  We present a theoretical study of spin-velocity injection (SVI) of a pure
spin current (PSC) induced by a linearly polarized light that impinges normally
on the surface of two 50\% hydrogenated noncentrosymmetric two-dimensional (2D)
graphene structures. The first structure, hydrogenated at only one side,
labeled Up, also known as graphone, and the second, labelled Alt, is 25\%
hydrogenated at both sides. The hydrogenation opens an energy gap in both
structures. We analyze two possibilities: in the first, the spin is fixed along
a chosen direction, and the resulting SVI is calculated; in the second, we
choose the SVI direction along the surface plane, and calculate the resulting
spin orientation. This is done by changing the energy $\hbar\omega$ and
polarization angle $\alpha$ of the incoming light. The results are calculated
within a full electronic band structure scheme using the Density Functional
Theory (DFT) in the Local Density Approximation (LDA). The maxima of the
spin-velocities are reached when $\hbar\omega=0.084$\,eV and $\alpha=35^\circ$
for the Up structure, and $\hbar\omega=0.720$\,eV and $\alpha=150^\circ$ for
the Alt geometry. We find a speed of 668\,Km/s and 645\,Km/s for the Up and the
Alt structures, respectively, when the spin points perpendicularly to the
surface. Also, the response is maximized by fixing the spin-velocity direction
along a high symmetry axis, obtaining a speed of 688Km/s with the spin pointing
at $13^\circ$ from the surface normal, for the Up, and 906 Km/s and the spin
pointing at $60^\circ$ from the surface normal, for the Alt system. These speed
values are of order of magnitude larger than those of bulk semiconductors, such
as CdSe and GaAs, thus making the hydrogenated graphene structures excellent
candidates for spintronics applications.
