Asap 2020 v3.04h

Two types of commercial biochars (Coconut shell biochar, Bamboo biochar) and one kind of homemade graphene58 (link) were used. Coconut shell carbon, bamboo biochar, and graphene were denoted as B1, B2 and GN, respectively. Analytics project test data: B1: Iodine value or 1100 mg/g, 800 °C high-temperature activation, pH value 7–9; B2: Iodine value 1420 mg/g, 1000 °C high-temperature activation, pH value 7–9.
In order to keep the biochar particles size uniformity, eliminate the interference of other substances and microbial interference in biochars, the original samples were treated as follows: the particle size of the biochar was 0.4–0.8 mm after grinding. The biochars and graphene samples were washed by deionized water to an invariable pH value and desiccated by vacuum freeze–drying. The microbial interference was excluded by 30 min UV irradiation. Finally, the carbon materials were characterized by SEM, FTIR spectrum and Raman spectrometer (InVia plus, Renishaw plc, Britain). Surface area of adsorbents (biochar and garphene) were determined by nitrogen adsorption using ASAP 2020 V3.04 H (Micromeritics).

The specific surface area of the fibers was determined by Brunauer, Emmett, and Teller (BET) nitrogen adsorption–desorption isotherms at −195 °C in a surface area analyzer (ASAP 2020 V3.04H, Micromeritics Co. Norcross, GA, USA). Prior to determination, the sample was degassed for 3 h at 80 °C under vacuum (P/P₀ = 0.25) to remove moisture and any other contaminants.
The surface micro-morphological structures of the exterior and interior surfaces of the samples were examined by scanning electron microscopy (SEM, S-3400 N, Hitachi Ltd. Tokyo, Japan) at a voltage of 15 kV. Specimens were prepared for SEM inspection by placing the samples on carbon glue and then plating them with Pt (7 nm). Ultrathin sections of fibers were utilized to observe the changes in cell walls detected by transmission electron microscopy (TEM) and atomic force microscopy (AFM). TEM was conducted on a JEM-2100 microscope (JEOL, Tokyo, Japan). AFM was conducted on a Dimension 3100 microscope (Veeco Instruments Inc. Plainview, NY, USA). Images were captured using silicone cantilevers. The scanning rate ranged from 0.5 to 1.5 Hz.

Scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX) were performed on the gold-coated samples using an acceleration of 5 kV, completed by a scanning electron microscope (Model Supra 50 VP). Surface area analysis was carried out using ASAP 2020 V3.04H (Micromeritics^®). The sample was automatically degassed at 90 °C for 1 h for the first stage and 350 °C for 4 h for the second stage, with the N₂ adsorption–desorption isotherm taken at −195.798 °C. The primary content of organic materials, which are carbon (C), hydrogen (H), nitrogen (N) and sulphur (S), were measured by a varioMICRO (V3.1.1) CHNS Elemental Analyser. The surface functional group of the prepared materials was determined using a Fourier transform infrared spectrometer (Nicolet Avatar 360 ESP FTIR) with 64 times scanning at a resolution of 4 cm⁻¹ over a region of 4000 to 400 cm⁻¹. The crystallinity index was measured using a Kristalloflex D-5000 X-ray diffraction system (Siemens, Munich, Germany). Scanning was performed at a diffraction angle 2θ ranging from 1.5° to 80°, corresponding to a scanning speed of 0.02° and 2°/min [39 (link)]. The thermal analysis was carried out under a nitrogen atmosphere with a heating rate set at 20 °C /min over temperatures ranging between 30 and 800 °C, using a Mettler Toledo TGA/SDTA851^e thermogravimeter (Mettler Toledo Corp., Greifensee, Switzerland).