Photometric study of the kinetics of TiO2 hydrosol coagulation in electrolyte solutions

Abstract

The aggregative stability of TiO 2 sols in aqueous solutions of NaCl, KCl, BaCl 2 , and LaCl 3 is stud ied by photometry at pH 3.2 and natural values of pH (5.0-5.6). Dramatic effects of coion type and charge on the aggregation kinetics and characteristics of resulting aggregates are revealed.

Photocatalytic performance and dispersion stability of nanodispersed TiO2 hydrosol in electrolyte solutions with different cations

“…In the presence of Al(NO 3 ) 3 , the particle size of nano TiO 2 was comparable with the initial Nano TiO 2 size at 0.005 mol/L, and the particle size increased and stayed around 0.5 and 3.0 μm at 0.1 and 0.5 mol/L, respectively. These results were consistent with the results in literature (Volkova et al, 2012) that the optical density of TiO 2 sols remains unchanged at low concentration (≤10 −2 mol/L) of coagulants (haloids) and increase begins from the coagulants concentration of 0.03 mol/L. The ion-electrostatic repulsive forces between TiO 2 particles contributed to the stability of sols in the low concentrations.…”

“…The cations like Fe 3+ (Wang et al, 2008) would improve the efficiency of photocatalytic oxidation of TiO 2 hydrosols in solutions by influencing the complex hydroxyl groups bond between TiO 2 surface and Fe 3+ . Volkova et al (2012Volkova et al ( , 2010 had studied the coagulation properties and fractionation of TiO 2 hydrosol in haloid salts solutions, and the results supported that the sol stability was strongly affected by the coion (refers to cation) nature and valence.…”

“…Due to TiO 2 hydrosol consisting of anatase nanoparticles are stable to disperse at high concentration and certain electrolytes and certain pH range, the stability of TiO 2 hydrosols caused by electrolytes has been studied both experimentally and theoretically (Pavlova-Verevkina et al, 2007, 2003Volkova et al, 2012Volkova et al, , 2010. In most of studies, the optical density increment is chosen as the evaluation index for the stability of TiO 2 .…”

“…According to the literature data (Holmberg et al, 2013;Leroy et al, 2011), the isoelectric point of TiO 2 nano particles without extra electrolytes are in a pH range of 5.6-6.0. When at a pH near 5.6-6.0, the TiO 2 sols undergo coagulation that results in a relatively low ionelectrostatic repulsion barrier, which cannot terminate particles agglomeration (Volkova et al, 2012). According to Volkova et al (2012Volkova et al ( , 2010, mental ions (Na + , K + , Ba 2+ and La 3+ ) caused the point of zero charge (PZC) shift to the acidic region, and the single charge anions (Cl − , Br − and I − ) did not affect the surface charge of anatase TiO 2 and the position in solutions of 1:1 background electrolytes.…”

“…In addition, few studies focus on the photochemical reactivity of nanodispersed TiO 2 hydrosols in aqueous solutions contaminated by cations with different valence. According to literature (Volkova et al, 2012(Volkova et al, , 2010Zhang et al, 2018), the effect of certain cations on the coagulation of TiO 2 hydrosol particles is very pronounced, and the effect is closely related to the valance of cations and the pH of the aquatic systems.…”