Levofloxacin is a commonly prescribed and extremely effective antibiotic. Unfortunately, because of its robust structure, it is increasingly accumulating in nature and poisoning animals. Researchers have now developed a photoelectric method with which the difficult-to-degrade active ingredient can be effectively removed from wastewater for the first time. The technique involves an electrode made of different metal oxides that, unlike previous approaches, can be reused.
The antibiotic levofloxacin works against many different bacteria by inhibiting their replication and growth. It is therefore often prescribed, especially for bacterial infections of the skin, urinary or respiratory tract – for example inflammation of the bladder, lungs or sinuses. However, residues of the antibiotic regularly end up in rivers and lakes via human urine and wastewater. Levofloxacin cannot be broken down well either in our bodies, in sewage treatment plants or in nature. The active ingredient accumulates and increasingly pollutes the environment. The molecule is toxic to many living beings even in small doses or interferes with their hormonal balance.
Looking for a catalyst
Researchers led by Carlos Fernandes from the University of São Paulo in Brazil have therefore been looking for ways to remove levofloxacin from aqueous environments. Their approach: convert the molecule into biodegradable, non-toxic substances. To do this, they developed an electrode made of titanium with several coatings of iridium dioxide (IrO2) and niobium pentoxide (Nb2O5). Through this structure with metallic semiconductor materials, the electrode catalyzes chemical reactions by supplying electricity and light, in which free radicals are formed and various organic active ingredients are oxidized, as previous analyzes suggested. Fernandes and his colleagues suspected that this photoelectric process also works with levofloxacin.
The scientists tested what actually happens to the antibiotic when the electrode is used, both in water samples artificially contaminated with the active ingredient and in real wastewater samples, each of which they treated with the method for 90 minutes. It was shown that this electrode was able to convert the antibiotic molecules reliably, quickly and effectively in both types of water samples. This resulted in the formation of several free radicals such as hydroxyl and sulfate radicals, as subsequent chemical analyzes revealed. “These effectively attack various chemical bonds and groups of atoms within levofloxacin, thus enabling them to be converted or broken down into various non-toxic and biodegradable ions,” say the researchers.
Electrode is reusable
Thanks to the niobium pentoxide used, the electrode itself remained stable and could be reused several times, as the experiments showed. This makes the electrode different from previous approaches using other metal oxides, which only had a short lifespan. The new technology could be used in the future to remove levofloxacin from wastewater and natural waters, as Fernandes and his colleagues report.
Source: Carlos Fernandes (University of São Paulo) et al., Electrochimica Acta, doi: 10.1016/j.electacta.2023.143586