“Hydrogel-Based Growth of Cobalt Tartrate Single Crystals and Their Morphological Study”

“Hydrogel-Based Growth of Cobalt Tartrate Single Crystals and Their Morphological Study”

Sachin J Nandre,

Dept of Physics, Uttamrao Patil College, Dahiwel (Dhule)

Abstract

Single crystals of cobalt tartrate (CoC₄H₄O₆·xH₂O) were successfully grown using the hydro-silica gel technique, which allows controlled nucleation and slow diffusion of reactants in a three-dimensional porous medium. Cobalt tartrate is a transition metal-organic complex with potential applications in catalysis, magnetic materials, and electrochemical sensors. The growth process was optimized by adjusting gel concentration, reactant molarity, and pH, resulting in well-faceted, transparent to pale pink crystals. The study demonstrates the effectiveness of the hydro-silica gel method for producing high-quality cobalt tartrate crystals and provides insights into their growth mechanism and morphology control.

Keywords: Hydrosilica gel, catalysis, electrochemical sensors.

1. Introduction

Cobalt tartrate, a coordination complex of cobalt and tartaric acid, exhibits unique optical, magnetic, and structural properties due to the d-orbital interactions of cobalt ions and the chelating behavior of tartarate ions. The controlled growth of single crystals of cobalt tartrate is essential for materials characterization and applications in electronics, optics, and catalysis.The hydro-silica gel technique is a soft chemical crystal growth method where reactants slowly diffuse through a gel matrix, enabling controlled nucleation and growth at ambient temperature. This method offers advantages over conventional solution growth, including, low temperature growth, avoiding thermal decomposition, control over crystal size and morphology, reduction of spontaneous precipitation.

This work aims to grow cobalt tartrate crystals using the hydro-silica gel method and study the effect of gel concentration, reactant molarity, and growth time on crystal morphology and size. Growth of crystal ranges from a small inexpensive technique to a complex sophisticated expensive process and crystallization time ranges from minutes, hours, days and to months. The starting points are the historical works of the inventors of several important crystal growth techniques and their original aim. The methods of growing crystals are very wide and mainly dictated by the characteristics of the material and its size.

2. Experimental Technique

2.1 Materials

The materials were purached from Lobachempvt ltd. All the materials were AR grade and they are used without any further purification. Cobalt chloride hexahydrate (CoCl₂·6H₂O), Tartaric acid (C₄H₆O₆), Sodium metasilicate (Na₂SiO₃·5H₂O) for gel preparation, Distilled water,Glacial acetic acid (for pH adjustment).

2.2 Preparation of Hydro-Silica Gel

Sodium metasilicate solution was prepared by dissolving 50 g of Na₂SiO₃·5H₂O in 100 mL of distilled water.The solution was acidified slowly with 1 M acetic acid under constant stirring until gelation occurred (pH ~4–5). The gel was allowed to set in test tubes and aged for 24–48 hours to strengthen the matrix. The following table 1 shows the standard optimized parameters for the crystal growth development.

Sr.No	Optimum Conditions	Cobalt Tartrate
1	Density of Sodium Meta Silicate	1.04gm/cm3
2	Conc. of Tartaric acid	0.5M
3	Volume of Tartaric acid	7ml
4	Volume of Sodium Meta Silicate	18ml
5	Volume of Cobalt Cholride	5ml
6	pH of the gel	4
7	Ageing Period	One week

The crystals were extracted by carefully breaking the gel after two to three weeks depend on the growth parameters.  The extracted crystals were subjected to study their physical properties particularly crystal size, growth morphology, crystal structure, and optical behavior. Growth morphology was studied by using scanning electron microscope. Crystal structure was identified by using X-ray diffraction technique.

3. Results and discussion

Crystal growth occurs via slow diffusion of Co²⁺ and tartrate ions through the hydro-silica gel.Gel acts as a porous medium, restricting rapid precipitation and promoting uniform nucleation.Chelation of cobalt ions by tartarate ions stabilizes the crystal lattice.Hydrogen bonding and van der Waals interactions within the gel network facilitate orderly crystal assembly. In the present experiment, a 0.1 M solution of cobalt chloride was carefully poured on top of the set silica gel and 0.1 M solution of tartaric acid was layered above the gel to allow slow diffusion. The test tubes were sealed to prevent evaporation and left undisturbed at room temperature (~25°C).Crystals started to appear after one week, and growth continued for up to three weeks in order to get full grown crystals with different facets.

It is observed that concentration of cobalt chloride and tartaric acid has significant effect on the growth of the crystals. It is found out that higher cobalt ion concentration increases the nucleation sites resulting smaller crystals and for lower concentration of cobalt ions slowed crystal growth, yielding larger but few crystals. However, the equimolar concentrations of cobalt chloride and tartaric acid resulted in optimal crystal quality.

Fig 1. Photographic image of Cobalt tartrate crystal obtained after three weeks.

Figure 2 shows the X-ray diffraction pattern of Cobalt Tartrate Single Crystals.  The orientations of (111), (200), (220), and (311) planes are observed which reveals well-defined crystal structure of the grown materials.

Figure 2:  XRD of Gel grown Cobalt Tartrate Crystal

Figure 3 shows the microscopic SEM images of cobalt tartrate crystals. These crystals were pale pink to pink in color with transparent, and prismatic properties. The grown crystals shaped changed with respect to pH of the gel concentration. The shape of the crystals changed from spherical granule to crystal size ranged from 1–6 mm, depending on gel concentration and reactant molarity.Lower gel density led to faster diffusion, resulting in smaller but more numerous crystals.Higher gel density slowed ion diffusion, producing fewer but larger, well-faceted crystals.

Figure 3: Scanning electron microscopy images of  Cobalt Tartrate Crystal grown by gel-gel technique.

4. Conclusions

Cobalt tartrate crystals were successfully grown using the hydro-silica gel technique. The study shows that gel density, reactant molarity, and pH are critical parameters in controlling crystal size and morphology. The hydro-silica gel method is effective in producing high-quality, well-faceted cobalt tartrate crystals at ambient temperature. These crystals can be used for further studies in materials characterization, optical properties, and catalytic applications.

Acknowledgements

The authors would like to express their sincere gratitude to Principal Dr Suresh Ahire Sir  for their valuable guidance and support throughout this work. We also thank the Dept. of Physics Uttmrao Patil College, Dahiwel for providing the necessary facilities and resources for the preparation and characterization of strontium malonate crystals. Special thanks are extended to colleagues and staff who assisted in experimental setup, observations, and discussions that contributed to the success of this research.

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