67

CHAPTER-3 (Section-A)

Bioinspired Synthesis of Morphologically Controlled SrCO3

Superstructures by Natural Gum Acacia

3A.1 Introduction

The field of biomineralization and its synthetic counterpart, biomimetic

mineralization, has been very active in recent years [1]. Development of bioinspired

strategies for the synthesis of inorganic crystals or hybrid inorganic–organic materials

with specific size, shape, orientation, organization, complex form, and related unique

properties, due to the potential to design new materials and devices in various fields

[2]. The main theme of biomineralisation is that nucleation, growth and controlled

patterning of inorganic materials takes place by the interactions between metal and

ligand. The controlled growth experiments of carbonate crystals are carried out in

aqueous solution, and some carbonates crystallize in the air-water interface/liquid-

liquid interface [3-4]. Proteins, glycoproteins and polysaccharides play vital role in the

precipitation of carbonates and act as nucleators, growth modifiers and anchoring

units in the mineral formation. Many investigations reveal that materials obtained

from nanosized particles have unknown properties/enhanced characteristics when

compared to common materials. It is very significant not only for biomineralisation

research but also for the synthesis of nanosized inorganic materials. Biomimetic

strategies have been developed for the synthesis of organized inorganic based

structures.

Strontium carbonate although itself is not an important biomineral, is

interesting since its crystallization yields insights into the formation of the

isostructural CaCO3 phase, aragonite of which pearls and nacre are largely composed.

SrCO3 has only one polymorph, so it is suitable for the study of biomineralisation.

Strontium carbonate (SrCO3), has wide applications as an additive in the production

of glass for color television tubes, chief constituent of ferrite magnets [5-6] and

nanometer sized SrCO3 is used in chemiluminescence sensors [7]. Various kinds of

68

SrCO3 crystals with morphologies such as spheroidal, needle-like, rod-like or ribbon-

like have been prepared with the aid of urease enzyme-catalyzed reaction [8], on

centered rectangular self-assembled monolayer substrates [9], within thermally

evaporated sodium bis-2 ethylhexylsulfosuccinate thin films [10], using the fungus

Fusarium oxysporum [11], or in a simple cationic microemulsion system under solvo-

thermal conditions [12]. Shape and size controlled growth of inorganic materials using

reverse micelles or microemulsions received considerable interest in the recent past

owing to its diverse application potential in areas such as catalysis, medicine,

electronics, ceramics, pigments, cosmetics, and separation technology[13 -15].

The use of natural materials as crystal growth modifiers has been extensively

studied in many crystal systems, including calcium carbonate [16-21], silica [22-25],

calcium phosphate [26], barium sulfate [27-30], barium carbonate [31-35] and strontium

carbonate [36-38]. The creation of superstructures resembling naturally existing

biominerals [39-41] with their unusual shapes and complexity, is meanwhile already an

important branch in the broad area of biomimetics [42-46]. The biological systems are

very effective at controlling crystal growth, especially polymers have been

successfully developed to control crystallization of inorganic particles in aqueous

solutions [47- 49]. Though there are many synthesizing procedures, still the preparation

methods using polymers as crystal growth modifiers are complicated and not so easily

available. Hence, we introduced an environmentally friendly route to generate

inorganic materials with controlled morphologies by using natural biopolymer - Gum

Acacia as crystal growth modifier for the crystallization of SrCO3 superstructures.

Gum Acacia is a natural gum made of hardened sap derived from Acacia

Senegal and Acacia Seyel. GA consists of mainly three fractions (1) The major one is

a highly branched polysaccharide consisting of β-(1-3) galactose backbone with

linked branches of arabinose and rhamnose, which terminate in glucoronic acid. (2) A

smaller fraction (~10 wt % of the total) arabinogalactan–protein complex (GAGP–GA

glycoprotein) in which arabinogalactan chains is covalently linked to a protein chain

through serine and hydroxyproline groups. The attached arabinogalactan in the

complex contains ~13% (by mole) glucoronic acid. (3) The smallest fraction (~1% of

the total) having the highest protein content (~50 wt %) is a glycoprotein which

69

differs in its amino acids composition from that of the GAGP complex. Here the

functional group (-OH) present in Arabinose and Rhamnose and (-COOH) of

glucoronic acids play a crucial role in the growth and formation metal carbonates

whereas the proteinaceous core with amino acids stabilize the formed metal

carbonates [50]. It not only acts as a stabilizer [51], but also acts as surfactant and

templating agent for which the functional group moieties (–OH, COOH & -NH2) have

been found to play a key role in mimicking the biomineralization process. The

crystallization involves the formation of different hierarchical structures like rice

grain, doughnut shaped, flower shaped, hexagonal rods and cross shaped which have

never been seen before in natural biominerals. Proteins and polysaccharides with

complicated patterns of various functional groups in GA selectively adsorb on to the

metal ion thereby hindering the crystal growth, followed by the mesoscale self-

assembly of nanometer-scale building block into hierarchial superstructures [52-57]. The

key reaction of CO2 with Sr2+ ions entrapped within GA polymer leads to the growth

of beautiful structures of strontianite nanocrystalline, such an aggregated morphology

not normally observed using other surfaces as templates. The objective of the present

work is to examine the process of biomineralisation utilize natural gums for the

synthesis of SrCO3 and its effect on the morphology. The study is very significant not

only for biomineralisation research, but also for the synthesis of functional inorganic

materials.

3A.2 Experimental Section

3A.2.1 Materials

Analytical grade chemicals of SrCl2, LaCl2, TbCl2 and Gum acacia, Sodium

bicarbonate purchased from Merck, India were used without further purification.

Double distilled water was used in all experiments.

3A.2.2 Preparation of Strontium Carbonate superstructures

In a typical experiment, at room temperature, 0.2662 g (1mM) of SrCl2 was taken

along with different proportions of homogenized GA (0.5 % and 1.0%) in different 25

70

ml glass beakers. They were dissolved in 20 ml distilled water and the mixed solution

was stirred thoroughly with the help of magnetic stirrer. Then NaHCO3 (2mM; 2 ml)

solution is added by continuous stirring and kept for 24 h at room temperature. After

24 h, the crystals are filtered washed several times with distilled water and dried at

room temperature. In the case of mixed metal carbonates, 0.2662 g (1mM) of SrCl2

and 0.1083 g (0.25mM) of LaCl2 or 0.0933 g (0.25mM) of TbCl2 were used.

Hydrothermal reactions were carried out in parallel using Teflon lined autoclaves with

internal volume of 10 ml at temperatures 60 and 90 °C under autogenous pressure.

After 24 h reaction time the autoclaves were allowed to cool to 50 °C and maintained

at that temperature for about 15 h before being allowed to cool slowly to ambient

temperature over 3 to 4 h. The sizes and morphologies of the products were examined

by XRD, SEM, EDAX, TEM, TGA-MS and FT-IR.

3A.2.3 Flow chart

Table 3A.1 shows the flow chart representation of experimental conditions

with GA.

Table 3A.1: Flow chart

71

3A.2.4 Characterization Methods

X-ray diffraction measurements of the Strontium carbonate hierarchial

structures were recorded using a Rigaku diffractometer (Cu Kα radiation, λ = 0.1546

nm) running at 40 kV and 40 mA (Tokyo, Japan). FT-IR spectra of SrCO3 structures

were recorded with a Thermo Nicolet Nexus (Washington, USA) 670

spectrophotometer. Thermogravimetric Analysis (TGA) coupled to Balzer Mass (MS)

was carried out on a TGA/SDTA Mettler Toledo 851e system using open alumina

crucibles containing samples weighing about 8–10 mg with a linear heating rate of

10°C min-1. Nitrogen was used as purge gas for all these measurements. TEM images

were observed on TECNAI FE12 TEM instrument operating at 120 kV using SIS

imaging software. The particles were dispersed in methanol and a drop of it was

placed on formvar-coated copper grid followed by air drying. Scanning electron

microscopy (FEI Quanta 200 FEG with EDS) was used for morphology assessment of

SrCO3 crystals. The crystals were collected on a round cover glass (1.2 cm), washed

with deionized water and dried in a desiccator at room temperature. The cover glass

was then mounted on a SEM stub and coated with gold for SEM analysis.

3A.3 Results and Discussion

3A.3.1 Structural characterization of SrCO3 superstructures

The phase composition and structure of as obtained samples was examined by

X-ray powder diffraction (XRD). Since all the different shapes have same

composition, we have shown only the XRD pattern of the synthesized material (1%

GA) at room temperature. As can be seen in Figure 3A.1, All the observed peaks can

be perfectly indexed to a pure orthorhombic phase and no other impurities have been

detected in the synthesized products. The observed diffraction peaks (2θ [°]): can be

correlated to the (hkl) indices (110), (111), (002), (012), (200), (130), (220), (221),

(132), and (113) respectively, of pure orthorhombic strontianite (JCPDS card number:

05-418). It may also be seen that the peak of (111) is the strongest, suggesting that

SrCO3 crystals obtained in gum acacia aqueous solution grow mainly along with

72

(111) face. Along with other several strong diffraction peaks, XRD pattern suggests

that the crystallinity of SrCO3 nanocrystallites obtained is excellent.

Figure 3A.1: XRD pattern of SrCO3 superstructures prepared with 1% GA obtained

at room temperature.

3A.3.2 Morphology control of SrCO3 superstructures

The morphologies of the as-synthesized products were examined by SEM-EDAX and

TEM. Figure 3A.2a shows the typical SEM image of SrCO3 crystals obtained in the

absence of GA prepared at room temperature. As can be seen, dendrimeric crystals

with sizes ranging from 2-4 µm length and 1-3 µm diameter are formed. Remarkable

changes were observed when GA was used as crystal growth modifier. Different

clusters of rice grain cross like, dumbbell like, hexagonal rod like, dough nut shaped

and flower shaped SrCO3 superstructures were observed for 0.5 % and 1.0 % GA

concentration depending on the reaction conditions. These hierarchical clusters

consist of nanocrystallites ranging from 30-150 nm {ambient at both concentrations

Fig. 3A.2b, c} and 20-500 nm {hydrothermal at both concentrations Fig. 3A.2d, e}.

73

At room temperature, with lower molar ratio (0.5 % of GA), rice grain shaped

(1µm – 1.4µm diameter), cross shaped structures (0.9 µm diameter) and two different

forms of dumbbell shaped (1µm - 1.4µm diameter) are obtained with nanocrystallites

in the range 30 – 150 nm. The SEM micrographs of each phase at higher

magnification are shown clearly (Fig. 3A.3a, b, c). Increase in concentration (1% of

GA) led to cross like (1.5 µm length, 750 nm diameter), dumbbell shape (1.5µm

length, 300-500 nm diameter) and flower shape (2.5 µm length, 2.1 µm diameter)

structures of nanocrystallites (20-100 nm). The higher magnification images of all the

phases are separately shown (Fig. 3A.3d, e & f). As can be seen TEM images of

these phases are similar to that observed in SEM micrographs (Fig. 3A.3j, k, l,) and

SAED pattern (Fig. 3A.3m) also shown that the synthesized strontium carbonate

crystals are crystalline. Cross like and dumbbell shaped morphology was observed

commonly in both the concentrations except variation in the size. With the increase in

concentration of GA the size of the cluster increases but the nanocrystallite size

decreases. This behavior can be attributed due to the effective passivation of the

surfaces and suppression of the growth of the nanoparticles through strong

interactions with the particles via there functional molecular groups of acacia namely,

hydroxyl groups of arabinose and rhamnose , galactose and carboxylic groups of

glucoronic acid moieties. Further crystal growth of SrCO3 was monitored under

hydrothermal conditions at 60 °C and 90 °C. At 90 °C stacks of hexagonal rods (1.8

µm length, 2.1 µm diameter) were observed at lower acacia concentration

(0.5%).These hexagonal rods are arranged in a stack like manner as seen [58] whereas

at higher concentration (1 %), doughnut shaped (4.3-4.6 µm length 5.6µm diameter)

and rice grain shaped (1.6-2 µm length, 0.6-0.8 µm diameter) clusters of 15-70 nm

crystallites are identified. No such variation was seen at 60 °C except in size

variation. Remarkable changes in both size and shape were observed in the

superstructures formed at ambient and hydrothermal (90°C) conditions for higher GA

concentration (1%). The higher magnification images of all the phases are separately

shown (Fig. 3A.3g, h, i). As can be seen, the crystallites size decreases from ambient

to hydrothermal condition. No other morphologies existed except for bigger structures

when continuously increasing the temperature conditions. On increasing the

concentration of GA at room temperature, the rice grain shaped structures aggregate

and produce flower shaped structures (Fig. 3A.2c). Siamilarly at hydrothermal

reaction, stack of hexagonal rods unite to form doughnut shaped structures (Fig.

74

3A.2e). The schematic composition of SrCO3 crystal morphology is shown in the

table 3A.2.

Table 3A.2: Schematic composition and morphology of SrCO3 at different

concentrations of gumacacia (GA).

Condition Without GA 0.5%wt GA 1.0%wt GA

Ambient

Dendrimeric SrCO3 crystals with 2-4µm length

Rice grain like, Cross like structures

Crosslike,dumbell shape and flower shaped super structures

Hydrothermal

(600)

Stack of hexagonal rods

Dough nut shaped and Rice grain shaped structures

Hydrothermal

(900)

Stack of hexagonal rods

Dough nut shaped and Rice grain shaped structures

75

Figure 3A.2: SEM images of SrCO3 superstructures. a) Dendrimeric structures in the

absence of additive. b) & c) Room temp reaction process at 0.5% & 1.0% GA. d) & e)

hydrothermal (900) reaction process at 0.5% & 1.0% GA.

76

Figure 3A.3: SEM images of SrCO3 superstructures at lower magnification using different

reaction conditions. (a, b, c)0.5% GA at room temperature. (d, e, f)1% GA at room temperature. g) 0.5% GA at hydrothermal 90 °C. (h, i)1% GA at hydrothermal 90 °C room temperature.(j, k, l)TEM images of SrCO3 superstructures of 1% GA at room temperature. m) SAED pattern SrCO3 superstructures.

77

3A.3.3 TEM & EDAX

Figure 3A.4b shows that TEM images of SrCO3 obtained at room temperature

and Figure 3A.4d shows TEM image of calcined product at 700 °C. SrCO3

superstructure was observed under TEM which also shows the nanocrystallites size in

nanometer range clearly. The images are in supporting with SEM images. Figure 3A.5

EDAX elemental analysis reveals that more carbon content is seen in normal room

temperature material than calcined product. Due to calcinations low carbon content is

noticed.

Figure 3A.4: SEM & TEM images (SAED inserted). a) & b) SrCO3 with 1%GA. c) &

d) Calcined product at 700οC.

78

Figure 3A.5: EDAX elemental analysis of SrCO3 a) with GA and b) Calcined product.

79

3A.3.4 Sr-LaCO3 system and Sr-TbCO3 system

Other than strontium carbonate, mixed metal carbonates such as Sr-LaCO3 and Sr-

TbCO3 were synthesized at room temperature using higher GA (1.0 %). Figure 3A.6a,

c show the SEM images of La doped SrCO3 and Tb doped SrCO3, respectively. As

can be seen, there is a clear morphological difference between SrCO3 structures

synthesized with and without the addition of rare earths. Rod-like crystals aggregate

in the form of bunches for La whereas spheroid shape resulted for Tb. The spheroid

structures have uniform morphology and size distribution with diameters ranging

between 400 – 900 nm. Inset shows the TEM image which also shows similar

morphological features as observed by SEM. It would be instructive to understand the

chemical composition of the different features observed for both Sr-LaCO3 and Sr-

TbCO3 nanostructures. This is conveniently done by spot-profile EDAX. In addition

to the expected Sr, C and O signals, strong signals of La and Tb are seen for La doped

SrCO3 and Tb doped SrCO3, respectively as shown in Figure 3A.6b, d. Table 3A.3

illustrates the morphology of as obtained products.

Table 3A.3: Schematic composition and morphology of Sr-LaCO3 and Sr-TbCO3 at

1.0% gum acacia (GA).

Condition

Morphology of Sr-LaCO3

(1.0% wt GA)

Morphology of Sr-TbCO3

(1.0% wt GA)

Ambient

Pack of rods

Spheroid clusters with

nanocrystallites

80

Figure 3A.6: SEM images of mixed metal carbonates. a) Pack of rod like clusters of

Sr- LaCO3 (TEM inserted). b) EDAX data of Sr-LaCO3. c) Spheroid shaped clusters

of Sr-TbCO3 (TEM inserted). d) EDAX data of Sr-TbCO3.

81

3A.3.5 TGA-MS analysis

Thermogravimetric analysis coupled to mass helps us to understand the

decomposition steps more precisely as we can know the evolved gas fragments as a

function of temperature or time. As representative systems, the TG/DTG-MS

thermograms of pure GA, SrCO3 synthesized without GA, as synthesized SrCO3

using GA and SrCO3 with GA calcined at 700 °C are shown (Figure 3A.7 a, b, c, d).

TGA-MS thermogram of pure GA (Fig. 3A.7a) shows a major decomposition

step (64.5% wt. loss) in the temperature range 260 - 400 °C and as can be seen it is

during this step the evolution of the gas with mass fragment 44 a.m.u characteristic of

CO2 from the decomposition of –COOH functional groups in GA is observed. TGA

profile of SrCO3 structures synthesized without gum acacia (Fig. 3A.7b) show single

step decomposition in the range 850 – 1050 °C. The mass fragment 44 a.m.u observed

in this range clearly suggests that the SrCO3 dendrimers decomposes into SrO and

CO2. The corresponding mass loss was quite similar to the theoretical value of the

mass loss of the above decomposition (29.81%) and almost the same with that

occurred for the thermal decomposition of the high pure SrCO3 phase between 900 –

1150°C [59]. The relatively low decomposition temperature of the present SrCO3

nanocrystallites might be ascribed to the size effect of the nanoparticles existed within

the nanocrystallites. Further, SrCO3 nanocrystallites synthesized using GA (Fig.

3A.7c) showed three step decomposition pattern. The first two steps in the

temperature range 200- 300 °C and 580 – 720 °C are due to the evolution of CO2

(mass fragment 44 a.m.u) from GA component in the inorganic and organic hybrid

SrCO3 nanocrystallites and the third step in the temperature range 800-1000 °C can be

attributed mainly due to the decomposition of SrCO3 nanocrystallites into SrO and

CO2. The corresponding mass loss was found to be 24.89%. The absence of the first

two decomposition steps in calcined (at 700°C) SrCO3 synthesized with gum acacia

(Fig. 3A.7d) clearly suggests that the as synthesized SrCO3 nanocrystalites are

inorganic and organic hybrid composite. The mass loss observed in this step of

28.41% is in consonance with the weight loss observed for SrCO3 dendrimers

synthesized without gum acacia.

82

Figure 3A.7: TGA-DTG-MS thermograms of a) pure gum acacia. b) SrCO3

synthesized without GA. c) as synthesized SrCO3 using GA. d) as synthesized SrCO3

with GA calcined at 700 °C. e) - - - - TGA, -.-.-.-.- DTG and ---------- MS.

83

3A.3.6 FT-IR spectra

FT-IR spectra of SrCO3 have been studied to determine the effect of GA on the

microstructure of nanocrystallites. The IR bands at 1454.48, 1460.65 and 1451.03cm-1

corresponds to the asymmetric stretching mode of C-O bond (Fig. 3A.8a, b, c),

respectively. The sharp peaks at 857.17 and 703.0 (Fig. 3A.8a), 857.69 and 703.0

(Fig. 3A.8b) and 855.77 and 697.62 (Fig. 3A.8c) are in plane and out plane bending

CO32-. In comparison with Figure 3A.8 the C-O stretching vibration peak around 1454

cm-1 in Figure 3A.8b shifts to higher frequency by 6 cm-1 (1460 cm-1), suggesting that

GA have an influence on the superstructure of strontium carbonate. This is probably

due to the GA molecules adsorb onto the surfaces of SrCO3 nuclei and influence the

mode of crystal growth with a little change of superstructure.

Figure 3A.8: FT-IR of SrCO3 particles nucleated a) in the absence of GA. b)

presence of GA. c) calcined product at 700 οC.

84

The exact growth mechanism of the micro and nano structures is not fully

understood. We predict that the various functional groups in gum acacia molecule

bind to alkali metal cations to form complexes. Hence, the anisotropic growth

phenomenon is due to the selective adsorption of gum acacia molecules on the

specified planes of growing crystal at different reaction conditions. Based on the

above analysis a possible growth mechanism for the formation of SrCO3

superstructures at the air/solution interface is schematically shown in Figure 3A.9.

Initially the functional moieties in GA inhibit the crystal growth by the encapsulation

of Sr2+ ions which in the presence of sodium bicarbonate forms SrCO3 nanoparticles

that act as building units in sequence with a brick by brick formation mechanism

resulting in superstructure crystals. These particles are formed homogeneously in the

solution and the crystallization is based on these SrCO3 superstructures that are made

up of nanocrystallites and are built up from individual nanocrystals and are aligned in

a common crystallographic pattern. In solution, rod like particles without any

boundaries aggregate together into hierarchical flower-like superstructure at the

air/solution interface as is schematically shown in figure. During the transformation of

rods to flower like structures under the control of GA (the functional groups

influences the nucleation, nanocrystal growth, alignment or self assembly and

aggregation into a superstructure), intermediate structures are formed such as rice-

like, cross-like, and dumbbell-like. The schematic representation of growth

mechanism of SrCO3 superstructures can be seen in Figure 3A.9.

85

Figure 3A.9: Schematic representation of growth mechanism of SrCO3

superstructures.

86

3A.4 Conclusion

Organic functional groups of GA have interaction with strontium and carbonate ions

which control the morphology of strontium carbonate via non classical crystallization

process. The use of natural material, GA in the synthesis of higher ordered

Strontionite superstructures have remarkable effect in control on the nucleation,

growth and alignment of SrCO3 particles in the reaction process. The utilization of

natural materials is one of the ways in which to synthesize particles with controlled

morphologies and this method may be potentially useful to other systems also

employed to produce materials with novel morphologies. This method would allow us

pragmatically realize the kind of morphological control of biomineralisation and

should be useful for synthesizing different superstructures which might find use in

catalysis, medicine, electronics, ceramics, pigments, cosmetics, and colour television

tubes.

87

3A.5 References

1. S. J. Homeijer, R. A. Barrett, L. B. E. Gower, Cryst. Des. Growth. 2010, 10,

1040.

2. S. Mann, G.A. Ozin, Nature. 1996, 382, 313.

3. Y. X. Gao, S. H. Yu, X. H. Guo, Langmuir. 2006, 22, 6125.

4. G. Hadiko, Y. S. Han, M. Fuji, M. Takahashi, Mater. Lett. 2005, 59, 2519.

5. M. B. Coope, G. M. Clarke, Metal Bullentin. 1983, 115.

6. Roskill, “The Economics of Strontium”, 5th ed., Roskill Information Services,

London, UK, 1989.

7. M. Cao, X. Wu, X. He, C.Hu, Langmuir. 2005, 21, 6093.

8. Sond, E. Matijevic, Chem. Mater. 2003, 15, 1322.

9. J. Küther, G. Nelles, R. Seshadri, M. Schaub, H. J. Butt, W. Tremel, Chem.

Eur. J. 1998, 4, 1834.

10. D. Rautaray, S. R. Sainkar, M. Sastry, Langmuir. 2003, 19, 888.

11. D. Rautaray, A. Sanyal, S. D. Adyanthaya, A. Ahmad, M. Sastry, Langmuir.

2004, 20, 6827.

12. G.S. Guo, F.B. Gu, Z.H. Wang, H.Y. Guo, Chinese Chemical Letters. 2005,

16, 1101.

13. M. P. Pileni, T.G. Krzywicki, J. Tanori, A. Filankembo, J. C. Dedieu,

Langmuir. 1998,14, 7359.

14. G. D. Rees, R.E. Gowing, S. J.Hammond, B. H. Robinson, Langmuir. 1999,

15, 1993.

15. L. Chen, Y. Shen, A. Xie, F. Huang, S. Li, Q. Zhang, Cryst. Res. Technol.

2008, 43, 797.

16. H. Colfen, Curr. Opin. Colloid Interface Sci. 2003, 8, 23.

17. L. A. Gower, D. A. Tirrell, J. Cryst. Growth. 1998, 191, 153.

18. L. B. Gower, D. J. Odom, J. Cryst. Growth. 2000, 210, 719.

88

19. N. Gehrke, N. Nassif, N. Pinna, M. Antonietti, H. S. Gupta, H. Colfen, Chem.

Mater. 2005, 17, 6514.

20. J. Aizenberg, G. Lambert, L. Addadi, S. Weiner, Adv. Mater. 1996, 8, 222.

21. Y. Y. Kim, E. P. Douglas, L. B. Gower, Langmuir. 2007, 23, 4862.

22. C. W. P. Foo, J. Huang, D. L. Kaplan, Trends Biotechnol. 2004, 22, 577.

23. D. D. Glawe, F. Rodriguez, M. O. Stone, R. R. Naik, Langmuir. 2005, 21,

717.

24. R. R. Naik, L. L. Brott, S. J. Clarson, M. O. Stone, J. Nanosci. Nanotechnol.

2002, 2, 95.

25. F. C. Meldrum, H. Colfen, Chem. Rev. 2008, 108, 4332.

26. M. J. Olszta, X. G. Cheng, S. S. Jee, R. Kumar, Y. Y. Kim, M. J. Kaufman, E.

P. Douglas, L. B. Gower, Mater. Sci. Eng. R-Rep. 2007, 58, 77.

27. L. M. Qi, H. Colfen, M. Antonietti, M. Li, J. D. Hopwood, A. J. Ashley, S.

Mann, Chem.-Eur. J. 2001, 7, 3526.

28. T. X. Wang, A. Reinecke, H. Colfen, Langmuir. 2006, 22, 8986.

29. S. H. Yu, M. Antonietti, H. Colfen, J. Hartmann, Nano Lett. 2003, 3, 379.

30. S. H. Yu, H. Colfen, M. Antonietti, Adv. Mater. 2003, 15, 133.

31. E. Bittarello, D. Aquilano, Eur. J. Mineral. 2007, 19, 345.

32. X. H. Guo, S. H. Yu, Cryst. Growth Des. 2007, 7, 354.

33. S. H. Yu, H. Colfen, K. Tauer, M. Antonietti, Nat. Mater. 2005, 4, 51.

34. T. X. Wang, A. W. Xu, H. Colfen, Angew. Chem. Int. Ed. 2006, 45, 4451.

35. S. J. Homeijer, M. J. Olszta, R. A. Barrett, L. B. Gower, J. Cryst. Growth.

2008, 310, 2938.

36. J. H. Collier, P. B. Messersmith, Ann. Rev. of Mat. Research. 2001, 31, 237.

37. M. Sastry, A. Kumar, C. Damle, S. R. Sainkar, M. Bhagwat, V. Ramaswamy,

CrystEngComm. 2001, 21, 1.

38. M. Balz, H. A. Therese, M. Kappl, L. Nasdala, W. Hofmeister, H.J. Butt, W.

Tremel Langmuir. 2005, 21, 3981.

89

39. H. A. Lowenstam, S. Weiner, On Biomineralization, Oxford University Press,

New York, 1989.

40. S. Mann, J. Webb, R. J. P. Williams, Biomineralization: Chemical and

Biochemical Perspectives, Wiley-VCH, Weinheim, 1989.

41. E. B. Uerlein, Biomineralization, Wiley-VCH, Weinheim, 2000.

42. S. H. Yu, H. Colfen, J. Mater. Chem. 2004, 14, 2124.

43. S. Mann, D. D. Archibald, J. M. Didymus, T. Douglas, B. R. Heywood, F. C.

Meldrum, N. J. Reeves, Science. 1993, 261, 1286.

44. S. A. Davis, M. Breulmann, K. H. Rhodes, B. Zhang, S. Mann, Chem. Mater.

2001, 13, 3218.

45. H. Colfen, Curr. Opin. Colloid Interface Sci. 2003, 8, 23.

46. F. C. Meldrum, Int. Mater. Rev. 2003, 48,187.

47. H. Colfen, S. H. Yu, MRS Bull. 2005, 30, 727.

48. S. H. Yu, H. Colfen, J. Mater. Chem. 2004, 14, 2123.

49. Y. X. Gao, S.H. Yu, H. Cong, J. Jiang, A.W. Xu, W. F. Dong, H. Colfen, J.

Phys. Chem. B. 2006,110, 6432.

50. D. K. Devi, S. V. Pratap, R. Haritha, K. S Sivudu, P. Radhika, B. Sreedhar, J.

Appl. Polym. Sci. (In press).

51. B. Sreedhar, P. S. Reddy, D. K. Devi, J. Org. Chem. 2009, 74, 8806.

52. S.H. Yu, H. Colfen, J. Mater.Chem. 2004, 14, 2124.

53. H. Colfen, M. Antonietti, Langmuir. 1998, 14, 582.

54. N. A. J. M. Sommerdijk, G. de, Chem. Rev. 2008, 108, 4499.

55. H. Colfen, Macromol. Rapid Commun. 2001, 22, 219.

56. L. M. Qi, H. Colfen, M. Antonietti, M. Li, J. D. Hopwood, A. J. Ashley, S.

Mann, Chem. Eur. J. 2001, 7, 3526.

57. L. M. Qi, H. Colfen, M. Antonietti, Angew. Chem. Int. Ed. 2000, 39, 604.

58. Kotachi, T. Miura, H. Imai, Cryst. Growth Des. 2004, 4, 725.

59. X. Liu, X. Peng, W. Xie, Q. Wei, Chin. J. Mater. Res. 2005, 19, 287.

90

SECTION-B

Shape Controlled synthesis of Barium Carbonate microclusters and

nanocrystallites using Natural polysachharide– Gum acacia.

3B.1 Introduction

The study of mineral formation in biological systems, biomineralization, provides

inspiration for novel approaches to the synthesis of new materials. Biomineralization

relies on extensive organic-inorganic interactions to induce and control the synthesis

of inorganic materials. Bio-inspired morphosynthesis of crystals have been explored

with hierarchal forms which mimic natural biominerals in the presence of organic

template with complex functionalizing patterns has been developed widely in recent

years [1-6]. Among a variety of construction methodologies of functional materials,

patterned crystal arrays of organic [7], inorganic [8,9], and their hybrid crystals [10,11],

have received considerable attention in recent years for their diverse application

potential in areas such as catalysis, medicine, pigments, cosmetics, separation

technology [12,13], nano-devices [14] and find diverse applications in nanotechnology [15,16].

Nanostructural materials have become attractive because of their unique

characteristics that can hardly be obtained from conventional bulk materials owing to

their quantum size and surface effects. So, there has been considerable interest in

fabrication of low-dimensional nanosized materials such as nanowires, nanorods and

nanotubes. Several processes have been explored in the literature for the synthesis of

nanomaterials. These processes involve both physical and chemical methods [17-

20].Various artificial complexations have been investigated as models of

biomineralization using modifier agents , e.g., urease [21], nitrilo triacetic acid, citric

acid [22], poly(acrylic acid) (PAA) [23], poly(methacrylic acid) PMMA, poly(ethylene

glycol) PEG [24], poly(allylamine hydrochloride) PAH, poly (sodium 4-styrene

sulfonate) PSS [25], (cetyl trimethyl ammonium bromide) CTAB [26]. These modifying

agents have also been thought to control the polymorph of the barium carbonate

clusters. However, the characterization of these native and modifier agents on the

crystal surface is still unclear.

91

BaCO3 has attracted a lot of recent research [27-31] due to its close relationship

with aragonite, a prevalent and important biomineral, with many important

applications in the ceramic and glass industries as well as its use as a precursor for

magnetic ferrites and/or ferroelectric materials [32]. Barium carbonate (BaCO3) is also

used as a precursor for producing superconductor and ceramic materials [33] and other

important applications in optical glass and electric condensers [34]. Therefore, in the

present study, we report the synthesis and characterization of BaCO3 nanocrystallite

using natural polymer, gum acacia.

Polymer-mediated mineralization of inorganic materials has been the subject

of intense research because polymers have been found to dramatically influence the

characteristics of an inorganic precipitate. The ability to influence the morphology

and phase of an inorganic precipitate has important technological implications [35],

because some physical properties of crystalline materials such as the brilliance of

color pigments or the dielectric function of electroceramics depend on crystal habit,

grain size, grain size distribution, impurities, or content of polymorphous

modifications. Control of nucleation, crystal growth, and organization of crystals to a

superstructure (“texture”) make these physical properties tunable and are thus

important for technical application [36].

The present investigation deals with the influence of Gum Acacia a natural

polysaccaharide as templating species for the formation of BaCO3 nanocrystallites

forming microclusters. Gum Acacia is a natural gum made of hardened sap derived

from Acacia Senegal and Acacia Seyel. GA consists of mainly three fractions (1) The

major one is a highly branched polysaccharide consisting of β-(1-3) galactose

backbone with linked branches of D-galactose (38%), L-arabinose (45%), L-

rhamnose (4%), which terminate in D-glucuronic acid (7%), and 4-O-methyl-D-

glucuronic acid (6%) . (2) A smaller fraction (~10 wt % of the total) arabinogalactan–

protein complex (GAGP–GA glycoprotein) in which arabinogalactan chains is

covalently linked to a protein chain through serine and hydroxyproline groups. The

attached arabinogalactan in the complex contains ~13% (by mole) glucoronic acid. (3)

The smallest fraction (~1% of the total) having the highest protein content (~50 wt %)

92

is a glycoprotein which differs in its amino acids composition from that of the GAGP

complex. Here the functional group (-OH) present in arabinose and rhamnose and (-

COOH) of glucoronic acids play a crucial role in the growth and formation metal

carbonates whereas the proteinaceous core with amino acids stabilize the formed

metal carbonates [37]. It not only acts as a stabilizer [38], but also acts as surfactant and

templating agent for which the functional group moieties (–OH, COOH & -NH2) have

been found to play a key role in mimicking the biomineralization process. The

crystallization involves the formation of different hierarchical structures like rods

through dumbbell to flower shaped which have never been seen before in natural

biominerals. Proteins and polysaccharides with complicated patterns of various

functional groups in GA selectively adsorb on to the metal ion thereby hindering the

crystal growth, followed by the mesoscale self-assembly of nanometer-scale building

block into hierarchial superstructures [39-44]. The key reaction of CO2 with Ba2+ ions

entrapped within GA polymer leads to the growth of beautiful structures of whitherite

nanocrystalline, such an aggregated morphology not normally observed using other

surfaces as templates. This templating species composed of many anionic moieties,

which interacts strongly with ions, crystal surfaces. Functional, water-soluble

polymers with the ability to bind ions and crystals play a major role as scale inhibitors

crystal faces and thus, promotes the crystal growth. This species also strongly modify

the morphology of growing crystals in an interesting manner. Indeed, in the presence

of such templating species, the nucleated crystals may adopt a variety of shapes. The

interacting part of the GA (a variety of functional groups) can be selected or designed

in such a way that it specifically adsorbs to a certain crystal face. The proteins and

inorganic ions regulate the phase of the deposited mineral [45, 46].

The aim of the study was to determine the effects of this GA on the

morphological and structural characteristics of the resulting different morphological

structures, with special emphasis on different phases in the growth process. Our

results demonstrate that the integration of gum acacia (GA) taking advantage of the

reaction conditions, will extend the possibilities for controlling the shape, size, and

microclusters of the inorganic crystals by means of a simple mineralization process

93

3B.2 Experimental Section

3B.2.1 Materials

Analytical grade chemicals of BaCl2, LaCl2, TbCl2, Gum acacia, Sodium

bicarbonate were purchased from Merck, India and used as such without further

purification. Double distilled water was used in all experiments.

3B.2.2 Preparation of Barium Carbonate microclusters and nanocrystallites

In a typical procedure, at room temperature, 0.24422 g (1mM) of BaCl2 was

taken along with different proportions of homogenized GA (0.5 % and 1.0%) in

different 25 ml glass beakers. They were dissolved in 20 ml distilled water and the

mixed solution was stirred thoroughly with the help of magnetic stirrer. Then

NaHCO3 (2mM; 2 ml) solution is added by continuous stirring and kept for 24 h at

room temperature. After 24 h, the crystals are filtered and washed several times with

distilled water and dried at room temperature. In the case of mixed metal carbonates,

0.24422 g (1mM) of BaCl2 and 0.1083 g (0.25mM) of LaCl2 or 0.0933 g (0.25mM) of

TbCl2 were used. Hydrothermal reactions were carried out in parallel using Teflon

lined autoclaves with internal volume of 10 ml at temperatures 60 and 90 °C under

autogenous pressure. After 24 h reaction time the autoclaves were allowed to cool to

50 °C and maintained at that temperature for about 15 h before being allowed to cool

slowly to ambient temperature over 3 to 4 h. The sizes and morphologies of the

products were examined by XRD, SEM-EDAX, TEM, and FT-IR.

94

3B.2.3 Flow chart

Table 3B.1 shows the flow chart representation of experimental conditions

with.

Table 3B.1: Flow chart.

3B.2.4 Characterization Methods

X-ray diffraction measurements of Barium carbonate clusters were recorded

using a Rigaku diffractometer (Cu Kα radiation, λ = 0.1546 nm) running at 40 kV and

40mA (Tokyo, Japan). FT-IR spectra of BaCO3 structures were recorded with a

Thermo Nicolet Nexus (Washington, USA) 670 spectrophotometer. TEM images

were observed on TECNAI FE12 TEM instrument operating at 120 kV using SIS

imaging software. The particles were dispersed in methanol and a drop of it was

placed on Formvar-coated copper grid followed by air drying. Scanning electron

microscopy (FEI Quanta 200 FEG with EDS) was used for morphology assessment of

SrCO3 crystals. The crystals were collected on a round cover glass (1.2 cm), washed

with deionized water and dried in a desiccator at room temperature. The cover glass

was then mounted on a SEM stub and coated with gold for SEM analysis.

95

3B.3 Results and Discussion

3B.3.1 Structural characterization of BaCO3 microclusters

The phase composition and structure of as obtained samples was examined by

X-ray powder diffraction (XRD). Since all the different shapes have same

composition, we have shown only the XRD pattern of BaCO3 synthesized without GA

and with GA (1%) at room temperature. The XRD pattern of BaCO3 crystals obtained

both in the presence as well as in the absence of GA was pure orthorhombic witherite

crystals (Fig. 3B.1). All the observed peaks can be perfectly indexed to a pure

orthorhombic witherite phase and no other impurities have been detected in the

synthesized products. The observed diffraction peaks (2θ [°]): can be correlated to the

(hkl) indices (111), (002), (012), (130), (221), (132) and (113), respectively, of pure

orthorhombic witherite (JCPDS card number: 71-2394).It may also be seen that the

peak of (111) is the strongest, suggesting that BaCO3 crystals obtained in gum acacia

aqueous solution grow mainly along with (111) face. Along with other several strong

diffraction peaks, XRD pattern suggests that the crystallinity of BaCO3

nanocrystallites obtained is excellent, that can be correlated from TEM (SAED)

micrograph. It can be concluded that GA has major influence on the growth and size

morphology of BaCO3 crystals formed. However, the addition of additive has no

effect on the crystal structure of the resulting BaCO3 crystals.

96

Figure 3B.1: XRD pattern of BaCO3. a) absence of GA. b) presence of GA.

97

3B.3.2 Effect of gum acacia on the morphology of BaCO3

Morphologies of the formed crystal aggregates were investigated using SEM-

EDAX and TEM. Under ambient conditions in the absence of any templating species

only rod-shaped crystals of aragonite type BaCO3 (Fig. 3B.2a) with different sizes

(700 nm to 20µm length, 200 nm to 2µm dia) were formed as expected. Remarkable

changes have been observed in the morphology of the products obtained in the

presence of the templating species – GA. Bunch of rods, dumbbell, double-dumbell

and flower shaped BaCO3 clusters were observed for 0.5 % and 1.0 % GA

concentration depending on the reaction conditions. These clusters are of sizes in

several micrometers to several nanometers in both ambient (Fig. 3B.2b, c) and

hydrothermal crystallization (Fig. 3B.2d, e). SEM images of the products formed after

24h of reaction at various concentrations of GA (0.5 % and 1.0 %) in both the reaction

conditions are shown in Figure 3B.2.

At ambient conditions, when the GA concentration was 0.5%, bunch of rods in

the form of clusters are seen as shown in Figure 3B.2b.The length of the rods present

in the clusters is in the size range from 100 nm to 400 nm. The enlarged image clearly

shows that the rods aggregate in the form of bunch like clusters (Fig. 3B.3a). When

the amount of GA added is increased to 1.0%, shorter assemblies of BaCO3

aggregates in the form of dumbbell, double dumbell and flower like clusters are

observed, as depicted in Figure 3b.2c.These clusters constitute nanosized subunits

with size around 30nm. The enlarged SEM images of both the concentrations are

separately shown in (Fig. 3B.3b).Close similar morphology was observed commonly

in both the concentrations except variation in the size of the cluster and alignment of

rods. With the increase in concentration of GA the size of the cluster increases but the

nanocrystallite size decreases. This behavior can be attributed due to the effective

passivation of the surfaces and suppression of the growth of the nanoparticles through

strong interactions with the particles via there functional molecular groups of acacia

namely, hydroxyl groups of arabinose, rhamnose and galactose and carboxylic groups

of glucoronic acid moieties. Progressive changes in the assembled BaCO3 clusters

indicated that the arrangement continued to grow principally in width rather than in

length when the crystals interlinked. Although the individual rods observed in the

absence of templating species are often disordered, they were structurally intact,

98

suggesting that there are strong interparticle interactions between adjacent rods.

Significantly, the HR-SEM images show that the BaCO3 crystals appear to be higher-

order superstructures, exhibiting close morphological alignment of the rod shaped

crystals as well as aligned growth steps. Further crystal growth of BaCO3 was

monitored under hydrothermal crystallization at 60 °C and 90 °C. Since there is no

much variation in the morphology observed, the results obtained at 90 °C are shown

in Figure 3B.2d, e. At 90 °C stacks of rods are arranged randomly and appear like

flowers at lower gum acacia concentration (0.5%), whereas at higher concentration (1

%), more number of flower like clusters are seen but there is no change in the

morphology as observed in Figure 3B.2d,e. From this it is evident that during

hydrothermal crystallization, at two different concentrations common morphology

i.e.; flower shaped clusters are seen except their number increased at higher ratio of

metal/ligand concentration, and the size of the clusters is also almost similar. This

attributes that increasing concentration does not have much effect on the crystal

morphology during hydrothermal crystallization. Moreover, temperature variation

also does not have any impact in the growth morphology except variation in size. On

the other hand, synthesis of BaCO3 nanostructures at ambient condition show

influence of concentration on the morphology and arrangement of the clusters formed.

The schematic illustration of BaCO3 crystal morphology is shown in the Table 3B.2.

Table 3B.2: Schematic composition and morphology of BaCO3 at different

concentration of gum acacia (GA).

Condition Morphology of BaCO3 without

GA

Morphology of BaCO3 (0.5%wt GA)

Morphology of BaCO3 (1.0% wt GA)

Ambient Rod like aragonite crystals

Bunch of rods in the form of cluster

Dumbell,doubledumbell and flower shaped clusters

Hydrothermal (60ο)

Rod like aragonite crystals

Flower like clusters

( less number)

Flower like clusters (more number)

Hydrothermal (90ο)

Rod like aragonite crystals

Flower like clusters

( less number)

Flower like clusters

( less number)

99

Figure 3B.2: SEM images of BaCO3 clusters. a) Rod shaped aragonite crystals in the

absence of additive. b) & c) Room temp reaction process at 0.5% & 1.0% GA. d) & e)

hydrothermal (900) reaction process at 0.5% & 1.0% GA.

100

Figure 3B.3: Enlarged SEM images of BaCO3 clusters at different reaction

conditions. a) 0.5% GA at room temperature. b) 1% GA at room temperature. c)

0.5% GA at hydrothermal 90°C. d) 1% GA at hydrothermal 90 °C.

101

3B.3.3 TEM & EDAX

Figure (3B.4) shows that TEM images of BaCO3 clusters obtained in aqueous

solution (a) before and (b) after calcinations at 700 °C. As can be seen, the

morphology of the particles obtained in the presence of GA at the air/solution

interface is dumbbell, double dumbell and flower like clusters(Fig. 3B.4a) However,

after calcination at 700 °C the structure appears to be deformed resulting in the

formation of agglomerates of smaller particles of size around 20 nm (Fig. 3B.4c) .

Figure 3B.4b, d shows the corresponding EDAX spectrum and selected area electron

diffraction (SAED) pattern of the BaCO3 clusters. Selected area electron diffraction

(SAED) pattern obtained for BaCO3 show a number of spots arranged in circular

manner which confirms the nanocrystalline nature of grown nanoparticles.

Meanwhile, the corresponding SAED pattern (Fig. 3B.4b) exerted some regularly

aligned bright spots and also blurr diffraction rings containing relatively bright spots

could be indexed as the planes of (111), (002), (012), (130), (221), (132) and (113),

which were thus in agreement with the previous XRD results .The BaCO3 clusters

were believed to be self assembled by the related crystalline nanoparticles in presence

of appropriate additives rather than the random agglomeration. From Figure 3B.4b,d,

the EDAX elemental analysis reveals that carbon content is seen more in the as-

prepared BaCO3 microclusters when compared to the calcined material, which can be

attributed to the formation of organic-inorganic hybrid material, the organic

component mainly from GA.

102

Figure 3B.4: SEM, TEM images (SAED inserted) and EDAX of BaCO3. (a, b) In the

presence of 1% GA. (c, d) Calcined product at 700 οC.

103

3B.3.4 Ba-LaCO3 System and Ba-TbCO3 System

Other than Barium carbonate, mixed metal carbonates such as Ba-LaCO3 and

Ba-TbCO3 were synthesized at room temperature using higher GA (1.0 %)

concentration. Figure 3B.5a, c shows the SEM images of La doped BaCO3 and Tb

doped BaCO3, respectively. As can be seen, there is a clear morphological difference

between BaCO3 structures synthesized with and without the addition of rare earths.

Ba-LaCO3 clusters are in form of rods whereas Ba-TbCO3 appear to be dendritic

clusters. Inset shows the TEM image in which similar morphological features are

observed and is in consonance with the observations by SEM. It would be instructive

to understand the chemical composition of the different features observed for both Ba-

LaCO3 and Ba-TbCO3 microclusters. This is conveniently done by spot-profile

EDAX. In addition to the expected Ba, C and O signals, strong signals of La and Tb

are seen for La doped BaCO3 and Tb doped BaCO3, respectively as shown in Fig.

3B.5b, d. The composition and morphology is represented in the table 3B.3.

Table 3B.3: Schematic composition and morphology of Ba-LaCO3 and Ba-TbCO3 at

1.0% gum acacia (GA).

Condition

Morphology of Ba-LaCO3

(1.0% wt GA)

Morphology of Ba-TbCO3

(1.0% wt GA)

Ambient

Short rods

Dendritic clusters

104

Figure 3B.5: SEM images of mixed metal carbonates. a) Rod like clusters of Ba-

LaCO3. b) EDAX data of Ba-LaCO3. c) Dendritic clusters of Ba-TbCO3. d) EDAX

data of Ba-TbCO3.

105

3B.3.5 FT-IR spectra

FT-IR spectra of BaCO3 have been studied to determine the effect of GA on the

microstructure of nanocrystallites. The IR bands at 1445.83 and 1426.95 cm-1

corresponds to the asymmetric stretching mode of C-O bond (Fig. 3B.6a, b),

respectively. The sharp peaks at 856.74 and 693.45 (Fig. 3B.6a), 856.44 and 689.80

(Fig. 3B.6b) are in plane and out plane bending CO32-. In comparison with Figure

3B.6a the C-O stretching vibration peak around 1426 cm-1 in Figure 3b.6b shifts to

lower frequency by 19 cm-1 (1460 cm-1), suggesting that GA have an influence on the

microstructure of barium carbonate. This is probably due to the GA molecules adsorb

onto the surfaces of BaCO3 nuclei and influence the mode of crystal growth with a

little change of superstructure.

Figure 3B.6: FT-IR of BaCO3 clusters. a) Nucleated in the presence of GA. b)

Calcined product at 700 ο C.

106

Based on the above analysis, a possible growth mechanism for the formation of

flower like BaCO3 clusters at air/solution interface are schematically shown in Figure

3B.7. First the BaCO3 rods grow under the control of GA through frequently observed

crystallization. The functional moieties in GA are selectively adsorbed on the back

bone of rods. Then these rods aggregate and self assemble to form clusters. These

clusters gives an intermediate dumbbell like arrangement and then finally to flower

shaped cluster. As we know that the rod-dumbbell-sphere morphogenesis mechanism

appears to be rather universal, however, it has to be pointed out that the exact growth

mechanism is still unknown, although some explanation was given in the literature

based on the role of intrinsic electric fields, which direct the growth of dipole crystals.

The schematic representation of growth mechanism of BaCO3 clusters are shown in

Figure 3B.7.

Figure 3B.7: Schematic representation of growth mechanism of BaCO3 clusters.

107

3B.4 Conclusions

The biomineral phase, shape and function in natural systems are often

controlled by rather complicated chemical species. Using natural gums, a variety of

crystal morphology could be produced when ambient and hydrothermal conditions

were employed. In summary, we demonstrated that simple GA can be used as crystal

growth modifiers to template unusual complex morphologies of BaCO3 crystals. We

have demonstrated the formation of micro clusters of Barium carbonate through the

ambient and hydrothermal method. Micro clusters of Barium carbonate are bunch-

like, dumbbell, double dumbbell and flowerlike arrangement, which is confirmed by

TEM micrographs. The crystalline nature of Barium carbonate is confirmed by XRD

spectra whereas FT-IR spectra confirm the structural features of Barium carbonate.

Using these simple Gums, research is being further extended for the morphogenesis of

other minerals with complex superstructures and nanostructures. The obtained BaCO3

assemblies could find applications in industrial field.

108

3B.5 References

1. D. B. Deoliveira, & R. A. Laursen, J. Am. Chem. Soc. 1997, 119, 10627.

2. T.Kato, A.Sugawara, & N. Hosoda, Adv. Mater. 2002, 14, 869.

3. H. Colfen, & S.Mann, Angew. Chem. Int. Ed. 2003, 42, 2350.

4. S. H. Yu, & H. Colfen, J. Mater. Chem. 2004, 14, 2124.

5. H. Colfen, & S. H. Yu, MRS Bull. 2005, 30, 727.

6. G. Falini, S. Albeck & L. Addadi, Science, 1996, 271, 67.

7. D.D. Sawall, R. M. Villahermosa, R.A. Lipeles, & A. R. Hopkins, Chem.

Mater. 2004, 16, 1606.

8. S. A. Morin, F. F.Amos, & S.Jin, J.Am.Chem. Soc. 2007, 129, 1377.

9. T. X. Wang, A. Reinecke, & H. Colfen, Langmuir. 2006, 22, 8986.

10. S. Tugulu, M. Harms, M. Fricke, D. Volkmer & H. A. Klok, Angew. Chem.

Int. Ed. 2006, 45, 7458.

11. S.Ludwigs, U.Steiner, A.N.Kulak, R.Lam, & F.Meldrum, Adv. Mater.2006,

18, 2270.

12. Pileni, M. P., Gulik-Krzywicki, T., Tanori, J., Filankembo, A. & Dedieu. J. C.

Langmuir. 1998, 14, 7359.

13. G.D. Rees, R.Evans-Gowing, S. J. Mammond, & B. H. Robinson, Langmuir.

1999, 15, 1993.

14. A.L. Briseno, S.B. Mannsfeld, M.M.Ling, S. H. Liu, J. R. Tseng, C.Reese,

M.E.Roberts, Y.Yang, F. Wudl, & Z. N. Bao, Nature. 2006, 444, 913.

15. Y. H. Li, V. P. Kotzeva, & D.J. Fray, Mater Lett. 2006, 60, 2743.

16. W. J. Liu, W. D. He, Z.C.Zhang, et al, J Cryst Growth. 2006, 290,592.

109

17. J. E. Schaefar, H. Kisker, H. Kronmuller, & R. Wurschum, Nanostruct Mater.

1992, 1,523.

18. S. Komarneni, M. C. D Arrigo, C. Leionelli, G. C. Pellacani, & H. Kotuku, J

Am Ceram Soc.1998, 81, 3041.

19. P.P. Phule,. & D.C.Grundy, Mater Sci Eng B. 1994, 23, 29.

20. Chatterjee, D. Das, S.K. Pradhan, & D. Chakravorty. J Magn Magn Mater.

1993,127, 214.

21. Sondi & E. Matijevic, Chem. Mater. 2003, 15, 1322-1326.

22. D. M. Sun, Q. S. Wu, & Y.P. Ding, J. Appl. Cryst. 2006, 39, 544–549.

23. T. Wang, A.W. Xu, & H. Colfen Angew.Chem. Int. Ed. 2006,45, 445 –4455.

24. S.H. Yu, H. Colfen, & M. Antonietti, J. Phys. Chem. 2003,107, 7396-7405.

25. S.H. Yu, H. Colfen, A.W. Xu, & W. Dong, Cryst. Growth & Des. 2004, 4, 33-

37.

26. L.Chen, Y. Shen, A. Xie, J. Zhu, Z. Wu, & L.Yang, Cryst. Res.Technol. 2007,

42, 886-889.

27. K. Kon-no, M. Koide, & A. Kitahara, J. Chem. Soc. Jpn. 1984, 6, 815.

28. K. Kandori, K. Kon-no, & A. Kitahara, J. Disp. Sci. Technol. 1988, 9, 61.

29. L. Qi, J. Ma, H. Cheng, & Z. Zhao, J. Phys. Chem. B. 1997,101, 3460.

30. M. Dinamani, P.V. Kamath, & R. Seshadri, Cryst. Growth Des. 2003, 3, 417.

31. Sondi, & E. Matijevic, Chem. Mater. 2003, 15, 1322.

32. B. Gutmann, & A. Chalup, Am. Ceram. Soc. Bull. 2000, 63.

33. B.F. Allen, N.M.Faulk, S.C. Lin, R. Semiat, D. Luss, & J.T. Richardson,

AIChE Symp. Ser. 1992, 88, 76.

110

34. J. J. Macketta, Encyclopedia of Chemical Processing and Design, Marcel

Dekker, New York, 1977, 51.

35. Taubert, G. Glasser, & D. Palms, Langmuir, 2002, 18, 4488-4494.

36. J. Norwig, W.H. Meyer, & G. Wegner Chem. Mater. 1998, 10, 460-463.

37. D. Devi, S.V. Pratap, R. Haritha, K.S. Sivudu, P. Radhika, & B. Sreedhar, J.

Appl. Polym. Sci. (In press).

38. B. Sreedhar, P.S. Reddy, & D.K.Devi, J. Org. Chem. 2009,74, 8806–8809.

39. S. H. Yu, & H. Colfen, J. Mater.Chem. 2004, 14, 2124 – 2147.

40. H. Colfen, & M. Antonietti, Langmuir. 1998,14, 582-589.

41. N. A. J. M. Sommerdijk, & G. De, Chem. Rev. 2008,108, 4499-4550.

42. H. Colfen, Macromol. Rapid Commun. 2001,22, 219-252.

43. L.M. Qi, H. Colfen, M. Antonietti, M. Li, J.D.Hopwood, A.J. Ashley, & S.

Mann, Chem. Eur. J. 2001, 7, 3526.

44. L.M. Qi, H. Colfen, & M. Antonietti, Angew.Chem. Int. Ed. 2000, 39, 604-

607.

45. A.M. Belcher, X.H. Wu, R.J. Christensen, P.K. Hansma, G.D. Stuky, &

D.E.Morse, Nature, 1996,381, 56-58.

46. S. Mann, B.R. Heywood, S. Rajam, & J.D. Birchall, Nature, 1988, 334, 692-

695.