Synthesis of Doped Sol-Gel Glasses as Adsorbents for Water Treatment

Doped sol-gel glasses of thiourea (THU), urea (U), n-propoylamine (PA), iso-propylamine (IPA), and 2-methoxyaniline (AN) were prepared and treated by two methods, thermal and microwave (MW) irradiation. The optical properties and particle sizes of the as-synthesized doped sol-gels and plain sol-gel (P) were measured. The sol-gels were then tested for their capacity to adsorb methylene blue dye (MB) and remove it from aqueous solutions. The highest removal efficiencies were exhibited by PA, IPA, and THU which were prepared by either the thermal or MW method. Amongst all the tested adsorbents, the thermally-prepared PA yielded the highest removal of over 95% for 12.5 mg/L of MB, and about 75% for 6.5 mg/L of MB. The MW-prepared PA showed the second highest removal efficiencies, while IPA, prepared thermally or by MW, showed comparable results to its PA counterpart. This behavior could be attributed to the higher basicity of aliphatic amines relative to aromatic amines, which resulted in increased interaction between the lone pair of electrons on amino nitrogen and MB. On the other hand, the interaction between U or THU and MB is suggested to have possibly occurred via electrostatic attraction or redox reaction between them. The characteristic Fourier Infrared (FTIR) spectra of PA and IPA before and after adsorption suggest that the C=O, N-H, and Si-OH groups, among others, could be involved in adsorption