Autosorb 3b

Ten chars from two feedstocks (i.e., oak wood-Quercus; and switchgrass-Panicum vigartum) were pyrolyzed from 300 to 700 °C under oxygen-limited condition in a muffle furnace (Model 550-58, Fisher Scientic, USA) for 2 h. The chars were subsequently cooled, ground, and passed through a sieve (mesh no. 70, ASTM Standard Test Sieve, E-11 Specication) to obtain the desired neness. The resulting chars were labelled WX and GX, where W and G represents wood or grass feedstock, respectively, and X indicates the pyrolysis temperature. The elemental analysis of chars was carried out by Galbraith Laboratories (Knoxville, TN) using a Flash 2000 Elemental Analyzer. The surface area of chars was characterized by N 2 sorption (Autosorb-3B, Quantachrome Instruments). The pH of chars was determined in a homogeneous suspension by equilibrating the respective char with DI water at a solid-to-liquid ratio of 100 g char L -1 following the American Society for Testing and Materials (ASTM) D3838-05 (Standard Test Method for pH of Activated Carbon; 2017). Key properties of chars, including elemental composition, atomic ratios, surface areas, and pH values were provided in Table S2. †

The structures of the obtained silica particles were evaluated using TEM and scanning electron microscopy (SEM: S-3400 Hitachi High-Technologies Corporation, Tokyo, Japan) . Infrared absorption spectra of the silica particles before and after sintering were obtained using Fouriertransform infrared spectrometer (FT-IR: FT/IR-6100, JASCO Corporation, Tokyo, Japan) employing the KBr disk method. The specific surface area was determined using nitrogen adsorption/desorption measurements (Autosorb-3B, Quantachrome Instruments Florida, USA) operated at 77K.