CO2-Responsive Switchable Solvents to Induce Self-assembled

Subscriber access provided by WEBSTER UNIV

Article 2

CO-Responsive Switchable Solvents to Induce Selfassembled Crystallization and Phase Control of CaCO

3

Benoit Rugabirwa, David Murindababisha, Yin Li, Yanzhen Hong, Yuzhong Su, Hongtao Wang, and Jun Li ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b06658 • Publication Date (Web): 21 Feb 2019 Downloaded from http://pubs.acs.org on February 26, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 26 1 2 3 4 5 6 7 8 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 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Sustainable Chemistry & Engineering

CO2-Responsive Switchable Solvents to Induce Self-assembled Crystallization and Phase Control of CaCO3 Benoit Rugabirwa, David Murindababisha, Yin Li, Yanzhen Hong, Yuzhong Su, Hongtao Wang, Jun Li* Department of Chemical and Biochemical Engineering, Department of Chemistry, College of Chemistry and Chemical Engineering, National Engineering Laboratory for Green Chemical Productions of Alcohols, Ethers and Esters, Xiamen University, 422 South Siming Road, Xiamen 361005, Fujian Province, China. Corresponding Author: [email protected] (J.L)

ABSTRACT We propose a novel and cyclic synthetic approach for controlling crystal polymorphs of CaCO3 by using green CO2-responsive switchable solvents which acted as both the CO2 capturer for the carbonate source and the polymorphisms director. Five solvents were employed, and various reaction conditions such as calcium resources, calcium concentration, reaction temperature, and reaction time were investigated. Results show that this developed framework permits to produce any crystalline CaCO3 phases including metastable vaterite and aragonite in pure phases by selecting a suitable solvent and adjustment of the reaction conditions. Furtherly, the mechanism study demonstrates that the solvents attach on the surface of the primary nanoparticles to selectively control and direct the growth of any specific polymorph phases. Eventually, the nuclei are self-assembled into an oriented geometry allowing the growth and stability of specific crystals; as such, spherical vaterite; rods and shuttle-like aragonite crystals can be obtained. This new configuration would be an appropriate and an efficient method to apply to 1

ACS Paragon Plus Environment

ACS Sustainable Chemistry & Engineering 1 2 3 4 5 6 7 8 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 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

large-scale production, therefore, a promising process attributed to complete solvent recovery and regeneration of the initial reactants, thus being an environmentally risk-free route. KEYWORDS: switchable solvent; CO2 capturer; polymorph director; vaterite; aragonite.

INTRODUCTION Polymorphism control is an essential and unavoidable aspect in the precipitation-crystallization of CaCO3; to some extent, because of an oriented interest to synthesize a particular polymorph or because of promoting a number of particular properties of crystallites for further potential applications.1 Recently, CaCO3 materials are subjects of advanced technology applications; for example, in thermal energy storage and solar-thermal conversion because of high thermal conductivity, better durability, and thermal stability among others in contrast to organic counterpart.2 Particularly, vaterite particles are recognized as CaCO3 materials of interest because of desired properties (high loading capacity, porous structure and high surface area)3 compared to other anhydrous phases. Previously, Lybaert et al. 4 fabricated CaCO3 engineered with immune stimulating and activating cues within the inner core and outsider shell matrix, respectively; for the anticancer vaccination use. Similarly, smaller sized-vaterite microspheres (average diameters of 0.8 to 5 µm) have demonstrated high loading capacity useful as vaccine adjuvants;3 and silver nanoparticles (nAg)/vaterite composite was successfully studied for the antibacterial paint development.5

Aragonite exhibits superior property suitable as a filler material6 over

thermodynamically stable calcite crystals; as such, aragonite was studied to induce B-type carbonate apatite for biomedical applications as a scaffold for bone tissue regeneration.7 In this 2


Page 2 of 26

Page 3 of 26 1 2 3 4 5 6 7 8 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 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


context, the fabrication of advanced materials with a diversity of structures or extraordinary properties is essential for the demand of the growing technology which definitely justifies a continuous research interest for the mineralization of CaCO3 materials; importantly they are cheap and are fashioned straightforward to better suitability of a selected application. The precipitation of CaCO3 polymorphs suffers from well-recognized limitations which include the selectivity and re-occurrence of the polymorphs, stabilization of metastable phases as well as controlling the crystal size and morphology.8 Advanced techniques and synthetic platforms have been proposed to control the polymorphisms of CaCO3;9 Among them, the biomimetic precipitation is well-known for simplicity to control the polymorphisms, morphologies and sizes of the particles by mixing CO32- and Ca2+ resources in the presence of soluble organic compounds.10 However, this technique suffers from recycling of these biomimetic agents and accumulation of salts wastage. CO2 bubbling reaction of slaked lime is the common route for industrial production and was reported for limitations to control the polymorphisms because it could mainly produce calcite11 even in the presence of an additive such as dodecanoic acid;12 vaterite and calcite could be also obtained in the presence of 2-amino 2-(hydroxymethyl)-1,3propanediol and carbonic anhydrase enzyme; and aragonite could be obtained if Mg2+ ions were added in the reaction under the same experimental conditions.13 Other synthetic methods include microwave which could produce a mixture of calcite and vaterite at lower power and a ratio of ethylene glycol: water (EG/water 1:9); pure vaterite could be obtained with increased EG/H2O ratio (9:1) at increased power14 but disfavored aragonite formation; nevertheless, the technique is simple for controlling particle sizes.8 Gas-solid carbonation reaction would be an alternative freerisk industrial method for producing CaCO3; however, the resulting product turns to be calcite and 3



vaterite, and the reaction achieved low conversion efficiency. Recently, we demonstrated an ecofriendly approach to produce vaterite with a high conversion efficiency using a high pressure gassolid reaction, but could not produce aragonite.15 Conclusively, these methods are costly, energyconsuming and yet raise environmental concerns.16 On one side, they are costly because of a large demand of expensive additives/solvents and because of many templates needed in the procedure formulation; on another side because of energy associated with a recycling process of the additives/solvents and surfactants. Furthermore, the nature of additives could negatively affect the biotic and abiotic environments with severe risks. From this perspective, looking into possible mitigation strategies to develop a green and sustainable chemical process would be of a great contribution for both applied and researcher’s communities. The challenging aspect for sustainable use of these structural directing agents is directly attached to their limit to manufacture all CaCO3 polymorphisms in a continuous process, thereby increasing the production cost. For example, solvents are extensively employed in the industrial sector such as in the extraction processes; however, the removal and recycling of these solvents account considerable drawbacks.19, 20 Definitely, the shortcoming of solvents recovery is attributed to their properties (volatility, flammability, miscibility et al.)20,

21

which increase the cost and wastage during the

recycling process; in some cases, many types of solvents ought to be introduced at different separation stages. Recently, switchable hydrophilicity solvents (SHS) have continuously attracted countless studies in the extraction field due to their properties of being miscible and immiscible in water when added and after removal of CO2, respectively.22 In this regards, they are easily separated from the extracting phase with a recovery possibility. N,N-dimethycyclohexylamine (DMCHA), a switchable solvent has been employed in the extraction of essential oils.23, 24 Lestari 4


Page 4 of 26

Page 5 of 26 1 2 3 4 5 6 7 8 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 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


et al. demonstrated the recovery of DMCHA by a combination of the addition of N2 and boiling methods;21 however, the recovery achieved a low efficiency (only 24%). Now, to select an appropriate organic matrix to induce both the phase change and structural modification of all CaCO3 crystalline forms would be an ideal solution in the design of a sustainable process because of simultaneous production of materials, phase-controlling process, and recovery-reusability of the solvent. Furthermore, achieving a high purity of the corresponding polymorphs should be addressed as well because of possible coexistence of these polymorphs as a mixture in the fine product. Notably, motivated by the above property of switchable solvents and their potential industrial application, we aimed at exploring a new manufacturing protocol of CaCO3 precipitation and crystallization solvent-based with expectation to design a continuous and cyclic process highly efficient compared to the conventional use of additives/surfactants or solvents which appear inadequate to control the polymorphisms transition and troublesome to recover from the system; moreover, switchable solvents haven’t been introduced or experimented for their potential ability as a structural controller. Herein, we examined a green route for CO2 capture and conversion to vaterite and aragonite crystals with a designed cyclic process by using a typical CO2-responsive switchable solvent DMCHA (Scheme 1) and two calcium resources (Ca(CH3COO)2 and CaCl2). The advantages of the designed protocol are, 1) DMCHA is used for CO2 absorption to produce bicarbonate source which is miscible in water, 2) the absorbed CO2 for the mineralization process produces vaterite and aragonite with DMCHA being the structure directing agent because of an amine functional group to form complex with calcium or carbonate,25 and 3) DMCHA is easily regenerated through phase change23, 26 for cyclic absorption of CO2 to ensure a promising green 5



and

continuous

process.

Besides

DMCHA,

2-

(dibutylamino)

Page 6 of 26

ethanol

(DBAE),

N-

butyldimethylamine (BDA), N-ethylpiperidine (EP) and 1,8-diazabicycloundec-7-ene (DBU) were also tested.

Scheme 1 Representation of CO2 capture and conversion to CaCO3 with different polymorphs in the presence of DMCHA with a designed continuous and cyclic process. Spheres: vaterite; cubes: calcite; rods: aragonite.

EXPERIMENTAL Materials, Preparation and Solvent Recovery. Calcium acetate (Ca(CH3COO)2 , purity ≥98.0%), calcium chloride (CaCl2 , purity ≥96.0%) and ethanol (purity ≥99%) were purchased from Sinophram Chemical Reagent Co., Ltd. (China). N,N-dimethylcyclohexylamine (DMCHA, purity 98%) was supplied from Aladdin Industrial Corporation. 2-(Dibutylamino) ethanol (DBAE, purity 99%) and N-butydimethylamine (BDA, purity 98%) were supplied from Energy Chemical (China). N-ethylpiperidine (EP, purity 99%) was purchased from Alfa Aesar (China), and 1,8diazabicycloundec-7-ene (DBU, purity ≥99%) from Chemxyz (China). CO2 (99.99%) was supplied

6


Page 7 of 26 1 2 3 4 5 6 7 8 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 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


from Linde Gas Co., Ltd; Double distilled water was provided by the school laboratory (Xiamen University). All chemicals were used without further purification. As shown in Scheme 1, in a typical synthetic process an appropriate concentration (0.5-2 M) of each calcium source solution (Ca(CH3COO)2 or CaCl2) in10 ml was added to a readily prepared suspension solution of 10 ml (1:1 volume ratio) of CO2-captured water/DMCHA (as a typical switchable solvent; the same working protocol was also applied for other switchable solvents). The obtained precipitate was stirred under the working temperature between 40 to 90 oC for contact duration between 30 and 240 min. At the end of the reaction, the resulting precipitate was recovered by centrifugation, and the solution was further treated with about 5 ml Ca(OH)2 (0.5-1M) as shown in the scheme 1 to regenerate the corresponding reactants and maximize the recovery of dissolved solvent in the aqueous phase. The precipitated CaCO3 powder was then washed three times with distilled water. Ethanol was latterly used to facilitate a fast drying at 80 oC.

Powder Characterization. Powder X-ray diffractometer (XRD, Rigaku Ultima IV, Japan) with Cu Kα radiation was used for phase detection; analysis of the XRD patterns was carried out using Highscore plus software. Images of the samples were obtained by scanning electron microscopy analysis (ZEISS Sigma, JEOL JFC-1600 instrument). Thermogravimetric analysis (TGA) was carried out on a SDT, Q600 instrument at a heating rate of 5 °C min-1 under air. The Fourier transform infrared (FTIR) spectroscopy on Nicolet 6700 FT-IR spectrophotometer by using KBr pellet in range of 4000-400 cm-1 was used to investigate the chemical nature of the particles. The pore volume, Brunauer-Emmet-Teller (BET) specific surface and Barrett-Joyner-Halenda (BJH) pore size of the powders were determined by the nitrogen adsorption-desorption measurement (ASAP 2020 7



Page 8 of 26

Micrometrics, USA). In situ FT-IR (Thermo Fisher IS50) enabled to study the online crystallization process. RESULTS AND DISCUSSION Control of CaCO3 Polymorphs by Using DMCHA. Experimental conditions and the as-produced crystal formulations are shown in Table 1. The crystal compositions from XRD and SEM imaging of some representative samples are shown in Figure 1.

Table 1 Experimental conditions and results of precipitation of CaCO3 polymorphs using DMCHA Sample

[Ca2+]

t

T

Phase composition (%)

(M)

(min)

(oC)

Vaterite

Calcite

Aragonite

S1

0.5

60

40

100.0

0.0

0.0

S2

1.0

60

40

100.0

0.0

0.0

S3

1.5

60

60

100.0

0.0

0.0

S4

2.0

60

60

99.7

0.3

0.0

S5

1.0

60

60

100.0

0.0

0.0

S6

1.0

90

60

99.6

0.0

0.4

S7

1.0

120

60

97.6

0.0

2.4

S8

1.0

120

90

99.6

0.4

0.0

8


Page 9 of 26

S9

1.0

240

60

92.8

0.0

7.2

S10

1.0

780

60

8.0

0.0

92.0

S11

1.0

1080

60

0.2

0.0

99.8

S1*

1.0

60

40

100.0

0.0

0.0

S2*

1.0

60

50

55.4

44.6

0.0

S3*

1.0

60

60

0.0

96.7

3.3

S4*

1.0

60

90

0.0

100.0

0.0

S5*

1.0

120

40

5.0

0.0

95.0

S6*

1.0

300

40

0.8

0.0

99.2

S7*

1.0

540

40

0.0

12.0

88.0

S8*

1.0

720

40

0.0

100.0

0.0

*Samples prepared with CaCl2 as the calcium precursor; otherwise Ca(CH3COO)2 was applied. T, reaction temperature; and t, reaction time.

c

a

a: aragonite c: calcite v: vaterite

S*6 S*4

va a v

vv

intensity (a.u)

a a a a a a a a v aa vv cc c c c v v v

intensity (a.u)

1 2 3 4 5 6 7 8 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 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


a aa

aa

aa

a S11

v c

S*2

v

S10

v

S8 S1

S*1 10

20

30

40

50

60

70

10

2 theta (degrees)

20

30

40

50

2theta (degrees)

9


60

70


Figure 1 XRD patterns and SEM images of typical samples: (a) S1*; (b) S2*; (c) S4*; (d) S6*; (e) S1; (f) S8; (g) S10, (h) S11

Table 1 clearly shows that precipitation of CaCO3 from different calcium precursors resulted in various phase compositions of the crystals. If CaCl2 is used, the powder existed in pure phase 10


Page 10 of 26

Page 11 of 26 1 2 3 4 5 6 7 8 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 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(S1*) at a lower temperature and multiphasic composition with increasing temperature from 5060 oC (samples S2*-S3*). At relatively elevated temperature (90 oC) pure calcite crystals were formed (sample S4*) which initially precipitated as unstable vaterite obtained at lower temperature. In contrast to those obtained at the temperature of 90 oC with CaCl2, vaterite particles were strongly stabilized at the same temperature if Ca(CH3COO)2 (sample S8) was used; this could be ascribed to the existence of additional acetate anions reported to have a significant role in polymorph discrimination.27-29 Anions have been investigated for their roles in CaCO3 polymorphs control and suggested to have preferential biding onto specific facets of calcium carbonate polymorphs and furtherly change the surface energy30-32 to hinder that particular polymorph transformation.28, 33 Because of acetate anions available in this system, ionic strength interaction-types are favorable to reduce the growth rate of metastable phases, thus switching the crystal facets surface energies of vaterite or aragonite to calcite is a slow driven process not observed for the CaCl2 system. For the latter, the effect of chloride ions at higher temperature are negligible so that the existing CaCO3-solvent interactions stabilizing vaterite become gradually weaker to induce a phase transformation upon extended reaction time (60 -120min, samples S1* and S5* for the obvious vaterite-aragonite transformation; 120-720 min; samples S5*-S8* for obvious aragonite-calcite transformation) or increased temperature (40-90 oC; samples S1*-S4* for apparent vaterite-calcite transformation). The effect of temperature on the phase transition is also confirmed by the SEM images (Figure 1a-c for S1*, S2* and S4*) which indicate that at elevated temperature vaterite switching phase does not pass through aragonite metastable phase rather it could directly transform to calcite. It is known that aragonite formation is favored at higher temperature6, 33 and lower pH;28 however, 11



in this study aragonite was formed at lower temperature (40 oC) via vaterite-aragonite phase transition (samples S1*, S5*, S6*). Temperature influences the phase composition; at 50 oC a mixture of vaterite and calcite was precipitated (sample S2*), while at 60 oC calcite-aragonite mixture was obtained (sample S3*).

In other word, vaterite could be unstable at higher

temperature if CaCl2 is used. This observation would suggest that elevating the temperature above 60 oC promoted a phase transformation of vaterite to calcite because of apparent deprotonation of DMCHA.21 At a high-temperature bicarbonate ions are more mobile to react within the bulk solution which led to calcite formation.34 However, as mentioned, if Ca(CH3COO)2 is the source, only a tiny vaterite could be converted to aragonite and calcite with rising temperature from 60 oC

to 90 oC (samples S7 and S8), respectively; supporting again the so-observed stability enforced

by calcium acetate-solvent system. When the concentration of Ca(CH3COO)2 was varied from 0.5 to 1.5M at 60 oC and reaction time of 60 min, all the samples (S1-S3) existed in pure vaterite phase (JCPDS card no. 24-0030); vaterite fabricated from CaCl2 at concentrations 1M (S2*-S4*) partly or completely transformed to calcite, supporting again the absence of a stabilizing effect of chloride anions on vaterite facets. Changing calcium acetate to higher concentrations (2.0 M) even at 60 oC resulted in a tiny calcite precipitation (S4); expectedly, increasing Ca2+ concentrations could create a higher supersaturation which could result into calcite precipitation in the first place.9 The results displayed in Table 1 demonstrate, however, that vaterite is still stabilized indicating that acetate ions in addition to DMCHA-CO32- interactions could slow down the diffusion in the bulk inhibiting the nuclei growth to promote vaterite stabilization. Note that along with the experimental findings

12


Page 12 of 26

Page 13 of 26 1 2 3 4 5 6 7 8 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 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(not shown in Table 1) we observed that [Ca2+] >1.0 M (CaCl2) resulted in calcite, suggesting a higher supersaturation was reached at 1.0 M. The influence of contact duration on the precipitation of CaCO3 crystals was investigated for both calcium precursor-systems. For Ca(CH3COO)2 if other parameters were fixed and the synthesis duration was increased from 90 min to 240 min (samples S6, S7, and S9), the vateritearagonite transformation could occur; at 240 min vaterite crystal were stabilized at 92.8%, and 7.2% aragonite content was formed. As it is mentioned above, the factors that govern the longterm stabilization of vaterite for Ca(CH3COO)2/DMCHA platform could be attributed to additional acetate anions coupled to the charged tertiary amine of protonated DMCHA which could attach on the specific plane to direct vaterite formation by altering the activation-energy to control the nucleation of the metastable phase. Therefore, the transformation of vaterite crystals to aragonite then to calcite crystalline forms is retarded and allowing step-by-step phase change monitoring. However, extending the synthesis duration to 13 h aragonite content of 90.0% was obtained, and almost pure aragonite was achieved at 18 h reaction time (samples S10, S11). Theoretically, it could be said that in the Ca(CH3COO)2/DMCHA system the crystallization pathway is controlled by kinetic steps which control the activation-energy associated with nucleation and growth of a particular phase.30,

35

For the CaCl2/DMCHA system, a vaterite-aragonite transition was easily

achieved at 40 oC: aragonite content increased from 0 to 95.0% when extending the reaction time from 60 min to 120 min; almost pure aragonite was obtained at 300 min. Further increase of the reaction time to 540 min, however, 12% calcite was found from the transformation of aragonite to reach 100.0% calcite after 720 min (sample No.S8*).

13



Page 14 of 26

From these observations we can clearly see that, under a certain scope of experimental conditions (adjustments of time and temperature) controlling CaCO3 polymorphism could be easily achieved by DMCHA system and fairly applied for both calcium sources (CaCl2 and Ca(CH3COO)2). For further characterization, the infrared measurements of samples S5 and S10 (Supplementary Figure S1A) peaks at 700, 712, 852 and 1083 cm-1 are assigned to aragonite. From the same figure, it could be seen that the characteristic peak at 744 cm-1 which serves to distinguish vaterite from a composition mixture of vaterite/aragonite decreases while peaks at 700 and 712 cm-1 increase,36 suggesting the vaterite-aragonite transition. A complete transformation of vaterite to aragonite was achieved for 18 h and the FT-IR measurements displayed only the characteristic peaks of aragonite. The TG analysis of powders S5 and S10 (Supplementary Figure S1B) revealed that the main decomposition process began at around 590 oC and reached the greatest at a temperature of 780 oC with a weight change of -41.4%. This result is in accordance with literature report.37 As for the BET measurements (Table 2), the surface area of sample S5 is 69.6 m2/g, and is reduced to 19.3m2/g for sample S11 after 18 h corresponding to a transformation of pure vaterite to pure aragonite phase. Table 2 BET measurements of sample Sample

Surface area

Pore volume

Pore size

(m2/g)

(cm3/g)

(nm)

S5

69.6

0.23

10.1

S11

19.3

0.13

22.7

S1*

30.9

0.2

16.0

14


Page 15 of 26 1 2 3 4 5 6 7 8 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 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


S6*

17.9

0.1

13.4

S8*

9.1

0.05

20.8

Mechanism Study. The formation mechanism of vaterite microspheres can be explained with help of Schemes 1 and 2, from which, three reactions (1-3) occur in the cyclic system. Firstly, DMCHA reacts with CO2 and water to form a protonated amine group of the solvent (DMCHAH+) with HCO3- anions in the aqueous solution (Eq. 1). Then [DMCHAH+][HCO3-] reacts with Ca2+ (from Ca(CH3COO)2) to form vaterite CaCO3(Eq. 2), which was revealed as a fast and almost complete reaction by both the experimental study ([Ca2+] change measurement in the reaction solution) and theoretical study (Supplementary Section S1). The fast reaction initiates nucleation with the pre-nucleation clusters (Scheme 2a; Supplementary Figure S2a) crystallizing into plate-like structure precursors of vaterite under the mediation of [DMCHAH+] which attaches on the surface of the nuclei and orienting their attachments. Subsequently, the precursors begin to assemble into building blocks of vaterite particles that have poor crystal structures at relatively short reaction times (5-40 min) (Scheme 2b; Supplementary Figure S2b-f); ultimately those poor crystals agglomerate into mature microsphere crystals (Scheme 2c; Supplementary Figure S2g-h) under further prolonged reaction time (60-90 min) due to the nucleation and growth of vaterite. DMCHAH+ in the solution restricts the crystallization growth to reach the mature spherical particles (1.0-2.2 µm). These particles can transform into rod-like structures (6-8 µm) at 120 min indicating vaterite-aragonite transition (Scheme 2d; Supplementary Figure S2i), and subsequently disintegrate into fragments which transform to calcite over about 18 h (Supplementary Figure S2j) via dissolution-recrystallization process. The in situ infrared kinetic study (Supplementary S3) also revealed that, upon immediately mixing the reacting solutions (1-60s), initial precipitates with foam-like white bubbles were produced without exhibiting distinct absorbance bands, suggesting the 15



formation of poorly ordered precipitates for nucleation. As the reaction progressed from 5 to 240 min, a rapid increase of absorbance bands corresponding to the vaterite crystal growth stage was observed, where the crystal underwent morphological and size changes. At 12 h reaction time the peaks at 745 and 849 cm1 started

to decay, suggesting vaterite transition to aragonite. Evidently, the crystallization of vaterite started

from the nucleation stage (a fast and short stage), and then experienced the crystal growth (a long stage), and finally occurred the phase-transformation. + CO2 + H2O

+ N

+ N

H HCO3-

+ N

+ CaCl2/Ca(Ac)2

+ N H Ac /Cl + Ca(OH)2

H Ac-/Cl-

N

H HCO3-

1 2 3 4 5 6 7 8 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 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(1)(1)

+ CaCO3 +CO2+ H2O (2)(2)

N + Ca(Ac)2/CaCl2 +H2O

(3) (3)

Scheme 2 mechanism pathway of polymorphs formation: (a) clusters precursors of vaterite, (b) assemblage of clusters into block of immature vaterite crystals, (c) mature vaterite, (d) opening of mature crystal to form rod-like structure.

16


Page 16 of 26

Page 17 of 26 1 2 3 4 5 6 7 8 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 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Solvent Recovery. DMCHA has a relatively low solubility in water (18 g/L)26 and many studies demonstrated some possibilities for its recovery, for example, 24%21, 64.8%23 and 83%39 by heating, N2 bubbling or combination of both40. In this context, the precipitation-crystallization of CaCO3 in the DMCHA system allows a restoring process of the solvent (> 95.0%) to its native hydrophobic state (Supplementary Figure S4A) for further cyclic CO2 absorption; thus, the reaction itself is a chemically induced technique. Note that the hydrophobic DMCHA phase could be observed since [DMCHAH+][HCO3-] could switch back to its initial state under the heating (Eq.1). To further extent, to ensure effective solvent recycling and avoid undesirable salt accumulation in the system, the aqueous phase was treated with Ca(OH)2 (Eq.3) resulting in the formation of the initial soluble calcium source (Supplementary Figure S4B) and deprotonated DMCHA ([DMCHAH+][HCO3-] switches back to its immiscible state on the top layer whereby it is easily collected from the water solution); and thus, becoming a sustainable continuous process as shown in Scheme 1. It should be noted that this technique is simple, effective, energy-conserving, and an environmentally risk-free and cyclic process; the small amount of dissolved DMCHA in the system does not affect the process; however, the fresh water formed in the process of DMCHA regeneration (Eqs. 2,3) should be partly evaporated in time to avoid any water accumulation. Furtherly, FT-IR analysis (Supplementary S5) of a washed sample indicated no solvent adsorbed on the powder surface after washing thus, no apparent solvent loss. Extension of the Protocol to Other Switchable Solvents. The investigation was extended by exploring other amine/amidine-contained switchable solvents as indicated in Table 3. Table 3 CaCO3 phase compositions influenced by other switchable solvents Solvent

pH

Time

Temp

Calcite Vaterite Aragonite

17



Initial Final DBU

11

8

DBAE

13

9

BDA

(h)

(oC)

(%)

(%)

0.5

40.0

0.0

99.3

0.0

5

70.0

0.0

0.0

100.0

72

70.0

2.0

0.0

98.0

1

60.0

0.0

100.0

0.0

26

90.0

0.8

0.0

98.2

72

90.0

100.0

0.0

0.0

0.0

100.0

0.0

13.5

0.0

86.5

100.0

0.0

0.0

0.0

100.0

0.0

5

4.2

0.0

95.8

8

100

0.0

0.0

1 5 12

8

EP 9

60.0

12 1

11

Page 18 of 26

40.0

(%)

Note: Only the conditions suitable to precipitate or form each specific polymorph according to the nature of solvent employed were indicated. The concentration of calcium acetate was fixed to 1.0 M. It could be seen that all the investigated switchable solvents can stabilize the least thermodynamically stable phases (aragonite and vaterite). A number of functional groups of the organic matrix play a vital role in stabilizing CaCO3 polymorphs.25 In addition to amine/amidine head groups-contained switchable solvents used in the current investigation DBAE possesses hydroxyl groups (amino-alcohol) which confine with a much-stabilizing effect on the crystal 18


Page 19 of 26 1 2 3 4 5 6 7 8 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 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


formation. It was reported that hydroxyl and amine groups can form complexes with Ca2+ through chelating or coordinating interactions which can enrich Ca2+ and providing nucleation sites to stabilize the less thermodynamically stable CaCO3 forms.25,

41Other

arguments suggested that

positively charged amine groups can be adsorbed onto the surface of the building moieties (CO32ions) for CaCO3 crystallization to promote the formation of high-energy {001} facet of vaterite thereby stabilizing, and enhancing the formation of vaterite with respect to calcite.

38, 42

DBU, a

switchable-polarity solvent (SPS) has proven to bear two functional -N-based groups which offered an increased interaction to stabilize aragonite at higher concentration of calcium precursor and slightly higher temperature (70 oC). It can be suggested that the charged amidine group of the DBU after CO2 is added increased a higher dielectric polarity20,

22

which could

promote the formation of high-energy facets of aragonite, thus, aragonite could be precipitated in the first place and stabilized within 37 h reaction time. The morphology of the so-obtained aragonite as identified by SEM imaging showed to be shorter, and shuttle-like aragonite microstructures (Supplementary Figure S6a-b). These shuttle-like microstructures have long axes of 1.5-3 µm and a median diameter of 0.6-1.3 ± 0.1µm. Nevertheless, the precipitated vaterite by DBU system showed irregular morphology with a defective structure. This could mean that DBU availed the higher-energy facet of aragonite and could stabilize the nuclei by biding on the surface to prevent early nucleation of vaterite. On the other hand, if DBAE is used, irregular spherical vaterite particles with a smooth surface are stabilized for a long duration and completely transformed to rod-like aragonite particles of 6-14µm of length within 72 h (Figure S6c-d). This could be attributed to the additional hydroxyl group of DBAE which could provide additional interaction with the nuclei, this way vaterite could be stabilized up to 24 h. It is reported that 19



hydroxyl groups would establish a strong association with calcium ions to increase the supersaturation to direct the nucleation near these bound ions than in the bulk in favor of vaterite.43 Furthermore, as the synthesis duration is extended to 72 h the as-obtained aragonite rod-like structures undergo fragmentation and dissolution of fragments to form rhombohedral particles of calcite (Table 3). It could be pointed out that the fragmentation and dissolution of aragonite particles could be promoted by the energy generated by the collision of the magnetic stirrer.36 As for BDA, an aliphatic compound has shown the stabilizing effect on vaterite nuclei within a short reaction time. Vaterite can be stabilized within an hour and transformed to a mixture of calcite-aragonite (Figure S6e-f). That is to say, the phase transformation from vaterite to calcite took place via aragonite phase-transit inhibiting aragonite stabilization. On the other hand, spherical vaterite of a rough surface could be obtained if EP is a choice of solvent and could be stabilized for 3 h before converting to aragonite within 5 h (Figure S6g-h). Herein, it could be concluded that the stabilizing roles of switchable solvents on vaterite and aragonite CaCO3 could be attributed to the molecular structure, nature, and presence of a number of functional groups. This way, DBAE can exert a stronger stabilizing effect over vaterite formation than DMCHA. DMCHA has a pronounced stabilizing effect on vaterite than EP tertiary amine and BDA while heterocyclic DBU can better precipitate aragonite than vaterite in the first place. CONCLUSION The advantages of employing switchable solvents in the mineralization process of CaCO3 include the selectivity of one particular crystal phase, controlling the morphologies and sizes of the particles as well as efficient solvent recovery. We demonstrated that this can be achieved by choosing an appropriate solvent or adjusting the experimental conditions. However, none of the 20


Page 20 of 26

Page 21 of 26 1 2 3 4 5 6 7 8 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 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


switchable solvents employed in this investigation behaves in the same way because these solvents could act differently on a preference of one phase over another. This observation could be attributed to the difference in molecular structures and/or the presence of functional groups which interact with a preferential high-energy facet of a given phase resulting in its stabilization. This way, at mild experimental conditions vaterite, could be stabilized if DMCHA, DBAE, EP, and BDO are employed as the choice of solvents while aragonite could be stabilized in the first place if DBU is the choice. However, if adjusting the experimental conditions to specific parameters of time, concentration and temperature, it could be observed that all switchable solvents employed in the current study successfully controlled the polymorphism of CaCO3 from less to most stable phases. Moreover, the crystals being produced exhibited different morphologies depending on the effect of every single switchable solvent. Regular spherical vaterite particles, long rods, and shuttle-like aragonite shapes are synthesized offering a wide range of material design for the specific application. Finally, this platform addresses the environmental mitigation using CO2, providing a continuous and cyclic process; and high potential for large-scale application. ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: Details of the CaCO3 formation reaction study; FT-IR spectra and TGA graphs of selected samples; In situ IR and SEM micrographs for kinetic study; FT-IR spectra of recycled DMCHA and XRD of new formed calcium acetate. Author Contributions 21



Page 22 of 26

B.R. conducted the study, D.M. implemented some experiments. Y.L. discussed and confirmed the mechanism. Y.H. and Y.S. supplied technical support for the study. H.W. partly supervised the work. J.L. designed and supervised the work. B.R. and J.L. wrote the manuscript. All the authors approved the manuscript. ACKNOWLEDGMENT This work was supported by the Natural Science Foundation of China (21476186). REFERENCES (1) Senarathna, K. G. C.; Mantilaka, M. M. M. G. P. G.; Peiris, T. A. N.; Pitawala, H. M. T. G. A.; Karunaratne, D. G. G. P.; Rajapakse, R. M. G. Convenient routes to synthesize uncommon vaterite nanoparticles and the nanocomposites of alkyd resin/polyaniline/vaterite: The latter possessing superior anticorrosive performance on mild steel surfaces. Electrochim. Acta 2014, 117460–469, DOI 10.1016/j.electacta.2013.11.137. (2) Jiang, Z.; Yang, W.; He, F.; Xie, C.; Fan, J.; Wu, J.; Zhang, K. Microencapsulated Paraffin PhaseChange Material with Calcium Carbonate Shell for Thermal Energy Storage and Solar-Thermal Conversion. Langmuir 2018, 3414254–14264, DOI 10.1021/acs.langmuir.8b03084. (3) Jia, J.; Liu, Q.; Yang, T.; Wang, L.; Ma, G. Facile fabrication of varisized calcium carbonate microspheres

as

vaccine

adjuvants.

J.

Mater.

Chem.

B

2017,

51611–1623,

DOI

10.1039/C6TB02845D. (4) Lybaert, L.; Ryu, K. A.; Nuhn, L.; De Rycke, R.; De Wever, O.; Chon, A. C.; Esser-Kahn, A. P.; De Geest, B. G. Cancer Cell Lysate Entrapment in CaCO3 Engineered with Polymeric TLR-Agonists: Immune-Modulating Microparticles in View of Personalized Antitumor Vaccination. Chem. Mater. 2017, 294209–4217, DOI 10.1021/acs.chemmater.6b05062. (5) Sahoo, P. C.; Kausar, F.; Lee, J. H.; Han, J. I. Facile fabrication of silver nanoparticle embedded CaCO3 microspheres via microalgae-templated CO2 biomineralization: application in antimicrobial paint development. RSC Adv. 2014, 432562–32569, DOI 10.1039/C4RA03623A. (6) Yang, C.; Zhang, J.; Li, W.; Shang, S.; Guo, C. Synthesis of aragonite CaCO3 nanocrystals by reactive crystallization in a high shear mixer. Cryst. Res. Technol. 2017, 521700002, DOI 10.1002/crat.201700002. (7) Akilal, N.; Lemaire, F.; Bercu, N. B.; Sayen, S.; Gangloff, S. C.; Khelfaoui, Y.; Rammal, H.; Kerdjoudj, H. Cowries derived aragonite as raw biomaterials for bone regenerative medicine. Mater. Sci. Eng. C 2019, 94894–900, DOI 10.1016/j.msec.2018.10.039. 22


Page 23 of 26 1 2 3 4 5 6 7 8 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 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(8) Juhasz-Bortuzzo, J. A.; Myszka, B.; Silva, R.; Boccaccini, A. R. Sonosynthesis of Vaterite-Type Calcium Carbonate. Cryst. Growth Des. 2017, 172351–2356, DOI: 10.1021/acs.cgd.6b01493. (9) Svenskaya, Y. I.; Fattah, H.; Inozemtseva, O. A.; Ivanova, A. G.; Shtykov, S. N.; Gorin, D. A.; Parakhonskiy, B. V. Key Parameters for Size- and Shape-Controlled Synthesis of Vaterite Particles. Cryst. Growth Des. 2018, 18331–337, DOI 10.1021/acs.cgd.7b01328. (10) Boyjoo, Y.; Pareek, V. K.; Liu, J., Synthesis of micro and nano-sized calcium carbonate particles and their applications. Mater. Sci. Eng. A 2014, 214270–14288, DOI: 10.1039/C4TA02070G. (11) Ibrahim, A.-R.; Zhang, X.; Hong, Y.; Su, Y.; Wang, H.; Li, J. Instantaneous Solid–Liquid–Gas Carbonation of Ca(OH)2 and Chameleonic Phase Transformation in CO2-Expanded Solution. Cryst. Growth Des. 2014, 142733–2741, DOI 10.1021/cg4014834. (12) Chen, Y.; Ji, X.; Zhao, G.; Wang, X. Facile preparation of cubic calcium carbonate nanoparticles with hydrophobic properties via a carbonation route. Powder Technol. 2010, 200144–148, DOI 10.1016/j.powtec.2010.02.017. (13) Chu, D. H.; Vinoba, M.; Bhagiyalakshmi, M.; Hyun Baek, II; Nam, S. C.; Yoon, Y.; Kim, S. H.; Jeong, S. K. CO2 mineralization into different polymorphs of CaCO3 using an aqueous-CO2 system. RSC Adv. 2013, 321722–21729, DOI 10.1039/C3RA44007A. (14) Chen, Y.; Ji, X.; Wang, X. Microwave-assisted synthesis of spheroidal vaterite CaCO3 in ethylene glycol–water mixed solvents without surfactants. J. Cryst. Growth 2010, 3123191–3197, DOI 10.1016/j.jcrysgro.2010.07.034 (15) Rugabirwa, B.; Murindababisha, D.; Wang, H.; Li, J. A High-Pressure Gas-Solid Carbonation Route to Produce Vaterite. Cryst. Growth Des. 2019, 19242–248, DOI 10.1021/acs.cgd.8b01314. (16) Zhao, T.; Guo, B.; Li, Q.; Sha, F.; Zhang, F.; Zhang, J. Highly Efficient CO2 Capture to a New-Style CO2-Storage Material. Energy & Fuels 2016, 306555-6560, DOI 10.1021/acs.energyfuels.6b00443. (17) Leukel, S.; Panthöfer, M.; Mondeshki, M.; Kieslich, G.; Wu, Y.; Krautwurst, N.; Tremel, W. Mechanochemical Access to Defect-Stabilized Amorphous Calcium Carbonate. Chem. Mater. 2018, 306040–6052, DOI 10.1021/acs.chemmater.8b02339. (18) Singh, R.; Yoon, H.; Sanford, R. A.; Katz, L.; Fouke, B. W.; Werth, C. J. Metabolism-Induced CaCO3 Biomineralization During Reactive Transport in a Micromodel: Implications for Porosity Alteration. Environ. Sci. Technol. 2015, 4912094–12104, DOI 10.1021/acs.est.5b00152. (19) Vanderveen, J. R.; Durelle, J.; Jessop, P. G. Design and evaluation of switchable-hydrophilicity solvents. Green Chem. 2014, 16 (3), 1187–1197, DOI 10.1039/C3GC42164C. (20) Jessop, P. G.; Mercer, S. M.; Heldebrant, D. J. CO2-triggered switchable solvents, surfactants, and other materials. Energy Environ. Sci. 2012, 57240–7253, DOI 10.1039/C2EE02912J. (21) Lestari, G.; Alizadehgiashi, M.; Abolhasani, M.; Kumacheva, E. Study of Extraction and Recycling of Switchable Hydrophilicity Solvents in an Oscillatory Microfluidic Platform. ACS Sustainable Chem. Eng. 2017, 54304–4310, DOI 10.1021/acssuschemeng.7b00339.

23



Page 24 of 26

(22) Phan, L.; Andreatta, J. R.; Horvey, L. K.; Edie, C. F.; Luco, A.-L.; Mirchandani, A.; Darensbourg, D. J.; Jessop, P. G. Switchable-Polarity Solvents Prepared with a Single Liquid Component. J. Org. Chem. 2008, 73 (1), 127–132, DOI 10.1021/jo7017697. (23) Zeng, S.; Tao, C.; Parnas, R.; Jiang, W.; Liang, B.; Liu, Y.; Lu, H. Jatropha curcas L. oil extracted by switchable solvent N, N-dimethylcyclohexylamine for biodiesel production. Chin. J. Chem. Eng. 2016, 241640–1646, DOI 10.1016/j.cjche.2016.04.023. (24) Lasarte-Aragonés, G.; Lucena, R.; Cárdenas, S.; Valcárcel, M. Use of switchable solvents in the microextraction context. Talanta 2015, 131645–649, DOI 10.1016/j.talanta.2014.08.031. (25) Schenk, A. S.; Cantaert, B.; Kim, Y.-Y.; Li, Y.; Read, E. S.; Semsarilar, M.; Armes, S. P.; Meldrum, F. C. Systematic Study of the Effects of Polyamines on Calcium Carbonate Precipitation. Chem. Mater. 2014, 26 (8), 2703–2711, DOI 10.1021/cm500523w. (26) Li, H.; Li, Q.; Hao, J.; Xu, Z.; Sun, D. Preparation of CO2-responsive emulsions with switchable hydrophobic

tertiary

amine.

Colloids

Surf.

A

2016,

502107–113,

DOI:

10.1016/j.colsurfa.2016.05.013. (27) Chen, S.-F.; Yu, S.-H.; Jiang, J.; Li, F.; Liu, Y. Polymorph Discrimination of CaCO3 Mineral in an Ethanol/Water Solution: Formation of Complex Vaterite Superstructures and Aragonite Rods. Chem. Mater. 2006, 18115–122, DOI 10.1021/cm0519028. (28) Trushina, D. B.; Bukreeva, T. V.; Kovalchuk, M. V.; Antipina, M. N. CaCO3 vaterite microparticles for biomedical and personal care applications. Mater. Sci. Eng.,C 2014, 45644–658, DOI 10.1016/j.msec.2014.04.050. (29) Luo, J.; Kong, F.; Ma, X. Role of Aspartic Acid in the Synthesis of Spherical Vaterite by the Ca(OH)2–CO2 Reaction. Cryst. Growth Des. 2016, 16728–736, DOI 10.1021/acs.cgd.5b01333. (30) Yu, S.-H.; Li, H.; Yao, Q.-Z.; Fu, S.-Q.; Zhou, G.-T. Hierarchically nanostructured shuttle-like aragonite mesocrystals: Preparation, characterization, growth mechanism, and removal ability to La(III). J. Environ. Chem. Eng.2017, 5893–905, DOI 10.1016/j.jece.2017.01.004. (31) Barhoum, A.; Rahier, H.; Abou-Zaied, R. E.; Rehan, M.; Dufour, T.; Hill, G.; Dufresne, A. Effect of Cationic and Anionic Surfactants on the Application of Calcium Carbonate Nanoparticles in Paper Coating. ACS Appl. Mater. Interface 2014, 62734–2744, DOI 10.1021/am405278j. (32) Dong, C.; Song, X.; Li, Y.; Liu, C.; Chen, H.; Yu, J. Impurity ions effect on CO2 mineralization via coupled reaction-extraction-crystallization process of CaCl2 waste liquids. J. CO2 Util. 2018, 27115–128, DOI 10.1016/j.jcou.2018.05.023. (33) Wang, L.; Sondi, I.; Matijević, E. Preparation of Uniform Needle-Like Aragonite Particles by Homogeneous

Precipitation.

J.

Colloid

Interface

Sci.

1999,

218545–553,

DOI

10.1006/jcis.1999.6463. (34) Wang, Y.; Zeng, M.; Meldrum, F. C.; Christenson, H. K. Using Confinement To Study the Crystallization Pathway of Calcium Carbonate. Cryst. Growth Des. 2017, 176787–6792, DOI 10.1021/acs.cgd.7b01359. 24


Page 25 of 26 1 2 3 4 5 6 7 8 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 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(35) Jimoh, O. A.; Okoye, P. U.; Otitoju, T. A.; Shah Ariffin, K. Aragonite precipitated calcium carbonate from magnesium rich carbonate rock for polyethersulfone hollow fibre membrane application. J. Cleaner Prod. 2018, 79–92, DOI 10.1016/j.jclepro.2018.05.192. (36) Sarkar, A.; Mahapatra, S. Synthesis of All Crystalline Phases of Anhydrous Calcium Carbonate. Cryst. Growth Des. 2010, 102129–2135, DOI 10.1021/cg9012813. (37) Popescu, M.-A.; Isopescu, R.; Matei, C.; Fagarasan, G.; Plesu, V. Thermal decomposition of calcium carbonate polymorphs precipitated in the presence of ammonia and alkylamines. Adv. Powder Technol. 2014, 25500–507, DOI 10.1016/j.apt.2013.08.003. (38) Zhang, J.; Li, Y.; Xie, H.; Su, B.-L.; Yao, B.; Yin, Y.; Li, S.; Chen, F.; Fu, Z. Calcium Carbonate Nanoplate Assemblies with Directed High-Energy Facets: Additive-Free Synthesis, High Drug Loading, and Sustainable Releasing. ACS Appl. Mater. Interfaces 2015, 715686–15691, DOI 10.1021/acsami.5b04819. (39) Boyd, A. R.; Champagne, P.; McGinn, P. J.; MacDougall, K. M.; Melanson, J. E.; Jessop, P. G. Switchable hydrophilicity solvents for lipid extraction from microalgae for biofuel production. Bioresour. Technol. 2012, 118628–632, DOI 10.1016/j.biortech.2012.05.084. (40) Jessop, P. G.; Kozycz, L.; Rahami, Z. G.; Schoenmakers, D.; Boyd, A. R.; Wechsler, D.; Holland, A. M. Tertiary amine solvents having switchable hydrophilicity. Green Chem. 2011, 13619–623, DOI 10.1039/C0GC00806K. (41) Liu, Y.; Chen, Y.; Huang, X.; Wu, G. Biomimetic synthesis of calcium carbonate with different morphologies and polymorphs in the presence of bovine serum albumin and soluble starch. Mater. Sci. Eng. C 2017, 79457–464, DOI 10.1016/j.msec.2017.05.085. (42) Xiao, C.; Li, M.; Wang, B.; Liu, M.-F.; Shao, C.; Pan, H.; Lu, Y.; Xu, B.-B.; Li, S.; Zhan, D.; Jiang, Y.; Tang, R.; Liu, X. Y.; Cölfen, H. Total morphosynthesis of biomimetic prismatic-type CaCO3 thin films. Nat. Commun. 2017, 81398, DOI 10.1038/s41467-017-01719-6. (43) Trushina, D. B.; Bukreeva, T. V.; Antipina, M. N. Size-Controlled Synthesis of Vaterite Calcium Carbonate by the Mixing Method: Aiming for Nanosized Particles. Cryst. Growth Des. 2016, 161311–1319, DOI 10.1021/acs.cgd.5b01422.

25



For Table of Contents Use Only

Synopsis DMCHA, a CO2- responsive switchable solvent with a cyclic CO2 uptake capacity and structural director ability can induce self-assembly of nuclei to generate phase-by-phase stabilization and kinetically controlled formation of metastable polymorphs.

26


Page 26 of 26

CO2-Responsive Switchable Solvents to Induce Self-assembled

Recommend Documents