Use of isoelectric point and pH to evaluate the synthesis of a nanotubular aluminosilicate

To follow the synthesis of imogolite, transmission electron microscopy is needed. In this paper, the isoelectric point (IEP) and the aging pH are proposed as alternative methods. Two synthetic procedures were used (S-I and S-II), both involving a co-precipitation followed by an aging treatment where the aluminosilicate evolves from proto-imogolite (detected after the co-precipitation step), to imogolite; its formation is reached after 120 h (S-I) or 168 h (S-II) of aging, depending on the co-precipitation method used. In S-I the isoelectric point increases from 7.1 to 10.5, while in S-II it increases from 6.6 to 9.2 during the aging treatment. Additionally, a linear relationship between the IEP and the pH at different aging steps was found. That relationship may be used to follow the process of synthesis by simply measuring the pH, becoming an alternative to more complex methods.

Research Highlights► During aging process the structural evolution is: globular, necklace-type and nanotube. ► The isoelectric point increased and pH decreased during aging process. ► A linear relation was found between pH and IEP.