Alkali-assisted hydrothermal preparation of g-C3N4/rGO nanocomposites with highly enhanced photocatalytic NOx removal activity

•g-C3N4/rGO nanocomposites were prepared via an alkali-assisted hydrothermal method.•NaOH played an important role in etching the bulk g-C3N4 into nanosheets.•The metal-free g-C3N4/rGO displayed outstanding photocatalytic performance.•A possible charge transfer and separation mechanism was proposed.