Figure 27.

(A) Schematic diagrams and TEM images of the hollow nanofibers with different numbers of channels produced by varying the ratio of PS to PAN in the range of 1:10 to 1:1. (B) Schematic of the “gradient” electrospinning and controlled pyrolysis method for the preparation of mesoporous hollow nanofibers: (1) electrospinning of a solution containing PVA with different molecular weights (low-, middle-, and high-molecular-weight PVA in a weight ratio of 3:2:1) and metal salt precursors; (2) pyrolyzed inner low-and middle-molecular-weight PVA, moving toward the high-molecular-weight PVA; (3) convergance of all of the pyrolyzed PVA and inorganic materials together in the tube’s wall; and (4) pyrolysis of all the PVA after sintering in air with uniform mesoporous hollow nanofibers being obtained. When sintering in Ar, hollow carbon nanofibers embedded with tiny inorganic nanoparticles are obtained. (C and D) TEM images of (C) LiV₃O₈ and (D) MnO₂ mesoporous hollow nanofibers, respectively, fabricated using this method. (A) Reprinted with permission from ref 438. Copyright 2015 Springer Nature. (B−D) Reprinted with permission from ref 439. Copyright 2015 Springer Nature.