*2.2. Chemical and Physical Material Properties*

Elemental analysis was done using a PerkinElmer 2400 CHNS/O series II analyzer (Waltham, MA, USA) using cysteine as a standard. Each measurement used approximately 2 mg of biochar and was done in triplicate. Ash content of the biochar samples was determined using a TA Instruments Q2950 thermogravimetric analyzer (New Castle, DE, USA) by heating to 1000 ◦C at a heating rate of 10 ◦C per minute in an air atmosphere. Ash content was determined to be the weight percentage remaining, and oxygen (O) was determined by difference from the original dried sample and the sum of C, H, N, and ash. Densities of the biochar samples were measured in triplicate using a Micromeritics Accupyc II 1340 helium pycnometer (Norcross, GA, USA) using the 10 cm<sup>3</sup> sample cup. Infrared spectra were obtained using a Frontier attenuated total reflectance (ATR) Fourier-Transform Infrared Spectrometer (FTIR) (Perkin Elmer, Waltham, MA, USA) fitted with a diamond crystal. The background scan was conducted under ambient atmosphere. Powdered samples were placed directly on the crystal. For each sample, 64 scans were conducted from 650–4000 cm−<sup>1</sup> at a spectral resolution of 4 cm−<sup>1</sup> . The baseline correction function of the Spectrum software was utilized for all samples.
