Introduction

Materials and methods

Acknowledgments

Results and Discussion Conclusions

Lanny Sapeia,*, Andika Pramuditab, Livia Budyanto Widjajab

aDepartment of Chemical Engineering, University of Surabaya, Raya Kalirungkut, Surabaya 60293 East Java, IndonesiabDepartment of Chemical Engineering, Parahyangan Catholic University, Ciumbuleuit 94, Bandung 40141 West Java, Indonesia

* Corresponding author. Tel.: +62-31-2981150; fax: +62-31-2981151. E-mail address: lanny.sapei@ubaya.ac.id.

Literature cited

AbstractRice husk is a by-product of rice milling process and abundantly available waste material in all rice producing countries. Upon calcination, rice husk produced of about 20% ash of which 90% was silica. Acid treatment ofrice husk prior to calcination was proved to be very effective in producing silica with high purity. In this experiment, rice husk was treated using hydrochloric acid and citric acid for the metal impurities removal. Thermaltreatment was conducted at 750oC and maintained for 5 hours. Silica was mostly deposited on the epidermal layer and showed similarity with the intact structure of rice husk based on SEM investigation. The resulted silicawas proved to be amorphous according to FTIR (Fourier Transform Infrared Spectroscopy) and XRD (X-Ray Diffraction) analysis. The BET (Brunauer-Emmett-Teller) specific surface areas of silica derived from calcinedhydrochloric acid treated and citric acid treated rice husks were about 312 and 255 m2/g, respectively. Silica with purity of about 99% was obtained in all calcined acid-leached rice husks based on XRF (X-ray Fluorescence)analysis. Citric acid treatment was less harmful and less corrosive as compared to hydrochloric acid and was still effective enough in producing high-grade silica with high purity and high surface area. Pure amorphoussilica derived from rice husk had a great potential to be used as adsorbents or catalyst supports or even as low-cost precursors for other silica based products.

Pure amorphous silica derived from calcined acid-leached rice husk

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1. Institut Teknologi Bandung (ITB)

2. Universitas Gadjah Mada (UGM)

3. Universitas Indonesia (UI)

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5. Universitas Diponegoro (Undip)

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Utilization of agricultural waste into value-

added products that could be useful for

various industrial applications.

Isolation of bio-silica from plants, the use of

bio-silica as catalyst supports or adsorbents,

development of silica-based materials.

Development of bio-based emulsifier for

food products in order to formulate highly

nutritious and healthier foods.

Focus of My Research and Future Perspectives

The use of renewable materials for sustainable

processes and products has to be

continuously developed.

We need to support a sustainable living for the

next generations.

2-theta (o)

10 20 30 40 50 60

Inte

ns

ity [

a.u

.]

0

40

80

120

160

200

without leaching

with hydrochloric leaching

with citric acid leaching

SamplesBET specific surface

area (m2/g)

without leaching 56.5

with hydrochloric leaching 311.6

with citric acid leaching 254.1

Wavenumber (cm-1)

400140024003400

Ab

so

rba

nce

0.0

0.4

0.8

1.2

1.6 without leaching

with hydrochloric leaching

with citric acid leaching

Figure 1. SEM images of thermal treated rice husks at 750oC. (A) without leaching; (B) with hydrochloric

leaching; (C) with citric acid leaching.

A B C

Table 1. Chemical composition of thermal treated rice husks at 750oC analyzed by XRF

Table 2. BET specific surface area of thermal

treated rice husks at 750oC

Figure 2. FTIR spectra of thermal treated rice husks at 750oC

Figure 3. XRD patterns of thermal treated rice husks at 750oC

• Three typical bands of four-coordinated silica are obviously

seen at the wavenumber of 1082 cm-1, 893 cm-1, and 457 cm-1.

• Small shoulder at 956 cm-1 could be attributed to silanol.

• Small peak at ~1630 cm-1 is attributed to adsorbed water and

a broad hump between 3700 -3200 cm-1 indicated the presence

of OH-.

• Silica is detected at 2θ = ~ 22o.

• A broad hump instead of a sharp peak indicates that

silica in rice husk is amorphous.

• Acid leaching could increase the specific

surface area for about 5-6 times.

• The calcined acid leached rice husks has a great

potential to be used as adsorbents or catalyst

supports.

SEM

XRF

(% wt) SiO2 K2O CaO P2O5 Fe2O3 MnO otherswithout leaching 91.5 3.3 1.74 2 0.545 0.578 0.337

with hydrochloric leaching 98.8 - 0.39 - 0.511 0.099 0.2

with citric acid leaching 99 - 0.629 - 0.14 0.12 0.111

FTIR

XRDBET – Nitrogen sorption

Silica accumulation in rice husk was

concentrated on the outer surface.Acid leaching treatment followed by

calcination at 750oC was effective inproducing bio-silica with high purity of~99%.

Rice husks derived silica is amorphousand can be used as raw materials for silica-based compounds.

Isolated silica has a relatively highspecific surface area of about ~300 m2/g andcould be useful for adsorbents/ catalystsupports.

Citric acid could be used as the HClsubstitute because it is less corrosive, lessharmful, and eco-friendly.

Preparation of rice husks: winnowing, washing, and sun-drying

Acid-leaching process for silica isolation

Sample A : Leaching with 10% hydrochloric acid at 100oC for 2 hours.2

Sample B : Leaching with 5% citric acid at 80oC for 15-20 minutes.4

Thermal treatment/ calcination of acid-leached rice husks at 750oC with a

heating rate of 10oC/min and a holding time of 5 hours.

Washing with demineralized water for 3-4 times, followed by drying in the

oven at 100oC for 1 hour.

Characterisation of rice husks derived silica with several analytical

methods, such as: SEM, XRF, FTIR, XRD, and BET nitrogen sorption

Furnace used for the thermal treatment/

calcination process

“Volcano ash”

crystalline silica

less reactive

harmful

Indonesia is one of the biggest agrarian country. Its unhulled paddy

production has been continually increased each year and reached to about

70 millions tons in 2013.1) Twenty percent of the paddy milling by-products

consist of about 20% rice husks which have not been optimally utilized.

Rice husk is highly rich in silica (~20%). Silica has been widely used in

various industries, such as building material, ceramic, filler, adsorbent.

Silica present in plants is amorphous and more reactive compared to

crystalline silica due to the presence of silanol groups upon their surface.

However, in order to obtain silica with high purity, other metallic

impurities (e.g. K2O, MgO, CaO) present in rice husks have to be removed.

Pre-treatment of rice husk with acids such as HCl 2,3) or citric acid 4) prior to

calcination has been proved to be very effective in producing high-grade

bio-silica.

1. Badan Pusat Statistik Republik Indonesia. www.bps.go.id

2. Sapei, L, Robert Noeske, Peter Strauch, Oskar Paris (2008), Chem. Mater., Vol 20, pp. 2020-2025.

3. Chandrasekhar, S., Pramada, P.N., and Majeed, J. (2006), Journal of Materials Science, Vol. 41, pp. 7926-7933.

4. Umeda, J. and Kondoh, K. (2008), Journal of Materials Science, Vol. 43(22), pp. 7084-7090.

Mt. Kelud (East Java, Indonesia)

Recent eruption on February 14, 2014

Rice husk

“Rice husk”

amorphous silica

more reactive

harmless

Financial support was provided by the researchgrant (number III/LPPM/2012-09/80-P) from theInstitute for Research and Community Services ofParahyangan Catholic University, Bandung,Indonesia.

Thanks to the American Chemical Society forcoordinating the Pittcon Travel Grant program.