  Based on first-principles and tight-binding calculations, we report that the
transport properties of topological edge states of zigzag Bi(111) nanoribbon
can be significantly tuned by H edge adsorption. The Fermi velocity is
increased by one order of magnitude, as the Dirac point is moved from Brillouin
zone boundary to Brillouin zone center and the real-space distribution of Dirac
states are made twice more delocalized. These intriguing changes are explained
by an orbital filtering effect of edge H atoms, which removes certain
components of $p$ orbits of edge Bi atoms that reshapes the topological edge
states. In addition, the spin texture of the Dirac states is also modified,
which is described by introducing an effective Hamiltonian. Our findings not
only are of fundamental interest but also have practical implications in
potential applications of topological insulators.
