Photocatalysis for disinfection and removal of ...

Chemical Engineering Journal 261 (2015) 1–2

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Editorial

Photocatalysis for disinfection and removal of contaminants of emerging concern This special issue of Chemical Engineering Journal is devoted to the advances and recent developments in photocatalysis and a special emphasis is given to the treatment of contaminants of emerging concern. A total of twelve manuscripts were accepted for publication after a rigorous peer-review process in the current special issue, which is expected to stimulate the knowledge of the research community working in the field of photocatalysis and advanced oxidation processes. Drinking polluted or contaminated water is one of the major reasons for over two million diarrheal deaths in the developing regions and 748 million people are still without access to an improved drinking water source [1]. Therefore, there is a huge interest in developing cost-effective methods, which are capable of reducing the risk of waterborne diseases in developing regions. Furthermore, contaminants of emerging concern, such as pharmaceuticals and algal toxins, are difficult to remove from water and these are a major challenge, even for developed regions. Photocatalytic technology is identified as a potential technology to effectively remove contaminants and microorganisms of emerging concern [2]. Research into the development of highly efficient photocatalysts based on semiconductors, such as ZnO and TiO2 has been explored recently, due to their extensive range of applications which tackle a number of energy and environmental issues [3,4]. Photocatalysis has also been widely used for degrading a large number of environmental pollutants including bacterial toxins. For example, the (N-F) co-doped titania showed excellent reactivity for the degradation of 6-HOMU (6-hydroxymethyl uracil; a model compound for cyanotoxins). Studies conducted in the presence of various scavengers for HO, 1O2 and O2 have shown that O2 is the major ROS (Reactive Oxidant Species) leading to the decontamination of 6-HOMU [5]. Similar investigations regarding the mechanistic aspects have significantly contributed to the understanding of the roles of ROS in TiO2 photocatalysis [3]. The papers selected in the current special issue cover a wide range of topics in photocatalysis and advanced oxidation processes. A major section of the special issue is devoted to the development of photocatalysts for applications in the area of destruction of organic contaminants. In addition, innovative materials such as TiO2-graphene composites for solar photocatalytic disinfection of water are also discussed. A photo-Fenton process using magnetically recoverable iron oxide nanoparticles as a catalyst for the degradation of diphenhydramine is also presented. Silver nanoparticles loaded on Cu-doped TiO2 are also reported as an effective material for the reduction of nitro-aromatic contaminants. Photocatalytic degradation of antibiotics in wastewater using visible light active TiO2 photocatalysts is also described in http://dx.doi.org/10.1016/j.cej.2014.11.001 1385-8947/Ó 2014 Elsevier B.V. All rights reserved.

this special issue. A brief summary of the accepted manuscripts in the current special issue is given below. The removal of the antibiotic spiramycin using N-doped TiO2 materials under visible light irradiation was reported by Vaiano et al. Reactions were carried out using a slurry type photoreactor attached to UV black light tube and blue LEDs. Reaction by-products were analysed in liquid-phase (TOC analysis), and in gasphase (by continuous analysers), measuring CO and CO2. This investigation showed that the photocatalytic process is highly effective in the complete mineralisation of spiramycin. TiO2 based heterogeneous photocatalysis of the fluoroquinolone antibiotic moxifloxacin (MOX) in hospital effluent was investigated by Doorslaer et al. While, employing a very systematic investigation, new insights have been obtained on both the adsorption– desorption equilibrium and initial photocatalytic degradation rate of moxifloxacin in water. This investigation showed that the MOX degradation is almost two times slower in a hospital effluent matrix than in demineralised water. Evaluation of the photocatalytic activity of TiO2 on the degradation and mineralisation of cyanobacterial toxins under UV-A, solar and visible light was reported by Fotiou et al. In the current investigation, photocatalysts including Degussa P25 and Kronos vlp-7000 and materials such as N-TiO2, GO-TiO2 and Ref-TiO2 have been analysed for their catalytic activity on the degradation of a cyanobacterial toxin (microcystin-LR) and off-odor causing compounds (e.g., geosmin, 2-methylisoborneol). It is shown that when solar irradiation is employed, all organic compounds are degraded when the doped materials such as N-TiO2, GO-TiO2 and Kronos vlp7000 are used as photocatalysts. Heterogeneous photocatalytic removal of U(VI) in aqueous solution in the presence of 2-propanol was studied by Salomone et al. Various effects such as the influence of counter-ion of the uranyl salt or anions present in the system and the use of quartz and glass photoreactors were investigated in detail. Kinetic and mechanistic analyses were performed to understand the reaction pathway. TiO2 graphene composites were employed for the solar photocatalytic disinfection of water (Fernandez-Ibanez et al.). TiO2reduced graphene oxide (TiO2-RGO) composites were formed via the photocatalytic reduction of exfoliated graphene oxide by UV irradiation and employing methanol as a ‘hole’ scavenger. Rapid disinfection was observed for E. coli and F. solani spores. An enhancement in the rate of inactivation of E. coli was shown with the TiO2-RGO composite as compared to the unmodified TiO2 (P25). Singlet oxygen production was also observed with visible light excitation of the TiO2-RGO composites.

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Editorial / Chemical Engineering Journal 261 (2015) 1–2

Degradation of diphenhydramine (an emerging pollutant) by photo-Fenton process using iron oxide nanoparticles is presented (Pastrana-Martínez et al.). Magnetically recoverable nanoparticles of iron oxide were synthesised by a solvothermal reaction when employing NaOH and FeCl3 as precursors. The catalytic properties of these nanoparticles were analysed for the degradation of diphenhydramine using photo-Fenton reaction. The optimum catalyst possessing a good catalytic activity and stability was obtained with magnetite nanoparticles prepared at 180 °C from a molar ratio of 4:1 between NaOH and FeCl3. These magnetic nanoparticles showed good stability and reusability properties and can be recovered from solution using a magnetic field. A sol–gel synthesis of Cu-doped TiO2 using a Cu-diglycinate complex followed by UV functionalisation using Ag nanoparticles was reported (Hernández-Gordillo et al.). Hydrazine (a sacrificial electron donor) with aqueous 4-nitrophenol solution, led to the in situ reduction of copper on TiO2. The presence of Ag nanoparticles on the Cu-doped TiO2 led to swift charge transfer process. The Ag decorated TiO2–Cu material showed the photoreduction of 4-nitrophenol into 4-aminophenol within 30 min. A detailed treatment line for a specific landfill leachate remediation is presented by Torres-Socías et al. The current investigation recommends a joint treatment line for a specific landfill leachate, consisting of an initial physical–chemical stage followed by solar photo-Fenton process and a final bio-treatment. An economic evaluation of the proposed treatment line was also reported in detail to provide information about chemicals required, electricity, and human cost associated with the solar photo-Fenton process. A new modeling method for the simulation of the degradation of organic molecules by using photocatalytic nanosuspensions was demonstrated by Eckert et al. Various parameters for the model were estimated by comparing the experimental findings using four model systems including ciprofloxacin or methylene blue combined with photocatalysts, TiO2 or ZnO. A systematic weathering test of photocatalytic facade paints containing ZnO and TiO2 were carried out by Baudys et al. Selfcleaning properties of these acrylic paint containing TiO2 and ZnO were analysed. These paints were exposed to simulated weathering tests in a QUV panel. Since the self-cleaning paint samples containing TiO2, the photocatalytic activity was enhanced, while paints containing ZnO showed an initially high photocatalyst activity and this was subsequently decreased under similar conditions due to possible ZnO photocorrosion. In the current investigation, Bianchi et al. propose the direct use of industrial pigmentary TiO2 as a potential photocatalyst for the degradation of NOx in air. Five different commercial pigmentary powders of TiO2 were selected and their photocatalytic properties on NOx degradation were tested and compared to that of P25 nano-powder. All samples show good photocatalytic activity for the degradation of NOx in gas phase with an obvious dominance of the nano-sized sample. However, it was showed that, the difference of activity between nano and micron samples tends to be insignificant when the NOx concentration was reduced and fixed from 1000 to 200 ppb, which is closer to the real pollution levels in many major cities. Determination of the photocatalytic deposition velocity is carried out by Engel et al. In the current investigation, photocatalytic deposition velocity is defined, and also method to determine the same is proposed based on ISO 22179-1, which deals with test methods for the determination of the air-purification performance of materials that contain a photocatalyst material on the surface.

In summary, the current special issue of Chemical Engineering Journal on photocatalysis covers vital aspects of both UV and visible light active photocatalysis, providing an overview of various fundamental scientific concepts and innovative applications that are highly relevant to environmental sustainability. We would like to thank all the authors (some of them were invited to contribute based on their excellent presentations at JEP 2013, the 3rd European Symposium on Photocatalysis, held at Portoroz, Slovenia, 25–27th September 2013) and reviewers of the manuscripts submitted to this special issue devoted to photocatalysis. Finally, the Editors would like to acknowledge the excellent support from the Elsevier publishers and also thank the Editorial Board of Chemical Engineering Journal for their support in successfully completing this special issue. References [1] WHO, Global Health Risks: Mortality and Burden of Disease Attributable to Selected Major Risks, World Health Organization, 2009. [2] D.A. Keane, K.G. McGuigan, P.F. Ibanez, M.I. Polo-Lopez, J.A. Byrne, P.S.M. Dunlop, K. O’Shea, D.D. Dionysiou, C. Pillai, Solar photocatalysis for water disinfection: materials and reactor design, Catal. Sci. Technol. 4 (2014) 1211– 1226. [3] S. Banerjee, S.C. Pillai, P. Falaras, Kevin E. O’Shea, J.A. Byrne, D.D. Dionysiou, New Insights into the Mechanism of Visible Light Photocatalysis, J. Phys. Chem. Lett. (2014) 2543–2554. [4] T. Matsunaga, R. Tomoda, T. Nakajima, H. Wake, Photoelectrochemical sterilization of microbial cells by semiconductor powders, FEMS Microbiol. Lett. 29 (1985) 211–214. [5] C. Zhao, M. Pelaez, D.D. Dionysiou, S.C. Pillai, J.A. Byrne, K.E. O’Shea, UV and visible light activated TiO2 photocatalysis of 6-hydroxymethyl uracil, a model compound for the potent cyanotoxin cylindrospermopsin, Catal. Today 224 (2014) 70–76.

Suresh C. Pillai Nanotechnology Research Group, Department of Environmental Science, Institute of Technology Sligo, Sligo, Ireland Centre for Precision Engineering, Materials and Manufacturing Research (PEM), Institute of Technology Sligo, Sligo, Ireland E-mail address: [email protected] Urška Lavrencˇicˇ Štangar Laboratory for Environmental Research, University of Nova Gorica, Nova Gorica, Slovenia E-mail address: [email protected] John A. Byrne Nanotechnology and Integrated Bio-Engineering Centre, School of Engineering, Faculty of Computing and Engineering, University of Ulster, Newtownabbey, Northern Ireland, United Kingdom E-mail address: [email protected] Alejandro Pérez-Larios University of Guadalajara, University Center of Los Altos, road Yahualica, Km. 7.5, Tepatitlán de Morelos, Jalisco, Mexico E-mail address: [email protected] Dionysios D. Dionysiou Environmental Engineering and Science Program, Department of Biomedical, Chemical, and Environmental Engineering, University of Cincinnati, Cincinnati, OH 45221-0012, USA E-mail address: [email protected]