fig2

Figure 2. (A) XRD patterns of the PBF, PBF@N, and PBF@N@S and (B) Raman spectra of PBF, PBF@N, and PBF@N@S. PBF@N: N-doped porous biochar fibers; PBF@N@S: N, S dual-doped porous biochar fibers; XRD: X-ray diffraction.