Demonstration of Visible Light-Activated Photocatalytic Self-Cleaning by Thin Films of Perovskite Tantalum and Niobium Oxynitrides

Abstract

Metal oxynitrides adopting the perovskite structure have been shown to be visible light-activated photocatalysts, and therefore, they have potential as self-cleaning materials where surface organic pollutants can be removed by photomineralization. In this work, we establish a route for the deposition of thin films for seven perovskite oxynitrides, CaTaO 2 N, SrTaO 2 N, BaTaO 2 N, LaTaON 2 , EuTaO 2 N, SrNbO 2 N, and LaNbON 2 , on quartz and alumina substrates using dip-coating of a polymer gel to form an amorphous oxide precursor film, followed by ammonolysis. The initially deposited oxide films were annealed at 800 °C, followed by ammonolysis at temperatures from 850 to 1000 °C. The perovskite oxynitride thin films were characterized using XRD and EDX, with band gaps determined using Tauc plots derived from UV−vis spectroscopic data. A cobalt oxide co-catalyst was deposited onto each film by drop casting, and the photocatalytic activity assessed under visible light using dichloroindophenol dye degradation in the presence of a sacrificial oxidant. The light source used was a solar simulator equipped with a 400 nm cut-off filter. The dye degradation test demonstrated photocatalytic activity in all samples except EuTaO 2 N and BaTaO 2 N. The three most active samples were SrNbO 2 N, CaTaO 2 N, and SrTaO 2 N. The cobalt oxide loading was optimized for these three films and found to be 0.3 μg cm −2 . Further, catalytic tests were conducted using stearic acid degradation, and this found the film of SrNbO 2 N with the cobalt oxide co-catalyst to be the most active for complete mineralization of this model pollutant.

3D printed SrNbO2N photocatalyst for degradation of organic pollutants in water

“…1 These photocatalytic properties (including a visible light absorption band) make perovskite oxynitrides (for example Sr, Nb and Ti based) promising materials for water splitting 2 and the degradation of organic pollutants and biological contaminants in water 3–5 including degradation of organic compounds such as acetone (LaTi(O,N) 3 ), 6 methyl orange (CaTaO 2 N; 7 CaNbO 2 N and SrNbO 2 N) 8 and methylene blue, 9 among others. 10…”

Visible-Light-Driven Photocatalysts for Self-Cleaning Transparent Surfaces

“…There has been a significant amount of work dedicated to enabling visible-light photocatalysis in self-cleaning films by doping of wide bandgap materials, − integration of plasmonically active nanoparticles, , or use of moderate bandgap materials or heterojunctions. − For example, Dunnill et al synthesized TiO 2 films with varying quantities of nitrogen as a dopant and evaluated the optimal photocatalytic activity and transparency for self-cleaning of organic contaminants and pathogens . Peeters et al.…”

A visible-light activated ROS generator multilayer film for antibacterial coatings

“…6,7 Self-cleaning surfaces that can be catalytically triggered by using external stimuli like light to generate bactericidal agents present themselves as a smart medium in the pursuit of light-regulated antibacterial activity. [8][9][10][11] Photoactive antimicrobial coatings are controllable, minimally invasive, effective and function using light as a stimulus. [12][13][14] Hence, photodynamic coatings hold great promise as antibacterial coatings and are superior to the conventional sterilization procedures for medical devices and storage containers.…”