Green Synthesis of Barium Sulfate Particles Using Plant Extracts

The biological molecules in the extracts of four fruits or vegetables: kiwifruit, oranges, tomato and carrot, were used as templates to synthesize barium sulfate (BaSO4) particles. The products were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy and X-ray power diffractometry. The results showed that, leaf-shaped barite BaSO4 crystals with toothed edge were obtained with kiwifruit extracts; thorn spherical barium sulfate crystals with diameter of 2-4 micrometers were produced with tomato extracts; rod-like or quasi-spherical BaSO4 crystals with size of several hundred nanometers to several micrometers were gained with orange extracts; while quasi-spherical BaSO4 nano-crystals were obtained with carrot extracts. The formation mechanism of BaSO4 is also discussed, showing that the proteins, carbohydrates, vitamins and organic acids in above four kinds of fruits or vegetables may provide nucleation sites, controlling the growth of BaSO4 crystals with different morphologies.


Introduction
Barium sulphate (BaSO 4 ) is generally white or colorless, chemically inert, insoluble in water, with high density, and the main source of barium [1]. It is widely used as a shading material for the x-ray photography, a gammaray absorber, a white pigment and etc because it is non-harmful to humans. BaSO 4 is also one of the most important fillers used in the plastics, rubber and paint industries, and is also used in pharmaceutical formulations [2]. It can be used for X-ray attenuation instead of shielding made from lead when incorporated into polymeric materials to form composite [3].
In recent years, more attention has been paid on synthesis of BaSO 4 nanoparticles for their multiple applications in the oil industry, electronics, TV screen, glass, car filters, paint industry, ceramics and medicine, etc. Many approaches have been chosen to control the size and morphology of BaSO 4 particles. These methods could be classified as direct precipitation, microemulsion, membrane separation and organic modification [1]. M.
Ismaiel et al have synthesized BaSO 4 nanoparticles by precipitation method using polycarboxylate as a modifier [4]. D. Adityawarman have obtained BaSO 4 nanoparticles in a non-ionic microemulsion [5]. G. Wu et al have precipited BaSO 4 nanoparticles through impinging streams [6]. A. Gupta have prepared BaSO 4 nanoparticles using sodium hexa metaphosphate as a stabilizer [7]. Very recently, the synthesis of BaSO 4 nanoparticles by a chemical precipitation route without polymer stabilizers has been reported [1].
In this paper, we have synthesized BaSO 4 particles by a very simple and green method.
The BaSO 4 particles especially nanoparticles obtained may be used as filler in plastics. The possible formation mechanism of the BaSO 4 particles directed by biomolecules of the fruits or vegetables including kiwifruit, oranges, tomato and carrot is discussed. This report may be very significant for biomineralization research and green synthesis of functional inorganic materials.

Materials and Instruments
Barium chloride dihydrate (BaCl 2· 2H 2 O), anhydrous sodium sulfate (Na 2 SO 4 ), and ethanol were purchased from reagent plant of Shanghai (Shanghai, China), and were analytically pure. They were used without further purification. Four kinds of fruits or vegetables: kiwifruit, oranges, tomato and carrot were purchased from a local farmer.

Methods
First, 80g of each fruit or vegetable were washed carefully, and then crushed to extract juice, and the juice was mixed proper amount of double-distilled water, obtaining 90 mL of the fruit or vegetable extracts aqueous solution. After that, 20 mL of each solution was mixed with 40 mL of 0.05 mol/L BaCl 2 , completely, obtaining 60 mL of mixed solution containing fruit or vegetable extracts and 0.0333 mol/L BaCl 2 . Then each of the mixed solution was blended with 40 mL of 0.05 mol/L Na 2 SO 4 very slowly. The white precipitates produced in the mixed systems. The control experiment was also performed without adding of fruit or vegetable extracts. The above five reaction systems were placed at room temperature for 24 hours.
The white precipitates produced in the reaction solutions were separated by centrifugation (centrifugating rate, 4000 rpm), washed three times with double-distilled water and ethanol, respectively, and then vacuum dried for further determination.
The sizes and morphologies of the precipitates were examined by scanning electron microscopy (SEM), while their crystal phases were determined by Fourier transform infrared spectroscopy (FT-IR) or X-ray powder diffractometry (XRD).  Fig.1a and b, it can be seen that the particles obtained without any exracts are leaf-shaped with toothed edge. The size of each "leaf" is about 4-8 ȝm. Fig. 1c and d shows that the particles obtained with kiwifruit extracts are also leaf-shaped, but the sizes of them become slightly smaller. When in the presence of tomato extracts, many thorn spheres with diameters of 2-4 ȝm are produced ( Fig. 1e and f). While with orange extracts, quasi-spherical or rod-like BaSO 4 particles with sizes of several hundred nanometers are gained ( Fig. 1g and h). At last, it can be seen from Fig. 1i   If seen clearly, the intensity of crystal face (020) in Fig. 3a is stronger than that of it in The extracts of fruits and vagetables including kiwifruit, tomato, orange and carrot contain mang kinds of organic macromolecules such as proteins, carbohydrates, vitamins and some organic acids. In previous reports, it is accepted that the soluble biomacromolecules such as acidic proteins, glycoproteins and polysaccharides in biological systems act as nucleators, growth modifiers, and anchoring units in the mineral formation [8]. Here, we speculate that Ba 2+

Summary
Green synthesis of BaSO 4 particles using the extracts of four fruits or vegetables including kiwifruit, oranges, tomato and carrot was performed. leaf-shaped barite BaSO 4 crystals with toothed edge were obtained in kiwifruit juice; thorn spherical barium sulfate crystals with diameter of 2-4 micrometers were produced in tomato juice; rod-like or quasi-spherical BaSO 4 crystals with size of several hundred nanometers to several micrometers were gained in orange juice; while quasi-spherical BaSO 4 nano-crystals were obtained in carrot juice. The formation mechanism of BaSO 4 was also discussed, showing that proteins, carbohydrates, vitamins and organic acids in above four kinds of fruits or vegetables can provide nucleation sites, controlling the formation of BaSO 4 particles with different morphologies.