TiO2 MOCVD coating for photocatalytic degradation of ciprofloxacin using 365 nm UV LEDs - kinetics and mechanisms

• Published in: Journal of environmental chemical engineering 2020-12, Vol.8 (6), p.104544, Article 104544
• Main Authors: Triquet, Thibaut, Tendero, Claire, Latapie, Laure, Manero, Marie-Hélène, Richard, Romain, Andriantsiferana, Caroline
• Format: Article
• Language: English
• Subjects: Antibiotic; Chemical and Process Engineering; Chemical engineering; Chemical Sciences; Engineering Sciences; HPLC-MS; Langmuir-Hinshelwood; MOCVD; Photocatalysis; Transformation products
• ISSN: 2213-3437; 2213-3437; 2213-2929
• DOI: 10.1016/j.jece.2020.104544

[Display omitted] •High efficiency was found by using MOCVD TiO2 coating at 365 nm.•The influence of a real water matrix on degradation efficiency was investigated.•Transformation products were identified by HPLC-MS investigation.•A potential degradation mechanisms of CIP degradation was proposed.•Kinetics degradation was performed by Langmuir-Hinshelwood model. This work presents a solution for the photocatalytic degradation of the antibiotic ciprofloxacin (CIP) in water, without using P25 TiO2 powder and thus getting rid of expensive separation steps. It consists in using a TiO2 coating that is directly deposited on the optical window of a photocatalytic micro-reactor and 365 nm UV LEDs as radiation source. P25 TiO2 powder was also studied as reference. HPLC-MS was used to determine the transformation products and the pathways reactions. CIP was slowly degraded by the photolysis reaction at 365 nm: (75 % removal after 8 h of UV irradiation). However, no significant decrease of the total organic carbon (TOC) was noticed, thus showing the presence of transformation products not degraded by the action of UV-light alone. For a low catalyst amount (i.e 0.12 g of TiO2, whatever the form, powder or coating, per liter of contaminated water,), excellent CIP degradation by photocatalysis was observed. Complete CIP degradation after 1 h of irradiation was required using P25 and 8 h using TiO2 coating. Different preferential reaction pathways were identified for both TiO2 catalysts. The Langmuir-Hinshelwood model showed a very good representation of the kinetics, unlike its simplified pseudo-first order model. Photocatalysis experiments did not show a complete mineralization (60–70 % of TOC removal), but most of the aromatic transformation products were degraded. The last transformation products were identified as small aliphatic acids. There is therefore a real interest in using MOCVD coating of TiO2 for sustainable wastewater treatment to avoid expensive catalyst separation. A study with a spiked real effluent from a wastewater treatment plant was performed and a satisfactory degradation was obtained. Slower kinetics were found due to the presence of additional organic products and scavenger compounds such as HCO3−.