English
Русский Photocatalysts based on Zn-Ti layered double hydroxide and its calcination products for self-cleaning concretes: Structure formation and photocatalytic activity
Abstract
Currently, the development of highly active photocatalytic additives for self-cleaning cement materials is a topical direction of building materials science. Mixed transition metal oxides are one of the effective types of photocatalysts, because they have improved functional characteristics compared to monometallic compounds. The purpose of this study was to establish the effects of synthesis conditions on the structure parameters and photocatalytic activity of zinc-titanium layered double hydroxide (Zn-Ti LDH) with Zn2+/Ti4+ molar ratio of 2/1, as well as its calcination products in the form of zinc-titanium mixed metal oxides (Zn-Ti MMOs). It was found that the mixing temperature of solutions of precursor salts and precipitators, as well as the temperature of sediment aging, were the main synthesis parameters that had the greatest impact on the phase composition and crystallite size of layered double hydroxide.
The research results showed differences in the kinetics of photodestruction of methylene blue (MB) in solution under UV radiation in the presence of Zn-Ti layered double hydroxide and Zn-Ti mixed metal oxides. The photocatalytic process involving Zn-Ti MMOs, corresponding to a pseudo-first order reaction kinetic, proceeded in a diffusion mode with limiting step in the form of dye adsorption on the surface of photocatalyst. The photodegradation of MB in the presence of Zn-Ti LDH, which was more accurately described by a pseudo-second order model, occurred in a kinetic regime, where the photocatalytic reaction was the limiting stage.
Mixed metal oxides of zinc and titanium had significantly higher functional characteristics compared to their Zn-Ti LDH precursor. The calcination of Zn-Ti layered double hydroxide at 200–500 °C allowed to achieve the highest photocatalytic activity of Zn-Ti MMO, which was due to phase transformations occurring during thermal treatment. The decomposition of Zn-Ti LDH at 200–250 °C resulted in the formation of a crystalline phase of zinc oxide (ZnO), which had a hexagonal wurtzite crystal structure with the ability to effectively absorb radiation from almost the entire UV spectral region. The rise of the Zn-Ti LDH calcination temperature to 500 °C led to an increase in the crystallinity degree of ZnO.
The research results showed differences in the kinetics of photodestruction of methylene blue (MB) in solution under UV radiation in the presence of Zn-Ti layered double hydroxide and Zn-Ti mixed metal oxides. The photocatalytic process involving Zn-Ti MMOs, corresponding to a pseudo-first order reaction kinetic, proceeded in a diffusion mode with limiting step in the form of dye adsorption on the surface of photocatalyst. The photodegradation of MB in the presence of Zn-Ti LDH, which was more accurately described by a pseudo-second order model, occurred in a kinetic regime, where the photocatalytic reaction was the limiting stage.
Mixed metal oxides of zinc and titanium had significantly higher functional characteristics compared to their Zn-Ti LDH precursor. The calcination of Zn-Ti layered double hydroxide at 200–500 °C allowed to achieve the highest photocatalytic activity of Zn-Ti MMO, which was due to phase transformations occurring during thermal treatment. The decomposition of Zn-Ti LDH at 200–250 °C resulted in the formation of a crystalline phase of zinc oxide (ZnO), which had a hexagonal wurtzite crystal structure with the ability to effectively absorb radiation from almost the entire UV spectral region. The rise of the Zn-Ti LDH calcination temperature to 500 °C led to an increase in the crystallinity degree of ZnO.