Fig. 4: Porosity analysis of MOFs via nitrogen adsorption–desorption.

BET isotherms for a Fe-MOFs (Type IV, mesoporous), b Ni-MOFs (Type II, non-porous), c Ni/Fe (3:1) MOFs (mixed Type II/IV), d Ni/Fe (1:1) MOFs, and e Ni/Fe (1:3) MOFs. Surface areas decrease with Ni incorporation, while pore sizes increase due to metal ion occupation.