Photocatalytic Degradation of Azithromycin by Nanostructured TiO2 Film: Kinetics, Degradation Products, and Toxicity

Abstract

In this paper, nanostructured TiO2 film was prepared by the by sol-gel process and dip-coating technique with titanium tetraisopropoxide as a precursor. After heat treatment at 550 °C, the deposited film was characterized by means of micro-Raman spectroscopy and atomic force microscopy (AFM). It was found that the TiO2 film consisted of only the TiO2 anatase phase and showed a granular microstructure. Photocatalytic degradation of azithromycin by using sol-gel nanostructured TiO2 film was studied to define the most effective degradation process for potential use in wastewater treatment. Different factors were evaluated during photocatalysis, such as pH (3, 7, and 10), water matrix (ultrapure water and synthetic municipal waste water effluent), influence of another pharmaceutically active compound (sulfamethoxazole, one of the most often detected pharmaceutic compounds in waste waters), and radiation sources (low pressure ultraviolet (UV) mercury lamps with a UV-A and UV-C range; a light-emitting diode (LED) lamp with a radiation peak at 365 nm). The most effective degradation process was achieved with the UV-C irradiation source in matrices at pH 10. The water matrix had little effect on the photocatalytic degradation rates of azithromycin. The presence of sulfamethoxazole in the water matrix decreased the degradation rate of azithromycin, however, only in matrices with a pH level adjusted to 10. During the experiments, five azithromycin degradation products were identified and none of them showed toxic properties, suggesting effective removal of azithromycin. LED 365 nm as the irradiation source was not as effective as the UV-C lamp. Nevertheless, considering the cost, energy efficiency, and environmental aspects of the irradiation source, the LED lamp could be a “real-life” alternative.

Titania-Coated Alumina Foam Photocatalyst for Memantine Degradation Derived by Replica Method and Sol-Gel Reaction

“…Generally, two types of photocatalytic reactors can be found in literature: slurry photoreactors (suspended photocatalyst particles) and fixed-bed photoreactors (immobilized photocatalyst particles or films on a surface of adequate planar substrates such as glass, quartz, stainless steel, polymers, or porous substrates such as pumice stone, clay, ceramics, polymeric materials, zeolites, carbon nanotubes, graphene oxide, fibers, etc.) [28][29][30][31]. In practice, immobilized catalyst photoreactors are preferred for advanced wastewater treatment as they avoid the complex separation step which is needed in the case of slurry photoreactors.…”

“…Therefore, the applicability of TiO 2 in the form of a suspension is not optimal for the applications in real systems. These disadvantages of the application of TiO 2 nanoparticles in the suspension form may be eliminated by the immobilization of TiO 2 on different substrates in the form of a stable nanostructured film [29][30][31]48], which was applied in this work. The most widely used method for producing the TiO 2 film is the sol-gel synthesis process [24,49].…”

Comparative removal of imidacloprid, bisphenol‐S, and azithromycin with ferrate and FeCl3 and assessment of the resulting toxicity

“…This is also the case for the ferrate treated AZM and BS, where the same by‐products (MW = 591, 290, 434) were formed. These correspond to the DBPs generated from AZM degradation by TiO 2 photocatalytic oxidations and to the by‐products (MW = 496, 265, 226) that resulted from the BS degradation by the heat activated persulfate and sonolytic oxidation in recent studies 48–52 …”

“…50,51 In contrast, lactone (2) and pyran-heterocyclic (3) rings in azithromycin are less active; especially, the lactone ring is less degradable than the pyran rings. [50][51][52] Comparative performance of FeCl 3 and ferrate in the treatment of three EMPs Figures 5 and 6 show the comparative removal of IMP, BS, and AZM by ferric chloride and ferrate at pH 5 ( Fig. 5) and pH 7 (Fig.…”

“…These correspond to the DBPs generated from AZM degradation by TiO 2 photocatalytic oxidations and to the by-products (MW = 496, 265, 226) that resulted from the BS degradation by the heat activated persulfate and sonolytic oxidation in recent studies. [48][49][50][51][52] Toxicity assessment of ferrate treated samples, and FeCl 3 treated samples Figure 9 presents an overview of toxicity test results. It can be observed that untreated solutions containing IMP, BS, and AZM at a concentration of 1000 μg L −1 had an inhibiting effect on the growth of luminescent bacteria (or had toxicity).…”