The weight ratio of the carbon deposition in the carbon/alumina composite was determined via thermogravimetry to calculate the average number of graphene layers as previously reported. The obtained carbon/alumina composite was immersed in an aqueous solution of HF (46~47 wt%, 100~200 g, Wako Pure Chemical Industries) at room temperature for 5 h with agitation using a shaker (Reciprocal Shaker NA-201N, Nissin) to remove the template. Then, the aqueous solution was filtered using a hydrophilic PTFE membrane filter (Advantec H100A047A or H050A047A, Toyo Roshi Kaisha, Ltd., ø = 0.50 or 1.00 μm), and the residue was washed with an aqueous solution of HF (46-47 wt%, 200 g, Wako Pure Chemical Industries) and water several times.