Contents lists available at ScienceDirect Ceramics International journal homepage: www.elsevier.com/locate/ceramint Ultra-high surface area nano-porous silica from expanded perlite: Formation and characterization Walt Wheelwright a , Ralph P. Cooney a, ⁎ , Sudip Ray a , Zoran Zujovic a,b , Karnika de Silva a a The Biocide Toolbox Research Programme, The University of Auckland, Auckland, New Zealand b The NMR Centre, School of Chemical Sciences, University of Auckland, Auckland, New Zealand ARTICLE INFO Keywords: Expanded perlite SiO 2 Zeolite Surfaces ABSTRACT Ultra-high surface area silica, UHSAS (N 2 BET surface area: > 700 m 2 g -1 ) was obtained from expanded perlite (EP) by a two-step process. In the first step, a hydrothermal process using aqueous sodium hydroxide (at 70 °C for 24 h) was employed to convert EP into an ordered intermediate zeolitic phase. The materials and the process dynamics were examined by various analytical techniques to elucidate the material transformation mechanism involved and to optimize the silica surface area. The structural details of conversion of EP to high surface silica has been identified by Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and Solid State Nuclear Magnetic Resonance (SSNMR). These analyses have confirmed that the conversion includes an intermediate zeolite phase, which is predominantly NaP1 type zeolite. In the next stage, this intermediate NaP1 type zeolite was converted to amorphous high surface-area silica by hydrochloric acid treatment. Amorphous high-surface area silica was also recovered from the supernatant solution obtained from hydrothermal process by hydrochloric acid treatment. The overall process of silica extraction from EP was optimized to achieve the UHSAS products. 1. Introduction Perlite is a glassy alumina-silicate volcanic rock containing 1–5% of incorporated water which if heated above 850 °C expands and trans- forms into a cellular (honeycomb or popcorn like structured) material, Expanded Perlite (EP), which has a very low bulk density [1,2]. Perlites are found in many geographic locations including New Zealand. Key indicators of Perlite and EP in data averaged based on silica and alumina content and Brunauer, Emmet and Teller (BET) N 2 surface areas over several international sources [3–13] are as follows: • EP surface areas 1–2m 2 g -1 (i.e. very low); Perlite surface areas are not known for most sources but have been reported for Italian Perlite as 1.05 m 2 g -1 . • EP (XRF analysis): SiO 2 about 74%; Al 2 O 3 about 13% with small variations associated with different source locations. • Perlite: SiO 2 72.71%; Al 2 O 3 13.21% averaged across 106 different internationally sourced samples [10,13]. The relative consistency of these compositions and surface areas demonstrate that Perlite is a consistent mineral type, internationally. Various chemical components of New Zealand Perlite are SiO 2 (74%), Al 2 O 3 (14%), Na 2 O (3.0%), K 2 O (4.0%), Fe 2 O 3 (1.0%), CaO (1.3%), MgO (0.3%) and TiO 2 (0.1%) [14], which correlate well with published data [3,11]. Precipitated silica with high surface area have great demand in several commercial applications such as reinforcing filler for rubber and plastic products, as sorbent for food and paper industries, carrier of biocides in agricultural industries, matting agent for paints and varnishes [15]. According to a recent market research, the global precipitated silica market is projected to reach USD 2.23 billion by 2021, at a CAGR of 9.1% from 2016 to 2021. High demand for precipitated silica from the tire and rubber products industry is expected to drive the growth of the market in near future [16]. The common method of manufacture of precipitated silica is the acidifica- tion of sodium silicate solutions [17]. Usually the specific surface area of commercial precipitated silica are in the range of 60–300 m 2 g -1 [17,18]. High surface area silica in the range of 475–800 m 2 g -1 are also available from Sigma Aldrich. The primary objective of this study is to develop viable methodolo- gies for producing nano-porous amorphous UHSAS from EP by simple chemical treatment. This conversion was first observed by serendipity, while exploring other aspects of the materials science of EP. The key research questions arising from this overall objective are as follows: http://dx.doi.org/10.1016/j.ceramint.2017.05.333 Received 24 April 2017; Received in revised form 22 May 2017; Accepted 27 May 2017 ⁎ Correspondence to: MBIE Biocide Toolbox Research Programme, The University of Auckland, Newmarket Campus 903.230C, Private Bag 92019, Auckland 1142, New Zealand. E-mail address: r.cooney@auckland.ac.nz (R.P. Cooney). Ceramics International xxx (xxxx) xxx–xxx 0272-8842/ © 2017 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Please cite this article as: Wheelwright, W., Ceramics International (2017), http://dx.doi.org/10.1016/j.ceramint.2017.05.333