- Email: [email protected]
Chemosynthesis of monodispersed porous BaSO4 nano powder by polymeric template process and its characterisation
Powder Technology 224 (2012) 51–56
Contents lists available at SciVerse ScienceDirect
Powder Technology journal homepage: www.elsevier.com/locate/powtec
Chemosynthesis of monodispersed porous BaSO4 nano powder by polymeric template process and its characterisation Nisha Nandakumar 1, Philip Kurian ⁎ Department of Polymer Science and Rubber Technology, Cochin University of Science and Technology, Cochin22, Kerala, India
a r t i c l e
i n f o
Article history: Received 22 September 2011 Received in revised form 5 February 2012 Accepted 11 February 2012 Available online 21 February 2012 Keywords: Barium chloride Nano powders Porous material Monodispersed Polyvinyl alcohol Facile synthesis
a b s t r a c t Monodispersed spheroid BaSO4 nano powders with porous structures were synthesised via a facile single step procedure. Liquid–liquid chemosynthesis involving direct precipitation of BaCl2 and (NH4)2SO4 in aqueous polyvinyl alcohol (PVA) solution as a polymeric template was employed. PVA, a polymeric surfactant, acts as a template for particle growth and assists morphology control and can be easily removed after synthesis by calcination. The dried and calcined nano powders were characterised by X-ray diffraction (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermo gravimetric analysis (TGA). The studies revealed that the porosity and size of the particle were highly governed by PVA content and calcination temperatures. The powder synthesised in 3% w/v PVA showed an average particle size ranging from 20 to 23 nm. The monodispersed porous powders were stable and showed spheroid like structures up to 600 °C; after which the nano structure is lost drastically and agglomeration leads to structure collapse forming lumpy flakes. © 2012 Elsevier B.V. All rights reserved.
1. Introduction The chemical synthesis of inorganic materials of nanometre size, specific morphology and superstructure has attracted considerable attention due to its potential application in sophisticated areas. Barium sulphate is one of the most important inorganic fillers used in the plastics, rubber and paint industries and also in pharmaceutical formulations. Preparation of BaSO4 particles has been widely studied in order to assess the effect of mixing, precipitation models, agitator speed and feed position on particle size distribution, crystal growth and morphology [1,2]. Nanometre barium sulphate has more scientific advantage on size reduction. Liquid–liquid precipitation is the principle preparation method of nano particles [3,4]. In general, barium sulphate is synthesised by adding SO42− ions directly into the solutions containing Ba 2+or complex of Ba 2+ [5]. Many different approaches have been reported for the preparation of BaSO4 nano particles including the addition of different additives [6] such as, induction by monolayer and micro emulsion [7], micro channel reactors [8] etc. So far, for controlling the size and morphology of BaSO4 particles, amino-carboxylate additives, phosphonate/phosphate inhibitors [9], PMMA [10], double-hydrophilic block copolymers, as well as waterin-oil micro emulsion systems [11,12] were used. Template-directed synthesis and morphosynthesis are the two distinct categories of ⁎ Corresponding author. Tel.: + 91 484 2575590; fax: + 91 484 2577747. E-mail addresses: [email protected] (N. Nandakumar), [email protected] (P. Kurian). 1 Tel.: + 91 484 2575590; fax: + 91 484 2577747. 0032-5910/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.powtec.2012.02.022
methods that have been developed to prepare particles and modify their structure. In template-directed synthesis, additives added to the reaction system govern nucleation and growth [13–17], whereas in morphosynthesis, synthesis is limited to micro reaction environment [3,18–20]. Barium sulphate crystals with a diameter in the sub200 nm range have wonderful optical characteristics and flow behaviour, and have been widely used in printing ink, pigment and medicine. There have been many reports on barium sulphate nano particle and nano filament synthesis using micro emulsion technology [13–17]. A number of researchers have attempted various methods to prepare nano powders. However, the exploration of facile chemosynthesis of porous and monodispersed BaSO4 nano powders in aqueous media at ambient conditions remains non-systematic. Until now, there have been no reports on the preparation of nano BaSO4 in PVA supported medium at room temperature. Herein, we investigated that nano BaSO4 can be successfully synthesised in aqueous polyvinyl alcohol solution. We investigated the influence of polyvinyl alcohol on morphology and size and its role in yielding porous nano materials. We varied the experimental conditions such as concentration of polyvinyl alcohol and calcination temperatures; and compared the nature of barium sulphate formed during each condition at constant molar ratio of reactants. 2. Experimental 2.1. Preparation Polyvinyl alcohol (mwt.1, 25,000) was purchased from Spectrochem. Barium chloride (BaCl2) and ammonium sulphate (NH4)2SO4 were
52
N. Nandakumar, P. Kurian / Powder Technology 224 (2012) 51–56
obtained from Merchem. All the chemicals were used without further purification. The preparations were carried out at ambient temperature (ca. 25 °C) in a glass beaker. In the synthesis of monodispersed spheroid BaSO4 nano powders with nano structures, 20 ml of 0.5 M BaCl2 was initially thoroughly mixed with 20 ml of water containing 0% w/v, 1% w/v, 3% w/v, 5% w/v and 7% w/v of PVA respectively and all solutions except 0% w/v showed a turbid appearance soon after mixing, though no visible precipitation was observed. Then 10 mL of 1.0 M (NH4)2SO4 was added drop wise from a micro burette at a minimised rate to the mixture under vigorous magnetic stirring. The mixture was stirred for another 1 min after complete addition of reagent and kept under static conditions for 5 h before the white precipitate was washed. The precipitate was washed thoroughly with distilled water to remove unused PVA, reactants and by-products, filtered and dried at 80 °C for 2 h prior to calcinations at 400 °C, 600 °C and 800 °C. 2.2. Characterisation The XRD patterns of the so prepared samples were recorded on a diffractometer Rigaku Geiger flex with nickel filtered Cu Kα (λ = 1.54 Å) as a radiation source and at a 2θ scan speed of 1°/min at 30 kV and 20 mA. The crystallite size of BaSO4 was calculated by X-ray line broadening technique using Debye–Scherrer equation = kλ/βcosθ, where k = 0.9 and D corresponds to BaSO4 crystallite size. Particle size distribution was analysed using Malvern Instruments MAL1008884 model particle size analyser at a count rate of 250.8 kcps. Scanning electron microscopy (SEM) [JOEL JSM-6390L] was used for morphological studies and the chemical purity of the samples was confirmed using energy dispersive X-ray spectroscopy (EDAX) attached along with the same equipment. The morphology, porosity and particle size were observed using transmission electron microscopy on a Philips TEM CM200 model. TGA profiles of nano powder were recorded on a thermo gravimetric analyzer (TGA Q-50, TA instruments) in which approximately 10 mg of the sample was heated from ambient temperature to 1000 °C. Nitrogen gas was continuously allowed to flow at the rate of 90 mL/min through the chamber. The surface characteristics of the powders were recorded with Bruker FT-5DX (Nicolet) spectrophotometer (infrared spectra) at wave numbers of 4000–400 cm− 1. 3. Results and discussion 3.1. X-ray diffraction (XRD) studies 3.1.1. Influence of PVA concentration on XRD The XRD patterns of the barium sulphate powders synthesised with 0, 1, 3, 5 and 7 weight by volume percentage aqueous solutions of PVA as mediums are shown in Fig. 1. The samples display the typical orthorhombic structure of BaSO4 .The d-values of BaSO4 nano material are 4.34x, 2.125 and 3.904 (JCPDS No: 83-1718), 3.44x, 3.10x and 2.127 (JCPDS No: 83-2053) with hkl values of (101), (311), (111) and (210), (211), (401) respectively. The XRD pattern was indexed with reference to the unit cell of the barite structure (a~ 8.87, b ~ 5.45, c ~ 7.15 A°; space group (Pnma)) [21]. Only BaSO4 peaks were observed in the XRD spectra. This indicated that all the powders had high purity. XRD reveals that as the PVA concentration increased the intensity and crystallinity of the peaks decreased as indicated by the shortening and broadening of peaks. The particle size obtained showed a minimum crystal grain size range as calculated using the Scherrer formula from broadening of XRD for {210} peak (~23 nm) with 3% PVA solution, whereas at higher concentrations the peaks shows negligible crystalline nature and on the other hand at lower concentrations of PVA they were crystalline; but with larger grain size as indicated by sharp peaks. Moreover all the powders prepared in the presence of PVA showed smaller grain size than the BaSO4 prepared without PVA
Fig. 1. X-ray diffraction spectra of nano BaSO4 prepared in aqueous medium with different concentrations of PVA (a) 0% (aqueous medium, 0% PVA), (b) 1% (1% PVA solution), (c) 3% (3% PVA solution), (d) 5% (5% PVA solution), and (e) 7% (7% PVA solution).
indicating that presence of PVA had a dispersive and protective effect on the powders. Thus XRD assisted analysis revealed that 3% PVA solution is an optimum medium for nano synthesis and this may be because at this concentration the polymer coating is perfect on each mole of the reactant and every single Ba 2+ ion coated in PVA reacts with a single SO42− leading to reduced agglomeration of powders formed. 3.1.2. Influence of calcination temperature on XRD The influence of calcination temperature on the particle size was analysed using XRD-spectra of nano BaSO4 synthesised in 3% PVA solution at different calcination temperatures viz. 400 °C, 600 °C and 800 °C for 4 h (Fig. 2). Only BaSO4 peaks were observed in the XRD spectra of all samples except for a calcination temperature of 400 °C. This indicated that all other powders had high purity. The intensity and width of diffraction peaks differed between samples calcined at different temperatures. The spectra revealed that as the calcination temperature increased the crystallinity of the sample increased and grain size increased, whereas at 600 °C the grain size fall into 23 nm range as calculated using the Scherrer formula from broadening of
Fig. 2. X-ray diffraction spectra of nano BaSO4 synthesised in aqueous medium with 0% PVA and in 3% PVA solution calcined at different temperatures (a) 0% PVA, dried at 80 °C, (b) 3%, 800 °C,(c)3%, 600 °C, and (d) 3%, 400 °C.
N. Nandakumar, P. Kurian / Powder Technology 224 (2012) 51–56
53
BaSO4 and the peaks in the spectra indicated the formation of controlled monodispersed powder at this temperature. Moreover all the calcined powders showed smaller grain size than the BaSO4 prepared in aqueous medium without PVA support indicating that, presence of PVA had a dispersive and protective effect on the powders which assists in size control even after its removal through calcination. These facts are again supported by the IR profiles (Fig. 7). 3.2. Particle size distribution Particle size distribution was analysed using Malvern Instruments MAL1008884 model particle size analyser at a count rate of 250.8 kcps and is shown in Fig. 3. The properties of nano particles are significantly depending on the particle size distribution. Especially evenly distributed particle size is of interest due to the size dependent physical and chemical properties of the nano particles. Most of the particles have particle size in the 20–25 nm range. This is in good agreement with the XRD result. Fig. 3. Particle size distribution of monodispersed porous BaSO4 nano material.
3.3. Studies using scanning electron microscopy (SEM) and transmission electron microscopy (TEM)
XRD for {210} peak. At 400 °C the grain size is small as indicated by the broadening and shortening of peaks. Appearance of the impurity peaks in nano BaSO4 synthesised in 3% PVA solution calcined at 400 °C clearly indicates that complete removal of all the carbonaceous species is not possible at this temperature, and hence is not sufficient for post synthesis treatment. At 800 °C pure nano barium sulphate was formed but agglomeration takes place as observed by narrow peak formation. Powder calcined at 600 °C yields small grain size with high purity. It is the optimum temperature that ensures complete removal of PVA template and other impurities from the nano
The porous monodispersed barium sulphate nano material was obtained by direct combination of Ba 2+ and SO42− in 3% aqueous PVA solution followed by calcination. Morphological analysis using SEM photographs of these sample shows that all nano powders were spheroid. Fig. 4 shows that synthesised barium sulphate without PVA had a flaky structure with high degree of agglomeration and microstructures; whereas all samples prepared in 3% aqueous PVA solution had spheroid morphology with uniformly arranged particles of almost similar shape and size. Thus the nano structures of the synthesised powders have a subtle relationship
Fig. 4. SEM photographs of monodispersed porous BaSO4 nano material synthesised in aqueous medium with 0% PVA and in 3% PVA solution calcined at different temperatures (a) 0% PVA, dried at 80 °C, (b) 3%, 400 °C , (c) 3%, 600 °C, and (d) 3%, 800 °C.
54
N. Nandakumar, P. Kurian / Powder Technology 224 (2012) 51–56
Fig. 5. EDAX spectra of BaSO4 nano material synthesised in 3% PVA and calcined at 600 °C.
with the presence of PVA, which leads directly to the formation of monodispersed porous nano powders. The dependence of structure on temperature of calcination is clear from SEM photographs of nano BaSO4 prepared in 3% PVA calcined at 3 different temperatures. At lower calcination temperatures the crystals had smaller size as it is clear from Fig. 4(b), (c) (barium sulphate calcined at 400 °C and 600 °C). As the calcination temperature increased from 600 °C to 800 °C, structure collapse leading to agglomeration is clearly depicted in Fig. 4(d) (barium sulphate calcined at 800 °C). Hence it can be concluded that up to a calcination temperature of 600 °C, the spheroid monodispersed structure is stable and after that there is a drastic change in the material due to agglomeration. This agglomeration of nano powders is due to structure collapse at higher temperature owing to the rapid removal of PVA from the surface. The related EDAX analysis of samples prepared in 3% aqueous PVA solution calcined at 600 °C is shown in Fig. 5. The EDAX contains only peaks for barium (Ba), sulphur (S) and oxygen (O), the absence of carbon (C) peaks indicates the complete removal of coated PVA from nano powders during
calcination. This is indicative of the purity of the material. The analysis of these results exhibits the presence of Ba, S and O in the ratio 1.0:0.9:4.0 close to the stoichiometry of BaSO4 within experimental error. Thus it can be deduced that pure BaSO4 was formed during the synthesis. The SEM photographs confirm the generation of monodispersed porous nano sized particles at an accelerating voltage of 25 kV. The TEM images (Fig. 6) of BaSO4 synthesised in 3% PVA solution and calcined at 600 °C confirm the formation of nano particles. The particle size obtained from TEM was 23 nm. The porous nature of sample is evidenced from uniform small pores in the particle, and these regions appear brighter than the surroundings because they have absorbed fewer electrons [2].
Fig. 6. TEM photographs of monodispersed porous BaSO4 nano material synthesised in 3% PVA solution calcined at 600 °C.
Fig. 7. FTIR-spectra of monodispersed porous nano BaSO4 synthesised in aqueous medium with 0% PVA and in 3% PVA solution. (a) 0% and (b) 3%.
3.4. Fourier transform infrared resonance — (FTIR) studies The infrared (IR) spectra of BaSO4 prepared in aqueous medium without PVA and porous monodispersed nano BaSO4 powder materials
N. Nandakumar, P. Kurian / Powder Technology 224 (2012) 51–56
prepared in 3% PVA solution calcined for 4 h at different temperatures are shown in Fig. 7. The presence of broad absorption band at 3405 cm− 1 in Fig. 7(d) for BaSO4 prepared in 3% PVA and dried at 80 °C corresponds to hydrogen bonding. This gets weakened as the calcination temperature increases as it is seen in Fig. 7(b) for BaSO4 prepared in 3% PVA calcined at 400 °C. From Fig. 7(c) for BaSO4 prepared in 3% PVA calcined at 600 °C, it can be observed that such molecular forces leading to particle aggregation are removed on increasing the calcination temperature. The weak absorption bands in Fig. 7(d) at 2932 and 2830 cm− 1 are due to stretching vibrations of methyl (υ (CH2) groups from PVA which disappeared as calcination temperature increased indicating that PVA is removed from nano BaSO4 powders at 400 °C itself. The IR spectrum of precipitated barium sulphate without PVA is shown in Fig. 7(a). IR spectra of all samples had peaks centred at 1197 and 1076 cm− 1 and shouldered at 980 and 818 cm− 1 which corresponds to symmetrical vibrations of sulphate and 610 cm− 1 for out of plane bending vibration of sulphate. All the above facts indicated that during the reaction, Ba 2+ ions were encapsulated in polyvinyl alcohol; the state at which the reactive chloride ions meet its counter ion in a dilute isolated state leading to reduced agglomeration. And the powders formed will be surrounded by PVA as indicated in IR spectra (Fig. 7d) which can be removed in the final stage by calcination as shown in Fig. 7(b) and (c). 3.5. Thermo gravimetric analysis Thermo gravimetric analysis of dried sample prepared in aqueous medium without PVA and in 3% PVA solution was carried out in the temperature range from 40 to 1000 °C. The thermal behaviour of these powders is shown in Fig. 8. The dotted lines represent TGA patterns of BaSO4 synthesised in aqueous medium wihout PVA and bold lines indicates that of the powder synthesised in 3% PVA solution. It is clear from the patterns that the thermograms showed a similar trend in weight loss up to 400 °C (1.364%) and the former powder showed no weight loss above that whereas in the latter case 1.855% of weight loss was recorded up to a calcination temperature of 600 °C. Increasing the calcination temperature from 400 to 600 °C the weight loss of ~0.50% accounts for the removal of coordinated organic groups. Moreover on increasing the temperature from 600 °C, the weight loss is negligible which prevails up to 790 °C. But since such a high temparature may lead to structure collapse a minimum calcination temparature of 600 °C is accepted in practice for the complete removal of impurities with consistent nano structure.
Fig. 8. TGA patterns of monodispersed porous nano BaSO4 synthesised in aqueous medium without PVA (- - -) and in 3% PVA solution (—).
55
4. Conclusions BaSO4 nano powder with a particle size in the range of 20–23 nm was synthesised by using a polymeric template. BaSO4 particles formed were encapsulated with PVA during the synthesis for preventing agglomeration. Liquid–liquid chemosynthesis involving direct precipitation of BaCl2 and (NH4)2SO4 in aqueous polyvinyl alcohol (PVA) solution as a polymeric template was employed. The morphology of synthesised nano particles was characterised using SEM as well as TEM. The analysis carried out revealed that 3% aqueous PVA solution is an optimum medium for synthesis. PVA assisted the formation of nano particles with smaller grain size and this could be removed at the final stage by calcination. Thermal studies revealed that the porous monodispersed nano structure is stable up to 600 °C with regular spheroid structures. The calcined powders yielded small grain size with high purity as indicated by the barite structure in XRD spectra and elemental composition in EDAX analysis.
Acknowledgement The authors are thankful to the Cochin University of Science and Technology, India for providing financial assistance for the work. References [1] B. Judat, M. Kind, Morphology and internal structure of barium — derivation of a new growth mechanism, Journal of Colloid and Interface Science 269 (2) (2004) 341–353. [2] H. Bala, W. Fu, J. Zhao, X. Ding, Y. Jiang, et al., Preparation of BaSO4 nanoparticles with self-dispersing properties, Colloids and Surfaces A: Physicochemical and Engineering Aspects 252 (2005) 129–134. [3] L.M. Qi, H. Colfen, M. Antonietti, Control of barite morphology by doublehydrophilic block copolymers, Chemical Material 12 (2000) 2392–2403. [4] M.H. Qu, Y.Z. Wang, C. Wang, X.G. Ge, D.Y. Wang, Q. Zhou, A novel method for preparing poly(ethylene terephthalate)/BaSO4 nanocomposites, European Polymer Journal 41 (2005) 2569–2574. [5] K. Takiyama, Formation and ageing of precipitates. IX. Formation of monodispersed particles. 2. Bariumsulfate precipitate by ethylenediamminetetraacetic acid method, Bulletin of the Chemical Society of Japan 31 (1958) 950–953. [6] F. Jones, A. Oliviera, G.M. Parkinson, A.L. Rohl, A. Stanley, et al., The effect of calcium cations on the precipitation of barium sulfate 1 calcium ions in the presence of organic additives, Journal of Crystal Growth 262 (2004) 572–580. [7] B.M. Nagaraja, H. Abimanyu, K.D. Jung, K.S. Yoo, Preparation of mesostructured bariumsulfate with high surface area by dispersion method and its characterization, Journal of Colloid and Interface Science 316 (2) (2007) 645–651. [8] Q.A. Wang, J.X. Wang, M. Li, L. Shao, J.F. Chen, et al., Large-scale preparation of bariumsulphate nanoparticles in a high-throughput tube-in-tube microchannel reactor, Chemical Engineering Journal 149 (2009) 473–478. [9] F. jones, W.R. Richmond, A.L. Rohl, Molecular modelling of phosphonate molecules onto bariumsulfate terraced surfaces, The Journal of Physical Chemistry. B 110 (2006) 7414–7424. [10] X. Zhao, J. Yu, H. Tang, J. Lin, Facile synthesis of monodispersed barium sulphate particles via an in situ templated process, Journal of Colloid and Interface Science 311 (2007) 89–93. [11] N.I. Ivanova, D.S. Rudelev, B.D. Summ, A.A. Chalykh, Synthesis of bariumsulfate nanoparticles in water-in-oil microemulsion systems, Colloid Journal 63 (2001) 714–717. [12] D. Adityawarman, A. Voigt, P. Veit, K. Sundmacher, Precipitation of BaSO4 nanoparticles in a non-ionic microemulsion: identification of suitable control parameters, Chemical Engineering Science 60 (12) (2005) 3373–3381. [13] P. Dutta, J.H. Fendler, Preparation of cadmium sulfide nanoparticles in selfreproducing reverse micelles, Journal of Colloid and Interface Science 247 (1) (2002) 47–53. [14] L. Mei, S. Mann, Emergence of morphological complexity in BaSO4 fibers synthesised in AOT microemulsions, Langmuir 16 (2000) 7088–7094. [15] J.D. Hopwood, S. Mann, Synthesis of bariumsulfate nanoparticles and naanofilaments in reverse micelles and micro emulsions, ChemicalMaterial 9 (1997) 1819–1828. [16] L.M. Gan, L.H. Zhang, H.S.O. Chan, C.H. Chew, Preparation of conducting polyaniline-coated bariumsulfate nanoparticles in inverse microemulsions, Materials Chemistry and Physics 40 (1995) 94–98. [17] M. Summers, J. Eastoe, S. Davis, Formation of BaSO4 nanoparticles in microemulsions with polymerised surfactant shells, Langmuir 18 (2002) 5023–5026. [18] M.P. Pileni, Nanostructured fluids in oil-rich regions: structural and templating approaches, Langmuir 17 (2001) 7476–7486. [19] Y. Xie, Y.T. Qian, W.Z. Wang, A benzene-thermal synthetic route to nanocrystalline GaN, Science 272 (1996) 1926–1927.
56
N. Nandakumar, P. Kurian / Powder Technology 224 (2012) 51–56
[20] W.Z. Zhou, J.M. Thomas, D.S. Shepard, Brian F.G. Johnson, D. Ozakaya, T. Maschmeyer, Robert G. Bell, Qingfeng Ge, Ordering of ruthenium cluster carbonyls in nanoporous silica, Science 280 (5364) (1998) 705–708. [21] R.J. Hill, The Canadian Mineralogist 15 (1977) 522–526.
Philip Kurian joined Cochin University of Science and Technology on 28-11-1978 as a Faculty in Polymer Science and Rubber Technology. He earned his PhD in Polymer Technology at Polymer Science and Rubber Technology CUSAT. His areas of research include polymer blends and composites, rubber ferrite composites, rubber compounding, novel compounding ingredients and polymer nanocomposites. He has 32 years of teaching experience and 22 years of research experience and has 35 publications in various international journals along with 16 conference papers. He have produced 4 PhDs so far and at present 5 students are been guided by him.
Nisha Nandakumar joined CUSAT on 01-09-2008 as a research student under the guidance of Dr. Philip Kurian in Polymer Science and Rubber Technology Department. She joined the institution after her post graduation in chemistry. Her research area is polymer nanocomposites of elastomers and has presented papers in three conferences.
Contents lists available at SciVerse ScienceDirect
Powder Technology journal homepage: www.elsevier.com/locate/powtec
Chemosynthesis of monodispersed porous BaSO4 nano powder by polymeric template process and its characterisation Nisha Nandakumar 1, Philip Kurian ⁎ Department of Polymer Science and Rubber Technology, Cochin University of Science and Technology, Cochin22, Kerala, India
a r t i c l e
i n f o
Article history: Received 22 September 2011 Received in revised form 5 February 2012 Accepted 11 February 2012 Available online 21 February 2012 Keywords: Barium chloride Nano powders Porous material Monodispersed Polyvinyl alcohol Facile synthesis
a b s t r a c t Monodispersed spheroid BaSO4 nano powders with porous structures were synthesised via a facile single step procedure. Liquid–liquid chemosynthesis involving direct precipitation of BaCl2 and (NH4)2SO4 in aqueous polyvinyl alcohol (PVA) solution as a polymeric template was employed. PVA, a polymeric surfactant, acts as a template for particle growth and assists morphology control and can be easily removed after synthesis by calcination. The dried and calcined nano powders were characterised by X-ray diffraction (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermo gravimetric analysis (TGA). The studies revealed that the porosity and size of the particle were highly governed by PVA content and calcination temperatures. The powder synthesised in 3% w/v PVA showed an average particle size ranging from 20 to 23 nm. The monodispersed porous powders were stable and showed spheroid like structures up to 600 °C; after which the nano structure is lost drastically and agglomeration leads to structure collapse forming lumpy flakes. © 2012 Elsevier B.V. All rights reserved.
1. Introduction The chemical synthesis of inorganic materials of nanometre size, specific morphology and superstructure has attracted considerable attention due to its potential application in sophisticated areas. Barium sulphate is one of the most important inorganic fillers used in the plastics, rubber and paint industries and also in pharmaceutical formulations. Preparation of BaSO4 particles has been widely studied in order to assess the effect of mixing, precipitation models, agitator speed and feed position on particle size distribution, crystal growth and morphology [1,2]. Nanometre barium sulphate has more scientific advantage on size reduction. Liquid–liquid precipitation is the principle preparation method of nano particles [3,4]. In general, barium sulphate is synthesised by adding SO42− ions directly into the solutions containing Ba 2+or complex of Ba 2+ [5]. Many different approaches have been reported for the preparation of BaSO4 nano particles including the addition of different additives [6] such as, induction by monolayer and micro emulsion [7], micro channel reactors [8] etc. So far, for controlling the size and morphology of BaSO4 particles, amino-carboxylate additives, phosphonate/phosphate inhibitors [9], PMMA [10], double-hydrophilic block copolymers, as well as waterin-oil micro emulsion systems [11,12] were used. Template-directed synthesis and morphosynthesis are the two distinct categories of ⁎ Corresponding author. Tel.: + 91 484 2575590; fax: + 91 484 2577747. E-mail addresses: [email protected] (N. Nandakumar), [email protected] (P. Kurian). 1 Tel.: + 91 484 2575590; fax: + 91 484 2577747. 0032-5910/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.powtec.2012.02.022
methods that have been developed to prepare particles and modify their structure. In template-directed synthesis, additives added to the reaction system govern nucleation and growth [13–17], whereas in morphosynthesis, synthesis is limited to micro reaction environment [3,18–20]. Barium sulphate crystals with a diameter in the sub200 nm range have wonderful optical characteristics and flow behaviour, and have been widely used in printing ink, pigment and medicine. There have been many reports on barium sulphate nano particle and nano filament synthesis using micro emulsion technology [13–17]. A number of researchers have attempted various methods to prepare nano powders. However, the exploration of facile chemosynthesis of porous and monodispersed BaSO4 nano powders in aqueous media at ambient conditions remains non-systematic. Until now, there have been no reports on the preparation of nano BaSO4 in PVA supported medium at room temperature. Herein, we investigated that nano BaSO4 can be successfully synthesised in aqueous polyvinyl alcohol solution. We investigated the influence of polyvinyl alcohol on morphology and size and its role in yielding porous nano materials. We varied the experimental conditions such as concentration of polyvinyl alcohol and calcination temperatures; and compared the nature of barium sulphate formed during each condition at constant molar ratio of reactants. 2. Experimental 2.1. Preparation Polyvinyl alcohol (mwt.1, 25,000) was purchased from Spectrochem. Barium chloride (BaCl2) and ammonium sulphate (NH4)2SO4 were
52
N. Nandakumar, P. Kurian / Powder Technology 224 (2012) 51–56
obtained from Merchem. All the chemicals were used without further purification. The preparations were carried out at ambient temperature (ca. 25 °C) in a glass beaker. In the synthesis of monodispersed spheroid BaSO4 nano powders with nano structures, 20 ml of 0.5 M BaCl2 was initially thoroughly mixed with 20 ml of water containing 0% w/v, 1% w/v, 3% w/v, 5% w/v and 7% w/v of PVA respectively and all solutions except 0% w/v showed a turbid appearance soon after mixing, though no visible precipitation was observed. Then 10 mL of 1.0 M (NH4)2SO4 was added drop wise from a micro burette at a minimised rate to the mixture under vigorous magnetic stirring. The mixture was stirred for another 1 min after complete addition of reagent and kept under static conditions for 5 h before the white precipitate was washed. The precipitate was washed thoroughly with distilled water to remove unused PVA, reactants and by-products, filtered and dried at 80 °C for 2 h prior to calcinations at 400 °C, 600 °C and 800 °C. 2.2. Characterisation The XRD patterns of the so prepared samples were recorded on a diffractometer Rigaku Geiger flex with nickel filtered Cu Kα (λ = 1.54 Å) as a radiation source and at a 2θ scan speed of 1°/min at 30 kV and 20 mA. The crystallite size of BaSO4 was calculated by X-ray line broadening technique using Debye–Scherrer equation = kλ/βcosθ, where k = 0.9 and D corresponds to BaSO4 crystallite size. Particle size distribution was analysed using Malvern Instruments MAL1008884 model particle size analyser at a count rate of 250.8 kcps. Scanning electron microscopy (SEM) [JOEL JSM-6390L] was used for morphological studies and the chemical purity of the samples was confirmed using energy dispersive X-ray spectroscopy (EDAX) attached along with the same equipment. The morphology, porosity and particle size were observed using transmission electron microscopy on a Philips TEM CM200 model. TGA profiles of nano powder were recorded on a thermo gravimetric analyzer (TGA Q-50, TA instruments) in which approximately 10 mg of the sample was heated from ambient temperature to 1000 °C. Nitrogen gas was continuously allowed to flow at the rate of 90 mL/min through the chamber. The surface characteristics of the powders were recorded with Bruker FT-5DX (Nicolet) spectrophotometer (infrared spectra) at wave numbers of 4000–400 cm− 1. 3. Results and discussion 3.1. X-ray diffraction (XRD) studies 3.1.1. Influence of PVA concentration on XRD The XRD patterns of the barium sulphate powders synthesised with 0, 1, 3, 5 and 7 weight by volume percentage aqueous solutions of PVA as mediums are shown in Fig. 1. The samples display the typical orthorhombic structure of BaSO4 .The d-values of BaSO4 nano material are 4.34x, 2.125 and 3.904 (JCPDS No: 83-1718), 3.44x, 3.10x and 2.127 (JCPDS No: 83-2053) with hkl values of (101), (311), (111) and (210), (211), (401) respectively. The XRD pattern was indexed with reference to the unit cell of the barite structure (a~ 8.87, b ~ 5.45, c ~ 7.15 A°; space group (Pnma)) [21]. Only BaSO4 peaks were observed in the XRD spectra. This indicated that all the powders had high purity. XRD reveals that as the PVA concentration increased the intensity and crystallinity of the peaks decreased as indicated by the shortening and broadening of peaks. The particle size obtained showed a minimum crystal grain size range as calculated using the Scherrer formula from broadening of XRD for {210} peak (~23 nm) with 3% PVA solution, whereas at higher concentrations the peaks shows negligible crystalline nature and on the other hand at lower concentrations of PVA they were crystalline; but with larger grain size as indicated by sharp peaks. Moreover all the powders prepared in the presence of PVA showed smaller grain size than the BaSO4 prepared without PVA
Fig. 1. X-ray diffraction spectra of nano BaSO4 prepared in aqueous medium with different concentrations of PVA (a) 0% (aqueous medium, 0% PVA), (b) 1% (1% PVA solution), (c) 3% (3% PVA solution), (d) 5% (5% PVA solution), and (e) 7% (7% PVA solution).
indicating that presence of PVA had a dispersive and protective effect on the powders. Thus XRD assisted analysis revealed that 3% PVA solution is an optimum medium for nano synthesis and this may be because at this concentration the polymer coating is perfect on each mole of the reactant and every single Ba 2+ ion coated in PVA reacts with a single SO42− leading to reduced agglomeration of powders formed. 3.1.2. Influence of calcination temperature on XRD The influence of calcination temperature on the particle size was analysed using XRD-spectra of nano BaSO4 synthesised in 3% PVA solution at different calcination temperatures viz. 400 °C, 600 °C and 800 °C for 4 h (Fig. 2). Only BaSO4 peaks were observed in the XRD spectra of all samples except for a calcination temperature of 400 °C. This indicated that all other powders had high purity. The intensity and width of diffraction peaks differed between samples calcined at different temperatures. The spectra revealed that as the calcination temperature increased the crystallinity of the sample increased and grain size increased, whereas at 600 °C the grain size fall into 23 nm range as calculated using the Scherrer formula from broadening of
Fig. 2. X-ray diffraction spectra of nano BaSO4 synthesised in aqueous medium with 0% PVA and in 3% PVA solution calcined at different temperatures (a) 0% PVA, dried at 80 °C, (b) 3%, 800 °C,(c)3%, 600 °C, and (d) 3%, 400 °C.
N. Nandakumar, P. Kurian / Powder Technology 224 (2012) 51–56
53
BaSO4 and the peaks in the spectra indicated the formation of controlled monodispersed powder at this temperature. Moreover all the calcined powders showed smaller grain size than the BaSO4 prepared in aqueous medium without PVA support indicating that, presence of PVA had a dispersive and protective effect on the powders which assists in size control even after its removal through calcination. These facts are again supported by the IR profiles (Fig. 7). 3.2. Particle size distribution Particle size distribution was analysed using Malvern Instruments MAL1008884 model particle size analyser at a count rate of 250.8 kcps and is shown in Fig. 3. The properties of nano particles are significantly depending on the particle size distribution. Especially evenly distributed particle size is of interest due to the size dependent physical and chemical properties of the nano particles. Most of the particles have particle size in the 20–25 nm range. This is in good agreement with the XRD result. Fig. 3. Particle size distribution of monodispersed porous BaSO4 nano material.
3.3. Studies using scanning electron microscopy (SEM) and transmission electron microscopy (TEM)
XRD for {210} peak. At 400 °C the grain size is small as indicated by the broadening and shortening of peaks. Appearance of the impurity peaks in nano BaSO4 synthesised in 3% PVA solution calcined at 400 °C clearly indicates that complete removal of all the carbonaceous species is not possible at this temperature, and hence is not sufficient for post synthesis treatment. At 800 °C pure nano barium sulphate was formed but agglomeration takes place as observed by narrow peak formation. Powder calcined at 600 °C yields small grain size with high purity. It is the optimum temperature that ensures complete removal of PVA template and other impurities from the nano
The porous monodispersed barium sulphate nano material was obtained by direct combination of Ba 2+ and SO42− in 3% aqueous PVA solution followed by calcination. Morphological analysis using SEM photographs of these sample shows that all nano powders were spheroid. Fig. 4 shows that synthesised barium sulphate without PVA had a flaky structure with high degree of agglomeration and microstructures; whereas all samples prepared in 3% aqueous PVA solution had spheroid morphology with uniformly arranged particles of almost similar shape and size. Thus the nano structures of the synthesised powders have a subtle relationship
Fig. 4. SEM photographs of monodispersed porous BaSO4 nano material synthesised in aqueous medium with 0% PVA and in 3% PVA solution calcined at different temperatures (a) 0% PVA, dried at 80 °C, (b) 3%, 400 °C , (c) 3%, 600 °C, and (d) 3%, 800 °C.
54
N. Nandakumar, P. Kurian / Powder Technology 224 (2012) 51–56
Fig. 5. EDAX spectra of BaSO4 nano material synthesised in 3% PVA and calcined at 600 °C.
with the presence of PVA, which leads directly to the formation of monodispersed porous nano powders. The dependence of structure on temperature of calcination is clear from SEM photographs of nano BaSO4 prepared in 3% PVA calcined at 3 different temperatures. At lower calcination temperatures the crystals had smaller size as it is clear from Fig. 4(b), (c) (barium sulphate calcined at 400 °C and 600 °C). As the calcination temperature increased from 600 °C to 800 °C, structure collapse leading to agglomeration is clearly depicted in Fig. 4(d) (barium sulphate calcined at 800 °C). Hence it can be concluded that up to a calcination temperature of 600 °C, the spheroid monodispersed structure is stable and after that there is a drastic change in the material due to agglomeration. This agglomeration of nano powders is due to structure collapse at higher temperature owing to the rapid removal of PVA from the surface. The related EDAX analysis of samples prepared in 3% aqueous PVA solution calcined at 600 °C is shown in Fig. 5. The EDAX contains only peaks for barium (Ba), sulphur (S) and oxygen (O), the absence of carbon (C) peaks indicates the complete removal of coated PVA from nano powders during
calcination. This is indicative of the purity of the material. The analysis of these results exhibits the presence of Ba, S and O in the ratio 1.0:0.9:4.0 close to the stoichiometry of BaSO4 within experimental error. Thus it can be deduced that pure BaSO4 was formed during the synthesis. The SEM photographs confirm the generation of monodispersed porous nano sized particles at an accelerating voltage of 25 kV. The TEM images (Fig. 6) of BaSO4 synthesised in 3% PVA solution and calcined at 600 °C confirm the formation of nano particles. The particle size obtained from TEM was 23 nm. The porous nature of sample is evidenced from uniform small pores in the particle, and these regions appear brighter than the surroundings because they have absorbed fewer electrons [2].
Fig. 6. TEM photographs of monodispersed porous BaSO4 nano material synthesised in 3% PVA solution calcined at 600 °C.
Fig. 7. FTIR-spectra of monodispersed porous nano BaSO4 synthesised in aqueous medium with 0% PVA and in 3% PVA solution. (a) 0% and (b) 3%.
3.4. Fourier transform infrared resonance — (FTIR) studies The infrared (IR) spectra of BaSO4 prepared in aqueous medium without PVA and porous monodispersed nano BaSO4 powder materials
N. Nandakumar, P. Kurian / Powder Technology 224 (2012) 51–56
prepared in 3% PVA solution calcined for 4 h at different temperatures are shown in Fig. 7. The presence of broad absorption band at 3405 cm− 1 in Fig. 7(d) for BaSO4 prepared in 3% PVA and dried at 80 °C corresponds to hydrogen bonding. This gets weakened as the calcination temperature increases as it is seen in Fig. 7(b) for BaSO4 prepared in 3% PVA calcined at 400 °C. From Fig. 7(c) for BaSO4 prepared in 3% PVA calcined at 600 °C, it can be observed that such molecular forces leading to particle aggregation are removed on increasing the calcination temperature. The weak absorption bands in Fig. 7(d) at 2932 and 2830 cm− 1 are due to stretching vibrations of methyl (υ (CH2) groups from PVA which disappeared as calcination temperature increased indicating that PVA is removed from nano BaSO4 powders at 400 °C itself. The IR spectrum of precipitated barium sulphate without PVA is shown in Fig. 7(a). IR spectra of all samples had peaks centred at 1197 and 1076 cm− 1 and shouldered at 980 and 818 cm− 1 which corresponds to symmetrical vibrations of sulphate and 610 cm− 1 for out of plane bending vibration of sulphate. All the above facts indicated that during the reaction, Ba 2+ ions were encapsulated in polyvinyl alcohol; the state at which the reactive chloride ions meet its counter ion in a dilute isolated state leading to reduced agglomeration. And the powders formed will be surrounded by PVA as indicated in IR spectra (Fig. 7d) which can be removed in the final stage by calcination as shown in Fig. 7(b) and (c). 3.5. Thermo gravimetric analysis Thermo gravimetric analysis of dried sample prepared in aqueous medium without PVA and in 3% PVA solution was carried out in the temperature range from 40 to 1000 °C. The thermal behaviour of these powders is shown in Fig. 8. The dotted lines represent TGA patterns of BaSO4 synthesised in aqueous medium wihout PVA and bold lines indicates that of the powder synthesised in 3% PVA solution. It is clear from the patterns that the thermograms showed a similar trend in weight loss up to 400 °C (1.364%) and the former powder showed no weight loss above that whereas in the latter case 1.855% of weight loss was recorded up to a calcination temperature of 600 °C. Increasing the calcination temperature from 400 to 600 °C the weight loss of ~0.50% accounts for the removal of coordinated organic groups. Moreover on increasing the temperature from 600 °C, the weight loss is negligible which prevails up to 790 °C. But since such a high temparature may lead to structure collapse a minimum calcination temparature of 600 °C is accepted in practice for the complete removal of impurities with consistent nano structure.
Fig. 8. TGA patterns of monodispersed porous nano BaSO4 synthesised in aqueous medium without PVA (- - -) and in 3% PVA solution (—).
55
4. Conclusions BaSO4 nano powder with a particle size in the range of 20–23 nm was synthesised by using a polymeric template. BaSO4 particles formed were encapsulated with PVA during the synthesis for preventing agglomeration. Liquid–liquid chemosynthesis involving direct precipitation of BaCl2 and (NH4)2SO4 in aqueous polyvinyl alcohol (PVA) solution as a polymeric template was employed. The morphology of synthesised nano particles was characterised using SEM as well as TEM. The analysis carried out revealed that 3% aqueous PVA solution is an optimum medium for synthesis. PVA assisted the formation of nano particles with smaller grain size and this could be removed at the final stage by calcination. Thermal studies revealed that the porous monodispersed nano structure is stable up to 600 °C with regular spheroid structures. The calcined powders yielded small grain size with high purity as indicated by the barite structure in XRD spectra and elemental composition in EDAX analysis.
Acknowledgement The authors are thankful to the Cochin University of Science and Technology, India for providing financial assistance for the work. References [1] B. Judat, M. Kind, Morphology and internal structure of barium — derivation of a new growth mechanism, Journal of Colloid and Interface Science 269 (2) (2004) 341–353. [2] H. Bala, W. Fu, J. Zhao, X. Ding, Y. Jiang, et al., Preparation of BaSO4 nanoparticles with self-dispersing properties, Colloids and Surfaces A: Physicochemical and Engineering Aspects 252 (2005) 129–134. [3] L.M. Qi, H. Colfen, M. Antonietti, Control of barite morphology by doublehydrophilic block copolymers, Chemical Material 12 (2000) 2392–2403. [4] M.H. Qu, Y.Z. Wang, C. Wang, X.G. Ge, D.Y. Wang, Q. Zhou, A novel method for preparing poly(ethylene terephthalate)/BaSO4 nanocomposites, European Polymer Journal 41 (2005) 2569–2574. [5] K. Takiyama, Formation and ageing of precipitates. IX. Formation of monodispersed particles. 2. Bariumsulfate precipitate by ethylenediamminetetraacetic acid method, Bulletin of the Chemical Society of Japan 31 (1958) 950–953. [6] F. Jones, A. Oliviera, G.M. Parkinson, A.L. Rohl, A. Stanley, et al., The effect of calcium cations on the precipitation of barium sulfate 1 calcium ions in the presence of organic additives, Journal of Crystal Growth 262 (2004) 572–580. [7] B.M. Nagaraja, H. Abimanyu, K.D. Jung, K.S. Yoo, Preparation of mesostructured bariumsulfate with high surface area by dispersion method and its characterization, Journal of Colloid and Interface Science 316 (2) (2007) 645–651. [8] Q.A. Wang, J.X. Wang, M. Li, L. Shao, J.F. Chen, et al., Large-scale preparation of bariumsulphate nanoparticles in a high-throughput tube-in-tube microchannel reactor, Chemical Engineering Journal 149 (2009) 473–478. [9] F. jones, W.R. Richmond, A.L. Rohl, Molecular modelling of phosphonate molecules onto bariumsulfate terraced surfaces, The Journal of Physical Chemistry. B 110 (2006) 7414–7424. [10] X. Zhao, J. Yu, H. Tang, J. Lin, Facile synthesis of monodispersed barium sulphate particles via an in situ templated process, Journal of Colloid and Interface Science 311 (2007) 89–93. [11] N.I. Ivanova, D.S. Rudelev, B.D. Summ, A.A. Chalykh, Synthesis of bariumsulfate nanoparticles in water-in-oil microemulsion systems, Colloid Journal 63 (2001) 714–717. [12] D. Adityawarman, A. Voigt, P. Veit, K. Sundmacher, Precipitation of BaSO4 nanoparticles in a non-ionic microemulsion: identification of suitable control parameters, Chemical Engineering Science 60 (12) (2005) 3373–3381. [13] P. Dutta, J.H. Fendler, Preparation of cadmium sulfide nanoparticles in selfreproducing reverse micelles, Journal of Colloid and Interface Science 247 (1) (2002) 47–53. [14] L. Mei, S. Mann, Emergence of morphological complexity in BaSO4 fibers synthesised in AOT microemulsions, Langmuir 16 (2000) 7088–7094. [15] J.D. Hopwood, S. Mann, Synthesis of bariumsulfate nanoparticles and naanofilaments in reverse micelles and micro emulsions, ChemicalMaterial 9 (1997) 1819–1828. [16] L.M. Gan, L.H. Zhang, H.S.O. Chan, C.H. Chew, Preparation of conducting polyaniline-coated bariumsulfate nanoparticles in inverse microemulsions, Materials Chemistry and Physics 40 (1995) 94–98. [17] M. Summers, J. Eastoe, S. Davis, Formation of BaSO4 nanoparticles in microemulsions with polymerised surfactant shells, Langmuir 18 (2002) 5023–5026. [18] M.P. Pileni, Nanostructured fluids in oil-rich regions: structural and templating approaches, Langmuir 17 (2001) 7476–7486. [19] Y. Xie, Y.T. Qian, W.Z. Wang, A benzene-thermal synthetic route to nanocrystalline GaN, Science 272 (1996) 1926–1927.
56
N. Nandakumar, P. Kurian / Powder Technology 224 (2012) 51–56
[20] W.Z. Zhou, J.M. Thomas, D.S. Shepard, Brian F.G. Johnson, D. Ozakaya, T. Maschmeyer, Robert G. Bell, Qingfeng Ge, Ordering of ruthenium cluster carbonyls in nanoporous silica, Science 280 (5364) (1998) 705–708. [21] R.J. Hill, The Canadian Mineralogist 15 (1977) 522–526.
Philip Kurian joined Cochin University of Science and Technology on 28-11-1978 as a Faculty in Polymer Science and Rubber Technology. He earned his PhD in Polymer Technology at Polymer Science and Rubber Technology CUSAT. His areas of research include polymer blends and composites, rubber ferrite composites, rubber compounding, novel compounding ingredients and polymer nanocomposites. He has 32 years of teaching experience and 22 years of research experience and has 35 publications in various international journals along with 16 conference papers. He have produced 4 PhDs so far and at present 5 students are been guided by him.
Nisha Nandakumar joined CUSAT on 01-09-2008 as a research student under the guidance of Dr. Philip Kurian in Polymer Science and Rubber Technology Department. She joined the institution after her post graduation in chemistry. Her research area is polymer nanocomposites of elastomers and has presented papers in three conferences.