An Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) Spectroscopic Study on the Oxytetracycline Sorption Mechanism on Variable Charge Minerals
Veterinary antibiotics have been used widely to treat diseases to maintain a healthy livestock and poultry production. Tetracycline (TC) is one of the most commonly used veterinary antibiotics in the United States. Understanding the fate of antibiotics in the environment is very important because it is directly linked to antibiotic resistance in microorganisms in soil and water system. Oxytetracycline (OTC), a frequently used tetracycline group antibiotic, possesses important chemical structure having various functional groups capable of binding to mineral surfaces. Previous studies indicated that OTC binds strongly with iron oxide and clay minerals using amide (-CONH2), phenolic –OH, and dimethyl amino [-N (CH3)2] functional groups. However, detailed information on the mechanisms of OTC binding on kaolinite, a common (1:1) clay mineral, is not available in the literature. Here I propose an in situ attenuated Fourier transform infrared spectroscopic (ATR-FTIR) investigation of OTC binding on kaolinite. In addition, since phosphate (P) is a co-occurring anion in the environment, I propose to investigate the effects of P competition on OTC sorption on kaolinite using in situ ATR-FTIR spectroscopy. Flow-cell experiments were conducted with a ZnSe horizontal ATR cell under various solution properties with OTC alone, P alone and P +OTC systems. The results indicated that OTC initial concentration affected the sorption mechanisms on kaolinite. In addition, variation of pH influenced the sorption mechanism of OTC on kaolinite. Participations of amide, methyl amino, and phenolic –OH functional groups of OTC in the sorption interactions are revealed by the characteristic infrared (IR) bands. Results indicated that the influence of P on OTC sorption on kaolinite was negligible irrespective of OTC: P ratio (1:1; 1:2; 1:10) and concentration (50µM OTC and; 50µM, 100µM and 500µM PO4). Analyses of IR peaks revealed that main P species on kaolinite was di-protonated P species (H2PO4-). At all pH values when P was added first, P and OTC has prominent IR peak, implying P has negligible effects on OTC adsorption. In the presence of P, no significant change of OTC binding mode was noticed. Our data will help to understand the binding mechanism of OTC and P on kaolinite at likely scenario. Detailed understanding of the mechanism will lead to better remediation strategy to remove antibiotics from the environment as well.^
Plant sciences|Soil sciences|Environmental science
"An Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) Spectroscopic Study on the Oxytetracycline Sorption Mechanism on Variable Charge Minerals"
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