Exploring superiority of silatranyl moiety as anchoring unit over its trialkoxysilyl analogue for covalent grafting via fabrication of functionalized mesoporous silica possessing azomethinic pincers for dye adsorption

In the present work an azomethinic pincer (P) possessing an ONNNO donor set was prepared via condensation reaction of diethylenetriamine and o-hydroxyacetophenone followed by silyl-functionalization (introduction of a triethoxysilylpropyl or silatranylpropyl group via urea linker) to afford P-Sil and P-Silt, respectively. The resulting products were characterized by various spectroscopic techniques, elemental analysis and single-crystal X-ray diffraction. They were further utilized for the fabrication of post-synthesis functionalized mesoporous silica nanoparticles (MSNs) using similar reaction conditions. The obtained hybrid materials (P-Sil@MSNs and P-Silt@MSNs) were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetry (TGA), nitrogen gas adsorption-desorption measurements and C,H,N microanalysis. The corresponding results revealed particularly high loading of organic moieties for the P-Silt functionalized particles. In addition, adsorption behavior of both materials towards the anionic dye eriochrome black T (EBT) was evaluated by examining the effect of pH, solution temperature, time and dye concentration. The maximum adsorption capacity of P-Silt@MSNs and P-Sil@MSNs at pH = 3 was found to be 101 mg g−1 and 69.9 mg g−1, respectively (calculated on the basis of Langmuir model). The characterization and adsorption studies revealed better loading of organic moieties in P-Silt@MSNs with respect to P-Sil@MSNs. Furthermore, P-Silt@MSNs was used to adsorb the cationic dye methylene blue (MB) at pH = 8. Its maximum adsorption capacity reached 28 mg g−1.