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

Abstract

This work presents a solution for the photocatalytic degradation of the antibiotic ciprofloxacin (CIP) in water, without using P25 TiO 2 powder and thus getting rid of expensive separation steps. It consists in using a TiO 2 coating that is directly deposited on the optical window of a photocatalytic micro-reactor and 365 nm UV LEDs as radiation source. P25 TiO 2 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 TiO 2 , 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 TiO 2 coating. Different preferential reaction pathways were identified for both TiO 2 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 TiO 2 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 HCO 3 − .

The Use of Composite TiO2/Activated Carbon Fibers as a Photocatalyst in a Sequential Adsorption/Photocatalysis Process for the Elimination of Ciprofloxacin

“…Moreover, by using ACF10-TiO2, 3 h of irradiation are sufficient to fully eliminate the CIP, whereas, as discussed previously, 6 h of irradiation was not sufficient in the absence of TiO2. This result shows that the kinetics of the photocatalytic reactions is much faster than that of photolysis, as already reported by Triquet et al for CIP [37]. Furthermore, since the concentration in the liquid is lower, faster kinetics is expected as reported for UV adsorption/photocatalysis coupling for the removal of bisphenol A and 2-chlorophenol [71].…”

“…Mineralization and Efficiency. For CIP, as shown by Triquet et al [37], further refractory ultimate transformation products could be present such as aliphatic acids (HCOOand C2O4 2-)and even the fluoride ion F -. These transformation products were searched for in the solution, but only fluorine Fwas detected and quantified.…”

“…Kinetics of CIP Elimination. As CIP can be degraded by photolysis, it is necessary to study the coupling of adsorption and photolysis (degradation under UV irradiation) before using the material with TiO2 coating to investigate the adsorption/photocatalysis coupling process [37]. For this study, the same volume of CIP solution (20 mg.L -1 ) has been used during the following steps of the process:…”

“…Aromatic Transformation Products. Every aromatic transformation product (A, B, C…) obtained during the photolysis of CIP was identified and their evolution investigated (each letter corresponds to one aromatic transformation product or isomer product -Table 6) [37]. Many ATPs were detected.…”

“…These hybrid processes can be implemented either sequentially or simultaneously. Supported TiO2 has already been studied and showed excellent results [37]. However, ACF/photocatalyst composite materials are little studied in the field of wastewater treatment [38].…”