and Iron as Catalysts of The DeNOx Process. Appl. Clay Sci. 2011, 53, 164–173. [15] Zehhaf, A.; Morallon, E.; Benyoucef, A. Polyaniline/Montmorillonite Nanocomposites Obtained by In Situ Intercalation and Oxidative Polymerization in Cationic Modified-Clay (Sodium, Copper and Iron). J. Inorg. Organomet. Polym. 2013, 23, 1485–1491. [16] Silbernagel, R.; Martin, C. H.; Clearfield, A. Zirconium(IV) Phosphonate–Phosphates as Efficient Ion-Exchange Materials. Inorg. Chem. 2016, 55, 1651−1656. [17] Silbernagel, R.; Shehee, T. C.; Martin, C. H.; Hobbs, D. T.; Clearfield, A. Zr/Sn(IV) Phosphonates as Radiolytically Stable Ion-Exchange Materials. Chem. Mater. 2016, 28, 2254-2259. [18] Zima, V.; Svoboda, J.; Melánová, K.; Beneš, L.; Casciola, M.; Sganappa, M.; Brus, J.; Trchová, M. Synthesis and Characterization of New Zirconium 4-Sulfophenylphosphonates. Solid State Ionics 2010, 181, 705-713. [19] Materials Studio Modeling Environment, Release 4.3 Documentation, Accelrys Software Inc., San Diego, CA, 2003. [20] Sun, H. COMPASS: An ab Initio Force-Field Optimized for Condensed-Phase ApplicationsOverview with Details on Alkane and Benzene Compounds J. Phys. Chem. B 1998, 102, 7338– 7364. [21] Karasawa, N.; Goddard III, W. A. Acceleration of Convergence for Lattice Sums. J. Phys. Chem. 1989, 93, 7320–7327. [22] Connolly, M. L. The Molecular Surface Package. J. Mol. Graphics 1993, 11, 139–141.



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List of Tables Table 1 Experimental and Calculated Basal Spacings and the Refined a, b and Calculated c Cell Parameters for ZrSPhP Intercalated with the Na+, Cu2+, and Fe3+ Cations. Table 2 Parameters of Connolly Surfaces for ZrSPhP with Na+, Cu2+, and Fe3+ and Etotal is Total Interaction Energy of All Interlayer Cations per One Supercell with Surrounding. Table 3 The Metal/Zr Ratio in the Starting Intercalates and after their Treatment with HCl and NaCl Solutions, as Determined by ICP and EDX.

List of Tables in the Electronic Supporting Information Table S1 The Content of Elements in the Reported Compounds, Found by ICP, and Their Formulas.

List of Figures Figure 1. Calculated and experimental X-ray diffraction patterns of ZrSPhP with the Na+ cations. Figure 2. Calculated and experimental X-ray diffraction patterns of ZrSPhP with the Cu2+ cations. Figure 3. Calculated and experimental X-ray diffraction patterns of ZrSPhP with Fe3+ cations. Figure 4. Side view along the y axis into the interlayer space of ZrSPhP containing the Na+ cations and water molecules. Figure 5. Side view along the y axis into interlayer space of ZrSPhP containing the Cu2+ cations and water molecules. Figure 6. Side view along the y axis into interlayer space of ZrSPhP containing the Fe3+ cations and water molecules.


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Figure 7. Comparison of different positions of the intercalated cations (Na+ on the left, Cu2+ in the middle, and Fe3+ on the right) between the ZrSPhP layers. Hydrogen bonds are represented by the dashed lines. Figure 8. Concentration profile of the Na+ cations, the water molecules and the sulfur atoms within the structure of Na+ intercalated ZrSPhP along the (001) direction. Figure 9. Concentration profile of the Cu2+ cations, the water molecules and the sulfur atoms within the structure of Cu2+ intercalated ZrSPhP along the (001) direction. Figure 10. Concentration profile of the Fe3+ cations, the water molecules and the sulfur atoms within the structure of Fe3+ intercalated ZrSPhP along the (001) direction. Figure 11. Connolly surfaces showing accessible volume for ZrSPhP with Na+ cations. Connolly surfaces are shown in grey on outer sphere and blue color represents inner surfaces. Figure 12. Connolly surfaces showing accessible volume for ZrSPhP with Cu2+ cations. Connolly surfaces are shown in grey on outer sphere and blue color represents inner surfaces. Figure 13. Connolly surfaces showing accessible volume for ZrSPhP with Fe3+ cations. Connolly surfaces are shown in grey on outer sphere and blue color represents inner surfaces.

List of Figures in the Electronic Supporting Information Figure S1. Determination of CEC: Titration of ZrSPhP with 0.095 M NaOH solution.

Figure S2. The thermogravimetric curves of parent ZrSPhP and its intercalates with sodium (NaZrSPhP), copper (Cu-ZrSPhP) and iron (Fe-ZrSPhP).

Figure S3. Powder X-ray diffraction pattern of parent ZrSPhP and its intercalates with sodium (Na-ZrSPhP), copper (Cu-ZrSPhP) and iron (Fe-ZrSPhP). 27 ACS Paragon Plus Environment


Figure S4. X-ray diffraction patterns of Fe-ZrSPhP before and after the cell refinement.

Figure S5. X-ray diffraction patterns of Na-ZrSPhP with difference curve. The cell refinement indices: Rwp = 28.34 %; Rp = 18.01 %.

Figure S6. X-ray diffraction patterns of Cu-ZrSPhP with difference curve. The cell refinement indices: Rwp = 21.99 %; Rp = 13.21 %.

Figure S7. X-ray diffraction patterns of Fe-ZrSPhP with difference curve. The cell refinement indices: Rwp = 16.56 %; Rp = 11.71 %.


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Table of Contents Graphic

Detailed view on different positions of intercalated cations (Na+ is on the left; Cu2+ is in the middle; Fe3+ is on the right) between zirconium sulfo phenyl phosphonate layers.



Figure 1. Calculated and experimental X-ray diffraction patterns of ZrSPhP with the Na+ cations. 82x62mm (300 x 300 DPI)

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Figure 2. Calculated and experimental X-ray diffraction patterns of ZrSPhP with the Cu2+ cations. 82x62mm (300 x 300 DPI)



Figure 3. Calculated and experimental X-ray diffraction patterns of ZrSPhP with the Fe3+ cations. 82x62mm (300 x 300 DPI)


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Figure 4. Side view along the y axis into the interlayer space of ZrSPhP containing the Na+ cations and water molecules. 80x70mm (300 x 300 DPI)



Figure 5. Side view along the y axis into interlayer space of ZrSPhP containing the Cu2+ cations and water molecules. 69x63mm (300 x 300 DPI)


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Figure 6. Side view along the y axis into interlayer space of ZrSPhP containing the Fe3+ cations and water molecules. 75x66mm (300 x 300 DPI)



Figure 7. Comparison of different positions of the intercalated cations (Na+ on the left, Cu2+ in the middle, and Fe3+ on the right) between the ZrSPhP layers. Hydrogen bonds are represented by the dashed lines. 82x41mm (300 x 300 DPI)


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Figure 8. Concentration profile of the Na+ cations, the water molecules and the sulfur atoms within the structure of Na+ intercalated ZrSPhP along the (001) direction. 82x63mm (300 x 300 DPI)



Figure 9. Concentration profile of the Cu2+ cations, the water molecules and the sulfur atoms within the structure of Cu2+ intercalated ZrSPhP along the (001) direction. 82x62mm (300 x 300 DPI)


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Figure 10. Concentration profile of the Fe3+ cations, the water molecules and the sulfur atoms within the structure of Fe3+ intercalated ZrSPhP along the (001) direction. 82x58mm (300 x 300 DPI)



Figure 11. Connolly surfaces showing accessible volume for ZrSPhP with Na+ cations. Connolly surfaces are shown in grey on outer sphere and blue color represents inner surfaces. 70x53mm (300 x 300 DPI)


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Figure 12. Connolly surfaces showing accessible volume for ZrSPhP with Cu2+ cations. Connolly surfaces are shown in grey on outer sphere and blue color represents inner surfaces. 68x52mm (300 x 300 DPI)



Figure 13. Connolly surfaces showing accessible volume for ZrSPhP with Fe3+ cations. Connolly surfaces are shown in grey on outer sphere and blue color represents inner surfaces. 70x52mm (300 x 300 DPI)


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Detailed view on different positions of intercalated cations (Na+ is on the left; Cu2+ is in the middle; Fe3+ is on the right) between zirconium sulfo phenyl phosphonate layers.

118x41mm (300 x 300 DPI)


How Intercalated Sodium, Copper, and Iron ... - ACS Publications

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