The influence of chemical and thermal treatment on the point of zero charge of hydrous zirconium oxide

Abstract

Two zirconia samples were prepared by precipitation from aqueous zirconium oxychloride and zirconil sulphate solutions with potassium hydroxide. The prepared zirconia samples were amorphous. The pHpzc values of zirconia samples, determined from NaCl and NaNO3 solutions, were 6.6 ± 0.1 and 6.9 ± 0.1, respectively. After prolonged hydration of zirconia in doubly distilled water, pHpzc decreased to 4.7 ± 0.3. Crystallization into tetragonal (metastable) + monoclinic zirconia appeared at 691 K. Above 873 K, tetragonal metastable phase changes to monoclinic one. It was shown that crystallite sizes of zirconia treated at 673 - 1273 K increased from 9.5 nm to 40.5 nm, respectively. The increase in temperature from 385 K to 1070 K increased the pHpzc of zirconia samples from 6.6 to 9.0, respectively. [Projekat Ministarstva nauke Republike Srbije, br. 45012

Experimental Design Modeling of the Effect of Hexagonal Wurtzite—ZnO Synthesis Conditions on Its Characteristics and Performance as a Cationic and Anionic Adsorbent

“…The D h of the synthesized ZnO is controlled by both nucleation and crystal growth [51,52]. According to Equations (2) and (3), Zn(OH) 2 and [Zn(OH) 4 ] 2− coexist in equilibrium.…”

“…Accordingly, relatively small particles are obtained. Conversely, when the growth unit [Zn(OH) 4 ] 2− exists in a large amount and Zn(OH) 2 nuclei exists in a small amount, the nucleation rate will be slower than the crystal growth rate, and thus, relatively large particles are obtained [52].…”

Adsorption of phosphate from water on lake sediments amended with zirconium-modified zeolites in batch mode

“…The pH PZC of aluminum oxides was reported to be above 8.0 (Lǔ et al, 2013). The pH PZC of hydrous zirconium oxides was reported be about 6.6 (Stankovic et al, 2013). When the water pH below the pH PZC of the metal oxides, the surface of the metal oxides is protonated and positively charged.…”

“…In the adsorption process, phosphate ions can replace the hydroxyl groups on the surface of zirconium oxides, and can form inner-sphere complexes (Su et al, 2013). The pH PZC (pH at the point of zero charge) of hydrous zirconium oxides, determined in NaCl solution, was found to be about 6.6 (Stankovic et al, 2013). When the pH of water below the pH PZC (6.6), the surface hydroxyl of zirconium oxides is protonated, making the surface charge of zirconium oxides in this pH region positive (Liu et al, 2008).…”

β-Cyclodextrin modified hydrous zirconium oxide: Synthesis, characterization and defluoridation performance from aqueous solution

“…Mixed oxides can behave in either fashion, depending on the relative pK a values of the different surface sites [39]. Fig S3 shows the pH change (∆pH) with respect to pH i which showed the pH pzc value of HZO at ~6.5, which remained in the range 6.4-6.7 [40,41]. In contrast, the pH pzc value of CY-HZO was analyzed to be 5.5, which has shifted to the lower side of pristine HZO which is probably due to the presence of copious C-OH groups in β-CD of the composite.…”