2022 Annual Meeting

Photocatalytic Decomposition of Crystal Violet over Metal Oxide Catalysts

Crystal violet (CV) is an organic chloride salt and a triphenylmethane dye. It is commonly used as a purple dye for textiles such as cotton and silk in the textile processing industry, as a biological stain in medicine, as a pH indicator, and as an external disinfectant. Although CV is widely used, it is shown to have toxic effects on the environment and on humans. These toxic effects are suspected of causing cancer in humans and promoting tumor growth in some species of fish. CV is also known to persist in the environment for an extended period of time. Metal oxides have been used in various studies for the efficient removal and decolorization of CV. The great photocatalytic properties of metal oxide nanoparticles allow them to be appealing as a method of water and soil pollutant decomposition. The role of the photocatalyst is to facilitate the oxidation and reduction processes by trapping light energy, and it can be separated and reused. This serves as both an environmentally friendly and cost-effective method of removal of pollutants.

In this work, we have investigated the different types of metal oxides (e.g., TiO2, CuO, Cu2O, Fe2O3, ZnO, Nb2O5, and ZrO2) for CV decomposition reaction at room temperature. To understand the physical property and molecular structure of the samples, several characteristic techniques (e.g., BET and Raman) were employed. Our results provide that CV decomposition is directly influenced by the type of metal oxide and the power of ultraviolet irradiation. Additionally, other leading factors were the band gap and water splitting relationship and recombination rate of electron-holes.

The condition of a one-hour pre-stir, in darkness, was found to mitigate color loss due to surface adsorption effects and ensure the establishment of adsorption/desorption equilibrium of the dye on the oxide surface. The photocatalytic water splitting boundaries of the reaction fall between the band gap edges of TiO2 and ZnO confirming the relationship and thus, these metal oxides decompose CV by 95% and 97% respectively in 100 minutes.