Do thermal effects cause the propulsion of bulk graphene material?

In a recent article, Zhang et al.¹ observed the direct propulsion of a bulk graphene sponge when exposed to laser light. They attributed this to the momentum of the light-induced ejected electrons. However, the force provided by the ejected electrons is about 2.7 × 10⁻¹¹ N (supposing that the average current and the kinetic energy of the ejected electrons are 9 × 10⁻⁷ A and 70 eV, respectively), which is far smaller than the gravitational force of a 0.86 mg graphene sponge. From our knowledge of rarefied gas dynamics, the horizontal, vertical and rotational motion of the laser-illuminated graphene sponge could be due to the radiometric force.