The thermal properties of PN and WS were obtained using a Thermogravimertic Analyzer (TGA, Pyris 1 TGA, PerkinElmer, USA) at 20 °C/min up to the final temperature of 700 °C under a flow of N2. The functional groups of biochar and the Si species in the filtrates of raw biochar were analyzed using Fourier Transform Infrared Spectroscopy (FTIR, Nicolet FTIR IS10, Thermo Scientific, USA). The methods of sample preparation and data analysis are shown in Supplementary S8. The surface of biochar was analyzed with X-ray Photoelectron Spectrometer (XPS, PHI-5000 Versaprobe, ULVAC-PHI, Japan) using an Al Kα excitation radiation. The pHs of raw biochars and pHs of point of zero charge (pHPZC) of de-ashed biochars were obtained by the pH drift method in Supplementary S9 and S10. The contents of K, Ca, Mg, Al, Fe, Zn, and P in biochars were analyzed after the microwave digestion of biochars with HNO3-HF-H2O2 (U.S. EPA 3502)58. The concentrations of K, Al, and Fe in the digestion solution were determined with ICP-AES. The digestion experiments were conducted in duplicate for each biochar.