Visible Light Driven Photocatalysts for Water Treatment and Purification

In the quest for alternative energy sources and eco-friendly technological processes there is a growing need for photocatalysts that are able to utilize visible light. Highly stable and practical visible light photocatalytic materials for purifying and disinfecting air and water have not been realized. Bismuth oxyhalides (common formula BiOX, X=F, Cl, Br, I) have a semiconducting electron structure that ensures excellent photocatalytic characteristics to pure oxyhalides as well as to their mixtures with other phases.

This new family of BiO(Cl_xBr_1-x) photocatalysts with x= 0.5 showed three times higher activity in removing aqueous Rhodamine B under visible light irradiation when compared to the standard Degussa P25 (TiO₂). RhB is a model for dyes that are essential water pollutants.

The research comes under is of interest to the fields of environment, cleantech, materials and water technologies. The proof of concept for the research has been achieved and formulation as thin films have been completed. A US patent application has also been filed.

Innovation

The research findings include a novel family of active photocatalysts based on bismuth oxyhalide-based semiconductor compounds that utilize visible light to improve oxidation reactions. Figures 1 and 2 show the decomposition of RhB (15 ppm) in aqueous BiOCl-BiOBr in different conditions.

Figure 1. Decomposition of RhB (15 ppm) in aqueous BiOCl-BiOBr with mild sun irradiation.

Figure 2. Decomposition of RhB (15 ppm) in aqueous BiOCl-BiOBr with 9W PL table lamp

Key Features

The key features of this technology include the following:

• Preparation of compounds uses a simple hydrothermal method under mild conditions
• It exhibits excellent photocatalytic activity under sun or artificial visible light when compared to the individual pure phases and to Degussa P25.
• The materials are robust and stable and can be formed into thin films supported on glass or on stainless steel.

Applications

The applications of the technology are listed below:

• Air purification and water purification systems
• For prevention and removal of biofouling in water systems that includes desalination plants and irrigation systems

Current Status

The researchers are looking for industrial cooperation or funding for the design and building of a laboratory scale continuous flow demonstration unit for water treatment and an air purification module.