The Brunauer–Emmett–Teller (BET) surface area and the pore structure analysis were conducted on a Micromeritics ASAP 2010 Surface Analyzer. The pore size distributions were calculated by the density functional theory (DFT) method. The absorbance of RhB was analyzed using a UV–vis spectrophotometer (UV2400). pH was measured by a pH meter (PHS-25).