Synthesis of surface-modified monoclinic ZrO2 nanoparticles using supercritical water

Abstract

We succeeded in simple and rapid synthesis of surface-modified monoclinic ZrO 2 nanoparticles using a supercritical hydrothermal method. The precursor Zr(OH) 4 was treated in the presence of various surface modifiers with carboxyl group (-COOH) in a batch-type reactor at 400 C for 10 min. Oleic, sebacic, dodecanedioic, and 12-aminododecanoic acids were used as surface modifiers. Addition of surface modifiers resulted in smaller particle (crystallite) sizes than the unmodified nanoparticles, suggesting that there is an interaction between the surface modifiers and the nanoparticles. The reduced particle size in the presence of surface modifiers was attributed to the inhibition of the growth of the crystalline surface due to the surface modification. The FT-IR spectra revealed that the surface modifiers were attached to the surface of the nanoparticles through coordination bonds between the carboxylate group (-COO À ) and the Zr ion. The FT-IR spectra also confirmed the presence of functional groups, such as methyl (-CH 3 ), carboxyl (-COOH), and amine (-NH 2 ), at the surface. The surface modification was also verified by the thermogravimetric analysis. The number of the surface modifiers attached to the surface of the products was about 2 molecules per nm 2 . The nanoparticles with carboxyl and amine surface functional groups were water dispersible; the isoelectric point shifted to low pH ranges because of the nature of the groups.

Influence of the crystal structure on the physical properties of monoclinic ZrO2 nanocrystals

“…The AN800 product had spherical particles, and this morphology appeared to have been retained from that of the AG product. The morphologies of the products were similar to those of the monoclinic ZrO 2 nanocrystals found in our previous studies [21,22]. However, the annealing process clearly changed the particle sizes, which were approximately 1.5 times higher after the annealing treatment.…”

“…Similarly increased lattice sizes were also observed in our previous studies of metal oxide nanocrystals [18][19][20][21][22]. Comprehensive experimental studies of metal oxide nanocrystals have also shown that the lattice constant tends to increase as the particle size decreases [26][27][28].…”

“…The methods enable us to prepare not only simple metal oxide nanocrystals but also surface-modified metal oxide nanocrystals. Previously, we succeeded in synthesizing nanosize ZrO 2 materials using the hydrothermal methods [21][22][23], and perfectly controlled the crystalline phase of the monoclinic structure to give 20 nm crystallites [23]. We can therefore investigate the physical properties of these ZrO 2 nanocrystals.…”

“…Recently, we developed hydrothermal methods for the one-pot rapid synthesis of metal oxides and their nanocrystals using sub or supercritical water [18][19][20][21][22][23]. The methods enable us to prepare not only simple metal oxide nanocrystals but also surface-modified metal oxide nanocrystals.…”

Fast and Tunable Synthesis of ZrO2 Nanocrystals: Mechanistic Insights into Precursor Dependence

“…16,42 Water is believed to increase the solubility of the formed ZrO2 precipitates during synthesis which facilitates the effective operation of dissolution and precipitation leading to the more stable m-ZrO2. 16,[43][44][45] To assess the role of water in in our synthesis method, distilled water was added to the propoxide precursor. From the resulting XRD and TEM analysis it is clear that the presence of water does not lead to a change in crystal phase of ZrO2 (Table 3, Figure 4 and SAED Figure 5B).…”