Removal Of Antibiotics From Aqueous Environment By Magnetic Fe₃O₄ Nanoparticles

Antibiotics are widely used in human and veterinary medicine, and most of them are routinely used as sub-therapeutic dose in concentrated animal feeding operations to prevent disease and promote growth. More than 75% of antibiotics are excreted into water or soil environment via variuos pathways without any metabolization after use, which has caused serious pollution of environment and brought potential adverse effect to microorganism, aquatic orgamisms, and soil plants and animals. More importantly, the presence of antibiotics in environment may lead to the potential development of super bugs amongst microorganisms and pose risk to human health and ecological system. In the recent years, the elimination of antibiotics from environment has attactted more attention based on the techniques of biodegradation, oxidation and photodegradation. However, there was no report on elimination of antibiotics by magnetic Fe₃O₄ nanoparticles. In this study, magnetic Fe₃O₄ nanoparticles (Fe₃O₄ MNPs) were used to remove antibiotics from aquatic environment.Quinolones are strongly resistant to biodegradation and insensitive to light. It is difficult to completely remove them from environment by biodegadation and photodegradation. In this chapter, norfloxacin existing in aquatic environment was degradated in the presence of Fe₃O₄ nanoparticles and H₂O₂. The effects of solution pH, temperature, dose of catalysts and concentration of H₂O₂ on norfloxacin degradation were surveyed. The degradation behaviors of different substrates by Fe₃O₄/H₂O₂ were investigated and the reaction mechanism of norfloxacin was discussed. The results showed that the reaction was favored in acidic solution (pH=3.5). The removal efficiency of norfloxacin was enhanced with the increase of temperature, catalysts dosage and H₂O₂ concentration. The degradation efficiency of norfloxacin by Fe₃O₄/H₂O₂ was significantly higher than those of sulfathiazole, phenolic and aniline compounds. In the presence of 4.4mmol·L^-1 of H₂O₂, 0.80g·L^-1 of Fe₃O₄ and T=303K, norfloxacin was degraded completely in 5min. The F element in norfloxacin molecule existed totally as F- in solution within 5min, and the removal efficiency of total organic carbon was 57% in 1h. In the ESR spectrum of nano-Fe₃O₄/H₂O₂ system, the characteristic peaks of BMPO-·OH adduct was detected, however, the intensity of the peaks was reduced to 5% with the addition of tert-butanol, a strong·OH scavenger, and the degradation efficiency of norfloxacin was correspondingly decreased to 10% in 1h. These results indicated that·OH played an important role on norfloxacin degradation, and the reaction proceeded based on a heterogeneous Fenton-like system. Sulfonamides antibiotics are the most widely used antibitics and most frequently detected in aqueous environment. They can not be efficiently degraded by the system of Fe₃O₄ MNPs/H₂O₂. To enhance the removal efficiency of sulfathiazole, humic acid coated Fe₃O₄ magnetic nanoparticles (HA@ Fe₃O₄ MNPs) were prepared in this chapter. The effects of solution pH, temperature, dose of catalysts and concentration of H₂O₂ on sulfathiazole degradation were surveyed. The degradation of sulfathiazole was strongly temperature-dependent and favored in acidic solution. The catalytic rate was increased with HA@Fe₃O₄ MNPs dosage and H₂O₂ concentration. HA@Fe₃O₄ MNPs exhibited high activity to produce hydroxyl (·OH) radicals through catalytic decomposition of H₂O₂.When 3 g·L^-1 of HA @Fe₃O₄ MNPs and 0.39 mol·L^-1 of H₂O₂ were introduced to the aqueous solution, most sulfathiazole was degraded within 1 h, and >90 % of total organic carbon (TOC) were removed in the reaction period (6 h). The major final products were identified as environmentally friendly ions or inorganic molecules (SO₄^2-, CO₂, and N₂). The corresponding degradation rate (k) of sulfathiazole and TOC was 0.034 and 0.0048 min^-1, respectively. However, when 3 g·L^-1 of bare Fe₃O₄ were used as catalyst, only 54 % of TOC was eliminated, and SO₄^2- was not detected within 6 h. The corresponding degradation rate for sulfathiazole and TOC was 0.01 and 0.0016 min^-1, respectively. The high catalytic ability of HA@Fe₃O₄ may be caused by the electron transfer among the complexed Fe(â…¡)-HA or Fe(â…¢)-HA, leading to rapid regeneration of Fe(â…¡) species and production of·OH radicals.In this section, environmentally friendly Fe₃O₄ MNPs were used to adsorb tetracyclines from aqueous media. Fe₃O₄ MNPs exhibited ultrahigh adsorption ability to this widely used antibiotic. The adsorption behavior of CTC on Fe₃O₄ MNPs fitted the pseudo-second-order kinetics model, and the adsorption equilibrium was achieved within 10 h. At pH 6.5, the maximum Langmuir adsorption capacity of chlortetracycline, tetracycline and oxytetracycline on Fe₃O₄ was 500 mg·g^-1, 476 mg·g^-1, 526 mg·g^-1, while the adsorption capacity of sulfathiazole and norfloxacin antibiotics were less than 10 mg g^-1. Thermodynamic parameters calculated from the adsorption data at different temperature showed that the adsorption reaction was endothermic and spontaneous. Low concentration of NaCl and foreign divalent cations hardly affected the adsorption. Negative effect of coexisting humic acid (HA) on CTC adsorption was also observed when the concentration of HA was lower than 20 mg·L^-1. But high concentration of HA (>20 mg·L^-1) increased CTC adsorption on Fe₃O₄ MNPs. The matrix effect of several environmental water samples on CTC adsorption was not evident. Fe₃O₄ MNPs were regenerated by treatment with H₂O₂ or calcination at 400 oC in N₂ atmosphere after separation from water solution by an external magnet. This research provided an efficient and reusable adsorbent to remove CTC selectively from aquatic media.