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50 SCIENCE & TECHNOLOGY DEVELOPMENT JOURNAL, Vol 20, No.K7- 2017 Synthesis of silica nanoparticles from rice husk ash Dang Thi Thuy Nhung, Tran Hoa, Nguyen Thuy Ai Trinh, Dang Van Phu, Phan Dinh Tuan, Nguyen Quoc Hien Abstract— Silica nanoparticles (SiO2 NPs) were synthesized from rice husk ash (RHA) by chemical treatment and calcination. The size of SiO2 NPs evaluated by transmission electron microscope (TEM) was of 20 - 50 nm and the size distribution of SiO2 NPs measured by dynamic laser scattering (DLS) was of Gaussian mode. The X-ray diffraction (XRD) pattern with only one peak at 2θ ~ 220 confirmed the amorphous phase of SiO2 NPs. The Fourier transform infrared (FTIR) and energydispersive X-ray (EDX) spectra were also used to evaluate the functional groups and the purity of SiO2 NPs. The SiO2 NPs powder with high purity could be suitably produced by calcination of acid treated RHA at 7000C for 2h. The obtained SiO2 NPs product can be potentially used for numerous purposes of application, especially as filler in paints. Index Terms— silica nano, rice husk ash, calcination, particle size. 1 INTRODUCTION Rice husk (RH) is a byproduct of rice milling process and RH is one of the abundant waste sources in rice growing countries such as Vietnam, Thailand, China,... It is estimated that one ton of Manuscript Received on June 12th, 2017, Manuscript Revised November 18th, 2017. Dang Thi Thuy Nhung, Nguyen Thuy Ai Trinh, Phan Dinh Tuan - Ho Chi Minh City of Natural Resources and Environment, 263B Le Van Sy Street, Ho Chi Minh City, Vietnam Tran Hoa - University of Science, Vietnam National University in Ho Chi Minh City, 227 Nguyen Van Cu Street, Ho Chi Minh City, Vietnam. Dang Van Phu, Nguyen Quoc Hien - Research and Development Center for Radiation Technology, Vietnam Atomic Energy Institute, 202A Street 11, Linh Xuan Ward, Thu Duc District, Ho Chi Minh City, Vietnam * Corresponding author. Email: dthnhung@hcmunre.edu.vn rice is created ~0.23 ton of RH. According to Chandrasehar et al. in India, in 1997-1998, about 26 million tons of RH were created [1]. In Vietnam, rice productivity is estimated of about 40 million tons/year, then the volume of RH waste is about 9.2 million tons/year. With silica content of about 10% in RH [2], the silica amount from RH in Vietnam is approximately one million ton/year. The presence of silica in the rice husk has been known since 1938 [1]. Commonly, RH is used as fuel with combustion energy of ~16,720 kJ/kg [3,4]. When RH is burned, it will create RH ash (RHA) with composition including: 72.1% SiO2; 0.3% Al2O3; 0.43% CaO; 0.5% Na2O; 0.72% K2O; 0.15% MnO; 0.05% TiO2; 0.7% MgO; 0.06% P2O5 and ~24.3% weight loss on ignition [3]. These components are subjected to change due to the different influenced factors such as geographic location, fertilizers, agro-chemicals,…[4]. Many studies on fabrication of silica from RH were conducted, especially silica nanoparticles (SiO2 NPs) produced from RH in order to increase the value of agricultural waste source [2,5-9]. RHA is also an abundant source that can be used to produce SiO2 NPs [3,4,10,11]. Silica was used for many applications such as adsorption material, carriers, fillers,.... Recently, silica from RH was used for production of porous ceramic doped with nano silver to induce antimicrobial property for treatment of microorganisms in water [12]. In addition, silica and SiO2 NPs were also used as growth promoter and elicitor for plants [9,13-17]. In the previous work [9], we studied to prepare SiO2 NPs from RH. In this work, SiO2 NPs was synthesized from RHA, which is also an abundant source obtained from factories using RH as burning fuel, especially in Mekong Delta region. TẠP CHÍ PHÁT TRIỂN KH&CN, TẬP 20, SỐ K7-2017 2 EXPERIMENTAL. 51 3 RESULTS AND DISCUSSION. 2.1 Materials and chemicals Raw RH was supplied by rice mill factory in the south of Vietnam. Analytical reagent-grade hydrochloric acid (HCl) was purchased from Merck, Germany. Distilled water and other chemicals were of pure grade. 2.2 Synthesis of SiO2 NPs from RHA SiO2 NPs from RHA was synthesized following the procedure of Sankar et al. [11] with some modifications. Briefly, raw RH was washed with tap water to remove sand, dust, soluble substances, and other contaminants. It was then dried at 60oC in forced air oven (Yamato, DNF 410, Japan). The cleaned RH was burned in open environment to collect RHA. 50 g of RHA was stirred with 500 ml of HCl 1N at room temperature for 2 hours and allowed to stand overnight to separate the metal ions in RHA. The acid treated RHA was filtered and washed with distilled water and dried at 60°C in forced air oven. Finally, the treated RHA was transferred into porcelain cup and calcined at 700°C for 2 hours in furnace Nabertherm, Germany with a ramp rate of ~20°C/min. The obtained product was SiO2 NPs white powder (Figure 1). Figure 1. Brief schematic description of synthesized process of SiO2 NPs from RHA The brief schematic description of synthesized process of SiO2 NPs from RHA was presented in Figure 1. 2.3 Characterization of SiO2 NPs The particle size of SiO2 NPs was evaluated by transmission electron microscope (TEM), model JEM1010, JEOL, Japan and the particle size distribution of SiO2 NPs was measured by dynamic laser scattering (DLS) on a particle size analyzer, LB550, HORIBA, Japan. The X-ray diffraction (XRD) pattern was determined on D8 Advance, Brucker, Germany. Element composition of SiO2 NPs was analyzed by energy dispersive xray spectrometer (EDX), Horiba 7593-H. The Fourier transform infrared (FTIR) spectrum was measured on FT-IR 8400S spectrometer (Shimadzu, Japan) using KBr pellet. Figure 2. TEM image of SiO2 NPs from RHA TEM image in Figure 2 showed that the particle size of SiO2 NPs from RHA was in the range from 20 to 50 nm. This result was consistent with the result of Sankar et al. [11], but the particle size was somewhat larger than that prepared from the RH (10-30 nm) in our previous study [9]. Figure 3. Particle size distribution of SiO2 NPs from RHA measured by DLS 52 SCIENCE & TECHNOLOGY DEVELOPMENT JOURNAL, Vol 20, No.K7- 2017 Result Figure 3 showed the particle size measured by DLS in the range from 800 to1400 nm that was higher than the size determined from TEM (20-50 nm). The reason is that DLS method usually determines the dynamic diameter particle sizes of SiO2 NPs dispersed in water [3]. Result in Figure 3 also showed that the particle size distribution of SiO2 NPs is a bell-shaped distribution (Gaussian distribution). Figure 4. XRD pattern of SiO2 NPs from RHA XRD pattern of SiO2 NPs in Figure 4 showed only 1 peak at 2θ ~22o. The obtained result confirmed the amorphous phase of SiO2 NPs synthesized from RHA treated with acid and calcined at 700oC for 2h [4,9]. Vietnam's RHA included K2O (0.39%), Al2O3 (0.48%), Fe2O3 (0.15%), CaO (0.73 %), MgO (0.55%), Na2O (0.12%) and SiO2 (96.15%). Thus, the metal impurities in RHA was efficiently extracted by HCl 1N. Carmora et al. [18] reported that organic acids such as acetic acid, citric acid can be used to extract the metal ions in RH to increase the purity of SiO2 NPs and to meet the demand for cleaner production. It can be deduced that organic acids could also be used to treat RHA. Figure 6. FTIR spectrum of SiO2 NPs from RHA The FTIR spectrum in Figure 6 exhibited characteristic peaks of silica framework, particularly at 1103 cm-1 for the O-Si-O asymmetric stretching vibration, at 794 cm-1 for the O-Si-O symmetric stretching vibration and at 491 cm-1 for the O-Si-O bending vibration [4,11,19]. The broad peak at 3460 cm-1 was due to the stretching vibration of surface silanol groups (Si-O-H) and physically adsorbed water [11,19,20]. In addition, the peak at 1629 cm-1 was assigned to H-O-H bending vibrations of trapped water molecules in the silica matrix [19,20]. Thus, the FTIR spectrum did not show any peaks confirming the presence of other organic and inorganic materials that demonstrated high purity of the obtained SiO2 NPs [2,11,19,20]. 4 CONCLUSION. Figure 5. EDX spectrum of SiO2 NPs from RHA The EDX spectrum of SiO2 NPs in Figure 5 showed 2 peaks at kα at 1.74 and 0.53 keV corresponding to silicon (Si) and oxygen (O) with content in weight of 41.16% for silicon and 58.84% for oxygen. This result also indicated that the synthesized SiO2 NPs was of high purity [4]. According to Le et al. [10], the composition of In this study, RHA-an abundant agriculture waste was used for the synthesis of SiO2 NPs. The SiO2 NPs with diameter of 20 - 50 nm and high purity was successfully obtained by calcination of HCl acid treated RHA at 700oC for 2h. The synthetic process is fairly suitable for large-scale production. Thus, the synthesized SiO2 NPs, a value-added product can be potentially used for different applications, especially as filler in paints TẠP CHÍ PHÁT TRIỂN KH&CN, TẬP 20, SỐ K7-2017 and helps to diminish the concerns of RHA disposal in environment as well. REFERENCES 53 production and crop protection: A review”, Crop Prot., vol. 35, pp. 64-70, 2012. [16] L. M. Kiirika, F. Stahl, K. Wydra, “Phenotypic and molecular characterization of resistance induction by single and combined application of chitosan and silicon in tomato against Ralstonia solanacearum,” Physiol. Mol. Plant Pathol., vol. 81, pp. 1-12, 2013. [17] S. Huang, L. Wang, L. Hou Y. Liu, L. Li, “Nanotechnology in agriculture, livestock, and aquaculture in China. A review”, Agron. Sustain. Dev., vol. 35, no. 2, pp. 369-400, 2015. [1] S. Chandrasekhar, K.G. Satyanarayana, P.N. Pramada, P. Raghavan, T.N. Gupta, “Review Processing, properties and applications of reactive silica from rice husk - an overview”, J. Mater. 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He received the BE and PhD degrees in chemical engineering from the Hanoi University of Science and Technology, Vietnam. From 1981 to 2001, he was a Researcher at Vietnam Atomic Energy Institute. Since 2001, he has joined the Hochiminh City University of Technology and then the Hochiminh City University of Natural Resources and Environment. Professor Phan Dinh Tuan is the author of five books, more than 100 articles. His research interests include chemical and environmental engineering, material science, climate change and renewable energy. He is an Editor of the Journal Science and Technology under Vietnam Academy of Science and Technology. Dang Thi Thuy Nhung was born in 1987, took BS in 2009 and MS in 2016 in the field of environmental science and management. She is now PhD student in environmental engineering. Tran Hoa, University of Science, Vietnam National University in Ho Chi Minh City, 227 Nguyen Van Cu Street, Ho Chi Minh City, Vietnam. Nguyen Thuy Ai Trinh was born in 1977, took BS in 2002, MS in 2010 and joined in PhD course from 2012 at the Hochiminh City University of Technology. 54 SCIENCE & TECHNOLOGY DEVELOPMENT JOURNAL, Vol 20, No.K7- 2017 Dang Van Phu was born in 1977, took BS in 1999, MS in 2013 in chemico-biology at the Hochiminh City University of Science. He is now researcher at the Research and Development Center for Radiation Technology (VINAGAMMA). materials, especially nano and bioactive materials, chemical and environmental sciences. Nguyen Quoc Hien was born in 1956 in Hatinh, Vietnam. He took BS in chemistry in 1977 and PhD in theoretical.and physico-chemistry in 1996 at the Hochiminh City University of Natural Science. Professor Nguyen Quoc Hien is the author of 7 books and more than 100 papers. His research interests include nouvel method for synthesis of Nghiên cứu tổng hợp nanosilica từ tro trấu Đặng Thị Thùy Nhung*, Trần Hòa, Nguyễn Thụy Ái Trinh, Đặng Văn Phú, Phan Đình Tuấn, Nguyễn Quốc Hiến Tóm tắt— Nanosilica được chế tạo từ tro trấu bằng phương pháp xử axít và nung. Kết quả cho thấy kích thước hạt của nanosilica xác định bằng chụp ảnh kính hiển vi điện tử truyền qua (TEM) trong khoảng 20 50 nm. Phân bố kích thước hạt nanosilica theo kiểu hình chuông (Gaussian) được đo bằng phương pháp tán xạ lase (DLS). Phổ hồng ngoại (FTIR) và phổ tán sắc năng lượng tia X (EDX) cũng được sử dụng để đánh giá nhóm chức năng và độ tinh khiết của vật liệu nanosilica. Kết quả cũng cho thấy vật liệu nanosilica có thể được chế tạo một cách thuận lợi bằng phương pháp nung tro trấu đã được xử lý với axít ở nhiệt độ 700oC trong thời gian 2 giờ. Sản phẩm nanosilica có tiềm năng đáp ứng nhu cầu ứng dụng trong nhiều lĩnh vực, đặc biệt là làm chất độn pha sơn. Từ khóa— Silica nano, tro trấu, thiêu kết, kích thước hạt.