Materials and Processes for Photocatalytic and (Photo)Electrocatalytic Removal of Bio-Refractory Pollutants and Emerging Contaminants from Waters

This volume is focused on materials and processes for the electro- and photoelectrochemical removal of biorefractory pollutants and emerging contaminants from waters to show the importance of electrochemistry and photoelectrochemistry in offering solutions to current environmental problems. In addition, we highlight their interdisciplinarity and emphasize the fundamental and applied aspects of these methods.

The research for innovative methods for removing pollutants from water has grown along with the detection of new contaminants in water bodies, the so-called emerging pollutants (EP), that can affect both flora and fauna and human health [1]: they include products used daily in households, industry, pharmaceuticals and personal care products, gasoline additives, plasticizers and microplastics [2]. Two main issues of EP are their dynamic character, which is also connected to the improvement of detection techniques, and the difficulty of removal by conventional wastewater treatment technologies. Moreover, emerging pollutants constitute a threat—even at a trace level—because their real impact on human health is unknown.

Although there are no discharge limits for most EP up to now, the European Commission has drawn up and implemented a watch list containing several chemical contaminants that must be monitored with the aim to generate high-quality data on their concentrations in the aquatic environment and to support the risk assessments that underpin the identification of priority substances [3].

During recent years, electro- and photoelectrochemical processes have demonstrated their capacity to efficiently oxidize many of these compounds. Starting from the early 1980s, research on the electrochemical methods for treated wastewater has grown significantly, and thousands of papers now appear in the literature. Although several tests demonstrate the effectiveness of pollutant removal from synthetic and real matrices, this technology is still far from full-scale applications. Its TRL (technology readiness level) is between 4 (technology validated in the lab) and 5 (technology validated in a relevant environment) [4].

More recently, photoelectrochemical processes in which electrochemical and photochemical processes are combined has attracted increasing interest, thanks to the synergy of the two processes: the application of a bias potential improves the photochemical process and the electrochemical process is more efficient since the photo-potential generated on the semiconductor allows for the depolarizing of the cell. This is why, in the last two decades, the number of articles on photochemical wastewater treatment has quickly increased, and the publication of these articles in specific journals indicates that the technology is moving from the fundamentals to real applications [5]. Nevertheless, the TRL of the photoelectrochemical treatment of wastewater is still at the lab scale, and much more efforts are required to push this technology toward applications in the field.

Thus, this special issue contributes to this context, addressing the synthesis, characterization, and application of new materials, as well as the study of catalytic processes and reaction kinetics.

I thank all of the authors for their valuable contribution to this Special Issue and the editorial team at Catalyst for their kindness and constant support.