Wastewater is a tremendous and concerning Global problem. The exponential growth of population, farming and industrial waste has increased the matter. Therefore, it is important to find new alternatives to minimize the environmental impact of wastewater and simultaneously obtain benefits from it.

The Chemical Reactor and Engineering Centre (CREC) at Western University Canada, is currently using photocatalysis as a new and environmentally friendly alternative technology for wastewater treatment. This research group has vast experience in the field. It has extensively published on the topic including: numerous peer-reviewed scientific articles; a book entitled “Photocatalytic Reactor Engineering” (de Lasa et al., 2005); and, several book chapters contributions. Additionally, it has developed state-of-the-art photocatalysts to evaluate reaction rates and quantum yields through a novel Photo-CREC Water II reactor unit.

The approach of this team is to consider food wastewater sources with high content of organic matter that will eventually ferment and become a sacrificial agent, helping to initiate the photocatalytic process. Some studies commonly use methanol or other alcohols, amines and organic or inorganic acids as scavengers. In understanding hydrogen production, kinetics and chemical reaction mechanisms in a photocatalytic process, CREC’s lab uses ethanol as a model compound (Escobedo Salas et al., 2013). It is believed that it can be easily generated from renewable biomass sources or obtained from food wastewater treatment plants in secondary settling tanks. Ethanol is one of the most investigated agents due to its nature, making it available and inexpensive.

Our goal is to find added value to wastewater treatment plants by using photocatalytic technologies for hydrogen generation. As reader you may be wondering:

Why Hydrogen?

We believe that hydrogen is a key energy carrier and an environmentally friendly energy vector that perhaps will play an important future role in the home, industrial and transportation sectors.

How does this Photocatalytic Process Work?

First, photons in the near-UV or Visible light are absorbed in a photocatalytic material (TiO₂) surpassing the energy band gap and generating excited electron-hole pairs. Second, photoexcited electron-holes pairs can be separated due to the sacrificial agent presence, allowing oxidation/reduction process. Finally, hydroxyl groups from dissociated water lead OH^• radical formation and contribute to the conversion of the scavenger (Escobedo et al., 2016).

What is a Photocatalytic Material?

These are materials capable of absorbing light either in the near-UV or Visible region or both, producing electron-holes pairs. The most well-known and used photocatalyst is titanium dioxide (TiO₂) due to its stability, resistance to corrosion, no pollutant, naturally available and inexpensive. However, to achieve hydrogen production TiO₂ is doped with noble metals such as Pt and Pd. This helps increasing the efficiency of the reaction, narrowing the band gap of the material and improving the semiconductor optoelectronic properties (Rusinque et al., 2019).

What is a Quantum Yield (QY)?

This is a parameter of extreme importance in photocatalytic reactor and photocatalyst materials. We can establish process efficiencies relating the photogenerated radicals over the absorbed photons (Escobedo et al., 2019).

Therefore, CREC’s group at the University of Western Ontario is ready to step up to the challenge and helps with ideas to reduce water pollution concerns. We will also continue contributing to the task with innovative technology and materials, assisting the environment for both wastewater treatment degradation and energy conversion for green energy (e.g., green hydrogen production), with minimum or zero carbon footprint impact.

References

de Lasa, H., Serrano, B., & Salaices, M. (2005). Photocatalytic Reaction Engineering (1st ed.). Springer US. https://doi.org/10.1007/0-387-27591-6

Escobedo, S., Rusinque, B., & de Lasa, H. (2019). Photochemical Thermodynamic Efficiency Factors (PTEFs) for Hydrogen Production Using Different TiO2 Photocatalysts. Industrial and Engineering Chemistry Research, 58(49), 22225–22235. https://doi.org/10.1021/acs.iecr.9b05086

Escobedo, S., Serrano, B., Calzada, A., Moreira, J., & de Lasa, H. (2016). Hydrogen production using a platinum modified TiO2 photocatalyst and an organic scavenger. Kinetic modeling. Fuel, 181, 438–449. https://doi.org/10.1016/j.fuel.2016.04.081

Escobedo Salas, S., Serrano Rosales, B., & De Lasa, H. (2013). Quantum yield with platinum modified TiO2photocatalyst for hydrogen production. Applied Catalysis B: Environmental, 140–141, 523–536. https://doi.org/10.1016/j.apcatb.2013.04.016

Rusinque, B., Escobedo, S., & de Lasa, H. (2019). Photocatalytic Hydrogen Production Under Near-UV Using Pd-Doped Mesoporous TiO2 and Ethanol as Organic Scavenger. Catalysts. https://doi.org/10.3390/catal9010033