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A novel and efficient method for the synthesis of amorphous nanosilica from fly ash tiles
Materials Today: Proceedings xxx (xxxx) xxx
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Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr
A novel and efficient method for the synthesis of amorphous nanosilica from fly ash tiles Virendra Kumar Yadav a, R. Suriyaprabha b, Samreen Heena Khan b, Bijendra Singh c, G. Gnanamoorthy d, Nisha Choudhary b,⇑, Amit Kumar Yadav e, Haresh Kalasariya a a
Department of Microbiology, Sankalchand Patel University, Visnagar, Gujarat 384315, India School of Nanosciences, Central University of Gujarat, Gandhinagar, Gujarat 382030, India School of Chemical Sciences, Central University of Gujarat, Gandhinagar, Gujarat 38030, India d Department of Inorganic Chemistry, University of Madras, Chennai, Tamil Nadu 600025, India e SESD, Central University of Gujarat, Gandhinagar, Gujarat 382030, India b c
a r t i c l e
i n f o
Article history: Received 29 October 2019 Received in revised form 13 November 2019 Accepted 1 January 2020 Available online xxxx Keywords: Calcination Nanosilica Alkali-fusion Fly ash Tiles Alkali-dissolution
a b s t r a c t The present study reveals an efficient and cost-effective one-step method for the synthesis of nano-silica from silico-aluminous fly ash-based tiles. The fly ash and their products being rich in silica act as renewable source material for the synthesis of silica. A simple alkali fusion method developed to synthesize white amorphous nano silica directly from the fly ash-tiles by the acidic treatment which was analysed by UV–Vis, Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and X-ray diffraction (XRD) and Field-Emission Scanning electron microscopy-electron diffraction spectroscopy (FESEMEDS). The XRD revealed a broad hump from 2h, 10–30° with a peak centered at 2h = 21.7° confirms the formation of amorphous nanosilica. FTIR also reveals the characteristic bands of silica in the range of 400–1200 cm1. While particle size analyser (PSA) confirmed the particle size distribution of nanosilica and FEMSEM confirmed the spherical shape and aggregated form of the synthesized nanosilica of size range varies from 10 to 60 nm. The prominent peak for Si and O confirmed the formation and purity of the nanosilica from the fly ash tiles. Around 99–100% of silicates were recovered by this method in the form of an insoluble precipitate. The developed method is an efficient and economical approach for the recovery of major fractions of silicates from the fly ash based tiles. Ó 2020 Elsevier Ltd. All rights reserved. Selection and of the scientific committee of the 10th International Conference of Materials Processing and Characterization.
1. Introduction Silica is one of the most abundant elements present on the earth’s crust. It is present in almost every mineral on and under the surface of the earth. For commercial applications, pure silica is generally obtained from the quartz rock and sodium silicates. Silica finds applications in electronics and optical materials [1], storage media, agriculture [2], precursor in photonic and solar cell industries for solar devices [3], medicine, drug delivery, wastewater treatment as an adsorbent [4], molecular separation [5], agriculture [6], in chemistry as molecular sieves [7] and catalysis [8], constructions & building materials [9], glass and ceramics industries [10]. The rich source of silica are rice husk, silica fume, silica ⇑ Corresponding author. E-mail address: [email protected] (N. Choudhary).
sludge and fly ash. Fly ash is a waste by-product of thermal power plants produced during the production of electricity [11]. Fly ash has silica are present in both amorphous and crystalline forms where 30% silica is glassy amorphous and the remaining 70% in the crystalline quartz, mullite and sillimanite form. Amorphous silica can be readily extracted from fly ash and their products like tiles, cement but the crystalline silica hardly reacts and leaches in the alkali solution. Fly ash silica content varies from 40 to 60% depending on the source and type of coal used in the thermal power plants [12] while their products like tiles, cement have generally lower silica content. Previously several methods have been reported for the extraction of silica from fly ash [12], clay [13], pumice-rock [14], rice husk [15;16;17;18], etc. by a two-step alkali dissolution method. Where generally strong hydroxides of either sodium or potassium have been used from 2 to 8 M along with stirring and heating at 90–95 °C for 90–180 min. Further, the filtrate
https://doi.org/10.1016/j.matpr.2020.01.013 2214-7853/Ó 2020 Elsevier Ltd. All rights reserved. Selection and of the scientific committee of the 10th International Conference of Materials Processing and Characterization.
Please cite this article as: V. Kumar Yadav, R. Suriyaprabha, S. Heena Khan et al., A novel and efficient method for the synthesis of amorphous nanosilica from fly ash tiles, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.013
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V. Kumar Yadav et al. / Materials Today: Proceedings xxx (xxxx) xxx
rich in silica in the form of sodium silicate has been titrated with 1–2 M HCl or H2SO4 for silica gel formation. The main drawback of such types of methods is that it is more time consuming as silica gel has to keep for 24 h aging at room temperature. Secondly lesser yield and thirdly there is generation of alumina and iron-rich residue as a chemical waste that can be a potential threat to the environment. In present work, fly ash based tiles has been used as a source of silica by a single step fusion method which eliminates the ageing step as well as the use of other harmful chemicals. The fly ash tiles powder and sodium bicarbonate were mixed in a 1:10 ratio which was calcined at 950 °C in a platinum crucible in a muffle furnace. At this high temperature, the mixture gets melted where the silicates from the powder react with sodium and form sodium silicate. Further, steps involve cooling, solidification and pouring of the molten mixture into diluted HCl that result in the precipitation of acidinsoluble silica. Finally, silica is collected by filtration which is neutralized by continuous washing with double distilled water. After calcination at 900 °C silica powder were analysed UV–Vis, FTIR, and Raman spectroscopy, PSA, XRD, and FESEM-EDS. 2. Materials and methods 2.1. Materials Fly ash-tiles (Okhla industrial area-Phase III, New Delhi), NaOH pellets (RENKEM), Platinum crucible, Na2CO3 (SRL), Conc. HCl (RENKEM), Whatman Filter paper No. 40 (AXIVA).
the residual sodium hydroxide moieties. The precipitate along with filter paper pulp was transferred into a porcelain crucible and calcined at 900 °C for two hours. The weight of the final white silica powder was measured and noted down. 2.5. Characterization The synthesized nanosilica was dispersed in double-distilled water and UV–Vis spectroscopic measurement was done on Shimadzu, UV-1800 double Beam spectrophotometer. The FTIR spectrum was obtained using a Perkin Elmer made instrument, Spectrum 6500, by KBr pellet method, using BaSO4 as standard. The transmission measurement was made from mid-IR region 400–4000 cm1 at a resolution of 2 cm1. The Raman spectrum was acquired by using a Witec, Germany, made instrument by placing the powder on the glass coverslips and passing laser of 633 nm and 532 nm for 5–10 s. The X-ray diffraction pattern was measured by using a Bruker made instrument in the powder form. The XRD patterns were recorded in the 2 theta range of 5–70°, with a step size of 0.02 and a time of 2 s per step at a 30 KV and a current of 30 mA. The particle size distribution of nanosilica was measured by Malvern Zetasizer model, Nano S90 (UK), by dispersing them in double distilled water followed by sonication for 10 min at room temperature. The size and eternal features, porosity and shape were analyzed by FESEM Carl Zeiss (V5.05, SIGMA) and elemental analysis was done by the attached EDS analyzer of Bruker made along with it. 3. Results and discussions
2.2. Sample collection and preparation Fly ash based tiles were collected from Okhla, Industrial area, New Delhi. The tiles was crushed into small pieces and grounded in a mortar pestle. The obtained powder was dried in an oven at 45 °C overnight. 2.3. Preparation of wet filter paper pulp A Whatman filter paper no. 42 was torn into pieces and dipped into hot distilled water and the pieces were finely grounded. It was allowed to cool and kept in a beaker for future use. The wet pulp has been used for the filtration of precipitate and leachate. The use of filter paper in such a way makes the process cheaper and also increases the filtration and recovery of silica. 2.4. Method About 0.49 g of powder were weighed and mixed with 5–6 g of sodium bicarbonate uniformly in a platinum crucible. The mixture was placed in a muffle furnace for half an hour at 900–950 °C for fusion. After calcination, the mixture was allow to cool at room temperature and then the mixture along with crucible was dipped in a hot diluted 1:1 aqueous solution of HCl: H2O and it was heated till the complete disintegration of the fused mass from the crucible. Initially, the colour of the solution was pale yellow. The lumps of the mixture were dissolved with the glass rods. The mixture was baked at hot plate till complete dryness; again excess of dilute HCl was added and heated. The silica attached to the side of the beaker was wiped with the filter paper and dipped in the acidic solution. This step ensured any loss of silica that has adhered to the side of the walls of the glass beaker. A clear solution with white precipitate was obtained which was filtered by Whatman filter paper no 42 pulp. The precipitate remained with the filter paper pulp while the acidic leachate obtained in the filtrate. The precipitate was washed several times with mild-warm water to remove
3.1. Step one alkali dissolution-fusion method All the glassy amorphous and crystalline silica (mullite and sillimanite) reacts with sodium bicarbonate at temperature 950 °C. The sodium bicarbonate and silicates get melted fuses to form a new product i.e. sodium silicate. The following reaction will help in understanding the reaction
SiO2 ðFly ash tiles powderÞ þ Na2 CO3 ¼ Na2 SiO3 þ CaCO3
ð1Þ
3.2. Second step- precipitation of silicates in HCl The silica is insoluble in acids, so the fused silicates in the form sodium silicates will form Hydrogen silicate or silica directly after reacting with the diluted HCl. The following step can be explained by the reaction given below:-
Na2 SiO3 þ 2H2 O þ 2HCl ¼ SiðOHÞ4 þ 2NaCl
ð2Þ
The silica being insoluble in acids gets precipitated at the bottom while all the acid-soluble metal dissolves in HCl and forms metal chlorides that can be collected at their respective pH mainly alumina and ferrous ions. The sodium silicate reacts with H2O to form silicic acid which later on polymerizes to form a silica gel by the above reaction (2). Further, the silicic acid condenses to form small particles, chains and ultimately to form a network resulting in a silica gel as shown below [20]:
ð3Þ
Please cite this article as: V. Kumar Yadav, R. Suriyaprabha, S. Heena Khan et al., A novel and efficient method for the synthesis of amorphous nanosilica from fly ash tiles, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.013
V. Kumar Yadav et al. / Materials Today: Proceedings xxx (xxxx) xxx
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Fig. 1. UV–Vis spectra of nanosilica.
Fig. 2. FTIR spectra of nanosilica.
The quantitative analysis of the nanosilica was done by subtracting the weight of obtained silica from the initial weight of fly ash-tiles taken. The initial fly ash-tiles powder taken was 0.4937 g while about 0.2937 g of nanosilica was obtained. By XRF it was found that 59–60% silica per gram is present in fly ash based tiles. The total yield of nanosilica was 59.5% i.e. almost 99–100% from fly ash based tiles.
Fig. 4. XRD diffractogram of nanosilica.
3.2.1. XRF spectroscopy XRF confirmed the silica content in the fly ash-tiles about 59– 60% as the major oxides, followed by alumina and iron oxides.
Fig. 3. Raman spectra of nanosilica.
Please cite this article as: V. Kumar Yadav, R. Suriyaprabha, S. Heena Khan et al., A novel and efficient method for the synthesis of amorphous nanosilica from fly ash tiles, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.013
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3.2.2. UV–Vis spectroscopy The UV–Vis measurement was done from 200 to 600 nm by a Halo double beam 1800 spectrophotometer. The nanosilica was dispersed in double distilled-water. The peak at 210 nm and 350 nm confirms the formation of nanosilica from fly ash-tiles. Fig. 1 shows the UV–Vis spectra of nanosilica.
3.2.3. FTIR The FTIR spectrum of nanosilica is shown in Fig. 2 which reveals that in the fingerprint region of the spectrum, there is a broad and intense peak at 1085 cm1 which are the characteristic bands of anti-symmetric stretching vibration of the Si-O-Si and a less intense band at 806 cm1 is attributed to the symmetric stretching
Fig. 5. Particle size distribution graph of nanosilica.
Fig. 6. FESEM images (a and b) and EDS-spot (c) spectra of nanosilica (d).
Please cite this article as: V. Kumar Yadav, R. Suriyaprabha, S. Heena Khan et al., A novel and efficient method for the synthesis of amorphous nanosilica from fly ash tiles, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.013
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vibrations of Si-O-Si [19]. The band at 470–464 cm1 attributed to the rocking vibrations of Si-O-Si (siloxanes) [20;23]. These bands are the characteristic of the nanosilica whereas the bands at 3400 cm1 and 1600 cm1 are due to the associated water molecules. The bound water molecule might have left during calcination or it may also be due to the moisture absorption during analysis.
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Acknowledgments The authors are thankful to the Central Instrumental facility (CIF), Central University of Gujarat, Centre for Nanosciences, Jamia Millia Islamia, New Delhi, CECRI (CSIR)-Karikudi, Tamil Nadu, Spectro Analytical Lab, Okhla New Delhi. References
3.2.4. Raman The Fig. 3 shows the Raman spectrum of the nanosilica, where the bands at 545 cm1, 578 cm1, 580 cm1, and 610 cm1 are the characteristics peaks of the synthesized nanosilica [21]. The Raman spectrum also confirms the amorphous nature of the synthesized nanosilica. 3.2.5. XRD The XRD pattern of the nanosilica shown in Fig. 4 reveals the amorphous nature of the synthesized nanosilica. There are diffused peaks corresponding to the [111], [220] and [311] planes of silica. A broad hump was noticed from two theta 15–30° with a centered peak at 2h (21.7°) confirms the formation of amorphous silicon dioxide [22;23]. Besides this, there are also a few small intensity peaks for quartz at 38, 44 and 63°. While the absence of other peaks of minerals indicate the removal of impurities and formation of pure nanosilica. 3.2.6. PSA The nanosilica powder was dispersed in the double-distilled water, followed by sonication for 10 min in an ultrasonicator of 40 kHz at room temperature. The particle size distribution of the dispersed nanosilica is shown in the PSA graph in Fig. 5 which reveals that the average size of the particle is 219.8 nm while the size of most of the particles is 239.1 nm and the PDI is 0.092. 3.2.7. FESEM-EDS The FESEM images and EDS spectra of nanosilica are shown in Fig. 6a-b and Fig. 6c-d respectively. From the FESEM micrographs it is clear that the particles are spherical in shape, but showing high aggregation whose size varies from 30 to 60 nm. The nanosilica is showing aggregation and pores on their surface. While the EDS spectra also confirm the formation of silica as there are sharp and prominent peaks for Si and O. While there is an impurity in the form of fluorine, Na and Al whose total composition is less than 2.5%. 4. Conclusions In present work, an efficient and cost-effective method was developed for the synthesis of nanosilica of size 30–60 nm from fly ash based tiles. The main groups present in the silica were siloxane and silanol was confirmed by FTIR. The synthesized nanosilica is amorphous, pure and highly aggregated as confirmed by the FESEM and XRD. The impurities are in the form of F, Na, and Al which is due to improper washing. The advantage of this method is that it reduces solid wastes and transforms it into useful products. The leachate rich in Al and other metals can be used for the recovery of elements at a specific pH. This method has an efficiency of 99% for the extraction of silica from fly ash based tiles. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
[1] Lorenzo Mangolini, Synthesis, properties, and applications of silicon nanocrystals, J. Vacuum Sci. Technol. B Nanotechnol. Microelectron. Mater. Process. Measure. Phenomena 31 (2013), 020801. [2] Yadav, Virendra Kumar and Priti Raj Pandita. ‘‘Fly Ash Properties and Their Applications as a Soil Ameliorant.” Amelioration Technology for Soil Sustainability. IGI Global, 2019. 59–89. Web. 13 Nov. 2019. doi:10.4018/9781-5225-7940-3.ch005 [3] L.-Y. Lin, J.-T. Kuo, H. Bai, J. Hazard. Mater. 192 (2011) 255–262. [4] M.N.V. Ravi Kumar, M. Sameti, S.S. Mohapatra, X. Kong, R.F. Lockey, et al., Cationic silica nanoparticles as gene carriers: synthesis, characterization and transfection efficiency in vitro and in vivo, J Nanosci Nanotechnol 4 (2004) 876–881. [5] H.T. Jang, Y. Park, Y.S. Ko, J.Y. Lee, B. Margandan, Highly siliceous MCM-48 from rice husk ash for CO2 adsorption, Int J Greenhouse Gas Control 3 (2009) 545– 549. [6] I.J. Bruce, J. Taylor, M. Todd, M.J. Davies, E. Borioni, C. Sangregorio, T. Sen, J. Magn. Magn. Mater. 284 (2004) 145–160. [7] Saurabh Singh, Bijendra Kumar Singh, S.M. Yadav, A.K. Gupta, Applications of nanotechnology in agricultural and their role in disease management, Res. J. Nanosci. Nanotechnol. 5 (2015) 1–5. [8] A. Corma, From, microporous to mesoporous molecular sieve materials and their use catalysis, Chem. Rev. 97 (1997) 2373–2419. [9] A. Rani, S. Sanal, T. Jacob, G. Jacob, P.K. Desy, N.K. Manivarnan, Silica nano particles synthesized from boiler spent ash: value addition to industrial waste, Chem. Mater. Res. 6 (2014) 93–99. [10] Pratibha Aggarwal, Rahul Pratap Singh, Yogesh Aggarwal, Use of nano-silica in cement-based materials—a review, Civil Environ. Eng. Cogent Eng. 2 (2015), 1078018. [11] Tatiana G. Pineda-Vasquez, Ana E. Casas-Botero, Margarita E. RamírezCarmona, Mabel M. Torres-Taborda, Carlos H.L. Soares, Dachamir Hotza, Biogeneration of silica nanoparticles from rice husk ash using fusarium oxysporum in two different growth media, Ind. Eng. Chem. Res. 53 (2014) 6959–6965. [12] Md. Ghazali, O.P. Kaushal, Characteristics of fly ash from thermal power plants and its management along with settling pond design, Inter. J. Eng. Res. Sci. IJOER 1 (4) (2015). [13] E.V. Sokol, N.V. Maksimova, N.I. Volkova, E.N. Nigmatulina, A.E. Frenkel, Hollow silicate microspheres from fly ashes of the Chelyabinsk brown coals (South Urals, Russia), Fuel Process. Technol. 67 (2000) 35–52. [14] Y. Abdullahi, E.A. Ali, A.O. Lawal, Roast –alkaline leaching of silica from kaolinitic, ARPN J. Eng. Appl. Sci. 8 (10) (2013). [15] Asmaa Mourhly, Mariam Khachani, Adnane El Hamidi, Mohammed Kacimi Mohammed Halim, Said Arsalane, The synthesis and characterization of lowcost mesoporous silica SiO2 from local pumice rock, Nanomater. Nanotechnol. 5 (2015) 35. [16] Noor Sheeraz Che Zulkifli, Ismail Ab Rahman, Dasmawati Mohamad, Adam Husein, A green sol-gel route for the synthesis of structurally controlled silica particles from rice husk for dental composite filler, Ceram. Int. 39 (2013) 4559–4567. [17] Tatiana G. Pineda-Vasquez, Mabel M. Torres-Taborda, Ana E. Casas-Botero, Carlos H.L. Soares, Margarita E. Ramírez-Carmona, Dachamir Hotza, Biogeneration of silica nanoparticles from rice husk ash using fusarium oxysporum in two different growth media, Ind. Eng. Chem. Res. 53 (2014) 6959–6965. [18] Vipul Bansal, Absar Ahmad, Murali Sastry, Fungus-mediated biotransformation of amorphous silica in rice husk to nanocrystalline silica, J. Am. Chem. Soc. 128 (2006) 14059–14066. [19] Jegan Athinarayanan, Vaiyapuri Subbarayan Periasamy, Mohammad Alhazmi, Khalid A. Alatiah, Ali A. Alshatwi, Synthesis of biogenic silica nanoparticles from rice husks for biomedical applications, Ceram. Int. 41 (2015) 275–281. [20] Jyoti L. Gurav, In-Keun Jung, Hyung-Ho Park, Eul Son Kang, Digambar Y. Nadargi, Silica aerogel: synthesis and applications, J. Nanomater. 2010 (2010) 11, 409310. [21] Riyas Sharafudeen, Jihad Mohammed Al-Hashim, Mohammed Olian Al-Harbi, Ahmed Ibrahim Al-Ajwad, Ali Abdulaziz Al-Waheed, Preparation and Characterization of Precipitated Silica using Sodium Silicate Prepared from Saudi Arabian Desert Sand, Silicon (2017), https://doi.org/10.1007/s12633016-9531-8. [22] Feng Yan, Jianguo Jiang, Kaimin Li, Nuo Liu, Xuejing Chen, Yuchen Gao, Sicong Tian, Green Synthesis of Nanosilica from Coal Fly Ash and Its Stabilizing Effect on CaO Sorbents for CO2 Capture, Environ. Sci. Technol. 51 (2017) 7606–7615. [23] Virendra Kumar Yadav, M.H. Fulekar, Green synthesis and characterization of amorphous silica nanoparticles from fly ash, Elsevier Mat. Today Proceed. 18P7 (2019) 4351–4359.
Please cite this article as: V. Kumar Yadav, R. Suriyaprabha, S. Heena Khan et al., A novel and efficient method for the synthesis of amorphous nanosilica from fly ash tiles, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.013
Contents lists available at ScienceDirect
Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr
A novel and efficient method for the synthesis of amorphous nanosilica from fly ash tiles Virendra Kumar Yadav a, R. Suriyaprabha b, Samreen Heena Khan b, Bijendra Singh c, G. Gnanamoorthy d, Nisha Choudhary b,⇑, Amit Kumar Yadav e, Haresh Kalasariya a a
Department of Microbiology, Sankalchand Patel University, Visnagar, Gujarat 384315, India School of Nanosciences, Central University of Gujarat, Gandhinagar, Gujarat 382030, India School of Chemical Sciences, Central University of Gujarat, Gandhinagar, Gujarat 38030, India d Department of Inorganic Chemistry, University of Madras, Chennai, Tamil Nadu 600025, India e SESD, Central University of Gujarat, Gandhinagar, Gujarat 382030, India b c
a r t i c l e
i n f o
Article history: Received 29 October 2019 Received in revised form 13 November 2019 Accepted 1 January 2020 Available online xxxx Keywords: Calcination Nanosilica Alkali-fusion Fly ash Tiles Alkali-dissolution
a b s t r a c t The present study reveals an efficient and cost-effective one-step method for the synthesis of nano-silica from silico-aluminous fly ash-based tiles. The fly ash and their products being rich in silica act as renewable source material for the synthesis of silica. A simple alkali fusion method developed to synthesize white amorphous nano silica directly from the fly ash-tiles by the acidic treatment which was analysed by UV–Vis, Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and X-ray diffraction (XRD) and Field-Emission Scanning electron microscopy-electron diffraction spectroscopy (FESEMEDS). The XRD revealed a broad hump from 2h, 10–30° with a peak centered at 2h = 21.7° confirms the formation of amorphous nanosilica. FTIR also reveals the characteristic bands of silica in the range of 400–1200 cm1. While particle size analyser (PSA) confirmed the particle size distribution of nanosilica and FEMSEM confirmed the spherical shape and aggregated form of the synthesized nanosilica of size range varies from 10 to 60 nm. The prominent peak for Si and O confirmed the formation and purity of the nanosilica from the fly ash tiles. Around 99–100% of silicates were recovered by this method in the form of an insoluble precipitate. The developed method is an efficient and economical approach for the recovery of major fractions of silicates from the fly ash based tiles. Ó 2020 Elsevier Ltd. All rights reserved. Selection and of the scientific committee of the 10th International Conference of Materials Processing and Characterization.
1. Introduction Silica is one of the most abundant elements present on the earth’s crust. It is present in almost every mineral on and under the surface of the earth. For commercial applications, pure silica is generally obtained from the quartz rock and sodium silicates. Silica finds applications in electronics and optical materials [1], storage media, agriculture [2], precursor in photonic and solar cell industries for solar devices [3], medicine, drug delivery, wastewater treatment as an adsorbent [4], molecular separation [5], agriculture [6], in chemistry as molecular sieves [7] and catalysis [8], constructions & building materials [9], glass and ceramics industries [10]. The rich source of silica are rice husk, silica fume, silica ⇑ Corresponding author. E-mail address: [email protected] (N. Choudhary).
sludge and fly ash. Fly ash is a waste by-product of thermal power plants produced during the production of electricity [11]. Fly ash has silica are present in both amorphous and crystalline forms where 30% silica is glassy amorphous and the remaining 70% in the crystalline quartz, mullite and sillimanite form. Amorphous silica can be readily extracted from fly ash and their products like tiles, cement but the crystalline silica hardly reacts and leaches in the alkali solution. Fly ash silica content varies from 40 to 60% depending on the source and type of coal used in the thermal power plants [12] while their products like tiles, cement have generally lower silica content. Previously several methods have been reported for the extraction of silica from fly ash [12], clay [13], pumice-rock [14], rice husk [15;16;17;18], etc. by a two-step alkali dissolution method. Where generally strong hydroxides of either sodium or potassium have been used from 2 to 8 M along with stirring and heating at 90–95 °C for 90–180 min. Further, the filtrate
https://doi.org/10.1016/j.matpr.2020.01.013 2214-7853/Ó 2020 Elsevier Ltd. All rights reserved. Selection and of the scientific committee of the 10th International Conference of Materials Processing and Characterization.
Please cite this article as: V. Kumar Yadav, R. Suriyaprabha, S. Heena Khan et al., A novel and efficient method for the synthesis of amorphous nanosilica from fly ash tiles, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.013
2
V. Kumar Yadav et al. / Materials Today: Proceedings xxx (xxxx) xxx
rich in silica in the form of sodium silicate has been titrated with 1–2 M HCl or H2SO4 for silica gel formation. The main drawback of such types of methods is that it is more time consuming as silica gel has to keep for 24 h aging at room temperature. Secondly lesser yield and thirdly there is generation of alumina and iron-rich residue as a chemical waste that can be a potential threat to the environment. In present work, fly ash based tiles has been used as a source of silica by a single step fusion method which eliminates the ageing step as well as the use of other harmful chemicals. The fly ash tiles powder and sodium bicarbonate were mixed in a 1:10 ratio which was calcined at 950 °C in a platinum crucible in a muffle furnace. At this high temperature, the mixture gets melted where the silicates from the powder react with sodium and form sodium silicate. Further, steps involve cooling, solidification and pouring of the molten mixture into diluted HCl that result in the precipitation of acidinsoluble silica. Finally, silica is collected by filtration which is neutralized by continuous washing with double distilled water. After calcination at 900 °C silica powder were analysed UV–Vis, FTIR, and Raman spectroscopy, PSA, XRD, and FESEM-EDS. 2. Materials and methods 2.1. Materials Fly ash-tiles (Okhla industrial area-Phase III, New Delhi), NaOH pellets (RENKEM), Platinum crucible, Na2CO3 (SRL), Conc. HCl (RENKEM), Whatman Filter paper No. 40 (AXIVA).
the residual sodium hydroxide moieties. The precipitate along with filter paper pulp was transferred into a porcelain crucible and calcined at 900 °C for two hours. The weight of the final white silica powder was measured and noted down. 2.5. Characterization The synthesized nanosilica was dispersed in double-distilled water and UV–Vis spectroscopic measurement was done on Shimadzu, UV-1800 double Beam spectrophotometer. The FTIR spectrum was obtained using a Perkin Elmer made instrument, Spectrum 6500, by KBr pellet method, using BaSO4 as standard. The transmission measurement was made from mid-IR region 400–4000 cm1 at a resolution of 2 cm1. The Raman spectrum was acquired by using a Witec, Germany, made instrument by placing the powder on the glass coverslips and passing laser of 633 nm and 532 nm for 5–10 s. The X-ray diffraction pattern was measured by using a Bruker made instrument in the powder form. The XRD patterns were recorded in the 2 theta range of 5–70°, with a step size of 0.02 and a time of 2 s per step at a 30 KV and a current of 30 mA. The particle size distribution of nanosilica was measured by Malvern Zetasizer model, Nano S90 (UK), by dispersing them in double distilled water followed by sonication for 10 min at room temperature. The size and eternal features, porosity and shape were analyzed by FESEM Carl Zeiss (V5.05, SIGMA) and elemental analysis was done by the attached EDS analyzer of Bruker made along with it. 3. Results and discussions
2.2. Sample collection and preparation Fly ash based tiles were collected from Okhla, Industrial area, New Delhi. The tiles was crushed into small pieces and grounded in a mortar pestle. The obtained powder was dried in an oven at 45 °C overnight. 2.3. Preparation of wet filter paper pulp A Whatman filter paper no. 42 was torn into pieces and dipped into hot distilled water and the pieces were finely grounded. It was allowed to cool and kept in a beaker for future use. The wet pulp has been used for the filtration of precipitate and leachate. The use of filter paper in such a way makes the process cheaper and also increases the filtration and recovery of silica. 2.4. Method About 0.49 g of powder were weighed and mixed with 5–6 g of sodium bicarbonate uniformly in a platinum crucible. The mixture was placed in a muffle furnace for half an hour at 900–950 °C for fusion. After calcination, the mixture was allow to cool at room temperature and then the mixture along with crucible was dipped in a hot diluted 1:1 aqueous solution of HCl: H2O and it was heated till the complete disintegration of the fused mass from the crucible. Initially, the colour of the solution was pale yellow. The lumps of the mixture were dissolved with the glass rods. The mixture was baked at hot plate till complete dryness; again excess of dilute HCl was added and heated. The silica attached to the side of the beaker was wiped with the filter paper and dipped in the acidic solution. This step ensured any loss of silica that has adhered to the side of the walls of the glass beaker. A clear solution with white precipitate was obtained which was filtered by Whatman filter paper no 42 pulp. The precipitate remained with the filter paper pulp while the acidic leachate obtained in the filtrate. The precipitate was washed several times with mild-warm water to remove
3.1. Step one alkali dissolution-fusion method All the glassy amorphous and crystalline silica (mullite and sillimanite) reacts with sodium bicarbonate at temperature 950 °C. The sodium bicarbonate and silicates get melted fuses to form a new product i.e. sodium silicate. The following reaction will help in understanding the reaction
SiO2 ðFly ash tiles powderÞ þ Na2 CO3 ¼ Na2 SiO3 þ CaCO3
ð1Þ
3.2. Second step- precipitation of silicates in HCl The silica is insoluble in acids, so the fused silicates in the form sodium silicates will form Hydrogen silicate or silica directly after reacting with the diluted HCl. The following step can be explained by the reaction given below:-
Na2 SiO3 þ 2H2 O þ 2HCl ¼ SiðOHÞ4 þ 2NaCl
ð2Þ
The silica being insoluble in acids gets precipitated at the bottom while all the acid-soluble metal dissolves in HCl and forms metal chlorides that can be collected at their respective pH mainly alumina and ferrous ions. The sodium silicate reacts with H2O to form silicic acid which later on polymerizes to form a silica gel by the above reaction (2). Further, the silicic acid condenses to form small particles, chains and ultimately to form a network resulting in a silica gel as shown below [20]:
ð3Þ
Please cite this article as: V. Kumar Yadav, R. Suriyaprabha, S. Heena Khan et al., A novel and efficient method for the synthesis of amorphous nanosilica from fly ash tiles, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.013
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Fig. 1. UV–Vis spectra of nanosilica.
Fig. 2. FTIR spectra of nanosilica.
The quantitative analysis of the nanosilica was done by subtracting the weight of obtained silica from the initial weight of fly ash-tiles taken. The initial fly ash-tiles powder taken was 0.4937 g while about 0.2937 g of nanosilica was obtained. By XRF it was found that 59–60% silica per gram is present in fly ash based tiles. The total yield of nanosilica was 59.5% i.e. almost 99–100% from fly ash based tiles.
Fig. 4. XRD diffractogram of nanosilica.
3.2.1. XRF spectroscopy XRF confirmed the silica content in the fly ash-tiles about 59– 60% as the major oxides, followed by alumina and iron oxides.
Fig. 3. Raman spectra of nanosilica.
Please cite this article as: V. Kumar Yadav, R. Suriyaprabha, S. Heena Khan et al., A novel and efficient method for the synthesis of amorphous nanosilica from fly ash tiles, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.013
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V. Kumar Yadav et al. / Materials Today: Proceedings xxx (xxxx) xxx
3.2.2. UV–Vis spectroscopy The UV–Vis measurement was done from 200 to 600 nm by a Halo double beam 1800 spectrophotometer. The nanosilica was dispersed in double distilled-water. The peak at 210 nm and 350 nm confirms the formation of nanosilica from fly ash-tiles. Fig. 1 shows the UV–Vis spectra of nanosilica.
3.2.3. FTIR The FTIR spectrum of nanosilica is shown in Fig. 2 which reveals that in the fingerprint region of the spectrum, there is a broad and intense peak at 1085 cm1 which are the characteristic bands of anti-symmetric stretching vibration of the Si-O-Si and a less intense band at 806 cm1 is attributed to the symmetric stretching
Fig. 5. Particle size distribution graph of nanosilica.
Fig. 6. FESEM images (a and b) and EDS-spot (c) spectra of nanosilica (d).
Please cite this article as: V. Kumar Yadav, R. Suriyaprabha, S. Heena Khan et al., A novel and efficient method for the synthesis of amorphous nanosilica from fly ash tiles, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.013
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vibrations of Si-O-Si [19]. The band at 470–464 cm1 attributed to the rocking vibrations of Si-O-Si (siloxanes) [20;23]. These bands are the characteristic of the nanosilica whereas the bands at 3400 cm1 and 1600 cm1 are due to the associated water molecules. The bound water molecule might have left during calcination or it may also be due to the moisture absorption during analysis.
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Acknowledgments The authors are thankful to the Central Instrumental facility (CIF), Central University of Gujarat, Centre for Nanosciences, Jamia Millia Islamia, New Delhi, CECRI (CSIR)-Karikudi, Tamil Nadu, Spectro Analytical Lab, Okhla New Delhi. References
3.2.4. Raman The Fig. 3 shows the Raman spectrum of the nanosilica, where the bands at 545 cm1, 578 cm1, 580 cm1, and 610 cm1 are the characteristics peaks of the synthesized nanosilica [21]. The Raman spectrum also confirms the amorphous nature of the synthesized nanosilica. 3.2.5. XRD The XRD pattern of the nanosilica shown in Fig. 4 reveals the amorphous nature of the synthesized nanosilica. There are diffused peaks corresponding to the [111], [220] and [311] planes of silica. A broad hump was noticed from two theta 15–30° with a centered peak at 2h (21.7°) confirms the formation of amorphous silicon dioxide [22;23]. Besides this, there are also a few small intensity peaks for quartz at 38, 44 and 63°. While the absence of other peaks of minerals indicate the removal of impurities and formation of pure nanosilica. 3.2.6. PSA The nanosilica powder was dispersed in the double-distilled water, followed by sonication for 10 min in an ultrasonicator of 40 kHz at room temperature. The particle size distribution of the dispersed nanosilica is shown in the PSA graph in Fig. 5 which reveals that the average size of the particle is 219.8 nm while the size of most of the particles is 239.1 nm and the PDI is 0.092. 3.2.7. FESEM-EDS The FESEM images and EDS spectra of nanosilica are shown in Fig. 6a-b and Fig. 6c-d respectively. From the FESEM micrographs it is clear that the particles are spherical in shape, but showing high aggregation whose size varies from 30 to 60 nm. The nanosilica is showing aggregation and pores on their surface. While the EDS spectra also confirm the formation of silica as there are sharp and prominent peaks for Si and O. While there is an impurity in the form of fluorine, Na and Al whose total composition is less than 2.5%. 4. Conclusions In present work, an efficient and cost-effective method was developed for the synthesis of nanosilica of size 30–60 nm from fly ash based tiles. The main groups present in the silica were siloxane and silanol was confirmed by FTIR. The synthesized nanosilica is amorphous, pure and highly aggregated as confirmed by the FESEM and XRD. The impurities are in the form of F, Na, and Al which is due to improper washing. The advantage of this method is that it reduces solid wastes and transforms it into useful products. The leachate rich in Al and other metals can be used for the recovery of elements at a specific pH. This method has an efficiency of 99% for the extraction of silica from fly ash based tiles. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
[1] Lorenzo Mangolini, Synthesis, properties, and applications of silicon nanocrystals, J. Vacuum Sci. Technol. B Nanotechnol. Microelectron. Mater. Process. Measure. Phenomena 31 (2013), 020801. [2] Yadav, Virendra Kumar and Priti Raj Pandita. ‘‘Fly Ash Properties and Their Applications as a Soil Ameliorant.” Amelioration Technology for Soil Sustainability. IGI Global, 2019. 59–89. Web. 13 Nov. 2019. doi:10.4018/9781-5225-7940-3.ch005 [3] L.-Y. Lin, J.-T. Kuo, H. Bai, J. Hazard. Mater. 192 (2011) 255–262. [4] M.N.V. Ravi Kumar, M. Sameti, S.S. Mohapatra, X. Kong, R.F. Lockey, et al., Cationic silica nanoparticles as gene carriers: synthesis, characterization and transfection efficiency in vitro and in vivo, J Nanosci Nanotechnol 4 (2004) 876–881. [5] H.T. Jang, Y. Park, Y.S. Ko, J.Y. Lee, B. Margandan, Highly siliceous MCM-48 from rice husk ash for CO2 adsorption, Int J Greenhouse Gas Control 3 (2009) 545– 549. [6] I.J. Bruce, J. Taylor, M. Todd, M.J. Davies, E. Borioni, C. Sangregorio, T. Sen, J. Magn. Magn. Mater. 284 (2004) 145–160. [7] Saurabh Singh, Bijendra Kumar Singh, S.M. Yadav, A.K. Gupta, Applications of nanotechnology in agricultural and their role in disease management, Res. J. Nanosci. Nanotechnol. 5 (2015) 1–5. [8] A. Corma, From, microporous to mesoporous molecular sieve materials and their use catalysis, Chem. Rev. 97 (1997) 2373–2419. [9] A. Rani, S. Sanal, T. Jacob, G. Jacob, P.K. Desy, N.K. Manivarnan, Silica nano particles synthesized from boiler spent ash: value addition to industrial waste, Chem. Mater. Res. 6 (2014) 93–99. [10] Pratibha Aggarwal, Rahul Pratap Singh, Yogesh Aggarwal, Use of nano-silica in cement-based materials—a review, Civil Environ. Eng. Cogent Eng. 2 (2015), 1078018. [11] Tatiana G. Pineda-Vasquez, Ana E. Casas-Botero, Margarita E. RamírezCarmona, Mabel M. Torres-Taborda, Carlos H.L. Soares, Dachamir Hotza, Biogeneration of silica nanoparticles from rice husk ash using fusarium oxysporum in two different growth media, Ind. Eng. Chem. Res. 53 (2014) 6959–6965. [12] Md. Ghazali, O.P. Kaushal, Characteristics of fly ash from thermal power plants and its management along with settling pond design, Inter. J. Eng. Res. Sci. IJOER 1 (4) (2015). [13] E.V. Sokol, N.V. Maksimova, N.I. Volkova, E.N. Nigmatulina, A.E. Frenkel, Hollow silicate microspheres from fly ashes of the Chelyabinsk brown coals (South Urals, Russia), Fuel Process. Technol. 67 (2000) 35–52. [14] Y. Abdullahi, E.A. Ali, A.O. Lawal, Roast –alkaline leaching of silica from kaolinitic, ARPN J. Eng. Appl. Sci. 8 (10) (2013). [15] Asmaa Mourhly, Mariam Khachani, Adnane El Hamidi, Mohammed Kacimi Mohammed Halim, Said Arsalane, The synthesis and characterization of lowcost mesoporous silica SiO2 from local pumice rock, Nanomater. Nanotechnol. 5 (2015) 35. [16] Noor Sheeraz Che Zulkifli, Ismail Ab Rahman, Dasmawati Mohamad, Adam Husein, A green sol-gel route for the synthesis of structurally controlled silica particles from rice husk for dental composite filler, Ceram. Int. 39 (2013) 4559–4567. [17] Tatiana G. Pineda-Vasquez, Mabel M. Torres-Taborda, Ana E. Casas-Botero, Carlos H.L. Soares, Margarita E. Ramírez-Carmona, Dachamir Hotza, Biogeneration of silica nanoparticles from rice husk ash using fusarium oxysporum in two different growth media, Ind. Eng. Chem. Res. 53 (2014) 6959–6965. [18] Vipul Bansal, Absar Ahmad, Murali Sastry, Fungus-mediated biotransformation of amorphous silica in rice husk to nanocrystalline silica, J. Am. Chem. Soc. 128 (2006) 14059–14066. [19] Jegan Athinarayanan, Vaiyapuri Subbarayan Periasamy, Mohammad Alhazmi, Khalid A. Alatiah, Ali A. Alshatwi, Synthesis of biogenic silica nanoparticles from rice husks for biomedical applications, Ceram. Int. 41 (2015) 275–281. [20] Jyoti L. Gurav, In-Keun Jung, Hyung-Ho Park, Eul Son Kang, Digambar Y. Nadargi, Silica aerogel: synthesis and applications, J. Nanomater. 2010 (2010) 11, 409310. [21] Riyas Sharafudeen, Jihad Mohammed Al-Hashim, Mohammed Olian Al-Harbi, Ahmed Ibrahim Al-Ajwad, Ali Abdulaziz Al-Waheed, Preparation and Characterization of Precipitated Silica using Sodium Silicate Prepared from Saudi Arabian Desert Sand, Silicon (2017), https://doi.org/10.1007/s12633016-9531-8. [22] Feng Yan, Jianguo Jiang, Kaimin Li, Nuo Liu, Xuejing Chen, Yuchen Gao, Sicong Tian, Green Synthesis of Nanosilica from Coal Fly Ash and Its Stabilizing Effect on CaO Sorbents for CO2 Capture, Environ. Sci. Technol. 51 (2017) 7606–7615. [23] Virendra Kumar Yadav, M.H. Fulekar, Green synthesis and characterization of amorphous silica nanoparticles from fly ash, Elsevier Mat. Today Proceed. 18P7 (2019) 4351–4359.
Please cite this article as: V. Kumar Yadav, R. Suriyaprabha, S. Heena Khan et al., A novel and efficient method for the synthesis of amorphous nanosilica from fly ash tiles, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.013