Physicochemical aspects of epoxide driven nano-ZrO2 hydrogel formation: milder kinetics for better properties

Abstract

Robust and highly transparent quasi amorphous ZrO₂-water-glycerol hydrogels were obtained in a mild one pot procedure, based on the 2,3-epoxy-1-propanol driven alkalinization. SAXS-based characterization of the sol–gel transition revealed that an homogeneously nucleated sol composed of 2 nm primary particles continuously grows up to a critical size of 5–6 nm, when gelation takes place. These particles reach a size of 8–10 nm, depending on the Zr(IV) concentration. Conductivity measurements offer an overall in situ assessment of the reaction rate. The gelled samples share a common trend: once the conductivity decays to 40% of the starting value, the primary particles nucleate and when this decay reaches 20%, the sol–gel transition takes place. The mild conditions employed herein prevent massive ripening and recrystallization leaving hydrogels with extremely low undesired visible light scattering. This suitable nanostructure was achieved in a wide range of total Zr(IV) concentrations or water to glycerol ratios.