*2.1. Material*

Rice husk (RH), used as a precursor for producing biochar, was obtained from an agricultural research and extension station (Pingtung County, Taiwan). The as-received biomass was cut by a rotary knife-type shredder. The shredded RH was further sieved to a broad range of mesh screen sizes, ranging from mesh no. 20 (opening size of 0.841 mm) to mesh no. 40 (opening size of 0.420 mm). The sieved RH was first dried in a forced air-circulation oven and then used for the pre-pyrolysis test involving thermogravimetric analysis (TGA) and the pyrolysis experiments. In line with the previous study [33], the dried RH contained high contents of carbon (45.28 wt%), hydrogen (5.51 wt%), oxygen (~44 wt%, estimated) and silicon (3.90 wt%), indicating that this biomass has a moderate calorific value (16.4 MJ/kg) [12].
