Researchers at the University of Birmingham (www.birmingham.ac.uk) have demonstrated a new production method for ultra-thin catalysts, unlocking new capabilities for the catalytic breakdown of persistent water pollutants. “The production method takes layered materials as the precursor, disperses them in a sustainable solvent (water and ethanol), and applies high strain rates to the liquid and solid phases in the dispersion. This mechanical strain overcomes the van der Waals attraction that binds the material together, separating the layers into micro- and nano-scale sheets that can have few atomic- or molecular-scale thicknesses,” explains Jason Stafford, associate professor of mechanical engineering at the University of Birmingham. In addition to creating uniquely thin materials with high quantum efficiency, the new process also readily supports combination of dissimilar materials, enabling the research team to experiment with “unique artificial materials, such as graphitic carbon nitride and molybdenum disulfide, two promising organic and inorganic layered semi-conductors that can support photocatalytic activity in ultraviolet (UV) and visible-light regions of the spectrum,” notes Stafford. Driven by mechanical force rather than thermal energy, the process has a smaller environmental footprint than some other catalyst manufacturing methods, and the solvent and precursors can be recovered and re-used in the process.
The focus on photocatalysis naturally led to a globally relevant application for the new material-design capabilities — the degradation of harmful pollutants in water, which often employ photocatalysts to carry out advanced oxidation processes (AOPs). “By enabling photocatalysis in both the UV and visible-light regions, these catalyst materials can utilize a higher proportion of incident sunlight than traditional photocatalysts, such as titanium dioxide, and avoid some of the drawbacks of other AOPs. This can open the door to passive, solar-powered wastewater processing that would typically require high-intensity lamps. Additionally, two-dimensional nanostructured nanomaterials provide larger surface areas per gram of material, facilitate increased reaction rates and more efficient light utilization,” says Irwing Ramirez, a research fellow at the University of Birmingham.
In the laboratory, the team has fabricated the new photocatalytic materials at the liter scale, which translates into about 100 g of catalyst. “Although this seems like a small amount in general, it can go a long way for wastewater applications, treating hundreds, if not thousands, of liters of water. This work also demonstrates that the synthesized nanomaterial can be supported on a substrate like glass, which avoids costly downstream catalyst separation, and enables treatment of significant volumes of wastewater, particularly relevant for scaling up to continuous-flow water-treatment systems,” adds Jacob Brown, a post-graduate researcher on Stafford’s team.
To demonstrate the catalyst itself in water-treatment settings, the team has scaled up from a small semi-batch process to a 5-L pilot-scale system that can use either UV light or solar illumination in an outdoor environment.