Review for "Acid-free and highly efficient one-step nitration of naphthalene with NO<sub>2</sub> promoted by O<sub>2</sub>-Ac<sub>2</sub>O in Fe- and Cu-modified S<sub>2</sub>O<sub>8</sub><SUP>2</SUP><SUP>-</SUP>/ZrO<sub>2</sub> catalyst to 1,5-dinitronaphthalene under mild conditions"