Adsorption of acid and basic dyes on NiO-SiO2 composites

A series of composites containing 2.5–21.0% NiO on a surface of macroporous silica is synthesized. The specific surface area of the composites measured by the thermal desorption of nitrogen decreases with an increase in the NiO content from 24 for the original silica carrier to 16 m²/g the for composite containing 21.0% NiO. The basic dye, methylene blue (MB), is only adsorbed on SiO₂ in water solutions, while acid blue anthraquinone (ABA) is only adsorbed on the NiO. The effective specific surface area Seff and effective diameters D _eff of NiO nanoparticles are calculated from the adsorption isotherms of ABA on NiO composites and on NiO synthesized without a carrier. S _eff of NiO nanoparticles decreases from 76 to 42 m²/g and D _eff increases from 8 to 14 nm with rising NiO content in the composites. The NiO nanoparticles synthesized without a carrier are characterized by the lowest S _eff (30 m²/g) and the largest D _eff (20 nm).