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Issue 39, 2019

From the journal:

CrystEngComm

Formation of spherical calcium sulfate mesocrystals: orientation controlled by subunit growth†

Qiaoshan Chen, Luchao Wu, Yaxiong Zeng, Caiyun Jia, Junming Lin, Matthew Z. Yates and Baohong Guan *

Abstract

The design and synthesis of highly ordered and oriented hierarchical structures such as mesocrystals is of great interest due

to their superior performance. However, the orientation mechanism is not yet fully understood. Here, we report a subcrystallite

growth controlled orientation process to synthesize anisotropic α-calcium sulfate hemihydrate (α-HH) spherical mesocrystals

in a Na EDTA-containing ethylene glycol–water system. The spherical mesocrystals consist of rod-like nanoparticles with

parallel crystallographic alignment along the c-axis. The time-dependent experiments indicate that the growth of

subcrystallites after self-assembly is crucial for mesocrystal formation, which changes the subunits from an irregular shape to

a uniform rod-like shape and synchronously aligns them in the same direction. The crystalline growth of subunits mainly

results from the supply of lattice ions released from Ca–EDTA complexes. The cross-section observation reveals that the

growth and orientation of the subcrystallites start exteriorly and proceed inward step by step. This work deepens the

understanding of mesocrystal formation and opens up a potential way for the design and synthesis of complex and highly

ordered structures.

Introduction

Previous Next

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Author affiliations

2

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Controlled self-organization of nanocrystals to form an ordered three-dimensional (3D) hierarchical structure, especially with

oriented alignment, has attracted great attention in recent years due to its outstanding performance. The superstructure

consisting of nonspherical nanocrystals aligned in the same crystallographic register was identified as mesocrystals in 2005.

As a new class of crystals, mesocrystals simultaneously possess high crystallinity and high porosity with respect to

conventional polycrystals and single crystals. To date, significant progress has been witnessed in preparing mesocrystals by

strategies like hydrothermal, ultrasonic-assisted and additive-free routes. Synthesized mesocrystals such as ZnO, TiO ,

ZnSnO and FeLiPO have exhibited extraordinary properties in the fields of catalysis, optics, electrochemistry and

biomedicine. However, as kinetically metastable species in the crystallization process leading to single crystals,

mesocrystals are commonly short-lived, leaving a challenge in their observation and exploration.

As opposed to the conventional “ion-by-ion” crystal growth, mesocrystals are formed through the bioinspired non-classical

“nanoparticle-by-nanoparticle” pathway. Several possible mechanisms have been proposed for the mesocrystal formation,

for example, physical fields, mineral bridges and spatial constraints. The generally accepted mechanism is oriented

attachment, which means that mesocrystals are formed by oriented self-assembly of nanocrystals through physical field

attraction after the nucleation, growth and stabilization of the subcrystallites. The oriented forces are assumed to include

steric repulsion, surface tension, van der Waals force, capillary effect and dipolar interactions. Besides the one-step

oriented attachment, Buscaglia reported the synthesis of SrTiO mesocrystals transforming from a single crystalline structure

induced by topochemical reactions, indicating that mesocrystals can be obtained through structure transformation.

In this work, we demonstrate the synthesis of α-calcium sulfate hemihydrate (α-HH) mesocrystals through structure

transformation from a polycrystalline structure induced by subunit growth. EDTA is introduced to slow down the crystallization

process for the mechanism study by regulating the chelation and release of lattice ions. With the help of ultramicrotomy, the

evolution in the morphology, orientation and interior structure of α-HH mesocrystals is fully exhibited through time-dependent

experiments. This work provides evidence for the importance of the mesoscopic process in typical crystallization processes

and the mechanism revealed here will be helpful in constructing complex, high-order structured materials.

Experimental section

Chemicals and materials

The following analytical reagents were all used as received without further purification: CaCl (Sigma-Aldrich Co., Llc. USA),

(NH ) SO , Na EDTA and ethylene glycol (Sinopharm Chemical Reagent Co., Ltd. Shanghai, China). Deionized water was

used throughout the experiments.

Synthesis of α-HH mesocrystals

The batch experiment was performed at a temperature of 95 °C (with a deviation of ±0.5 °C) in a 500 mL three-necked flask

reactor equipped with a thermometer, glass condenser and Teflon impeller with a constant rate of 250 rpm.

For each synthesis, two homogeneous precursor solutions of Ca and SO were firstly prepared and heated to be

transparent at 95 °C, separately. The Ca precursor solution was prepared by dissolving CaCl and Na EDTA in 20 mL

ethylene glycol in concentrations of 40 mM and 8.7 mM, respectively. The SO precursor solution was composed of 1056

mg (NH ) SO , 584 mg Na EDTA, 33 mL water and 147 mL ethylene glycol. The molar ratio of Ca to SO (Ca/S) was

kept at 1.0. At reaction times of 5 min, 30 min, 1 h, 2 h, 3 h, 6 h and 12 h, the hot suspension was extracted and washed

immediately with boiling water and anhydrous ethanol three times to terminate the reaction and quickly vacuum filtered to

obtain the solid products. The solid products were then dried in a vacuum oven at 60 °C for 6 h. The reaction medium

1,2

3

4

5–72

3 48–10

11–13

14

15,16

17,18

19–21

322

23,24

2

4 2 4 2

2+42−

2+2 2

42−

4 2 4 22+

42−

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obtained at each interval reaction time was diluted 100 times with deionized water for the measurement of Ca and SO

concentrations.

Measurements and characterization

The phase composition was characterized by thermogravimetry and differential scanning calorimetry (TG-DSC, STA 409 PC,

NETZSCH, Germany) and X-ray diffraction (XRD, D/Max 2550 PC, Rigaku Inc., Tokyo, Japan) in the 2θ range from 5° to 80°

with Cu Kα radiation at a scanning rate of 8° min . The morphology evolution of the particles was examined by field emission

scanning electron microscopy (FESEM, SU8010, Hitachi, Tokyo, Japan). Transmission electron microscopy (TEM) and

selected-area electron diffraction (SAED) were performed on a TEM (Titan ChemiSTEM, USA) at an acceleration voltage of

200 kV. Particle size distribution analysis was conducted using a laser particle size analyzer (Mastersizer 2000, Malvern

Instruments Ltd., Worcestershire, U.K.). Ultramicrotomy was applied for the investigation into the inner structure evolution of

the particles. The dry powder was embedded in an epoxy resin matrix of Agar 100, methyl nadic anhydride (MNA) and

dodecenylsuccinic anhydride (DDSA) and dried at 60 °C for 12 h. Then, the block was cut to obtain the cross-sections of the

particles with a 35° DiATOME diamond knife (radius of 5 nm) mounted on a Reichert-Jung Ultracut E ultramicrotome in a dry

environment at room temperature. The concentrations of Ca and SO were detected using an inductively coupled plasma-

atomic emission spectrometer (ICP, ICPE-9000, Shimadzu, Tokyo, Japan) and an ion chromatograph (IC, ICS-1000, Dionex,

USA), respectively. The solid products were dispersed with anhydrous ethanol for zeta potential determination (ZEN3690,

Malvern Instruments Ltd., Worcestershire, U.K.).

Results and discussion

Fabrication of α-HH mesocrystals

The calcium sulfate microspheres were synthesized by mixing Ca and SO precursor solutions in the presence of

Na EDTA at 95 °C. The diagnostic peaks at 14.72°, 25.65°, 29.71°, 31.87° and 49.34° in the XRD pattern (Fig S1†) show that

the as-formed microspheres are HH (PDF-ICDD 041-0224). The endothermic peak at 157 °C and the exothermic peak at 182

°C in the DSC curve (Fig 1a) confirm the HH to be α-HH. The first weight loss of 5.49 wt% in the TG analysis refers to the

elimination of 0.5 crystal water in the phase transformation from hemihydrate into anhydrite, and the subsequent loss of 5.91

wt% is assigned to the pyrolysis of EDTA according to the sharp exothermic peak at 409 °C. The elimination of residual

organic compounds results in a 3.55 wt% weight loss, generating a broad peak at 690 °C. Accordingly, the microspheres are

composed of 90.54 wt% α-HH and 9.46 wt% EDTA. The α-HH microspheres with a diameter of ∼3 μm have a uniform size

and high monodispersity (Fig. 1b). The hierarchical structure consists of nanocrystals with a length of ∼300 nm and a width of

∼100 nm regularly aligned side-by-side along the vertical axis (Fig. 1c). The rough surface and orderly arranged subunits

suggest a change of the crystallization pathway from the classical ion-by-ion growth to the non-classical particle-mediated

crystallization.

2+42−

−1

2+42−

2+42−

2 .

.

25,26

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Fig. 1 TG/DSC curve (a), FESEM images at low magnification (b) and high magnification (c), TEM image (d) and SAED patterns (e) of the

α-HH mesocrystals formed in ethylene glycol–water solution at 95 °C for 3 h. The α-HH lattice structure and a schematic illustration showing that

the subunits in the mesocrystal are aligned parallel to each other along the c-axis (f).

An α-HH microsphere is structurally characterized by TEM analysis and presents a dense structure with stacked nanorods

(Fig. 1d). Selected area electron diffraction (SAED) was performed in different areas (from 1 to 4) of the microsphere and the

results are shown in Fig. 1e. The single crystal-like pattern with bright and scattered spots gives evidence of the

crystallographically equivalent and orientation relationship between the subunits in the selected area. The consistent patterns

taken from the different areas further demonstrate that the subunits of the microsphere are well aligned in the same

crystallographic fashion, which confirms the formation of the mesocrystal structure (Fig. 1c). The appearance of some discrete

diffraction spots and arcs in image 4 is caused by the loss of some crystal water due to the long-term electron irradiation. As

shown in Fig. 1f, the crystal lattice of α-HH (space group I 121, lattice parameters a = 12.034, b = 6.929, and c = 12.676) is

constructed from repeating, ionically bonded SO and Ca atoms in chains of –Ca–SO –Ca–SO – along the c-axis. Herein,

each S atom is covalently bonded to four O atoms, forming a tetrahedral corner. The chain's structure may explain the 1D

growth of nanorods along the c-axis. All the information demonstrates that the microsphere is an α-HH mesocrystal with

subunits oriented towards the (001) direction.

Orientation evolution with the growth of subunits

To investigate the formation mechanism of the mesocrystal structure, time-dependent experiments were conducted and the

morphological change was firstly revealed with FESEM images. At the early stage of 5 min, the initial aggregate is loosely

organized by irregularly-shaped nanoparticles in a random arrangement (Fig. 2a). The nanorods, instead of the irregular

subunits, serve as the building blocks to construct the microspheres at 30 min (Fig. 2b). The formation of nanorods is possibly

attributed to the fusion or growth of the early formed domains. The microspheres are still incompact and many holes and

gaps are visible at this time. After 3 h of reaction, an anisotropic microsphere with its subunits tightly aligned side by side is

observed, indicating the formation of mesocrystals (Fig. 2c). When the reaction time is prolonged to 6 h, the mesocrystals

become more compact, leaving less and smaller holes on the surface (Fig. 2d). With a further increase to 12 h, the surface of

the mesocrystals becomes entirely dense (Fig. 2e). Some particles exhibit a hexagonal outline, implying the possibility of the

full development of subunits. According to the particle size distribution curves, the mesocrystals keep growing after the self-

assembly process. The average size of newly formed aggregates is only 1.78 μm, which steadily increases to 2.06 μm at 30

min (Fig. 2f). As the reaction time increases to 1 h, the particle size becomes larger (2.24 μm) and more uniform. At 3 h, the

mesocrystals have a surface weighted mean (D) of 2.72 μm, slowly increasing to 2.93 μm at 6 h and finally reaching 3.16 μm

4 4 427

28

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at 12 h. With the extension of the reaction time, the microspheres increase gradually in particle size and achieve a denser

surface.

Fig. 2 FESEM images of α-HH microspheres obtained at 5 min (a), 30 min (b), 3 h (c), 6 h (d) and 12 h (e) to show the shape evolution of

the subunits. Particle size distribution of the microspheres obtained at different reaction times to verify the crystalline growth of the subunits with

time (f).

TEM analysis was then applied to investigate the evolution in the microstructure. The preliminarily formed microsphere is an

aggregate with a loose structure (Fig. 3a). The α-HH domains (marked by white arrows) in the aggregates are interspaced by

its amorphous phase or organic compounds, as shown in the HRTEM image (Fig. 3b). The discrete but random electron

diffraction spots indicate that the subunits have different orientations (Fig. 3b insert). After 2 h evolution, a dense microsphere

appears with some rod-like nanoparticles on the edge (Fig. 3c). The intact and parallel lattice fringes imply the crystallization

and development of the α-HH domains (Fig. 3d). The well-organized spot pattern indicates that the subunits align themselves

towards the same direction during the growth stage, although there is still some lattice mismatch in a narrow range suggested

by several spots with arcs (Fig. 3d insert). Fig. 3e shows some of the microspheres formed at 3 h, confirming that the α-HH

microspheres are composed of rod-like nanoparticles. The appearance of periodic diffraction spots demonstrates that the

subunits adjust into a perfect crystallographic fashion and form a highly ordered microsphere, diffracting like a single crystal

(Fig. 3e insert). The result is in good agreement with Fig. 1e, confirming the formation of the α-HH mesocrystals. The

orientation of the α-HH mesocrystals proceeds with the further growth of subunits, which happens after the assembly stage

instead of during the assembly stage.

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Fig. 3 TEM, HRTEM and SAED (insert) images of the microspheres obtained at 5 min (a and b) and 2 h (c and d), TEM and SAED (insert)

images of the microspheres obtained at 3 h (e), and TEM image of microspheres obtained at 30 min (f), illustrating the structure evolution of the

microspheres into a mesocrystal.

We applied ultramicrotomy to obtain the cross-section of the particles formed at 30 min and core–shell structures were

observed (Fig. S2†). From Fig. 3f, it is obvious that the subunits in the outer sphere (indicated by white arrows) transform into

rod-like nanoparticles in advance of those in the inner sphere. The core–shell structure probably results from the different

shapes and order degrees of the subunits.

More specific evolution is presented in the FESEM images in Fig. 4. At the early stage of 5 min, the spherical aggregates

are entirely composed of irregular nanoparticles, which are loosely organized in a microsphere (Fig. 4a). After 30 min, the

subunits in the outer sphere develop into a rod-like shape with a length of 200 ± 23 nm and the thickness of the shell part is

about 500 ± 36 nm (Fig. 4b). More subunits change into nanorods as the reaction time prolongs to 1 h and the shell thickness

increases to 800 ± 51 nm (Fig. 4c). With an increment of the reaction time to 2 h, the nanorod-comprised shell has a width of

1.2 ± 0.05 μm and takes a dominant place (Fig. 4d). Until 3 h, the growth of the irregular nanoparticles is completed and the α-

HH microspheres contain only nanorods arranged in the same crystallographic direction (Fig. 4e).

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Fig. 4 FESEM images of the cross-sections of α-HH microspheres with different reaction times: 5 min (a), 30 min (b), 1 h (c), 2 h (d) and 3

h (e), and zeta potential of the microspheres at 5 min, 30 min, 1 h, 3 h, 6 h and 12 h (f) to demonstrate the increase in the shell thickness of the

microspheres and the gradual extraction of EDTA from the microspheres.

During the subunit evolution, the EDTA in the microspheres is gradually excluded, which is verified by TG analysis (Fig. S3†).

Upon completion of the self-assembly at 5 min, the content of EDTA in the microspheres is 13.06 wt% according to the weight

loss in the TG curve, which shows a rapid decrease to 11.93 wt% at 1 h. When the mesocrystals form, the α-HH microspheres

contain only 9.46 wt% EDTA. In the subsequent stage, the extraction of EDTA remains steady, gradually dropping to 6.25 wt%

at 6 h. Finally, the content is only 2.07 wt% at 12 h, enabling the crystalline fusion of subunits in the mesocrystals. The

exclusion of EDTA is further confirmed by the change of the zeta potential (Fig. 4f), since the negative surface charge comes

from the COO– group of EDTA. In the first hour, the zeta potential of the microspheres rapidly increases from −42.35 mV to

−34.37 mV. A continuous increase of zeta potential appears after the formation of the mesocrystals, rising from −27.68 mV at

3 h to −15.49 mV at 6 h and finally to −4.11 mV at 12 h.

Effect of EDTA

The synthesis of α-HH in ethylene glycol–water media in the presence of Na EDTA involves the following reactions:

2Cl + Ca + EDTA + 2Na + 2H → [Ca − EDTA] + 2Na + 2Cl + 2H (1)

EDTA + jH → HjEDTA (1a)

[Ca − EDTA] + H → [CaHEDTA] (1b)

Ca − EDTA′ + SO + 2Na + 0.5H O → CaSO ·0.5H O ↓ + EDTA′ + 2Na (2)

2

− 2+ 4− + + 2− + − +

4− + 4−j

2− + −

42− +

2 4 2+

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The EDTA molecule contains four carboxyl groups, and thus Ca and EDTA can form Ca–EDTA complexes in solution

(eqn (1)). The pH affects the ability of EDTA to chelate Ca and the forms of the complex as shown in eqn (1a). Ca–EDTA′

and EDTA′ in eqn (2) denote all the possible intermediate complex species.

The influence of EDTA ions on the reaction kinetic process is illustrated by detecting the concentration change of lattice

ions. As shown in Fig. 5, the Ca concentration drops sharply from 40 mM to 30.51 mM in the initial 2 min and decreases

continuously to 15.45 mM at 5 min, indicating that 61.37 wt% Ca ions are consumed in the nucleation and self-assembly

stage. The Ca concentration experiences a gentle decrease to 11.47 mM at 1 h and reaches 9.12 mM at 3 h when the α-HH

mesocrystal forms. The 15.83 wt% decline of lattice ions is responsible for the obvious increase in the particle size of the α-

HH microspheres (Fig. 2f). The consumption of Ca ions is relatively slow after 3 h and the concentration finally reduces to

6.23 mM at 12 h. Similarly, the concentration of SO ions at 5 min, 3 h and 12 h is 14.09 mM, 8.35 mM and 5.20 mM,

respectively (Fig. S4†). In total, 84.43 wt% Ca ions participate in the α-HH synthesis. It is inferred that 61.37 wt% Ca ions

are consumed at a fast rate in the nucleation–assembly stage and the remaining 23.06 wt% are responsible for the subunit

growth at a slow rate.

Fig. 5 Concentration change of Ca ions in the reaction solution along with the reaction time showing the consumption of Ca ions at

different reaction stages of the α-HH microsphere formation and evolution.

In solutions with different pH values, EDTA can be present in seven forms: H Y , H Y , H Y, H Y , H Y , HY , and Y

(where Y = EDTA). The most negative anions like Y are the ligand species with the strongest complexing ability and the

stability of the complex improves with the increasing pH value. At pH above 7, the anions HY and Y predominate in the

solution and Ca ions are not easily released from the complex. The pH value remains stable at ∼6 during the α-HH

synthesis, enabling the slow and steady release of Ca ions. As reported elsewhere, the stoichiometry values of Ca

bonding to EDTA in solutions with pH 6 are 0.97–1.04. In our work, 8.7 mM EDTA is added to 40 mM Ca precursor

solution, and thus about 23.0 wt% Ca is excluded by EDTA from the nucleation and self-assembly stage and then is

released to supply the crystalline growth, which is consistent with the change of Ca concentration.

The EDTA ions in the Ca and SO precursor solutions play different roles in the formation process of the α-HH

microspheres. As reported in our previous work, only needle-like particles were obtained without adding EDTA to both

precursor solutions. As shown in Fig. 6a, when EDTA is only added to the SO precursor solution, the final particles are

composed of several small spheres with an irregular outline. The EDTA ions in the Ca solution have the ability to chelate

Ca ions and decrease the number of the as-formed α-HH nuclei due to the reduced initial supersaturation, avoiding the

ultrafast assembly forming disordered aggregates. When EDTA is only added to the Ca precursor solution, the final particles

precipitate in a kind of spherical shape, but with an uneven surface (Fig. 6b). The EDTA ions in the SO solution guide the

2+ 2−

2+ 29

2+

2+

2+

2+

42−

2+ 2+

2+ 2+

62+

5+

4 3−

22− 3− 4−

30 4−

3− 4−

2+ 31

2+ 2+

32 2+

2+

2+

2+42−

3342−

2+

2+

2+

42−

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ordered and steady assembly of the α-HH nuclei to guarantee the spherical outline and smooth surface of the final particles.

When EDTA is added to both Ca and SO precursor solutions, uniform and intact α-HH microspheres can be achieved

(Fig. 2c). The EDTA in the SO solution guarantees the assembly process to be well-organized in the initial stage, while

EDTA in the Ca solution chelates Ca ions to form Ca–EDTA complexes to decrease the initial supersaturation and release

Ca ions to supply the subsequent growth of subunits.

Fig. 6 FESEM images of α-HH microspheres formed with different EDTA addition modes: added only to SO precursor solution (a) and

added only to Ca precursor solution (b) to indicate different functions of EDTA in the crystallization process.

Mechanism

The reported microspheres commonly have a disordered structure or an ordered structure but in a radial arrangement.

Moreover, the subunits of the microspheres usually have an irregular shape, since subunits with a rod-like shape easily

constitute particles with a shuttle-like shape. It is a unique demonstration of this work in obtaining microspheres composed

of rod-like subunits with a parallel arrangement. The formation stages of a microsphere are shown in Fig. 7. In the initial stage,

the mixing of two precursor solutions triggers numerous α-HH nuclei and they start to assemble into microspheres with the

help of free EDTA ions to obtain the minimum free energy. After the completion of self-assembly, a loosely structured

microsphere forms with subunits in irregular shape. The following evolution shows the underdeveloped α-HH nuclei changing

into nanoparticles by crystalline fusion or partial dissolution–recrystallization with the exclusion of EDTA. Meanwhile, the

Ca ions released from Ca–EDTA complexes and the free SO ions in solution also supply the growth of α-HH

nanoparticles in the forms of ions or clusters (Fig. S5a†). The subunits in the microspheres gradually modify their irregular

morphology into a regular rod-like shape from the surface layer to the interior part. A short-lived core–shell structure appears

due to the difference in the subunit shape and arrangement (Fig. S2†). The disordered core shrinks with the growth of

subunits until the full development of the mesocrystal structure. The orientation of the α-HH nanorods gradually optimizes

along with the steady growth of the subunits. When the mesocrystal structure forms, the α-HH microspheres are completely

constructed from uniform rod-like subunits arranged in the same crystallographic orientation (Fig. 1). The EDTA interspaced in

the microspheres are considered as the orientation force for the rod-like subunits. EDTA has four carboxylate groups and two

are used in the Ca–EDTA interaction. The other two respectively serving as the free hydrogen bonding donor (hydroxyl) and

acceptor (carboxylate) groups can interact with the nearby EDTA. The intermolecular hydrogen bonds align EDTA side-by-

side to form a well-ordered organization, which accounts for the orientation of the α-HH subunits due to the electrostatic

interactions between the carboxylate groups and Ca ions (Fig. S5b†). Since EDTA is a strong chelator of many metal

ions, this strategy is readily extended to other metals, metal oxides and mineral systems for mesocrystal formation.

2+42−

42−

2+ 2+

2+

42−

2+

34,35

36

37

38

2+42−

2+ 39,40

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Fig. 7 Schematic illustration of the formation process of microsphere mesocrystals: crystal structure evolution inside the microsphere.

Conclusions

The present study unfolds a picture of mesoscopic structure evolution and paves an alternative way for mesocrystal formation.

α-HH spherical mesocrystals with different top and side views are composed of nanorods aligned parallel to each other along

the c-axis. The orientation of the subunits proceeds with their shape change from irregular to rod-like resulting from crystalline

growth. The ordered organization of EDTA interspaced in the microspheres guides the arrangement of the α-HH subunits. A

core–shell structure caused by the distinction in the shape and order degree of the subunits appears in the intermediate stage

for the reason that the growth and orientation proceed gradually from the exterior towards the interior. The shell thickness

increases with reaction time and a solid mesocrystal forms finally instead of a hollow one since the supply of lattice ions is

sufficient during the formation process. This work sheds light on the importance of the mesoscopic process and deepens the

understanding of the mesocrystal formation mechanism.

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

We greatly appreciate the financial support from the National Key Research and Development Program of China (Grants

2016YFB0301800) and the National Natural Science Foundation of China (Project 21176219).

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4/2/2020 Formation of spherical calcium sulfate mesocrystals: orientation controlled by subunit growth - CrystEngComm (RSC Publishing)

https://pubs-rsc-org.ezp.lib.rochester.edu/en/content/articlelanding/2019/CE/C9CE00982E#!divAbstract 12/15

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Footnote† Electronic supplementary information (ESI) available: XRD pattern, TG curve, additional TEM image and concentration analysis of lattice ions.

See DOI: 10.1039/c9ce00982e

This journal is © The Royal Society of Chemistry 2019

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Submitted25 Jun 2019

Accepted11 Sep 2019

First published11 Sep 2019

CitationCrystEngComm, 2019,21, 5973-5979

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4/2/2020 Formation of spherical calcium sulfate mesocrystals: orientation controlled by subunit growth - CrystEngComm (RSC Publishing)

https://pubs-rsc-org.ezp.lib.rochester.edu/en/content/articlelanding/2019/CE/C9CE00982E#!divAbstract 13/15

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4/2/2020 Formation of spherical calcium sulfate mesocrystals: orientation controlled by subunit growth - CrystEngComm (RSC Publishing)

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4/2/2020 Formation of spherical calcium sulfate mesocrystals: orientation controlled by subunit growth - CrystEngComm (RSC Publishing)

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