Introduction by the guest editors

This issue of Photochemical & Photobiological Sciences contains a selection of papers presented at the 8th European Meeting on Solar Chemistry & Photocatalysis: Environmental Applications – SPEA 8 – held in Thessaloniki, Greece, between 25th and 28th of June, 2014.

The meeting was co-organized by the departments of Chemistry, of the Aristotle University of Thessaloniki, and Chemical Engineering, of the University of Patras. In line with the history of previous SPEA meetings, the event intended to create an opportunity for participants from academia, research centers, small and medium enterprises, industry and governmental decision makers, working in the field of environmental photocatalysis and photochemistry, to convene and share their experiences and knowledge.

The conference attracted just over 250 participants including 5 invited speakers, who delivered stimulating plenary lectures, and nearly 100 doctoral students and young researchers at early stages of their careers. Although 80% of the participants came from Europe, SPEA 8 has broken the geographical borders and people from four other continents were also present, including Americas (11%), Asia (6%), Australia and Africa. The central themes to SPEA meetings are water and air treatment/disinfection, novel materials and technologies for solar photocatalysis, environmental photochemistry, modeling and mechanistic studies, commercial applications and standardization. All of these were present in the following topics, used to group the 340 oral and poster contributions presented at the meeting: (i) water treatment and disinfection; (ii) air treatment; (iii) green synthesis by solar photochemistry and photocatalysis; (iv) developments, perspectives and new materials in photochemistry and photocatalysis; (v) process fundamentals, modeling and applications; (vi) photocatalytic hybrid systems; (vii) experimental standardization; (viii) systems for hydrogen production and CO₂ utilization.

The present collection includes 18 articles dealing with new semiconductor photocatalysts, wastewater treatment, water disinfection and applications for energy production and organic transformations. Although not exhaustive, the selection reflects the most relevant aspects of the state of the art, and the excellent perspectives for application of the processes described. The following papers briefly summarize these contributions. The photocatalytic degradation of humic acid was studied by evaluating the effect on molecular size distribution. A photocatalytic approach to achieve increased cytotoxicity of urothelial carcinoma cells was also proposed.

In the area of TiO₂ semiconductor modification there are contributions on transparent thin films of Cu–TiO₂ and nitrogen-doped ZnO for visible light applications. Waste water treatment was approached considering different AOPs such as peroxymonosulfate/UVC and UV/H₂O₂ and different photocatalysts such as ZnOFe₂O₃ and ZnO–Fe, but also TiO₂ photoelectrocatalysis and photosentitized oxidation with singlet oxygen. These studies also included identification of intermediates, genotoxicity and ecotoxicity evaluation including evaluation of residual antimicrobial activity on antibiotics during the phototreatment. Water disinfection was considered using either visible light induced photocatalytic inactivation of bacteria such as Escherichia coli and Staphylococcus aureusor or direct solar irradiation using novel Mn and Co-doped TiO₂ for eliminating Klebsiella pneumoniae. Another paper focused on potential environmental issues that are involved in the process and influence the design and operation of solar applications, based on the local conditions.

The theme of photocatalytic transformation for energy production through reduction was addressed by Pd/TiO₂ photocatalysis towards the formation of methane, but also for organic transformations by polyoxometalates or TiO₂ nanoparticles. Reduction processes were also applied to wastewater remediation for treating hexavalent chromium.

The invited editors wish to express their appreciation to all the authors for their contributions to this special issue and thank the editorial staff of Photochemical & Photobiological Sciences for assistance. Sixto Malato wishes to thank the Spanish Ministry of Economy and Competitiveness for financial support under the AQUAFOTOX Project (Reference: CTQ2012-38754-C03-01).

---