Asap 2460

The carbon (C), hydrogen (H), and nitrogen (N) contents of each biochar sample were determined using an Element Analyzer (Elementar Vario EL III, Frankfurt, Germany). The yield data of biochar were calculated based on mass balance. The ash was analyzed according to the approach reported by He et al.^{16 (link)} and its weight percent calculated using the following equation: $$Ash(\%)=\frac{W_f}{W_i}\times 100$$ where W_f and W_i represent the final and initial mass of the biochar sample, respectively. The biochar samples’ oxygen (O) content was calculated on the basis of the mass balance assuming that whatever was not ash, C, H, and N had to be O^{17 (link)}: $$O\%=100\%-Ash\%-C\%-H\%-N\%$$
The surface area and pore properties of biochar were analyzed using a surface area and pore size analyzer (Micrometrics ASAP 2460, Norcross, USA). The surface structure and morphology of all biochar samples were observed with a FIELD Scanning Electron Microscope (SEM, Hitachi S-4800, Tokyo, Japan). The pH_pzc (pH at point of zero charges) values of biochar samples were measured using a Zeta potential analyzer (Nano Brook Zeta Plus, Suffolk, USA). Fourier-transform infrared (FTIR) spectra (recorded using a Bruker Vertex 80 spectrometer, Karlsruhe, Germany) were collected in the 400–4000 cm⁻¹ wavenumber range to identify the functional groups present on the surface of biochar samples.

Mesoporous BG NPs used in this study were prepared using a cetyl pyridine bromide (CPB) template method according to the previously published protocol (Sui et al., 2018 (link)). Briefly, 0.23 g NaOH and 1.0 g of polyvinylpyrrolidone (PVP) were dissolved in 120 ml ddH₂O. After stirring for 10 min, 1.4 g of CPB (Sigma-Aldrich, St. Louis, United States) was dissolved in the solution and stirred continuously for one hour. Next, tetraethyl orthosilicate (TEOS), calcium nitrate tetrahydrate, and TEP (the molar ratio of Ca: P: Si = 15: 5: 80) were subsequently added and stirred for 24 h. The solution was collected and washed with ddH₂O three times and then sealed in Teflon-lined autoclaves at 80°C for 48 h. Finally, the dispersion was dried at 80°C for 12 h and calcined at 550°C for five hours to obtain mesoporous BG NPs.
The structure and morphology of the BG NP sample were characterized by high-resolution transmission electron microscopy (TEM, JEM-2100, JEOL), and the size distribution was calculated by using ImageJ analysis software (Media Cybernetics Inc., United States). The Brunauer–Emmett–Teller (BET) specific surface area and pore size distribution of MBG were determined using a micromeritics porosimeter (ASAP 2460, Micrometrics Instrument).

The X-ray diffraction (XRD) patterns were recorded on X’Pert–PRO, Panalytical, Almelo, The Netherlands, 2012 using Cu Kα radiation.
The N₂ sorption isotherms were measured at −196 °C using an ASAP Sorption Surface Area and Pore Size Analyzer (ASAP 2460, Micrometrics, Norcross, GA, USA 2018).
Scanning electron microscopy was performed with an SU8020 Ultra-High Resolution Field Emission Scanning Electron Microscope (Hitachi Ltd., Ibaraki, Japan, 2012). The elemental analysis was conducted using Energy-Dispersive X-ray spectrometers (EDX) with the same instrument. The samples for SEM were sputter-coated with 40 nm of chromium in order to reduce charging.
FT-IR spectra of the catalyst were obtained using a Thermo Finnigan Nicolet 380 FT-IR instrument with an ATR Smart iTX attachment (Thermo Fisher Scientific Inc., Waltham, MA, USA) in the wavenumber range from 490 to 4000 cm⁻¹.
Diffuse reflectance UV-Vis spectra of the catalyst in the wavelength range from 190 to 900 nm were obtained using a Jasco 650 (V-650, Jasco, Tokyo, Japan) spectrometer with a PIV-756 horizontal integrating sphere.