Fig. 6

3D response surface plots for Ni (II) removal using rGO with the interaction effects of (a) Ni (II) concentration (Conc.) x pH, (b) Dose x pH, and (c) Dose x Initial Ni (II) concentration (Conc.).
3D response surface plots for Ni (II) removal using rGO with the interaction effects of (a) Ni (II) concentration (Conc.) x pH, (b) Dose x pH, and (c) Dose x Initial Ni (II) concentration (Conc.).