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), o-anisidine (AN) and o-aminophenol (AP) were prepared and treated by two methods, thermal and microwave (MW) irradiation. The optical properties and particle size of the as-synthesized doped sol-gels and plain sol-gel (P) were measured, and their characteristic Fourier Infrared Radiation (FTIR) spectra were analyzed. 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 that 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 6.5 mg/L of MB, and about 75% for 12.5 mg/L of MB. The MW-prepared PA showed the second highest removal efficiencies. 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.