ABSTRACT

Nano-silica was synthesised from pumice by extraction method using sodium hydroxide (NaOH), sulphuric acid (H₂SO₄) and hydrochloric acid (HCl). The raw material of pumice was collected from local area, Tanggamus-Lampung Indonesia. After grinding, the pumice powder was activated at 450°C for 2 h before mixing with NaOH for extraction. After extraction, the powder was heated at 800°C for 4 h, to maintain the silica is in amorphous phase. Physical characteristics were analysed using transmission electron microscopy (TEM) for measuring particle size, Brunauer-Emmett-Teller (BET) technique for surface area measurement, x-ray diffraction (XRD) for structure and x-ray fluorescence (XRF) for determination of oxides. XRD analysis proved that besides amorphous nano-silica, there are peaks of sodium sulfate (Na₂SO₄) as representation of crystalline structure. The maximum silicon dioxide (SiO₂) content was found on 3.0 molar (M) NaOH. The highest surface area of 165 m²/g was obtained in sample of 3.5 M NaOH. The truly amorphous nano-silica content was found in NaOH of 3.0 M. The formation temperature may occur between 1100°C–1200°C. The particle size is in the range of 9 nm–17 nm.

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